Supermassive stars (SMSs; M>10^5 Msun) and their remnant black holes are promising progenitors for supermassive black holes (SMBHs) observed in the early universe at z>7. It has been postulated that SMSs forms through very rapid mass accretion onto a protostar at a high rate exceeding 0.01 Msun/yr. According to recent studies, such rapidly accreting protostars evolve into "supergiant protostars", i.e. protostars consisting of a bloated envelope and a contracting core, similar to giant star. However, like massive stars as well as giant stars, both of which are known to be pulsationally unstable, supergiant protostars may also be also unstable to launch strong pulsation-driven outflows. If this is the case, the stellar growth via accretion will be hindered by the mass loss. We here study the pulsational stability of the supergiant protostars in the mass range M<10^3 Msun through the method of the linear perturbation analysis. We find that the supergiant protostars with M>600 Msun and very high accretion rate Mdot>1.0 Msun/yr are unstable due to the kappa mechanism. The pulsation is excited in the He^+ ionization layer in the envelope. Even under a conservative assumption that all the pulsation energy is converted into the kinetic energy of the outflows, the mass-loss rate is ~10^-3 Msun/yr, which is lower than the accretion rate by more than two orders of magnitude. We thus conclude that the supergiant protostars should grow stably via rapid accretion at least in the mass range we studied. As long as the rapid accretion is maintained in the later stage, protostars will become SMSs, which eventually produce seeds for the high-z SMBHs.
Pulsations in the Late-type B Supergiant Star HD 202850
HD 202850是一颗B型超巨星。众所周知，这类恒星的光球线是变化的。由于宏观湍流，谱线比预期的要宽得多。宏观湍流与恒星脉动有关。据报道，有几颗B超巨星经历了脉动。在我们以前的工作中，我们从Ondrejov 2-m望远镜拍摄的数据中检测到该物体的脉动周期为1.59小时。我们继续研究这个物体，并用DAO 1.2米望远镜拍摄了几个时间序列。我们的新数据表明，这颗恒星可能存在一些额外的脉动周期。我们在这张海报中展示了我们的新结果。
Pulsational instability of pre-main sequence models from accreting protostars. I. Constraining the input physics for accretion with spectroscopic parameters and stellar pulsations
Pulsational instability of pre-main-sequence models from accreting protostars II. Modelling echelle diagrams of $δ$ Scuti stars without rotational splitting
Periodic 6.7 GHz $\mathrm{CH_3OH}$ maser emission in G353.273+0.641: First candidate for a pulsating high-mass protostar
Graduate School of Sciences and Technology for Innovation, Yamaguchi University（山口大学理工学创新研究科）；The Research Institute for Time Studies, Yamaguchi University（山口大学时间学研究研究所）；Center for Astronomy, Ibaraki University（茨城大学天文学中心）
The IACOB project: IV. New predictions for high-degree non-radial mode instability domains in massive stars and connection with macroturbulent broadening
Evolution and Final Fates of Rapidly Accreting Supermassive Stars
超大质量恒星的形成是宇宙早期产生超大质量黑洞的可能途径。本章总结了最近的理论努力，以了解他们的演变，突出的影响非常快速的吸积率$\dot{M}_* \gtrsim 0.1~$ M $_\odot$年$^{-1}$。恒星演化计算预测，这种吸积SMS具有一个特征，即，一个非常大的半径，随着恒星质量的增加而单调增加。当恒星吸积大于$10^3$ M $_\odot$的气体后，半径超过$7000$ R $_\odot$（或$30$ AU）。我们发现，“超巨星原恒星”阶段的出现是形成SMSs的关键，因为由此产生的辐射反馈对吸积流在此阶段大大减弱。我们还表明，这些SMS结束他们的生活，而吸积继续，他们的最终命运不同的吸积率。
