“Where to Study Planet Formation?

The Nearest, Youngest Stars”

Eric MamajekHarvard-Smithsonian Center for Astrophysics

Space Telescope Science Institute - 17 January 2008

Some “Big Questions”

How do planetary systems vary by

the following:

stellar mass?

stellar multiplicity?

stellar age?

birth environment?

etc…

Is our Earth & Solar System “normal” ?

Pulsar Planets

Hot JupitersEccentric Jupiters

Multi-planet Systems

Neptunes

High Mass Star Planets

Low Mass Star Planets

Normal Jupiters

Super-Earths

Transiting Hot Jupiters

Star+planetary system formation paradigm (cartoon)

T. Greene (2001)

Is this a normal outcome?

Early hints: protoplanetary disks are nearly ubiquitous!

1990s:

Circumstellar gas and

dust appears to be

common around

<1 Myr stars.

HST resolves disks.

2000s:

Spitzer Space Telescope

(3-160um) now showing

diversity of spectral energy

distributions (disk geometries,

dust properties, etc.)

Evolution of Circumstellar Disks

M. Meyer (U. Arizona)

Reservoir of solids needed to regenerate short-lived dust grains

around older (>10 million year-old) stars

Need Samples of

Different ages to

Study disk evolution!

(Burrows et al. 1997)

“Stars”

“Planets”

“Brown Dwarfs”

Lu

min

osit

y

Age

Sun (Now)

X

Jupiter (Now)

X

Finding the Nearest, Youngest Stars

Nearby Young Stars (& Groups)

Why do we care?

Disk Evolution: ~3-100 Myr is interesting

age range for planet formation. Photospheres of

low-mass stars are bright; easier to detect disks.

Some disks are resolvable! (e.g. Beta Pic)

Eta Cha cluster(Mamajek et al. 1999, 2000,

Lyo et al. 2003)

Discovered w/

ROSAT & Hipparcos

Galactic Star-Formation: census of clusters

is not complete, even within 100 pc! Can make

complete stellar censuses, study dynamics, etc.

Substellar Objects: best chance to image

luminous young planets and brown dwarfs

Theoretical

Isochrones

Problem

for deriving

ages:

Main

Sequence

stars

evolve very

slowly!

Activity

Scales with

Rotation…

Rotation

slows

with age

Mamajek &

Hillenbrand

(2008, in prep.)

Rotation period ~ age^0.5

(Skumanich 1972,

Barnes 2007)

* Sun

<100 Myr

~600 Myr

Lithium

Depletion

Li burned at

~1-2 MK in stellar

interiors…

Li depletion rate

varies with Mass

(secondary effects

are metallicity &

rotation)

Why we need

optical

Spectroscopy!

* Sun

Stellar Aggregates in the Solar Neighborhood(1997)

Stellar Aggregates in the Solar Neighborhood(2007)Nearby younglow-mass starsare X-ray luminous& Li-rich. Thosein groups are co-moving…

Key: ROSAT All-Sky Survey (X-ray)Hipparcos/Tycho-2(astrometry)

Mamajek (2005, 2006)Zuckerman & Song (2004), Torres et al. (2006)

Mu Oph

group (Mamajek 2006)

~120 Myr

~173 pc

Epsilon Cha

group

(Mamajek+ 2000,

Feigelson+ 2003)

~5 Myr

~115 pc

Eta Cha

group

(Mamajek+ 2000,

Feigelson+ 2003)

~7 Myr

~97 pc

32 Ori

group

(Mamajek,

in prep.)

~25 Myr

~95 pc

Our nearest OB association/Star-forming Complex: the “big picture”

32 Ori Group @ d = 95 pc

(Mamajek, in prep.)First northern pre-MS stellar group within 100 pc!

32 Ori Group

~25 Myr

Follow-up: Spitzer Cycle 4 survey for disks at 3-24um with

IRAC & MIPS (Mamajek, Meyer, Kim)

Snapshot of Disk Evolution across the Mass Spectrum at 5 Myr

Disk

Fraction

>2.5 Mo 1.5-2.5 Mo 0.5-1.5 Mo <0.5 Mo

Carpenter, Mamajek, Meyer, Hillenbrand (2006)

FEPS

Dusty Debris Common Around Normal Stars

CAIs Vesta/Mars LHB Chondrules Earth-Moon

Rieke et al. (2005); Gorlova et al. (2006); Siegler et al. (2007); Meyer et al. (2008).

Fractionw/24umExcess

Age

Primary sources of

Dust grains: ~10-100km

Planetesimals

To be a detectable

“excess”: ~10^3 X

Solar system

zodiacal dust!

2M1207:

A young

“planetary mass object”

gone wrong…

Substellar Binary 2M12072M1207 “A”: * discovered by J. Gizis (2002) in 2MASS. * ~8 Million year old TW Hya group member * distance = 53 +- 1 pc * ~25 Jupiter mass brown dwarf accretor

2M1207 “B”: * discovered by G. Chauvin et al. (2004) with VLT/NACO * common motion with “A” confirmed (HST) * ~late L-type spectrum, no methane * ~0.01 X luminosity of “A” * 0.8” separation => 41 AU

What is the mass and origin of “B”?

B

A

Because we know… …we think we know…

The distance to the 2M1207 system …the luminosity of “B” (1/50,000x Sun)

The infrared colors and spectrum of “B” …its temperature (1600K)

The distance and 3D motion of

the 2M1207A

…its age, as it appears to be a

member of the ~8 Million-year-old

“TW Hydra Association”

Any combination of two of these variables

(temperature, luminosity, age) should allow

us to uniquely estimate the mass!

“A” and “B” have common motion …“A” and “B” are coeval and bound

Temperature [K]

Lu

min

osit

y

2M1207 “A”

2M1207 “B”

“B” Predicted

Temperature & Age

“B” Predicted

Luminosity & Age

Mohanty, Jayawardhana, Huelamo,

Mamajek (2007; ApJ 657, 1064)

Cooler -><- Hotter

Dimmer

Brighter

Edge-on Gray Dust Disk hypothesis (Mohanty et al. 2007)

Predictions:Resolved disk?

Polarization?

KH15D-type eclipses?

Afterglow of a protoplanetary collision?

(Mamajek & Meyer,

2007 ApJ, 668, L175)

?

(e.g. Stern 1994, Zhang & Sigurdsson 2003, Anic, Alibert, & Benz 2007)

Predictions:Radius ~50,000 km

Mass ~ tens of Earths

Lower gravity

Higher Z

Closer-in unseen giant?

Mass Time Disk Surface Density

Orbital Radius Primary Mass

Analytical Estimate of Protoplanet Growth

Conclusion: one can form a small gas giant

around 2M1207A within ~10 Myr, but at ~< 5 AU!

Lodato et al.

(2005)

James Webb Space Telescope Giant Magellan Telescope(JWST) 6.5-meter, ~2013 (GMT) 25-meter, ~2015

“Hot Protoplanet Collision Afterglows” might constitute a new class of object

seen by the next generation of observatories!

Can we see the lingering afterglows of titanic protoplanetary accretion events?

Can exoplanets be imaged?

Why do we care?

MMT/AO + Clio

15” FOV; 4.5um;

Altair (A7V, 8 pc)

NO extrasolar planet has been yet imaged!

Our knowledge of exoplanet atmospheres is

limited to a few transiting “Hot Jupiters”.

No extrasolar objects with photospheres with

Teff < 650K (T8.5 type) are known -

i.e. new atmospheric chemistry & physics

Previous surveys mostly limited to near-IR --

We are exploring L & M-bands (3.5-4.8 um)

where giant planet spectra are predicted to peak

Imaging Planets w/ MMT

“Still looking” to image an exoplanet• Giant planets should be brightest in

IR (~5 um), especially young ones

• Searches in near-IR with adaptive optics on large telescopes or HST have thus far only upper limits on the numbers of <13 Jupiter mass companions to nearby stars

• Surveys @ VLT, Keck, HST, MMT• (e.g., Macintosh et al. 2001, 2003, Metchev

et al. 2003, Chauvin et al. 2004, 2005, Masciadri et al. 2005, Hinz et al. 2006, Biller et al. 2007, Apai et al. 2007, Kaspar et al. 2007, Heinze PhD Thesis, Mamajek et al., in prep.)

• Jupiters are rare at ~>30 AU

Radial Velocity Searches Imaging

(D. Apai,

M. Meyer)

Background star;

equivalent in

brightness to a

planet of ~5 M_Jup

Digital Snapshots with MMT f/15 AO+CLIO (L&M-band imager)

P. Hinz, A. Heinze M. Kenworthy, E. Mamajek, D. Apai& M. Meyer

Surveys:Heinze+ (FGK *s)Apai+, (M*s <6pc),Mamajek+ (A*s <25pc)So far no planets…

5” (30AU @ 6 pc)

MMT 6.5-m f/5 Adaptive Optics

Secondary

Clio 3-5um

Imager(InSb 320x256 array)

+ ++

Apodized

Phase Plate

1” radius

MMT/AO

+ Clio

+ phase plate

~1 hr

Dec. 2006

Sirius

~0.3 Gyr ~3 pc

Following up

Nearest northern

A-type stars

with phase plate

(Mamajek et al.)

(M. Kenworthy)

ConclusionsThe nearest, youngest stars can provide the best targets for studying planet formation

and disk evolution “up close”.

Something is wrong with the infamous “planetary mass companion” 2M1207b - it is either way too hot or way to dim. Why?

We are using MMT/AO + Clio imaging in the thermal IR to search for planets around nearby stars (so far no detections). Apodized phase plate optic is allowing us to probe at smaller orbital radii (~0.5”; ~5 AU @ 10 pc)

Future looks bright for studying giant planets and dusty debrisdisk systems at large radii - we need more nearby young targets!