scholarly journals Contact Binaries of the W UMa Type as Distance Tracers

2005 ◽  
Vol 13 ◽  
pp. 458-459 ◽  
Author(s):  
Slavek M. Rucinski
Keyword(s):  
Binary Stars ◽  
Surface Brightness ◽  
Primary Component ◽  
Period Range ◽  
Wide Range ◽  
Massive Component ◽  
Contact Binaries ◽  
Contact Binary Stars ◽  
Contact Binary ◽  
The Common

Contact binary stars of the W UMa-type (also known as W) are unique objects: The luminosity, produced almost exclusively in the more massive component is efficiently distributed through the common envelope so that the surface brightness is practically identical over the whole visible surface of the binary. Mass ratios are known to span the whole wide range, from almost unity to very small values, as small as q = 0.066. Typically, the primary component provides the luminosity, while both components provide the radiating area. The range of the primary masses is moderate and corresponds to Main Sequence spectral types from middle A to early K and roughly maps into the orbital-period range of about 1.5 days to 0.22 days.

scholarly journals W Ursae Majoris Star Models: Observational Constraints

1988 ◽  
Vol 108 ◽  
pp. 213-214
Author(s):  
Albert P. Linnell
Keyword(s):  
Binary Stars ◽  
Relaxation Oscillation ◽  
Thermal Relaxation ◽  
Type Systems ◽  
Light Curves ◽  
Primary Minimum ◽  
Star Models ◽  
Massive Component ◽  
Contact Binary Stars ◽  
Contact Binary

W Ursae Majoris stars can be understood as contact binary stars with a common envelope (Lucy 1968). They subdivide into two types: The A-type are earlier inspectral class than about F5, are believed to have radiative envelopes, and associate primary (deeper) eclipse minimum with transit eclipse. The W-type have spectral classes later than F5, are believed to have convectlve envelopes, and associate primary minimum with occultation eclipse. Controversy has surrounded the explanation of W-type light curves.Four distinct models have been introduced to describe the envelopes or photospheres of W UMa stars. (1) The Rucinski hot secondary model directly explains W-type light curves on a postulational basis. Since 70%-90% of the emitted radiation from the secondary (less massive) component is believed to reach the secondary via circulation currents from the primary, there is an apparent thermodynamic mystery why the secondary should be hotter. (2) The Lucy Thermal Relaxation Oscillation (TRO) model argues that the secondary component is perpetually out of thermal equilibrium and that the components are in contact only during part of a given TRO cycle. During contact the photosphere is supposed to be barotropic. In this case primary minimum always associates with transit eclipse, in disagreement with observation for W-type systems. (3) The Shu et al. thermal discontinuity (DSC) model also argues for a barotropic photosphere but differs from Lucy on the gravity brightening exponent. The changes are insufficient to produce W-type light curves, (4) Webbink (1977), and, separately, Nariai (1976), argue for a baroclinic envelope. If the baroclinicity extends to the photosphere there is a possibility that W-type l i g h t curves could be explained. In particular, the Webbink scenario produces a hot secondary.

scholarly journals Structure and evolution of W UMa-type systems

2008 ◽  
Vol 4 (S252) ◽  
pp. 423-424 ◽  
Author(s):  
Lifang Li ◽  
Fenghui Zhang ◽  
Zhanwen Han ◽  
Dengkai Jiang ◽  
Tianyu Jiang
Keyword(s):  
Binary Stars ◽  
Type Systems ◽  
Magnetic Activity ◽  
Activity Level ◽  
Average Lifetime ◽  
Type Contact ◽  
Contact Binaries ◽  
Contact Binary Stars ◽  
Contact Binary ◽  
Low Mass

AbstractWe summarize and discuss our recent works on the structure and evolution of low-mass W UMa-type contact binary stars. Three conclusions are given as followings: (1) The energy transfer is taken place in the radiative region of common envelope of W UMa systems; (2) The magnetic activity level of W UMa systems is weaker than that of non-contact binaries or rapid-rotating single stars; (3) The evolutionary outcome of W UMa systems might be the rapid-rotating single stars, and an average lifetime is derived to be about 7 Gyr for W UMa systems.

scholarly journals Energy Transfer by Circulation in W Ursae Majoris Systems

1980 ◽  
Vol 88 ◽  
pp. 495-499
Author(s):  
David H. Smith ◽  
Robert Connon Smith ◽  
J. Alistair Robertson
Keyword(s):  
Large Scale ◽  
Vertical Motion ◽  
Spherically Symmetric ◽  
Convective Envelope ◽  
Common Envelope ◽  
Binary Model ◽  
Contact Binaries ◽  
Contact Binary ◽  
Horizontal Pressure ◽  
The Common

After Lucy (1968) introduced the contact-binary model with a common convective envelope, it was envisaged by Hazlehurst & Meyer-Hofmeister (1973) that a sideways flow of convective elements would carry energy from the more luminous star, the primary, to the less luminous star, the secondary, as a result of horizontal pressure variations. Webbink (1977) extended this picture by noting that the interaction between vertical entropy gradients and large-scale smooth circulation currents in the common envelope would provide the necessary redistribution of flux. That is, energy is absorbed by the flow during its vertical motion in the primary and is released during its vertical motion in the secondary. Webbink (1977) mentioned two mechanisms by which a large-scale circulation could be generated: (1) the non-spherically symmetric force field due to rotation and tides which will drive an analogue of classical Eddington-Sweet circulation and (2) differential heating of the base of the common envelope. Although these mechanisms are conceptually different, they are not in practice easy to disentangle, and will certainly both be operating in contact binaries.

scholarly journals On the properties of contact binary stars

2004 ◽  
Vol 426 (3) ◽  
pp. 1001-1005 ◽  
Author(s):  
Sz. Csizmadia ◽  
P. Klagyivik
Keyword(s):  
Binary Stars ◽  
Contact Binary Stars ◽  
Contact Binary

scholarly journals A Cyclic Thermal Instability in Contact Binary Stars

1976 ◽  
Vol 73 ◽  
pp. 331-331
Author(s):  
Brian P. Flannery
Keyword(s):  
Mass Exchange ◽  
Binary Stars ◽  
Thermal Evolution ◽  
Normal Population ◽  
Equal Mass ◽  
General Nature ◽  
Convective Envelope ◽  
Short Period ◽  
Contact Binary Stars ◽  
Contact Binary

Contact binary stars coupled by a common convective envelope in which the entropy is constant, the Lucy model, are unstable against mass exchange: if either component begins to transfer mass, it will continue to do so. A detailed sequence of models is calculated which follows the thermal evolution of a 2M⊙ contact binary of normal Population I abundances (X=0.70, Z = 0.02), starting at nearly equal mass. The initial instability develops into a cyclic mass-exchange with the mass fraction oscillating between 0.56≤m2/(m1 + m2)≤0.62 with a period of ~107yr. Throughout the cycle the component stars are not in thermal equilibrium. The instability is of a general nature, and such oscillating systems can satisfactorily populate the short period, red region of the period color relation for WUMa stars.

scholarly journals Energy Transfer in Contact Binaries

1976 ◽  
Vol 73 ◽  
pp. 333-333
Author(s):  
A. P. Moses ◽  
R. C. Smith
Keyword(s):  
Energy Transfer ◽  
Large Scale ◽  
Approximate Model ◽  
Convective Envelope ◽  
Large Scale Circulation ◽  
Coriolis Forces ◽  
Contact Binaries ◽  
Contact Binary ◽  
The Common ◽  
Major Factors

The anomalous mass-luminosity relation for the components of a contact binary system is usually explained by postulating strong energy transfer from the primary to the secondary. It has been assumed that the transfer occurs in the common convective envelope surrounding the two stars, but so far the only attempt at a model for the energy transfer has been the sideways convection model of Hazlehurst and Meyer-Hofmeister (1973), which assumes a large-scale circulation of material between the two components.Any detailed discussion of the dynamics in the common envelope must take account of the predominantly vertical motions associated with normal thermal convection, of Coriolis forces and of viscosity. We have constructed an approximate model for the horizontal transfer of energy between the two components, using a mixing-length approach and taking all three factors into account. The major factors are the vertical convection and the Coriolis forces, which together prevent a large-scale circulation of the type proposed by Hazlehurst and Meyer-Hofmeister. Instead, the flow breaks up into smallscale eddies whose horizontal scale is determined by the interaction of convection, Coriolis forces and viscosity. This has the important qualitative consequence that horizontal energy transfer will occur only if the mean horizontal pressure gradient between the two stars exceeds a certain minimum value. This condition can easily be satisfied in the adiabatic zone of the envelope, but may be an important restriction in the super-adiabatic zone.Using our model, we were able to estimate the entropy difference between components which is required to transfer enough energy to explain the observed mass-luminosity relation. We found that equal entropy models are possible only if the contact is deep. Unequal entropy models are possible for any degree of contact, so long as the contact extends down as far as the adiabatic zone. If, as has been suggested, the depth of contact increases during evolution then zero-age models must have shallow contact and hence unequal entropies. Deep contact equal entropy models would then form as a result of evolution.A difficulty is that in our model insufficient energy transfer can occur in the super-adiabatic zone to produce WUMa light curves for the unequal entropy models. This may mean that further work is needed on the exact surface conditions in these stars.

scholarly journals Origin of the orbital period change in contact binary stars

2019 ◽  
Vol 28 (06) ◽  
pp. 1950044 ◽  
Author(s):  
V. V. Sargsyan ◽  
H. Lenske ◽  
G. G. Adamian ◽  
N. V. Antonenko
Keyword(s):  
Orbital Period ◽  
Binary Stars ◽  
Binary Systems ◽  
Binary Star ◽  
Period Change ◽  
Mass Asymmetry ◽  
Contact Binary Stars ◽  
Contact Binary ◽  
Energy Formula ◽  
Orbital Periods

The evolution of contact binary star systems in mass asymmetry (transfer) coordinate is considered. The orbital period changes are explained by an evolution in mass asymmetry towards the symmetry (symmetrization of binary system). It is predicted that decreasing and increasing orbital periods are related, respectively, with the nonoverlapping and overlapping stage of the binary star during its symmetrization. A huge amount of energy [Formula: see text][Formula: see text]J is converted from the potential energy into internal energy of the stars during the symmetrization. As shown, the merger of stars in the binary systems, including KIC 9832227, is energetically an unfavorable process. The sensitivity of the calculated results to the values of total mass and orbital angular momentum is analyzed.

The evolutionary state of contact and near-contact binary stars

1988 ◽  
Vol 231 (2) ◽  
pp. 341-352 ◽  
Author(s):  
R. W. Hilditch ◽  
D. J. King ◽  
T. M. McFarlane
Keyword(s):  
Binary Stars ◽  
Evolutionary State ◽  
Contact Binary Stars ◽  
Contact Binary
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