Collaborative Research: Using Brown Dwarfs to Understand Exoplanetary Atmospheres: Spectral Inversions of an Analog Population

天文学家开始直接对系外行星进行成像，并获得光谱数据。解释这些数据的主要障碍之一是对凝析云的完全理解。通常，来自系外行星大气的数据不够好（而且样本量太小），无法直接确定云的性质。标准技术包括使用网格技术从第一性原理对行星大气进行“正演模拟”。这项工作将使用孤立的年轻褐矮星作为大质量系外行星大气的类似物。该团队将利用光谱反演技术对这一群体的数据进行直接解释。这些褐矮星通常具有与成像的系外行星非常相似的特性：温度、光度、年龄、颜色、光谱特征。然而，它们缺少一颗隐蔽的母星。这使得光谱更容易收集，并允许更大的样本量。该团队将研究一组26个年轻的（5-130迈）孤立的褐矮星，这些褐矮星来自于已经发现并成像的大型系外行星所在的恒星群。他们将使用由团队合作者之一开发的BREWSTER代码来进行光谱反演。这些反演，以及使用BT SETTL代码的经验光谱能量拟合和转发建模，将用于(1)推导和比较基本参数，(2)评估云动力学对源对象的环境，颜色和光谱特征的依赖性，以及(3)检查直接成像的系外行星和系外行星类似物之间的成分变化。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。

Astronomers are beginning to directly image exoplanets and obtain spectroscopic data. One of the chief barriers in interpreting the data is a complete understanding of condensate clouds. Typically, the data from exoplanet atmospheres are not good enough (and the sample size is too small) for direct determination of cloud properties. The standard technique involves 'forward-modeling' of planetary atmospheres from first principles using a grid technique. This work will use isolated, young brown dwarfs as analogs for massive exoplanet atmospheres. The team will use spectral inversion techniques on data from this population to make direct interpretations of brown dwarf atmospheres. These brown dwarfs typically have properties very similar to imaged exoplanets: temperature, luminosity, age, color, spectral features. However, they lack an obscuring parent star. This makes the spectra greatly easier to collect and allows for a much larger sample size.The team will examine a set of 26 young (5-130 Myr) isolated brown dwarfs from the same stellar associations in which large exoplanets have been discovered and imaged. They will use the BREWSTER code, developed by one of the team collaborators, to conduct spectral inversions. These inversions, along with empirical spectral energy fits and forwarding modeling using the BT SETTL code, will be used to (1) derive and compare fundamental parameters, (2) assess the dependence of cloud dynamics on environment, color and spectral features of the source object, and (3) examine compositional variations among directly-imaged exoplanets and exoplanet analogs.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.