Collaborative Research: A Fresh Look at M Dwarf Stars

超过70%的恒星是“M矮星”，它们比太阳小得多，温度低得多，亮度也低得多。更好地了解它们的物理性质涉及到星系的化学演化、星系的动力学、恒星大气、分子天体物理、恒星形成、行星形成和系外行星的特征。这个小组将联合最好的恒星内部和大气物理模型，并用高质量的观测来测试它们，从而促进我们的理解。这些项目有一个重要的培训部分，因为大部分工作将由加州大学圣克鲁斯分校、亚利桑那州立大学和波士顿大学的研究生完成。本科生也将参与这项研究，该团队将创建新的课程和培训材料，包括让学生了解未来职业的网络研讨会。该团队将对M矮星的大气、内部和进化进行彻底的建模研究。之前关于M矮星物理的工作使用了为质量更大的恒星设计的方法和代码，工作人员将质量降低到M矮星。这个小组将使用为褐矮星开发的建模工具，这些棕矮星的质量略低于M星，然后移动到质量更高的位置来对这些物体进行建模。M矮星和棕矮星有许多共同的性质，比如分子主导的大气和部分退化的内部。该团队将使用M星的光谱“恢复”模型，这是一种完全贝叶斯数据驱动的方法，以得出不受预先计算的大气层网格限制的最合适的温度结构和丰度。他们将把重点放在围绕类太阳初级恒星轨道上经过充分研究的基准M星上。根据这项工作的结果，他们将计算辐射对流模式大气的大网格，以得出温度、重力和金属丰度的趋势，这将对整个天文学社区有用。这样的模型也将作为新的自洽M矮星演化模型的上边界条件，该模型将包括一个新的氢状态方程。这将使他们能够与之前关于M矮星大气的理论和观测工作、它们在H-R图上的位置以及观测到的质量-半径关系进行详细的比较。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Over 70% of all stars are “M dwarfs”, which are much smaller, cooler, and less luminous than the Sun. A better understanding of their physical properties touches on galactic chemical evolution, the dynamics of the galaxy, stellar atmospheres, molecular astrophysics, star formation, planet formation, and exoplanet characterization. This group will advance our understanding by uniting the best physical models of stellar interiors and atmospheres and testing them with high-quality observations. These projects have an important training component, as much of the work will be done by graduate students at UC Santa Cruz, Arizona State University, and Boston University. Undergraduate students will also be involved in the research, and the team will create a new curriculum and training materials, including a webinar for students to learn about future careers. The team will carry out a thorough modeling study of M dwarf atmospheres, interiors, and evolution. Previous work on M dwarf physics has used methods and codes devised for more massive stars, with workers moving down in mass to M dwarfs. This group will use modeling tools developed for brown dwarfs, just lower in mass than the M stars, and then move up in mass to model these objects. M dwarfs and brown dwarfs share many properties, like molecule-dominated atmospheres and partially degenerate interiors. This team will use spectral "retrieval" models for M stars, a fully Bayesian data-driven method, to yield best-fit temperature structures and abundances that are not bound to pre-computed atmosphere grids. They will focus on benchmark, well-studied M stars in orbit around Sun-like primaries. Based on the outcomes of this work, they will then compute a large grid of radiative-convective model atmospheres to yield trends in temperature, gravity, and metallicity, which will be of use to the entire astronomical community. Such models will also serve as the upper boundary conditions for new self-consistent M dwarf evolution models with MESA, which will include a new hydrogen equation of state. This will allow them to pursue detailed comparisons with previous theoretical and observational work on M dwarf atmospheres, their locations on the H-R diagram, and observed mass-radius relations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.