LTE analysis of the far-ultraviolet variations of 21 Comae.

Abstract

The far-ultraviolet variations of the cool Ap star 21 Com in the spectral region 1450 - 1510 A are studied by using synthetic spectra. The integrated flux of the star is calculated, and the effective temperature of the star is derived and found to be lower than previous estimates. The computation of synthetic spectra indicates that the flux at the ultraviolet maximum can be reproduced by a model with the effective temperature of 9000 +/- 200 K. It is observed that the large flux variations in this region cannot be reproduced only by altering the abundance of iron, the main absorber in the region. Instead, models with both different iron abundances and effective temperatures account for variations. At the ultraviolet minimum, a model with the effective temperature 9300 +/- 200 K and iron overabundance reproduces the spectrum.