Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aca....51..117s&link_type=abstract
Acta Astronomica, v.51, pp.117-150, (2001). /2001
Astronomy and Astrophysics
Astronomy
6
Binaries: Eclipsing - Novae, Cataclysmic Variables - X-Rays: Stars -, Stars: Individual: Vsge
Scientific paper
Five sets of mean UBV light curves of V Sge covering 2 mag of its large scale variations are analyzed. The mass ratio adopted in the analysis q=M_2/M_1=3.76 is that obtained by Herbig etal (1965) from radial velocity curves based on fluorescent OIII lines (arising from the surfaces of the two components). Models with an accretion disk around the white dwarf primary (or a very massive neutron star secondary) fail completely to reproduce the shapes of the observed light curves. Successful solutions are obtained with a model involving contact configuration, modified by the presence of a hot, gaseous envelope (needed to explain the behavior of colors and the variable depth of the primary eclipse). At inclination i approx 71 arcd the resulting masses of the components are: M_1 approx 0.9 M_odot and M_2 approx 3.3 M_odot. In the faintest state the secondary is a main sequence star with R_2 approx 1.2 R_odot and T_2 approx 12000 K, while the main parameters of the primary are: R_1 approx 2.1 R_odot, T_1 approx 70000 K, and L_1 approx 1038 erg/s. Due to the high radiation pressure from the primary an expanding gaseous envelope is formed, leading to the mass outflow from the system. Large scale variations involve significant increase of the temperatures of both components, up to about 140000 K for the primary and about 50000 K for the secondary, and a considerable thickening of the gaseous envelope, which contributes up to 20-30% of the total UBV flux. These variations are interpreted as being due - in part - to the instability and large variations in the rate of mass outflow from the secondary. No obvious explanation, however, is offered for the major increase of the temperature and luminosity of the primary component in the brightest state. The temperature of the primary in the faint and intermediate states (T_1 approx 70000 K) is too low to explain the supersoft X-ray flux (observed only during those states), the only alternative being that it must come from the envelope surrounding the two stellar components. Such a hypothesis can also explain the origin of the OIII and OVI lines. The distance and interstellar reddening, resulting from the solution, are d=4 kpc and E_{B-V} approx 0.30-0.36 mag. The far ultraviolet fluxes, calculated with model parameters obtained from the solution, do not agree with the observed IUE fluxes, corrected for interstellar extinction using the standard extinction law. The agreement becomes satisfactory, however, when arbitrarily chosen examples of non-standard extinction curves are used instead.
Belczynski Krzysztof
Smak Jozef I.
Zola St.
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