Ultraviolet and optical spectral variability in the Be star. gamma. Cassiopeiae: A coronal model for the emission
Ultraviolet spectrophotometric data from Copernicus, along with photoelectric H..cap alpha.. scans obtained at the Lowell Observatory, are used together with data from the literature to discuss emission-line variability in the spectrum of ..gamma.. Cas. The ultraviolet data show MgII emission at 2800 A which is apparently optically thin, and which showed velocities between late 1974 and late 1976 ranging from -75 km s/sup -1/ to +75 km s/sup -1/ with respect to the stellar rest frame, and a total power (in both the h and k lines) ranging between 1.0 and 4 x 10/sup 32/ ergs s/sup -1/. Strong Si IV lines are present at 1400 A, and show emission spikes in their cores, which are also variable in velocity over times of several months, and contain about a factor of 2 more power than the MgII emission lines. No prominent NV lines are evident at 1240 A, but variability in the spectrum combined with earlier rocket UV data demonstrates the probable existence of broad NV absorption in the stellar wind. The H..cap alpha.. profile showed small variations both in emission equivalent width and in asymmetry during the period from late 1975 to late 1976.The detached-ring hypothesis and the late-type companion mass-exchange model for explaining the observed V/R variations are reviewed and regarded as implausible for ..gamma.. Cas. In fact, none of the models presently existing can incorporate all of the observational data for ..gamma.. Cas. A new model is thus proposed, based on that of Poeckert and Marlborough in which the emission lines, the infrared free-free emission, and the intrinisic linear polarization are produced in the inner part of a stellar wind, the denser parts of which have low terminal velocity (<100kms/sup -1/) and are strongly concentrated to the equatorial plane. Turbulence induced by differential rotation in this latter region is assumed to lead to the production of a corona in the less dense regions at larger distances from the equatorial plane.
- Research Organization:
- University of Western Ontario
- OSTI ID:
- 6618732
- Journal Information:
- Astrophys. J.; (United States), Vol. 224:1
- Country of Publication:
- United States
- Language:
- English
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