The expanding envelope of ζ Aurigae.

Abstract

We redetermine the basic parameters of the circumstellar envelope of ζ Aur by means of the UV binary technique. The analysis consists of comparing IUE observations with theoretical profiles calculated with a newly developed 2-D radiative transfer code. We show that the B-type secondary causes an open HII region. The electron temperature and the ionization of the metals are calculated explicitly inside of the HII region using standard nebular methods. By application of a modified curve of growth analysis we obtain a stochastic velocity of v_sto_=20km/s and an acceleration parameter β=3.5. Detailed matching of SiII and FeII resonance lines yields a mass-loss rate of ˙(M)=6x10^-9^M_sun_/yr and a wind velocity of v_infinity_=90km/s.