Photometric Determination of Orbital Inclinations and Mass Loss Rates for Wolf-Rayet Stars in WR+O Binaries

Abstract

We analyze the atmospheric "eclipse" light curves of all 13 short-period (P&lt;30<SUP>d</SUP>) Galactic binary WR+O systems with solved orbits, excluding the 3 known photospheric eclipsers. Some of the light curves are based on newly obtained data; others are taken from the literature. Most of the 13 WR+O systems show V-shaped dips in their light curves. When accurate orbital ephemerides are available, maximum light attenuation is reached when the 0 star passes farthest behind the WR star. The dips can be explained by phase-dependent electron scattering opacity of 0-star light by WR-wind material, which to good approximation can be assumed to be expanding spherically symmetrically from the WR star, as the 0 star orbits. A simple model is derived for the light curves, whose shapes lead to an estimate of the orbital inclinations. The values obtained agree reasonably well with those from polarimetry or from companion spectra. For a given orbit and inclination, the depth of the dip leads to an estimate for the mass loss rate of the WR star. We derive masses and mass loss rates, based on photometry, for i and M<SUB>sun</SUB> and spectroscopy for M<SUB>sun</SUB> sin<SUP>3</SUP>i, for most of the 13 WR stars. These are briefly discussed in the context of stellar evolution.