Carbon and Oxygen in Nearby Stars: Keys to Protoplanetary Disk Chemistry

We present carbon and oxygen abundances for 941 FGK stars—the largest such catalog to date. We find that planet-bearing systems are enriched in these elements. We self-consistently measure N_C /N_O , which is thought to play a key role in planet formation. We identify 46 stars with N_C /N_O >= 1.00 as potential hosts of carbon-dominated exoplanets. We measure a downward trend in [O/Fe] versus [Fe/H] and find distinct trends in the thin and thick disks, supporting the work of Bensby et al. Finally, we measure sub-solar N_C /N_O = 0.40^+0.11 _{- 0.07}, for WASP-12, a surprising result as this star is host to a transiting hot Jupiter whose dayside atmosphere was recently reported to have N_C /N_O >= 1 by Madhusudhan et al. Our measurements are based on 15,000 high signal-to-noise spectra taken with the Keck 1 telescope as part of the California Planet Search. We derive abundances from the [O I] and C I absorption lines at λ = 6300 and 6587 Å using the SME spectral synthesizer.

Based in part on observations obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.