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Session 26 - Proto Stars to Supernovae.
Oral session, Monday, June 08

[26.02] Light Synthesis and Spectrum Synthesis Constraints on a Model for \beta Lyrae

A. P. Linnell (MSU), I. Hubeny (NASA/GSFC), P. Harmanec (Astronomical Institute, Academy of Sciences, Czech Republic)

We have used the program suite BINSYN (Linnell amp; Hubeny 1996) to simulate recent optical light curves (Harmanec et al. 1996), OAO2 light curves, and IUE spectra of \beta Lyrae.

\beta Lyrae A is a mass transfer system in which the mass donor is the component eclipsed at primary minimum (optical wavelengths). That component has a mass of about 2.9 M_\sun (Harmanec amp; Scholz 1993). The companion has a mass of about 13.1 M_\sun and is embedded in a thick accretion disk.

The only successful simulation of observed \beta Lyrae light curves, particularly OAO2 UV light curves, has been by Wilson amp; Lapasset (1981,WL). WL modeled the mass gainer as a greatly flattened oblate spheroid.

A standard model accretion disk representation was developed by Hubeny amp; Plavec (1981,HP). The continuum requires the presence of a high T_eff component which HP attribute to a small visible segment of the hot central star. HP point out that the WL model, which is not a standard accretion disk model, cannot represent the required high T_eff component, and so cannot be an acceptable model.

The HP model leads to deep UV stellar eclipses of the visible segment of the hot central star; but the OAO2 data exclude this model. The OAO2 data require an accretion disk thick enough completely to hide the central star. Extensive tests with BINSYN show that no standard model accretion disk can represent the optical wavelength light curves, the OAO2 data, and the IUE spectra. The crux of the problem is an inability to provide the high T_eff source, required by both the UV light curves and the IUE spectra. To resolve this impasse, we propose the existence of a corona which scatters light from the otherwise hidden hot central star into the line of sight to the observer. We plan to develop a BINSYN addition to test this proposal.

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