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Astron. Astrophys. 331, 1119-1129 (1998)

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The Hipparcos proper motion link to the extragalactic reference system using NPM and SPM *

I. Platais 1, V. Kozhurina-Platais 1, T.M. Girard 1, W.F. van Altena 1, C.E. López 2, R.B. Hanson 3, A.R. Klemola 3, B.F. Jones 3, H.T. MacGillivray 4, D.J. Yentis 5, J. Kovalevsky 6 and L. Lindegren 7

1 Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101, USA
2 Felix Aguilar Observatory and Yale Southern Observatory, San Juan, Argentina
3 UCO/Lick Observatory, University of California, Santa Cruz, CA 95064, USA
4 Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
5 Department of the Navy, Naval Research Laboratory, Washington, DC 20375, USA
6 CERGA, Observatoire de la Côte d'Azur, Avenue Copernic, F-06130 Grasse, France
7 Lund Observatory, Box 43, S-22100 Lund, Sweden

Received 13 August 1997 / Accepted 11 November 1997


We describe the use of the Lick Northern Proper Motion (NPM) program and its southern-sky complement, the Yale/San Juan Southern Proper Motion (SPM) program, to determine the Hipparcos proper motion link to the extragalactic reference system defined by galaxies. In total [FORMULA] 9,100 Hipparcos stars were chosen for the NPM link solution and [FORMULA] 4,100 for the SPM solution. The typical accuracy of the NPM absolute proper motions is 5 mas yr-1. For the SPM proper motions it varies from 2 to 4 mas yr-1. The link solutions indicate a presence of magnitude equation in both the NPM and SPM. In the case of the NPM three different approaches (i.e., introducing a magnitude cutoff, additional linear magnitude terms, and including a fictitious zone of avoidance) were examined to alleviate the magnitude equation problem. The SPM proper motions show a notable correlation between the postfit residuals and the size of the magnitude equation correction applied. It is quite likely that galaxies have a magnitude equation different from that affecting the stellar images. We note an improvement in the spin solution with re-calibrated galaxy magnitudes and, subsequently, changed magnitude-equation corrections for the galaxies.

Key words: astrometry – catalogs – reference systems – methods: data analysis

* Based on observations made with the ESA Hipparcos satellite

Send offprint requests to: I. Platais

© European Southern Observatory (ESO) 1998

Online publication: March 3, 1998