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 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 High Mass Ratio Contact Binaries: Recent Evolution into Contact?

1989 ◽  
Vol 107 ◽  
pp. 348-349
Author(s):  
Bruce J. Hrivnak
Keyword(s):  
Mass Transfer ◽  
Angular Momentum ◽  
Primary Component ◽  
High Mass ◽  
Mass Ratio ◽  
Origin And Evolution ◽  
Momentum Loss ◽  
Angular Momentum Loss ◽  
Mass Ratios ◽  
Contact Binaries

Recent theories of the origin and evolution of contact binaries suggest that the two stars evolve into contact through angular momentum loss (AML; Mochnacki 1981, Vilhu 1982). When in contact, the system then evolves toward smaller mass ratio through mass transfer from the secondary to the primary component (Webbink 1976, Rahunen and Vilhu 1982). Most contact binaries have mass ratios of 0.3 to 0.5.

scholarly journals W UMa Stars and Angular Momentum Loss

1980 ◽  
Vol 88 ◽  
pp. 491-494 ◽  
Author(s):  
Osmi Vilhu ◽  
Timo Rahunen
Keyword(s):  
Time Scale ◽  
Type Systems ◽  
Light Curves ◽  
Theoretical Studies ◽  
Mass Ratio ◽  
Subsequent Evolution ◽  
Convective Envelope ◽  
Angular Momentum Loss ◽  
Envelope Model ◽  
The Common

The structure and evolution of W UMa stars is still unsolved although considerable progress has been achieved in recent years. Most theoretical studies are based on the common convective envelope model by Lucy (1968a,b), which almost satisfactorily explains the nearly equal minima of the light curves. All A-type (Wilson, 1978) and some W-type systems (Whelan et al., 1979) may contain an evolved primary. In this case stable models exist (Hazlehurst, 1970; Moss and Whelan, 1970). Computations performed for the subsequent evolution (Moss, 1971; Hazlehurst and Meyer-Hofmeister, 1973; Rahunen and Vilhu, 1977) show nuclear time scale evolution towards more extreme mass ratio, supplemented by possible thermal time scale oscillations.

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 Local merger rates of double neutron stars

2018 ◽  
Vol 14 (S346) ◽  
pp. 433-443 ◽  
Author(s):  
Martyna Chruslinska
Keyword(s):  
Mass Transfer ◽  
The Other ◽  
Local Universe ◽  
Common Envelope ◽  
Model Predictions ◽  
Angular Momentum Loss ◽  
History Of ◽  
The Common ◽  
The Universe ◽  
Rule Out

AbstractThe first detection of gravitational waves from a merging double neutron star (DNS) binary implies a much higher rate of DNS coalescences in the local Universe than typically estimated on theoretical grounds. The recent study by Chruslinska et al. (2018) shows that apart from being particularly sensitive to the common envelope treatment, DNS merger rates appear rather robust against variations of several factors probed in their study (e.g. conservativeness of the mass transfer, angular momentum loss, and natal kicks), unless extreme assumptions are made. Confrontation with the improving observational limits may allow to rule out some of the extreme models. To correctly compare model predictions with observational limits one has to account for the other factors that affect the rates. One of those factors relates to the assumed history of star formation and chemical evolution of the Universe and its impact on the final results needs to be better constrained.

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.

Common EOFs in atmospheric science and large-scale flow

2021 ◽  
Author(s):  
Abdel Hannachi ◽  
Kathrin Finke ◽  
Nickolay Trendafilov
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Sequential Algorithm ◽  
Atmospheric Variability ◽  
Orthogonal Function ◽  
Conventional Analysis ◽  
The Common ◽  
Climate Model Simulations ◽  
Large Scale Flow

<p>Conventional analysis of the large-scale atmospheric variability and teleconnections are obtained using the empirical orthogonal function (EOF) method, which was developed mainly to deal with single fields. With the increase of the amount of observed/simulated large-scale atmospheric data including climate models, e.g., CMIP, there is a need to develop methods with efficient algorithms that enable analysis and comparison/validation of climate model simulations. Here we describe the common EOF method, which finds common patterns of a set of large scale atmospheric fields, and enables comparing several model outputs simultaneously. A step-wise/sequential algorithm is presented, which avoids the difficulty encountered in previous algorithms related to the lack of simultaneous monotonic change of the eigenvalues of all fields. The theory and algorithm are presented, and the application to large-scale teleconnections from various reanalysis products and CMIP6 are discussed.</p>

scholarly journals Substellar Secondaries in Zero-Age Cataclysmic Variables

2004 ◽  
Vol 194 ◽  
pp. 89-91
Author(s):  
M. Politano
Keyword(s):  
Orbital Period ◽  
Formation Rate ◽  
Cataclysmic Variables ◽  
Population Synthesis ◽  
Mass Ratio ◽  
Brown Dwarf ◽  
Common Envelope ◽  
Efficiency Parameter ◽  
The Common ◽  
Orbital Periods

AbstractThe present-day formation of cataclysmic variables (CVs) with brown dwarf (BD) secondaries is investigated using a population synthesis technique. Results from the latest, detailed models for BDs have been incorporated into the population synthesis code. We find that zero-age CVs (ZACVs) with BD secondaries have orbital periods in the range 46 min to 2.5 hrs, and that they comprise 18% of the total, present-day ZACV population. Consequently, we find that 15% of the present-day ZACV population should have orbital periods shorter than the observed orbital period minimum for CVs. We also investigate the dependence of the present-day formation rate of CVs with BD secondaries on the assumed value of the common envelope efficiency parameter, αCE, for three different assumed mass ratio distributions in ZAMS binaries. We find that the common envelope process must be extremely inefficient (αCE < 0.1) in order for CVs with BD secondaries not to be formed. Finally, we find that the progenitor binaries of ZACVs with BD secondaries have ZAMS orbital separations < 3 AU and ZAMS primary masses between ~1-10 M⊙ , with ~75% of the primary masses less than ~ 1.6 M⊙. Interestingly, these ranges in orbital separation and primary mass place the majority of the progenitor binaries within the so-called “brown dwarf desert.”

scholarly journals From Common Envelope to Pre-Cataclysmic Variables: An Observational Test of Common Envelope Evolution

1996 ◽  
Vol 158 ◽  
pp. 453-456
Author(s):  
M. J. Sarna
Keyword(s):  
Gravitational Radiation ◽  
Planetary Nebula ◽  
Cataclysmic Variables ◽  
Orbital Energy ◽  
Dwarf Star ◽  
Common Envelope ◽  
Evolutionary Scenario ◽  
Angular Momentum Loss ◽  
Red Giant ◽  
Detached Binaries

The generally accepted evolutionary scenario for cataclysmic variables (CVs) is common envelope (CE) evolution (Iben & Livio 1993) proposed by Paczyñski (1976). The secondary spirals towards the giant’s compact core converting orbital energy into kinetic energy of the giant’s envelope and the envelope is ejected. The dynamics of the red dwarf and red giant envelope interaction have been studied by several groups (Livio & Soker 1988; Taam & Bodenheimer 1991). After the ejection of the red giant envelope the post common envelope detached binaries (PCEBs) are formed. These can be divided into three groups:• Hot subdwarf with a red dwarf star inside a planetary nebula.• Hot subdwarf with a red dwarf star without a planetary nebula.• Hot white dwarf with a red dwarf star without a planetary nebula. Next, due to angular momentum loss by magnetic braking and/or gravitational radiation, the red dwarf component fills its Roche lobe and a cataclysmic variable is formed.

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