北极星的好奇案例：北极星演化模型和测量之间的持续紧张关系
The Curious Case of the North Star: the continuing tension between evolution models and measurements of Polaris
摘要：
北极星是离我们最近的造父变星，因此在我们对造父变星的理解和莱维特定律中占有特殊的地位。在过去的几十年里，我们已经了解了许多关于这颗恒星作为造父变星和多星系统的主要组成部分的新事物。因此，我们正在更精确地测量北极星的质量，半径和演变。然而，随着我们了解的越来越多，很明显我们了解的越来越少。有证据表明，北极星的质量比恒星演化模型所显示的要小得多，而且北极星比它的主序星要年轻得多。在这项工作中，我们回顾了一些最近的测量和他们与过去的研究。然后，我们提出了新的恒星演化模型和种群合成计算，以与Evans等人（2018）的新质量测量进行比较。我们发现北极星的质量偏差约为50%.我们还发现，北极星和它的同伴之间可能存在年龄差异，但也有很小的可能性，这种差异是不真实的。
英文摘要：
Polaris is the nearest Cepheid to us and as such holds a special place in our understanding of Cepheids in general and the Leavitt Law. In the past couple of decades, we have learned many new things about the star as a Cepheid and as the primary component of a multiple star system. As such, we are more precisely measuring the mass, radius and evolution of Polaris. However, as we learn more, it is becoming clear that we understand less. There is evidence that Polaris is much less massive than stellar evolution models suggest and that Polaris is a much younger star than its main sequence companion. In this work, we review some of the recent measurements and their connections with past studies. We then present new stellar evolution models and populations synthesis calculations to compare with the new mass measurements by Evans et al. (2018). We find that the mass discrepancy for Polaris is about 50\%. We also find that there is a likely age discrepancy between Polaris and its companion, but that there is also a very small probability that the discrepancy is not real.
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