Understanding Stellar Convection

了解恒星对流

• 批准号: RGPIN-2018-04195
• 负责人: Lovekin, Catherine
• 金额: $ 2.11万
• 依托单位: Mount Allison University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=711879
• 关键词: Understanding; Stellar; Convection

All elements heavier than hydrogen and helium are made in stars. The most common elements in the universe (carbon, oxygen) are made in the cores of stars, while heavier elements are made during the final phases of a stars death, and the details of this process are very sensitive to the size of the stellar core at the end of the main sequence. Convection, especially convective overshoot, can change the amount of material available to stellar cores, but the amount of convective overshoot is largely unknown. We will use stellar pulsation to constrain the amount of convective overshoot in a sample of six stars (Objective 1). Measuring the convective overshoot for individual stars is difficult, and has been done for only a handful of main sequence stars so far. This sample of six stars will significantly increase the number of stars with known convective overshoot parameters. As this measurement is made in more stars, we will be better able to characterize how the convective overshoot varies with the mass and age of a star. We will also investigate techniques that will allow measurements of convective overshoot in large numbers of stars (Objective 2). I have recently developed a technique that can in principle be used to constrain the convective overshoot in a sample of one type of variable star, the delta Scuti stars. We will investigate whether this technique holds when the composition of a star is allowed to vary, and also whether this technique can be extended to other classes of variable stars. Again, this will significantly increase the number of stars with known convective overshoots, allowing us to characterize the behaviour of the convective overshoot parameter with mass and age. Finally, we will investigate the effects of convection in more evolved stars. The Cepheid variables are important distance indicators in astronomy, and are expected to have significant convective envelopes. While most Cepheids are observed to have a single pulsation period, a significant number are multi-periodic. The origin of the multiple periods is unknown, but it has been proposed that it is related to the interaction between convection and pulsation in the stellar envelope. We will perform 2 and 3 dimensional simulations of Cepheid variables to investigate this interaction and explain the origin of the multi-periodic Cepheids. This will have important implications for the accuracy of the Cepheid distance scale, and hence for our understanding of the scale and history of the universe.

所有比氢和氦重的元素都是在恒星中形成的。 宇宙中最常见的元素（碳，氧）是在恒星的核心中产生的，而较重的元素是在恒星死亡的最后阶段产生的，这个过程的细节对主序结束时恒星核心的大小非常敏感。 对流，特别是对流过冲，可以改变恒星核心可用的物质数量，但对流过冲的数量在很大程度上是未知的。 我们将使用恒星脉动来限制六颗恒星样本中的对流过冲量（目标1）。 测量单个恒星的对流过冲是困难的，到目前为止，只有少数主序星做到了。 这六颗恒星的样本将显着增加已知对流过冲参数的恒星数量。 随着这种测量在更多的恒星中进行，我们将能够更好地描述对流过冲如何随着星星的质量和年龄而变化。 我们还将调查技术，将允许在大量的恒星对流过冲的测量（目标2）。 我最近开发了一种技术，原则上可以用来限制一种类型的变星星星（盾牌座δ星）样本中的对流过冲。 我们将研究当星星的成分允许变化时，这种方法是否成立，以及这种方法是否可以扩展到其他类型的变星。 同样，这将显着增加已知的对流过冲的恒星数量，使我们能够表征对流过冲参数与质量和年龄的行为。 最后，我们将研究对流在更演化的恒星中的影响。 造父变星是天文学中重要的距离指标，预计会有显著的对流包络。 虽然大多数造父变星被观察到有一个单一的脉动周期，但有相当数量的是多周期的。 多重周期的起源尚不清楚，但有人提出它与恒星包层中对流和脉动之间的相互作用有关。 我们将对造父变星进行二维和三维模拟，以研究这种相互作用，并解释多周期造父变星的起源。 这将对造父变星距离尺度的准确性产生重要影响，从而对我们理解宇宙的尺度和历史产生重要影响。