北极星的轨道与动力学质量：基于CHARA阵列的观测
The Orbit and Dynamical Mass of Polaris: Observations with the CHARA Array
AI总结：
本研究利用CHARA阵列等观测数据拟合北极星轨道，得出其动力学质量为5.13±0.28倍太阳质量，发现其光度高于演化预测，并提出含脉动模式、近星点通过的情景可解释其特殊性质。
摘要：
我们利用CHARA阵列（高角分辨率天文中心）在2016年至2021年间的观测数据，追踪了造父变星北极星为期30年的轨道运行情况，还通过阿帕奇波因特天文台的斑点干涉测量获得了额外的测量数据。由于伴星相对较暗，存在极高的流量比，因此对其的探测难度较大。角直径测量结果显示，其数值会随脉动相位发生一定变化。我们采用定制的基于网格的模型拟合程序测量了伴星的天体测量位置，并通过CANDID软件进行了验证。将这些位置数据与Torres（2023）论述的大量径向速度数据相结合，拟合出了轨道。由于天体测量数据集与径向速度数据集的规模不均衡，我们探讨了多种加权方法。最终得出的造父变星质量为5.13±0.28倍太阳质量（$M_\text{sun}$）。由于轨道偏心率相对较大（0.63），推导得出的质量对偏心率的取值较为敏感。将质量与距离结合分析可知，这颗造父变星的光度高于演化轨迹对该质量恒星的预测值。我们还探讨了表面黑子的识别问题，这将为周期约120天的光度变化是自转周期的观点提供依据。北极星具备一些特殊性质：周期快速变化、存在相位跳变、振幅可变、偏振异常。不过，包含脉动模式、轨道近星点通过（Torres 2023）以及低脉动振幅的脉动情景，能够在造父变星常见的脉动框架内解释这些特征。
英文摘要：
The 30 year orbit of the Cepheid Polaris has been followed with observations by the CHARA Array (Center for High Angular Resolution Astronomy) from 2016 through 2021. An additional measurement has been made with speckle interferometry at the Apache Point Observatory. Detection of the companion is complicated by its comparative faintness--an extreme flux ratio. Angular diameter measurements appear to show some variation with pulsation phase. Astrometric positions of the companion were measured with a custom grid-based model-fitting procedure and confirmed with the CANDID software. These positions were combined with the extensive radial velocities discussed by Torres (2023) to fit an orbit. Because of the imbalance of the sizes of the astrometry and radial velocity datasets, several methods of weighting are discussed. The resulting mass of the Cepheid is 5.13$\pm$ 0.28 $M_\odot$. Because of the comparatively large eccentricity of the orbit (0.63), the mass derived is sensitive to the value found for the eccentricity. The mass combined with the distance shows that the Cepheid is more luminous than predicted for this mass from evolutionary tracks. The identification of surface spots is discussed. This would give credence to the identification of photometric variation with a period of approximately 120 days as a rotation period. Polaris has some unusual properties (rapid period change, a phase jump, variable amplitude, unusual polarization). However, a pulsation scenario involving pulsation mode, orbital periastron passage (Torres 2023), and low pulsation amplitude can explain these characteristics within the framework of pulsation seen in Cepheids.
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