Ultracompact X-ray binaries with He star companions

ABSTRACT Ultracompact X-ray binaries (UCXBs) are low-mass with hydrogen-deficient mass donors and ultrashort orbital periods. They have been suggested to be the potential Laser Interferometer Space Antenna (LISA) sources in low-frequency region. Several channels for formation of UCXBs proposed so far. In this paper, we carried out a systematic study on He star donor channel, which neutron (NS) accretes matter from main-sequence (MS) through Roche lobe overflow, where transfer is driven by gravitational wave radiation. First, followed long-term evolution NS+He MS employing stellar code Modules Experiments Stellar Astrophysics (mesa ), thereby obtained initial parameter spaces production UCXBs. We then used these results perform detailed binary population synthesis approach obtain Galactic rates channel. estimate appearing as LISA ${\sim} 3.1\!-\!11.9\, \rm Myr^{-1}$ number such UCXB-LISA Galaxy can reach about 1–26 calibrated observations. This work indicates that channel may contribute significantly UCXB rate. found evolutionary tracks account location five transient relatively long periods quite well. also identified their locations mass-transfer rate versus period diagram.