DI武仙座再访：星点、重力变暗和三维倾角
DI Herculis Revisited: Starspots, Gravity Darkening, and 3-D Obliquities
摘要：
武仙座DI是一颗食双星，以理论和观测之间长期存在的拱点进动率的分歧而闻名，当发现两颗恒星与轨道严重偏离时，这一分歧得到了解决。我们使用凌日系外行星勘测卫星（TESS）的数据来完善我们对恒星进动的了解，并加强观测和理论进动率之间的比较。TESS数据显示的变化周期为1.07天，我们将其解释为主星上恒星黑子的旋转调制。这一解释得到了支持的光度异常检测期间的主食一致的星点交叉。二次日食的光变曲线显示了一种可重复的不对称性，我们将其解释为重力变暗的影响。通过将TESS数据与先前获得的数据相结合，我们确定了两颗恒星的三维自旋方向。利用这些信息，理论拱点进动率（包括潮汐、自转和广义相对论的影响）的更新值为$1.35^{+0.58}_{-0.50}$ arcsec/cycle。观测速率的更新值（包括新的TESS日食时间后）为$1.41^{+0.39}_{-0.28}$ arcsec/cycle。考虑到观测值和理论值之间的一致性，我们同时拟合了所有相关数据，假设理论是正确的。这使我们能够对恒星的平行度施加更严格的限制，主星和副星的平行度分别为$75^{+3}_{-3}$和$80^{+3}_{-3}$度。
英文摘要：
DI Herculis is an eclipsing binary famous for a longstanding disagreement between theory and observation of the apsidal precession rate, which was resolved when both stars were found to be severely misaligned with the orbit. We used data from the Transiting Exoplanet Survey Satellite (TESS) to refine our knowledge of the stellar obliquities and sharpen the comparison between the observed and theoretical precession rates. The TESS data show variations with a 1.07-day period, which we interpret as rotational modulation from starspots on the primary star. This interpretation is supported by the detection of photometric anomalies during primary eclipses consistent with starspot crossings. The secondary eclipse light curve shows a repeatable asymmetry which we interpret as an effect of gravity darkening. By combining the TESS data with previously obtained data, we determined the three-dimensional spin directions of both stars. Using this information, the updated value of the theoretical apsidal precession rate (including the effects of tides, rotation, and general relativity) is $1.35^{+0.58}_{-0.50}$ arcsec/cycle. The updated value of the observed rate (after including new TESS eclipse times) is $1.41^{+0.39}_{-0.28}$ arcsec/cycle. Given the agreement between the observed and theoretical values, we fitted all the relevant data simultaneously assuming the theory is correct. This allowed us to place tighter constraints on the stellar obliquities, which are $75^{+3}_{-3}$ and $80^{+3}_{-3}$ degrees for the primary and secondary stars, respectively.
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