Parkes observations for project P1000 semester 2018OCTS_01

Hot subdwarf (sdB) stars are core-helium burning stars with thin hydrogen envelopes and masses around 0.5 Msun. A large fraction of sdBs are members of short-period binaries with periods below a few days. Orbital shrinkage through a common envelope phase is the only likely formation channel for such short-period sdB binaries. \r\nAlthough most of the companions are low mass main sequence stars or white dwarfs, one proposed evolutionary channel produces an sdB with a recycled pulsar companion where the pulsar forms after two common envelope phases and a short X-ray binary phase. Theoretical models predict that about 1% of the compact sdB binaries should have pulsar companions. \r\nSo far no pulsar companion to an sdB has yet been detected unambiguously whereas six candidates have been identified. Here we propose 13.5 hrs of observing time to conduct a deep search for radio pulsars around four candidate sdB+pulsar systems which are accessible with Parkes. A detection would (a) be the first time a pulsar bound to an sdB star has been detected, confirming the efficacy of the predicted binary-evolution channel; and (b) allow for an accurate estimate of the sdB mass, testing models for these enigmatic stars.

热亚矮星（Hot subdwarf，缩写sdB）是进行核心氦燃烧的恒星，拥有稀薄的氢包层，质量约为0.5倍太阳质量（Msun）。绝大多数sdB属于轨道周期不足数日的短周期双星系统。通过共包层阶段实现轨道收缩，是这类短周期sdB双星唯一可行的形成通道。
尽管这类双星的伴星大多为低质量主序星或白矮星，但已有理论提出一类演化通道：可形成带有再循环脉冲星伴星的sdB系统，该脉冲星需历经两次共包层阶段与一段短暂的X射线双星阶段后方可形成。理论模型预测，约1%的致密sdB双星应拥有脉冲星伴星。
截至目前，尚未明确探测到与sdB绑定的脉冲星伴星，但已确认6颗候选体。本文计划申请13.5小时的观测时长，对4个可利用帕克斯（Parkes）望远镜观测的sdB+脉冲星候选系统开展深场射电脉冲星搜寻工作。若成功探测到此类脉冲星，将实现两大科学意义：(a) 首次发现与sdB恒星绑定的脉冲星，验证该预言的双星演化通道的有效性；(b) 实现对sdB质量的精确估算，从而检验这类神秘恒星的理论模型。