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Astron. Astrophys. 325, 457-472 (1997)

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A UBV / variability / proper motion QSO survey from Schmidt plates

I. Method and success rate

R.-D. Scholz 1, 2, H. Meusinger 3 and M. Irwin 4

1 WIP Astronomie/Universität Potsdam, Sternwarte Babelsberg, An der Sternwarte 16, D-14482 Potsdam, Germany
2 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany,
3 Thüringer Landessternwarte Tautenburg, D-07778 Tautenburg, Germany
4 Royal Greenwich Observatory, Madingley Road, Cambridge CB3 OEZ, UK

Received 5 February 1997 / Accepted 26 March 1997

Abstract

We describe the first combined variability-proper motion survey for QSOs on Schmidt plates. 85 Tautenburg Schmidt plates covering about 9 square degrees near the north Galactic pole were digitised by means of the APM facility in Cambridge. Variability indices have been derived from U and B data, both with a time-baseline of three decades. Structure function analysis has been applied to search for long-term variability. An almost complete set of proper motions were obtained to a mean B [FORMULA] 20 with a mean error of about 2.0 mas/yr for [FORMULA]. Adopting a limiting (completeness) magnitude of [FORMULA] the success rate of the survey is estimated to [FORMULA] per cent. The completeness of the QSO sample detected by this survey is expected to about 90 per cent. The final sample contains 168 QSO candidates; only one has a radio counterpart. The variability-proper motion survey is compared with the selection based on the two-colour index diagram.

Key words: quasars: general – galaxies: photometry – stars: variables: other – astrometry – methods: statistical – surveys

Send offprint requests to: R.-D. Scholz

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998

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