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