Carbon and oxygen abundances of field RR Lyrae stars. I - Carbon abundances

Use of conventional LTE line-formation formalism to deduce carbon abundances and carbon-to-iron ratios for a large number of field RR Lyrae stars is reported. For the most metal-rich stars, estimations are made for nitrogen abundances that are considerably less certain than those for carbon. The photometric indices, spectroscopic observations, the C I and N I line equivalent widths, atmospheric parameters, solar equivalent widths and log gf values, abundances and variational relations are shown.