Ultraviolet observations of the circumstellar envelope of alpha1 HER in the line of sight of alpha2 Her.

Abstract

We establish an empirical model of the circumstellar envelope of the red giant α¹ Her, using spectroscopic UV and optical observations of its visual binary companion α² Her. In particular, we obtained high-resolution IUE long wavelength spectra of α² Her, in which for the first time α¹ Her could be excluded.

The circumstellar lines along the line of sight to α² Her are used to conduct curve-of-growth analyses, explicitly including the wind velocity field. The new UV-data of Cr, Fe, Mn, and Ni give a total mass loss rate of M^ṡ = (1.5±0.3) × 1O^-7 M_sun yr^-1, which agrees well with the value of Reimers (1977, M^ṡ = 1.1 × 1O^-7 M_sun yr^-1), determined from visible wavelengths Ti II data, and with Mauron & Caux's (1992) value of 1O^-7 M_sun yr^-1, determined from K I and Na I scattering observations.

With curve-of-growth fits to the UV data and to the optical data from Reimers (1977), we derive ionization ratios for Ca, Cr, Fe, Mg, Ni, and Si.

By comparing the continuum stellar fluxes in the lUE spectra to theoretical models from Kurucz (1979), we determine an effective temperature of 7350 K±150 K(=^{^} A9) for α² Her B and a spectral type of G8 III for α² Her A. With the assumption that α² Her B is a main sequence star we find a distance of about 70 Pc.

We use the resulting stellar radiation fields for an analysis of the ionization structure in the envelope of α¹ Her.