Formation and Destiny of White Dwarf and Be Star Binaries

The binary systems consisting of a Be star and a white dwarf (BeWDs) are very interesting. They can originate from the binaries composed of a Be star and a subdwarf O or B star (BesdOBs), and they can merge into red giants via luminous red nova or can evolve into double WD potentially detected by the LISA mission. Using the method of population synthesis, we investigate the formation and the destiny of BeWDs, and discuss the effects of the metallicity (Z) and the common envelope evolution parameters. We find that BesdOBs are significant progenitors of BeWDs. About 30% (Z = 0.0001)-50% (Z = 0.02) of BeWDs come from BesdOBs. About 60% (Z = 0.0001) -70% (Z = 0.02) of BeWDs turn into red giants via a merger between a WD and a non-degenerated star. About 30% (Z = 0.0001) -40% (Z = 0.02) of BeWDs evolve into double WDs which are potential gravitational waves of the LISA mission at a frequency band between about 3 x 10(-3) and 3 x 10(-2) Hz. The common envelope evolution parameter introduces an uncertainty with a factor of about 1.3 on BeWD populations in our simulations.