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Astronomy Reports - Variations in the orbital period of eclipsing binaries RY Aqr, AK Vir, and AX Vul are studied. It is shown these variations can be represented with equal accuracy in two ways:... 相似文献
2.
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. 相似文献
3.
We show that hydrostatically equilibrium models for the thin photospheres of helium stars based on new opacities κR (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 τenv≈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 (Гmax≈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. 相似文献
4.
Astronomy Reports - Variations of the orbital period of the eclipsing binaries TT Del, EU Hya, and SV Tau have been studied. It has been shown that they can be represented by cyclic fluctuations... 相似文献
5.
Orbital-period variations of the low-mass, semi-detached eclipsing binary RT Per are analyzed. In addition to the secular variation of the orbital period determined by the mass transfer between the components, cyclic variations are also present. Both the light-time effect and magnetic oscillations can describe the cyclic orbital-period variations of RT Per. The secular period increase can be explained by a uniform flow of matter from the lower-mass to the higher-mass component at a rate of 0.60 × 10−8M-/year, with the total angular momentum being conserved. The period variations can be represented equally accurately by either a superposition of two cyclic variations or a superposition of a secular period increase and two cyclic variations. Approximately the same parameters are derived for the lower-period (36.8 year) variations when the times of minima are fitted with a linear or a quadratic formula. For the longer-period variation, a period of 275 years and amplitude of 0.104 days are found using the linear formula, or 89 years and 0.045 days using the quadratic formula.
相似文献6.
Variations of the orbital periods of the eclipsing binaries RY Aur, GG Cas, RS Lep, and RV Tri are analyzed. The period variations in all of these systems can be represented as a superposition of a secular period decrease and cyclic variations that can be explained with the light-time effect due to the presence of a third body in the system. The secular period decrease could be due to magnetic braking.
相似文献7.
A. I. Khaliullina 《Astronomy Reports》2016,60(9):807-815
Orbital-period variations of the Algol-type eclipsing binaries RW CrB and AO Ser are analyzed. It is shown that the period variations of these systems are due mainly to the light-time effect due to the eclipsing binary’s motion in its long-period orbit. The period variations of RW CrB are reproduced by motion of the eclipsing binary with a period of 55.8 years around a third body with the mass M 3 > 0.36M⊙. The period variations of AO Ser can be reproduced either solely with the light-time effect, or by a superposition of the light-time effect and a slow secular decrease in the period. In the former case, the period of the long-period orbit is 111.5 years; in the latter case, it is 108 years. Both cases imply the same mass for the third body in the AO Ser system: M 3 > 0.35M⊙. The residual small-amplitude orbitalperiod variations of the two systems can be due to magnetic cycles. 相似文献
8.
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. 相似文献
9.
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 ～ 0.007m) 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. 相似文献
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