Chemical constraints on Theories of Planet Formation
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Chemical constraints on Theories of Planet Formation
Vincent GeersInstitute for Astronomy, ETH Zurich
Star & Planet Formation group
A. Banzatti, S. Bruderer, F. Lahuis, I. Pascucci, Th. Henning, P. Ábrahám, A. Juhász
M. Meyer, U. Gorti, E. Mamajek, D. Hollenbach, A. Benz
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Outline
• EX Lup: molecular emission lines toward variable YSO
• Limits on timescale ice-giant formation with Herschel
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Different Flavors of Planet Formation
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The carbon problem
Lee, Bergin & Nomura 2010• C under abundant in Earth and meteorites compared to what is available at formation => primordial carbon grains are destroyed, while silicon grains remain intact
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Different Flavors of Planet Formation
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Discontinuities in disks provide observational tests
From M. Meyer, Physics World, November, 2009 Based on Dullemond et al. (2001) with artwork from R. Hurt (NASA)
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Chemistry in planet-forming zone
• Wide range of molecules now detected in planet-forming zone (0.1-10AU) around few dozen YSOs(H2O, HCN, C2H2, OH, CO)
• Concurrent C, N, O in inner disks imply complex chemistry!
Pontoppidan et al. 2010
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Gas disk chemistry may vary with stellar mass
Pascucci et al. (2009)
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EX Lup: temporal domain experiment
• EX Lup– young M star with disk– Eruptive variable star, on timescale of decades– Recent outburst in January 2008, accretion rate
up ~40, luminosity ~4 (Aspin et al. 2010)– Spitzer observed it before and during outburst
• Unique experiment:What happens to the gas and dust content when only 1 parameter, luminosity, is changed?
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Episodic formation of cometary material
• Witnessed formation of silicate crystals during outburst• Previous big outburst in 1955 => no trace in 2005 =>
efficient removal of crystalline silicates from surface
Ábrahám et al. 2009 Nature
ISM Pre-outburst Outburst Halley/Tempelcomets
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Water line variations in disk around EX Lup
H2O features (Banzatti et al. in prep.)
Quiescent phaseMarch 2005
Outburst phaseApril 2008
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Results of water modeling• Line ratios suggest larger
surface area with constant water abundance in outburst
• Grid of simple LTE models (NH2O, T, area)– best fit outburst : cooler
water and 4-5 x larger emitting area than when in quiescence
• Ice line moving outward during outburst?
Modified from Pontoppidan et al. 2010
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C2H2, HCN, OH also change!
• OH: undetected in quiescence, detected in outburst– photo-dissociation from H2O ? (Tappe et al. 2008)– compare with predictions for self-shielding by Bethell & Bergin 2010
• HCN & C2H2: detected in quiescence, not in outburst– Line flux ratio HCN/C2H2 in quiescence consistent with solar-type
star, cf. Pascucci et al. (2009)
Banzatti et al. (in prep.)
C2H2HCNOH OH
Quiescent phaseMarch 2005
Outburst phaseApril 2008
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What is the timescale for forming ice-giants?
• Do young 10-100 Myr stars with debris disk systems have enough gas (> 10 Mearth) to form planets like Uranus and Neptune?
• Debris disks assumed gas-poor, but counter-examples exist: 49 Cet, Beta Pic (10-20 Myr)
• Modest amounts of gas may still significantly influence grain dynamics, thus planetesimals growth
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Herschel is best for limits of ice-giant formation!
• [OI] one of the strongest gas emission lines originating from 10-50 AU region (ice-giant planet forming zone)=> sensitive probe of remnant gas available to form ice-giants
Based on Gorti & Hollenbach 2008
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Limits on ice-giant formation with Herschel
• Search for remnant gas in 10-100 Myr debris disks, with detected planets and/or signs of planet formation:– GT program (2.5 hr) : HR 8799, HD 15115
to be scheduled hopefully next window Nov-Jan– OT program (4.9 hr) : 4 young stars with well-studied dust
distributions: HD 61005, HD377, MML17, RXJ1852.3-3700
• Observations will probe down to 0.01 – 4 Mearth of gas:– Non-detections => strong upper limits for formation of ice-
giants (M ~ 10 Mearth)– Detections => will need follow-up (e.g. CO, [CII]) to
determine relative abundances of C, N and O in photo-evaporating disks
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Take home message
• EX Lup: molecular emission lines changing dramatically with luminosity during outburst :– H2O, OH lines stronger, C2H2 and HCN weaker– Simple LTE model of water consistent with
cooler water and larger emitting area
• Herschel will provide important constraints on timescale for formation of ice-giants
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Gordon Research Conferences
Origins of Solar SystemsComposition of Forming Planets: A Tool to Understand Processes
July 17-22, 2011Mount Holyoke College
South Hadley, MA
Program available later this fall. Registration open athttp://www.grc.org/
or Google “GRC 2011 Origins”
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