Hypercompact HII Regions: A New Stage of O-star Evolution?

最近对大质量恒星形成区域的射电观测发现了一类新的非常致密的电离氢（HII）气体区域，它们被称为“超致密HII”区域。它们有几个共同的特性，将它们与超紧凑的HII区域和其他热射电源区分开来。例如，它们的电子密度比典型的超紧凑HII区域大100倍，直径比典型的超紧凑HII区域小10倍。此外，它们似乎成对或多个系统出现，并位于大质量恒星形成区。首席研究员推测，超致密区可能代表了从热分子核心的大质量原恒星的快速吸积阶段到吸积结束并形成易于检测的电离氢区阶段的过渡。在这个项目中，PI通过增加样本量，测量它们的特性，以及从高分辨率甚大阵列射电连续体图像中确定双星的表观频率和投影距离，来表征这些超致密区域的特性，以确定它们在大质量原恒星早期演化中的位置。从新的数据和模型中，PI正在获得结构（形态学，直径范围），物理性质（速度结构和电子密度和温度的分布）以及超致密区域的演化状态，从而对大质量恒星形成有更深的了解。更广泛的影响：这个项目是科学领域一个代表性不足的群体的成员的博士论文主题。一些本科生通过参与这个项目，从第一手的观察经验和数据简化分析方法中获得了他们第一次接触基础研究的经验。每年都有许多受欢迎的讲座给学校团体和服务团体。对社会的好处是更好地理解科学是如何工作的，特别是恒星是如何形成的。

AST 0303689PI ChurchwellRecent radio observations of massive star formation regions have discovered what appears to be a new class of very compact regions of ionized hydrogen (HII) gas that have been dubbed "hypercompact HII" regions. They have several common properties that distinguish them from ultracompact HII regions and other thermal radio sources. For example they have electron densities ~100 times larger and diameters ~10 times smaller than typical ultracompact HII regions. In addition, they appear to occur in pairs or multiple systems and are located in massive star formation regions. The Principle Investigator speculates that hypercompact regions may represent the transition from the rapid accretion phase of massive protostars in hot molecular cores to the stage where accretion has terminated and an easily detectable ionized hydrogen region has been formed. In this project the PI is characterizing the properties of these hypercompact regions to determine their niche in the early evolution of massive protostars by increasing the sample size, measuring their properties, and also determining the apparent binary frequency and projected separations from high resolution Very Large Array radio continuum images. From new data plus models, the PI is obtaining the structure (morphology, range of diameters), physical properties (velocity structure and distributions of electron density and temperature), and state of evolution of hypercompact regions and hence developing a deeper understanding of massive star formation.Broader Impacts: This project is the PhD thesis topic of a member of an under-represented group in science. Some undergraduates receive their first experience with basic research from first-hand observing experience and data reduction and analysis methods by working on this project. Numerous popular talks are given each year to school groups and service groups. Benefits to society are a generally better understanding of how science works and specifically how stars are made.