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On the Orbital Period and Models of V Sge

Smak J.

Acta Astronomica

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2022

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Vol. 72, No. 1

21--29

EN

The orbital period of V Sge is decreasing at a rate which increased from dP/dt=-(4.11±0.33)×10-10 in 1962 to -(5.44±0.61)× 10-10 in 2022. This implies that the mass transfer from the secondary component is accelerating. From the evidence based on the orbital period variations, combined with estimates of the mass loss from the system based on radio observations, it follows that (1) the mass transfer rate from the secondary component is larger than M2=-5×10-6 M☉/yr, possibly as large as M2=-2.5×10-5 M☉/yr, and (2) the mass loss rate from the primary component is M1=-4×10-7 M☉/yr or larger. Close similarity of V Sge to binary Wolf-Rayet stars supports the model with primary component being a hot, evolved star loosing its mass. Several arguments are presented which exclude the alternative model with primary component being a white dwarf with an accretion disk.

2

ASAS Photometry of ROSAT Sources. I. Periodic Variable Stars Coincident with Bright Sources from the ROSAT All Sky Survey

Kiraga M.

Acta Astronomica

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2012

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Vol. 62, No. 1

67--95

EN

Photometric data from the ASAS - South (declination less than 29°) survey have been used for identification of bright stars located near the sources from the ROSAT All Sky Survey Bright Source Catalog (RBSC). In total 6028 stars brighter than 12.5 mag in I- or V-bands have been selected and analyzed for periodicity. Altogether 2302 variable stars have been found with periods ranging from 0.137 d to 193 d. Most of these stars have X-ray emission of coronal origin with a few cataclysmic binaries and early type stars with colliding winds. Whenever it was possible we collected data available in the literature to verify periods and to classify variable objects. The catalog includes 1936 stars (1233 new) considered to be variable due to presence of spots (rotationally variable), 127 detached eclipsing binary stars (33 new), 124 contact binaries (11 new), 96 eclipsing stars with deformed components (19 new), 13 ellipsoidal variables (4 new), 5 miscellaneous variables and one pulsating RR Lyr type star (blended with an eclipsing binary). More than 70% of new variable stars have amplitudes smaller than 0.1 mag, but for ASAS 063656-0521.0 we have found the largest known amplitude of brightness variations due to the presence of spots (up to ΔV=0.8 mag). The table with the compiled data and figures with light curves can be downloaded from Acta Astronomica Archive.

3

XROM and RCOM: Two New OGLE-III Real Time Data Analysis Systems

Udalski A.

Acta Astronomica

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2008

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Vol. 58, No. 3

187--192

EN

We describe two new OGLE-III real time data analysis systems: XROM and RCOM. The XROM system has been designed to provide continuous real time photometric monitoring of the optical counterparts of X-ray sources while RCOM system provides real time photometry of R Coronae Borealis variable stars located in the OGLE-III fields. Both systems can be used for triggering follow-up observations in crucial phases of variability episodes of monitored objects.

4

V Sge: a Hot, Peculiar Binary System

Smak J., Belczyński K., Zoła S.

Acta Astronomica

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2001

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Vol. 51, No. 2

117--150

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 Msolar and M2≈3.3 Msolar. 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 Rsolar, 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 EB-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.