利用 TESS 数据改进快速自转恒星 Altair 的星震学年龄
An improved asteroseismic age of the rapid rotator Altair from TESS data
AI总结：
本文用 TESS 晕测光提取 Altair 的新振荡频率，并结合 MESA 与 ESTER 模型约束核心氢丰度，将其年龄改进为 88±10 Myrs。
摘要：
理解自转在恒星演化中的影响，是模拟早型星的关键；这类恒星中有一半的赤道速度超过 100 km/s。近邻恒星 Altair 就是此类快速自转恒星的一个例子，而且它还拥有一项优势：已有一个精细的二维协调模型对其进行模拟，该模型能够再现其大多数可观测量。本文的目标是纳入新的星震学频率，以增进我们对 Altair 的认识，尤其是其年龄。我们使用晕测光技术处理了凌星系外行星巡天卫星（Transiting Exoplanet Survey Satellite，TESS）于 2022 年 7 月获得的 Altair 图像，从而得到该观测时段内的光变曲线。通过分析光变曲线，我们在 Altair 的振荡频谱中提取出一组 22 个新频率，并确认了 12 个此前已知的频率。与模型预测相比，我们能够将其中 10 个频率与 10 个轴对称模对应起来。这一识别基于模型计算得到的模式可见度。此外，在将协调模型的核心氢质量分数设定为 $X_{\rm core}/X_{\rm ini}\simeq0.972$（其中 $X_{\rm ini}=0.739$）后，模型中的 9 个频率可以经过调整，同时匹配其对应的观测频率。利用计算前主序阶段的一维 MESA 模型与计算主序阶段的二维含时 ESTER 模型的联合结果，我们发现这一核心氢丰度将 Altair 的年龄确定为 88±10 Myrs，略小于此前的估计值。
英文摘要：
Understanding the effects of rotation in stellar evolution is key to modelling early-type stars, half of which have equatorial velocities over 100 km/s. The nearby star Altair is an example of such fast-rotating stars, and furthermore, it has the privilege of being modelled by a detailed 2D concordance model that reproduces most of its observables. The aim of this paper is to include new asteroseismic frequencies to improve our knowledge of Altair, especially its age. We processed images of Altair obtained during July 2022 by the Transiting Exoplanet Survey Satellite using the halo photometry technique to obtain its light curve over this observation period. By analysing the light curve, we derived a set of 22 new frequencies in the oscillation spectrum of Altair and confirmed 12 previously known frequencies. Compared with model predictions, we could associate ten frequencies with ten axisymmetric modes. This identification is based on the modelled visibility of the modes. Moreover, nine of the modelled frequencies can be adjusted to simultaneously match their corresponding observed frequencies, once the core hydrogen mass fraction of the concordance model is set to $X_{\rm core}/X_{\rm ini}\simeq0.972$, with $X_{\rm ini}=0.739$. Using the combined results of a 1D MESA model computing the pre-main sequence and a 2D time-dependent ESTER model computing the main sequence, we find that this core hydrogen abundance sets the age of Altair to 88$\pm$10 Myrs, which is slightly younger than previous estimates.
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