The chemical composition of Algol systems - IV. The primary of R CMa.

Low-noise Reticon observations of visible and near-infrared C, N, O, S, and Fe lines were used to determine the abundances of these elements in the F1 V primary of the eclipsing binary R CMa. It was found that C/H = 0.0 + or - 0.2, N/H = 0.4 + or - 0.2, O/H = 0.3 + or - 0.3, S/H = 0.1 + or - 0.2, and Fe/H = 0.1 + or - 0.1. Except for a possible reduction of the C/N ratio (C/N = -0.4 + or - 0.2) resulting from a small C depletion and N enhancement, this composition is the same as the solar one enriched by approximately 0.1 dex. The very low-mass secondary of this semi-detached system must have lost a large fraction of its original mass. Some of this material would have been extensively processed during the secondary's main-sequence lifetime and would therefore have had a highly non-solar CNO-abundance distribution. A discussion of the primary's observed CNO abundances suggests that they are consistent with most, but not all, plausible mass-transfer scenarios.