“Where to Study Planet Formation? The Nearest, Youngest Stars” Eric Mamajek Harvard-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 Jupiters Eccentric 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” Luminosity 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 young low-mass stars are X-ray luminous & Li-rich. Those in 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 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 Mo 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). Fraction w/24um Excess 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 2M1207 2M1207 “A”: * discovered by J. Gizis (2002) in 2MASS. * ~8 Million year old TW Hya group member * distance = 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] Luminosity 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 ( 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 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” 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 Sirius ~0.3 Gyr ~3 pc Following up Nearest northern A-type stars with phase plate (Mamajek et al.) (M. Kenworthy)

Conclusions The 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 10 pc) Future looks bright for studying giant planets and dusty debris disk systems at large radii - we need more nearby young targets!