Probing the Milky Way Disk with Massive Stars

星系的生死取决于恒星的形成。星系，比如我们的银河系，富含星际气体和尘埃云。重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星之所以出现在它们的诞生地，是因为在它们短暂的生命中，它们没有时间远离形成它们的坍缩星际云。这些OB星发出的光能量足以形成“HII区域”。HII区域是围绕其母星OB的完全电离气体的热气泡。OB恒星的形成和与之相伴的HII区域大多局限于星系的旋臂。HII区域是银河系螺旋结构的示踪剂。与干草堆天文台和绿岸天文台（GBO）的合作将为波士顿大学的本科生带来射电天文学的兴奋，并为在绿岸举行的九年级女孩和男孩的物理激励下一代（PING）夏令营提供导师。PING是GBO和全国黑人物理学家协会的合作项目。OB星的化学丰度表明了星际气体的现状，并揭示了许多恒星世代的核处理所引起的元素富集。因此，它们提供了数十亿年银河系化学演化（GCE）的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将成功的格林班克望远镜和阿雷西博HRDS项目扩展到南方天空；银河系近一半的圆盘都无法从北半球观测到。SHRDS将改善银河系HII区域的人口普查，在银河系盘中最大的未探索部分，螺旋臂和星系棒的位置尤其不确定。它将首次给出整个银河系中大质量恒星形成位置的完整地图。这张地图将允许详细分析银河系中ob星形成地点的整体结构，以及HII区域的物理性质如何在磁盘上变化。新的银河系HII区域是通过探测来自候选HII区域目标的无线电重组线（RRL）辐射发现的。这些目标是通过比较来自现有天空调查的红外和射电连续图像来确定的。比较远红外和射电连续体的调查数据可以得出银河系中大约2000个候选HII区域。RRL光谱确认需要证明一个候选者是一个H II区，并给出它的速度。重组线给出了星云的运动距离和电子温度。总之，这些可以推导出电离恒星的性质和HII区域气体的重元素丰度，金属丰度。HII区域金属丰度的银河系比例尺图可以告知GCE和银河系的合并历史。该项目将获得分布在整个银盘上的源的面密度，可以显示金属富集（或枯竭）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一个新工具。

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.