Evolution Through Mass Exchange in Close Binary Systems of Total Mass 2.5 M ⊙

Refsdal, S.; Weigert, Alfred

doi:10.1007/978-94-010-3405-0_32

Cited by 100 publications

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“…However, none of these processes have been applied to a binarystar evolution code that consistently follows the stellar spin velocity and all torques owing to mass accretion and mass loss. A&A 557, A40 (2013) It has also been shown that some Algol systems must be nonconservative to comply with observations of mass ratios (for example Refsdal et al 1974;Massevitch & Yungelson 1975;Mezzetti et al 1980;Sarna 1993;Nelson & Eggleton 2001). Yet, only mass loss through the outer Lagrangian point L 3 (Sytov et al 2007), bipolar jets (Ak et al 2007) or hotspot formation (van Rensbergen et al 2011) have been proposed to account for this kind of evolution.…”

Section: Introductionmentioning

confidence: 99%

Critically-rotating accretors and non-conservative evolution in Algols

Deschamps

Siess

Davis

et al. 2013

A&A

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Context. During the mass-transfer phase in Algol systems, a large amount of mass and angular momentum are accreted by the gainer star, which can be accelerated up to its critical Keplerian velocity. The fate of the gainer once it reaches this critical value is unclear. Aims. We investigate the orbital and stellar spin evolution in semi-detached binary systems, specifically for systems with rapidly rotating accretors. Our aims are to better distinguish between the different spin-down mechanisms proposed that can consistently explain the slow rotation observed in Algols' final states and to assess the degree of non-conservatism due to the formation of a hotspot. Methods. We use our state-of-the-art binary evolution code, Binstar, which incorporates a detailed treatment of the orbital and stellar spin and includes all torques due to mass transfer, the interactions between a star and its accretion disc, tidal effects, and magnetic braking. We also present a new prescription for mass loss due to the formation of a hotspot based on energy conservation. Results. The coupling between the star and the disc via the boundary layer prevents the gainer from exceeding the critical rotation. Magnetic-field effects, although operating, are not the dominant spin-down mechanism for sensible field strengths. Spin down owing to tides is 2-4 orders of magnitudes too weak to compensate the spinning-up torque due to mass accretion. Moreover, we find that the final separation strongly depends on the spin-down mechanism. The formation of a hotspot leads to a large event of mass loss during the rapid phase of mass transfer. The degree of conservatism strongly depends on the opacity of the impacted material. Conclusions. A statistical study and new observational constraints are needed to find the optimal set of parameters (magnetic-field strength, hotspot geometry, etc.) to reproduce Algol evolutions.

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Section: Introductionmentioning

confidence: 99%

Critically-rotating accretors and non-conservative evolution in Algols

Deschamps

Siess

Davis

et al. 2013

A&A

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“…It has been shown that systemic angular-momentum losses (and thus mass losses) must be involved to reproduce the current state of some observed Algols. For example, Refsdal et al (1974) found that only a nonconservative evolution can reproduce the system AS Eridani. Massevitch & Yungelson (1975) noticed that Algol models must lose at least 40% of their mass in order to reproduce the observed Appendices are available in electronic form at http://www.aanda.org properties.…”

Section: Introductionmentioning

confidence: 99%

Non-conservative evolution in Algols: where is the matter?

Deschamps

Braun

Jorissen

et al. 2015

A&A

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Context. There is indirect evidence of non-conservative evolutions in Algols. However, the systemic mass-loss rate is poorly constrained by observations and generally set as a free parameter in binary-star evolution simulations. Moreover, systemic mass loss may lead to observational signatures that still need to be found. Aims. Within the "hotspot" ejection mechanism, some of the material that is initially transferred from the companion star via an accretion stream is expelled from the system due to the radiative energy released on the gainer's surface by the impacting material. The objective of this paper is to retrieve observable quantities from this process and to compare them with observations. Methods. We investigate the impact of the outflowing gas and the possible presence of dust grains on the spectral energy distribution (SED). We used the 1D plasma code Cloudy and compared the results with the 3D Monte-Carlo radiative transfer code Skirt for dusty simulations. The circumbinary mass-distribution and binary parameters were computed with state-of-the-art binary calculations done with the Binstar evolution code. Results. The outflowing material reduces the continuum flux level of the stellar SED in the optical and UV. Because of the timedependence of this effect, it may help to distinguish between different ejection mechanisms. If present, dust leads to observable infrared excesses, even with low dust-to-gas ratios, and traces the cold material at large distances from the star. By searching for this dust emission in the WISE catalogue, we found a small number of Algols showing infrared excesses, among which the two rather surprising objects SX Aur and CZ Vel. We find that some binary B[e] stars show the same strong Balmer continuum as we predict with our models. However, direct evidence of systemic mass loss is probably not observable in genuine Algols, since these systems no longer eject mass through the hotspot mechanism. Furthermore, owing to its high velocity, the outflowing material dissipates in a few hundred years. If hot enough, the hotspot may produce highly ionised species, such as Si iv, and observable characteristics that are typical of W Ser systems. Conclusions. If present, systemic mass loss leads to clear observational imprints. These signatures are not to be found in genuine Algols but in the closely related β Lyraes, W Serpentis stars, double periodic variables, symbiotic Algols, and binary B[e] stars. We emphasise the need for further observations of such objects where systemic mass loss is most likely to occur.

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“…Past work (Paczyński & Ziółkowski 1967;Refsdal et al 1974;De Greve & De Loore 1992;Chen & Han 2002 employed mass transfer efficiency β = 0.5 for the calculation of stellar evolution in nonconservative cases. However, De Mink et al (2007) suggested that mass transfer efficiency should not be a single constant by comparing their models with a sample of 50 doublelined eclipsing binaries in the Small Magellanic Cloud, which could be affected by spin up of the accreting star and tidal interaction.…”

Section: Discussionmentioning

confidence: 99%

“…We take the mass transfer efficiency β = 1.0 for the conservative case, and β = 0.5 for the nonconservative case, since the results of Paczyński & Ziółkowski (1967) and Refsdal et al (1974) indicate that β is around 0.5 in the nonconservative case. The parameter space for the model grid is three dimensional:…”

Section: Introductionmentioning

confidence: 99%

Hot subdwarfs from the stable Roche lobe overflow channel

2009

A&A

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Context. Hot subdwarfs are core-helium-burning stars with extremely thin envelopes. We discuss the formation and evolution of hot subdwarfs formed through the stable Roche lobe overflow (RLOF) channel of intermediate-mass binaries, although their formation channels are various. Aims. In this study, we concentrate on the formation and evolution of hot subdwarfs binaries through the stable RLOF channel of intermediate-mass binaries. We aim at setting out the properties of hot subdwarfs and their progenitors, so that we can understand the formation and evolution of hot subdwarfs. Methods. Employing Eggleton s stellar evolution code, we have computed conservative and nonconservative population I binary evolution sequences. The initial mass of the primary ranges from 2.2 to 6.3 M , spaced by approximately 0.1 in log M, the initial mass ratio q i = M 1 /M 2 is between 1.1 and 4.5, and the Roche lobe overflow begins at the main sequence, the Hertzsprung gap and the first giant branch. In nonconservative binary evolution, we assume that 50 percent of the mass lost from the primary leaves the system, carrying away the specific angular momentum of the primary, and the remaining mass is accreted on to the secondary during the RLOF. Also, we have studied the distributions of the mass and orbital periods of hot subdwarfs using the population synthesis approach. Results. We have obtained the ranges of the initial parameters of progenitor binaries and the properties of hot subdwarfs through the stable RLOF channel of intermediate-mass binaries, e.g. mass, envelope mass and age of hot subdwarfs. We have found that hot subdwarfs could be formed through stable Roche lobe overflow at the main sequence and Hertzsprung gap. We have also found that some subdwarf B or OB stars have anomalously high mass (∼1 M ) with a thick envelope (∼0.07 M -∼0.16) in our models. By comparing our theoretical results with observations on the hot subdwarfs in open clusters, we suggest that more hot subdwarfs in binary systems might be found in open clusters in the future.

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Evolution Through Mass Exchange in Close Binary Systems of Total Mass 2.5 M ⊙

Cited by 100 publications

References 0 publications

Critically-rotating accretors and non-conservative evolution in Algols

Critically-rotating accretors and non-conservative evolution in Algols

Non-conservative evolution in Algols: where is the matter?

Hot subdwarfs from the stable Roche lobe overflow channel

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