T. GirardStars: Young, Old and Variable – May 18-21, 2014 T. Girard Yale University The Glint on...

T. GirardStars: Young, Old and Variable – May 18-21, 2014

T. GirardYale University

The Glint on Magellan's Prow:

Young Stars in the Leading Arm

of the Magellanic Stream______________________________________________________


“Score Machine” Ames city-league softball, ~ early 1980’s


A more relevant team... Casetti-Dinescu et al. 2014, (ApJL 784, 37)“Recent Star Formation in the Leading Arm of the

Magellanic Stream”

Christian Moni Bidin Univ. Catolica del Norte, Antofagasta, Chile

Dana Casetti SCSU & Yale University

Rene Mendez Universidad de Chile Santiago, Chile

Kathy Vieira CIDA Merida, Venezuela

Vladimir Korchagin Southern Federal UniversityRostov-on-Don, Russia

Bill van Altena Yale University


Location, location, location…

credit: www.eso.org – Yuri Beletsky


“a conglomerate of stars put together in a manner of two clouds”

Antonio Pigafetta (1524)

Magellanic Clouds:

Over the Edge of the World by Laurence Bergreen


Magellanic Clouds: The Gaseous Stream

Nidever et al. 2010 Figure 9. Magellanic Stream and Clouds in HI (red) with an optical all-sky image (blue, white, and brown; Mellinger 2009) in Aitoff projection with the direction to the Galactic Center at the center.


Magellanic Clouds: The Gaseous Stream

Nidever et al. 2008

Gas velocity

Gas density

Model constraints:

Reproduce the various components of the gaseous Magellanic Stream; spatial and 1D velocity distribution.

Reproduce the current locations and 3D velocities of the Clouds.


Magellanic Clouds: Orbits & Interaction

“New” orbit: HST-based , Kallivayalil et al. 2006

Old orbit: (based on matching MS, spatially)

MW-Clouds interaction is currently under dispute!


Magellanic Clouds: Modeling the Interaction

Diaz & Bekki (2012)

SMC: N-body LMC, MW: rigid potentials

Cloud-cloud interaction:1st encounter:

~2 Gyr ago, MS formation

2nd encounter: ~200 Myr ago, Bridge formation

MW-Clouds interaction:1st pericenter passage:

~2.5 Gyr ago2nd pericenter passage:

now



Diaz & Bekki (2012)

SMC: N-body LMC, MW: rigid potentials



Diaz & Bekki 2012 (model) Nidever et al. 2010 (observations)

Radial velocity distribution



Diaz & Bekki 2012, Nidever et al. 2010

Spatial distribution:

MS, LA, Bridge are of tidal origin, primarily material pulled out from the SMC.

LA is poorly explained by all models; gas hydrodynamics most likely plays a role.


Magellanic Clouds: LMC Absolute Proper Motion

Diaz (2013, personal communication)


OB-type Star Search: A Cross-Catalog Approach

Photometry

Astrometry/Photometry

GALEX DR5 (Bianchi et al. 2011)

2MASS (Skrutskie et al. 2006)

APASS (Henden et al. 2011)

NUV

J

V

all-sky1771-2831Å, eff = 2315.7Å, NUVlim= 20.8

all-sky (also made use of 6x2MASS)

AAVSO all-sky survey (B,V, g, r, i) 10 < V < 17.0, V ~ 0.06 mag

SPM4 (Girard et al. 2011)

, V < -20o, Vlim~17.5V ~ 0.05 mag



-2.0 ≤ (NUV-V)0 ≤ 0.0

-1.2 ≤ (V-J)0 ≤ -0.2

(NUV ≤ 0.10, J ≤ 0.15)

≤ 8.0 mas/yr

( ≤ 4.0 mas/yr)

13.0 ≤ V0 ≤ 17.0

E(B-V) ≤ 0.5

Final Selection Criteria


Results:

567 OB-type star candidates(from an initial ~4 million)

Casetti-Dinescu et al. 2012

HI density

(Nidever et al. 2010)



OB star candidates include

• a well-populated SMC wing, extending in a narrow band toward the LMC to RA ~ 3.4h, possibly reaching to the LMC;

• two branches partially surrounding the SMC;

• well-defined concentrations at the ends of the LMC bar, and a well-populated LMC periphery;

• several groupings in the LA;

• a few scattered candidates in the MS.

OB-type Star Search: The Extended Clouds Region


OB-type Star Search: The Extended Clouds Region

OB star candidates include

• a well-populated SMC wing, extending in a narrow band toward the LMC to RA ~ 3.4h, possibly reaching to the LMC;

• two branches partially surrounding the SMC;

• well-defined concentrations at the ends of the LMC bar, and a well-populated LMC periphery;

• several groupings in the LA;

• a few scattered candidates in the MS.


OB-type Stars in the Leading Arm: Spectroscopic Follow-up

Obtained spectra of 42 candidates in the Leading Arm, in April 2013

IMACS on 6.5m Baade telescope,1 Å resolution, 3700-5300 Å range

Spectral Type, RV, log g, Teff

( υsini, log[NHe/NH] )

Twin 6.5m Magellan telescopes: Baade and Clay Las Campanas, Chile


OB-type Stars in the Leading Arm: Spectroscopic Findings

= fast rotator




Found 19 young, massive stars, including...

five with RVs consistent with Leading Arm membership;

plus

one O6V star, i.e., ~40 M and very young (~1 Myr).



OB-type Stars in the Leading Arm: Stars of Interest

ID RV (kms)

vsini (kms)

Teff (K)

log g log[NHeNH

]Sp.Type

B.02 168 ± 4 [ 0 ] 16000 ± 400

3.76 ± 0.09

[ -1 ] B4III

B.03 229 ± 5 [ 0 ] 17500 ± 1100

3.86 ± 0.18

-1.60 ± 0.18

B3IV

B.14 207 ± 5 300 15800 ± 700

3.60 ± 0.15

[ -1 ] B4/5III

B.15 248 ± 5 [ 0 ] 14800 ± 700

4.17 ± 0.15

-2.10 ± 0.33

sdB

A.15 166 ± 6 280 13400 ± 600

3.67 ± 0.18

[ -1 ] B7III

A.19 234 ± 6 260 17200 ± 1900

4.03 ± 0.36

-1.58 ± 0.42

B3IV

A.08 71 ± 11

[ 0 ] 43700 ± 1200

4.47 ± 0.12

-1.20 ± 0.39

O6V



For the five young, LA members (RV>150 km/s)...

Distances are ~20 kpc from the Sun, (or ~18 kpc from the Galactic center, i.e. roughly the extent of the Galactic disk).

Ages are ~100 Myr, i.e. recently formed.

Gray band is kinematical distance to a particular high-velocity cloud in the LA. (McClure-Griffiths et al. 2008)

= RV>150km/s, = O6V star Casetti-Dinescu et al. 2014


Summary:

Young, massive stars have been found in the Leading Arm of the gaseous Magellanic Stream

Their location suggests recent interaction of gas in the Leading Arm with that of the outer edge of the Milky Way

Implying that hydrodynamical effects are at play and must be included in Clouds/MW interaction models

A single, more distant and extremely massive/young O6V star also has been identified, unquestionably formed in situ

Stay tuned for more...


And a little press is always nice...

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