THE STAR FORMATION NEWSLETTERreipurth/newsletter/newsletter251.pdfNo. 251 — 8 November 2013...

THE STAR FORMATION NEWSLETTERAn electronic publication dedicated to early stellar/planetary evolution and molecular clouds

No. 251 — 8 November 2013 Editor: Bo Reipurth ([email protected])

The Star Formation Newsletter

Editor: Bo [email protected]

Technical Editor: Eli [email protected]

Technical Assistant: Hsi-Wei [email protected]

Editorial Board

Joao AlvesAlan Boss

Jerome BouvierLee Hartmann

Thomas HenningPaul Ho

Jes JorgensenCharles J. Lada

Thijs KouwenhovenMichael R. MeyerRalph Pudritz

Luis Felipe RodrıguezEwine van Dishoeck

Hans Zinnecker

The Star Formation Newsletter is a vehicle forfast distribution of information of interest for as-tronomers working on star and planet formationand molecular clouds. You can submit materialfor the following sections: Abstracts of recentlyaccepted papers (only for papers sent to refereedjournals), Abstracts of recently accepted major re-views (not standard conference contributions), Dis-sertation Abstracts (presenting abstracts of newPh.D dissertations), Meetings (announcing meet-ings broadly of interest to the star and planet for-mation and early solar system community), NewJobs (advertising jobs specifically aimed towardspersons within the areas of the Newsletter), andShort Announcements (where you can inform or re-quest information from the community). Addition-ally, the Newsletter brings short overview articleson objects of special interest, physical processes ortheoretical results, the early solar system, as wellas occasional interviews.

Newsletter Archivewww.ifa.hawaii.edu/users/reipurth/newsletter.htm

List of Contents

Interview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

My Favorite Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Abstracts of Newly Accepted Papers . . . . . . . . . . 15

Abstracts of Newly Accepted Major Reviews . 50

Dissertation Abstracts . . . . . . . . . . . . . . . . . . . . . . . . 51

New Jobs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Summary of Upcoming Meetings . . . . . . . . . . . . . 54

Short Announcements . . . . . . . . . . . . . . . . . . . . . . . . 55

Cover Picture

This image shows the reflection nebula NGC 1579located in the dark cloud L1482 at an approximatedistance of 700 pc. The nebulosity is illuminatedby the peculiar object LkHα 101, which is a heavilyreddened massive star in a very early evolutionarystage (seen as a faint optical star just south of thebrightest part of the reflection nebula). The figureis a composite of B-, V-, and R-band images, andcovers approximately 6×7 arcmin, with north upand east left.

Image from G. H. Herbig, S. M. Andrews, & S. E.Dahm, AJ, 128, 1233, 2004

Submitting your abstracts

Latex macros for submitting abstractsand dissertation abstracts (by e-mail [email protected]) are appended to eachCall for Abstracts. You can also submit via theNewsletter web interface at http://www2.ifa.

hawaii.edu/star-formation/index.cfm

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.

George Herbig (1920 – 2013)

George Herbig passed away on October 12th at his home in

Honolulu. He was the “father” of low-mass star formation studies,

building the foundation upon which all of our current studies rest.

A brief biography of George Herbig can be found at

http://www.ifa.hawaii.edu/info/press-releases/Herbig/

A more detailed obituary will appear in Nature later this month.

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Cecilia Ceccarelliin conversation with Bo Reipurth

Q: You grew up and studied in Italy, but have made yourcareer in France, in Bordeaux and Grenoble. How did thatcome about, and was it an easy transition?

A: It was not an easy transition, as I changed not only thecountry but also changed scientific direction, moving to as-trochemistry and millimetre line observations, in additionto having two young kids (2 years old and one new bornbaby). For all these reasons it took some time, but theLaboratoire d’Astrophysique de Grenoble was welcomingand extremely fertile in ideas and competences, so thingswere very much facilitated by that. I have also to saythat I had the luck to meet Alain Castets, who introducedme to the field of astrochemistry and with whom I had agreat collaboration. The second person that played a hugerole in my transition was Emmanuel Caux at CESR (nowIRAP) in Toulouse.

Q: What was your PhD about, and who were your mostimportant early influences?

A: My thesis was on cosmology, on the Cosmic Back-ground Radiation field, and specifically on the Sunyaev-Zeldovich effect. Although these topics are very far awayfrom my present field of research, I learned a lot duringthat period. First of all I felt real enthusiasm for the re-search, I learned the necessary patience to obtain results(my thesis was an experimental one, I worked on instru-ments), and, last but not least, I realized the importanceof intuition, to understand and explain with simple ideaseven very complex problems. I think that this was thegreat education I received from my supervisor, FrancescoMelchiorri.

Q: So up until 1986 you worked on extragalactic astron-omy and the cosmic microwave background, and suddenlyyou saw the light and switched to the earliest phases of

star formation. What triggered that significant change ofdirection?

A: For a not very romantic reason: the salary! I won apermanent position at CNR in Italy to work in a groupwhose field of research was star formation. But I have toadd that I instantaneously felt in love with this field, sodifferent from the cosmology at the time, and not only forthe subject, but even more for the methods. In cosmology,we had very few observations and lot of theories, whereasin star formation it was exactly the other way around, alot of data and much less theory to explain them.

Q: The protostar IRAS 16293-2422 has played an impor-tant role in your research, as it has for many other re-searchers. Do you think IRAS 16293-2422 is a specialobject, or in a special evolutionary stage, or is just veryclose and therefore more easily accessible?

A: I think that this object has become a benchmark forastrochemistry studies in solar type protostars, mainly be-cause of its close distance but also because it has still arelatively massive and extended envelope. It is clear thatyoung protostars can be different from IRAS16293-2422,for example we have the case of L1527 which shows a verydifferent chemical composition. ALMA and NOEMA willcertainly provide data on many other sources, which havebeen difficult to observe so far, and this will allow us tounderstand whether and how IRAS16293-2422 is unique,whether it is a special case as Orion is for high mass starformation.

Q: You have taken a particular interest in deuteration, asoutlined in your major review for Protostars and PlanetsV. What have been your main insights, and where is thatsubject headed?

A: In the 90s models did not predict the observabilityof multiply deuterated molecules, which were thought tohave a too low abundance. Our and others’ observationsdemonstrated that those theories were wrong. After morethan a decade we still have troubles in reproducing the ob-served abundances of doubly and triply deuterated molecules,which means that something is still missing, even thoughwe have made huge progress. Two reasons make it im-portant to understand the origin of such a large moleculardeuteration: (i) it provides us with very stringent con-straints on the pre-collapse phase of the relevant objectand on its evolution; (ii) molecular deuteration provides asort of Ariadne’s thread that allows us to follow the historyof the birth and early evolution of the Solar System. Withrespect to this last point, we are preparing together withsix other colleagues who are experts in comets, meteoritesand Solar Nebula models, a chapter for the PP VI bookon the deuteration across the star and planet formationprocess, from the very first pre-collapse phase up to theformation of the terrestrial oceans.

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Q: You have extensively used data from ISO. How impor-tant was ISO, and what do you see as the major legacy ofthat satellite?

A: After IRAS, which provided us with the list of IRsources in the sky, ISO was the first observatory in theFIR. It allowed us to study the IRAS sources (and more),making maps, SEDs and, even more innovative, high tomoderate resolution spectra in the IR to FIR. It was a rev-olution in several fields, from the studies of the ices to theline spectra of galactic and extragalactic objects, whichallowed us to understand the gas cooling mechanisms andthe distribution of the oxygen, the most abundant elementafter hydrogen and helium, in molecules, including water.The importance of ISO is testified by the large number ofpublished articles and by the fact that new articles withISO data are still being published!

Q: Your most-cited paper deals with far-infrared line emis-sion from collapsing protostellar envelopes. Has Herschelvindicated your views, and what has Herschel contributedin this area?

A: Basically yes, the protostellar envelopes contain ob-servable amounts of water and, as predicted, water is par-ticularly abundant in the inner regions where the dusttemperature is high enough for the grain mantles to sub-limate. This is important not only because it allows usto probe the inner regions, where water is particularly im-portant, but also because water plays a major role for thecooling, and in some cases also the heating, of the gas.Obviously, Herschel has provided us with many more de-tails showing that the reality is complex, water from pro-tostars does not only originate from a spherical envelope,but outflows play a role too. But we know that nature isnot simple in its applications.

Q: Water line emission has been a focus of your work formany years. Is this a direction you maintain?

A: Although water has indeed been a focus of my workduring the ISO epoch, at a time when nothing was knownabout it as we did not have observations, lately astrochem-istry in general has attracted my attention, especially theinformation that we can extract from the observations ofyoung protostars and that can help to understand the firstphases of the Solar System’s life. Deuteration and com-plex organic molecules have played a major role in themost recent years of my research.

Q: Herschel obviously has revolutionized mid- and far-infrared spectroscopy. What has been your main interestamong the wealth of Herschel data?

A: The chemical diversity of protostellar objects, depend-ing on their evolutionary status and mass. As coordinatorof the Herschel Key Program CHESS (Chemical Herschelsurveys of star forming regions), I have the privilege toaccess HIFI 500-2000 GHz spectra of several sources, pro-

viding us with plenty of information on their content interms of water and many other species, many of whichare not detectable with groundbased telescopes. Notableexamples are the deuteration of water in different objects,including a shock spot caused by a molecular outflow, themysterious chlorine chemistry – we haven’t understood sofar where chlorine is as just a little fraction is observed inthe gas phase even in sites where it should be all gaseous–, the nitrogen chemistry, also very poorly understood.

Q: You have an important leadership role as the head of theAstroMol group in Grenoble. With cutbacks everywhere,do you still encourage young people to enter science andget a PhD in molecular astronomy?

A: I have left the leadership of the group to my colleaguessince a while. At present, Bertrand Lefloch is the very ap-preciated group leader. But I’m still engaged in promotingmolecular astronomy, I teach and regularly propose PhDtheses, for even in these times of cutbacks we need to keepexploring the Universe. For this reason, I do encourageyoung people to enter science. It is true that it is tougherthan ever to get a permanent position in astronomy, but ifwe think this is what would make us happy, that is enoughreason to try. At the same time, one has to be flexible andunderstand when it is time to make a career change. It isnot only talent, but also luck that is required to get a po-sition. I myself left research for two years at the beginningof my career and worked in industry. When, by chance, Iwon the CNRS position I hesitated going back to research,as the work I did was interesting and left me much moretime than when I was doing research. Time that I used fordoing many more and nice things (that now I can’t do!).

Q: France has, I believe, a larger fraction of women inastronomy than most other countries. Is this a cause forcelebration, or are there still barriers to be crossed?

A:Women account for about 20% of astronomers in France.I do not think that this is something to celebrate, whenwomen constitute 50% of the population, so there is stillmuch to do. Unfortunately, the trend is not even positive:this number has not increased for the last two decadesand, on the contrary, in the last few years the number ofyoung women in astronomy has decreased. Besides, as isknown, the 20% is an overall average, but when it comesto women in higher positions this number decreases, theso-called glass ceiling. I want here to take the opportunityto say to young women who wish to become astronomersthat this is fully compatible with a ”normal” family life,meaning that we can have children and husbands if wewish so and still be astronomers. Maybe it is a bit morecomplicated, but there is no need to make a drastic choicebetween being astronomers and being women. My dreamis that women and men share the same amount of respon-sibilities at home, which also means joys. I think thateverybody would gain, not only women.

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My Favorite ObjectThe Elephant Trunk Nebula

Konstantin Getman

Motivation

Rich young stellar clusters produce H ii regions whose ex-pansion into the nearby molecular cloud is thought to trig-ger the formation of new stars. However, the importanceof this mode of star formation is uncertain. A handfulof studies attempted to estimate the effect of triggeredstar formation (TSF) on the star formation rate of H ii

regions. Deharveng et al. (2010) find that over 20% of themid-IR shells from the Spitzer-GLIMPSE survey harborUCH iis and/or methanol masers, likely indicating trig-gering of massive star formation. From comparison of po-sitions of very young and massive stars in respect to loca-tions of numerous mid-IR shells, Thompson et al. (2012)estimate the fraction of Galactic massive stars triggered byexpanding H ii regions to be 14− 30%. From a theoreticalperspective, by turning on and off an irradiation feedbackon a turbulent, giant molecular cloud, Dale, Clark & Bon-nell (2007) find that TSF might increase the total amountof star formation by as much as 30%.

One of the principal signatures of small-scale TSF — astar cluster in and around the cloudlet on the peripheryof an expanding H ii region — may be erased through re-moval of the cloudlet by stellar winds and UV radiation, orthe kinematic dispersal of the unbound cluster within lessthan a few million years. Thus, it is often difficult to iden-tify sites of TSF and to quantify the impact of triggeringprocesses. IC 1396 is a nearby (D ∼ 870 pc; Contrerasetal. 2002), large (∼ 12 pc in radius) shell-like H ii region,where traces of recent triggered star formation are stillevident.

The goal of our recent study of the region (Getman etal. 2012, hereafter G12) was to identify, understand, andquantify the young stellar population in the central partof the region associated with the largest bright-rimmed

cloud, IC 1396A (aka The Elephant Trunk Nebula), andto estimate the contribution of the recent generation ofyoung stars to the total stellar population in both thecentral part and, with some additional assumptions, theentire H ii region. It is important to emphasize thatthese estimates are independent of the formationmechanism; we use the term ‘TSF’ to reflect ourview of the most likely formation mechanism forthese young stars.

Figure 1: (a) A 3◦ × 3◦ image of the emission nebula IC1396 from the Digitized Sky Survey (DSS). The primaryionizing source of the region, the O6 star HD 206267, andthe bright-rimmed globule IC 1396A are marked in red.The blue polygon outlines the 17′ × 17′ Chandra-ACISfield centered on the IC 1396A. (b) Close-up, combined X-ray and IR image of IC 1396A. The adaptively smoothedChandra-ACIS image in the 0.5 − 8.0 keV band (blue) issuperposed on the Spitzer-IRAC composite image in the3.6 µm (green) and 8.0 µm (red) bands. The ACIS field isoutlined in blue; the head and the trunk of the cloud aremarked in red. The positions of the two brightest featuresof the ionized optical rim in front of the cloud are markedin red as Rims A and Aa. North is up, east is to the left.

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IC 1396 H ii region and IC 1396A globule

The IC 1396 H ii region resides on the periphery of the gi-ant (∼ 70 pc in radius) infrared emission shell, the CepheusBubble (see Fig. 2. in Kun et al. 2008), which was pos-sibly produced by the mutual action of radiation, winds,and supernovae from the older generation of stars in theCepheus OB2 association. The IC 1396 H ii region, at(l, b) = (99.3◦, 3.7◦), is excited mainly by the O6.5f starHD 206267 located at the center of the region in the 4 Myrold cluster Tr 37 (Sicilia-Aguilar et al. 2005, hereafterSA05). IC 1396 has a rich population of > 20 bright-rimmed and cometary globules (Sugitani, Fukui & Ogura1991; Froebrich et al. 2005, and Fig. 1 here). Many ofthe clouds reside on the large molecular shell surround-ing the H ii region, which expands at a speed of 5 km s−1

with an inferred expansion time around 2.5 Myr (Patel etal. 1995). Sites of possible star-formation have been iden-tified in/around at least several globules (e.g., Schwartz,Wilking & Giulbudagian 1991; Ogura, Sugitani & Pickles2002; Froebrich et al. 2005) including sites of substantialstar-formation in IC 1396N (Nisini et al. 2001; Getmanet al. 2007; Beltran et al. 2009; Choudhury, Mookerjea &Bhatt 2010), SFO 37 (Ikeda et al. 2008), and IC 1396A(Reach et al. 2004; SA05; Sicilia-Aguilar et al. 2006;Morales-Calderon et al. 2009; Barentsen et al. 2011).

Lying ∼ 15′ (∼ 3.7 pc projected distance) west of HD206267, IC 1396A is the bright-rimmed cloud closest onthe sky to HD 206267. Its optical rim is the brightest of allrims and the cloud is thus likely to be the physically closestto HD 206267 (Weikard et al. 1996). Following Weikardet al. we designate the two brightest features of the rim asRim A located in front of the > 1 pc diameter head of theglobule and Rim Aa located further west at the shoulder(trunk) of the cloud (Fig. 1). The part of the cloud behindRim Aa has its own designation: SFO 36 (Sugitani et al.1991). A 0.3 pc diameter cavity in the molecular cloud ispresent in the head of the globule produced by the HerbigAe star LkHa 349 (Hessman et al. 1995). Outside this‘hole’, the globule is optically thick (AV ∼ 10 mag) withmolecular mass ∼ 200 M⊙ (Patel et al. 1995; Weikard etal. 1996).

Census of young stellar objects in/aroundIC 1396A

Early Spitzer images revealed both bright diffuse mid-infrared (MIR) emission and 17 Class II/I stars in theIC 1396A globule (Fig. 2 in Reach et al. 2004; hereafterR04). A spectacular multi-band movie of the cloud wasone of the first press releases of the Spitzer mission.

Figure 2: Spatial distribution of known young membersof the region over-plotted on DSS2-Red (a) and Spitzer-IRAC 8 µm (b) images. On both panels the big red circleoutlines the area of the central cluster Tr 37 of radiusR = 15′ centered on the O6 star HD 206267. The bluepolygon outlines the Chandra-ACIS field. The green poly-gon demarcates the globule, tracing 8.0 µm emission fromhot dust and PAHs. (a) Positions of young members fromthe SA05-optical (red ◦) and the G12-X-ray (blue ×) cat-alogs. ‘C1’ through ‘C5’ label five equal-area segmentsat the edge of the central cluster. Notice that the stellarsurface density of the SA05 stars (red only) in the ‘C5’ seg-ment is ∼ 2 times higher than that of the other segments.The two optically bright rims are marked by arrows andlabeled. (b) Positions of all known YSO members of theregion within the ACIS field: optical SA05 (red ◦), X-rayselected (blue ×), MIR YSOs from MC09 (green box, in-cluding all YSOs from R04 and SA06), Hα stars from B11(magenta +), and additional MIR selected stars from G12(cyan ⋄). This figure does not include a hundred or morelow-mass PMS members recently identified by SA13.

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SA05 and Sicilia-Aguilar et al. (2006, hereafter SA06)combined new deeper and wider-area Spitzer photometrywith optical photometry and spectroscopy to reveal a richlightly obscured population of > 200 Hα emission and/orLi 6707 A absorption stars. The population is a mix-ture of ∼ 4 Myr old members of the central Tr 37 clusterand ∼ 1 Myr stars spatially concentrated in an arc infront of the globule (see Fig. 11 in SA05). In addition,∼ 50 heavily obscured IR-excess-selected young stellar ob-jects (YSOs) were found inside the cloud (SA06). Usingarchived X-ray Chandra grating data, Mercer et al. (2009)identifed 22 new pre-main sequence (PMS) stars aroundHD 206267. Deeper Spitzer-IRAC maps from the time-series monitoring of the globule (Morales-Calderon et al.2009, hereafter MC09) uncovered a dozen new heavily em-bedded Class I/II YSOs. The spatial distribution of sixtyfive disky members in/around the globule is shown in Fig.16 of MC09. Using the data from the INT Photometric H-Alpha Survey (IPHAS), Barentsen et al. (2011, hereafterB11) identified about two dozen low-mass high-accretionT-Tauri systems spatially concentrated in an arc in frontof the globule (Fig. 18a in B11). About half of these werenewly discovered stellar members of the region. Spatialclustering of optical stars with younger ages and increas-ing accretion rates away from the ionizing star HD 206267(SA05, B11) led SA05 and B11 to propose the presence of astellar population in front of the IC 1396A globule whoseformation has been triggered by HD 206267. Using theChandra-ACIS and the auxiliary Spitzer-IRAC and opticalFLWO/LAICA data, G12 further uncovered over 130 pre-viously unknown members of the Tr 37/IC 1396A stellarpopulations (Fig. 2). Sicilia-Aguilar et al. (2013, here-after SA13), using the SAO-RAS-SCORPIO and MMT-Hectospec optical spectroscopy data combined with theLAICA optical photometry and the Spitzer-IRAC/MIPSdata, report another 78 new members and 64 probablemembers of the Tr 37/IC 1396A region, mostly M-typestars.

Age-spatial gradient

Fig. 3 shows the spatial distribution of the optical andX-ray selected PMS stars stratified by the ages obtainedfrom the optical FLWO photometry data (assuming thetime scale of Siess et al. 2000), as detailed in G12. Theregion is divided into two sub-regions: the East sub-regionnear/around the O6 ionizing star HD 206267 is associatedwith the central stellar cluster Tr 37, while the West sub-region near/around the IC 1396A globule is expected tobe associated mainly with stars that have been recentlyformed in the globule. The data provide strong evidencethat the stars in the East sub-region (median age of 3.6Myr) are systematically older than the stars in the Westsub-region (median age of 2.2 Myr). These are consistent

with the previously reported average age of 4 Myr for theTr 37 cluster (SA05). Typical age estimates for the starsin front of the globule are t < 2 − 3 Myr. Meanwhile,younger ages t < 1 Myr are inferred from the radiativetransfer model fits to the optical-IR-radio band data forthe disky YSOs embedded in the globule (Reach et al.2009). Thus, the stellar age increases from < 1 Myr insidethe cloud, to < 2−3 Myr in front of the cloud, to ∼ 4 Myrtowards the central Tr 37 cluster.

Figure 3: Age analysis for the combined optical SA05 andX-ray G12 selected young stellar sample. Age-stratifiedstellar sub-samples are shown on different panels: t <2 Myr (a), 2 < t < 3.5 Myr (b), and 3.5 < t < 10 Myr(c). The polygon indicates the ACIS field of view. Thedashed line at roughly half projected distance between theO6 star HD 206267 and the IC 1396A globule is a demar-cation line that divides the region into two sub-regions,East and West. (d) Cumulative distributions of age arecompared between the 30 East and 57 West stars withavailable ages.

Stellar surface density gradient

A map of the combined optical/IR/X-ray YSO sample isshown in Fig. 4. The YSOs appear clustered rather thanuniformly distributed, and the distributions of the disky(blue +) and diskless (red ×) stars appear to be offsethorizontally from each other.

Directly in front of the molecular globule, most of the disk-less and a portion of the disky stars lie in a > 3 pc long and

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∼ 0.7 pc wide layer. The position of the layer is consistentwith the positions of the very young optical stars (SA05,B11) and with the excess of the optical stars on the westernborder of Tr 37 (Fig. 2a). The layer can be further sub-divided into a few stellar groupings (‘G1’,‘G2’,‘G6’, and‘G7’). Some groupings are disky and others diskless, indi-cating possibly different ages from distinct star formationevents in different cloud cores over millions of years.

Inside the globule, the stellar population is dominated bydisky objects, whose spatial distribution is also highly non-uniform and clumpy (stellar groups ‘G3’ and ‘G4’), withthe bulk of the stars lying along the western edge of theglobule that faces the ionizing system HD 206267. Thegroup ‘G3’ lies at the head of the globule behind the brightoptical Rim A. The smaller group ‘G4’ is located behindoptical Rim Aa in the portion of the cloud named SFO 36.

Figure 4: (a) Separation on diskless stars (red ×) anddisky stars (blue +) as detailed in G12. (b) Contour mapsof source surface densities from panel (a) smoothed witha Gaussian σ = 1.4′.

XLFs and IMFs for the stellar populationsin the Tr 37/IC 1396A region

From the X-ray luminosity function (XLF) and initial massfunction (IMF) analyses (Fig. 5), G12 infer the followingtotal numbers of YSOs for different sub-regions of interest:∼ 480 stars down to 0.1 M⊙ in the central part of Tr 37;∼ 250 stars down to 0.1 M⊙ around the IC 1396A globulewithin the Chandra-ACIS field; and > 60 YSOs embeddedin the IC 1396A globule.

Figure 5: IMF of the central part of Trumpler 37 (redpanel). XLF and IMF of the stellar population aroundthe IC 1396A globule (blue panel). IMF of the disky YSOpopulation inside the IC 1396A globule (green panel).

Observational evidence for TSF

Triggered star formation in H ii regions might take placein the gravitationally unstable fragments of a molecularshell swept up by an expanding H ii region (Collect &Collapse mechanism; Hosokawa & Inutsuka 2006; Dale,Bonnell, & Whitworth 2007), in pre-existing molecularclumps shocked by UV photo-ionization from early OB-type stars (Radiation-Driven Implosion mechanism; e.g.,Miao et al. 2009; Bisbas et al. 2011), and in thin elongated

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pillar-like structures produced through hydrodynamic in-stabilities in ionization fronts (e.g., Whalen & Norman2008) or through ionization of large turbulent clouds (e.g.,Gritschneder et al. 2010). These different types of trigger-ing processes are not exclusive and are likely intermixedon different scales within an H ii region (e.g., Walch et al.2012).

Spatial-age gradients found in stellar populations in/aroundbright-rimmed clouds (BRCs) are often viewed as strongobservational evidence for TSF. The youngest stars aretypically embedded at the edge of the cloud facing theionizing star, and older stars are aligned within and infront of the bright rim towards the ionizing star. For ex-ample, spatio-temporal gradients and triggered star for-mation have been reported in BRCs and pillars on theedges of large H ii regions in the Eagle Nebula (Sugitaniet al. 2002), IC 1848 (Matsuyanagi et al. 2006; Oguraet al. 2007), IC 1396 (Getman et al. 2007; Ikeda et al.2008; Choudhury et al. 2010), Sharpless 155 (Getman etal. 2009), Sharpless 171 and Sharpless 296 (Chauhan etal. 2009), and the Carina Nebula (Smith et al. 2010).

The results of G12, combined with the results from theprevious studies, provide strong evidence that the Tr 37/IC1396A region possesses many of the observational featuresof TSF:

• The presence of an exciting star (HD 206267) and abright-rimmed cloud (IC 1396A) protruding inside the H ii

region and surrounded by an ionized rim (Rim A and RimAa) facing the exciting star (Fig. 1).

• The presence of dense molecular cores close to the rim(Patel et al. 1995, their Fig. 8) and (Weikard et al. 1996,their Fig. 14a). This is consistent with the scenario wherethe expanding ionization front from HD 206267 penetratesthe inter-core cloud region and drives shocks into the cores,compressing them sufficiently to trigger gravitational col-lapse.

• A rough equilibrium between the H ii pressure and thecloud pressure found at the interfaces between the Rim Aand the head of the IC 1396A globule (Reach et al. 2009)and the Rim Aa and the SFO 36 cloud (Morgan et al.2004). This indicates that the cloud could have been re-cently shocked by a photoionization shock. In addition, forthe SFO 36 cloud, Morgan, Urquhart & Thompson (2009)and Morgan et al. (2010) measure relatively high valuesof CO excitation temperature and turbulent velocity dis-persion, which are consistent with those of other shockedcloud candidates.

• A clumpy spatial distribution of young stars both insideand in front of the cloud (Fig. 4) suggesting recent for-mation in distinct molecular cores. The proximity of thestars to the ionized rim immediately suggests a physical re-lationship between star formation and the ionization front

propagating through the globule, and can be explainedwithin the framework of the enhancement of multiple pre-existing density substructures and their subsequent globalimplosion (Walch et al. 2011).

• The spatio-temporal gradient of young stars, both ageand disk-gradient, oriented towards the exciting star (Figs.3 and 4 here, Fig. 11 in SA05, and Fig. 18a in B11).

• The high apparent star formation efficiency (∼ 30%,G12), a property characteristic of other TSF cloud candi-dates, for example, Cep B/OB3b (Getman et al. 2009), Sh2-233IR (Yan et al. 2010), and L935/NGC 7000 (Toujimaet al. 2011).

The fraction of the current generation ofyoung stars in the total stellar populationof IC 1396

Based on the estimates of the stellar density in the Tr37/IC 1396A region (Figs. 2 and 4) and on the XLF/IMFestimates of the total numbers of YSOs for different sub-regions of interest (Fig. 5), G12 calculate the currentcontribution of the younger stellar populations associatedwith the IC 1396A globule to the total population of thecentral part of the IC 1396 H ii region to be ∼ 25%.

Further, G12 extrapolate the results for the IC 1396Aglobule to the entire H ii region. This extrapolation makesuse of the survey of the entire IC 1396 H ii region from B11,and requires the following additional assumptions. First,the total number of stars in the entire IC 1396 H ii regionis similar to that of the Orion Nebula Cluster (based onthe equal numbers of known massive stars). Second, > 40observed high-accretion B11 stars clustered in front of therims ‘Rim E’, ‘Rim B’, ‘Rim J’, and ‘Rim H’ are likely as-sociated with the star formation in the respective globules(see Fig. 9 in B11). Third, the ratio of the number of theobserved B11 stars associated with the globules to the to-tal number of the globule stars is constant across the H ii

region. With these assumptions G12 estimate the contri-bution of the recent generation of young stars to the totalpopulation of the entire IC 1396 H ii region to be > 14%.Thus, the currently active clouds on the periphery of IC1396 add at least 14 − 25% to the current cluster popu-lation. When past and future clouds are considered, thecontribution of younger generation of stars (likely formedby triggering) to the star formation in the molecular cloudcould be higher.

References:

Barentsen G. et al., 2011, MNRAS, 415, 103 (B11)

Beltran M. T., Massi F., Lopez R., Girart J. M., Estalella R., 2009,A&A, 504, 97

Bisbas T. G., Wunsch R., Whitworth A. P., Hubber D. A., Walch

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S., 2011, ApJ, 736, 142

Chauhan N., Pandey A. K., Ogura K., Ojha D. K., Bhatt B. C.,Ghosh S. K., Rawat P. S., 2009, MNRAS, 396, 964

Choudhury R., Mookerjea B., Bhatt H. C., 2010, ApJ, 717, 1067

Contreras M. E., Sicilia-Aguilar A., Muzerolle J., Calvet N., BerlindP., Hartmann L., 2002, AJ, 124, 1585

Dale J. E., Bonnell I. A., Whitworth A. P., 2007, MNRAS, 375, 1291

Dale J. E., Clark P. C., Bonnell I. A., 2007b, MNRAS, 377, 535

Deharveng L. et al., 2010, A&A, 523, A6

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11

Perspective

HH jets from binary starsby Alex Raga

Even though physical phenomena at a given spatial scaleare generally coupled to phenomena at larger and smallerscales, it is usual to study them as partially decoupledsystems, in which the phenomena at other scales are con-sidered only as simplified prescriptions. An example ofthis is the modelling of stellar jets, in which the mech-anism by which the jets are produced is reduced to an“injection condition” and the environment into which thejet is moving is fixed with some simple prescription. Forexample, one can assume the environment to be homo-geneous, clumpy, or to have an initial stratification givenby some simple model (e.g., the stratification of a steady,constant velocity wind).

In such “spatially decoupled” jet models, the presence ofa binary source is introduced by including:

1. a precession of the outflow axis,

2. the orbital motion of the outflow source,

3. a time-variability of the ejection.

Evidence for a precession of the outflow axis is seen inmany HH outflows, one of the more dramatic examples be-ing the S-shaped giant HH 34 jet (see Devine et al. 1997).Examples of point-symmetric deviations in the loci of jet/counterjet systems are also seen in jets associated withprotoplanetary nebulae (PPNe).

The most promising mechanism for the production of point-symmetric direction deviations in a protostellar outflow isthe precession of an accretion disk due to a binary compan-ion of the outflow source (see, e.g., Larwood et al. 1996).In the case of a mass-exchanging binary system (as appar-ently present in some PPNe), time-dependencies in the ac-

cretion stream could produce disk warping and precession(see, e.g., Montgomery 2012), but it is not clear whether ornot this kind of effect could be present in YSO disks. Also,warps and precession motions in accretion disks could inprinciple be produced by a magnetic warping instability(Lai 2003).

An unresolved question is what would be the effect of adisk precession on a magneto-centrifugal outflow drivenfrom the inner regions of the disk and/or from the disk/stellar magnetosphere boundary. However, the observa-tional fact that many observed jet/counterjet systems havepoint-symmetric direction deviations strongly suggests thatthe ejection mechanism is indeed affected by the disk pre-cession.

From this, we see that while one does expect to have pre-cession in an accretion disk around a star with a binarycompanion, the presence of a precession does not neces-sarily imply the existence of such a companion. Therefore,jets with point-symmetric jet/counterjet deviations do notfully imply the presence of a binary source.

A theoretically clearer consequence of a binary source ona bipolar outflow is the effect of the orbital motion. Thismotion introduces a time-dependence in the position ofthe outflow source, which is unlikely to be important indetermining the structure observed in jets at spatial scalesof ∼ 100-105 AU. However, the effect that can be impor-tant is the time-dependent velocity of the outflow sourceas it goes around its orbit.

If the outflow is ejected from the star perpendicular to theorbital plane at a constant velocity vj , the orbital velocityvo will introduce a deviation α = tan−1(vo/vj) ≈ vo/vjbetween the locus of the jet and the orbital axis. Thisdeviation of course rotates as the source goes around itsorbit, resulting in a mirror symmetric spiral shape for theloci of the jet and the counterjet. The spatial “step” ofthe spiral (i.e., the distance along the axis associated witha full loop of the spiral) of course is given by L = vjτo,where τo is the orbital period. The ballistic jet problemgives a full analytic solution for the case of a circular orbit(Masciadri & Raga 2002) but requires a numerical solutionof Kepler’s equation (for the eccentric anomaly) for thecase of an elliptical orbit (Gonzalez & Raga 2004).

Therefore, if one observes a mirror symmetric jet/counterjetspiral structure, the semi-opening angle of the spiral is (inthe limit of small angles and assuming a circular orbit withejection along the orbital axis) α = vo/vj , and the step ofthe spiral is L = vjτo. Therefore, if we have an obser-vational measurement of the jet velocity (through radialvelocity and proper motion measurements), the shape ofthe spiral structure gives us a determination of the orbitalvelocity vo and period τp, through which one can obtainan estimate of the mass of the binary companion needed

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to produce this orbit.

The main difficulty for doing this is that mirror-symmetricdeviations along the jet/counterjet axis are not generallydetected in HH jets. This is probably due to the fact thatin binary outflow sources we have orbital velocities of atmost a few km/s, while jet velocities are in the hundredsof km/s, resulting in very small opening angles α for theresulting spiral jet/counterjet loci. Also, it is necessary tohave high angular resolution observations in the radio tofar infrared wavelength range, as observations at shorterwavelengths generally do not detect the more highly ex-tinguished outflow lobe.

As far as I am aware, there are only two papers that claimto have detected such mirror symmetric spirals:

• Lee et al. (2010) present submillimetric observationsof HH 211 showing mirror symmetric deviations con-sistent with an orbital motion of the outflow sourcearound a companion of a mass ∼ 60 MJup,

• Noriega-Crespo et al. (2011) present far IR obser-vations of HH 111, showing a mirror symmetric jet/counterjet pattern consistent with an orbital motionof the source around a companion of mass ∼ 1 M⊙.These observations (together with a fit from a bal-istic, orbital jet model) are shown in Figure 1, inwhich we see that the observed effect is quite subtle!

Interestingly, at angular scales of ∼ 20′, the HH 111 jet/counterjet system shows point-symmetric directional de-viations of ∼ 1◦, which would be consistent with a preces-sion of the outflow axis (see Reipurth et al. 1997) with asemi-opening angle of ∼ 4◦ and a period τp ≈ 23000 yr.Therefore, the HH 111 outflow shows evidence not only foran orbital motion of the source, but also for a precessionwith a period τp ∼ 13 τo (where τo is the orbital period,given at the end of the caption of Figure 1). This resultis in good qualitative agreement with the disk precessionmodels of Terquem et al. (1999), which predict that theprecession period is ∼ 10 times the orbital period of thestellar companion (responsible for the disk precession).

In general, a bipolar outflow should present a mirror- sym-metric, small opening angle spiral close to the outflowsource (resulting from the orbital motion) and a point-symmetric spiral at larger distances from the source (re-sulting from the longer period, possibly larger openingangle precession motion). Ballistic models and numeri-cal simulations including these two effects were calculatedby Raga et al. (2009) for the case of a circular orbit, andFigure 2 shows results from one of their models. Observa-tionally, as far as I am aware the only object in which boththe point- and the mirror-symmetric spirals have been de-tected is the HH 111 outflow.

The third interesting effect, which would only be found

Figure 1: Right: the region around the HH 111 outflowsource (at the origin of the coordinate system, rotatedso that the outflow axis is approximately parallel to theordinate) observed in the 4.5 µm channel of the IRACcamera of Spitzer. The circles are the measured positionsof emission knots and the white, solid line is a fit to thedata of a ballistic jet model. Left: the region around theoutflow source with an expanded abscissa, fitted positionsto the knots along the jet/counterjet (crosses) and a leastsquares fit of a ballistic jet model from a source with acircular orbital motion (the fit is given by the solid curve,and the dashed curves give the 1 σ deviations from the bestfit). The best fit model has an orbital period τo ≈ 1800 yrand orbital velocity vo ≈ 3 km s−1.

13

Figure 2: Column density maps obtained from a simula-tion of a jet from a source with a circular, orbital motionand a precession of the outflow axis. Three different pro-jections (in two perpendicular planes parallel to the or-bital axis, and one on a plane perpendicular to this axis)are shown. The parameters of the simulation are given inRaga et al. (2009).

in outflow sources in highly eccentric orbits, is that theclose approaches of the companion at periastron couldproduce enhanced accretion in the disk around the outflowsource, and therefore also increased ejection. More generalpossibilites along these lines were proposed by Reipurth(2000), who suggested that close encounters in disinte-grating multiple systems could lead to the production of“accretion/outflow events”.

As far as I am aware, no theoretical models of this possi-ble effect have yet been presented. However, there is thevery interesting observational study of Witt et al. (2009),who find a strong correlation between outflow velocity andorbital phase (with higher velocities at apoastron) in thecentral source of the Red Rectangle protoplanetary neb-ula. This result should definitely inspire theoreticians tolook into this problem!

The lack of theoretical models of orbitally modulated ejec-tions has not stopped “jet modellers” from exploring theproperties of jets with outflow velocities which are syn-chronized with phase along an elliptical orbit. Velazquezet al. (2013) have presented ballistic models and numericalsimulations of such outflows.

The field of jets from binary stars is still in its infancyboth from the observational and theoretical point of view.Many of the relevant processes have not been studied inany kind of detail, and many of the essential observationsare still to be carried out. For example, models of the pro-duction of jets under the perturbation of a binary compan-ion have not yet been studied, and observations followingboth the binary orbit and the ejected material have mostlynot yet been done. Observations and models of these ef-fects in the well constrained HH outflows probably offerthe best way forward.

References:

Devine, D., Bally, J., Reipurth, B., Heathcote, S. 1997, AJ, 114,2095

Gonzalez, R. F., Raga, A. C. 2004, RMxAA, 40, 61

Lai, D. 2003, ApJ, 591, L119

Larwood, J. D., Nelson, R. P., Papaloizou, J. C. B., Terquem, C.1996, MNRAS, 282, 597

Lee, C.-F. et al. 2010, ApJ, 713, 737

Masciadri, E., Raga, A. C. 2002, ApJ, 568, 733

Montgomery, M. M. 2012, ApJ, 753, L27

Noriega-Crespo, A., Raga, A. C., Lora, V., Stapelfeldt, K. R., Carey,S. J. 2011, ApJ, 732, L16

Raga, A. C., Esquivel, A., Velazquez, P. F., Canto, J., Haro-Corzo,S., Riera, A., Rodrıguez-Gonzalez, A. 2009, ApJ, 707, L6

Reipurth, B. 2000, AJ, 120, 3177

Reipurth, B., Bally, J., Devine, D. 1997, AJ, 114, 2708

Terquem, C. et al. 1999, ApJ, 512, L131

Witt, A. N. et al. 2009, ApJ, 693, 1946

14

Abstracts of recently accepted papers

Chemistry of Dark Clouds: Databases, Networks, and Models

Marcelino Agundez1 and Valentine Wakelam2

1 Univ. Bordeaux, LAB, UMR 5804, F-33270 Floirac, France2 CNRS, LAB, UMR 5804, F-33270 Floirac, France

E-mail contact: wakelam at obs.u-bordeaux1.fr

Chemical models have been developed over the years by astrophysicists to study the processes at play in the variousenvironments of the interstellar medium (ISM) that define the chemical composition of the gas and the dust. Thesequalitative aspects of the model predictions have been improved from a chemical point of view thanks to many recentdevelopments of the experimental technics and theoretical methods that aim at studying the individual reactions inconditions as close to the ISM conditions as possible and characterize the rate constants of their efficiency. Thesemodels have also been more and more associated with dynamical evolution of the ISM physical conditions (for starforming regions for instance) since the chemical composition is far from steady-state in such regions. In this paper,we try to assess the state of the art concerning the chemical modeling of dark clouds, the initial step for the formationof stars and disks.

Accepted by Chemical Reviews

http://arxiv.org/pdf/1310.3651

X-Shooter spectroscopy of young stellar objects: IV – Accretion in low-mass stars andsub-stellar objects in Lupus

J.M. Alcala1, A. Natta2,9, C.F. Manara7, L. Spezzi7, B. Stelzer3, A. Frasca4, K. Biazzo4, E. Covino1,S. Randich2, L. Testi2,7,11, F. Comeron7, G. Cupani5 and V. D’Elia6,10

1 INAF-Osservatorio Astronomico di Capodimonte, via Moiariello 16, I-80131 Napoli, Italy2 INAF-Osservatorio Astrofisico di Arcetri, via Moiariello 16, Largo E. Fermi 5, I-50125 Firenze, Italy3 INAF-Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134 Palermo, Italy4 INAF-Osservatorio Astrofisico di Catania, via S. Sofia 78, I-95123 Catania, Italy5 INAF- Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy6 INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monteporzio Catone, Italy7 European Southern Observatory, Karl Schwarzschild Str. 2, 85748 Garching, Germany8 Department of Planetary Science, Lunar and Planetary Lab. University of Arizona, 1629, E. University Blvd, 85719,Tucson, AZ, USA9 DIAS/Dublin Institute for Advanced Studies, Burlington Road, Dublin 4, Ireland10 ASI-Science Data Centre, Via Galileo Galilei, I-00044 Frascati, Italy11 Excellence Cluster Universe, Boltsmannstr. 2, D-85748 Garching, Germany

E-mail contact: alcala at oacn.inaf.it

We present X-Shooter/VLT observations of a sample of 36 accreting low-mass stellar and sub-stellar objects (YSOs) inthe Lupus star forming region, spanning a range in mass from∼0.03 to∼1.2M⊙, but mostly with 0.1M⊙ <M⋆ < 0.5M⊙.Our aim is twofold: firstly, analyse the relationship between excess-continuum and line emission accretion diagnostics,and, secondly, to investigate the accretion properties in terms of the physical properties of the central object. Theaccretion luminosity (Lacc), and from it the accretion rate (Macc), is derived by modelling the excess emission, fromthe UV to the near-IR, as the continuum emission of a slab of hydrogen. The flux and luminosity (Lline) of a largenumber of emission lines of H, He, Ca II, etc., observed simultaneously in the range from ∼330nm to 2500nm, werecomputed. The luminosity of all the lines is well correlated with Lacc. We provide empirical relationships betweenLacc and the luminosity of 39 emission lines, which have a lower dispersion as compared to previous relationships in

15

the literature. Our measurements extend the Paβ and Brγ relationships to Lacc values about two orders of mag-nitude lower than those reported in previous studies. We confirm that different methodologies to measure Lacc andMacc yield significantly different results: Hα line profile modelling may underestimate Macc by 0.6 to 0.8 dex withrespect to Macc derived from continuum-excess measures. Such differences may explain the likely spurious bi-modalrelationships between Macc and other YSOs properties reported in the literature. We derive Macc in the range 2×10−12

– 4×10−8M⊙ yr−1 and conclude that Macc ∝ M⋆1.8(±0.2), with a dispersion lower by a factor of about 2 than in pre-

vious studies. A number of properties indicate that the physical conditions of the accreting gas are similar over morethan 5 orders of magnitude in Macc, confirming previous suggestions that it is the geometry of the accretion flow thatcontrols the rate at which the disc material accretes onto the central star.

Accepted by Astronomy & Astrophysics


Herschel survey of brown dwarf disks in ρ Ophiuchi

C. Alves de Oliveira1, P. Abraham2, G. Marton2, C. Pinte3, Cs. Kiss2, M. Kun2, A. Kospal4, P. Andre5

and V. Konyves5,6

1 European Space Astronomy Centre (ESA/ESAC), P.O. Box, 78, 28691 Villanueva de la Canada, Madrid, Spain2 Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, PO Box67, 1525 Budapest, Hungary3 UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG) UMR5274, Greno-ble,38041, France4 European Space Research and Technology Centre (ESA/ESTEC), P.O. Box 299, 2200 AG Noordwijk, The Nether-lands5 Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, IRFU/Service d’Astrophysique, C.E. Saclay, Ormedes Merisiers, 91191 Gif-sur-Yvette, France6 IAS, CNRS (UMR 8617), Universite Paris-Sud 11, Batiment 121, 91400 Orsay, France

E-mail contact: calves at sciops.esa.int

Context. Young brown dwarfs are known to possess circumstellar disks, a characteristic that is fundamental to theunderstanding of their formation process, and raises the possibility that these objects harbour planets.Aims. We want to characterise the so far scarcely studied far-IR emission of disks around the young brown dwarfpopulation of the ρ Ophiuchi cluster in LDN 1688.Methods. Recent observations of the ρ Ophiuchi cluster with the Herschel Space Observatory allow us to probe thespectral energy distribution (SED) of the brown dwarf population in the far-IR, where the disk emission peaks. Weperformed aperture photometry at 70, 100, and 160 µm, and constructed SEDs for all previously known brown dwarfsdetected. These were complemented with ancillary photometry at shorter wavelengths. We compared the observedSEDs to a grid of synthetic disks produced with the radiative transfer code MCFOST, and used the relative figure ofmerit estimated from the Bayesian inference of each disk parameter to analyse the structural properties.Results. We detected 12 Class II brown dwarfs with Herschel, which corresponds to one-third of all currently knownbrown dwarf members of ρ Ophiuchi. We do not detect any of the known Class III brown dwarfs. Comparison tomodels reveals that the disks are best described by an inner radius between 0.01 and 0.07 AU, and a flared diskgeometry with a flaring index between 1.05 and 1.2. Furthermore, we can exclude values of the disk scale-height lowerthan 10 AU (measured at a fiducial radius of 100 AU). We combined the Herschel data with recent ALMA observationsof the brown dwarf GY92 204 (ISO−Oph 102), and by comparing its SED to the same grid of disk models, we derivedan inner disk radius of 0.035 AU, a scale height of 15 AU with a flaring index of β ∼1.15, an exponent for dust settlingof −1.5, and a disk mass of 0.001 M⊙. This corresponds to a disk-to-central object mass ratio of ∼1%.Conclusions. The structural parameters constrained by the extended SED coverage (inner radius and flaring index)show a narrow distribution for the 11 young brown dwarfs detected in ρ Ophiuchi, suggesting that these objects sharethe same disk evolution and, perhaps, formation.

Accepted by A&A


16

Scattering from dust in molecular clouds: Constraining the dust grain size distributionthrough near-infrared cloudshine and infrared coreshine

M. Andersen1, J. Steinacker1, W-F. Thi1, L. Pagani2, A. Bacmann1, and R. Paladini3

1 (UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Greno-ble, F-38041, France2 LERMA, UMR 8112 du CNRS, Observatoire de Paris, 61, Av. de l’Observatoire, 75014, Paris, France3 Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA

E-mail contact: morten.andersen at obs.ujf-grenoble.fr

Context. The largest grains (0.5–1 µm) in the interstellar size distribution are efficient in scattering near- and mid-infrared radiation. These wavelengths are therefore particularly well suited to probe the still uncertain high-end ofthe size distribution.Aims. We investigate the change in appearance of a typical low-mass molecular core from the Ks (2.2 µm) band tothe Spitzer IRAC 3.6 and 8 µm bands, and compare with model calculations, which include variations of the grainsize distribution.Methods. We combine Spitzer IRAC and ground-based near-infrared observations to characterize the scattered lightobserved at the near- and mid-infrared wavelengths from the core L260. Using a spherical symmetric model core, weperform radiative transfer calculations to study the impact of various dust size distributions on the intensity profilesacross the core.Results. The observed scattered light patterns in the Ks and 3.6 µm bands are found to be similar. By comparisonwith radiative transfer models the two profiles place constraints on the relative abundance of small and large (morethan 0.25 µm) dust grains. The scattered light profiles are found to be inconsistent with an interstellar silicate graindistribution extending only to 0.25 µm and large grains are needed to reach the observed fluxes and the flux ratios.The shape of the Ks band surface brightness profile limits the largest grains to 1–1.5 µm.Conclusions. In addition to observing coreshine in the Spitzer IRAC channels, the combination with ground-basednear-infrared observations are suited to constrain the properties of large grains in cores.

Accepted by A&A


Two timescale dispersal of magnetized protoplanetary disks

Philip J. Armitage1,2, Jacob B. Simon1 and Rebecca G. Martin1

1 JILA, University of Colorado and NIST, 440 UCB, Boulder, Colorado, USA2 Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder

E-mail contact: pja at jilau1.colorado.edu

Protoplanetary disks are likely to be threaded by a weak net flux of vertical magnetic field that is a remnant of themuch larger fluxes present in molecular cloud cores. If this flux is approximately conserved its dynamical importancewill increase as mass is accreted, initially by stimulating magnetorotational disk turbulence and subsequently byenabling wind angular momentum loss. We use fits to numerical simulations of ambipolar dominated disk turbulenceto construct simplified one dimensional evolution models for weakly magnetized protoplanetary disks. We show thatthe late onset of significant angular momentum loss in a wind can give rise to ”two timescale” disk evolution in whicha long phase of viscous evolution precedes rapid dispersal as the wind becomes dominant. The wide dispersion in disklifetimes could therefore be due to varying initial levels of net flux. Magnetohydrodynamic (MHD) wind triggereddispersal differs from photoevaporative dispersal in predicting mass loss from small (less that 1 AU) scales, wherethermal winds are suppressed. Our specific models are based on a limited set of simulations that remain uncertain,but qualitatively similar evolution appears likely if mass is lost from disks more quickly than flux, and if MHD windsbecome important as the plasma beta decreases.

Accepted by ApJ Letters


17

Non-Ideal Magnetohydrodynamic Simulations of the Two-Stage Fragmentation Modelfor Cluster Formation

Nicole D. Bailey1,2 and Shantanu Basu1

1 Department of Physics and Astronomy, University of Western Ontario, 1151 Richmond Street, London, Ontario,Canada, N6A 3K72 Current Address: School of Physics and Astronomy, University of Leeds, Leeds, United Kingdom, LS2 9JT

E-mail contact: N.Bailey at leeds.ac.uk

We model molecular cloud fragmentation with thin disk non-ideal magnetohydrodynamic simulations that includeambipolar diffusion and partial ionization that transitions from primarily ultraviolet dominated to cosmic ray dom-inated regimes. These simulations are used to determine the conditions required for star clusters to form through atwo-stage fragmentation scenario. Recent linear analyses have shown that the fragmentation length and time scales canundergo a dramatic drop across the column density boundary that separates the ultraviolet and cosmic ray dominatedionization regimes. As found in earlier studies, the absence of an ionization drop and regular perturbations leads toa single-stage fragmentation on parsec scales in transcritical clouds, so that the nonlinear evolution yields the samefragment sizes as predicted by linear theory. However, we find that a combination of initial transcritical mass-to-fluxratio, evolution through a column density regime in which the ionization drop takes place, and regular small perturba-tions to the mass-to-flux ratio are sufficient to cause a second stage of fragmentation during the nonlinear evolution.Cores of size ∼ 0.1 pc are formed within an initial fragment of ∼ pc size. Regular perturbations to the mass-to-fluxratio also accelerate the onset of runaway collapse.

Accepted by Astrophysical Journal


A UV-to-MIR monitoring of DR Tau: exploring how water vapor in the planet formationregion of the disk is affected by stellar accretion variability

Andrea Banzatti1,3, Michael R. Meyer1, Carlo F. Manara2, Klaus M. Pontoppidan3 and Leonardo Testi2

1 ETH Zurich, Institute for Astronomy, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland2 European Southern Observatory, Karl Schwarzschild Str. 2, D-85748 Garching bei Muenchen, Germany3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

E-mail contact: banzatti at stsci.edu

Young stars are known to show variability due to non-steady mass accretion rates from their circumstellar disks.Accretion flares can produce strong energetic irradiation and heating that may affect the disk in the planet formationregion, close to the central star. During an extreme accretion outburst in the young star EX Lupi, the prototype ofEXor variables, remarkable changes in molecular gas emission from ∼ 1 AU in the disk have recently been observed(Banzatti et al. 2012). Here, we focus on water vapor and explore how it is affected by variable accretion luminosity inT Tauri stars. We monitored a young highly variable solar-mass star, DR Tau, using simultaneously two high/medium-resolution ESO-VLT spectrographs: VISIR at 12.4 µm to observe water lines from the disk, and X-shooter coveringfrom 0.3 to 2.5 µm to constrain the stellar accretion. Three epochs spanning timescales from several days to severalweeks were obtained. Accretion luminosity was estimated to change to within a factor ∼ 2, and no change in wateremission was detected at a significant level. In comparison to EX Lupi and EXor outbursts, DR Tau suggests thatthe less long-lived and weaker variability phenomena typical of T Tauri stars may leave water at planet-forming radiiin the disk mostly unaffected. We propose that these systems may provide evidence for two processes that act overdifferent timescales: UV photochemistry in the disk atmosphere (faster) and heating of the disk deeper layers (slower).

Accepted by The Astrophysical Journal


Collapse of a molecular cloud core to stellar densities: stellar-core and outflow formationin radiation magnetohydrodynamics simulations

Matthew R. Bate1, Terrence S. Tricco2 and Daniel J. Price2

1 School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, United Kingdom

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2 Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Clayton, Vic 3800, Australia

E-mail contact: mbate at astro.ex.ac.uk

We have performed smoothed particle radiation magnetohydrodynamics (SPRMHD) simulations of the collapse ofrotating, magnetised molecular cloud cores to form protostars. The calculations follow the formation and evolution ofthe first hydrostatic core, the collapse to form a stellar core, the launching of outflows from both the first hydrostaticcore and stellar cores, and the breakout of the stellar outflow from the remnant of the first core. We investigatethe roles of magnetic fields and thermal feedback on the outflow launching process, finding that both magnetic andthermal forces contribute to the launching of the stellar outflow. We also follow the stellar cores until they grow tomasses of up to 20 Jupiter-masses, and determine their properties. We find that at this early stage, before fusionbegins, the stellar cores have radii of ≈ 3 R⊙ with radial entropy profiles that increase outward (i.e. are convectivelystable) and minimum entropies per baryon of s/kB ≈ 14 in their interiors. The structure of the stellar cores is foundto be insensitive to variations in the initial magnetic field strength. With reasonably strong initial magnetic fields,accretion on to the stellar cores occurs through inspiralling magnetised pseudo-discs with negligible radiative losses,as opposed to first cores which effectively radiate away the energy liberated in the accretion shocks at their surfaces.We find that magnetic field strengths of > 10 kG can be implanted in stellar cores at birth.

Accepted by MNRAS

Preprint at: http://arxiv.org/pdf/1310.1092Animations available at: http://www.astro.ex.ac.uk/people/mbate/Animations/stellarcore.htmlDataset available at: http://hdl.handle.net/10871/13883

Magnetic and Gravitational Disk-Star Interactions: An Interdependence of PMS StellarRotation Rates and Spin-Orbit Misalignments

Konstantin Batygin1 and Fred C. Adams2,3

1 Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics 60 Garden St., Cambridge,MA 02138, USA2 Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA3 Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA

E-mail contact: kbatygin at cfa.harvard.edu

The presence of giant gaseous planets that reside in close proximity to their host stars may be a consequence of large-scale radial migration through the proto-planetary nebulae. Within the context of this picture, significant orbitalobliquities characteristic of a substantial fraction of such planets can be attributed to external torques that perturbthe disks out of alignment with the spin axes of their host stars. Therefore, the acquisition of orbital obliquity exhibitssensitive dependence on the physics of disk-star interactions. Here, we analyze the primordial excitation of spin-orbitmisalignment of Sun-like stars, in light of disk-star angular momentum transfer. We begin by calculating the stellarpre-main sequence rotational evolution, accounting for spin-up due to gravitational contraction and accretion as wellas spin-down due to magnetic star-disk coupling. We devote particular attention to angular momentum transfer byaccretion, and show that while generally subdominant to gravitational contraction, this process is largely controlled bythe morphology of the stellar magnetic field (i.e. specific angular momentum accreted by stars with octupole-dominatedsurface fields is smaller than that accreted by dipole-dominated stars by an order of magnitude). Subsequently, weexamine the secular spin-axis dynamics of disk-bearing stars, accounting for the time-evolution of stellar and diskproperties and demonstrate that misalignments are preferentially excited in systems where stellar rotation is notoverwhelmingly rapid. Moreover, we show that the excitation of spin-orbit misalignment occurs impulsively, throughan encounter with a resonance between the stellar precession frequency and the disk-torquing frequency. Cumulatively,the model developed herein opens up a previously unexplored avenue towards understanding star-disk evolution andits consequences in a unified manner.

Accepted by ApJ


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Quantifying Observational Projection Effects Using Molecular Cloud Simulations

Christopher N. Beaumont1,2, Stella S.R. Offner3, Rahul Shetty4, Simon C.O. Glover4, and Alyssa A.Goodman2

1 Max-Planck Institut fur Astronomie, Konigstuhl 17, 69117 Heidelberg, Germany2 Universitat Heidelberg, Zentrum fur Astronomie, Inst. fur Theor. Astrophysik, Albert-Ueberle-Str. 2, 69120Heidelberg, Germany3 Purple Mountain Observatory & Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, Nanjing210008, China4 Institut fur Theoretische Physik und Astrophysik, Universitat Kiel, Leibnizstr. 15, 24118 Kiel, Germany5 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile6 Inst. of Planetology & Astrophysics Grenoble, 414, Rue de la Piscine, Domaine Universitaire, 38400 Saint-Martind’Heres, France7 Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago, Chile

E-mail contact: viki at mpia.de

The physical properties of molecular clouds are often measured using spectral-line observations, which provide the onlyprobes of the clouds’ velocity structure. It is hard, though, to assess whether and to what extent intensity featuresin position-position-velocity (PPV) space correspond to “real” density structures in position-position-position (PPP)space. In this paper, we create synthetic molecular cloud spectral-line maps of simulated molecular clouds, and presenta new technique for measuring the reality of individual PPV structures. Our procedure projects density structuresidentified in PPP space into corresponding intensity structures in PPV space and then measures the geometric overlapof the projected structures with structures identified from the synthetic observation. The fractional overlap betweena PPP and PPV structure quantifies how well the synthetic observation recovers information about the 3D struc-ture. Applying this machinery to a set of synthetic observations of CO isotopes, we measure how well spectral-linemeasurements recover mass, size, velocity dispersion, and virial parameter for a simulated star-forming region. Bydisabling various steps of our analysis, we investigate how much opacity, chemistry, and gravity affect measurementsof physical properties extracted from PPV cubes. For the simulations used here, our results suggest that superpositioninduces a ∼40% uncertainty in masses, sizes, and velocity dispersions derived from 13CO. The virial parameter ismost affected by superposition, such that estimates of the virial parameter derived from PPV and PPP informationtypically disagree by a factor of ∼2. This uncertainty makes it particularly difficult to judge whether gravitational orkinetic energy dominate a given region, since the majority of virial parameter measurements fall within a factor of 2of the equipartition level α ∼ 2.

Accepted by ApJ


Deep near-infrared imaging of W3 Main: constraints on stellar cluster formation

A. Bik1, A. Stolte2, M. Gennaro1,3, W. Brandner1, D. Gouliermis1,4, B. Hußmann2, E. Tognelli5, B.Rochau1, Th. Henning1, A. Adamo1, H. Beuther1, A. Pasquali6 and Y. Wang7

1 Max-Planck-Institut fur Astronomie, Konigstuhl 17, 69117 Heidelberg, Germany2 Argelander Institut fur Astronomie, Auf dem Hugel 71, 53121 Bonn, Germany3 Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA4 Universitat Heidelberg, Zentrum fur Astronomie, Institut fur Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120Heidelberg, Germany5 Department of Physics, University of Pisa, Largo Bruno Pontecorvo 3, 56127, Pisa, Italy6 Universitat Heidelberg, Zentrum fur Astronomie, Astronomisches Rechen Institut, Monchhofstrasse 12 - 14, 69120Heidelberg, Germany7 Purple Mountain Observatory, Chinese Academy of Sciences, 210008, Nanjing, PR China

E-mail contact: abik at mpia.de

Embedded clusters like W3 Main are complex and dynamically evolving systems that represent an important phaseof the star formation process. We aim at the characterization of the entire stellar content of W3 Main in a statisticalsense to identify possible differences in evolutionary phase of the stellar populations and find clues about the formation

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mechanism of this massive embedded cluster. Deep JHKs imaging is used to derive the disk fraction, Ks-band lumi-nosity functions and mass functions for several subregions in W3 Main. A two dimensional completeness analysis usingartificial star experiments is applied as a crucial ingredient to assess realistic completeness limits for our photometry.We find an overall disk fraction of 7.7 ± 2.3%, radially varying from 9.4 ± 3.0 % in the central 1 pc to 5.6 ± 2.2 %in the outer parts of W3 Main. The mass functions derived for three subregions are consistent with a Kroupa andChabrier mass function. The mass function of IRSN3 is complete down to 0.14 M⊙ and shows a break at M ∼ 0.5 M⊙.We interpret the higher disk fraction in the center as evidence for a younger age of the cluster center. We find that theevolutionary sequence observed in the low-mass stellar population is consistent with the observed age spread amongthe massive stars. An analysis of the mass function variations does not show evidence for mass segregation. W3 Mainis currently still actively forming stars, showing that the ionizing feedback of OB stars is confined to small areas (∼0.5pc). The FUV feedback might be influencing large regions of the cluster as suggested by the low overall disk fraction.

Accepted by Astronomy and Astrophysics


A lithium depletion boundary age of 21 Myr for the Beta Pictoris moving group

Alex Binks1 and Rob Jeffries1

1 Keele University, Lennard Jones Building, Keele, Staffordshire, UK, ST55BG

E-mail contact: a.s.binks at keele.ac.uk

Optical spectroscopy is used to confirm membership for 8 low-mass candidates in the young Beta Pic moving group(BPMG) via their radial velocities, chromospheric activity and kinematic parallaxes. We searched for the presence ofthe Li I 6708A resonance feature and combined the results with literature measurements of other BPMG members tofind the age-dependent lithium depletion boundary (LDB) – the luminosity at which Li remains unburned in a coevalgroup. The LDB age of the BPMG is 21 +/- 4 Myr and insensitive to the choice of low-mass evolutionary models.This age is more precise, likely to be more accurate, and much older than that commonly assumed for the BPMG. Asa result, substellar and planetary companions of BPMG members will be more massive than previously thought.

Accepted by MNRAS


Multiple spiral patterns in the transitional disk of HD 100546

A. Boccaletti1, E. Pantin2, A.-M. Lagrange3, J.-C. Augereau3, H. Meheut2., and S.P. Quanz4

1 LESIA, Observatoire de Paris, CNRS, University Pierre et Marie Curie Paris 6 and University Denis Diderot Paris7, 5 place Jules Janssen, 92195 Meudon, France2 Laboratoire AIM, CEA/DSM-CNRS-University Paris Diderot, IRFU/Service d’Astrophysique, CEA/Saclay, 91191Gif-sur-Yvette Cedex, France3 Institut de Planetologie et d’Astrophysique de Grenoble, Universite Joseph Fourier, CNRS, BP 53, 38041 Grenoble,France4 Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland

E-mail contact: anthony.boccaletti at obspm.fr

Protoplanetary disks around young stars harbor many structures related to planetary formation. Of particular interest,spiral patterns were discovered among several of these disks and are expected to be the sign of gravitational instabilitiesleading to giant planets formation or gravitational perturbations caused by already existing planets. In this context,the star HD100546 presents some specific characteristics with a complex gas and dusty disk including spirals as wellas a possible planet in formation. The objective of this study is to analyze high contrast and high angular resolutionimages of this emblematic system to shed light on critical steps of the planet formation. We retrieved archival imagesobtained at Gemini in the near IR (Ks band) with the instrument NICI and processed the data using advanced highcontrast imaging technique taking advantage of the angular differential imaging. These new images reveal the spiralpattern previously identified with HST with an unprecedented resolution, while the large-scale structure of the diskis mostly erased by the data processing. The single pattern at the southeast in HST images is now resolved into amulti-armed spiral pattern. Using two models of a gravitational perturber orbiting in a gaseous disk we attempted

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to bring constraints on the characteristics of this perturber assuming each spiral being independent and we derivedqualitative conclusions. The non-detection of the northeast spiral pattern observed in HST allows to put a lower limiton the intensity ratio between the two sides of the disk, which if interpreted as forward scattering yields a largeranisotropic scattering than derived in the visible. Also, we found that the spirals are likely spatially resolved witha thickness of about 5–10AU. Finally, we did not detect the candidate forming planet recently discovered in the Lpband, with a mass upper limit of 16–18 MJ .

Accepted by A&A


Inside Out Planet Formation

Sourav Chatterjee1 and Jonathan C. Tan1,2

1 Department of Astronomy, University of Florida, Gainesville, FL 32611, USA2 Department of Physics, University of Florida, Gainesville, FL 32611, USA

E-mail contact: s.chatterjee at ufl.edu

The compact multi-transiting planet systems discovered by Kepler challenge planet formation theories. Formation insitu from disks with radial mass surface density, Σ, profiles similar to the minimum mass solar nebula (MMSN) butboosted in normalization by factors >∼10 has been suggested. We propose that a more natural way to create theseplanets in the inner disk is formation sequentially from the inside-out via creation of successive gravitationally unstablerings fed from a continuous stream of small (∼cm–m size) “pebbles”, drifting inwards via gas drag. Pebbles collectat the pressure maximum associated with the transition from a magneto-rotational instability (MRI)-inactive (“deadzone”) region to an inner MRI-active zone. A pebble ring builds up until it either becomes gravitationally unstable toform an ∼1 Mearth planet directly or induces gradual planet formation via core accretion. The planet may undergoType I migration into the active region, allowing a new pebble ring and planet to form behind it. Alternatively ifmigration is inefficient, the planet may continue to accrete from the disk until it becomes massive enough to isolateitself from the accretion flow. A variety of densities may result depending on the relative importance of residual gasaccretion as the planet approaches its isolation mass. The process can repeat with a new pebble ring gathering atthe new pressure maximum associated with the retreating dead zone boundary. Our simple analytical model for thisscenario of inside-out planet formation yields planetary masses, relative mass scalings with orbital radius, and minimumorbital separations consistent with those seen by Kepler. It provides an explanation of how massive planets can formwith tightly-packed and well-aligned system architectures, starting from typical protoplanetary disk properties.

Accepted by The Astrophysical Journal, Oct. 29, 2013


Deuterated water in the solar-type protostars NGC 1333 IRAS 4A and IRAS 4B

A. Coutens1,2,3,4, C. Vastel1,2, S. Cabrit5, C. Codella6, L. E. Kristensen7, C. Ceccarelli8, E. F. vanDishoeck9,10 and the CHESS/WISH/HEXOS collaboration

1 Universite de Toulouse, UPS-OMP, IRAP, Toulouse, France2 CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, F-31028 Toulouse Cedex 4, France3 Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø., Denmark4 Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, ØsterVoldgade 5-7, DK-1359 Copenhagen K., Denmark5 LERMA, Observatoire de Paris, UMR 8112 CNRS/INSU, 61 Av. de l’Observatoire, 75014 Paris, France6 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy7 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA8 Institut de Planetologie et d’Astrophysique de Grenoble (IPAG), UMR 5274, UJF-Grenoble 1/CNRS, F-38041Grenoble, France9 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands10 Max-Planck-Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany

E-mail contact: acoutens at nbi.dk

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Context. The HDO/H2O ratio is a relevant tool for understanding mechanisms of water formation and evolution fromthe prestellar phase to the formation of planets and comets.Aims. The aim of this paper is to study deuterated water in the solar-type protostars NGC 1333 IRAS 4A andIRAS 4B, compare their HDO abundance distribution with other star-forming regions and constrain their HDO/H2Oratios.Methods. Using the Herschel/HIFI instrument as well as ground-based telescopes, we observed several HDO linescovering a large excitation range (Eup/k = 22–168 K) towards these protostars and an outflow position. Non-LTEradiative transfer codes were then used to determine the HDO abundance profiles in these sources.Results. The HDO fundamental line profiles show a very broad component, tracing the molecular outflows, in additionto a narrower emission component as well as a narrow absorbing component. In the protostellar envelope of NGC 1333IRAS 4A, the HDO inner (T ≥ 100 K) and outer (T < 100 K) abundances with respect to H2 are estimated with a3σ uncertainty at 7.5+3.5

−3.0 × 10−9 and 1.2+0.4−0.4 × 10−11 respectively, whereas, in NGC 1333 IRAS 4B, they are 1+1.8

−0.9

× 10−8 and 1.2+0.6−0.4 × 10−10 respectively. Similarly to the low-mass protostar IRAS 16293-2422, an absorbing outer

layer with an enhanced abundance of deuterated water is required to reproduce the absorbing components seen inthe fundamental lines at 465 and 894 GHz in both sources. This water-rich layer is probably extended enough toencompass the two sources, as well as parts of the outflows. In the outflows emanating from NGC 1333 IRAS 4A, theHDO column density is estimated at about (2–4) × 1013 cm−2, leading to an abundance of about (0.7–1.9) × 10−9.An HDO/H2O ratio between 7 × 10−4 and 9 × 10−2 is also derived in the outflows. In the warm inner regions ofthese two sources, we estimate the HDO/H2O ratios at about 1 × 10−4 – 4 × 10−3. This ratio seems higher (a few%) in the cold envelope of IRAS 4A, whose possible origin is discussed in relation to formation processes of HDO andH2O.Conclusions. In low-mass protostars, the HDO outer abundances range in a small interval, between ∼10−11 and a few10−10. No clear trends are found between the HDO abundance and various source parameters (Lbol, Lsmm, Lsmm/Lbol,Tbol, Lbol

0.6/Menv). A tentative correlation is observed however between the ratio of the inner and outer abundanceswith the submillimeter luminosity.

Accepted by A&A


Three-Dimensional Radiation-Hydrodynamics Calculations of the Envelopes of YoungPlanets Embedded in Protoplanetary Disks

Gennaro D’Angelo1, 2, 4 and Peter Bodenheimer3

1 NASA Ames Research Center, MS 245-3, Moett Field, CA 94035, USA2 SETI Institute, 189 Bernardo Avenue, Mountain View, CA 94043, USA3 UCO/Lick Observatory, University of California, Santa Cruz, CA 95064, USA4 Visiting Research Scientist, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

E-mail contact: gennaro.dangelo at nasa.gov

We perform global three-dimensional (3-D) radiation-hydrodynamics calculations of the envelopes surrounding youngplanetary cores of 5, 10, and 15 Earth masses, located in a protoplanetary disk at 5 and 10 AU from a solar-mass star.We apply a nested-grid technique to resolve the thermodynamics of the disk at the orbital-radius length scale andthat of the envelope at the core-radius length scale. The gas is modeled as a solar mixture of molecular and atomichydrogen, helium, and their ions. The equation of state accounts for both gas and radiation, and gas energy includescontributions from rotational and vibrational states of molecular hydrogen and from ionization of atomic species.Dust opacities are computed from first principles, applying the full Mie theory. One-dimensional (1-D) calculationsof planet formation are used to supplement the 3-D calculations by providing energy deposition rates in the envelopedue to solids accretion. We compare 1-D and 3-D envelopes and find that masses and gas accretion rates agree withinfactors of 2, and so do envelope temperatures. The trajectories of passive tracers are used to define the size of 3-Denvelopes, resulting in radii much smaller than the Hill radius and smaller than the Bondi radius. The moments ofinertia and angular momentum of the envelopes are determined and the rotation rates are derived from the rigid-bodyapproximation, resulting in slow bulk rotation. We find that the polar flattening is ¡ 0.05. The dynamics of theaccretion flow is examined by tracking the motion of tracers that move into the envelope. The anisotropy of this flowis characterized in terms of both its origin and impact site at the envelope surface. Gas merges with the envelope

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preferentially at mid- to high latitudes.

Accepted by ApJ


CO (3 – 2) High-Resolution Survey of the Galactic Plane: R1

J. T. Dempsey1, H. S. Thomas1 and M. J. Currie1

1 Joint Astronomy Centre, 660 N Aohoku Place, Hilo, HI 96720, USA

E-mail contact: j.dempsey at jach.hawaii.edu

We present the first release (R1) of data from the CO High-Resolution Survey (COHRS), which maps a strip of theinner Galactic plane in 12CO (J = 3 – 2). The data are taken using the Heterodyne Array Receiver Programme onthe James Clerk Maxwell Telescope (JCMT) in Hawaii, which has a 14 arcsec angular resolution at this frequency.When complete, this survey will cover |b| ≤ 0.◦5 between 10◦ < l < 65◦. This first release covers |b| ≤ 0.◦5 between10.◦25 < l < 17.◦5 and 50.◦25 < l < 55.◦25, and |b| ≤ 0.◦25 between 17.◦5 < l < 50.◦25. The data are smoothed to avelocity resolution of 1 km s−1, a spatial resolution of 16 arcsec and achieve a mean rms of ∼1 K. COHRS data areavailable to the community online at http://dx.doi.org/10.11570/13.0002. In this paper we describe the dataacquisition and reduction techniques used and present integrated intensity images and longitude–velocity maps. Wealso discuss the noise characteristics of the data. The high resolution is a powerful tool for morphological studies ofbubbles and filaments while the velocity information shows the spiral arms and outflows. These data are intended tocomplement both existing and upcoming surveys, e.g., the Bolocam Galactic Plane Survey (BGPS), ATLASGAL, theHerschel Galactic Plane Survey (Hi-GAL) and the JCMT Galactic Plane Survey with SCUBA-2 (JPS).

Accepted by ApJ Suppl. Ser.

http://iopscience.iop.org/0067-0049/209/1/8/article

Diffuse ionizing radiation within HH jets

A. Esquivel1 and A. C. Raga1

1 Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-543, 04510 MexicoD.F., Mexico

E-mail contact: esquivel at nucleares.unam.mx

We present numerical hydrodynamical simulations of a time dependent ejection velocity, precessing jet. The parametersused in our models correspond to a high excitation Herbig-Haro object, such as HH 80/81. We have included thetransfer of ionizing radiation produced within the shocked regions of the jet. The radiative transfer is computed witha ray-tracing scheme from all the cells with an emissivity above a certain threshold. We show the development of aradiative precursor, and compare the morphology with a model without the diffuse radiation. Our simulations showthat the morphology of the Hα emission is affected considerably if the diffuse ionizing radiation is accounted for. Thepredicted Hα position-velocity diagram (i.e., spatially resolved emission line profiles) from a model with the transferof ionizing radiation has a relatively strong component at zero velocity, corresponding to the radiative precursor.Qualitatively similar “zero velocity components” are observed in HH 80/81 and in the jet from Sanduleak’s star inthe LMC.

Accepted by Astroph. J.

http://www.nucleares.unam.mx/astroplasmas/images/stories/pdf/jetdiff.pdf

On the corotation torque for low-mass eccentric planets

Stephen M. Fendyke1 and Richard P. Nelson1

1 Astronomy Unit, School of Physics and Astronomy, Queen Mary, University of London, United Kingdom

E-mail contact: S.M.Fendyke at qmul.ac.uk

We present the results of high resolution 2D simulations of low mass planets on fixed eccentric orbits embedded in

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protoplanetary discs. The aim of this study is to determine how the strength of the sustained, non-linear corotationtorque experienced by embedded planets varies as a function of orbital eccentricity, disc parameters, and planetarymass. In agreement with previous work we find that the corotation torque diminishes as orbital eccentricity, e,increases. Analysis of the time-averaged streamlines in the disc demonstrates that the width of the horseshoe regionnarrows as the eccentricity increases, and we suggest that this narrowing largely explains the observed decrease in thecorotation torque. We employ three distinct methods for estimating the strength of the unsaturated corotation torquefrom our simulations, and provide an empirical fit to these results. We find that a simple model where the corotationtorque, ΓC, decreases exponentially with increasing eccentricity (i.e. ΓC ∝ exp(e/ef)) provides a good global fit tothe data with an e-folding eccentricity, ef , that scales linearly with the disc scale height at the planet location. Weconfirm that this model provides a good fit for planet masses of 5 and 10 M⊕ in our simulations. The formation ofplanetary systems is likely to involve significant planet-planet interactions that will excite eccentric orbits, and this islikely to influence disc-driven planetary migration through modification of the corotation torque. Our results suggestthat high fidelity models of planetary formation should account for these effects.

Accepted by MNRAS


Radiation Magnetohydrodynamics in Global Simulations of Protoplanetary Disks

M. Flock1,2, S. Fromang1,2, M. Gonzalez2,3 and B. Commercon4

1 CEA, Irfu, SAp, Centre de Saclay, 91191 Gif-sur-Yvette, France2 UMR AIM, CEA-CNRS-Univ. Paris Diderot, Centre de Saclay, 91191 Gif-sur-Yvette, France3 Universit Paris Diderot, Sorbonne Paris Cit, AIM, UMR 7158, CEA, CNRS, F-91191 Gif-sur-Yvette, France4 Laboratoire de radioastronomie, UMR 8112 du CNRS, Ecole normale superieure et Observatoire de Paris, 24 rueLhomond, F-75231 Paris Cedex 05, France

E-mail contact: Mario.Flock at cea.fr

Our aim is to study the thermal and dynamical evolution of protoplanetary disks in global simulations, includingthe physics of radiation transfer and magneto-hydrodynamic turbulence caused by the magneto-rotational instability.We develop a radiative transfer method based on the flux-limited diffusion approximation that includes frequencydependent irradiation by the central star. This hybrid scheme is implemented in the PLUTO code. The focus of ourimplementation is on the performance of the radiative transfer method. Using an optimized Jacobi preconditionedBiCGSTAB solver, the radiative module is three times faster than the magneto-hydrodynamic step for the disk setup weconsider. We obtain weak scaling efficiencies of 70% up to 1024 cores. We present the first global 3D radiation magneto-hydrodynamic simulations of a stratified protoplanetary disk. The disk model parameters are chosen to approximatethose of the system AS 209 in the star-forming region Ophiuchus. Starting the simulation from a disk in radiativeand hydrostatic equilibrium, the magneto-rotational instability quickly causes magneto-hydrodynamic turbulence andheating in the disk. We find that the turbulent properties are similar to that of recent locally isothermal globalsimulations of protoplanetary disks. For example, the rate of angular momentum transport α is a few times 10−3.For the disk parameters we use, turbulent dissipation heats the disk midplane and raises the temperature by about15% compared to passive disk models. The vertical temperature profile shows no temperature peak at the midplaneas in classical viscous disk models. A roughly flat vertical temperature profile establishes in the disk optically thickregion close to the midplane. We reproduce the vertical temperature profile with a viscous disk models for whichthe stress tensor vertical profile is flat in the bulk of the disk and vanishes in the disk corona. The present paperdemonstrates for the first time that global radiation magneto-hydrodynamic simulations of turbulent protoplanetarydisks are feasible with current computational facilities. This opens up the windows to a wide range of studies of thedynamics of protoplanetary disks inner parts, for which there are significant observational constraints.

Accepted by A&A


Water in Protoplanetary Disks: Deuteration and Turbulent Mixing

Kenji Furuya1, Yuri Aikawa1, Hideko Nomura2,3,4, Franck Hersant5,6 and Valentine Wakelam5,6

1 Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan2 Department of Astronomy, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan

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3 National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588, Japan4 Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan5 Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac, France6 CNRS, LAB, UMR 5804, F-33270, Floirac, France

E-mail contact: furuya at stu.kobe-u.ac.jp

We investigate water and deuterated water chemistry in turbulent protoplanetary disks. Chemical rate equationsare solved with the diffusion term, mimicking turbulent mixing in vertical direction. Water near the midplane istransported to the disk atmosphere by turbulence and destroyed by photoreactions to produce atomic oxygen, whilethe atomic oxygen is transported to the midplane and reforms water and/or other molecules. We find that this cyclesignificantly decreases column densities of water ice at r < 30 AU, where dust temperatures are too high to reformwater ice effectively. The radial extent of such region depends on the desorption energy of atomic hydrogen. Ourmodel indicates that water ice could be deficient even outside the sublimation radius. Outside this radius, the cycledecreases the D/H ratio of water ice from ∼ 2× 10−2, which is set by the collapsing core model, to 10−4–10−2 in 106

yr, without significantly decreasing the water ice column density. The resultant D/H ratios depend on the strengthof mixing and the radial distance from the central star. Our finding suggests that the D/H ratio of cometary water(∼10−3-10−4) could be established (i.e. cometary water could be formed) in the solar nebula, even if the D/H ratioof water ice delivered to the disk was very high (∼10−2).

Accepted by ApJ

http://arxiv.org/pdf/1310.3342v1.pdf

Face to phase with RU Lupi

Gosta F. Gahm1, Henricus C. Stempels2, Frederick M. Walter3, Peter P. Petrov4 and Gregory J.Herczeg5

1 Stockholm Observatory, AlbaNova University Centre, SE-10691 Stockholm, Sweden2 Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden3 Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800, USA4 Crimean Astrophysical Observatory, p/o Nauchny, Crimea, 98409 Ukraine5 The Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian Qu, Beijing100871, P. R. China

E-mail contact: gahm at astro.su.se

We present new results on the classical T Tauri star RU Lupi based on three observing runs collecting high-resolutionoptical spectra. In connection to the third run, complementary NIR spectra, multicolour photometric data, and X-rayobservations were obtained. RU Lupi has an extremely rich emission line spectrum, but the photospheric absorptionlines are weakened. This veiling becomes extremely strong on occasion, and we show that this effect is due to narrowemission lines that fills in the photospheric lines. Only at low degrees of veiling does the continuous excess emission,originating at the hot spot on the stellar surface, dominate. We also find that the radial velocities of narrow emissioncomponents in lines of He I vary in anti-phase with the periodically changing photospheric lines, reflecting the locationand motion of the accretion footprint.The blue-shifted wings in the optical emission lines of He I, attributed to a stellar wind, are remarkably stable inequivalent width. In contrast, the red-shifted wings change dramatically in strength depending on rotational phase.From the pattern of variability we infer that these wings originate in accreting gas close to the star, and that theaccretion funnels are bent and trail the hot spot. Forbidden emission lines are very stable over the entire observingperiod and originate in the disk wind. A system of narrow, blue-shifted absorption features seen in lines of Ca II andNa I can be traced to a disk wind as well. Slightly blue-shifted emission components are present in the forbidden linesand might be related to a wide angle molecular disk wind.

Accepted by Astronomy and Astrophysics


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Three-dimensional off-lattice Monte Carlo kinetics simulations of interstellar grain chem-istry and ice structure

Robin T. Garrod1

1 Center for Radiophysics & Space Research, Cornell University

E-mail contact: rgarrod at astro.cornell.edu

The first off-lattice Monte Carlo kinetics model of interstellar dust-grain surface chemistry is presented. The positionsof all surface particles are determined explicitly, according to the local potential minima resulting from the pair-wiseinteractions of contiguous atoms and molecules, rather than by a pre-defined lattice structure. The model is capableof simulating chemical kinetics on any arbitrary dust-grain morphology, as determined by the user-defined positionsof each individual dust-grain atom. A simple method is devised for the determination of the most likely diffusionpathways and their associated energy barriers for surface species. The model is applied to a small, idealized dustgrain, adopting various gas densities and using a small chemical network. Hydrogen and oxygen atoms accrete ontothe grain, to produce H2O, H2, O2 and H2O2. The off-lattice method allows the ice structure to evolve freely; icemantle porosity is found to be dependent on the gas density, which controls the accretion rate. A gas density of2× 104 cm−3, appropriate to dark interstellar clouds, is found to produce a fairly smooth and non-porous ice mantle.At all densities, H2 molecules formed on the grains collect within the crevices that divide nodules of ice, and withinmicropores (whose extreme inward curvature produces strong local potential minima). The larger pores produced inthe high-density models are not typically filled with H2. Direct deposition of water molecules onto the grain indicatesthat amorphous ices formed in this way may be significantly more porous than interstellar ices that are formed bysurface chemistry.



A measurement of the turbulence-driven density distribution in a non-star-formingmolecular cloud

Adam Ginsburg1,2, Christoph Federrath3 and Jeremy Darling1

1 CASA, University of Colorado, 389-UCB, Boulder, CO 80309, USA2 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Mnchen, Germany3 Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Vic 3800, Australia

E-mail contact: adam.g.ginsburg at gmail.com

Molecular clouds are supersonically turbulent. This turbulence governs the initial mass function and the star formationrate. In order to understand the details of star formation, it is therefore essential to understand the properties ofturbulence, in particular the probability distribution of density in turbulent clouds. We present H2CO volume densitymeasurements of a non-star-forming cloud along the line of sight towards W49A. We use these measurements inconjunction with total mass estimates from 13CO to infer the shape of the density probability distribution function.This method is complementary to measurements of turbulence via the column density distribution and should beapplicable to any molecular cloud with detected CO. We show that turbulence in this cloud is probably compressivelydriven, with a compressive-to-total Mach number ratio b = MC/M > 0.4. We measure the standard deviationof the density distribution, constraining it to the range 1.5 < σs < 1.9 assuming that the density is lognormallydistributed. This measurement represents an essential input into star formation laws. The method of averagingover different excitation conditions to produce a model of emission from a turbulent cloud is generally applicable tooptically thin line observations. Molecular clouds are supersonically turbulent. This turbulence governs the initialmass function and the star formation rate. In order to understand the details of star formation, it is therefore essentialto understand the properties of turbulence, in particular the probability distribution of density in turbulent clouds.We present H2CO volume density measurements of a non-star-forming cloud along the line of sight towards W49A.We use these measurements in conjunction with total mass estimates from 13CO to infer the shape of the densityprobability distribution function. This method is complementary to measurements of turbulence via the columndensity distribution and should be applicable to any molecular cloud with detected CO. We show that turbulence inthis cloud is probably compressively driven, with a compressive-to-total Mach number ratio b = MC/M > 0.4. Wemeasure the standard deviation of the density distribution, constraining it to the range 1.5 < σs < 1.9 assuming that

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the density is lognormally distributed. This measurement represents an essential input into star formation laws. Themethod of averaging over different excitation conditions to produce a model of emission from a turbulent cloud isgenerally applicable to optically thin line observations.

Accepted by ApJ


The IRAM-30m line survey of the Horsehead PDR: IV. Comparative chemistry of H2COand CH3OH

V.V. Guzman1, J.R. Goicoechea2, J. Pety1,3, P. Gratier1, M. Gerin3, E. Roueff4, F. Le Petit4, J. LeBourlot4, and A. Faure5

1 Institut de Radioastronomie Millimetrique (IRAM), 300 rue de la Piscine, 38406 Saint Martin d’Heres, France2 Departamento de Astrofısica. Centro de Astrobiologıa. CSIC-INTA. Carretera de Ajalvir, Km 4. Torrejon de Ardoz,28850 Madrid, Spain3 LERMA - LRA, UMR 8112, Observatoire de Paris and Ecole normale Superieure, 24 rue Lhomond, 75231 Paris,France4 LUTH UMR 8102, CNRS and Observatoire de Paris, Place J. Janssen, 92195 Meudon Cedex, France5 UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041Grenoble, France

E-mail contact: guzman at iram.fr

Aims. We investigate the dominant formation mechanism of H2CO and CH3OH in the Horsehead PDR and itsassociated dense core.Methods. We performed deep integrations of several H2CO and CH3OH lines at two positions in the Horsehead,namely the PDR and dense core, with the IRAM-30m telescope. In addition, we observed one H2CO higher frequencyline with the CSO telescope at both positions. We determine the H2CO and CH3OH column densities and abundancesfrom the single-dish observations complemented with IRAM-PdBI high-angular resolution maps (6′′) of both species.We compare the observed abundances with PDR models including either pure gas-phase chemistry or both gas-phaseand grain surface chemistry.Results. We derive CH3OH abundances relative to total number of hydrogen atoms of ∼ 1.2×10−10 and ∼ 2.3×10−10

in the PDR and dense core positions, respectively. These abundances are similar to the inferred H2CO abundance inboth positions (∼ 2 × 10−10). We find an abundance ratio H2CO/CH3OH of ∼2 in the PDR and ∼1 in the densecore. Pure gas-phase models cannot reproduce the observed abundances of either H2CO or CH3OH at the PDRposition. Both species are therefore formed on the surface of dust grains and are subsequently photodesorbed intothe gas-phase at this position. At the dense core, on the other hand, photodesorption of ices is needed to explain theobserved abundance of CH3OH, while a pure gas-phase model can reproduce the observed H2CO abundance. Thehigh-resolution observations show that CH3OH is depleted onto grains at the dense core. CH3OH is thus present inan envelope around this position, while H2CO is present in both the envelope and the dense core itself.Conclusions. Photodesorption is an efficient mechanism to release complex molecules in low FUV-illuminated PDRs,where thermal desorption of ice mantles is ineffective.

Accepted by A&A


Effects of grain growth mechanisms on the extinction curve and the metal depletion inthe interstellar medium

Hiroyuki Hirashita1 and Nikolai V. Voshchinnikov2

1 Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan

2 Sobolev Astronomical Institute, St. Petersburg University, Universitetskii prosp., 28, St. Petersburg 198504, Russia

E-mail contact: [email protected]

Dust grains grow their sizes in the interstellar clouds (especially in molecular clouds) by accretion and coagulation. Here

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we model and test these processes by examining the consistency with the observed variation of the extinction curvesin the Milky Way. We find that, if we simply use the parameters used in previous studies, the model fails to explainthe flattening of far-UV extinction curve for large RV (flatness of optical extinction curve) and the existence of carbonbump even in flat extinction curves. This discrepancy is resolved by adopting a ‘tuned’ model, in which coagulation ofcarbonaceous dust is less efficient (by a factor of 2) and that of silicate is more efficient with the coagulation thresholdremoved. The tuned model is also consistent with the relation between silicon depletion (indicator of accretion) andRV if the duration of accretion and coagulation is >∼ 100(nH/10

3cm−3)−1 Myr, where nH is the number density ofhydrogen nuclei in the cloud. We also examine the relations between each of the extinction curve features (UV slope,far-UV curvature, and carbon bump strength) and RV . The correlation between UV slope and RV , which is thestrongest among the three correlations, is well reproduced by the tuned model. For far-UV curvature and carbonbump strength, the observational data are located between the tuned model and the original model without tuning,implying that the large scatters in the observational data can be explained by the sensitive response to the coagulationefficiency. The overall success of the tuned model indicates that accretion and coagulation are promising mechanismsof producing the variation of extinction curves in the Milky Way, although we do not exclude possibilities of otherdust-processing mechanisms changing extinction curves.

Accepted by MNRAS


The impact of freeze-out on collapsing molecular clouds

S. Hocuk1, S. Cazaux1and M. Spaans1

1 Kapteyn Astronomical Institute, University of Groningen, P. O. Box 800, 9700 AV Groningen, Netherlands

E-mail contact: seyit at astro.rug.nl

Atoms and molecules, and in particular CO, are important coolants during the evolution of interstellar star-forming gasclouds. The presence of dust grains, which allow many chemical reactions to occur on their surfaces, strongly impactsthe chemical composition of a cloud. At low temperatures, dust grains can lock-up species from the gas phase whichfreeze out and form ices. In this sense, dust can deplete important coolants. Our aim is to understand the effects offreeze-out on the thermal balance and the evolution of a gravitationally bound molecular cloud. For this purpose, weperform 3D hydrodynamical simulations with the adaptive mesh code FLASH. We simulate a gravitationally unstablecloud under two different conditions, with and without grain surface chemistry. We let the cloud evolve until onefree-fall time is reached and track the thermal evolution and the abundances of species during this time. We see thatat a number density of 104 cm3 most of the CO molecules are frozen on dust grains in the run with grain surfacechemistry, thereby depriving the most important coolant. As a consequence, we find that the temperature of the gasrises up to ∼25 K. The temperature drops once again due to gas-grain collisional cooling when the density reaches afew × 104 cm3. We conclude that grain surface chemistry not only affects the chemical abundances in the gas phase,but also leaves a distinct imprint in the thermal evolution that impacts the fragmentation of a star-forming cloud. Asa final step, we present the equation of state of a collapsing molecular cloud that has grain surface chemistry included.

Accepted by MNRAS Letters


Classical T Tauri stars: magnetic fields, coronae, and star-disc interactions

C.P. Johnstone1, M. Jardine2, S.G. Gregory2, J.-F. Donati3, and G. Hussain4

1 University of Vienna, Department of Astronomy, Turkenschanzstrasse 17, 1180 Vienna, Austria2 School of Physics and Astronomy, Universtiy of St Andrews, St Andrews, Scotland KY16 9SS3 LATT-UMR 5572, CNRS & Univ. P. Sabatier, 14 Av. E. Belin, Toulouse, F-31400, France4 ESO, Karl-Schwarzchild-Str. 2, D-85748 Garching, Germany

E-mail contact: colin.johnstone at univie.ac.at

The magnetic fields of young stars set their coronal properties and control their spin evolution via the star-discinteraction and outflows. Using 14 magnetic maps of 10 classical T Tauri stars (CTTSs) we investigate their closedX-ray emitting coronae, their open wind-bearing magnetic fields, and the geometry of magnetospheric accretion flows.

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The magnetic fields of all the CTTSs are multipolar. Stars with simpler (more dipolar) large-scale magnetic fieldshave stronger fields, are slower rotators, and have larger X-ray emitting coronae compared to stars with more complexlarge-scale magnetic fields. The field complexity controls the distribution of open and closed field regions across thestellar surface, and strongly influences the location and shapes of accretion hot spots. However, the higher orderfield components are of secondary importance in determining the total unsigned open magnetic flux, which dependsmainly on the strength of the dipole component and the stellar surface area. Likewise, the dipole component aloneprovides an adequate approximation of the disc truncation radius. For some stars, the pressure of the hot coronalplasma dominates the stellar magnetic pressure and forces open the closed field inside the disc truncation radius. Thisis significant as accretion models generally assume that the magnetic field has a closed geometry out to the inner discedge.

Accepted by MNRAS


OTS44: Disk and accretion at the planetary border

V. Joergens1,2, M. Bonnefoy1, Y. Liu3,4, A. Bayo1,5, S. Wolf4, G. Chauvin6 and P. Rojo7

1 Max-Planck Institut fur Astronomie, Heidelberg, Germany2 Universitat Heidelberg, Zentrum fur Astronomie, Inst. fur Theor. Astrophysik, Heidelberg, Germany3 Purple Mountain Observatory & Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, Nanjing,China4 Institut fur Theoretische Physik und Astrophysik, Universitat Kiel, Germany5 European Southern Observatory, Santiago, Chile6 Inst. of Planetology & Astrophysics Grenoble, France7 Departamento de Astronomia, Universidad de Chile, Santiago, Chile

E-mail contact: viki at mpia.de

We discover that the very low-mass brown dwarf OTS 44 (M9.5, ∼12MJup) has significant accretion and a substantialdisk, which demonstrates that the processes that accompany canonical star formation occur down to a central massof a few Jupiter masses. We discover in VLT/SINFONI spectra that OTS44 has strong, broad, and variable Paβemission that is evidence for active accretion at the planetary border. We also detect strong Hα emission of OTS 44in a literature spectrum and determine an Hα EW of -141 A, which indicates active accretion. Both the Paβ and Hαemission lines have broad profiles with wings extending to velocities of about ±200kms−1. We determine the massaccretion rate of OTS 44 based on Hα to 7.6×10−12M⊙ yr−1. This result shows that OTS 44 has a relatively high mass-accretion rate considering its small central mass. This mass rate is nevertheless consistent with the general decreasingtrend found for stars of several solar masses down to brown dwarfs. Furthermore, we determine the properties ofthe disk surrounding OTS 44 through radiative transfer modeling of flux measurement from the optical to the far-IR(Herschel) by applying a Bayesian analysis. We find that OTS44 has a highly flared disk (β >1.2) with a mass of9.1+1.7

−5.5 × 10−5M⊙, i.e. ∼0.1MJup or 30MEarth. We show that the ratio of the disk-to-central-mass of about 10−2

found for objects between 0.03M⊙ and 14M⊙ is also valid for OTS 44 at a mass of ∼0.01M⊙. Our observations arein line with an isolated star-like mode of the formation of brown dwarfs down to 0.01M⊙.

Accepted by A&A Letter

http://www.mpia.de/homes/joergens/publications/ots44.pdf


Water and Methanol Maser Survey of Protostars in the Orion Molecular Cloud Complex

Miju Kang1, Jeong-Eun Lee2, Minho Choi1, Yunhee Choi3,4, Kee-Tae Kim1, James Di Francesco5,6 andYong-Sun Park7

1 Korea Astronomy and Space Science Institute, 776 Daedeokdaero, Yuseong, Daejeon 305-348, Republic of Korea2 Department of Astronomy and Space Science, Kyung Hee University, Yongin-shi, Kyungki-do 446-701, Republic ofKorea3 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands

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4 SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands5 National Research Council of Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Rd., Victoria, BC,V9E 2E7, Canada6 University of Victoria, Department of Physics and Astronomy, PO Box 3055, STN CSC, Victoria, BC, V8W 3P6,Canada7 Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republicof Korea

E-mail contact: mjkang at kasi.re.kr

The results of a maser survey toward ninety-nine protostars in the Orion molecular cloud complex are presented. Thetarget sources are low-mass protostars identified from infrared observations. Single-dish observations were carried outin the water maser line at 22 GHz and the methanol class I maser lines at 44, 95, and 133 GHz. Most of the detectedsources were mapped to determine the source positions. Five water maser sources were detected, and they are excitedby HH 1–2 VLA 3, HH 1–2 VLA 1, L1641N MM1/3, NGC 2071 IRS 1/3, and an object in the OMC 3 region. Thewater masers showed significant variability in intensity and velocity with time scales of a month or shorter. Fourmethanol emission sources were detected, and those in the OMC 2 FIR 3/4 and L1641N MM1/3 regions are probablymasers. The methanol emission from the other two sources in the NGC 2071 IRS 1–3 and V380 Ori NE regions areprobably thermal. For the water masers, the number of detections per protostar in the survey region is about 2%,which suggests that the water masers of low-mass protostars are rarely detectable. The methanol class I maser oflow-mass protostars is an even rarer phenomenon, with a detection rate much smaller than 1%.

Accepted by ApJS


ALMA observations of the molecular gas in the debris disk of the 30 Myr old starHD21997

A. Kospal1, A. Moor2, A. Juhasz3, P. Abraham2, D. Apai4, T. Csengeri5, C. A. Grady6,7, Th. Henning8,A. M. Hughes9, Cs. Kiss2, I. Pascucci10, and M. Schmalzl3

1 European Space Agency (ESA-ESTEC, SRE-SA), P.O. Box 299, 2200AG, Noordwijk, The Netherlands2 Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, P.O.Box 67, 1525 Budapest, Hungary3 Department of Astronomy and Department of Planetary Sciences, The University of Arizona, Tucson, AZ 85721,USA4 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany5 NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771, USA6 Eureka Scientific, 2452 Delmer Street, Suite 100, Oakland, CA 94602, USA7 Max-Planck-Institut fur Astronomie, Konigstuhl 17, 69117 Heidelberg, Germany8 Astronomy Department, Wesleyan University, Middletown, CT 06459, USA9 Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2333 CA Leiden, The Netherlands10 Lunar and Planetary Laboratory, Department of Planetary Sciences, University of Arizona, 1629 E. UniversityBoulevard, Tucson, AZ 85721, USA

E-mail contact: akospal at rssd.esa.int

The 30 Myr old A3-type star HD21997 is one of the two known debris dust disks having a measurable amount of coldmolecular gas. With the goal of understanding the physical state, origin, and evolution of the gas in young debrisdisks, we obtained CO line observations with the Atacama Large Millimeter/submillimeter Array (ALMA). Here, wereport on the detection of 12CO and 13CO in the J=2–1 and J=3–2 transitions and C18O in the J=2–1 line. Thegas exhibits a Keplerian velocity curve, making our observation one of the few direct measurements of Keplerianrotation in a young debris disk. The measured CO brightness distribution could be reproduced by a simple star+disksystem, whose parameters are rin < 26AU, rout =138± 20AU, M∗ = 1.8+0.5

−0.2M⊙, and i=32.6◦± 3.1◦. The total COmass, as calculated from the optically thin C18O line, is about (4–8)×10−2M⊕, while the CO line ratios suggest aradiation temperature on the order of 6–9K. Comparing our results with those obtained for the dust component of theHD21997 disk from ALMA continuum observations by Moor et al., we conclude that comparable amounts of CO gasand dust are present in the disk. Interestingly, the gas and dust in the HD21997 system are not co-located, indicating

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a dust-free inner gas disk within about 55AU of the star. We explore two possible scenarios for the origin of the gas.A secondary origin, which involves gas production from colliding or active planetesimals, would require unreasonablyhigh gas production rates and would not explain why the gas and dust are not co-located. We propose that HD21997is a hybrid system where secondary debris dust and primordial gas coexist. HD 21997, whose age exceeds both themodel predictions for disk clearing and the ages of the oldest TTauri-like or transitional gas disks in the literature,may be a key object linking the primordial and the debris phases of disk evolution.

Accepted by The Astrophysical Journal (Volume 776, A77)


Energy dissipation in head-on collisions of spheres

S. Krijt1, C. Guttler2,3, D. Heißelmann3, C. Dominik4,5 and A.G.G.M. Tielens1

1 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands2 Department of Earth and Planetary Sciences, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan3 Institut fur Geophysik und extraterrestrische Physik, Technische Universitat Braunschweig, Mendelssohnstraße 3,38106 Braunschweig, Germany4 Astronomical Institute ’Anton Pannekoek’, University of Amsterdam, PO Box 94249, 1090 GE Amsterdam, TheNetherlands5 Afdeling Sterrenkunde, Radboud Universiteit Nijmegen, Postbus 9010, 6500 GL, Nijmegen, The Netherlands

E-mail contact: krijt at strw.leidenuniv.nl

Collisions between spheres are a common ingredient in a variety of scientific problems, and the coefficient of restitution(COR) is a key parameter to describe their outcome. We present a new collision model that treats adhesion andviscoelasticity self-consistently, while energy losses arising from plastic deformation are assumed to be additive. Resultsshow that viscoelasticity can significantly increase the energy that is dissipated in a collision, enhancing the stickingvelocity. Furthermore, collisions well above the sticking velocity remain dissipative. We systemically compare themodel to a large and unbiased set of published laboratory experiments to show its general applicability. The model iswell capable of reproducing the important relation between impact velocity and COR as measured in the experiments,covering a wide range of materials, particle sizes, and collision velocities. Furthermore, the fitting parameters fromthose curves provide physical parameters such as the surface energy, yield strength, and characteristic viscous relaxationtime. Our results show that all three aspects – adhesion, viscoelastic dissipation and plastic deformation – are requiredfor a proper description of the kinetic energy losses in sphere collisions.

Accepted by Journal of Physics D: Applied Physics

http://iopscience.iop.org/0022-3727/46/43/435303/

Growing dust grains in protoplanetary discs - I. Radial drift with toy growth models

Guillaume Laibe1, Jean-Francois Gonzalez2, and Sarah T. Maddison3

1 Monash Centre for Astrophysics (MoCA) and School of Mathematical Sciences, Monash University, Clayton, Vic3800, Australia2 Universite de Lyon, Lyon, F-69003, France; Universite Lyon 1, Villeurbanne, F-69622, France; CNRS, UMR 5574,Centre de Recherche Astrophysique de Lyon; Ecole normale superieure de Lyon, 46, allee dItalie, F-69364 Lyon Cedex07, France3 Centre for Astrophysics and Supercomputing, Swinburne University, PO Box 218, Hawthorn, VIC 3122, Australia

E-mail contact: guillaume.laibe at monash.edu

In a series of papers, we present a comprehensive analytic study of the global motion of growing dust grains inprotoplanetary discs, addressing both the radial drift and the vertical settling of the particles. Here we study how theradial drift of dust particles is affected by grain growth. In a first step, toy models in which grain growth can eitherbe constant, accelerate or decelerate are introduced. The equations of motion are analytically integrable and thereforethe grains dynamics is easy to understand.The radial motion of growing grains is governed by the relative efficiency of the growth and migration processeswhich is expressed by the dimensionless parameter Lambda, as well as the exponents for the gas surface density and

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temperature profiles, denoted p and q respectively. When Lambda is of order unity, growth and migration are stronglycoupled, providing the most efficient radial drift. For the toy models considered, grains pile up when −p+ q+1/2 < 0.Importantly, we show the existence of a second process which can help discs to retain their solid materials. Foraccelerating growth, grains end up their migration at a finite radius, thus avoiding being accreted onto the centralstar.

Accepted by MNRAS


Growing dust grains in protoplanetary discs - II. The Radial drift barrier problem

Guillaume Laibe1

1 Monash Centre for Astrophysics (MoCA) and School of Mathematical Sciences, Monash University, Clayton, Vic3800, Australia


We aim to study the migration of growing dust grains in protoplanetary discs, where growth and migration are tightlycoupled. This includes the crucial issue of the radial-drift barrier for growing dust grains. We therefore extend thestudy performed in Paper I, considering models for grain growth and grain dynamics where both the migration andgrowth rate depend on the grain size and the location in the disc. The parameter space of disc profiles and growthmodels is exhaustively explored. In doing so, interpretations for the grain motion found in numerical simulations arealso provided.We find that a large number of cases is required to characterise entirely the grains radial motion, providing a largenumber of possible outcomes. Some of them lead dust particles to be accreted onto the central star and some of themdon’t.We find then that q < 1 is required for discs to retain their growing particles, where q is the exponent of the radialtemperature profile T (R) ∝ R−q. Additionally, the initial dust-to gas ratio has to exceed a critical value for grains topile up efficiently, thus avoiding being accreted onto the central star. Discs are also found to retain efficiently smalldust grains regenerated by fragmentation. We show how those results are sensitive to the turbulent model considered.Even though some physical processes have been neglected, this study allows to sketch a scenario in which grains cansurvive the radial-drift barrier in protoplanetary discs as they grow.

Accepted by MNRAS


Growing dust grains in protoplanetary discs - III. Vertical settling

Guillaume Laibe1, Jean-Francois Gonzalez2, Sarah T. Maddison3, and Elisabeth Crespe2

1 Monash Centre for Astrophysics (MoCA) and School of Mathematical Sciences, Monash University, Clayton, Vic3800, Australia2 Universite de Lyon, Lyon, F-69003, France; Universite Lyon 1, Villeurbanne, F-69622, France; CNRS, UMR 5574,Centre de Recherche Astrophysique de Lyon; Ecole normale superieure de Lyon, 46, allee dItalie, F-69364 Lyon Cedex07, France3 Centre for Astrophysics and Supercomputing, Swinburne University, PO Box 218, Hawthorn, VIC 3122, Australia


We aim to derive a simple analytic model to understand the essential properties of vertically settling growing dustgrains in laminar protoplanetary discs. Separating the vertical dynamics from the motion in the disc midplane, weintegrate the equations of motion for both a linear and an exponential grain growth rate. Numerical integrations areperformed for more complex growth models.We find that the settling efficiency depends on the value of the dimensionless parameter gamma, which characterisesthe relative efficiency of grain growth with respect to the gas drag. Since gamma is expected to be of order as theinitial dust-to-gas ratio in the disc (of order 10−2), grain growth enhances the energy dissipation of the dust particlesand improve the settling efficiency in protoplanetary discs. This behaviour is mostly independent of the growth modelconsidered as well as of the radial drift of the particles.

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Accepted by MNRAS


Early Star-Forming Processes in Dense Molecular Cloud L328; Identification of L328-IRS as a Proto-Brown Dwarf

Chang Won Lee1, Mi-Ryang Kim1,2, Gwanjeong Kim1,3, Masao Saito4, Philip C. Myers5 and YasutakaKurono4

1 Korea Astronomy & Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon, Korea2 Chungbuk National University, 52 Naesudong-ro, Heungdeok-gu, Cheongju Chungbuk, 361-763, Korea3 University of Science & Technology, 217 Gajungro, Yuseong-gu, Daejeon, 305-333, Korea4 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan5 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

E-mail contact: cwl at kasi.re.kr

This paper presents the results of mm to sub-mm observations of CO, HCN, N2H+, and HCO+ lines in the dense

molecular cloud L328, which harbors L328-IRS, a Very Low Luminosity Object (VeLLO). Our analysis of the line-widthfinds that 13CO and N2H

+ lines are broadened right over the smallest sub-core S2 where L328-IRS is located, whilethey are significantly narrower in other region of L328. Thus L328-IRS has a direct association with the sub-core. COobservations show a bipolar outflow from this VeLLO with an extent of ∼ 0.08 pc. The outflow momentum flux andefficiency are much less than those of low-mass protostars. The most likely mass accretion rate (∼ 3.6×10−7M⊙ yr−1)inferred from the analysis of the CO outflow is an order of magnitude smaller than the canonical value for a protostar.If the main accretion lasts during the typical Class 0 period of a protostar, L328-IRS will accrete the mass of a browndwarf, but not that of a star. Given that its envelope mass is small (∼ 0.09 M⊙) and 100% star formation rate isunlikely, we suggest that L328-IRS is likely a proto-brown dwarf. Inward motions are found in global scale in L328cloud and its sub-cores with a typical infall speed found in starless cores. L328 is found to be fairly well isolated fromother nearby clouds and seems to be forming three sub-cores simultaneously through a gravitational fragmentationprocess. Altogether these all leave L328-IRS as the best example supporting the idea that a brown dwarf forms like anormal star.


http://stacks.iop.org/0004-637X/777/50

A 500 pc filamentary gas wisp in the disk of the Milky Way

Guang-Xing Li1, Friedrich Wyrowski1, Karl Menten1 and Arnaud Belloche1

1 Max-Planck Institut fuer Radioastronomie, Auf dem Huegel 69, 53121, Bonn, Germamy

E-mail contact: gxli at mpifr-bonn.mpg.de

Star formation occurs in molecular gas. In previous studies, the structure of the molecular gas has been studied interms of molecular clouds, but has been overlooked beyond the cloud scale. We present an observational study of themolecular gas at 49.5◦ < l < 52.5◦ and −5.0 km s−1 < vlsr < 17.4 km s−1. The molecular gas is found in the formof a huge (>∼500 pc) filamentary gas wisp. This has a large physical extent and a velocity dispersion of ∼ 5 km s−1.The eastern part of the filamentary gas wisp is located ∼ 130 pc above the Galactic disk (which corresponds to 1.5–4e-folding scale-heights), and the total mass of the gas wisp is >

∼1 × 105M⊙. It is composed of two molecular cloudsand an expanding bubble. The velocity structure of the gas wisp can be explained as a smooth quiescent componentdisturbed by the expansion of a bubble. That the length of the gas wisp exceeds by much the thickness of the moleculardisk of the Milky Way is consistent with the cloud-formation scenario in which the gas is cold prior to the formationof molecular clouds. Star formation in the filamentary gas wisp occurs at the edge of a bubble (G52L nebula), whichis consistent with some models of triggered star formation.

Accepted by A&A


34

The Link between Magnetic Fields and Filamentary Clouds: Bimodal Cloud Orienta-tions in the Gould Belt

Hua-bai Li1,2, Ming Fang3, Thomas Henning1 and Jouni Kainulainen1

1 Max-Planck-Institut fur Astronomie, Knigstuhl 17, 69117 Heidelberg, Germany2 Department of Physics, The Chinese University of Hong Kong, Hong Kong3 3. Purple Mountain Observatory, 2 west Beijing Road, Nanjing, 210008, China

E-mail contact: hbli at phy.cuhk.edu.hk

The orientations of filamentary molecular clouds in the Gould Belt and their local ICM (inter-cloud media) magneticfields are studied using near-infrared dust extinction maps and optical stellar polarimetry data. These filamentaryclouds are a few-to-ten parsecs in length, and we find that their orientations tend to be either parallel or perpendicularto the mean field directions of the local ICM. This bimodal distribution is not found in cloud simulations with super-Alfvenic turbulence, in which the cloud orientations should be random. ICM magnetic fields that are dynamicallyimportant compared to inertial-range turbulence and self-gravity can readily explain both field-filament configurations.Previous studies commonly recognize that strong magnetic fields can guide gravitational contraction and result infilaments perpendicular to them, but few discuss the fact that magnetic fields can also channel sub-Alfvenic turbulenceto form filaments aligned with them. This strong-field scenario of cloud formation is also consistent with the constantfield strength observed from ICM to clouds (Crutcher et al. 2010) and is possible to explain the ”hub-filament” cloudstructure (Myers 2009) and the density threshold of cloud gravitational contraction (Kainulainen et al. 2009).

Accepted by MNRAS


The Extremely Red, Young L Dwarf PSO J318.5-22: A Free-Floating Planetary-MassAnalog to Directly Imaged Young Gas-Giant Planets

Michael C. Liu1, Eugene A. Magnier1, Niall R. Deacon2, Katelyn N. Allers3, Trent J. Dupuy4, MichaelC. Kotson1, Kimberly M. Aller1, W. S. Burgett1, K. C. Chambers1, P. W. Draper5, K. W. Hodapp1,R. Jedicke1, N. Kaiser1, R.-P. Kudritzki1, N. Metcalfe5, J. S. Morgan1, P. A. Price6, J. L. Tonry1 andR. J. Wainscoat1

1 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu HI 96822, USA2 Max Planck Institute for Astronomy, Konigstuhl 17, D-69117 Heidelberg, Germany3 Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837, USA4 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA5 Department of Physics, Durham University, South Road, Durham DH1 3LE, UK6 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

E-mail contact: mliu at ifa.hawaii.edu

We have discovered using Pan-STARRS1 an extremely red late-L dwarf, which has (J − K)MKO = 2.84 and (J −K)2MASS = 2.78, making it the reddest known field dwarf and second only to 2MASS J1207−39b among substellarcompanions. Near-IR spectroscopy shows a spectral type of L7±1 and reveals a triangular H-band continuum andweak alkali (K I and Na I) lines, hallmarks of low surface gravity. Near-IR astrometry from the Hawaii Infrared ParallaxProgram gives a distance of 24.6±1.4 pc and indicates a much fainter J-band absolute magnitude than field L dwarfs.The position and kinematics of PSO J318.5−22 point to membership in the β Pic moving group. Evolutionary modelsgive a temperature of 1160+30

−40 K and a mass of 6.5+1.3−1.0 MJup, making PSO J318.5−22 one of the lowest mass free-

floating objects in the solar neighborhood. This object adds to the growing list of low-gravity field L dwarfs and isthe first to be strongly deficient in methane relative to its estimated temperature. Comparing their spectra suggeststhat young L dwarfs with similar ages and temperatures can have different spectral signatures of youth. For the twoobjects with well constrained ages (PSO J318.5−22 and 2MASS J0355+11), we find their temperatures are ≈400 Kcooler than field objects of similar spectral type but their luminosities are comparable, i.e., these young L dwarfs arevery red and unusually cool but not “underluminous.” Altogether, PSO J318.5−22 is the first free-floating objectwith the colors, magnitudes, spectrum, luminosity, and mass that overlap the young dusty planets around HR 8799and 2MASS J1207−39.

Accepted by ApJ Letters

35


Gaseous CO Abundance—An Evolutionary Tracer for Molecular Clouds

Tie Liu1, Yuefang Wu1 and Huawei Zhang1

1 Department of Astronomy, Peking University, 100871 Beijing, China

E-mail contact: liutiepku at gmail.com

Planck cold clumps are among the most promising objects to investigate the initial conditions of the evolution ofmolecular clouds. In this work, by combing the dust emission data from the survey of Planck satellite with themolecular data of 12CO/13CO/C18O (1-0) lines from observations with the Purple Mountain Observatory (PMO)13.7 m telescope, we investigate the CO abundance, CO depletion and CO-to-H2 conversion factor of 674 clumpsin the early cold cores (ECC) sample. The median and mean values of the CO abundance are 0.89×10−4 and1.28×10−4, respectively. The mean and median of CO depletion factor are 1.7 and 0.9, respectively. The median valueof XCO−to−H2

for the whole sample is 2.8 × 1020 cm−2K−1km−1 s. The CO abundance, CO depletion factor andCO-to-H2 conversion factor are strongly (anti-)correlated to other physical parameters (e.g. dust temperature, dustemissivity spectral index, column density, volume density and luminosity-to-mass ratio). To conclude, the gaseous COabundance can be used as an evolutionary tracer for molecular clouds.

Accepted by ApJL


Competitive accretion in the protocluster G10.6-0.4?

Tie Liu1, Yuefang Wu1, Jingwen Wu2, Sheng-Li Qin3 and Huawei Zhang1

1 (Department of Astronomy, Peking University, 100871 Beijing, China;2 UCLA Astronomy, PO Box 951547, Los Angeles, CA 90095-1547, USA3 I. Physikalisches Institut, Universitat zu Koln, Zulpicher Str. 77, D-50937 Koln, Germany

E-mail contact: liutiepku at gmail.com

We present the results of high spatial resolution observations in the 1.1-mm waveband with the Submillimetre Array(SMA) towards the protocluster G10.6-0.4. The 1.1-mm continuum emission reveals seven dense cores. Redshiftedabsorption dips are seen in the HCN (3–2) lines in these cores, suggesting infalling of gas towards the dense cores. Thisis the first time that infall has been seen towards multiple sources in a protocluster. We also identified four infraredpoint sources in this region, which are most likely Class 0/I protostars. Two jet-like structures are also identified fromSpitzer/Infrared Array Camera (IRAC) images. The dense core located in the centre has a much larger mass than theoff-centre cores. The clump is in overall collapse and the infall motion is supersonic. The standard deviations of corevelocities and the velocity differences between the cores and the cloud/clump are all larger than the thermal velocitydispersion. The picture of G10.6-0.4 seems to favour the ’competitive accretion’ model, but this needs to be testedthrough further observations.

Accepted by MNRAS

http://adsabs.harvard.edu/doi/10.1093/mnras/stt1650

The intrinsic shapes of starless cores in Ophiuchus

Oliver Lomax1, Anthony Whitworth1 and Annabel Cartwright1

1 School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA

E-mail contact: oliver.lomax at astro.cf.ac.uk

Using observations of cores to infer their intrinsic properties requires the solution of several poorly constrained inverseproblems. Here we address one of these problems, namely to deduce from the projected aspect ratios of the cores inOphiuchus their intrinsic three-dimensional shapes. Four models are proposed, all based on the standard assumptionthat cores are randomly orientated ellipsoids, and on the further assumption that a core’s shape is not correlated

36

with its absolute size. The first and simplest model, M1, has a single free parameter, and assumes that the relativeaxes of a core are drawn randomly from a log-normal distribution with zero mean and standard deviation σ

O. The

second model, M2a, has two free parameters, and assumes that the log-normal distribution (with standard deviationσ

O) has a finite mean, µ

O, defined so that µ

O< 0 means elongated (prolate) cores are favoured, whereas µ

O> 0

means flattened (oblate) cores are favoured. Details of the third model (M2b, two free parameters) and the fourthmodel (M4, four free parameters) are given in the text. Markov chain Monte Carlo sampling and Bayesian analysisare used to map out the posterior probability density functions of the model parameters, and the relative merits ofthe models are compared using Bayes factors. We show that M1 provides an acceptable fit to the Ophiuchus datawith σ

O≈ 0.57 ± 0.06; and that, although the other models sometimes provide an improved fit, there is no strong

justification for the introduction of their additional parameters.

Accepted by MNRAS


Fitting density models to observational data - The local Schmidt law in molecular clouds

Marco Lombardi1, Charles J. Lada2, and Joao Alves3

1 University of Milan, Department of Physics, via Celoria 16, I-20133 Milan, Italy2 Harvard-Smithsonian Center for Astrophysics, Mail Stop 72, 60 Garden Street, Cambridge, MA 021383 University of Vienna, Turkenschanzstrasse 17, 1180 Vienna, Austria

E-mail contact: marco.lombardi at unimi.it

We consider the general problem of fitting a parametric density model to discrete observations, taken to follow anon-homogeneous Poisson point process. This class of models is very common, and can be used to describe manyastrophysical processes, including the distribution of protostars in molecular clouds. We give the expression for thelikelihood of a given spatial density distribution of protostars and apply it to infer the most probable dependenceof the protostellar surface density on the gas surface density. Finally, we apply this general technique to model thedistribution of protostars in the Orion molecular cloud and robustly derive the local star formation scaling (Schmidt)law for a molecular cloud. We find that in this cloud the protostellar surface density, ΣYSO, is directly proportionalto the square gas column density, here expressed as infrared extinction in the K-band, AK : more precisely, ΣYSO =(1.65± 0.19)(AK/mag)(2.03±0.15) stars pc−2.

Accepted by A&A


The Formation of Population III Stars in Gas Accretion Stage: Effects of MagneticFields

Masahiro N. Machida1 and Kentaro Doi2

1 Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku,Fukuoka, Japan2 Department of Physics, Konan University, Okamoto 8-9-1, Kobe, Japan

E-mail contact: machida.masahiro.018 at m.kyushu-u.ac.jp

The formation of Population III stars is investigated using resistive magnetohydrodynamic simulations. Startingfrom a magnetized primordial prestellar cloud, we calculate the cloud evolution several hundreds of years after firstprotostar formation, resolving the protostellar radius. When the natal minihalo field strength is weaker than B <10−13(n/1 cm)−2/3 G (n is the hydrogen number density), magnetic effects can be ignored. In this case, fragmentationoccurs frequently and a stellar cluster forms, in which stellar mergers and mass exchange between protostars contributeto the mass growth of these protostars. During the early gas accretion phase, the most massive protostar remainsnear the cloud centre, whereas some of the less massive protostars are ejected. The magnetic field significantly affectsPopulation III star formation when Bamb > 10−12(n/1 cm)−2/3 G. In this case, because the angular momentum aroundthe protostar is effectively transferred by both magnetic braking and protostellar jets, the gas falls directly onto theprotostar without forming a disk, and only a single massive star forms. In addition, a massive binary stellar systemappears when Bamb ∼ 10−12(n/1 cm)−2/3 G. Therefore, the magnetic field determines the end result of the formation

37

process (cluster, binary or single star) for Population III stars. Moreover, no persistent circumstellar disk appearsaround the protostar regardless of the magnetic field strength, which may influence the further evolution of PopulationIII stars.

Accepted by MNRAS


ALMA continuum observations of a 30 Myr old gaseous debris disk around HD21997

A. Moor1, A. Juhasz2 A. Kospal3, P. Abraham1, D. Apai4, T. Csengeri5, C. Grady6,7, Th. Henning8,A. M. Hughes9, Cs. Kiss1, I. Pascucci4, M. Schmalzl2, and K. Gabanyi1

1 Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, P.O.Box 67, H-1525 Budapest, Hungary2 Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2333-CA Leiden, The Netherlands3 European Space Agency (ESA-ESTEC, SRE-SA), P.O. Box 299, 2200-AG, Noordwijk, The Netherlands4 Department of Astronomy and Department of Planetary Sciences, The University of Arizona, Tucson, AZ 85721,USA5 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, D-53121 Bonn, Germany6 NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771, USA7 Eureka Scientific, 2452 Delmer Street, Suite 100, Oakland, CA 94602, USA8 Max-Planck-Institut fur Astronomie, Konigstuhl 17, D-69117 Heidelberg, Germany9 Wesleyan University Department of Astronomy, Van Vleck Observatory, 96 Foss Hill Dr., Midletown, CT 06457,USA

E-mail contact: moor at konkoly.hu

Circumstellar disks around stars older than 10 Myr are expected to be gas-poor. There are, however, two examplesof old (30–40 Myr) debris-like disks containing a detectable amount of cold CO gas. Here we present ALMA andHerschel Space Observatory observations of one of these disks, around HD 21997, and study the distribution andorigin of the dust and its connection to the gas. Our ALMA continuum images at 886µm clearly resolve a broadring of emission within a diameter of ∼4.5′′, adding HD21997 to the dozen debris disks resolved at (sub)millimeterwavelengths. Modeling the morphology of the ALMA image with a radiative transfer code suggests inner and outerradii of ∼55 and ∼150AU, and a dust mass of 0.09 M⊕. Our data and modeling hints at an extended cold outskirtof the ring. Comparison with the morphology of the CO gas in the disk reveals an inner dust-free hole where gasnevertheless can be detected. Based on dust grain lifetimes, we propose that the dust content of this gaseous disk is ofsecondary origin produced by planetesimals. Since the gas component is probably primordial, HD21997 is one of thefirst known examples of a hybrid circumstellar disk, a so-far little studied late phase of circumstellar disk evolution.

Accepted by The Astrophysical Journal Letters (Volume 777, L25)


A Keplerian disk around a Class 0 source: ALMA observations of VLA1623A

Nadia M. Murillo1, Shih-Ping Lai2,3, Simon Bruderer1, Daniel Harsono4,5, and Ewine F. van Dishoeck1,4

1 Max-Planck-Insitut fur extraterrestrische Physik, Geissenbachstrae 1, 85748, Garching bei Munchen, Germany2 Institute of Astronomy and Department of Physics, National Tsing Hua University, 101 Section 2 Kuang Fu Road,Hsinchu 30013, Taiwan3 Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan4 Leiden Observatory, Leiden University, Niels Bohrweg 2, 2300 RA, Leiden, the Netherlands5 SRON Netherlands Institute for Space Research, P.O. Box 800, 9700 AV Groningen, The Netherlands

E-mail contact: nmurillo at mpe.mpg.de

Context. Rotationally supported disks are critical in the star formation process. The questions of when do they formand what factors influence or hinder their formation have been studied but are largely unanswered. Observations ofearly stage YSOs are needed to probe disk formation.Aims. VLA1623 is a triple non-coeval protostellar system, with a weak magnetic field perpendicular to the outflow,

38

whose Class 0 component, VLA1623A, shows a disk-like structure in continuum with signatures of rotation in lineemission. We aim to determine whether this structure is in part or in whole a rotationally supported disk, i.e. aKeplerian disk, and what are its characteristics.Methods. ALMA Cycle 0 Early Science 1.3 mm continuum and C18O (2–1) observations in the extended configurationare presented here and used to perform an analysis of the disk-like structure using PV diagrams and thin disk modellingwith the addition of foreground absorption.Results. The PV diagrams of the C18O line emission suggest the presence of a rotationally supported component witha radius of at least 50 AU. Kinematical modelling of the line emission shows that the disk out to 180 AU is actuallyrotationally supported, with the rotation being well described by Keplerian rotation out to at least 150 AU, and thecentral source mass to be ∼0.2 M⊙ for an inclination of 55◦. Pure infall and conserved angular momentum rotationmodels are excluded.Conclusions. VLA1623A, a very young Class 0 source, presents a disk with an outer radius Rout = 180 AU with aKeplerian velocity structure out to at least 150 AU. The weak magnetic fields and recent fragmentation in this regionof ρ Ophiuchi may have played a lead role in the formation of the disk.

Accepted by A&A


Modelling Accretion in Transitional Disks

Tobias W. A. Muller1 and Wilhelm Kley1

1 Institut fur Astronomie and Astrophysik, Eberhard Karls Universitat Tubingen, Auf der Morgenstelle 10, D-72076Tubingen, Germany

E-mail contact: Tobias Mueller at twam.info

Transitional disks are protoplanetary disk around young stars that display inner holes in the dust distribution within afew AU, which is accompanied nevertheless by some gas accretion onto the central star. These cavities could possiblybe created by the presence of one or more massive planets. If the gap is created by planets and gas is still present init, then there should be a flow of gas past the planet into the inner region. It is our goal to study the mass accretionrate into the gap and in particular the dependency on the planet’s mass and the thermodynamic properties of thedisk. We performed 2D hydro simulations for disks with embedded planets. We added radiative cooling from the disksurfaces, radiative diffusion in the disk midplane, and stellar irradiation to the energy equation to have more realisticmodels. The mass flow rate into the gap region depends, for given disk thermodynamics, non-monotonically on themass of the planet. Generally, more massive planets open wider and deeper gaps which would tend to reduce the massaccretion into the inner cavity. However, for larger mass planets the outer disk becomes eccentric and the mass flowrate is enhanced over the low mass cases. As a result, for the isothermal disks the mass flow is always comparable tothe expected mass flow of unperturbed disks Md, while for more realistic radiative disks the mass flow is very small forlow mass planets (≤4 Mjup) and about 50% for larger planet masses. For the radiative disks that critical planet massfor the disk to become eccentric is much larger that in the isothermal case. Massive embedded planets can reducethe mass flow across the gap considerably, to values of about an order of magnitude smaller than the standard diskaccretion rate, and can be responsible for opening large cavities. The remaining mass flow into the central cavity is ingood agreement with the observations.

Accepted by A&A


Kinematics of the Orion Trapezium Based on Diffracto-Astrometry and Historical Data

J. Olivares1, L.J. Sanchez1, A. Ruelas-Mayorga1, C. Allen1, R. Costero1, and A. Poveda1

1 Instituto de Astronomıa, Universidad Nacional Autonoma de Mexico, Apdo. Postal 70-264, 04510, Mexico D.F.,Mexico

E-mail contact: jromero at astro.unam.mx

Using the novel Diffracto-Astrometry technique, we analyze 44 Hubble Space Telescope Wide Field Planetary Camera2 images of the Orion Trapezium (OT) taken over a span of 12 yr (1995–2007). We measure the relative positions of

39

the six brighter OT components (A–F) and supplement these results with measurements of the relative separationsand position angles taken from the literature, thus extending our analysis time base to ∼200 yr. For every pair ofcomponents we find the relative rate of separation as well as the temporal rate of change of their position angles,which enable us to determine the relative kinematics of the system. Component E shows a velocity larger than theOT’s escape velocity, thus confirming that it is escaping from the gravitational pull of this system.

Accepted by AJ


Cosmic-ray ionisation in collapsing clouds

Marco Padovani1, Patrick Hennebelle2 and Daniele Galli3

1 Laboratoire de Radioastronomie Millimetrique, UMR 8112 du CNRS, Ecole Normale Superieure et Observatoire deParis, 24 rue Lhomond, 75231 Paris cedex 05, France2 CEA, IRFU, SAp, Centre de Saclay, 91191 Gif-Sur-Yvette, France3 INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

E-mail contact: padovani at lra.ens.fr

Cosmic rays play an important role in dense molecular cores, affecting their thermal and dynamical evolution andinitiating the chemistry. Several studies have shown that the formation of protostellar discs in collapsing clouds isseverely hampered by the braking torque exerted by the entrained magnetic field on the infalling gas, as long asthe field remains frozen to the gas. In this paper we examine the possibility that the concentration and twistingof the field lines in the inner region of collapse can produce a significant reduction of the ionisation fraction. Tocheck whether the cosmic-ray ionisation rate can fall below the critical value required to maintain good coupling, wefirst study the propagation of cosmic rays in a model of a static magnetised cloud varying the relative strength ofthe toroidal/poloidal components and the mass-to-flux ratio. We then follow the path of cosmic rays using realisticmagnetic field configurations generated by numerical simulations of a rotating collapsing core with different initialconditions. We find that an increment of the toroidal component of the magnetic field, or, in general, a more twistedconfiguration of the field lines, results in a decrease in the cosmic-ray flux. This is mainly due to the magnetic mirroringeffect that is stronger where larger variations in the field direction are present. In particular, we find a decrease of thecosmic-ray ionisation rate below 10−18 s−1 in the central 300–400 AU, where density is higher than about 109 cm−3.This very low value of the ionisation rate is attained in the cases of intermediate and low magnetisation (mass-to-fluxratio λ = 5 and 17, respectively) and for toroidal fields larger than about 40% of the total field. Magnetic field effectscan significantly reduce the ionisation fraction in collapsing clouds. We provide a handy fitting formula to computeapproximately the attenuation of the cosmic-ray ionisation rate in a molecular cloud as a function of the density andthe magnetic configuration.



Pre-main-sequence population in NGC 1893 region: X-ray properties

A.K. Pandey1, M.R. Samal2, Ram Kesh Yadav1, Andrea Richichi3, Sneh Lata1, J.C. Pandey1, D. K.Ojha4, and W.P. Chen5

1 Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital, India 263 0022 Laboratoire dAstrophysique de Marseille - LAM, Universite d’Aix-Marseille & CNRS, UMR7326, 13388 MarseilleCedex 13, France3 National Astronomical Research Institute of Thailand, 191 Siriphanich Bldg., Huay Kaew Rd., Suthep, Muang,Chiang Mai 50200, Thailand4 Tata Institute of Fundamental Research, Mumbai - 400 005, India5 Institute of Astronomy, National Central University, Chung-Li 32054, Taiwan

E-mail contact: ramkesh at aries.res.in

Continuing the attempt to understand the properties of the stellar content in the young cluster NGC 1893 we havecarried out a comprehensive multi-wavelength study of the region. The present study focuses on the X-ray properties

40

of T-Tauri Stars (TTSs) in the NGC 1893 region. We found a correlation between the X-ray luminosity, LX , andthe stellar mass (in the range 0.2–2.0 M⊙) of TTSs in the NGC 1893 region, similar to those reported in some otheryoung clusters, however the value of the power-law slope obtained in the present study (∼0.9) for NGC 1893 is smallerthan those (∼1.4–3.6) reported in the case of TMC, ONC, IC 348 and Chameleon star forming regions. However, theslope in the case of Class III sources (Weak line TTSs) is found to be comparable to that reported in the case of NGC6611 (∼1.1). It is found that the presence of circumstellar disks has no influence on the X-ray emission. The X-rayluminosity for both CTTSs and WTTSs is found to decrease systematically with age (in the range ∼ 0.4 Myr – 5Myr). The decrease of the X-ray luminosity of TTSs (slope ∼ −0.6) in the case of NGC 1893 seems to be faster thanobserved in the case of other star-forming regions (slope −0.2 to −0.5). There is indication that the sources havingrelatively large NIR excess have relatively lower LX values. TTSs in NGC 1893 do not follow the well establishedX-ray activity - rotation relation as in the case of main-sequence stars.

Accepted by New Astronomy


Supernova enrichment and dynamical histories of solar-type stars in clusters

Richard J. Parker1, Ross P. Church2, Melvyn B. Davies2 and Michael R. Meyer1

1 Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland2 Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, SE-221 00 Lund, Sweden

E-mail contact: rparker at phys.ethz.ch

We use N -body simulations of star cluster evolution to explore the hypothesis that short-lived radioactive isotopesfound in meteorites, such as 26Al, were delivered to the Sun’s protoplanetary disc from a supernova at the epoch ofSolar System formation. We cover a range of star cluster formation parameter space and model both clusters withprimordial substructure, and those with smooth profiles. We also adopt different initial virial ratios – from cool,collapsing clusters to warm, expanding associations. In each cluster we place the same stellar population; the clusterseach have 2100 stars, and contain one massive 25M⊙ star which is expected to explode as a supernova at about6.6Myr. We determine the number of Solar (G)-type stars that are within 0.1 – 0.3 pc of the 25M⊙ star at the timeof the supernova, which is the distance required to enrich the protoplanetary disc with the 26Al abundances found inmeteorites. We then determine how many of these G-dwarfs are unperturbed ‘singletons’; stars which are never inclose binaries, nor suffer sub-100 au encounters, and which also do not suffer strong dynamical perturbations.The evolution of a suite of twenty initially identical clusters is highly stochastic, with the supernova enriching over 10 G-dwarfs in some clusters, and none at all in others. Typically only ∼25per cent of clusters contain enriched, unperturbedsingletons, and usually only 1 – 2 per cluster (from a total of 96 G-dwarfs in each cluster). The initial conditionsfor star formation do not strongly affect the results, although a higher fraction of supervirial (expanding) clusterswould contain enriched G-dwarfs if the supernova occurred earlier than 6.6Myr. If we sum together simulations withidentical initial conditions, then ∼1 per cent of all G-dwarfs in our simulations are enriched, unperturbed singletons.

Accepted by MNRAS


Unveiling the circumstellar environment towards a massive young stellar object

S. Paron1,2, C. Farina3, and M.E. Ortega1

1 Instituto de Astronomia y Fisica del Espacio (IAFE), CC 67, Suc. 28, 1428 Buenos Aires, Argentina2 FADU and CBC, Universidad de Buenos Aires, Argentina3 Isaac Newton Group of Telescopes, E-38700, La Palma, Spain

E-mail contact: sparon at iafe.uba.ar

As a continuation of a previous work, in which we found strong evidence of massive molecular outflows towards amassive star forming site, we present a new study of this region based on very high angular resolution observations withthe aim of discovering the outflow driven mechanism. Using near-IR data acquired with Gemini-NIRI at the broadH- and Ks-bands, we study a region of 22′′ × 22′′ around the UCHII region G045.47+0.05, a massive star formingsite at the distance of about 8 kpc. To image the source with the highest spatial resolution possible we employed the

41

adaptative optic system ALTAIR, achieving an angular resolution of about 0.15′′. We discovered a cone-like shapenebula with an opening angle of about 90 degree extending eastwards the IR source 2MASS J19142564+1109283, avery likely MYSO. This morphology suggests a cavity that was cleared in the circumstellar material and its emissionmay arise from scattered continuum light, warm dust, and likely emission lines from shock-excited gas. The nebula,presenting arc-like features, is connected with the IR source through a jet-like structure, which is aligned with the blueshifted CO outflow found in a previous study. The near-IR structure lies ∼3′′ north of the radio continuum emission,revealing that it is not spatially coincident with the UCHII region. The observed morphology and structure of thenear-IR nebula strongly suggest the presence of a precessing jet. In this study we have resolved the circumstellarambient (in scale of a thousand A.U.) of a distant MYSO, indeed one of the farthest cases.

Accepted by A&A Letters


Morphologies of protostellar outflows: An ALMA view

Thomas Peters1, Pamela D. Klaassen2, Daniel Seifried3, Robi Banerjee3 and Ralf S. Klessen4

1 Institut fur Theoretische Physik, Universitat Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland2 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands3 Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany4 Universitat Heidelberg, Zentrum fur Astronomie, Institut fur Theoretische Astrophysik, Albert-Ueberle-Str. 2,D-69120 Heidelberg, Germany

E-mail contact: tpeters at physik.uzh.ch

The formation of stars is usually accompanied by the launching of protostellar outflows. Observations with the AtacamaLarge Millimetre/sub-millimetre Array (ALMA) will soon revolutionalise our understanding of the morphologies andkinematics of these objects. In this paper, we present synthetic ALMA observations of protostellar outflows based onnumerical magnetohydrodynamic collapse simulations. We find significant velocity gradients in our outflow modelsand a very prominent helical structure within the outflows. We speculate that the disk wind found in the ALMAScience Verification Data of HD 163296 presents a first instance of such an observation.

Accepted by MNRAS


Molecular line and continuum study of the W40 cloud

L. Pirogov1, D.K. Ojha2, M. Thomasson3, Y.-F. Wu4 and I. Zinchenko1

1 Institute of Applied Physics RAS, Ulyanova 46, Nizhny Novgorod 603950, Russia2 Department of Astronomy and Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India3 Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden4 School of Physics, Peking University, Beijing, 100871, China

E-mail contact: pirogov at appl.sci-nnov.ru

The dense cloud associated with W40, which is one of the nearby HII regions, has been studied in millimetre-wavemolecular lines and in the 1.2-mm continuum. Moreover, 1280- and 610-MHz interferometric observations have beencarried out. The cloud has a complex morphological and kinematical structure, including a clumpy dust ring andan extended dense core. The ring has probably been formed by the “collect and collapse” process as a result of theexpansion of the neighbouring HII region. Nine dust clumps in the ring have been deconvolved. Their sizes, massesand peak hydrogen column densities are ∼ 0.02− 0.11 pc, ∼ 0.4− 8.1 M⊙ and ∼ (2.5− 11)× 1022 cm−2, respectively.Molecular lines are observed at two different velocities and have different spatial distributions, which implies that thereis strong chemical differentiation over the region. The CS abundance is enhanced towards the eastern dust clump 2,while the NH3, N2H

+ and H13CO+ abundances are enhanced towards the western clumps. HCN and HCO+ do notcorrelate with the dust, probably tracing the surrounding gas. The number densities derived towards selected positionsare ∼ (0.3− 3.2)× 106 cm−3. The two western clumps have kinetic temperatures of 21 and 16K and are close to virialequilibrium. The eastern clumps 2 and 3 are more massive, have a higher extent of turbulence and are probably moreevolved than the western clumps. They show asymmetric CS(2–1) line profiles because of infalling motions, which is

42

confirmed by model calculations. An interaction between ionized and neutral material is taking place in the vicinityof the eastern branch of the ring and probably triggers star formation.

Accepted by Monthly Notices of the RAS


The galactocentric radius dependent upper mass limit of young star clusters: stochasticstar formation ruled out

Jan Pflamm-Altenburg1, Rosa A. Gonzalez-Lopezlira2, and Pavel Kroupa1

1 Helmholtz-Institut fur Strahlen- und Kernphysik (HISKP), University of Bonn, Nussallee 14-16, D-53115 Bonn,Germany2 Centro de Radioastronomıa y Astrofısica, UNAM, Campus Morelia, Michoacan, Mexico, C.P. 58089

E-mail contact: jpflamm at astro.uni-bonn.de

It is widely accepted that the distribution function of the masses of young star clusters is universal and can be purelyinterpreted as a probability density distribution function with a constant upper mass limit. As a result of this picturethe masses of the most-massive objects are exclusively determined by the size of the sample. Here we show, with veryhigh confidence, that the masses of the most-massive young star clusters in M33 decrease with increasing galactocentricradius in contradiction to the expectations from a model of a randomly sampled constant cluster mass function witha constant upper mass limit. Pure stochastic star formation is thereby ruled out. We use this example to elucidatehow naive analysis of data can lead to unphysical conclusions.

Accepted by MNRAS


Application of the Baade-Wesselink method to a pulsating cluster Herbig Ae star:H254 in IC348

V. Ripepi1, R. Molinaro1, M. Marconi1, G. Catanzaro2, R. Claudi3, J. Daszynska-Daszkiewicz4, F.Palla5, S. Leccia1, and S. Bernabei6

1 INAF-Osservatorio Astronomico di Capodimonte, I-80131, Napoli, Italy2 INAF-Osservatorio Astrofisico di Catania, I-95123, Catania, Italy3 INAF-Osservatorio Astronomico di Padova, I-35122, Padova, Italy4 Instytut Astronomiczny, Uniwersytet Wrocawski, ul. Kopernika 11, PL-51-622 Wrocaw, Poland5 INAF-Osservatorio Astrofisico di Arcetri, I-50125, Firenze, Italy6 INAF-Osservatorio Astronomico di Bologna, I-40127, Bologna, Italy

E-mail contact: ripepi at oacn.inaf.it

In this paper we present new photometric and radial velocity data for the PMS δ Sct star H254, member of the youngcluster IC 348. Photometric V,RC ,IC light curves were obtained at the Loiano and Asiago telescopes. The radialvelocity data was acquired by means of the SARG@TNG spectrograph. High-resolution spectroscopy allowed us toderive precise stellar parameters and the chemical composition of the star, obtaining: Teff = 6750 ± 150K; log g =4.1 ± 0.4 dex; [Fe/H] = −0.07± 0.12 dex. Photometric and spectroscopic data were used to estimate the total absorp-tion in the V band AV = 2.06± 0.05 mag, in agreement with previous estimates. We adopted the technique of thedifference in phase and amplitude between different photometric bands and radial velocities to verify that H254 is (def-initely) pulsating in a radial mode. This occurrence allowed us to apply the CORS realization of the Baade–Wesselinkmethod to obtain a value for the linear radius of H254 equal to 3.3±0.7 R⊙.This result was used in conjunction with photometry and effective temperature to derive a distance estimate of 273±23pc for H254, and, in turn for IC 348, the host cluster. This value is in agreement within the errors with the resultsderived from several past determinations and the evaluation obtained through the Hipparcos parallaxes. Finally, wederived the luminosity of H254 and studied its position in the Hertzsprung–Russell diagram. From this analysis itresults that this δ–Scuti occupies a position close to the red edge of the instability strip, pulsates in the fundamentalmode, has a mass of about 2.2 M⊙ and an age of 5±1 Myr, older than previous estimates.

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Accepted by MNRAS


The role of low-mass star clusters in forming the massive stars in DR 21

V. M. Rivilla1, I. Jimenez-Serra2, J. Martın-Pintado1 and J. Sanz-Forcada1

1 Centro de Astrobiologıa (CSIC-INTA), Ctra. de Torrejon-Ajalvir, km. 4, E-28850 Torrejon de Ardoz, Madrid, Spain2 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748, Garching, Germany

E-mail contact: rivilla at cab.inta-csic.es

We have studied the young low-mass pre-main sequence (PMS) stellar population associated with the massive star-forming region DR 21 by using archival X-ray Chandra observations and by complementing them with existing opticaland IR surveys. The Chandra observations have revealed for the first time a new highly extincted population of PMSlow-mass stars previously missed in observations at other wavelengths. The X-ray population exhibits three mainstellar density peaks, coincident with the massive star-forming regions, being the DR 21 core the main peak. Thecross-correlated X-ray/IR sample exhibits a radial ”Spokes-like” stellar filamentary structure that extends from theDR 21 core towards the northeast. The near IR data reveal a centrally peaked structure for the extinction, whichexhibits its maximum in the DR 21 core and gradually decreases with the distance to the N-S cloud axis and to thecluster center. We find evidence of a global mass segregation in the full low-mass stellar cluster, and of an stellar agesegregation, with the youngest stars still embedded in the N-S cloud, and more evolved stars more spatially distributed.The results are consistent with the scenario where an elongated overall potential well created by the full low-massstellar cluster funnels gas through filaments feeding stellar formation. Besides the full gravitational well, smaller-scalelocal potential wells created by dense stellar sub-clusters of low-mass stars are privileged in the competition for thegas of the common reservoir, allowing the formation of massive stars. We also discuss the possibility that a stellarcollision in the very dense stellar cluster revealed by Chandra in the DR 21 core is the origin of the large-scale andhighly-energetic outflow arising from this region.

Accepted by MNRAS


Optical/Near-IR Polarization Survey of Sh 2-29: Magnetic Fields, Dense Cloud Frag-mentations and Anomalous Dust Grain Sizes

Fabio P. Santos1, Gabriel A. P. Franco1, Alexandre Roman-Lopes2, Wilson Reis1 and Carlos G. Roman-Zuniga3

1 Departamento de Fısica - ICEx - UFMG, Caixa Postal 702, 30.123-970, Brazil2 Departamento de Fisica - Universidad de La Serena, Cisternas 1200, La Serena, Chile3 Instituto de Astronomıa – Universidad Nacional Autonoma de Mexico, Unidad en Ensenada, Ensenada BC 22860,Mexico

E-mail contact: fabiops at fisica.ufmg.br

Sh 2-29 is a conspicuous star-forming region marked by the presence of massive embedded stars as well as severalnotable interstellar structures. In this research, our goals were to determine the role of magnetic fields and to studythe size distribution of interstellar dust particles within this turbulent environment. We have used a set of optical andnear-infrared polarimetric data obtained at OPD/LNA (Brazil) and CTIO (Chile), correlated with extinction maps,2MASS data and images from DSS and Spitzer. The region’s most striking feature is a swept out interstellar cavitywhose polarimetric maps indicate that magnetic field lines were dragged outwards, pilling up along its borders. Thisled to a higher magnetic strength value (≈ 400µG) and an abrupt increase in polarization degree, probably due to anenhancement in alignment efficiency. Furthermore, dense cloud fragmentations with peak AV between 20 and 37 magwere probably triggered by its expansion. The presence of 24µm point-like sources indicates possible newborn starsinside this dense environment. A statistical analysis of the angular dispersion function revealed areas where field linesare aligned in a well-ordered pattern, seemingly due to compression effects from the Hii region expansion. Finally,Serkowski function fits were used to study the ratio of the total-to-selective extinction, reveling a dual population ofanomalous grain particles sizes. This trend suggests that both effects of coagulation and fragmentation of interstellargrains are present in the region.

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Erosion of dust aggregates

A. Seizinger1, S. Krijt2 and W. Kley1

1 Institut fur Astronomie and Astrophysik, Eberhard Karls Universitat Tubingen, Auf der Morgenstelle 10, D-72076Tubingen, Germany2 Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

E-mail contact: alexs at tat.physik.uni-tuebingen.de

Aims: The aim of this work is to gain a deeper insight into how much different aggregate types are affected by erosion.Especially, it is important to study the influence of the velocity of the impacting projectiles. We also want to providemodels for dust growth in protoplanetary disks with simple recipes to account for erosion effects.Methods: To study the erosion of dust aggregates we employed a molecular dynamics approach that features a detailedmicro-physical model of the interaction of spherical grains. For the first time, the model has been extended byintroducing a new visco-elastic damping force which requires a proper calibration. Afterwards, different samplegeneration methods were used to cover a wide range of aggregate types.Results: The visco-elastic damping force introduced in this work turns out to be crucial to reproduce results obtainedfrom laboratory experiments. After proper calibration, we find that erosion occurs for impact velocities of 5 m/s andabove. Though fractal aggregates as formed during the first growth phase are most susceptible to erosion, we observeerosion of aggregates with rather compact surfaces as well.Conclusions: We find that bombarding a larger target aggregate with small projectiles results in erosion for impactvelocities as low as a few m/s. More compact aggregates suffer less from erosion. With increasing projectile size thetransition from accretion to erosion is shifted to higher velocities. This allows larger bodies to grow through highvelocity collisions with smaller aggregates.



Multi-Object and Long-Slit Spectroscopy of Very Low Mass Brown Dwarfs in OrionNebular Cluster

Takuya Suenaga1, Motohide Tamura1,2, Masayuki Kuzuhara2,3, Kenshi Yanagisawa4, Miki Ishii5, andPhilip W. Lucas6

1 Department of Astronomical Science, The Graduate University for Advanced Studies (Sokendai), 2-21-1 Osawa,Mitaka, Tokyo, 181-85882 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-85883 Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Tokyo, 113-00334 Okayama Astronomical Observatory, National Astronomical Observatory of Japan, 3037-5 Honjo, Kamogata, Asaguchi,Okayama, 719-02325 Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku place, Hilo, HI, 96720, USA6 Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hateld AL10 9AB

E-mail contact: takuya.suenaga at nao.ac.jp

We present the results of aH- andK-band multi-object and long-slit spectroscopic survey of substellar mass candidatesin the outer regions of the Orion Nebula Cluster. The spectra were obtained using MOIRCS on the 8.2-m Subarutelescope and ISLE on the 1.88-m telescope of Okayama Astronomical Observatory. Eight out of twelve spectra showstrong water absorptions and we confirm that their effective temperatures are ≤ 3000 K (spectral type ≥ M6) from aχ2 fit to synthetic spectra. We plot our sources on an HR diagram overlaid with theoretical isochrones of low-massobjects and identify three new young brown dwarf candidates. One of the three new candidates is a cool object nearthe brown dwarf and planetary mass boundary. Based on our observations and those of previous studies, we determinethe stellar (0.08 < M/M⊙ < 1) to substellar (0.03 < M/M⊙ < 0.08) mass number ratio in the outer regions of theOrion nebular cluster to be 3.5 ± 0.8. In combination with the number ratio reported for the central region (3.3+0.8

−0.7),

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this result suggests the number ratio does not simply change with the distance from the center of the Orion nebularcluster.

Accepted by PASJ


The Dynamics of Massive Starless Cores with ALMA

Jonathan C. Tan1,2, Shuo Kong1, Michael J. Butler1, Paola Caselli3 and Francesco Fontani4

1 Dept. of Astronomy, University of Florida, USA2 Dept. of Physics, University of Florida, USA3 School of Physics & Astronomy, University of Leeds, UK4 INAF - Osservatorio Astrofisico di Arcetri, Italy

E-mail contact: jt at astro.ufl.edu

How do stars that are more massive than the Sun form, and thus how is the stellar initial mass function established?Such intermediate and high-mass stars may be born from relatively massive pre-stellar gas cores, which are moremassive than the thermal Jeans mass. The Turbulent Core Accretion model invokes such cores as being in approximatevirial equilibrium and in approximate pressure equilibrium with their surrounding clump medium. Their internalpressure is provided by a combination of turbulence and magnetic fields. On the other hand, the Competitive Accretionmodel requires strongly sub-virial initial conditions that then lead to extensive fragmentation to the thermal Jeansscale, with intermediate and high-mass stars later forming by competitive Bondi-Hoyle accretion. To test thesemodels, we have identified four prime examples of massive (∼ 100M⊙) clumps from mid-infrared (MIR) extinctionmapping of Infrared Dark Clouds (IRDCs). Fontani et al. found high deuteration fractions of N2H

+in these objects,which are consistent with them being starless. Here we present ALMA Cycle 0 observations of these 4 clumps thatprobe the N2D

+(3-2) line at 2.3 arcsec resolution. We find 6 N2D+cores and determine their dynamical state. Their

observed velocity dispersions and sizes are broadly consistent with the predictions of the Turbulent Core model ofself-gravitating, magnetized (with Alfven Mach number mA ∼ 1) and virialized cores that are bounded by the highpressures of their surrounding clumps. However, in the most massive cores, with masses up to ∼ 60M⊙, our resultssuggest that moderately enhanced magnetic fields (so that mA ≃ 0.3) may be needed for the structures to be in virialand pressure equilibrium. Magnetically regulated core formation may thus be important in controlling the formationof massive cores, inhibiting their fragmentation, and thus helping to establish the stellar initial mass function.



VLA and CARMA Observations of Protostars in the Cepheus Clouds: Sub-arcsecondProto-Binaries Formed via Disk Fragmentation

John Tobin1, Claire Chandler2, David Wilner3, Leslie Looney4, Laurent Loinard5, Hsin-Fang Chiang6,Lee Hartmann7, Nuria Calvet7, Paola D’Alessio5, Tyler Bourke3 and Woojin Kwon8

1 Hubble Fellow, National Radio Astronomy Observatory, Charlottesville, VA2 National Radio Astronomy Observatory, Socorro, NM3 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA4 University of Illinois at Champaign-Urbana, Urbana, IL5 Centro de Radioastronomia y Astrofisica, UNAM, Morelia, Mexico6 University of Hawaii Institute for Astronomy, Hilo, HI7 University of Michigan, Ann Arbor, MI8 SRON Netherlands Institute for Space Research, Groningen, The Netherlands

E-mail contact: jtobin at nrao.edu

We present observations of three Class 0/I protostars (L1157-mm, CB230 IRS1, and L1165-SMM1) using the Karl G.Jansky Very Large Array (VLA) and observations of two (L1165-SMM1 and CB230 IRS1) with the Combined Arrayfor Research in Millimeter-wave Astronomy (CARMA). The VLA observations were taken at wavelengths of λ = 7.3mm, 1.4 cm, 3.3 cm, 4.0 cm, and 6.5 cm with a best resolution of ∼0.06 arcsec (18 AU) at 7.3 mm. The L1165-SMM1

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CARMA observations were taken at λ = 1.3 mm with a best resolution of ∼ 0.3 arcsec (100 AU), and the CB230IRS1 observations were taken at λ = 3.4 mm with a best resolution of ∼3 arcsec (900 AU). We find that L1165-SMM1 and CB230 IRS1 have probable binary companions at separations of ∼0.3 arcsec (100 AU) from detectionsof secondary peaks at multiple wavelengths. The position angles of these companions are nearly orthogonal to thedirection of the observed bipolar outflows, consistent with the expected protostellar disk orientations. We suggestthat these companions may have formed from disk fragmentation; turbulent fragmentation would not preferentiallyarrange the binary companions to be orthogonal to the outflow direction. For L1165-SMM1, both the 7.3 mm and 1.3mm emission show evidence of a large (R > 100 AU) disk. For the L1165-SMM1 primary protostar and the CB230IRS1 secondary protostar, the 7.3 mm emission is resolved into structures consistent with ∼ 20 AU radius disks. Forthe other protostars, including L1157-mm, the emission is unresolved, suggesting disks with radii < 20 AU.

Accepted by ApJ


Herbig Stars’ Near-Infrared Excess: An Origin in the Protostellar Disk’s Magnetically-Supported Atmosphere

N. J. Turner1,2, M. Benisty2,3, C. P. Dullemond2,4 and S. Hirose5

1 Jet Propulsion Laboratory, California Institute of Technology, USA2 Max-Planck-Institut fur Astronomie, Germany3 Observatoire de Grenoble, Universite Joseph Fourier, France4 Institut fur Theoretische Astrophysik, Zentrum fur Astronomie, Universitat Heidelberg, Germany5 Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Japan

E-mail contact: neal.turner at jpl.nasa.gov

Young stars with masses 2–8 Suns, called the Herbig Ae and Be stars, often show a near-infrared excess too largeto explain with a hydrostatically-supported circumstellar disk of gas and dust. At the same time the accretionflow carrying the circumstellar gas to the star is thought to be driven by magneto-rotational turbulence, whichaccording to numerical MHD modeling yields an extended low-density atmosphere supported by the magnetic fields.We demonstrate that the base of the atmosphere can be optically-thick to the starlight and that the parts lying near1 AU are tall enough to double the fraction of the stellar luminosity reprocessed into the near-infrared. We generatesynthetic spectral energy distributions (SEDs) using Monte Carlo radiative transfer calculations with opacities forsub-micron silicate and carbonaceous grains. The synthetic SEDs closely follow the median Herbig SED constructedrecently by Mulders and Dominik, and in particular match the large near-infrared flux, provided the grains have amass fraction close to interstellar near the disk’s inner rim.

Accepted by Ap.J.


The RMS Survey: Galactic distribution of massive star formation

J. S. Urquhart1, C. C. Figura2, T. J. T. Moore3, M. G. Hoare4, S. L. Lumsden4, J. C. Mottram5, M.A. Thompson6, & R. D. Oudmaijer4

1 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, D-53121 Bonn, Germany2Wartburg College, 100 Wartburg Blvd, Waverly, IA 50677, USA3Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool, L3 5RF, UK4School of Physics and Astrophysics, University of Leeds, Leeds, LS2 9JT, UK5Leiden Observatory, Leiden University, NL-2300 RA Leiden, the Netherlands6Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, CollegeLane, Hatfield, AL10 9AB, UK

E-mail contact: jurquhart at mpifr-bonn.mpg.de (MPIfR)

We have used the well-selected sample of ∼1750 embedded, young, massive stars identified by the Red MSX Source(RMS) survey to investigate the Galactic distribution of recent massive star formation. We present molecular-lineobservations for ∼800 sources without existing radial velocities. We describe the various methods used to assign

47

distances extracted from the literature, and solve the distance ambiguities towards approximately 200 sources locatedwithin the Solar circle using archival H i data. These distances are used to calculate bolometic luminosities andestimate the survey completeness (∼ 2× 104L⊙). In total, we calculate the distance and luminosity of ∼1650 sources,one third of which are above the survey’s completeness threshold. Examination of the sample’s longitude, latitude,radial velocities and mid-infrared images has identified ∼120 small groups of sources, many of which are associatedwith well known star formatio! n complexes, such as G305, G333, W31, W43, W49 and W51.We compare the positional distribution of the sample with the expected locations of the spiral arms, assuming a modelof the Galaxy consisting of four gaseous arms. The distribution of young massive stars in the Milky Way is spatiallycorrelated with the spiral arms, with strong peaks in the source position and luminosity distributions at the arms’Galactocentric radii. The overall source and luminosity surface densities are both well correlated with the surfacedensity of the molecular gas, which suggests that the massive star formation rate (SFR) per unit molecular mass isapproximately constant across the Galaxy. A comparison of the distribution of molecular gas and the young massivestars to that in other nearby spiral galaxies shows similar radial dependencies.We estimate the total luminosity of the embedded massive star population to be ∼ 0.76 × 108L⊙, 30 per cent ofwhich is associated with the ten most active star forming complexes. We measure the scale height as a function ofGalactocentric distance and find that it increases only modestly from ∼20-30pc between 4 and 8 kpc, but much morerapidly at larger distances.

Accepted by MNRAS


Organic species in Infrared Dark Clouds

T. Vasyunina1, A.I. Vasyunin1, Eric Herbst1, Hendrik Linz2, Maxim Voronkov3, Tui Britton4, IgorZinchenko5, and Frederic Schuller6

1 Department of Chemistry, University of Virginia, Charlottesville, VA 22904 USA2 Max Planck Institute for Astronomy (MPIA), Konigstuhl 17, D-69117 Heidelberg, Germany3 Australia Telescope National Facility, CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710,Australia4 Department of Physics and Astronomy, Macquarie University, NSW 2109, Australia5 Institute of Applied Physics of the Russian Academy of Sciences, Ulyanova 46, 603950 Nizhny Novgorod, Russia6 European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile

E-mail contact: vasyunina at mpia.de

It is currently assumed that infrared dark clouds (IRDCs) represent the earliest evolutionary stages of high-mass stars(> 8 M⊙). Submillimeter and millimeter-wave studies performed over the past 15 years show that IRDCs possess abroad variety of properties, and hence a wide range of problems and questions that can be tackled. In this paper,we report an investigation of the molecular composition and chemical processes in two groups of IRDCs. Using theMopra, APEX, and IRAM radio telescopes over the last four years, we have collected molecular line data for CO,H2CO, HNCO, CH3CCH, CH3OH, CH3CHO, CH3OCHO, and CH3OCH3. For all of these species we estimatedmolecular abundances. We then undertook chemical modeling studies, concentrating on the source IRDC028.34+0.06,and compared observed and modeled abundances. This comparison showed that to reproduce observed abundancesof complex organic molecules (COMs), a 0-D gas-grain model with constant physical conditions is not sufficient. Weachieved greater success with the use of a warm-up model, in which warm-up from 10 K to 30 K occurs following acold phase.

Accepted by ApJ


Molecular Jet of IRAS 04166+2706

Liang-Yao Wang1,2,3, Hsien Shang2,3, Yu-Nung Su2, Joaquın Santiago-Garcıa4, Mario Tafalla5, QizhouZhang6, Naomi Hirano2 and Chin-Fei Lee2

1 Graduate Institute of Astronomy and Astrophysics, National Taiwan University, No. 1, Sec. 4, Roosevelt Road,

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Taipei 10617, Taiwan2 Academia Sinica, Institute of Astrophysics (ASIAA), P.O. Box 23-141, Taipei 106, Taiwan3 Theoretical Institute for Advanced Research in Astrophysics (TIARA), Academia Sinica, P.O. Box 23-141, Taipei10641, Taiwan4 Instituto de Radioastronomıa Milimetrica (IRAM), Avenida Divina Pastora 7, Nucleo Central, 18012 Granada, Spain5 Observatorio Astronomico Nacional (IGN), Alfonso XII 3, E-28014 Madrid, Spain6 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

E-mail contact: lywang at asiaa.sinica.edu.tw

The molecular outflow from IRAS 04166+2706 was mapped with the Submillimeter Array (SMA) at 350 GHz contin-uum and CO J = 3–2 at an angular resolution of ∼1 arcsec. The field of view covers the central arc-minute, whichcontains the inner four pairs of knots of the molecular jet. On the channel map, conical structures are clearly present inthe low velocity range (|V−V0| <10 km s−1), and the highly collimated knots appear in the Extremely High Velocityrange (EHV, 50> |V−V0| >30 km s−1). The higher angular resolution of ∼ 1 arcsec reveals the first blue-shiftedknot (B1) that was missing in previous PdBI observation of Santıago-Garcıa et al. (2009) at an offset of ∼6 arcsec tothe North-East of the central source. This identification completes the symmetric sequence of knots in both the blue-and red-shifted lobes of the outflow. The innermost knots R1 and B1 have the highest velocities within the sequence.Although the general features appear to be similar to previous CO J = 2–1 images in Santıago-Garcıa et al. (2009),the emission in CO J = 3–2 almost always peaks further away from the central source than that of CO J = 2–1 inthe red-shifted lobe of the channel maps. This gives rise to a gradient in the line-ratio map of CO J = 3–2/J = 2–1from head to tail within a knot. A large velocity gradient (LVG) analysis suggests that the differences may reflect ahigher gas kinetic temperature at the head. We also explore possible constraints imposed by the non-detection of SiOJ = 8–7.


http://arxiv.org/pdf/1310.8432v1

A Wide-field Near- and Mid-Infrared Census of Young Stars in NGC 6334

S. Willis1,3, M. Marengo1, L. Allen2, G.G. Fazio3, H.A. Smith3, and S. Carey4

1 Department of Physics and Astronomy, Iowa State University, Ames, IA 50010, USA2 National Optical Astronomy Observatories, Tucson, AZ 85719, USA3 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA4 Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125, USA

E-mail contact: swillis at cfa.harvard.edu

This paper presents a study of the rate and efficiency of star formation in the NGC 6334 star forming region. Weobtained observations at J , H , and Ks taken with the NOAO Extremely Wide-Field Infrared Imager (NEWFIRM)and combined them with observations taken with the Infrared Array Camera (IRAC) camera on the Spitzer SpaceTelescope at wavelengths λ = 3.6, 4.5, 5.8, and 8.0 µm. We also analyzed previous observations taken at 24 µm usingthe Spitzer MIPS camera as part of the MIPSGAL survey. We have produced a point source catalog with >700,000entries. We have identified 2283 YSO candidates, 375 Class I YSOs and 1908 Class II YSOs using a combination ofexisting IRAC-based color classification schemes that we have extended and validated to the near-IR for use with warmSpitzer data. We have identified multiple new sites of ongoing star formation activity along filamentary structuresextending tens of parsecs beyond the central molecular ridge of NGC 6334. By mapping the extinction we derivedan estimate for the gas mass, 2.2 × 105 M⊙. The heavy concentration of protostars along the dense filamentarystructures indicates that NGC 6334 may be undergoing a “mini-starburs” event with ΣSFR > 8.2 M⊙ Myr−1 pc−2

and SFE > 0.10. We have used these estimates to place NGC 6334 in the Kennicutt-Schmidt diagram to help bridgethe gap between observations of local low-mass star forming regions and star formation in other galaxies.

Accepted by ApJ


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Abstracts of recently accepted major reviews

Braking down an accreting protostar: disc-locking, disc winds, stellar winds, X-windsand Magnetospheric Ejecta

Jonathan Ferreira1

1 UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Gernoble,F-38041, France

E-mail contact: [email protected]

Classical T Tauri stars are low mass young forming stars that are surrounded by a circumstellar accretion disc fromwhich they gain mass. Despite this accretion and their own contraction that should both lead to their spin up, thesestars seem to conserve instead an almost constant rotational period as long as the disc is maintained. Several scenarioshave been proposed in the literature in order to explain this puzzling ’disc-locking’ situation: either deposition in thedisc of the stellar angular momentum by the stellar magnetosphere or its ejection through winds, providing therebyan explanation of jets from Young Stellar Objects.In this lecture, these various mechanisms will be critically detailed, from the physics of the star-disc interaction to thelaunching of self- confined jets (disc winds, stellar winds, X-winds, conical winds). It will be shown that no simplemodel can account alone for the whole bulk of observational data and that ’disc locking’ requires a combination ofsome of them.

Accepted by ”Role and Mechanisms of Angular Momentum Transport During the Formation and Early Evolution ofStars”, (Evry Schatzman School 2012), Editors: P. Hennebelle and C. Charbonnel, EAS Publications Series, Volume62


Chemistry in Protoplanetary Disks

Thomas Henning1 and Dmitry Semenov1

1 Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg, Germany

E-mail contact: henning at mpia.de, semenov at mpia.de

This comprehensive review summarizes our current understanding of the evolution of gas, solids and molecular icesin protoplanetary disks. Key findings related to disk physics and chemistry, both observationally and theoretically,are highlighted. We discuss which molecular probes are used to derive gas temperature, density, ionization state, andkinematics in protoplanetary disks.

Accepted by Chem. Reviews, a thematic issue ”Astrochemistry”


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Dissertation Abstracts

Star Formation in the Perseus Molecular Cloud:A Detailed Look at Star-Forming Clumps with Herschel

Sarah Sadavoy

University of Victoria, Victoria BC, Canada

Max Planck Institute for Astronomy, Konigstuhl 17, 69117, Heidelberg, Germany

Electronic mail: sadavoy at mpia-hd.mpg.de

Ph.D dissertation directed by: James Di Francesco

Ph.D degree awarded: August 2013

This dissertation presents new Herschel observations at 70 µm, 160 µm, 250 µm, 350 µm, and 500 µm of the Perseusmolecular cloud from the Herschel Gould Belt Survey. The Perseus molecular cloud is a nearby star-forming regionconsisting of seven main star-forming clumps. The Herschel observations are used to characterize and contrast theproperties of these clumps, and to study their embedded core populations. First, we probed the exceptionally youngclump, B1-E. Using complementary molecular line data, we demonstrate that B1-E is likely fragmenting into a firstgeneration of dense cores in relative isolation. Such a core formation region has never been observed before. Second,we use complementary long wavelength observations at 850 µm to study the dust properties in the larger, more activeB1 clump. We find that Herschel data alone cannot constrain well the dust properties of cold dust emission andthat long wavelength observations are needed. Additionally, we find evidence of dust grain growth towards the densecores in B1, where the dust emissivity index, β, varies from the often assumed value of β = 2. In the absence oflong wavelength observations, however, assuming β = 2 is preferable over measuring β with the Herschel -only bands.Finally, we use the source extraction code, getsources, to identify the core populations within each clump from theHerschel data. In addition, we use complementary archival infrared observations to study their populations of youngstellar objects (YSOs). We find that the more massive clumps have an excess of older stage YSOs, suggesting thatthese regions contracted first. Starless cores are typically associated with peaks in the column density, where thosefound towards regions of higher column density also have higher average densities and colder temperatures. Starlesscores associated with a strong, local interstellar radiation field, however, have higher temperatures. We find that theclumps with the most prominent high column density tails also had the highest fractions of early-stage YSOs. Thisrelation suggests that the quantity of high column density material corresponds to recent star formation activity.

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New Jobs

Postdoc position in Star Cluster Formation and Evolution

The Institute for Astronomy of the ETH Zurich, Star and Planet Formation Research Group (led by Professor MichaelMeyer) invites applications for a post-doctoral position to study the formation and evolution of star clusters. Ourgroup is involved in two large surveys to collect radial velocities of stars in young clusters in advance of the ESAGAIA Mission: the ESO-GAIA Public Spectroscopic Survey (PIs: G. Gilmore and S. Randich) and the SDSS-IIIAPOGEE ancillary science program IN-SYNC (PIs: K. Covey and J. Tan). We have also undertaken a suite ofN-body simulations in support of this work (under the leadership of R. Parker). More information can be found athttp://www.astro.ethz.ch/meyer/index

Salaries will be commensurate with experience, beginning at CHF 85,300, with initial appointments of 2+1 years, upto a maximum of six. Successful applicants will have the opportunity to work with students at all levels and will beexpected to contribute to our on-going participation in existing large surveys and simulations, as well as propose newavenues for research.

Switzerland is a member of ESO and ESA, and successful applicants will have full access to their facilities. TheInstitute for Astronomy maintains a network of workstations, as well as a wide range of high performance computingoptions. Members of the Institute also play a leading role in the Swiss STARFORM project, linking observations,simulations, and theoretical models of molecular clouds and subsequent star formation in the Milky Way and othergalaxies. Interested applicants will also be welcome to explore research opportunities in the Laboratory for Astronom-ical Instrumentation.

Applications are invited from all nationalities and should consist of a CV and brief descriptions of past/proposedresearch (combined length not to exceed 10 pages). A separate publication list should be attached. Materials shouldbe sent electronically in a single pdf file. This file, as well as three letters of reference (sent directly by the referees)should be sent to [email protected]. Review of applications will begin December 1, 2013 and willcontinue until the position is filled.

The ETH Zurich will provide benefits for maternity leave, retirement, accident insurance, and relocation costs. We-blink: http://www.pa.ethz.ch/

PhD positions in Star and Planet Formation and Exoplanets

The Institute for Astronomy of the Swiss Federal Institute of Technology (ETH Zurich) Star and Planet FormationResearch Group invites applications for new PhD positions related to i) the direct detection and characterizationof extra-solar planets (with Prof. M.R. Meyer); ii) calibration and scientific exploitation of the ZIMPOL/SPHEREinstrument to be commissioned in 2014 on the VLT (with Prof. H.M. Schmid); and iii) interdisciplinary research onplanet formation theory utilizing astronomical, cosmochemical, and geophysical constraints (with Prof. M.R. Meyer).

Salaries for PhD students start at CHF 52,500. Students will have the opportunity to study experimental andtheoretical aspects of astronomy through formal coursework, conducting research with local experts in planet formationand exoplanet science as well as our international network of collaborators, and utilize state-of-the-art facilities.Successful applicants are expected to have a Master of Science degree in Physics, Astronomy, or related discipline, andto have already participated in one (or more) research projects (preferably in astrophysics).

Switzerland is a member of ESO and ESA, and successful applicants will have full access to their facilities, includingdata from the GTO Program of the SPHERE Project. The Institute for Astronomy maintains a network of worksta-tions, as well as a wide range of high performance computing options. Members of the Institute also play a leading role

52

in the interdisciplinary PLANET-Z initiative linking research groups at the ETH Zurich in astronomy, earth science,and computational astrophysics at the University of Zurich. Qualified applicants will be able to explore researchopportunities in the Laboratory for Astronomical Instrumentation.

Applications are invited from all nationalities and should consist of a CV (1-2 pages), description of relevant researchexperience (2 pages), academic transcripts, scores from relevant standardized tests (e.g. TOEFL, Physics GRE) apersonal statement of interests and goals (1 page), and the names of three referees that can be contacted if necessary.Materials should be sent electronically in a single pdf file to [email protected]. Review of applicationswill begin December 1, 2013 and will continue until all positions are filled.

The ETH Zurich will provide benefits for maternity leave, retirement, accident insurance, and relocation costs. We-blink: http://www.pa.ethz.ch/

Tenure-Track Faculty Position in Astrophysics with Focus on Star andPlanet Formation - Rice UniversityThe Department of Physics and Astronomy at Rice University invites applications for a tenure-track faculty positionin astrophysics with an emphasis on the formation of stars and planets within the Milky Way and in the low-redshiftuniverse. This search seeks an outstanding individual whose research will complement and extend existing activities instar and planet formation at Rice University (see http://physics.rice.edu/). While some preference will be givento observational astrophysicists, outstanding candidates with a theoretical or computational focus will also receivefull consideration. In addition to developing an independent and vigorous research program, the successful applicantwill normally be expected to teach one undergraduate or graduate course each semester. The department expects tomake an appointment at the assistant professor level. A PhD in astronomy/astrophysics or related field is required.Applicants should send a curriculum vitae, statements of research and teaching interests, a list of publications, andtwo or three selected reprints, in a single PDF file, to [email protected] with subject line ’Astrophysicist Search’ or toProf. Hartigan, Chair, Search Committee, Dept. of Physics and Astronomy - MS 61, Rice University, 6100 MainStreet, Houston, TX 77005. Applicants should also arrange for at least three letters of recommendation to be sent byemail or post. Applications will be accepted until the position is filled, but only those received by January 15, 2014will be assured full consideration. The appointment is expected to start in July 2014. Rice University is an affirmativeaction/equal opportunity employer; women and underrepresented minorities are strongly encouraged to apply.

Tenure-Track Assistant Professor Position in Observational Astronomywith a focus on star formation or exo-planets - Stony Brook UniversityThe Department of Physics and Astronomy at Stony Brook University (http://www.physics.sunysb.edu/Physics/)seeks applications for a tenure track assistant professor in observational astronomy, with a focus on star formation(galactic a/o extragalactic) a/o exo-planets. The ideal candidate will be able to make use of such facilities as ALMA,JWST, and the LSST. The current interests of the astronomy group can be found at http://www.astro.sunysb.edu/.

Stony Brook faculty and students conduct experimental and theoretical research in a broad range of topics in physicsand astronomy both in facilities on our campus and at laboratories around the world.

The successful candidate will have a PhD in Astronomy, Astrophysics, Physics or related field. S/he will be expected tocarry out an independent research program and to attract federal grant support for it. S/he will contribute to the teach-ing activities in the department at both the undergraduate and graduate levels. The appointment could start as early asin Fall 2014. To receive full consideration the application should be submitted by November 15, 2013. Interested candi-dates should go to the web page https://academicjobsonline.org/ajo/StonyBrook/PhysicsandAstronomy/2801and follow the links and instructions for uploading all application materials (including CV, a statement of teachingphilosophy, a brief (3-page limit) description of research and research interests, and the names, institutions, and emailaddresses for 3 referees) to a secure web site. The letters of references should be submitted electronically on the sameWEB site. Electronic submission via academicjobsonline is strongly preferred.

Alternatively, applicants may submit the application materials by mail to: Nathan Leoce-Schappin, Assistant to theChair, P-104 Physics Bldg., Stony Brook, NY 11794-3800.

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Summary of Upcoming Meetings

The Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments18 - 22 November 2013 Taipei, Taiwanhttp://events.asiaa.sinica.edu.tw/meeting/20131118/

Exoplanets and Disks: Their Formation and Diversity II8 - 12 December 2013, Kona, Hawaii, USAhttp://exoplanets.astron.s.u-tokyo.ac.jp/SubaruConf13/index.html

Exoplanet Observations with the E-ELT3 - 6 February 2014 Garching, Germanyhttp://www.eso.org/sci/meetings/2014/exoelt2014.html

Herbig Ae/Be stars: The missing link in star formation7 - 11 April 2014 Santiago, Chilehttp://www.eso.org/haebe2014.html

The Olympian Symposium on Star Formation26 - 30 May 2014 Paralia Katerini’s, Mount Olympus, Greecehttp://zuserver2.star.ucl.ac.uk/~ossf14/

EPoS2014 The Early Phase of Star Formation1 - 6 June 2014 Ringberg Castle, Tegernsee, Germanyhttp://www.mpia-hd.mpg.de/homes/stein/EPoS/epos.php

The Dance of Stars: Dense Stellar Systems from Infant to Old2 - 6 June 2014 Bad Honnef, Germanyhttp://www.astro.uni-bonn.de/$\sim$sambaran/DS2014/index.html

The 18th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun9 - 13 June 2014 Flagstaff, Arizona, USAhttp://www2.lowell.edu/workshops/coolstars18/

Summer School on Protoplanetary Disks: Theory and Modeling meet Observations16 - 20 June 2014 Groningen, The Netherlandshttp://www.diana-project.com/summer-school

Characterizing Planetary Systems Across the HR Diagram28 July - 1 August 2014 Inst. for Astronomy, Cambridge, USAhttp://www.ast.cam.ac.uk/meetings/2013/AcrossHR

Living Together: Planets, Stellar Binaries and Stars with Planets8 - 12 September 2014 Litomysl Castle, Litomysl, Czech Republichttp://astro.physics.muni.cz/kopal2014/

Planet Formation and Evolution 20148 - 10 September 2014 Kiel, Germanyhttp://www.astrophysik.uni-kiel.de/kiel2014

Towards Other Earths II. The Star-Planet Connection15 - 19 September 2014 Portugalhttp://www.astro.up.pt/toe2014

Other meetings: http://www1.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/meetings/

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Short Announcements

Herbig 1962 review now available

George Herbig’s major review The Properties and Problems of T Tauri Stars and Related Objects, which appeared inthe now defunct series ’Advances in Astronomy and Astrophysics’ (vol. 1, p. 47-103, 1962) has long been unavailable.In the intervening half a century, it has obviously become superseded by major new advances, but the review is still ofgreat historical interest. George Herbig was the brilliant trailblazer, who found and lit the way that new generationswill continue to explore.

http://adsabs.harvard.edu/abs/1962AdA%26A...1...47H

I am grateful to Edwin Henneken of the NASA ADS for getting permission from the publisher and for making thisreview available.

Bo Reipurth

Orion workshop talks

The talks at last month’s workshop at STScI The Orion Nebula Cluster as a Paradigm of Star Formation are nowavailable at the STScI Webcasting site:

https://webcast.stsci.edu/webcast/searchresults.xhtml?searchtype=20&eventid=198&sortmode=1

Moving ... ??

If you move or your e-mail address changes, pleasesend the editor your new address. If the Newsletterbounces back from an address for three consecutivemonths, the address is deleted from the mailing list.

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