Variations in the Orbital Period of the Eclipsing Binary System V505 Sgr
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ations in the Orbital Period of the Eclipsing Binary System V505 Sgr A. I. Khaliullinaa,* a
Sternberg Astronomical Institute, Moscow State University, Moscow, 119234 Russia *e-mail: [email protected] Received April 22, 2020; revised June 10, 2020; accepted June 30, 2020
Abstract—The variations in the orbital period of the eclipsing binary system V505 Sgr, which is a part of the visual binary system CHR 90, have been analyzed. It has been shown that the variations in the period can be represented as a superposition of the secular decrease in the period at a rate of 2.97 × 10–7 days/year and the light-time effect with a period of 72.8 years. The secular decrease in the period can be explained by the loss of angular momentum due to magnetic braking on the secondary component of a late spectral type. The lighttime effect is explained by the presence of a third body in the system, which was discovered from both spectral and speckle interferometric observations. DOI: 10.1134/S1063772920110049
1. INTRODUCTION The star V505 Sgr (BD-145578, HD 187949, Vmax = 6.46m, P = 1.18287d) was discovered as an eclipsing variable by Hoffmeister [1]. Subsequently, he also plotted the first (photographic) light curve, determined that V505 Sgr was a semi-detached Algol-type system, and calculated the ephemerides [2]. The spectral type of the main component, A2V, was found from spectral observations [3]; the spectral type of the secondary component, G5IV, was estimated from photometric data [4]. Popper [5] plotted the first radial velocity curve for this system (for the main component). In [6], the radial velocity curves were constructed for both components and their masses were determined. Tomkin [3] not only plotted the radial velocity curves for both components, but also found the lines of a third body of spectral type F8 in the spectrum. The third component of this system was discovered in 1985 using speckle interferometry [7]. The visual binary system was named CHR 90; its designation in the WDS catalog is WDS 19531-1436. The first orbital elements for the visual pair were determined by Mayer [8]; he found the orbital period of 38.4 years by combining the observations of the times of minima (lighttime effect) and speckle interferometry data. With the accumulation of observational data, new studies appeared in which the parameters of the visual orbit were determined: Cvetković obtained a period of 60 years [9] and then 70 years [10]. In [11], two solutions were found for the parameters of the visual orbit with periods of 29 and 94 years, and arguments in
favor of the longer period were given. Mason et al. [12] derived a period of 32.2 years from the same data. Concurrently with determining the parameters of the visual orbit, variations in the orbital period of the eclipsing binary V505 Sgr were studied. The first study of the period of V505 Sgr was carried out in [13]. The authors found that the period varied; however, the character of these variations was impossible to determine due to the lack of data. Mayer [8] explained the variatio
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