Comparison of ground-based proper motions from meridian observations and Astrographic Catalogue plates with HIPPARCOS proper motions
During the preparation of the Hipparcos Input Catalogue the Bordeaux automatic meridian circle has measured the positions of about 2800 stars in the declination zone -2degto +31deg. These stars concentrate mainly in the visual magnitude range 10mag to 11mag. In this zone the (x,y) measurements of all Astrographic Catalogue (AC) plates have been newly reduced, and at least two independent positions with epochs around 1905 are available for the great majority of the 2800 stars. The proper motions obtained by combining the AC positions with the Bordeaux meridian circle observations (BXAC) have a formal mean error of +/-3mas/yr. A comparison with Luyten's NLTT catalogue allowed the elimination of spurious high proper motions. After the application of additional verifications altogether 2509 new proper motions can be assured with very high probability. As a by-product it turned out that in the corresponding magnitude range the mean errors of the mainly photographically determined NLTT proper motions are in the order of 23mas/yr. Comparison of the BXAC proper motions with the 30-months solution (H30) of the Hipparcos catalogue for 1029 stars in common provides for the first time a reliable and independent assessment of the precision to be expected by combining a new reduction of the fainter stars in the Astrographic Catalogue with modern ground-based observations. The H30 data proved that the accuracy of the BXAC proper motions is on average about 6mas/yr, i.e. a factor of two less accurate than internally determined. This is obviously due to the fact that the adopted errors of the AC positions of fainter objects were underestimated. In addition, it turned out that the systematic deviations of the BXAC proper motions were throughout smaller than +/-4mas/yr.
Astronomy and Astrophysics
- Pub Date:
- December 1995