Narrow Absorption Components and Variability in Ultraviolet P Cygni Profiles of Early-Type Stars

Abstract

An extensive set of velocity and column density measurements of both narrow absorption components and 'underlying' P Cygni profiles is presented for a sample of 21 main-sequence, giant, and supergiant stars with spectral types B1-O4, selected as having at least one of the NV, Si IV, and CIV resonance doublets unsaturated. To study variability characteristics, every unsaturated doublet profile was modeled in each of 322 high-resolution spectra, and, to ensure uniformity, all data were obtained from the two-dimensional photometrically corrected IUE images. Supplementary data were obtained from an additional 54 images of three stars. Mass-loss rates (M-dot) are given for 19 stars; variability in M-dot is usually at the 10 percent level, on time scales of a day or longer; changes of a factor of 2 or greater are not observed. Narrow components are observed at least some of the time in every star with unsaturated P Cygni profiles. In many cases, Copernicus observations taken a decade earlier show features at the same velocities. A search for correlations among different aspects of the data reveals few systematic trends, but there is a suggestion that rapid rotators may be exceptional in some respects. Models for the formation of narrow absorption components are discussed in light of the results.