Carbon-to-Oxygen Ratios in M dwarfs and Solar-type stars

Initial C/O ratios of circumstellar disks have been obtained in solar-type stars by differential photospheric abundance analysis with respect to the Sun. We present C/O ratios of M dwarfs obtained by absolute abundance analysis derived from CO and H2O spectra in the K-band. We compare the distributions of C/O ratios in M dwarfs and solar-type stars using the Kolmogorov-Smirnov test. The C/O distribution of M dwarfs is consistent with low frequency of high C/O ratios in solar-type stars.