Formation of a Rapidly Rotating Classical Be-star in a Massive Close Binary System

This paper investigates the spin-up of a mass-accreting star in a close binary system passing through the first stage of mass exchange in the Hertzsprung gap. Inside an accreting star, angular momentum is carried by meridional circulation and shear turbulence. The circulation carries part of the angular momentum of the accreted layers to the accretor's surface. The greater the rate of arrival of angular momentum in the accretor is, the greater this part. It is assumed that this part of the angular momentum can be removed by the disk further from the accretor. If the angular momentum in the matter entering the accretor is more than half the Keplerian value, then the angular momentum obtained by the accretor during mass exchange stage does not depend on the rate of arrival of angular momentum. The accretor may have the characteristics of a Be-star immediately after the end of mass exchange.

The Spin-up of a Star Gaining Mass in a Close Binary System on the Thermal Time Scale

We investigate the exchange of mass in a binary system as a channel through which a Be star can receive a rapid rotation.The mass-transfer phase in a massive close binary system in the Hertzsprung-gap is accompanied by the spinning up of the accreting component.We consider a case when the mass of the accreting component increases by 1.5 times.The component acquires mass and angular momentum while in a state of critical rotation.The angular momentum of the component increases by 50 times.Meridional circulation effectively transports angular momentum inside the component during the mass-transfer phase and during the thermal timescale after the end of the mass-transfer phase.As a result of mass transfer,the component acquires the rotation typical of classical Be stars.

Is the additional increase of star luminosity due to partial mixing real?

The partial mixing of matter between the radiative envelope and convective core in an early Btype star produces an additional increase of star luminosity during main sequence evolution. High quality data on stellar mass and luminosity defined from studies of detached double-lined eclipsing binaries are used to check the existence of such additional increase. It is shown that the additional luminosity increase does not contradict observed high quality data, if the intensity of partial mixing is restricted by the observed increase in surface helium content.