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Quick Technical Facts
The SIM Lite Astrometric Observatory will open up many areas of astrophysics, via astrometry with unprecedented accuracy. Distances to stars can be determined to an accuracy of 1% out to about 1000 light years, and to 10% across the Milky Way galaxy.
SIM Lite is designed as a space-based 6-m baseline optical Michelson interferometer operating in the visible waveband. Over a narrow field of view (1°), SIM will achieve an accuracy of 1 µas in a single measurement. In this mode, SIM will search for planetary companions to nearby stars, by detecting the astrometric 'wobble' relative to nearby reference stars. The distances and masses of the rarest hot, bright stars and the common but coolest and faintest red dwarf stars can be uniquely determined with this accuracy by SIM Lite. They will be used with measurements of the star’s brightness to determine their luminosities, with application to testing theories of stellar processes to unprecedented accuracy. The proper motion of stars (across the sky) can be measured in the Andromeda Galaxy.
For targets separated by larger angles SIM has the goal to reach 4 micro-arcsecond precision in absolute position measurements at the end of the 5-year mission. These wide-angle measurements will be made relative to an astrometric grid of reference stars covering the entire sky. The astrometric grid is constructed from repeated relative measurements of the separation of stars within overlapping "tiles." Each tile has a diameter of 15 degrees and represents the area of the sky accessible to SIM by repointing the optics without changing the orientation of the spacecraft. Studies of the motions and distances of Milky Way stars with this precision permits investigations of the quantity and distribution of dark matter in the Milky Way and Local Group of galaxies, the mass spectrum of the Milky Way, and the ages of stars and clusters (with application to distant galaxies). Observations of quasars will unveil the source of their variability.
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