The chemical compositions of Algol systems - V. Confirmation of carbon deficiencies in the primaries of eight systems.

Abstract

We use low-noise CCD spectra of 4267-Å C II line in the spectra of eight Algol-type eclipsing binaries to measure the C abundances of their primaries. A differential LTE analysis of the Algol binaries with respect to single standard stars of the same spectral type shows marginal to moderate deficiencies of C in the primaries of the binaries. We find [C/H] abundances of -0.62 for U CrB, -0.34 for u Her, ≤+0.24 for δ Lib, -0.22 for β Per, -0.18 for U Sge, -0.48 for λ Tau, -0.35 for TX UMa and -0.16 for RS Vul with respect to the average C abundance of single B-type standard stars. These results confirm those of Cugier and Hardorp, who have used IUE observations of the 1300-Å C II lines to determine C abundances in the same stars. The C deficiencies are a consequence of a previous episode of mass transfer in which the secondary, which was initially the more massive star, has transferred C-deficient, CNO-cycle processed material to the primary. A comparison of observed and theoretical abundances suggests that the mass transfer cannot have been extremely non-conservative, although it may have been mildly so.