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S. R. Majewski (U. Virginia), J. N. Bahcall (IAS), D. Geisler, W. Gieren (U. Concepcion), E. Grebel (MPIfA), C. Grillmair (IPAC), M. Irwin (Cambridge U.), K. V. Johnston (Wesleyan U.), R. J. Patterson (U. Virginia), I. N. Reid (STScI), D. Spergel, S. Tremaine (Princeton U.)
We plan to undertake fundamental measurements of the gravitational potential (mass distribution) and dynamical structure of the Milky Way using the Space Interferometry Mission (SIM). Among our goals will be:
1. The determination of two fundamental parameters that play a central role in virtually every problem in Galactic astronomy, namely (a) the solar distance to the center of the Milky Way (b) the solar angular velocity around the Galactic center
2. The measurement of fundamental dynamical properties of the Milky Way, among them (a) the pattern speed of the central bar (b) the rotation field and velocity-dispersion tensor in the disk (c) the kinematics (mean rotational velocity and velocity dispersion tensor) of the halo as a function of position
3. The definition of the mass distribution of the Galaxy, which is dominated by the presence of dark matter. We intend to measure (a) the relative contribution of the disk and halo to the gravitational potential (b) local volume and surface mass density of the disk (c) the shape, mass and extent of the dark halo of the Milky Way out to 250 kpc
We will take advantage of the data already being obtained for sub-solar metallicity K giants in the SIM Astrometric Grid. These data will be supplemented by SIM observations of other targets, among them: (1) counterparts to the Astrometric Grid stars at greater distances,(2) a sample of disk Mira and Cepheid variables, (3) a sample of disk open clusters with a well-defined and restricted age range, (4) the brightest few stars in every Galactic globular cluster and satellite dwarf galaxy, and (5) stars in tidal tails of disrupted satellite galaxies and globular clusters.
In addition, we intend to address the wealth of information these data will yield on Galactic stellar populations and the insight they will provide into the formation history of the Milky Way. Therefore, we intend to supplement the astrometric data with ground-based observations of abundances, radial velocities, and other properties, to maximize the benefits of the SIM data for analyses of stellar populations.
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