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 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 Contact binaries

1986 ◽  
Vol 118 ◽  
pp. 159-172
Author(s):  
S.M. Ruciński
Keyword(s):  
Angular Momentum ◽  
Convective Zone ◽  
X Rays ◽  
Common Envelope ◽  
Contact Stage ◽  
Orbital Decay ◽  
Angular Momentum Loss ◽  
Contact Binaries ◽  
Contact Binary ◽  
The Common

The most promising mechanism for the formation of contact binaries involves the orbital angular momentum loss (AML) and the resulting orbital decay of detached but close synchronized binaries. The efficiency of magnetic wind braking should abruptly decrease upon formation of a contact binary because of the transformation into a system of earlier spectral type and (possibly) of longer orbital period. The new primary of the contact system should have convective zone thinner than indicated by the surface temperature of the common envelope. The decrease in the coronal (X-rays and radio) activity of contact binaries, which is indeed observed, is used as an agrument that the AML efficiency in contact is relatively low and that the contact stage is considerably prolonged relative to adjacent stages. This small modification to the AML models is capable of explaining why many different contact binaries are observed in old systems like NGC188. The AML evolution is not the only mechanism leading to formation of contact binaries; some of them may have originated via Algol-like evolution. Thus, the observed contact binaries are probably a mixture of systems formed in different ways.

scholarly journals Contact Binaries

1976 ◽  
Vol 73 ◽  
pp. 323-327
Author(s):  
J. Hazlehurst
Keyword(s):  
Heat Transport ◽  
Convective Heat ◽  
Thermal Equilibrium ◽  
Current Theory ◽  
Convective Envelope ◽  
Common Envelope ◽  
Short Period ◽  
Contact Binaries ◽  
The Common

Observational statements about close and contact binaries are compared with the theoretical consequences of assuming that contact binaries have a common convective envelope. It is concluded that such contact systems cannot be in thermal equilibrium, and that the inefficiency of convective heat transport in the common envelope must be allowed for. Even so, current theory seems to predict about equal numbers of contact and semidetached systems of short period, in conflict with the observations.

scholarly journals The Later Evolution of the Contact Binaries AP Leo, AK Her, AB And and AM Leo

2002 ◽  
Vol 187 ◽  
pp. 331-336
Author(s):  
L. Li ◽  
Z. Han ◽  
F. Zhang
Keyword(s):  
Light Curve ◽  
Rapid Change ◽  
Cataclysmic Variables ◽  
Light Curves ◽  
Common Envelope ◽  
Physical Mechanisms ◽  
Contact Binaries ◽  
The Common ◽  
Long Term Variations

AbstractA detailed study of the periods and light curves of binaries AK Her, AP Leo, AB And and AM Leo is presented. Based on the study of the O – C curves, we find that the period variation of each system contains several components with different frequencies, and we suggest that the periodical variations in the periods are likely influenced by different mechanisms. Based on the study of the light curve changes, we find that the light curves exhibit two kinds of variations: rapid variations and long-term variations. We investigate the physical mechanisms which may underlie the variations of the period and the light curve of each system and obtain some new conclusions. According to the characteristics of the rapid light variation in these systems, we suggest that the rapid change in the light curve is probably caused by pulsation of the common envelope, and that the mechanism(s) causing the pulsation may be mass transfer through the inner Lagrangian point L1 or its variation. Finally, the evolutionary trends of these systems are discussed, and we suggest that these systems may be progenitors of cataclysmic variables.

scholarly journals Evolutionary scenario for W UMa-type stars

2008 ◽  
Vol 4 (S252) ◽  
pp. 427-428 ◽  
Author(s):  
K. Stepień ◽  
K. Gazeas
Keyword(s):  
Thermal Equilibrium ◽  
Large Scale ◽  
Primary Component ◽  
Mass Ratio ◽  
Common Envelope ◽  
Evolutionary Scenario ◽  
Angular Momentum Loss ◽  
Temperature Equalization ◽  
The Common ◽  
Large Scale Flow

AbstractAn alternative to TRO model of a W UMa-type star is presented in which the binary is past mass exchange with mass ratio reversal. The secondary is hydrogen depleted and both components are in thermal equilibrium. Evolution in contact is driven by orbital angular momentum loss and mass transfer from the secondary to primary component, similarly as it is observed in Algols. Temperature equalization of both components results from an assumed energy transfer by a large scale flow encircling the whole system in the common envelope.

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 Identifying Large Scale Features on the Surface of Contact Binaries with Sub-Arcsecond Techniques

2001 ◽  
Vol 205 ◽  
pp. 314-315
Author(s):  
P.G. Niarchos ◽  
I. Pustylnik
Keyword(s):  
Large Scale ◽  
Hot Spot ◽  
X Rays ◽  
Surface Features ◽  
Trigonometric Parallax ◽  
Preferential Site ◽  
Promising Target ◽  
Optical Region ◽  
Contact Binaries ◽  
Contact Binary

We summarize multifold evidence for the presence of a hot spot region in contact binary VW Cephei. We interpret this feature as a photospheric burn and the preferential site of flares in EUV and X rays. With its trigonometric parallax of 0.041 arcsec VW Cep is a promising target for a milliarcsecond resolution investigation of the nature of surface features both in optical region and in IR.

Doppler profiles of the interacting contact binary W Corvi

2020 ◽  
Vol 500 (1) ◽  
pp. 145-152
Author(s):  
Joel A Eaton ◽  
Andrew P Odell ◽  
Christian Nitschelm
Keyword(s):  
Light Curve ◽  
Effective Temperature ◽  
Surface Flow ◽  
Orbital Velocity ◽  
Common Envelope ◽  
Secondary Star ◽  
Contact Binary ◽  
Small Flow ◽  
The Common ◽  
Hot Surface

ABSTRACT We use spectra from 2011 and 2012 to investigate the distribution of local effective temperature and non-orbital velocity over the surface of the common envelope of this peculiar contact binary. There seems to be a hot surface flow from the more massive to the less massive (secondary) component, possibly equatorial, which extends roughly one quarter-way around both sides of that secondary star, corresponding to the hotspot postulated to explain the star’s light-curve peculiarities. This feature is clear in the shape of the profiles of metallic lines, but it shows up in H α/H β profiles, as well. The profiles imply small flow velocities in contrast to those detected in some A-type W UMa systems, less than a few km s−1 for the primary but indeterminate for the secondary. We also classify the star’s spectrum (G1-2 V) and present more radial velocities confirming the Ruciński–Lu radial-velocity solution.

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