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

TL;DR

This study models the wind, metallicity, rotation, and mass loss of the hot contact binary TU Muscae using spectrophotometric data, revealing unexpected wind characteristics and variable metallicity effects.

Contribution

It provides a detailed physical and geometric characterization of TU Muscae's wind envelopes, with novel insights into its wind ionization and mass loss rates.

Findings

Mass loss rate is about 10^-6 solar masses per year.

No evidence of P Cygni profiles or shock fronts in the system.

Metallicity and wind properties vary with orbital phase and time.

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.