Composition of Stars in the Galactic Bulge and Inner Disk

银河系凸起/棒状星系的起源和化学演化仍然是一个未解决的问题。凸起径向速度测定（BRAVA）发现，恒星穿过凸起的径向速度与n体棒模型一致。然而，在相同的体积上，可以观察到恒星化学成分的梯度。如果条形图是通过一个纯粹的动态过程产生的，那么就不应该存在丰度梯度。也许这个凸起是一个伪凸起，有很长的形成历史，但从它的关闭年龄和恒星丰度比的证据来看，它是一个形成早、形成快的旧凸起。现在有几项研究表明，这个凸起由不同年龄、金属丰度、运动和空间范围的多个恒星亚群组成。关于凸起中恒星的丰度和运动是否相关，研究仍然存在分歧。还有一种可能性是，大质量原星系团的解体形成了银河系凸起。在过去的几年里，对高度放大的透镜状凸起亚矮星进行的高分辨率光谱分析显示，似乎有一个富含金属的恒星群，年龄为2-7 Gyr，比从彩色星等图分析中推断出的凸起场群要年轻得多。最近的两项光谱研究也表明，这个凸起与厚圆盘相似，甚至可能是厚圆盘的一部分。尽管在银河纬度低于8度的地方没有“经典”凸起的运动学证据，但红外彩色星等图和一些光谱研究发现了在高纬度星系存在类似凸起的星系群的证据。里奇博士和他的合作者对内部凸起和凸起球状星团的重元素进行了调查，以确保凸起与厚盘或光晕之间的联系。比较星团恒星和星场恒星的组成，有助于确定凸起是否由解体的球状星团形成。这项工作的另一部分是对星系纬度在20度以上的红巨星进行高色散光谱分析，以评估这个群体的形成历史是否与内部凸起的形成历史不同。研究成果通过评审论文、学术讨论会、科学会议和公开讲座传播。

The origin and chemical evolution of the Galactic bulge/bar remains an unsolved problem. The Bulge Radial Velocity Assay (BRAVA) has found that the radial velocities of stars across the bulge are consistent with an N-body bar model. Yet over the same volume, a gradient in the chemical composition of stars is observed. If the bar was created via a purely dynamical process, no abundance gradient should be present. Maybe the bulge is a pseudo-bulge, and has an extended formation history, but evidence from both the turnoff age and abundance ratios of stars in the bulge are consistent with an old bulge that formed early and rapidly. Several studies now suggest that the bulge consists of multiple stellar subpopulations of differing age, metallicity, kinematics, and spatial extent. Studies continue to disagree on whether the abundances and kinematics of stars in the bulge are correlated. There is also the possibility that the disintegration of massive proto-clusters built the Galactic bulge. Within the last few years, high resolution spectroscopy of highly magnified, lensed bulge subdwarfs revealed what appears to be a stellar population that is metal rich, and 2-7 Gyr old- considerably younger than is inferred for the bulge field population from the analysis of color-magnitude diagrams. Two recent spectroscopic studies also suggest that the bulge is similar to and perhaps part of, the thick disk. Although there is no kinematic evidence for a 'classical' bulge at galactic latitudes below 8 degrees, infrared color-magnitude diagrams and some spectroscopic studies find evidence for a bulge-like population at high galactic latitude. Dr. Rich and his collaborators conduct a survey of the heavy elements across the inner bulge and bulge globular clusters to securely relate the bulge to the thick disk or the halo. Comparison of the composition of field and globular cluster stars helps to address whether the bulge formed from disintegrated globular clusters. Another part of this work is to undertake high dispersion spectroscopy of red giants at galactic latitudes above 20 degrees to assess whether the formation history of this population differs from that of the inner bulge. The research results are disseminated via refereed papers, colloquia, scientific meetings, and public lectures.