C/O AND Mg/Si RATIOS OF STARS IN THE SOLAR NEIGHBORHOOD

1John M. Brewer, 1Debra A. Fischer
The Astrophysical Journal 831, 20 Link to Article [http://dx.doi.org/10.3847/0004-637X/831/1/20]
1Department of Astronomy, Yale University, 260 Whitney Avenue, New Haven, CT 06511, USA

The carbon-to-oxygen ratio in a protoplanetary disk can have a dramatic influence on the compositions of any terrestrial planets formed. In regions of high C/O, planets form primarily from carbonates, and in regions of low C/O, the ratio of magnesium to silicon determines the types of silicates that dominate the compositions. We present C/O and Mg/Si ratios for 852 F, G, and K dwarfs in the solar neighborhood. We find that the frequency of carbon-rich dwarfs in the solar neighborhood is $\lt 0.13 \% $ and that 156 known planet hosts in the sample follow a similar distribution as all of the stars as a whole. The cosmic distribution of Mg/Si for these same stars is broader than the C/O distribution and peaks near 1.0, with $\sim 60 \% $ of systems having $1\,\leqslant $ Mg/Si $\lt \,2$, leading to rocky planet compositions similar to the Earth. This leaves 40% of systems that can have planets that are silicate-rich and that may have very different compositions than our own.

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