Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998dda....30.0202u&link_type=abstract
American Astronomical Society, DDA meeting #30, #02.02; Bulletin of the American Astronomical Society, Vol. 30, p.1140
Astronomy and Astrophysics
Astronomy
Scientific paper
The Space Interferometry Mission will be the first spatial long-baseline optical interferometer in space. SIM, scheduled to launch in 2005, is designed to perform wide-angle astrometry with 4 mu arcsec precision on objects as faint as V = 20, using a 10-meter baseline. This level of precision will allow SIM to measure stellar parallax distances to 10% and transverse velocities to 200 m/s, out to the far side of the Galaxy. SIM will also perform synthesis imaging and interferometric nulling. Among the many outstanding problems in Galactic dynamics that accurate astrometry can address are: (1) Looking for perturbations to stellar motion due to density enhancement by measuring kinematics of a sample of stars near a spiral arm; the presence or absence of such a perturbation pointing towards the density-wave or self-propagating star formation theories of spiral arm formation. (2) Providing substantially improved distances to out-of-plane K giants used in determining the surface density of the Galactic disk in the solar neighborhood; and the K_z-force law. (3) Extending the Galactic rotation curve outside the solar circle by accurately measuring the distances and proper motion of early-type stars towards the anticenter. (4) Determining 3-D velocity dispersions for halo K giants in order to discriminate between a change in the orbital structure of the Galaxy in the outer halo, or a decrease in the halo's mass density. (5) Probing the density and kinematics of dark matter, via astrometry of MACHOs; with global astrometry, SIM can directly measure lens masses, distances, and transverse velocities.
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