Studies in Non-Gray Stellar Atmospheres. III. The Metal Abundances of Sirius and VEGA

The analyses presented here for Vega and Sirius indicate that Sirius has many of the abundance anomalies characteristic of metallic-line A stars, while Vega has a chemical composition very similar to that deduced for the Sun. This investigation is based on a newly calculated, detailed grid of model stellar atmospheres that incorporates hydrogen-line blanketing and includes a range of metal opacities. Owing to their eflect, of reducing the predicted Balmer discontinuity, the abundances of Si and Mg are shown to be important in the choice of appropriate models for A stars. The stellar-atmosphere grid used in conjunction with a careful abundance analysis very closely predicts the observed continuous spectra of Vega and Sirius and leads to reasonably self-consistent values of chemical composition. Moreover, the values of effective temperature, T.11 = 9000 + 5000 K for both stars, and surface gravity, log g = 4.0 i 0.2 and 3.8 + 0.2 for Sirius and Vega, respectively, obtained from this analysis, are in excellent agreement with independent measures of these parameters.