The HI 21-cm Line as a Probe of Stellar Mass-Loss and Evolution

该奖项将支持对一种高度演化的低质量至中等质量星星（称为渐近巨星分支（AGB）星星）包络中的中性氢（HI）进行观测研究。 这类恒星有着非常大的外层包层，并且正在向星际介质中损失质量;它们也是大量尘埃的制造者。 这种恒星的质量损失机制和速率知之甚少，这项研究将测量星周氢的无线电发射和吸收，以探测气体中的条件和运动学。 该项目旨在增进对星周包层的总质量和范围、质量损失的持续时间和几何形状以及行星状星云的形成的了解，预期该项目将增进对演化恒星外层物理条件的了解。 它还将为本科生提供研究机会，这项研究的结果将纳入公共讲座和播客。

This award will support an observational study of neutral hydrogen (HI) in the envelopes of a type of highly-evolved low- to intermediate-mass star known as an asymptotic giant branch (AGB) star. Such stars have very large outer envelopes and are losing mass into the interstellar medium; they also are copious producers of dust. The mechanism and rates of mass loss in such stars are poorly known, and this study will measure radio emission and absorption in the circumstellar hydrogen to probe the conditions and kinematics in the gas. The project aims for an improved knowledge of the total mass and extent of circumstellar envelopes, of the duration and geometry of mass loss, and of the formation of planetary nebulae.The project is expected to provide improved understanding of the physical conditions in the outer layers of evolved stars. It will also provide research opportunities for undergraduates, and the results from this study will be incorporated into public lectures and podcasts.