1994A&A...288..273S

We present an analysis of chromospheric absorption lines in the ζ Aur binary 22 Vul (G5 Ib-II + B8V), extracted from observations made during its ingress and total eclipse of 1988 September-October. By means of a modified curve-of-growth technique and an investigation of the CaII K-line profile, we obtain column densities for atoms and ions at different projected heights and convert them into empirical density models. The total hydrogen and electron densities are estimated from the FeI/FeII ratio by applying a simplified ionization equilibrium. We find that the chromosphere of 22 Vul is cool and extended, with an ionization of 2 to 4% at heights between 4 and 8 Gm, and is in many respects very similar to that of ζ Aur. In the HR diagram the cool-giant region where the primary components of 22 Vul and of the other ζ Aur giants are located is one in which dramatic variations in the properties of the circumstellar material are clearly manifested and where transitions from hot coronae to cool winds occur. Since the ζ Aur systems offer some degree of height resolution of the circumstellar region through the `binary-star' technique, they are immensely valuable for investigating the very diverse nature of that material. This analysis of the chromosphere of 22 Vul serves to establish some of the essential boundary conditions for such investigations.