near-ir spectroscopy of simple organic molecules in gv tau n dr. erika gibb june 19, 2014
TRANSCRIPT
Near-IR Spectroscopy of Simple Organic Molecules in GV Tau N
Dr. Erika Gibb
June 19, 2014
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
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
Anatomy of a Disk
• 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
• Intermediate layer rich ion-molecule chemistry, absorption
Lahuis et al. 2006
Follow the Volatiles: Disks
Follow the Volatiles: Disks/Comets?
• Midplane cold, volatiles frozen onto grains
GV Tau
• Low mass binary system• Close to edge on• Surrounded by circumbinary material • Warm HCN & C2H2 absorption toward GV Tau N
– Located in warm molecular layer of circumstellar disk
(Gibb et al. 2007; Doppman et al. 2008)
GV Tau
• Recently reported CH4 … first detection in a disk
(Gibb & Horne 2013)
Note: Molecules like C2H2 & CH4 have no pure rotational transitions and cannot be done with ALMA.
GV Tau
CH4 Toward GV Tau• CH4 in GV Tau N disk
– Trot ~750 K
CH4 Toward GV Tau• CH4 in GV Tau N disk
– Trot ~750 K
Where is the gas located?
Walsh et al. 2010
Results
• Trot ~ 750 K
• Abundances?– If assume gas is co-spatial– HCN/CH4 ~ 50%
– (similar to ratio found in comets)
• Spectral features are variable– Indicating structure/clumpiness in inner disk?
Mystery left to solve: Why are the 2006 and 2010 spectra so different?
Acknowledgements• Students
– Logan Brown, Nathan Roth• Disks
– David Horne (Washington College)• Funding
– NASA Exobiology, NSF Stellar Astronomy
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