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G.M. Harper, A. Brown, P.D. Bennett (CASA)
We have detected and monitored the eclipsing binary \zeta~Aurigae (K4~Ib + B5~V) with the VLA at 3.5 and 6~cm. The observations cover one complete orbital cycle of 972~days and is the first radio dataset to cover an orbit of a \zeta~Aur system. The system is unresolved in A-Configuration at 3.5~cm. The thermal radio emission comes from an extended partially ionized region at the base of the K supergiant's wind, and not a localized H~II surrounding the B star.
We compare the VLA data with predictions from (1) 1-D atmospheric density model based on 2-D radiative transfer calculations of spectral features observed with the HST/GHRS, and (2) density structure derived from a \tau-v analysis of absorption lines observed near eclipse, together with estimates of electron temperature. The hydrogen ionization in the K star wind is computed using escape probabilities and advection.
We discuss the implications of the radio flux variations observed during the orbit, in terms of temporal variability of the mass-loss rate.
This research was funded by NASA LTSA grants NAG 5-4804 and NAG5-3226.
The author(s) of this abstract have provided an email address for comments about the abstract: gmh@casa.colorado.edu