Study On The Formation Channel Of Throne-(?)ytkow Objects

In 1975,Throne and （?）ytkow proposed a special object,called as Throne-（?）ytkow Object（T（?）O）,which has 1MO degenerate neutron core and a massive envelope（≥ 2M（?））.It looks like a red giant or red supergiant stars.There are three channels for the formation of T（?）Os:（i）a collision between low mass main-sequence star and neutron star in globular cluster;（ii）due to additional "kick" velocity,new born neutron star directly embedded into its companion center;（iii）the coalescence of a neutron star with its massive companion after a high-mass X-ray binary（HMXB）phase.The first two channels are very rare,and most of T（?）Os form via the third channel.Investigating the formation of these T（?）Os help us to understand not only binary evolution（including common envelope evolution,coalescence）,but also special objects,such as HV 2112,1E2259+586,4U0142+62,RXJ 1838.4-0301 and so on.However,up to now,there is not detailed simulation for the formation of T（?）Os.In this thesis,we investigate the formation channel of T（?）Os in close binaries,and discuss the properties of T（?）Os’ progenitors.We use Monte Carlo Simulation method and the rapid binary evolution code to simulate the evolutions of 2 x 107 binary systems.About 0.3%of them evolve into binaries composed of a neutron star and a companion.About 0.08%of these binary systems undergo Roche lobe overflow,in which 0.07%experience dynamical mass transfer or common envelope evolution,and 0.02%occur the mergers of neutron stars and their companions.About 0.015%of these binary systems form T（?）Os.We estimate that the Galactic birth rate of T（?）Os is about 1.5 × 10-4yr^-1,which is consistent with the previous estimate.Their progenitors may be composed of a neutron star and a main-sequence star,a star in Hertz-sprung gap or core-helium burning,or a naked helium star.The birth rates of T（?）Os via above progenitors are 1.7 x 10-5yr^-1,1.2× 10-4yr^-1,0.7 × 10-5 yr^-1,0.6 x 10-5yr^-1,respectively.We find that T（?）Os’ envelopes are not only rich hydrogen,but also rich helium.It is well known that the massive companion of neutron stars in three HMXBs（SMCX-1,Cen X-3 and LMC X-4）may closely overflow their Roche lobes.We find the companion masses and their orbital periods agree with these of T（?）Os’ progenitors.