10971(  1) - 04/03/06 11:16  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10971

Version: 1    Check-in Time: 03-Apr-2006 15:16:16

Title
The Proper Motion of the Sagittarius Dwarf Spheroidal Galaxy
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Type             Cycle     Parallel Pointing Tolerance
AR               15        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Slawomir Stanislaw Piatek     New Jersey Institute of Technology
   CoI: Dr. Carlton P. Pryor              Rutgers the State University of New Jersey    N
   CoI: Dr. Edward W. Olszewski           University of Arizona                         N

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Abstract

We propose to measure the proper motion for the Sagittarius dwarf spheroidal galaxy
using archival WFPC2 images for three fields, each with three epochs covering a time
baseline of four years. The relative proper motion of Sagittarius with respect to
the mean motion of bulge stars will have an accuracy of 0.1 mas/yr. The absolute
proper motion with respect to galaxies in the fields will have an accuracy of no
worse than 0.9 mas/yr and most likely better -- approaching the 0.2 mas/yr accuracy
of the best ground-based measurement. Our measurement will provide an independent
check of the ground-based measurement and better determine the Galactic orbit of
Sagittarius. The latter will help to determine, for example, the evolution of the
orbit with time, the relation of the orbit to the star-formation history of
Sagittarius, and the shape of the Galactic dark-matter halo.
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