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W. H. Bauer, C. L. Tiffany (Wellesley), P. D. Bennett (Saint Mary's Univ. and Univ. of Colorado), A. Brown (Univ. of Colorado)
The eclipsing binary system VV Cephei consists of an M2 Iab primary with an extended atmosphere, and a hot (spectral class around B0.5 V) star, with a 20-year orbital period. The hot component emerged from its most recent eclipse in November 1998, and we have used the Hubble Space Telescope to observe changes in the spectrum as orbital motion causes the light from the hot star to pass through successively higher layers in the outer atmosphere (or chromosphere) of the M supergiant.
We present column densities at several levels in the M star atmosphere derived from observations of lines with strong damping wings (Lyman-alpha, Mg II h and k, and UV multiplet 1 of Fe II).
Other lines which have weakened substantially as the eclipse has progressed include lines of neutral elements such as Fe I, Ni I, and Cr I, and some doubly-ionized species (with low first ionization potentials) such as V II and Ti II. These lines often show a doubled structure. We present radial velocity measurements for these chromospheric lines, as well as for lines arising from the extensive wind of the M supergiant.
We acknowledge support from STScI grants GO-08257.03-A and GO-08257.01-A.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.