The twin-degenerate interacting binary G61-29

Abstract

The star G61-29 has a spectrum showing exclusively broad emission lines of He I and He II. The spectroscopic observations of this object demonstrate that it is an interacting binary system with an orbital period of 46.5 minutes. The system consists of two white dwarfs, with the lower mass star, a helium white dwarf, transferring mass to the higher mass star by way of an accretion disk. It is suggested that G61-29 can be understood as the evolutionary descendant of a binary system similar to HZ 29, another twin-degenerate binary with a shorter orbital period. It is also suggested that with continued evolution, both systems must inevitably evolve into single DB white dwarf stars.