Probing the Milky Way Disk with Massive Stars

银河系的生死取决于它们的星星的形成。 银河系，像我们的银河系一样，富含星际气体和尘埃云。 引力使一些星际云坍缩并形成恒星。 形成的最大、最亮、最热、质量最大的恒星被称为“OB星”。“OB星在它们的诞生地被看到，因为在它们短暂的生命期内，它们没有时间远离它们形成的坍塌的星际云。 这些OB星发出的光能量足以形成“HII区”。“HII区域是完全电离气体的热气泡，围绕着它们的母OB星。 OB星星的形成和随之而来的HII区主要局限于星系的旋臂中。 HII区域是银河螺旋结构的示踪物。与Haystack天文台和绿色银行天文台（GBO）的合作将为波士顿大学本科生带来射电天文学的兴奋，并在绿色银行为9年级男女学生举办的物理学下一代（PING）夏令营中提供导师。 PING是GBO和美国国家黑人物理学家协会的合作项目，OB星星化学丰度表明了星际气体的现状，揭示了许多恒星世代核处理导致的元素富集。 因此，它们为数十亿年的银河系化学演化（GCE）提供了独特而重要的示踪剂。 南部HII区域发现调查（SHRDS）将使用澳大利亚望远镜紧凑阵列来寻找数百个迄今未知的HII区域。 SHRDS将成功的绿色银行望远镜和阿雷西博HRDS项目扩展到南半球的天空;从北方半球无法观察到近一半的银河系圆盘。 SHRDS将改善银河系HII区域的人口普查，该区域是银河系盘中最大的未探索部分，螺旋臂和银河棒的位置尤其不确定。 它将给出第一张完整的大质量恒星在整个银河系盘中形成的地图。 这张地图将允许详细分析银河系中OB-恒星形成点的整体结构以及HII区域的物理性质如何在整个磁盘上发生变化。通过检测来自候选HII区域目标的射电复合线（RRL）辐射，发现新的银河系HII区域。这些目标是通过比较来自现有天空调查的红外和无线电连续图像来识别的。 通过比较远红外线和无线电连续测量数据，得出了银河系中大约2 000个HII候选区域的清单。 需要RRL光谱确认来证明候选者是H II区域并给出其速度。 复合线给出了星云的运动学距离和电子温度。 总之，这些允许推导的电离恒星和重元素丰度，金属丰度，HII区气体的属性。 HII区域金属丰度的银河尺度地图可以为GCE和银河系的合并历史提供信息。 该项目将实现分布在整个银河系盘的源的面密度，可以显示金属富集（或耗尽）的局部区域。 这将为合并提供证据，从而为银河系考古学的研究增加了一个新的工具。

Galaxies live and die by their star formation. Galaxies, like our Milky Way, are rich in interstellar gas and dust clouds. Gravity causes some interstellar clouds to collapse and form stars. The largest, brightest, hottest, and most massive stars that form are called "OB stars." OB stars are seen at their birthplaces because in their short lifetimes they do not have time to move very far from the collapsing interstellar clouds from which they formed. The light from these OB stars is energetic enough to create "HII Regions." HII regions are hot bubbles of fully ionized gas that surround their parent OB stars. OB star formation and the HII regions that go with it are mostly confined to the spiral arms of galaxies. HII regions are tracers of Galactic spiral structure.Collaborations with Haystack Observatory and Green Bank Observatory (GBO) will bring the excitement of radio astronomy to Boston University undergraduates and provide mentors at the Physics Inspiring the Next Generation (PING) Summer Camp for 9th grade girls and boys held at Green Bank. PING is a collaboration between GBO and the National Society of Black Physicists.The OB star chemical abundances indicate the present state of the interstellar gas and reveal the elemental enrichment caused by the nuclear processing of many stellar generations. They thus provide unique and important tracers of billions of years of Galactic chemical evolution (GCE). The Southern HII Region Discovery Survey (SHRDS) will use the Australian Telescope Compact Array to find hundreds of heretofore unknown HII regions. The SHRDS extends the successful Green Bank Telescope and Arecibo HRDS projects to the Southern sky; nearly half of the Milky Way disk cannot be observed from the Northern Hemisphere. The SHRDS will improve the Galactic HII region census in the largest unexplored part of the Milky Way disk where the location of the spiral arms and the galactic bar is especially uncertain. It will give the first complete map of where massive stars are forming in the entire Milky Way disk. This map will allow a detailed analysis of the overall structure of OB-star formation sites in the Milky Way and how the physical properties of HII regions change across the disk.New Galactic HII regions are discovered by detecting radio recombination line (RRL) radiation from candidate HII region targets. These targets are identified by comparing infrared and radio continuum images from existing surveys of the sky. Comparing far-IR and radio continuum survey data leads to a list of some 2,000 candidate HII regions in the Galaxy. RRL spectroscopic confirmation is needed to prove that a candidate is an H II region and to give its velocity. The recombination lines give kinematic distances and electron temperatures for the nebulae. Together, these allow derivation of the properties of the ionizing stars and the heavy element abundances, the metallicities, of the HII region gas. A Galactic scale map of HII region metallicities can inform both GCE and the merger history of the Milky Way. This project will achieve an areal density of sources, distributed throughout the Galactic disk, that can show local zones of metal enrichment (or depletion). This would provide evidence for mergers, thus adding a new tool for the study of Galactic archaeology.