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Session 108 - The Galactic Stellar Disk & Halo.
Display session, Saturday, January 10
Exhibit Hall,
Results of the Yale/San Juan Southern Proper Motion program (SPM) are presented for an extended region around the South Galactic Pole. The SPM yields absolute proper motions, positions, and B,V photographic photometry for stars in the magnitude range 5 < V < 18. The proper motions are measured relative to external galaxies and the positions are on the system of the ICRS via the Hipparcos/Tycho catalog.
A key feature of the SPM plate material is the use of an objective grating in conjunction with two exposures of different duration. This not only produces measureable images of both galaxies and bright reference stars, but just as importantly, provides a means of correcting each individual plate for the effects of magnitude equation. Indeed, this internal method of magnitude-equation correction proves superior, in the case of the SPM, to a direct calibration using the Tycho catalog.
Measurements and reductions are complete for 30 fields, \sim 700 square degrees, surrounding the South Galactic Pole (SGP). This Catalog is now avaliable. Tests indicate the precision of the derived proper motions ranges from 1 to 4 mas yr^-1, depending on the number of measurable images per individual star. The uncertainty in the correction to absolute proper motion is approximately 1 mas yr^-1 per field. In addition to the SGP data, over one hundred other SPM fields have been measured and reduced. These data will be available shortly. In total, the SPM data provide, among other things; i) an observational data set with which to constrain models of Galactic structure and kinematics, ii) a dense, faint reference frame of astrometric utility, (e.g., for deep, narrow-field (CCD) astrometry, or multi-object spectrograph positioning), and iii) a means of direct magnitude-equation calibration of deep Schmidt-plate surveys currently underway.
