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Near-IR Spectroscopy of Simple Organic Molecules in GV Tau N Dr. Erika Gibb June 19, 2014
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Motivation Understanding how volatiles evolve from dark clouds to disks around young stars to protoplanets –Where/how are volatiles processed? –How are volatiles distributed through disks? –Where did Earth’s water, organics come from? Method –Infrared spectroscopy of clouds, disks and comets –Comparison with chemical models
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Keck Observatory 10 meter telescope NIRSPEC: Near-Infrared Spectrometer High resolving power ( / ~ 25,000) 2-5 m region Simple organic molecules have ro-vibrational transitions
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Anatomy of a Disk
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Surface layer emission lines Follow the Volatiles: Disks Spectral features can be used to determine temperature, then combine with disk model to estimate location → non unique solutions
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Intermediate layer rich ion-molecule chemistry, absorption Lahuis et al. 2006 Follow the Volatiles: Disks
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Follow the Volatiles: Disks/Comets? Midplane cold, volatiles frozen onto grains
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GV Tau Low mass binary system Close to edge on Surrounded by circumbinary material Warm HCN & C 2 H 2 absorption toward GV Tau N – Located in warm molecular layer of circumstellar disk (Gibb et al. 2007; Doppman et al. 2008)
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GV Tau Recently reported CH 4 … first detection in a disk (Gibb & Horne 2013) Note: Molecules like C 2 H 2 & CH 4 have no pure rotational transitions and cannot be done with ALMA.
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GV Tau
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CH 4 Toward GV Tau CH 4 in GV Tau N disk –T rot ~750 K
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CH 4 Toward GV Tau CH 4 in GV Tau N disk –T rot ~750 K
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Where is the gas located? Walsh et al. 2010
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Results T rot ~ 750 K Abundances? –If assume gas is co-spatial –HCN/CH 4 ~ 50% –(similar to ratio found in comets) Spectral features are variable –Indicating structure/clumpiness in inner disk?
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Mystery left to solve: Why are the 2006 and 2010 spectra so different?
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Acknowledgements Students –Logan Brown, Nathan Roth Disks –David Horne (Washington College) Funding –NASA Exobiology, NSF Stellar Astronomy
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Disk Processing Surface of disk processed by UV, X-ray, cosmic ray Inner region: ion-molecule chemistry, photochemistry Outer region: grain-surface, ion-molecule, neutral-neutral reaction Bulk motions: turbulence, migration inward vertical & radial mixing
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