Wind Roche-Lobe Overflow

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Wind Roche-lobe overflow (WRLOF) is a transfer mechanism of matter between the components of an interacting double star . Another name is gravitational focusing .

Interacting binary stars such as the algol stars , the double-period variables , the cataclysmic variables , the X-ray binary stars and the symbiotic stars show a multitude of mostly eruptive behavior, which is caused by a flow of matter from a star to its companion in a close binary star system . The mass transfer is either the result of wind accretion or the Roche limit being exceeded by the mass donating star.

In wind accretion, matter from the stellar wind of a companion is caught by a star and collected via an accretion disk . The mass donating star is usually a giant like the blue supergiants in X-ray binary stars of high mass. Since most of the matter is not picked up by the companion star during wind accretion, the accretion rates are quite low. If a star in a binary system exceeds its Roche limit, the outer layer of its atmosphere is no longer bound to it and is accreted by the companion, as is the case with cataclysmic variables and X-ray binary stars of low mass. Since it is a self-reinforcing process, because the mass-donating star tries to restore its equilibrium through further expansion, very high mass transfer rates are achieved.

In particular with symbiotic stars such as Mira and SS Leporis , mass transfer rates are observed that are above the values ​​of wind accretion and below the values ​​of Roche boundary rivers. In the case of the Roche-Lobe Overflow wind, the red giant is still completely within the Roche limit, but the zone of wind acceleration is already partially outside the Roche limit. Since in this configuration the dust particles that form in the stellar wind are no longer accelerated to their final speed, as in a single star or in a large binary star system, before they come under the gravitational influence of the companion star, the companion can achieve a higher accretion rate. It is also assumed that the Roche-Lobe Overflow also causes the accumulation of carbon in the atmospheres of CEMP stars .

literature

  • C. Abate, OR Pols, RG Izzard, SS Mohamed, SE de Mink: Wind Roche-lobe overflow: Application to carbon-enhanced metal-poor stars . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1302.4441v1 .
  • M. de Val-Borro, M. Karovska, D. Sasselov: Numerical Simulations of Wind Accretion in Symbiotic Binaries . In: Astrophysical Journal . tape 700 , 2009, pp. 1148 .
  • Z. Chen, A. Frank, EG Blackman, J. Nordhaus, J. Carroll-Nellenback: Mass Transfer and Disc Formation in AGB Binary Systems . In: Monthly Notices of the Royal Astronomical Society . doi : 10.1093 / mnras / stx680