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W.J. Fischer, N.D. Morrison (U. Toledo)
The star 6 Cas (A3 Ia+) is typical of the optically brightest stars in external galaxies, which have been proposed as extragalactic distance indicators through the wind momentum-luminosity relation (e.g., McCarthy et al. 1997, ApJ, 482, 757). In this method, usually a single high-resolution, long-exposure spectrum is modeled to derive the stellar parameters, including the wind momentum. Therefore, variability in the profile is a potentially significant source of error. The aims of our study are to estimate the magnitude of this error by quantifying the H alpha profile variability in this nearby example of the class and to gain better insight into the nature and cause of the wind variability. Our observational material consists of 55 high-resolution (R ~ 26,000) spectra of 6 Cas obtained between 1993 and 2001 and including H alpha and several photospheric lines. Our previous results (W. J. Fischer and N. D. Morrison 1999, BAAS, 31, 845), based on analysis of the data from 1993 to 1998, included the finding that the photospheric radial velocities and the positions and strengths of the absorption and the emission components of H alpha are variable, but no single, dominant periodicity appeared in a PDM analysis. Our new results affirm that the absorption component shows variable structure, which may be caused by blended, moving subcomponents; they sometimes emerge to appear as discrete absorption components (DACs). The present report will feature further analysis based on an unusually complete series of observations in 1999 and 2000.