Dr. WU You and his cooperators, from Yunnan Observatories of Chinese Academy of Sciences, investigate the Hot subdwarf-B stars (sdBs) with neutron star (NS) companions to obtain the population properties of Galactic sdB+NS binaries through BPS studies. The result has been published recently in Astronomy & Astrophysics.

sdBs have been identi？ed as helium(He)-core burning stars with very thin hydrogen-rich envelopes. They are located on the extreme horizontal branch (EHB) in the Hertzsprung-Russell diagram (HRD). Binary population synthesis(BPS) predicts the existence of sdBs with neutron star (NS) companions. Several works have been dedicated to search such systems, but none has been found yet.

Researchers systematically investigate the formation of sdB+NS binaries using binary evolution, then obtain their population properties by combining their models with BPS methods. There are ～ 7,000 ？ 21,000 sdB+NS binaries in the Galaxy at the present epoch, which contributes to 0.3-0.5% of the total sdB binaries.

Regardless of whether they are produced by the stable RLOF channel or the CE ejection channel, the sdB+NS binary populations have similar delay time distributions, which peak at around 0.2Gyr. This indicates that sdB+NS binaries are predominantly found in very young populations, probably in the Galactic disk.

The sdB+NS systems resulting from CE ejection have very short orbital periods. This work estimate that about 100 ？ 300 sdB+NS systems in the Milky Way are potential gravitational wave sources which could be resolved by the Laser Interferometer Space Antenna (LISA) in the future. This research provides some guidance for observational efforts, e.g. the project Massive Unseen Companions to Hot Faint Under-luminous Stars from SDSS (MUCHFUSS).

Contact: WU You, YNAO, CAS, youwu@ynao.ac.cn

Appendix: Hot subdwarf B stars with neutron star components II: Binary population synthesis