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

该奖项将支持在一种被称为渐近巨支（AGB）星的高度演化的低到中质量恒星外壳中对中性氢（HI）的观测研究。这样的恒星有非常大的外包层，它们的质量正在向星际介质中流失；它们也是大量灰尘的制造者。这类恒星的质量损失机制和速率尚不清楚，本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。该项目旨在提高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形成的认识。该项目有望提高对演化恒星外层物理条件的理解。它还将为本科生提供研究机会，这项研究的结果将被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.