Apsidal motion in the eclipsing binary system V 451 Ophiuchi

MulticolourWBVR photoelectric observations of the eclipsing binary V 451 Oph were carried out, and a highly accurate light curve was obtained. The angular velocity of the orbital rotation, =2.1 deg yr^–1, and the apsidal motion constantk ₂=0.0045 are given.     

Precision W BV R photoelectric photometry of the eclipsing system RR Lyncis

We carried out accurate ( $\sigma _{obs} \approx 0\mathop .\limits^m 003$ ) W BV R photoelectric photometry of RR Lyn and obtained light curves of this eclipsing system. Our analysis of the light curves using an iterative differential-correction method yields a self-consistent system of geometrical and physical characteristics of the two components of the system and their evolutionary states. The system's age is estimated to be t=(1.08±0.15)×10⁹ yr. Observations in all filters are fitted satisfactorily by the same geometry (r _1,2, i, e, and ω). An analysisof blanketing effects in the W, B, V, and R bands indicates that the atmospheric chemical compositions of both components of the system are peculiar: the primary shows an excess ([Fe/H]_I=0.31±0.08) and the secondary a deficit ([Fe/H]_II=?0.24±0.06) of heavy elements. This is in qualitative and quantitative agreement with the results of an earlier spectroscopic study of RR Lyn by Lyubimkov and Rachkovskaya (1995). The derived physical characteristics of RR Lyn provide evidence that the metallicity effects are probably restricted to the stellar surface layers, while their interiors have normal chemical abundances.     

Unsteady mass outflow from Wolf-Rayet stars

We show that hydrostatically equilibrium models for the thin photospheres of helium stars based on new opacities κ_R (OPAL and OP) can be constructed only for masses M<5M _⊙. The parameter Г=κL/4πGMc, defined as the ratio of light pressure to gravity, exceeds a critical value of 1.0 for larger masses, which must result in mass outflow under light pressure. This mass limit matches the observed lower limit for the masses of Wolf-Rayet stars (M _WR>5M _⊙)), which is an additional argument that the Wolf-Rayet stellar cores are actually helium stars. By solving the equation of radiative transfer in extended atmospheres, we construct a semiempirical model for a WN5 star (M _WN5=10M _⊙)) with a helium core and an expanding envelope, whose physical and geometric parameters are known mainly from light-curve solution for the eclipsing binary V444 Cyg (WN5+06): outflow rate $\dot M \approx 1.0 \times 10^{ - 5} M_ \odot yr^{ - 1} $ , terminal velocity V _∞≈2000 km s^?1, and expanding-envelope optical depth τ_env≈25. The temperature at the outer boundary of the photosphere of a helium star surrounded by such an envelope is approximately 130 kK higher than that in the absence of an envelope, being T _ph≈240 kK. Because of the high temperatures, the absorption coefficients at the corresponding photospheric levels are smaller than those in models with no envelope; therefore, the photosphere turns out to be in hydrostatic equilibrium and stable against light pressure (Г_max≈0.9). As a way out of this conflicting situation (an expanding envelope together with a hydrostatically equilibrium photosphere), we propose a model of discrete mass outflow, which is also supported by the observed cloudy structure of the envelopes in this type of stars. To quantitatively estimate parameters of the nonuniform outflow model requires detailed gas-dynamical calculations.     

Photometric light curves and physical paramters of the eclipsing binary systems IT Cas,CO Cep,AI Hya with possible apsidal motions

Multi-colourWBVR photoelectric observations of the eclipsing binaries IT Cas, CO Cep, and AI Hya were carried out. The photometric elements and the absolute parameters of the orbits and components were obtained. The valuation of the angular rate of the apsidal motion of AI Hya based on the comparison of our observations with the previous photoelectric light curve of this system was derived.     

Photometric elements and apsidal motion of the eclipsing binary NSV 18773

The photometric elements of the eclipsing binary NSV 18773 (HD 99898) have been determined for the first time by analyzing its V-and I-band light curves from the ASAS-2 and ASAS-3 catalogs. Based on these elements and using other published spectroscopic and photometric data, we constructed a consistent system of geometrical and physical parameters for the system that consists of two stars (M ₁ = 20M _⊙, Sp₁=B0V, R ₁ = 5.0R _⊙ and M ₂ = 14M _⊙, Sp₂ = B1V, R ₂ = 6.5R _⊙) in elliptical orbits (P = 5 _. ^d 049, e = 0.365, a = 40.1R _⊙). The distance to the system is d = 3.3 kpc, the interstellar extinction is A _V = 2 _. ^m 0, and the age is t = 2.8 × 10⁶ yr. NSV 18773 is a visual binary with components V _A = 9 _. ^m 9 and V _B = 10 _. ^m 3 separated by 0 _. ^" 8. The third light (L ₃ = 0.61) that we found by analyzing the light curves shows that the eclipsing binary is the system’s fainter component B. We confirmed the rapid apsidal motion of the star detected by Otero and Wils (2006) and refined its observed period: U _obs = 150 ± 6 yr. Our photometric elements and physical parameters allowed the apsidal parameter $\bar k_2^{obs} = 0.0135(14)$ , which reflects the density distribution along the radii of the component stars, to be determined. Within the error limits, the derived parameter agrees with its theoretically expected value, $\bar k_2^{th} = 0.0119(8)$ , from current evolutionary models of stars of the corresponding masses and ages.     

The eclipsing binary HS hercules: Photometric elements and the evolutionary stages of its components

We used a photoelectric photometer designed by V.M. Lyutyi and the Zeiss-600 telescope of the Sternberg Astronomical Institute’s Crimean Observatory to acquire precise UBV brightness measurements (σ _obs ^V ～ 0.007^m) for the eclipsing binary system HS Her in 1984–1991. These measurements continue the homogeneous series of observations of this star commenced in 1969 by D.Ya. Martynov using the same equipment. Our detailed analysis of this homogeneous 22-year series of photoelectric observations has yielded a self-consistent set of physical and geometric parameters of the binary, and enabled us to establish the evolutionary stages of its components. The systems’s primary, M ₁ = 5 M _⊙, is at the beginning of its main-sequence evolution, whereas its secondary, M ₂ = 1.6 M _⊙, has not yet reached the main sequence. The binary’s age is estimated to be t = (17 ± 3) × 10⁶ years.     

Apsidal motion and physical parameters of the eclipsing binary system AR Cas

Using the four-channel automatic photoelectric photometer of the Sternberg Astronomical Institute’s Tien Shan Mountain Observatory, we have acquired accurate (σ_obs≈0.004^m) W BV R brightness measurements for the eclipsing binary AR Cas during selected phases before eclipse ingress and after egress, as well as at the center of minima. A joint analysis of these measurements with other published data has enabled us to derive for the first time a self-consistent set of physical and geometrical parameters for the star and the evolutionary age of its components, t=(60±3)×10⁶ years. We have found the period of the apsidal motion (U_obs=1100±160 years, \(\dot \omega _{obs} = 0^\circ .327 \pm 0^\circ .049\) years^?1) and the apsidal parameter of the primary, logk _2,1 ^obs =?2.41±0.08, with the apsidal parameter being in good agreement with current models of stellar evolution. There is an ultraviolet excess in the primary’s radiation, Δ(U?B)=?0.12^m and Δ(B?V)=?0.06^m, possibly due to a metal deficiency in the star’s atmosphere.     

Apsidal motion in the eclipsing binary GG Ori

High-precision WBVR photoelectric observations of the eclipsing binary GG Ori (B9.5V+B9.5V), which has an eccentric orbit (e=0.22), were carried out in 1988–2001 at the Moscow and high-altitude Tian-Shan Observatories of the Sternberg Astronomical Institute. The aim of these observations was investigation of the apsidal motion of the system. Analysis of the resulting 12-year series of observations enabled us for the first time to accurately (to within 11%) measure the rate of rotation of the orbit $\dot \omega _{obs} = 0.046 \pm 0.005^\circ /yr$ and to appreciably improve estimates of the photometric and absolute parameters. The observed value of $\dot \omega _{obs}$ is 28% higher than the theoretical prediction of $\dot \omega _{th} = \dot \omega _{cl} + \dot \omega _{rel} = 0.036 \pm 0.001^\circ /yr$ . The relativistic part of the apsidal motion in this system $\dot \omega _{rel}$ is a factor of 2.5 greater than the classical term $\dot \omega _{cl}$ due to the tidal and rotational deformations of the components. The interstellar extinction in the direction of the star (at a distance of r=425 pc) is very large (A _v =1.75 ^m ). A number of recently published results (in particular, the conclusion that the components of this eclipsing binary are young) are confirmed.