The winds, metallicity, rotational velocities and mass loss rate of the hot, contact binary TU Muscae (HD100213)

Abstract

A model of the TU Muscae binary system has been developed by a study of 23 SWP spectrophotometric images obtained with the IUE satellite telescope and downloaded from the IUE Archive. The images are well distributed in Keplerian orbital phase thereby permitting a simultaneous fitting of the C IV wind-line profile by the SEI method and the light curve for the same bandpass by means of a program similar to that of Wilson and Devinney. The result is a set of parameters characterizing the physical and geometric properties of the wind envelopes surrounding the stars. Surprisingly, there is no evidence for a P Cygni profile or strong, distinguishable shock front in the system, as has been found for similar investigations of EM Carinae and HD159176. This is probably a result of the contact nature of the binary and the high temperature environment of such a shock. That is, most of the carbon ions in the shock are more highly ionized. Based on the parameters for the SEI fit to the C IV profile, the value for the ionization fraction of C IV in the wind was calculated to be 10-4. With this value, the mass loss rate calculated from two independent equations, was found to be about 10-6 solar masses/yr. The line blanketing or metallicity was found to be erratically variable with orbital phase and time, indicating a variable amount of fast moving, dense clouds in the winds and/or a great amount of turbulence. The meaning of rotational velocities for the stars is problematic and depends on what point on the photospheres one is considering.