AAS 195th Meeting, January 2000
Session 46. Space Interferometry Mission
Display, Thursday, January 13, 2000, 9:20am-6:30pm, Grand Hall

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[46.03] The Grid Giant Star Survey for the SIM Astrometric Grid

R.J. Patterson, S.R. Majewski, A. Kundu (UVa), W.E. Kunkel (LCO), K.V. Johnston (Wesleyan U.), D.P. Geisler, W. Gieren, R. Muñoz (U.Concepciòn)

Metal-poor giant stars, by virtue of their luminosity, can probe to greater distances than almost any other stellar type at the same apparent magnitude. This makes them desirable as candidate Space Interferometry Mission (SIM) Astrometric Grid objects, since any astrometric jitter related to dynamical effects (stellar motion, binarity, parallax, planetary systems) will be correspondingly lower for giant stars compared to other stars at the same apparent magnitude. The Grid Giant Star Survey (GGSS) is a patch-work all-sky survey intended to find such stars to satisfy SIM's need for an Astrometric Grid composed of astrometrically stable reference stars at a density of 0.1 deg-2, with V\lesssim12, and spaced no more than 5\circ apart. At present, the GGSS is being conducted with the 1-m Swope Telescope at Las Campanas Observatory, in strips of declination separated by 3\fdg5, from -90\circ < \delta < +20\circ, but we have proposed to survey the remainder of the sky. The GGSS is conducted in two phases: (1) a photometric search for intermediate to metal-poor giants using a specialized set of filters that allow dwarf/giant star separation, and (2) a spectroscopic phase to verify the luminosity class of the giant candidates, obtain abundances, and measure rough radial velocities. Aside from meeting the needs of the SIM Astrometric Grid, the GGSS will yield a scientifically valuable sample of giant star candidates to \gtrsim50 kpc. Thus, the GGSS may be used to address a host of problems relating to Galactic structure and kinematics, especially if SIM provides parallaxes and proper motions for a fraction of them. These include (1) mapping the Galactic rotation curve to 2Ro, and (2) tracing stellar debris streams (from the tidal disruption of satellite bodies), which can then be used to map the shape of the Galactic potential to large R.

We appreciate funding from NASA JPL Grant #AST-1201670.

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