冷与热：仙后座β和狮子座α的干涉成像
Colder and Hotter: Interferometric imaging of β Cassiopeiae and α Leonis
摘要：
近红外干涉仪最近对一些快速旋转的A型恒星进行了成像，发现重力变暗的程度与理论预期不一致。在这里，我们使用CHARA阵列和MIRC仪器在H波段对较冷的恒星β Cas（F2 IV）和较热的恒星α Leo（B7 V）进行了新的成像。采用一个简单的重力暗化公式的固体旋转模型，我们模拟了恒星的几何特性和表面温度分布，证实了两颗恒星都在快速旋转，并显示出重力暗化异常。我们估计的质量和年龄，这些快速旋转的L-Rpol和HR图构建的非旋转的恒星通过跟踪其非旋转的等价物。演化中的次巨星β Cas出人意料的快速旋转为恒星核壳耦合提供了一个独特的测试，揭示了过去~ 0.5 Gyr的相当有效的耦合。最后，我们总结了我们所有的干涉测定的重力暗化系数的快速旋转，发现没有匹配的期望，从广泛使用的冯Zeipel重力暗化法律。由于冯蔡佩尔定律的条件已知会在快速旋转的恒星中被违反，我们建议对这类具有辐射主导包层的恒星使用计算得出的β = 0.19。此外，我们注意到，不存在自洽建模严重重力暗化恒星的范式，这些恒星显示热辐射极和冷对流赤道。
英文摘要：
Near-infrared interferometers have recently imaged a number of rapidly rotating A-type stars, finding levels of gravity darkening inconsistent with theoretical expectations. Here, we present new imaging of both a cooler star β Cas (F2IV) and a hotter one α Leo (B7V) using the CHARA array and the MIRC instrument at the H band. Adopting a solid-body rotation model with a simple gravity darkening prescription, we modeled the stellar geometric properties and surface temperature distributions, confirming both stars are rapidly rotating and show gravity darkening anomalies. We estimate the masses and ages of these rapid rotators on L-Rpol and HR diagrams constructed for non-rotating stars by tracking their non-rotating equivalents. The unexpected fast rotation of the evolved subgiant β Cas offers a unique test of the stellar core-envelope coupling, revealing quite efficient coupling over the past ~ 0.5 Gyr. Lastly we summarize all our interferometric determinations of the gravity darkening coefficient for rapid rotators, finding none match the expectations from the widely used von Zeipel gravity darkening laws. Since the conditions of the von Zeipel law are known to be violated for rapidly rotating stars, we recommend using the empirically-derived β = 0.19 for such stars with radiation-dominated envelopes. Furthermore, we note that no paradigm exists for self-consistently modeling heavily gravity-darkened stars that show hot radiative poles with cool convective equators.
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