Johanna K. Teske¹, Katia Cunha^1,2, Verne V. Smith³, Simon C. Schuler⁴ and Caitlin A. Griffith⁵

¹Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
²Observatório Nacional, Rua General José Cristino, 77, 20921-400 São Cristóvão, Rio de Janeiro, RJ, Brazil
³National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA
⁴University of Tampa, 401 West Kennedy Boulevard, Tampa, FL 33606, USA
⁵Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA

The relative abundances of carbon and oxygen have long been recognized as fundamental diagnostics of stellar chemical evolution. Now, the growing number of exoplanet observations enable estimation of these elements in exoplanetary atmospheres. In hot Jupiters, the C/O ratio affects the partitioning of carbon in the major observable molecules, making these elements diagnostic of temperature structure and composition. Here we present measurements of carbon and oxygen abundances in 16 stars that host transiting hot Jupiter exoplanets, and we compare our C/O ratios to those measured in larger samples of host stars, as well as those estimated for the corresponding exoplanet atmospheres. With standard stellar abundance analysis we derive stellar parameters as well as [C/H] and [O/H] from multiple abundance indicators, including synthesis fitting of the [O i] λ6300 line and non-LTE corrections for the O i triplet. Our results, in agreement with recent suggestions, indicate that previously measured exoplanet host star C/O ratios may have been overestimated. The mean transiting exoplanet host star C/O ratio from this sample is 0.54 (C/O_☉ = 0.54), versus previously measured C/O_host star means of ~0.65–0.75. We also observe the increase in C/O with [Fe/H] expected for all stars based on Galactic chemical evolution; a linear fit to our results falls slightly below that of other exoplanet host star studies but has a similar slope. Though the C/O ratios of even the most-observed exoplanets are still uncertain, the more precise abundance analysis possible right now for their host stars can help constrain these planets’ formation environments and current compositions.

Reference
Teske JK, Cunha K, Smith VV, Schuler SC and Griffith CA (2014) C/O ratios of stars with transiting hot Jupiter exoplanets. The Astrophysical Journal  788:39.
[doi:10.1088/0004-637X/788/1/39]

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