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

最近对大质量恒星形成区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，这些区域被称为“超致密HII”区域。它们有几个共同的性质，使它们有别于超致密的HII区域和其他热射电源。例如，它们的电子密度比典型的超致密HII区大100倍，直径小10倍。此外，它们似乎成对或多个系统发生，并位于大质量恒星形成区域。原理调查者推测，超致密区域可能代表着从热分子核中大质量原恒星的快速吸积阶段过渡到吸积终止并形成了容易探测到的电离氢区的阶段。在这个项目中，PI正在表征这些超致密区域的属性，以通过增加样本大小、测量它们的属性以及从高分辨率甚大阵列射电连续图像中确定视二进制频率和投影分离来确定它们在大质量原恒星早期演化中的利基位置。从新的DATA PLUS模型中，PI正在获得超致密区域的结构(形态、直径范围)、物理性质(速度结构、电子密度和温度分布)以及演化状态，从而加深对大质量恒星形成的理解。广泛影响：该项目是科学中一个代表性不足的小组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整理和分析方法中获得了他们的第一次基础研究经验。每年都会为学校团体和服务团体举办许多受欢迎的讲座。对社会的好处是，总体上更好地理解了科学是如何工作的，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.