DDA2001, April2001
Session 3. Astrometry
Monday, 4:00-5:20pm

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[3.01] Preliminary SPM catalog of positions in the Southern Hemisphere

I. Platais (USRA), T.M. Girard, W.F. van Altena (Yale U.), D.G. Monet (USNO, Flagstaff), S.E. Urban, G.L. Wycoff, N. Zacharias (USNO, Washington DC)

We present a preliminary catalog of the Southern Proper Motion program (SPM) first-epoch positions containing over 30 million stars. The goal of this work is to provide precise positions at the mean epoch of ~970 in support of the UCAC, and any other large catalog requiring earlier epoch positions for proper motions. The catalog covers about 80% of the Southern Hemisphere, approximately coincident with the UCAC1 catalog (Zacharias et. al (2000) - AJ, {\bf120}, 2131) and has the same limiting magnitude as UCAC. We have used both blue and visual sets of the SPM plates, which have been digitized at the USNO Flagstaff station using the Precision Measuring Machine. We discuss the reduction process of the measurements, attained precision, systematic errors, and other features of the catalog. External comparisons of positions are available only for the stars brighter than V=12.

We have also combined the SPM and UCAC positions to obtain proper motions. It is estimated that an average 30-yr epoch difference between the UCAC and SPM positions can provide absolute proper motions with a standard error of 4 mas yr-1, down to V=15. Some nearby open clusters are used to estimate the external accuracy of the proper motions and, hence, to get an indirect verification of positional accuracy for the fainter stars. Conversely, these proper motions allow us to identify previously unknown members of the open clusters.

The author(s) of this abstract have provided an email address for comments about the abstract: imants@usno.navy.mil

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