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 Theories of Contact Binary Stars

1980 ◽  
Vol 88 ◽  
pp. 477-484
Author(s):  
Frank H. Shu
Keyword(s):  
Binary Stars ◽  
Relaxation Oscillation ◽  
Inversion Layer ◽  
Thermal Relaxation ◽  
Oscillation Theory ◽  
Temperature Inversion ◽  
Theoretical Issue ◽  
Contact Binary Stars ◽  
Contact Binary ◽  
Discontinuity Theory

We review and contrast two current theories for the structure of contact binary stars: discontinuity theory and thermal relaxation oscillation theory. We find that the two theories are complementary with the crucial theoretical issue to be resolved being the secular stability of the temperature inversion layer. Critical observational tests remain to be performed.

Investigation on the mass transferring near-contact binary TT Cet

2020 ◽  
Vol 37 ◽  
Author(s):  
Xiao-Man Tian ◽  
Lin-Feng Chang
Keyword(s):  
Mass Transfer ◽  
Light Curve ◽  
Hot Spot ◽  
Relaxation Oscillation ◽  
Thermal Relaxation ◽  
Light Curves ◽  
Primary Star ◽  
Contact Stage ◽  
Short Period ◽  
Contact Binary

Abstract First multi-colour complete light curves and low-resolution spectra of short-period eclipsing binary TT Cet are presented. The stellar atmospheric parameters of the primary star were derived through spectra fitting as: $T_{eff}=7\,091\pm124\,{\text{K}}$ , $\log g = 4.15\pm0.33\,{\text{cm}}/\text{s}^2$ , and $[Fe/H]=-0.23\pm0.04\,\text{dex}$ . The light curves were analysed using the Wilson–Devinney code. The photometric solution suggests that this target should be a near-contact binary with the primary component filling its critical Roche lobe (i.e. SD1-type NCB). The luminosity enhancement around the primary light maximum (phase 0.10–0.40) on the light curve was detected like other SD1-type NCBs, which could be caused by a hot spot near the facing surface of the secondary component due to mass transfer. Long-term decrease of the orbital period at a rate of $dP/dt=-5.01\,({\pm}0.06)\times 10^{-8}\,{{\text{d}} \cdot{yr}}^{-1}$ was detected by the O–C analysis, which supports the mass transfer from the primary to the secondary and is consistent with its primary filling configuration. No third body was found through the light curve and O–C analysis. TT Cet may locate in the broken contact stage predicted by the thermal relaxation oscillation theory (TRO) and will evolve to the contact stage eventually. It is another good observational example supporting the TRO theory. We have collected all known SD1-type NCBs with absolute parameters from the literatures. The relations of these parameters are summarised for these rare systems.

CSS J075415.6+191052 and NW Leo: two contact binaries at different evolutionary stages

2021 ◽  
Author(s):  
Xu-Dong Zhang ◽  
Shengbang Qian ◽  
Ergang Zhao ◽  
Qijun Zhi ◽  
Aijun Dong ◽  
...  
Keyword(s):  
Relaxation Oscillation ◽  
Thermal Relaxation ◽  
Light Curves ◽  
Secondary Component ◽  
High Mass ◽  
Dark Spot ◽  
Left Shoulder ◽  
Mass Ratio ◽  
Convective Envelope ◽  
Contact Binary

Abstract Multi-color light curves of CSS J075415.6+191052 and NW Leo are presented and the photometric solutions suggest that CSS J075415.6+191052 is a low mass ratio (q=0.178) and slightly deep contact binary (f=34.9%), while NW Leo with high mass ratio (q=0.707) and shallow degree of contact (f=2.3%). For CSS J075415.6+191052, the RI light curves show weakening around the left shoulder of secondary minimum, which indicates that there may be a dark spot on the secondary component. However, the light curves of BV bands are totally symmetric. It is unreasonable if the dark spot is caused by magnetic activity or mass transfers between two components. Therefore, the weakening of the light curves in this contact binary is caused by something else. A possible explanation is mass transferring from primary component to common convective envelope through the inner Lagrangian point, and this part of the mass, for some reason, weakens RI bands of light from secondary component. O - C analysis of NW Leo reveals a cyclic period change with a modulation period of 4.7 years, which may be caused by the light travel time effect of a third body. The positions of CSS J075415.6+191052 and NW Leo in P - J_{orb}' diagram suggest that the former is more evolved, which is in agreement with their photometric solutions. In the current stage, CSS J075415.6+191052 is dominated by the angular momentum loss theory, but NW Leo mainly follow the thermal relaxation oscillation theory.

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 Massive Contact Binary Systems

1991 ◽  
Vol 143 ◽  
pp. 207-212
Author(s):  
Kam-Ching Leung
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Binary Stars ◽  
Binary Systems ◽  
Type Systems ◽  
Early Type ◽  
Late Type ◽  
Long Period ◽  
Massive Component ◽  
Contact Binary

In recent years very massive single stars have been found to be upward of 90 M⊙. Massive contact binary systems have been found among the early-type systems, but their masses are far less than those reported for single stars. The most massive component found is about 60 M⊙.It is generally believed that no late-type very massive stars have been detected (Humphreys and Davidson). This may be due to the large amount of mass loss from stellar wind. Recently, several extremely long-period late-type binary systems have been found to be contact systems. Two systems, UU Cnc and 5 Cet, have their primary components with masses exceeding 40 M⊙, and K spectra. This result tends to suggest that close or interacting binary stars may be able to preserve the mass loss from stellar wind within the binary systems.

scholarly journals Contact Binary Stars

1983 ◽  
Vol 71 ◽  
pp. 447-461 ◽  
Author(s):  
A.K. Dupree
Keyword(s):  
Binary Stars ◽  
Rotational Velocity ◽  
Type Systems ◽  
Ultraviolet Emission ◽  
X Ray ◽  
Contact Binary Stars ◽  
Contact Binary ◽  
Turn Over

Abstract:Ultraviolet and X-ray surveys of the W Ursae Majoris type stars are reviewed. These systems exhibit extended coronas and transition regions that are confined close to the optically determined surfaces. Correlations of X-ray activity with period or rotational velocity indicate a turn-over or saturation of emission at the short periods or high velocities found in the W UMa-type systems. For a number of systems, ultraviolet emission appears to be anti-correlated with the strength of X-ray emission. These observations are discussed in terms of solar structures, activity, and evolution.

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 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
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