V Sge: a Hot, Peculiar Binary System

• Autorzy: Smak J. , Belczyński K. , Zoła S.
• Języki publikacji: EN

Abstrakty

EN

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=M₂/M₁=3.76 is that obtained by Herbig et al. (1965) from radial velocity curves based on fluorescent O III 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≈71° the resulting masses of the components are: M₁≈0.9 M_solar and M₂≈3.3 M_solar. In the faintest state the secondary is a main sequence star with R₂≈1.2 Rsolar and T₂≈12 000 K, while the main parameters of the primary are: R₁≈2.1 R_solar, T₁≈70 000 K, and L₁≈1×10³⁸ 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 140 000 K for the primary and about 50 000 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 (T₁≈70 000 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 O III and O VI lines. The distance and interstellar reddening, resulting from the solution, are d=4 kpc and E_B-V≈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.

Słowa kluczowe

EN

binaries: eclipsing; novae; cataclysmic variables; X-rays: stars; stars: individual: V Sge

• Wydawca: Copernicus Foundation for Polish Astronomy
• Czasopismo: Acta Astronomica
• Rocznik: 2001
• Tom: Vol. 51, No. 2
• Strony: 117--150
• Opis fizyczny: Bibliogr. 46 poz., tab., wykr.

Twórcy

autor

Smak J.

• Józef I. Smak N. Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland

autor

Belczyński K.

• Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA

autor

Zoła S.

• Astronomical Observatory, Jagellonian University ul. Orla 171, 30-244 Cracow, Poland
• Mt. Suhora Observatory, Pedagogical Academy ul. Podchorążych 2, 30-084 Cracow, Poland

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