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“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” ? Super-Earths Neptunes High Mass Star Planets Low Mass Star Planets Multi-planet Systems Transiting Hot Jupiters Normal Jupiters Eccentric Jupiters Hot Jupiters Pulsar Planets Star+planetary system formation paradigm (cartoon) Is this a normal outcome? T. Greene (2001) 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 Need Samples of Different ages to Study disk evolution! Reservoir of solids needed to regenerate short-lived dust grains M. Meyer (U. Arizona) around older (>10 million year-old) stars Sun (Now) X “Stars” “Brown Dwarfs” “Planets” Jupiter (Now) X (Burrows et al. 1997) Age Finding the Nearest, Youngest Stars Why do we care? Nearby Young Stars (& Groups) Substellar Objects: best chance to image luminous young planets and brown dwarfs 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 Galactic Star-Formation: census of clusters (Mamajek et al. 1999, 2000, is not complete, even within 100 pc! Can make Lyo et al. 2003) complete stellar censuses, study dynamics, etc. Discovered w/ ROSAT & Hipparcos Theoretical Isochrones Problem for deriving ages: Main Sequence stars evolve very slowly! Activity Scales with <100 Myr Rotation… ~600 Myr Rotation slows with age Rotation period ~ age^0.5 * Sun (Skumanich 1972, Barnes 2007) Mamajek & Hillenbrand (2008, in prep.) 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 * Sun optical Spectroscopy! 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 comoving… Key: ROSAT All-Sky Survey (X-ray) Hipparcos/Tycho-2 (astrometry) Mamajek (2005, 2006) Zuckerman & Song (2004), Torres et al. (2006) Eta Cha Epsilon Cha group group (Mamajek+ 2000, (Mamajek+ 2000, Feigelson+ 2003) Feigelson+ 2003) ~7 Myr ~5 Myr ~97 pc ~115 pc Mu Oph 32 Ori group group (Mamajek 2006) (Mamajek, ~120 Myr in prep.) ~173 pc ~25 Myr ~95 pc Our nearest OB association/Star-forming Complex: the “big picture” 32 Ori Group @ d = 95 pc First northern pre-MS stellar group within 100 pc! (Mamajek, in prep.) 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) Dusty Debris Common Around Normal Stars CAIs Vesta/Mars Chondrules Earth-Moon LHB Primary sources of Dust grains: ~10-100km Planetesimals Fraction w/24um Excess FEPS To be a detectable “excess”: ~10^3 X Solar system zodiacal dust! Age Rieke et al. (2005); Gorlova et al. (2006); Siegler et al. (2007); Meyer et al. (2008). 2M1207: A young “planetary mass object” gone wrong… Substellar Binary 2M1207 2M1207 “A”: 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”: 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”? Because we know… …we think we know… The infrared colors and spectrum of “B” …its temperature (1600K) “A” and “B” have common motion …“A” and “B” are coeval and bound The distance to the 2M1207 system …the luminosity of “B” (1/50,000x Sun) The distance and 3D motion of …its age, as it appears to be a the 2M1207A 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! Brighter 2M1207 “A” “B” Predicted Luminosity Temperature & Age “B” Predicted Luminosity & Age Dimmer 2M1207 “B” <- Hotter Mohanty, Jayawardhana, Huelamo, Mamajek (2007; ApJ 657, 1064) Cooler -> Temperature [K] Edge-on Gray Dust Disk hypothesis (Mohanty et al. 2007) Predictions: Resolved disk? Polarization? KH15D-type eclipses? Afterglow of a protoplanetary collision? (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? (Mamajek & Meyer, 2007 ApJ, 668, L175) Analytical Estimate of Protoplanet Growth Mass Time Disk Surface Density Lodato et al. (2005) Orbital Radius Primary Mass Conclusion: one can form a small gas giant around 2M1207A within ~10 Myr, but at ~< 5 AU! “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? James Webb Space Telescope (JWST) 6.5-meter, ~2013 Giant Magellan Telescope (GMT) 25-meter, ~2015 Can exoplanets be imaged? Why do we care? Imaging Planets w/ MMT 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 MMT/AO + Clio 15” FOV; 4.5um; Altair (A7V, 8 pc) 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 “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) 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) Background star; equivalent in brightness to a planet of ~5 M_Jup Clio 3-5um + + + Imager (InSb 320x256 array) MMT 6.5-m f/5 Adaptive Optics Secondary 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) 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 AU @ 10 pc) Future looks bright for studying giant planets and dusty debris disk systems at large radii - we need more nearby young targets!