Abundances of carbon, nitrogen, and oxygen and their isotopes in the atmospheres of four SC stars

The C-12/C-13, O-16/O-17, and CNO abundances in the four SC stars GP Ori, FU Mon, CY Cyg, and RZ Peg are presently determined on the basis of Fourier transform spectra in the 2.2-micron region. C and O abundances were derived from spectrum synthesis of CO and CN lines, together with the assumption of approximate equality between C and O. If C = O, then the N abundances indicate depletion relative to the first ascent of the giant branch. If O = 1.01, the abundance total C + N + O is nearly solar except in RZ Peg, where C is greater than O. Suggestions are made concerning the evolutionary history of the SC stars, with attention to the similarity in composition of the SC and Ba II stars. 101 references