Orbits of Milky Way Globular Clusters and Satellite Galaxies

Yale Southern Observatory, Inc., New Haven CT

Investigators

Abstract

AST 0098687 Van Altena With 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. ***