Semi-detached Binaries Research Articles

Three-dimensional numerical simulation of gaseous flow structure in semidetached binaries

The results of numerical simulation of mass transfer in semidetached non-magnetic binaries are presented. We investigate the morphology of gaseous flows on the basis of three-dimensional gas-dynamical calculations of interacting binaries of different types (cataclysmic variables and low-mass X-ray binaries). We find that taking into account a circumbinary envelope leads to significant changes in the stream–disc morphology. In particular, the obtained steady-state self-consistent solutions show an absence of impact between the gas stream from the inner Lagrangian point L1 and the forming accretion disc. The stream deviates under the action of the gas of the circumbinary envelope, and does not cause the shock perturbation of the disc boundary (traditional hotspot). At the same time, the gas of the circumbinary envelope interacts with the stream and causes the formation of an extended shock wave, located on the stream edge. We discuss the implication of this model without hotspot (but with a shock wave located outside the disc) for interpretation of the observations. The comparison of synthetic light curves with observations proves the validity of the discussed gas-dynamical model without hotspot. We have also considered the influence of the circumbinary envelope on the mass transfer rate in semidetached binaries. The obtained features of flow structure in the vicinity of L1 show that the gas of the circumbinary envelope plays an important role in the flow dynamics, and that it leads to significant (in order of magnitude) increase of the mass transfer rate. The most important contribution to this increase is from the stripping of the mass-losing star atmosphere by interstellar gas flows. The parameters of the formed accretion disc are also given in the paper. We discuss the details of the obtained gaseous flow structure for different boundary conditions on the surface of mass-losing star, and show that the main features of this structure in semidetached binaries are the same for different cases. The comparison of gaseous flow structure obtained in two- and three-dimensional approaches is presented. We discuss the common features of the flow structures and the possible reasons for revealed differences.

The optical gravitational lensing experiment. Variable stars in globular clusters

Three elds covering the central part of the globular cluster! Cen were surveyed in a search for variable stars. We present V -band light curves for 39 periodic variables: 24 SX Phe stars, 7 contact binaries, 5 detached or semi-detached binaries, and 3 likely spotted variables (FK Com or RS CVn type stars). Only 2 of these variables were previously known. All SX Phe stars and all contact binaries from our sample belong to blue stragglers. Observed properties of these stars are consistent with their cluster membership. Of particular interest is detection of two well detached binaries with periods P =1.50 day and P =2.47 day. Further study of these two binaries can provide direct information about properties of turno stars in ! Cen. An incomplete light curve of a Mira variable known as V 2w as obtained. We present V vs. V I color-magnitude diagrams for the monitored part of the cluster.

The optical gravitational lensing experiment. Variable stars in globular clusters. I. Fields 5139A-C in ω Centauri

Three fields covering the central part of the globular cluster ω Cen were surveyed in a search for variable stars. We present V-band light curves for 39 periodic variables: 24 SX Phe stars, 7 contact binaries, 5 detached or semi-detached binaries, and 3 likely spotted variables (FK Com or RS CVn type stars). Only 2 of these variables were previously known. All SX Phe stars and all contact binaries from our sample belong to blue stragglers. Observed properties of these stars are consistent with their cluster membership. Of particular interest is detection of two well detached binaries with periods P=1.50 day and P=2.47 day. Further study of these two binaries can provide direct information about properties of turnoff stars in ω Cen. An incomplete light curve of a Mira variable known as was obtained. We present V vs. color-magnitude diagrams for the monitored part of the cluster.

Have superhumps been seen in black hole soft X-ray transients?

Yes. Superhumps are always seen in the superoutbursts of the SU UMa subclass of dwarf novae. Current understanding of the phenomenon as arising from tidal stressing of accretion discs in high-mass-ratio (q > 3) interacting binaries suggests that they should be detectable in other kinds of semidetached binaries with extreme mass ratios, including the black hole soft X-ray transients (SXTs). Superhumps in SXTs during outburst have been reported in the literature. These claims have usually been based on data sets acquired and analysed shortly after the discovery of the system while it is still in outburst. At such times, key parameters such as the binary orbital period are not known with adequate certainty. This paper presents a systematic re-analysis of all the available optical photometry of three SXTs during their main outbursts, concluding that superhumps have been seen in Nova Mus 1991 and GRO J0422 + 32, and probably in GS 2000 + 25. These conclusions are interpreted using the tidal theory of superhumps, including an explanation of the ‘glitches’ seen in the X-ray light curves of SXTs. Estimates of the mass ratio and compact object mass are made, and found to be in satisfactory agreement with measurements of these quantities made by other means.

Stream formation at the inner Lagrangian point in close binaries

Abstract Stream formation at the inner Lagrangian point was calculated for different types of binaries on the basis of non-stationary hydrodynamical equations, the “big-particle” code by Belotserkovskii and Davydov and the atmosphere model from Kurucz's grid. The types of binaries are W Ser stars, semi-detached binaries and W UMa stars. Our calculations show that physical conditions for the Roche lobe overflow are different for different binaries and a standard Roche lobe overflow regime does not occur for all the binaries. The stream size is 0.02 (U Gem)-0.15(β Lyr) in units of the orbital separation of the binary components. The degree of the Roche lobe overflow is such that atmosphere layers occur at the inner Lagrangian point with optical thickness equal to 100 for W UMa stars, 70 for W Ser stars, and less than 1 for the semi-detached binaries.

Double-degenerate semidetached binaries with helium secondaries: cataclysmic variables, supersoft X-ray sources, supernovae and accretion-induced collapses

Double-degenerate semidetached binaries with helium secondaries: cataclysmic variables, supersoft X-ray sources, supernovae and accretion-induced collapses

A Model for the Galactic Population of Supersoft X-Ray Sources

AbstractThree major sub-populations of Galactic supersoft X-ray sources may exist: semi-detached binaries with main sequence or subgiant donors, and symbiotic binaries (~550, ~460, and ~600 objects, respectively). Each group contains both permanent and transient sources. The intrinsic and interstellar absorptions reduce the number of observable sources to ~25. We derive the distributions of the sources over orbital periods, masses of the components, and ‘on’-times. The rate at which white dwarfs in Galactic binaries reach MCh is ~ 3 10−5 yr−1. The rate of He-shell detonations which may lead to supernovae may be up to 3 10−4 yr−1.

Statistical study of semi-detached and near contact semi-detached binaries

We carried out a statistical study of 107 semi-detached with combined light curve solutions. 1. We derived an empirical period-dependent mass-radius relation, thereby revealing the impossibility of having evolved semi-detached systems with very short periods. 2. Statistically, the near-contact semi-detached systems have the common properties of nearly equal mass densities of the components, larger mass-ratios, shorter periods and smaller specific angular momenta and their A- F-type secondaries generally have greater densities than the secondaries of classical Algol systems of the same spectral types. A detailed discussion is also made in this paper on the evolution of near-contact semi-detached binaries.

The relation between RS CVn and Algol

Late-type secondaries in Algol binaries are rapidly rotating convective stars and thus should be chromospherically active (CA). They are examined with respect to observational manifestations which characterize already known CA stars: Ca II H and K emission cores, photometric variability attributable to starspots, soft x-ray emission, non-thermal radio emission, ultraviolet and infrared excess, and alternating period changes. The conclusion is that they can be regarded as another class of CA stars. In most respects they are literally indistinguishable from other CA stars. Ca II H and K emission cores are observed in the lobe-filling component of six semi-detached binaries: U Cep, RT Lac, RV Lib, AR Mon, S Vel, HR 5110. Alternating period changes are shown to occur only in Algols containing a late-type (convective) star. It is proposed, therefore, that the Matese-Whitmire mechanism explains these changes. Specifically, the interval from one increase (or decrease) to the next can be equated with the star's magnetic cycle. Cycle lengths for 31 stars, derived in this way, range between 7 years and 109 years, with a median of 50 years.

Evidence for Transient Colour Changes of Algol in the Past

Most Algol-type variables are believed to be close, semi-detached binaries which have evolved from a rapid mass-transfer phase, which reversed the initial mass-ratio, to a relatively quiescent stage where only small-scale transient events perturb the dynamical and the photo-metrical properties of the system.Of all Algol-systems, only the prototype Algol (β Per) itself is bright enough to be traceable in astronomical records reaching back more than 2000 years. Evidence based on medieval stellar lists and 19th-century visual observations strongly suggest that the intrinsic colour of Algol has been subject to substantial variations within historical times. On a few occasions Algol was apparently observed as reddish, which is at variance with its present blue-white appearance (B-V = −0.05 to +0.10).

The Relation Between RS CVn and Algol

AbstractLate-type secondaries in Algol binaries are rapidly rotating convective stars and thus should be chromospherically active (CA). They are examined with respect to observational manifestations which characterize already known CA stars: Ca II H and K emission cores, photometric variability attributable to starspots, soft x-ray emission, non-thermal radio emission, ultraviolet and infrared excess, and alternating period changes. The conclusion is that they can be regarded as another class of CA stars. In most respects they are literally indistinguishable from other CA stars. Ca II H and K emission cores are observed in the lobe-filling component of six semi-detached binaries: U Cep, RT Lac, RV Lib, AR Mon, S Vel, HR 5110. Alternating period changes are shown to occur only in Algols containing a late-type (convective) star. It is proposed, therefore, that the Matese-Whitmire mechanism explains these changes. Specifically, the interval from one increase (or decrease) to the next can be equated with the star’s magnetic cycle. Cycle lengths for 31 stars, derived in this way, range between 7 years and 109 years, with a median of 50 years.

Evolution of Low-Mass Helium Dwarfs in Interacting Binaries: Application to 4U1820-30

A number of evolutionary scenarios have been proposed that lead to the formation of binary systems consisting of a degenerate dwarf in orbit with a neutron star. In fact, most degenerate dwarfs in close-binary systems are probably the cores of evolved stars whose envelopes have been stripped by one or more episodes of common-envelope evolution. Once the envelope has been removed, the newly exposed core of the giant will have an effective temperature and radius that are considerably larger than the corresponding quantities in an older, highly degenerate dwarf. It is important for at least two reasons to evaluate the subsequent cooling history of such objects: (i) For detached binaries, we want to be able to infer from the current effective temperature and luminosity of the degenerate dwarf the elapsed time since the core of its progenitor giant was exposed, (ii) For semi-detached binaries, we must know the evolution of the radius of the degenerate dwarf in order to compute important relationships among the orbital period and its rate of change, the mass of the degenerate dwarf, and the mass-transfer rate.

Mass and Energy Transfer in Semi-Detached Binary Systems

Recently, Kitamura and Nakamura have found that the anomalous gravity darkening occurs in semi-detached binary systems. The exponent of gravity darkening for the secondary components, which is defined by where F is the radiative flux and g is the gravitational accerelation, is significantly greater than the unity as shown in Table 1. We interpret this in terms of the energy transport by the mass outflow from the secondary component filling the Roche-lobe.Table 1.Empirical αc-values and physical quantities of five semi-detached binary systems.From the analysis based on this interpretation, we show that 1) the mass out-flow carries energy if ∇ < ∇ad and 2) the anomalous gravity darkening requires that the flow must originate from deep interior. The mass loss rate can be estimated from the anomalous gravity darkening. Thus, the anomalous gravity darkening can be used not only to estimate the mass transfer rate but also to probe the interior structure and the evolution of the secondary star of the semi-detached binary. This model links Morton’s instability[2] of the secondary with the accretion disk of the primary.

FO Virginis - A pre-contact binary

view Abstract Citations (13) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS FO Virginis : a pre-contact binary. Mochnacki, S. W. ; Fernie, J. D. ; Lyons, R. ; Schmidt, F. H. ; Gray, R. O. Abstract The star FO Vir, a recently discovered eclipsing binary with a period of 0.776 days, has been observed photometrically and spectroscopically. Light-curve and line-profile synthesis shows that FO Vir is semidetached with a mass ratio of 0.15 + or - 0.02. The A7 V primary component very nearly fills its Roche lobe. Radial velocities from the observed and synthesized profiles have been measured by cross correlation. The theoretical radial-velocity curve fits the observations well, to yield a mass of 1.9 + 0.9 or - 0.6 solar mass for the primary and 0.29 + 0.08 or - 0.06 solar mass for the secondary. The mean density is 0.17 + or - 0.02 g/cu cm for the primary, 0.33 + or - 0.03 g/cu cm for the secondary, with log g about 3.9 and Mv about 1.7 for the primary. This suggests the primary has evolved off the zero-age main sequence, while the secondary has a density that shows that for its mass it is highly evolved. The period and mass ratio are typical of the more extreme 'A-type' W UMa systems, which suggests that FO Vir will evolve into a contact binary of this type. Short-period semidetached binaries may be the progenitors of at least some W UMa systems. Publication: The Astronomical Journal Pub Date: May 1986 DOI: 10.1086/114094 Bibcode: 1986AJ.....91.1221M Keywords: Eclipsing Binary Stars; Stellar Evolution; Stellar Spectrophotometry; Curve Fitting; Light Curve; Radial Velocity; Stellar Mass; Stellar Models; Astrophysics full text sources ADS | data products SIMBAD (3)

Determinacy of the eclipse elements from a part of the light curves of eclipsing binaries

A part of the light curves of two detached (CD Tau and V909 Cyg) and one semi-detached (Algol) binaries have been analysed with the emphasis on the determinacy of the parameters of different systems from a part of their eclipse curves. A model light curve for whichr1=0.050,r2=0.150,i=90°, andL1=0.800 were chosen, has also been considered for a further clarification of the determinacy problem of the eclipse parameters. Some insight into the determinacy is gained by varying one parameter and adjusting the others for the best fit to the light curves in the considered eclipse phases. It was realised that the determinacy problem of the unknown parameters is stored in the determinacy of the type of the eclipse minima. The attempts of the solutions with a false choice of initial elements result in finding (i) no minimum of ϰ2 to give any acceptable solution, (ii) rapid departure from the false start and convergence on the correct solution, or (iii) a false solution mostly with a true inclinationi, but wrong sense of the ratio of the radii.

Hydrogen-Poor Binary Stars

AbstractHydrogen-poor and helium-rich stars are easy to produce in interacting binaries. Thus they should be found among Population I binaries, in which a large-scale mass transfer has occurred between the components (possibly associated with mass loss from the system). For in such cases, those layers are now on the surface of the “loser” (and, most likely, also on the surface of the “gainer”) that were subject to hydrogen burning and the associated mixing of processed material. Helium overabundance in these objects will be accompanied by an overabundance of nitrogen and underabundance of carbon, as a result of the CNO process. All the Algol-like semidetached binaries should be mild helium stars; so far this has been demonstrated only in β Lyrae, for the He/H ratio is not extreme in such cases. Extreme helium stars require a more complex process, with two stages of mass transfer and/or loss (“case BB”); υ Sagittarii and KS Persei seem to be good examples of this process. The optically invisible components of these two stars seem to have been detected with the IUE. Good model atmospheres do not exist yet, so caution must be exercised in interpreting the UV data.

Effects of encounters with field stars on the evolution of low-mass semidetached binaries

Consequences of close encounters on the binary parameters and on the mass transfer rate and its stability are discussed. Thousands of numerical experiments have been performed in order to obtain accurate cross sections for inducing eccentricity in binaries with initially circular orbits. Analytic formulae are presented relating the radius excess of the secondary component over its Roche lobe to the mass transfer rate, for two extreme models of mass outflow: adiabatic and isothermal. Mass transfer is found to be stable even if there is no angular momentum transferred from the disk around the primary component back into binary orbit, provided the mass ratio M/sub 1//M/sub 2/>4.6. It is not likely that close encounters significantly affect the evolution of bright globular cluster X-ray sources, unless central densities in the cores of those clusters are much higher than commonly believed.

Semi-detached binaries: The origin and present status of TU Mon, SX Cas, and DM Per

Semi-detached binaries: The origin and present status of TU Mon, SX Cas, and DM Per

Mass loss in semi-detached binaries

Mass loss in semi-detached binaries

Semi-Detached Binaries: The Origin and Present Status of TU Mon, SX Cas, and DM Per

AbstractAn attempt is made to trace back the possible progenitor systems of the Algol-type binaries TU Mon, SX Cas, and DM Per. The present characteristics are compared to the result of the evolution of 9 M0 + 5.4 M0. The position of the hot components in the HRD is discussed with regard to the theoretical models.