The progenitors of Be-stars paired with O-subdwarfs: the spin-up of a Be star at the stage of conservative mass exchange

TL;DR

This paper models how conservative mass exchange in binary systems can spin up a star to Be-type rotation speeds, highlighting angular momentum transfer and removal processes.

Contribution

It provides a detailed analysis of angular momentum transfer during conservative mass exchange leading to Be-star formation in binary systems.

Findings

Accretion transfers 80-85% of angular momentum to the star.

The accretor reaches rotation speeds typical of classical Be stars.

Angular momentum is removed by a disk after mass exchange.

Abstract

The spinning-up of the accreting component in the process of conservative mass exchange is considered in binary systems - progenitors of systems consisting of a main sequence Be-star and an O-subdwarf. During the mass exchange, the meridional circulation transfers 80-85\% of the angular momentum that entered the accretor together with the accreted matter to the accretor surface. This angular momentum is removed from the accretor by the disk. When the mass exchange finishes, the accretor has a rotation typical of classical Be-type stars.