Spectroscopy of the Optical Photosphere of the Hot Pulsating Star BW Vulpeculae

The data and analysis of spectroscopic observations of BW Vul, which were made at high spectral and temporal resolution while preserving high signal-to-noise ratio are presented. The observations are of a set of weak absorption lines which arise from the same general layers as does the optical continuum, and a synchronous, narrow-band, photometric light curve which establishes unambiguously the temporal relationship between structures in the light curve and spectroscopic line behavior is presented. The systemic radial velocity is derived, and a radial velocity curve in the rest frame of the star is presented which represents the actual kinematics of the optical photosphere, and which implies that the pulsation results in a symmetrical expansion and contraction of the stellar atmosphere by a total of about 7 percent of the stellar radius. Finally, the variations of the eqivalent widths of the lines are analyzed, and it is concluded that much of that variation, as well as some of the structure observed in the light curve of the continuum, is due to variations in the continuous opacity which result from the changes in the temperature and density of the radiating plasma.