Orbits of Milky Way Globular Clusters and Satellite Galaxies

有了这个奖项，耶鲁南方天文台的William Van Altena博士将确定大约20个银河系球状星团和几个银河系卫星星系的绝对固有运动，从而确定切向速度。切向速度结合测量到的距离和径向速度，以及假设的银河系质量模型，将使Van Altena博士能够计算出它们的轨道，并及时预测它们的轨迹，以研究它们与现有或新发现的残余流的关系。特别是，目标球状星团的分布是这样的，它将为银河系内部提供一个很好的探针，使研究人员能够从运动学上解开它的各种组成部分。在这个为期三年的奖励期内，将确定大麦哲伦云、小麦哲伦云、云间区域、人马座矮星系和众多银河系球状星团的切向速度和星系中心轨道，这些星团位于第一代南方固有运动计划（SPM）板块的赤经和星等限制范围内。绝对固有运动将通过第谷-2恒星锚定到国际天体参考系统（ICRS），这将形成这个固有运动参考系。大多数球状星团的切向速度的预期精度在10到20公里/秒之间，其余的星团和人马座矮球星团的切向速度大约在35公里/秒之间，三个独立的麦哲伦云场的切向速度在70到90公里/秒之间。在计划中的天体测量卫星任务（如FAME和SIM）产生结果之前，通过该合同获得的全部数据应该可以获得。事实上，FAME仪器测量高密度场的能力的局限性，使得它无法接近这些提议的目标。SIM将为大多数（如果不是全部的话）这些目标提供明确的措施，但要到2015年。利用SPM材料，Van Altena博士将在2004年之前提供相当准确的测定结果。在未来的某个日期，当SPM完成时，将有可能将目前正在建设的施密特巡天目录减少到SPM系统中，并使用这些转换后的施密特数据进一步提高切向速度的精度

AST 0098687Van AltenaWith this award Dr. William Van Altena of Yale Southern Observatory will determine the absolute proper motions, and hence tangential velocities, for approximately twenty Galactic globular clusters and several Milky Way satellite galaxies. The tangential velocities in combination with their measured distances and radial velocities, and assumed Galactic mass models, will enable Dr. Van Altena to calculate their orbits and project their trajectories backwards in time to study their association with existing or newly identified remnant streams. In particular, the distribution of target globular clusters is such that it will provide an excellent probe of the inner Galaxy, allowing the researchers to kinematically disentangle its various components.Tangential velocities and Galactocentric orbits will be determined for the Large Magellanic Cloud, the Small Magellanic Cloud, an Intercloud region, the Sagittarius dwarf galaxy, and numerous Galactic globular clusters within the declination and magnitude limits of the first-epoch Southern Proper Motion program (SPM) plates, during this three-year award period. The absolute proper motions will be anchored to the International Celestial Reference System (ICRS), via Tycho-2 stars, which will serve to form this proper- motion reference frame. The anticipated accuracy of the derived tangential velocities ranges from 10 to 20 km/s for the majority of the globular clusters, roughly 35 km/s for the remaining clusters as well as for the Sagittarius dwarf spheroidal, and from 70 to 90 km/s for the three separate Magellanic Cloud fields.The entire set of data obtained with this award should be available prior to the results from planned astrometric satellite missions, such as FAME and SIM. In fact, limitations in the ability of the FAME instrumentation to measure high-density fields, renders most of these proposed targets inaccessible to it. SIM will provide definitive measures for most if not all of these targets, but not until 2015. With the use of the SPM material, Dr. Van Altena will provide reasonably accurate determinations by 2004. At some future date, when the SPM has been completed, it will be possible to reduce the currently under-construction Schmidt sky survey catalogs into the SPM system and use those transformed Schmidt data to improve the accuracy of the tangential velocities further.***