IUE observations of 32 Cygni: the effects of the B star within the upper chromosphere of a late-type supergiant.

Abstract

The object 32 Cygni is a Aurigae-type system, comprised of a KS supergiant and a dwarf, which undergoes atmospheric eclipses. We have obtained high-resolution ultraviolet spectra of this system with IUEnear orbital phase 0.2, covering the 1175-3000 A region. The UV spectrum is striking, since all resonance and other strong lines exhibit marked P Cygni characteristics. Further, the absorption portion of these lines is generally complex, revealing multiple absorption components at high velocities (-400 km s -1) which have not previously been seen with such strength or so far from primary eclipse. The origin of the excess UV flux seen in OA 0 2 observations is explained by strong chromospheric line emission during primary eclipse. The spectral type of the B star is reevaluated from its photospheric line strengths. Earlier hypotheses of multiple condensations in the supergiant chromosphere are discussed in light of overionization effects and Saito's hypothesis of Lyman photon driven shocks. Ionization modeling supports the hypothesis that the B star resides within the upper chromosphere of the K supergiant. We determine a line-of-sight density of 1.6 x 10 cm -3 at 4 K star radii, which coupled with measured velocities leads to a mass loss rate of 4 x 10- M0 yr -1, consistent with previous investigations. Finally, the effect of the B star on the K supergiant atmosphere is reviewed in light of the small separation between the stars compared with the Str6mgren ionization radius of the B star. Subject headings: line identifications - stars: chromospheres - stars: eclipsing binaries - stars: individual - ultraviolet: spectra