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1.
We critically re-examine the available data on the spectral types, masses and radii of the secondary stars in cataclysmic variables (CVs) and low-mass X-ray binaries (LMXBs), using the new catalogue of Ritter &38; Kolb as a starting point. We find there are 55 reliable spectral type determinations and only 14 reliable mass determinations of CV secondary stars (10 and 5, respectively, in the case of LMXBs). We derive new spectral type–period, mass–radius, mass–period and radius–period relations, and compare them with theoretical predictions. We find that CV secondary stars with orbital periods shorter than 7–8 h are, as a group, indistinguishable from main-sequence stars in detached binaries. We find that it is not valid, however, to estimate the mass from the spectral type of the secondary star in CVs or LMXBs. We find that LMXB secondary stars show some evidence for evolution, with secondary stars which are slightly too large for their mass. We show how the masses and radii of the secondary stars in CVs can be used to test the validity of the disrupted magnetic braking model of CV evolution, but we find that the currently available data are not sufficiently accurate or numerous to allow such an analysis. As well as considering secondary star masses, we also discuss the masses of the white dwarfs in CVs, and find mean values of − ⊙ below the period gap, and − ⊙ above the period gap. 相似文献
2.
S. G. Sichevskij 《Astrophysical Bulletin》2017,72(1):51-57
Based on the spectral observations of the LAMOST (DR2) survey, the radii, masses, and luminosities of 700 481 stars were estimated. These stars belong to spectral types A, F, G, and K, and have metallicities between ?0.845 and 0.0. To determine the properties of the stars, we used up-to-date models of the stellar interior structure, computed with account for the stellar evolution rate and the initial mass function. The use of evolutionary estimates for two types of stars—with and without rotation—allowed us to account for the uncertainty associated with the lack of data on the rotation velocity of the stars under consideration. The obtained stellar radii, together with the photometric estimates of interstellar extinction and angular diameters can be used to study the dependence of interstellar extinction on distance as well as to estimate the stellar distances. 相似文献
3.
O. Yu. Malkov S. G. Sichevskij D. A. Kovaleva 《Monthly notices of the Royal Astronomical Society》2010,401(1):695-704
Stellar masses and ages are not directly observable parameters, and the methods used to determine them are based on the calibrating relations. In particular, the mass–luminosity relation, based on the masses of less than 200 well-studied binaries, is virtually the only way to estimate the mass of single stars. Thus, the development of methods for estimating stellar masses with accuracy comparable to direct methods is a problem of vital importance.
Here, we describe a method for estimating stellar masses and ages, which is based on the geometric similarity of evolutionary tracks for the stars at the same evolutionary stage in the Hertzsprung–Russell (HR) diagram. To examine the proposed approach, it has been applied to various test data sets. Application of the method, using synthetic stellar spectra Basel Stellar Library (of theoretical spectra; BaSeL), demonstrates that it allows determination of masses and ages of stars with a predictable distribution of uncertainties.
This statistical approach allows us to demonstrate the viability of the method using it on the set of double-lined eclipsing binaries with intermediate-mass and low-mass components which allows us to compare calculated characteristics with observational ones. As a result, the uncertainties of the stellar masses estimated with the proposed method are comparable with the accuracy of ones obtained from direct observations. This allows us to recommend the method for mass estimates of masses of single stars by the localization in the HR diagram.
As for the ages, the estimates for intermediate-mass stars are more reliable, while those obtained for low-mass stars are very uncertain, due both to slower movement of these stars in the HR diagram with age at stages close to the main sequence and to certain disagreements between theoretical models for this mass range. 相似文献
Here, we describe a method for estimating stellar masses and ages, which is based on the geometric similarity of evolutionary tracks for the stars at the same evolutionary stage in the Hertzsprung–Russell (HR) diagram. To examine the proposed approach, it has been applied to various test data sets. Application of the method, using synthetic stellar spectra Basel Stellar Library (of theoretical spectra; BaSeL), demonstrates that it allows determination of masses and ages of stars with a predictable distribution of uncertainties.
This statistical approach allows us to demonstrate the viability of the method using it on the set of double-lined eclipsing binaries with intermediate-mass and low-mass components which allows us to compare calculated characteristics with observational ones. As a result, the uncertainties of the stellar masses estimated with the proposed method are comparable with the accuracy of ones obtained from direct observations. This allows us to recommend the method for mass estimates of masses of single stars by the localization in the HR diagram.
As for the ages, the estimates for intermediate-mass stars are more reliable, while those obtained for low-mass stars are very uncertain, due both to slower movement of these stars in the HR diagram with age at stages close to the main sequence and to certain disagreements between theoretical models for this mass range. 相似文献
4.
The surface gravities and radii of stars are calculated for different MK spectral types using the masses of stars determined from their evolutionary tracks in the HR diagram and the most reliable values of effective temperatures and absolute bolometric magnitudes. MK spectral types are calibrated in absolute visual magnitudes using the studies ofM
v published since 1965. The calibration of MK types in temperatures is based on the newest investigations including the results both from the ultraviolet and the infrared. The obtained masses, gravities, and the mass-luminosity relationship show reasonable agreement with independent observational data. 相似文献
5.
《New Astronomy》2020
Photometric observations of four totally-eclipsing W UMa binaries, NSVS 6673994, NSVS 4316778, PP Lac and NSVS 1926064, are presented. Their global parameters were determined from the light curve solutions and GAIA distances. The main results are as follows: (i) NSVS 6673994, NSVS 4316778 and PP Lac are of W subtype while NSVS 1926064 is of A subtype; (ii) The mass ratios of NSVS 4316778 and NSVS 1926064 are close to the lower mass-ratio limit; (iii) NSVS 4316778 has double contact configuration while NSVS 1926064 is in deep contact; (iv) The changes of the PP Lac period seem cyclic and are accompanied with episodes of essentially constant value; (v) The relations between the global parameters of the four W UMa stars differ considerably from those of Main Sequence (MS) stars. The deviations of the radii, temperatures and luminosities of the stellar components from those of MS stars with the same masses are bigger for the two targets with extremely small mass ratio. 相似文献
6.
W. Thnert 《Astronomische Nachrichten》1970,292(5):251-262
The behaviour of the masses, the luminosities, the radii, and the colours of the RR Lyrae stars situated in 7 globular, clusters is investigated in dependence upon the clusters' age. The ages were determined according to a method by SANDAGE ; the determination of the masses is based on relations derived by BAKER . In is found that, with increasing age of the clusters, the mean values of masses, luminosities, and radii of the RR Lyrae variables decrease whereas the periods become larger and the centres of the RR Lyrae gaps bluer. The masses tend (with large scattering) to values smaller than one solar mass and support in this respect the models by CHRISTY and by FAULKNER and IBEN . 相似文献
7.
8.
Leonid S. Lyubimkov Tamara M. Rachkovskaya Sergey I. Rostopchin David L. Lambert 《Monthly notices of the Royal Astronomical Society》2002,333(1):9-26
Effective temperatures T eff , surface gravities log g and interstellar extinctions A V are found for 107 B stars. Distances d of the stars, which are based on the derived T eff , log g and A V values, show good agreement with those obtained from the Hipparcos parallaxes. Comparing the T eff and log g values with evolutionary computations, we infer masses, radii, luminosities, ages and relative ages of the stars. Empirical relations between the T eff and log g parameters, on the one hand, and the photometric indices Q , [ c 1 ] and β , on the other hand, are constructed; these relations give a fast method for the T eff and log g estimation of early and medium B stars. Inclusion of the infrared J , H and K colours into the T eff , log g and A V determination shows that (i) the T eff and log g parameters are altered only slightly; (ii) the A V value is rather sensitive to these colours, so an accuracy better than 0.05 mag in the JHK data is necessary for precise A V evaluation. 相似文献
9.
I. Ribas 《Astrophysics and Space Science》2006,304(1-4):89-92
Eclipsing binaries with M-type components are still rare objects. Strong observational biases have made that today only a few eclipsing binaries with component masses below 0.6 M⊙ and well-determined fundamental properties are known. However, even in these small numbers the detailed comparison of the observed masses and radii with theoretical predictions has revealed large disagreements. Current models seem to predict radii of stars in the 0.4--0.8 M⊙ range to be some 5--15% smaller than observed. Given the high accuracy of the empirical measurements (a few percent in both mass and radius), these differences are highly significant. I review all the observational evidence on the properties of M-type stars and discuss a possible scenario based on stellar activity to explain the observed discrepancies. 相似文献
10.
The effective temperatures of the classical Cepheids RT Aur and T Vul have been determined by a comparison of their spectral scans with appropriate model atmospheres. The radii of the stars have been determined through the Wesselink method. Using these temperatures and the Wesselink radii, the luminosities of the stars have been determined. These radii estimates, including the radii of SU Cas (Joshi & Rautela 1980) andζ Gem (unpublished) fit better in the theoretical period-radius relationship given by Cogan (1978), as compared to earlier determinations of Wesselink radii. The pulsation masses and evolutionary masses of the stars have been calculated. The pulsation to evolutionary mass ratio is derived to be 0.85. Based on the effective temperatures obtained by us at different phases of the stars aθ c ? (B-V)0 relationship is found of the form, \(\begin{gathered} \theta _e = 0.274 (B - V)_0 + 0.637 \\ \pm 0.011 \pm 0.007 \\ \end{gathered} \) 相似文献
11.
Eclipsing binary stars are gratifying objects because of their unique geometrical properties upon which all important physical parameters such as masses, radii, temperatures, luminosities and distance may be obtained in absolute scale. This poses strict demand on the model to be free of systematic effects that would influence the results later used for calibrations, catalogs and evolution theory. We present an objective scheme of obtaining individual temperatures of both binary system components by means of color-index constraining, with the only requirement that the observational data-set is acquired in a standard photometric system. We show that for a modest case of two similar main-sequence components the erroneous approach of assuming the temperature of the primary star from the color index yields temperatures which are systematically wrong by ∼ 100K. 相似文献
12.
We perform a detailed physical analysis for a class of exact solutions for the Einstein–Maxwell equations. The linear equation of state consistent with quark stars has been incorporated in the model. The physical analysis of the exact solutions is performed by considering the charged anisotropic stars for the particular nonsingular exact model obtained by Maharaj, Sunzu and Ray. In performing such an analysis we regain masses obtained by previous researchers for isotropic and anisotropic matter. It is also indicated that other masses and radii may be generated which are in acceptable ranges consistent with observed values of stellar objects. A study of the mass-radius relation indicates the effect of the electromagnetic field and anisotropy on the mass of the relativistic star. 相似文献
13.
Assuming that soft X-ray sources in symbiotic stars result from strong thermonuclear runaways, and supersoft X-ray sources from weak thermonuclear runaways or steady hydrogen burning symbiotic stars, we investigate the Galactic soft and supersoft X-ray sources in symbiotic stars by means of population synthesis. The Galactic occurrence rates of soft X-ray sources and supersoft X-ray sources are from ～2 to 20 yr?1, and ～2 to 17 yr?1, respectively. The numbers of X-ray sources in symbiotic stars range from 2390 to 6120. We simulate the distribution of X-ray sources over orbital periods, masses and mass accretion rates of white dwarfs. The agreement with observations is reasonable. 相似文献
14.
The eclipsing and double-lined spectroscopic binary system V453 Cygni consists of two early B-type stars, one of which is nearing the terminal age main sequence and one which is roughly halfway through its main-sequence lifetime. Accurate measurements of the masses and radii of the two stars are available, which makes a detailed abundance analysis both more interesting and more precise than for isolated stars. We have reconstructed the spectra of the individual components of V453 Cyg from the observed composite spectra using the technique of spectral disentangling. From these disentangled spectra, we have obtained improved effective temperature measurements of 27 900 ± 400 and 26 200 ± 500 K , for the primary and secondary stars, respectively, by fitting non local thermodynamic equilibrium theoretical line profiles to the hydrogen Balmer lines. Armed with these high-precision effective temperatures and the accurately known surface gravities of the stars we have obtained the abundances of helium and metallic elements. A detailed abundance analysis of the primary star shows a normal (solar) helium abundance if the microturbulence velocity derived from metallic lines is used. The elemental abundances show no indication that CNO-processed material is present in the photosphere of this high-mass terminal age main-sequence star. The elemental abundances of the secondary star were derived by a differential study against a template spectrum of a star with similar characteristics. Both the primary and secondary components display elemental abundances which are in the ranges observed in the Galactic OB stars. 相似文献
15.
Ren-Xin XuDepartment of Astronomy School of Physics Peking University Beijing rxxu@bac.pku.edu.cn 《中国天文和天体物理学报》2003,3(1):33-37
The mass-radius relations for bare and crusted strange stars are calculated with the bag model. Comparing these relations with the observed one derived from the redshift of EXO 0748-676, we come to the conclusion that it is incorrect to say that EXO 0748 676 cannot be a strange star. Various strange star models can show that EXO 0748-676 could have a mass of (1.3 - 1.7)M⊙ and a radius of(8.4 - 11.4) km. It is proposed that a proportion of nascent strange stars could be bare and have masses - 0.1 M⊙, and their masses increased over a long period of accretion. 相似文献
16.
Parag Seal 《Astrophysics and Space Science》1990,174(2):321-325
A H-R diagram is drawn from the bolometric luminosities and effective temperatures of 24 symbiotic stars and compared with theoretical evolutionary tracks of Population I metal-rich stars. It is shown that the S-type and D-type symbiotic stars are classified very clearly in course of their evolution and it is suggested that it depends on their cool components, whether it is a normal giant or an asymptotic giant branch star. The recurrent novae are less evolved than classical novae or symbiotic novae. 相似文献
17.
We determine the masses and radii of central regions of open star cluster (OCL) models with small or zero entropy production and estimate the masses of oscillation generation regions in clustermodels based on the data of the phase-space coordinates of stars. The radii of such regions are close to the core radii of the OCL models. We develop a new method for estimating the total OCL masses based on the cluster core mass, the cluster and cluster core radii, and radial distribution of stars. This method yields estimates of dynamical masses of Pleiades, Praesepe, and M67, which agree well with the estimates of the total masses of the corresponding clusters based on proper motions and spectroscopic data for cluster stars.We construct the spectra and dispersion curves of the oscillations of the field of azimuthal velocities v φ in OCL models. Weak, low-amplitude unstable oscillations of v φ develop in cluster models near the cluster core boundary, and weak damped oscillations of v φ often develop at frequencies close to the frequencies of more powerful oscillations, which may reduce the non-stationarity degree in OCL models. We determine the number and parameters of such oscillations near the cores boundaries of cluster models. Such oscillations points to the possible role that gradient instability near the core of cluster models plays in the decrease of the mass of the oscillation generation regions and production of entropy in the cores of OCL models with massive extended cores. 相似文献
18.
D. K. Galloway † F. Özel ‡ D. Psaltis ‡ 《Monthly notices of the Royal Astronomical Society》2008,387(1):268-272
Eddington-limited X-ray bursts from neutron stars can be used in conjunction with other spectroscopic observations to measure neutron star masses, radii and distances. In order to quantify some of the uncertainties in the determination of the Eddington limit, we analysed a large sample of photospheric radius-expansion thermonuclear bursts observed with the Rossi X-ray Timing Explorer . We identified the instant at which the expanded photosphere 'touches down' back on to the surface of the neutron star and compared the corresponding touchdown flux to the peak flux of each burst. We found that for the majority of sources, the ratio of these fluxes is smaller than ≃1.6, which is the maximum value expected from the changing gravitational redshift during the radius expansion episodes (for a 2 M⊙ neutron star). The only sources for which this ratio is larger than ≃1.6 are high-inclination sources that include dippers and Cyg X-2. We discuss two possible geometric interpretations of this effect and show that the inferred masses and radii of neutron stars are not affected by this bias. On the other hand, systematic uncertainties as large as ∼50 per cent may be introduced to the distance determination. 相似文献
19.
D. R. Gadelshin G. G. Valyavin M. V. Yushkin E. A. Semenko G. A. Galazutdinov O. V. Maryeva A. F. Valeev Byeong-Cheol Lee 《Astrophysical Bulletin》2017,72(3):330-336
We present the results of spectroscopic confirmation of exoplanet candidates from the “Kepler” space mission catalog. We used the NES spectrometer of the 6-m Russian BTA telescope to investigate the Doppler variability of the radial velocities of the host stars of KOI-974.01, KOI-2687.01/02, and KOI-2706.01. According to the derived upper limits, KOI-2706.01 has a mass significantly smaller than 12 Jupiter masses, which directly indicates its planetary nature. We show that KOI-2687.01 and KOI-2687.02, which have Earth-size or white dwarf-size radii according to photometric data, cannot be white dwarfs, and are therefore exoplanets. Radial velocity analysis for KOI-974, an F-type star, has shown noticeable variations with a half-amplitude of 400 ms?1, which correlate poorly with the phase of its orbital rotation. This can indicate a presence of other massive planets in the system, with orbits closer or farther from the host star than the orbit of KOI-974.01, or a low mass star in a distant outer orbit. Using the method of synthetic spectra, we obtained more accurate atmospheric parameter and radius estimates for all the program host stars, which, in turn, allowed us to refine the radii of the studied exoplanet candidates. 相似文献