CAREER: Mixing and Oscillations in Novae

白矮星是像太阳这样的恒星在核燃料耗尽后的密集残留物。通常，它们是在双星系统中发现的（两颗恒星相互绕轨道运行）。在这样的系统中，随着年龄的增长和大小的变化，两颗恒星可以交换物质。当白矮星从伴星那里获得物质时，它们的表面会发生爆炸，也就是所谓的新星，部分或全部获得的物质会流失到太空中。如果这样一颗白矮星的质量可以在许多新星上明显增长，它就可以在被称为Ia型超新星的大爆炸中完全毁灭。Ia型超新星产生了宇宙中大约一半的铁，在宇宙学中被用作距离测量，但我们并不完全了解它们的原因。在这个项目中，研究者和一组本科生研究人员将使用恒星天体物理学实验模块（MESA）软件工具来研究质量增加的白矮星。他们将阐明新星爆炸如何影响白矮星质量的长期演化。此外，他们还将研究如何利用新星发出的x射线来测量白矮星的质量。将开发利用MESA在本科天体物理学课程中免费提供的教育活动。本程序将探讨扩散、旋转和对流边界混合对新星质量保持效率的影响。该小组将分别研究每一种机制，然后将两种机制和三种机制同时结合起来。由于这些混合机制可以导致核心物质在新星事件中被喷射出来，它们可能导致单个新星周期的净质量损失。这项研究将限制在什么情况下，如果有的话，允许白矮星仅通过氢吸积就增长到钱德拉塞卡质量，从而揭示Ia型超新星祖先的问题。为了帮助测量白矮星质量，该小组和合作者将用开源的GYRE恒星振荡软件分析MESA模型，以确定新星模型中主要的核心振荡模式是否与新星爆发后x射线发射中观测到的振荡相匹配。如果这种联系能够建立起来，它将为白矮星的质量和组成提供一个可靠的测量方法。研究人员将开发在线材料，培训其他研究人员使用MESA。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

White dwarfs are the dense remnants of stars like our sun after their nuclear fuel runs out. Often, they are found in binary systems (two stars orbiting each other). In such systems, the two stars can exchange matter as they age and change size. When white dwarfs gain material from a companion, they undergo explosions on their surfaces, known as novae, losing some or all of the gained matter to space. If such a white dwarf can grow in mass appreciably over many novae, it can be totally destroyed in a massive explosion known as a type Ia supernova. Type Ia supernovae produce roughly half of the iron in the universe and are used as distance measures in cosmology, but we do not fully understand what causes them. In this project, the investigator and a team of undergraduate researchers will use the Modules for Experiments in Stellar Astrophysics (MESA) software tool to study mass-gaining white dwarfs. They will clarify how nova explosions affect the long-term evolution of white dwarf masses. Additionally, they will investigate how X-ray emission from a nova may be used to measure the mass of the underlying white dwarf. Freely available educational activities utilizing MESA for use in undergraduate astrophysics courses will be developed.This program will probe the effects of diffusion, rotation, and convective boundary mixing on the mass retention efficiency of novae. The group will investigate each mechanism individually before combining two and all three at a time. Since these mixing mechanisms can cause core material to be ejected in the nova event, they may lead to a net mass loss over a single nova cycle. This study will constrain what circumstances, if any, allow a white dwarf to grow to the Chandrasekhar mass from hydrogen accretion alone, shedding light on the Type Ia supernova progenitor problem. To aid in measuring white dwarf masses, the group and collaborators will analyse the MESA models with the open-source GYRE stellar oscillation software to determine if the dominant core oscillation modes in nova models match the observed oscillations in the post-outburst X-ray emission of novae. If such a link can be established, it would provide a robust measure of white dwarf mass and perhaps composition. The investigator will develop online materials to train other researchers on using MESA.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.