AAS 201st Meeting, January, 2003
Session 76. Astronomers and Their Tools
Poster, Wednesday, January 8, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[76.13] Improving History: the re-calibration of POSS I and POSS II using SDSS

B. Sesar, D. Svilkovic (Zagreb University), Z. Ivezic, R.H. Lupton (Princeton University)

We utilize the Sloan Digital Sky Survey Early Data Release to astrometrically and photometrically re-calibrate the Palomar Observatory Sky Survey catalogs (USNO-A2.0 catalog for POSS I, and GSC2.2 catalog for POSS II) in about 300 deg2 of sky. A piecewise re-calibration of the POSSI and POSSII data in 100 arcmin2 patches (SDSS fields) results in photometric errors of 0.15 mag (POSSI O and E bands), and 0.1 mag (POSSII J and F bands), and astrometric errors (rms per coordinate) of 0.16 arcsec (POSSI) and 0.08 arcsec (POSSII), relative to SDSS, or nearly twice as accurate as in the input POSS catalogs. This improvement is mostly due to a very dense grid of calibration stars provided by SDSS, which rectifies the intrinsic inhomogeneities of Schmidt plates.

Using the resulting catalog of point sources observed by both POSS and SDSS, we construct samples of photometrically variable, and of high proper motion, objects. In particular, we discuss long-term (1/2 century) quasar variability, and mean proper motion of various stellar classes selected by SDSS five-color photometry (e.g. white dwarfs, blue thick disk stars, red thin disk stars). The improvement in accuracy is especially important for proper motion studies where it is analogous to extending the baseline from half a century to a century.

The author(s) of this abstract have provided an email address for comments about the abstract: ivezic@astro.princeton.edu

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