SPECTRAL-LINE BROADENING FUNCTIONS OF WUMA-TYPE BINARIES .1. AW UMA

We describe a method for determining the spectral-line broadening function based on simple linear mapping between sharp-line and broadline spectra that can be used when the broadening function is much narrower than the spectral window. The equations can be solved using linear least-squares techniques, with orthogonalization to remove linear dependencies resulting from the presence of featureless continuum bands in the sharp-line spectra. The broadening functions derived from high resolution, high S/N spectra of the contact binary AW UMa using our method are consistent with the contact model with the possible exception that the primary component's profiles tend to be slightly more symmetric than expected. This may indicate that the surface brightness of the inner region of the primary is lower than expected or that it has a more symmetric rotational velocity law than predicted by solid-body contact models. Fits of theoretical broadening profiles to the observed ones were used to determine the velocity scale factor, K1 + K2, and to constrain the degree of contact of AW UMa. The primary mass is independent of the mass rato within the range 0.07 < q < 0.08, but it is sensitive to the strength of the lines used to derive the radial velocity scale factor. Our best estimate of the primary mass, M1 = 1.28 +/- 0.14 M., suggests that AW UMa lies on the TAMS. We were unable to determine the degree of contact from our data, but we found indications that the surface of AW UMa lies close to the outer critical equipotential surface (f congruent-to 0.9).