Dr. Casetti and her team will continue work on the Yale/San Juan Southern Proper Motion (SPM) survey, which measures the tiny motions of stars across the sky over multiple decades, to test models for the Milky Way's formation. In the present project they will measure absolute proper motions for stars torn off the Sagittarius dwarf galaxy, for stars in an over-dense region of the sky in the constellation of Canis Major, and for 15 globular star clusters, to determine their orbits around the Galactic center. To improve accuracy, photographic plates taken early in the survey (the first epoch) will be re-measured using the Yale PDS microdensitometer, to improve the precision. Second-epoch CCD observations will be made to cover the Canis Major overdensity and both the leading and trailing tails of the Sagittarius dwarf, and to enlarge the sample of globular clusters. The new observations amount to about 8000 pointings, or 2.5 years observing at El Leoncito observatory with the Cesco double astrograph.
The team will also probe the Milky Way's thick disk by combining their measured proper motions with radial velocities to find all 3 components of a star's motion through space. They will do this for a sample of 1160 red giants near the South Galactic Pole surveyed by a PhD student at the University of Chile, and with measurements of stars at intermediate Galactic latitudes from RAVE, a survey of stellar radial velocities using a telescope in Australia. Comparing these motions to what is predicted by dynamical models, the group will explore the force on these stars perpendicular to the mid-plane of the Milky Way, and hence the degree of flattening in the gravitational potential.
The measured proper motions, positions and photographic photometry for the SPM3.3 catalog with 11 million stars is now available by ftp from Yale's website, and the fourth catalog SPM4 will be released shortly. Undergraduates at the Universities of San Juan, Cordoba and La Plata in Argentina will be trained as they obtain observations for the project. The group provides materials for the very active visitor center at El Leoncito observatory.
This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
