Photospheric CNO abundances of solar-type stars

We determined the C, N, and O abundances of 160 nearby F, G, and K dwarfs and subgiants by using spectra obtained with the HIDES spectrograph at Okayama Astrophysical Observatory, with the purposes of (1) establishing the runs of [C/Fe], [N/Fe], and [O/Fe] for these galactic disk stars in the metallicity range of -1 less than or similar to [Fe/H] less than or similar to + 0.4, (2) searching for any difference in the CNO abundances of planet-host stars as compared to non-planet-host stars, and (3) examining the consistency of the abundances derived from different lines to check the validity of the analysis. The non-LTE effect on the abundance determination was taken into consideration based on our extensive statistical-equilibrium calculations. We confirmed that consistent abundances are mostly accomplished between different lines, and that [C/Fe] as well as [O/Fe] progressively increase with a decrease in [Fe/H] with the slope of the former (similar to 0.2-0.3) being shallower than the latter (similar to 0.4-0.5), while [N/Fe] does not show any clear systematic trend with the metallicity. The [C/Fe], [N/Fe], and [O/Fe] values of 27 planet-harboring stars (included in our sample of 160 stars) were shown to be practically indistinguishable from those exhibited by non-planet-harboring stars of similar metallicities.