A Two-Wind Radiation Driven Model for the Atmospheric Features of Beta-Lyrae

Details A Two-Wind Radiation Driven Model for the Atmospheric Features of Beta-Lyrae A Two-Wind Radiation Driven Model for the Atmospheric Features of Beta-Lyrae

Feb 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...254..241m&link_type=abstract

Astronomy and Astrophysics, Vol.254, NO. FEB(I), P. 241, 1992

Astronomy and Astrophysics

Astrophysics

16

Stars: Algol, Stars: Individual (Β Lyrae), Stars: Mass Loss, Lines: Formation Non-Lte

Scientific paper

The properties of the non-degenerate interacting binary system of β Lyrae (B6.5 II p+BO V) are investigated via the analysis of its mass loss features.
As a first step, it is shown that the UV emission lines, observed in high dispersion by lUE, can be divided into two groups: one including the `superionised' hot-star wind resonance lines (N V, Si IV, C IV), which display P-Cygni profiles superimposed on broad emission features; the other including lines of moderately ionised species (Al II, Al III, Mg II, Fe III, Ni III), which show pure P-Cygni profiles. The P-Cygni profiles have rounded shapes, unlike normal hot stars. The velocities and the ionisation conditions suggest that high- and low-ionisation groups form in two distinct winds: the first group in the wind of the BO V gainer, and the second in that of the B6.5 II loser.
A radiation-driven wind code, which calculates the wind dynamics and the non-LTE occupation numbers in the envelope self-consistently from the stellar parameters, along with the Wind-cum-Rotation code, a 3D code based on the Sobolev approximation and designed to calculate the radiative transfer in winds from rotating stars via the inclusion of angular momentum conservation in the flow, appropriate to describe the physics of β Lyrae, are used to calculate emerging line profiles, which are then compared to the observed ones.
The two winds are modelled separately. The models confirm that the highly ionised lines are formed in a high ν∞, small Mṡ wind from the gainer. The observed profiles can be reproduced if a photo spheric model which includes line blocking in an approximate form is used. The broad features form in the outer part of the gainer's wind, due to the physical blocking of the wind on and near the equatorial plane caused by the accretion disc surrounding the gainer. The moderately ionised lines are formed in the loser's wind. A mass loss rate of 7 10-7 Msun yr-1, about two dex higher than the self-consistent value, is required to produce the observed strength of these lines, and is attributed to Roche lobe overflow. The loser's wind has therefore large Mṡ but low ν∞. An analysis of the rotational and orbital properties of the two winds is also performed.

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