Optical spectra of ζ Aurigae binary systems. V: The 1988 eclipse of 22 Vulpeculae

• Published in: Astronomy and astrophysics (Berlin) 1993-07, Vol.274 (1), p.225-244
• Main Authors: GRIFFIN, R. E. M, HÜNSCH, M, MARSHALL, K. P, GRIFFIN, R. F, SCHRÖDER, K.-P
• Format: Article
• Language: English
• Subjects: Astronomy; Binary and multiple stars; Earth, ocean, space; Eclipsing binaries; Exact sciences and technology; Stars
• ISSN: 0004-6361; 1432-0746

High-dispersion, high-S/N photographic spectra of the eclipsing composite-spectrum binary system 22 Vul have been obtained. From them we isolate the spectrum of the secondary component and the additional absorption features that arise during chromospheric eclipse. The spectral types of the components are classified as mid-G supergiant and B8 dwarf. We derive individual masses of 5.4 solar masses and 3.4 solar masses from a measured mass ratio of 1.6 +/- 0.2. We present measurements of the equivalent widths and, where feasible, the wavelength displacements of 260 unblended chromospheric lines seen on at least one of the three nights on which we were able to observe the chromospheric eclipse phase. We collate photometry relating to five different eclipses and from it we construct a geometrical model in which the radii of the components are 77 and 3.3 solar radii, the minimum projected linear separation between the center of the giant and the eclipse trajectory is 63 solar radii, and the inclination of the plane of the orbit is 80 deg. An empirical approximation is made to the structure and opacity of the chromosphere of the supergiant. We derive a rotation period from the velocity offset of the chromospheric spectra and show that, although the supergiant may be rotating in synchronism with its orbital period, the chromospheric material in the region sampled exhibits additional mass motions.