The Carbon Abundance and 12C/13C Isotopic Ratio in the Atmosphere of Arcturus from 2.3 micron CO Bands

Absorption lines of the 12CO and 13CO molecular bands (Delta v = 2) at 2.29 -- 2.45 micron are modelled in spectrum of Arcturus (K2III). We compute a grid of model atmospheres and synthetic spectra for giant of Teff = 4300, log g = 1.5, and the elemental abundances of Peterson et al. (1993), but abundances of carbon, oxygen and the carbon isotopic ratio 12C/13C are varied in our computations. The computed spectra are fitted to the observed spectrum of Arcturus from the atlas of Hinkle et al. (1995). The best fit to observed spectrum is achieved for log N(C) = -3.78 +/- 0.1, 12C/13C = 8 +/- 1. A dependence of the determined 12C/13C vs. log N(C) and log N(O) in atmospheres of red giants is discussed.