3.5
Contribution of the Bordeaux CCD meridian circle to modern astrometry
Bruno Viateau, Yves Réquième, J. François Le Campion, Guy Montignac, Jean-Marie Mazurier, Bordeaux
Complete text (abstract only):
A first CCD 512 × 512 camera with a 19 µm pixel size working in scan mode (declination field 14') was mounted in 1994 on the Bordeaux CCD meridian circle. After a testing period, this camera was installed on the Valinhos CCD meridian circle (near Sao Paulo, Brazil), as part of a collaboration between Bordeaux Observatory and the Instituto Astronomico e Geofisico of Sao Paulo (see Teixeira et al., 1998). A second improved CCD 1024 × 1024 camera, with a declination field of 28', was installed on the Bordeaux instrument in June 1996. The spectral bandwidth is 520-680 nm. The field to be measured is covered by coincident or overlapping strips (mean length between 30 minutes and 1 hour) scanned during different nights. The extraction of the sky background is made either by fitting a polynomial, or by using a median filter. The search for the photocentre of the objects is made by using a two-dimensional flux distribution. A global iterative reduction procedure, which uses the Gauss-Seidel algorithm, is applied. Use of spline corrections is suggested for modelizing the long-period atmospheric fluctuations. The catalogue of reference stars comprises the Hipparcos Catalogue and the ACT Catalogue (Urban et al. 1998) for those Tycho stars which are not present in the Hipparcos catalogue. The mean internal precision of a single observation is about 0.04 arcsec in both coordinates for 9 V 14. In the same magnitude range, magnitudes can also be obtained with an internal precision of about 0.05 mag. The limiting magnitude is larger than 16.
Among other duties, the Bordeaux CCD meridian circle is being used since January 1997 for completing the Méridien 2000 project, which is a survey during 3 years of the Bordeaux zone of the Astrographic Catalogue (11 < Decl. < 18) so as to build a catalogue of positions and proper motions for stars up to V-magnitude 15 (see Colin et al., 1998). The Bordeaux CCD meridian circle is also used for the observation of solar system objects (outer planets for improving their ephemerides, natural satellites for improving their theories and selected asteroids for mass determination). Most of these programmes are jointly carried out with Valinhos. Among the other programmes running in Bordeaux, regions of the sky near the anticentre of the Galaxy are observed in order to determine accurate positions and proper motions for this zone, which corresponds to a small part of the Méridien 2000 zone (see Odenkirchen et al., 1998). This instrument is also used for photometric studies (study of the variability of selected extragalactic sources jointly with Valinhos, photometric studies in the field around M81). Other programmes, such as the search for variable stars, the realization of astrometric catalogues of clusters, or the observation of a comet for the determination of non-gravitational effects on its orbit are in discussion, and all proposals are welcome.
References
Colin J., et al., 1998, »The Bordeaux Meridian Circle Survey«, this volume, p. 141
Odenkirchen M., Soubiran C., Le Campion J. F., 1998, »Early epoch stellar positions from the Bordeaux Carte du Ciel«, this volume, p. 145
Teixeira R., Benevides-Soares P., et al., 1998, »CCD meridian observations at Valinhos Observatory«, this volume, p. 190
Urban S. E., Corbin T. E., Wycoff G. L., 1998, AJ 115, 2161
Bibliographical details:
Bruno Viateau, Yves Réquième, J. François Le Campion, Guy Montignac, Jean-Marie Mazurier: Contribution of the Bordeaux CCD meridian circle to modern astrometry. In: Peter Brosche, Wolfgang R. Dick, Oliver Schwarz, Roland Wielen (Eds.): The Message of the Angles - Astrometry from 1798 to 1998. Proceedings of the International Spring Meeting of the Astronomische Gesellschaft, Gotha, May 11-15, 1998. (Acta Historica Astronomiae ; 3). Thun ; Frankfurt am Main : Deutsch, 1998, p. 191-192.
