We report the detection of 8.914 hr variability in both optical and ultraviolet light curves of LP 40−365 (also known as GD 492), the prototype for a class of partly burnt runaway stars that have been ejected from a binary due to a thermonuclear supernova event. We first detected this 1.0% amplitude variation in optical photometry collected by the Transiting Exoplanet Survey Satellite (TESS). Reanalysis of observations from the Hubble Space Telescope at the TESS period and ephemeris reveal a 5.8% variation in the ultraviolet of this 9800 K stellar remnant. We propose that this 8.914 hr photometric variation reveals the current surface rotation rate of LP 40−365, and is caused by some kind of surface inhomogeneity rotating in and out of view, though a lack of observed Zeeman splitting puts an upper limit on the magnetic field of <20 kG. We explore ways in which the present rotation period can constrain progenitor scenarios if angular momentum was mostly conserved, which suggests that the survivor LP 40−365 was not the donor star but was most likely the bound remnant of a mostly disrupted white dwarf that underwent advanced burning from an underluminous (Type Iax) supernova.

我们报告了在 LP 40−365（也称为 GD 492）的光学和紫外光曲线中检测到 8.914 小时的变化，这是一类部分燃烧的失控恒星的原型，由于热核超新星而从双星中弹出事件。我们首先在凌日系外行星勘测卫星 (TESS) 收集的光学测光中检测到这种 1.0% 的幅度变化。对哈勃太空望远镜在 TESS 周期和星历的观测结果进行再分析，揭示了这颗 9800 K 恒星残骸的紫外线有 5.8% 的变化。我们建议，这个 8.914 小时的光度变化揭示了 LP 40-365 的当前表面旋转速率，并且是由某种表面不均匀性旋转进出视野引起的，尽管缺乏观察到的塞曼分裂对磁场施加了上限场<20 kG。