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W. H. Bauer (Wellesley), P. D. Bennett, A. Brown (CASA, U. of Colorado)
VV Cephei is an eclipsing binary system consisting of an M supergiant primary and a hot (Be-shell?) companion. The orbital period is 20.3 years. The 1997-98 eclipse of the hot companion behind the M supergiant was observed by the HST/STIS echelle spectrograph at medium and high resolution, and observations of egress are continuing in order to study the atmosphere and wind of the M supergiant.
Observations made with IUE over nearly the entire out-of-eclipse portion of the orbit revealed a complex absorption spectrum and numerous emission lines, the strongest of which were double-peaked. The continuum and the lines were seen to vary significantly over time scales as short as two weeks (c.f. Bauer and Bennett, 2000, PASP, 112, 31). Many strong emission lines were double-peaked, with central absorption attributed to the wind from the M supergiant. Peak intensities were highly variable.
During totality, a rich emission spectrum is seen, largely corresponding to the absorption seen out of eclipse. The strong double-peaked emission features remain double-peaked in totality, with the central wind absorption feature. The long-wavelength peak, presumably arising mostly from the extended M star wind, remains at about the same intensity it has outside eclipse. However, the short-wavelength peak, apparently associated with material surrounding the hot component, is much weaker than observed outside eclipse.
VV Cephei was observed nine times between mid-totality and egress, spanning eleven months. In contrast to the apparently stochastic behavior of the emission components outside eclipse, systematic line profile behavior was observed as the system moved from mid-totality toward egress. While the long-wavelength peak gradually weakened, the short-wavelength peak strengthened in intensity and broadened on the short-wavelength side.
This research was supported by grant GO-08257.03-97A from STScI.