Atmospheric Chemistry in Brown Dwarfs and Low Mass Stars

化学是理解任何给定天文物体的演化和光谱外观的基础。光谱观察探测化学，为了解释这种观察，了解化学是如何运作的是至关重要的。在低质量恒星和棕矮星的寒冷大气中，分子和云凝聚化学特别重要，因为它决定了光度和光谱观测的主要结果。在这个项目中，研究人员正在确定冷矮星大气中的气体和云凝聚化学作为温度、总压和金属丰度的函数。化学平衡只取决于压力、温度和成分。因此，平衡丰度网格可以独立于任何特定的大气模型来计算。另一方面，大气和光谱模型需要可靠的化学输入。因此，第二个主要目标是提供一个可靠的气体、液体和固体化合物丰度网格，这些化合物来自热化学平衡，并在必要时提供热化学动力学计算。这项工作对于解决低质量天体的关键问题至关重要，包括以下几个问题：L和T矮星的有效温度标度是多少？它们的大气成分是什么？由于垂直输送过程而偏离化学平衡的情况有多常见？云和“天气”如何影响棕矮星的光谱？一个自然的扩展是应用化学来产生新的大气模型和低质量物体的高分辨率合成光谱，以确定有效温度、重力和成分作为质量和年龄的函数的光谱诊断。更广泛的影响。这项工作是对低质量天体观测研究的补充，并为解释来自地面观测站的各种仪器未来的观测提供了指南。未来的结果将在科学论文、专业会议的演讲和公开演讲中描述。研究人员在行星科学的热化学和动力学大气建模方面的长期经验有利于现有的与从事光谱模型工作的其他研究小组的跨学科协作。本科生的参与已经在进行中，正在扩展到目前的工作。

Chemistry is the foundation for understanding the evolution and spectral appearance of any given astronomical object. Spectroscopic observations probe the chemistry, and in order to interpret such observations, it is crucial to know how the chemistry operates. In the cool atmospheres of low-mass stars and brown dwarfs, molecular and cloud condensation chemistry is of particular importance as it determines the major outcome of photometric and spectroscopic observations. In this project, the investigators are determining the gas and cloud condensation chemistry in cool dwarf star atmospheres as a function of temperature, total pressure, and metallicity. Chemical equilibrium depends only on pressure, temperature, and composition. Thus a grid of equilibrium abundances can be calculated independently from any particular atmospheric model. On the other hand, atmospheric and spectral models require reliable input chemistry. Hence the second major objective is to provide a reliable abundance grid of gaseous, liquid, and solid compounds derived from thermochemical equilibrium, and, where necessary, thermochemical kinetic computations. The work is essential to address key questions about low-mass objects, including the following: What are the effective temperature scales of L and T dwarfs? What are their atmospheric compositions? How common are departures from chemical equilibrium due to vertical transport processes? How do clouds and 'weather' affect the spectra of brown dwarfs? A natural extension is to apply the chemistry to generate new atmospheric models and high-resolution synthetic spectra of low-mass objects to determine spectral diagnostics of effective temperature, gravity, and composition as functions of mass and age. Broader Impacts. The work is complementary to observational studies of low-mass objects and provides a guide to interpret future observations from a wide variety of instruments from ground-based observatories. Future results will be described in scientific papers, in talks at professional meetings, and in public lectures. The long standing experience of the investigators with thermochemical and kinetic atmospheric modeling in planetary science benefits the existing interdisciplinary collaboration with other research groups working on spectral models. Undergraduate student participation, already ongoing, is being extended to the current work.