Astrometry and Stellar Motions

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Session 38 -- Digitizing the Sky Part II
Oral presentation, Tuesday, 31, 1994, 2:00-5:30

[38.02] Astrometry and Stellar Motions

D. Monet (U.S. Naval Observatory Flagstaff Station)

In these twilight hours of astronomical photography, special efforts must be taken to extract useful information from the photographic archive before the plates degrade and the technology required to measure them disappears. Wide-field astrometry is one area where the photographic archive provides useful information, and will continue to do so for the next decade. The TYCHO catalog provides a dense enough reference catalog so that many of the traditional difficulties involved in removing field distortions from Schmidt or other large field telescopes can be minimized. Therefore, dense star catalogs with errors of a few tenths of an arcsecond can be compiled. Atmospheric turbulence is the dominant source of astrometric uncertainty for short exposure times and large fields of view. This means that the typical CCD survey produces astrometric errors only a factor of two or three smaller than that obtained from photographic plates, and that photographic surveys are still the most accurate way to determine proper motions for large numbers of stars. Many groups are now digitizing and reducing the POSS-I and -II plates, and there are many other plates that could provide useful data. Channels of communication between those needing such databases and those who produce them need to be opened, and potential users should contemplate methods for analyzing catalogs containing astrometric and photometric data for many hundreds of millions of stars.

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