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“Where to Study Planet Formation? The Nearest, Youngest Stars”

“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?

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“Where to Study Planet Formation? The Nearest, Youngest Stars”

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  1. “Where to Study Planet Formation?The Nearest, Youngest Stars” Eric Mamajek Harvard-Smithsonian Center for Astrophysics Space Telescope Science Institute - 17 January 2008

  2. 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” ?

  3. 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

  4. Star+planetary system formation paradigm (cartoon) Is this a normal outcome? T. Greene (2001)

  5. 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.)

  6. Evolution of Circumstellar Disks Need Samples of Different ages to Study disk evolution! Reservoir of solids needed to regenerate short-lived dust grains around older (>10 million year-old) stars M. Meyer (U. Arizona)

  7. Sun (Now) X “Stars” “Brown Dwarfs” Luminosity “Planets” Jupiter (Now) X Age (Burrows et al. 1997)

  8. Finding the Nearest, Youngest Stars

  9. 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) Galactic Star-Formation: census of clusters is not complete, even within 100 pc! Can make complete stellar censuses, study dynamics, etc. Eta Cha cluster (Mamajek et al. 1999, 2000, Lyo et al. 2003) Discovered w/ ROSAT & Hipparcos

  10. Theoretical Isochrones Problem for deriving ages: Main Sequence stars evolve very slowly!

  11. Activity Scales with Rotation… Rotation slows with age <100 Myr ~600 Myr Rotation period ~ age^0.5 (Skumanich 1972, Barnes 2007) * Sun Mamajek &Hillenbrand (2008, in prep.)

  12. 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

  13. Stellar Aggregates in the Solar Neighborhood (1997)

  14. 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)

  15. Epsilon Cha group (Mamajek+ 2000, Feigelson+ 2003) ~5 Myr ~115 pc Eta Cha group (Mamajek+ 2000, Feigelson+ 2003) ~7 Myr ~97 pc Mu Oph group (Mamajek 2006) ~120 Myr ~173 pc 32 Ori group (Mamajek, in prep.) ~25 Myr ~95 pc

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

  17. 32 Ori Group @ d = 95 pc (Mamajek, in prep.) First northern pre-MS stellar group within 100 pc!

  18. 32 Ori Group ~25 Myr Follow-up: Spitzer Cycle 4 survey for disks at 3-24um with IRAC & MIPS (Mamajek, Meyer, Kim)

  19. 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)

  20. Dusty Debris Common Around Normal Stars CAIs Vesta/Mars LHB Chondrules Earth-Moon Primary sources of Dust grains: ~10-100km Planetesimals To be a detectable “excess”: ~10^3 X Solar system zodiacal dust! Fraction w/24um Excess FEPS Rieke et al. (2005); Gorlova et al. (2006); Siegler et al. (2007); Meyer et al. (2008). Age

  21. 2M1207: A young “planetary mass object” gone wrong…

  22. Substellar Binary 2M1207 A 2M1207 “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

  23. 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 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!

  24. Brighter 2M1207 “A” “B” Predicted Temperature & Age “B” Predicted Luminosity & Age Luminosity 2M1207 “B” Dimmer <- Hotter Cooler -> Temperature [K] Mohanty, Jayawardhana, Huelamo, Mamajek (2007; ApJ 657, 1064)

  25. Edge-on Gray Dust Disk hypothesis (Mohanty et al. 2007) Predictions: Resolved disk? Polarization? KH15D-type eclipses?

  26. 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)

  27. 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!

  28. “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 Giant Magellan Telescope (JWST) 6.5-meter, ~2013 (GMT) 25-meter, ~2015

  29. Can exoplanets be imaged?

  30. 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 - 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 MMT/AO + Clio 15” FOV; 4.5um; Altair (A7V, 8 pc)

  31. “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

  32. Imaging Radial Velocity Searches (D. Apai, M. Meyer)

  33. 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

  34. Clio 3-5um Imager (InSb 320x256 array) + + + MMT 6.5-m Apodized Phase Plate f/5 Adaptive Optics Secondary 1” radius

  35. 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)

  36. 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!

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