Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...254..397z&link_type=abstract
Astronomy and Astrophysics, Vol.254, NO. FEB(I), P. 397, 1992
Astronomy and Astrophysics
Astrophysics
18
Astrometry, Photographic Astrometry, Photographic Position Catalog, Cpc 2 Catalog, Plate Reduction Techniques
Scientific paper
The Second Cape Photographic Catalog CPC 2, containing positions and visual magnitudes of 276 t 31 stars in the approximate magnitude range V= 6.5-10.5 is the first modern photographic catalog project on the southern hemisphere with an optimal fourfold plate overlap pattern and an astrometrically optimized spectral bandpass in the yellow - red region (530-640 nm).
During the period 1962-1972 a total number of 5820 plates has been taken at Cape Observatory with a newly designed 4-element lens (F:10, f=20O0 mm, 4°.1 × 4°.1 field, scale = 100" mm-1). All plates have two 3 min exposures, shifted by about 50" in declination.
Plate measurement has been accomplished on the GALAXY astrometric measuring machine at RGO Herstmonceux. As a joint effort of RGO and Hamburg Observatories the astrometric data reduction and catalog construction is being performed at Hamburg Observatory whereas the photographic photometry which provided visual magnitudes for all program stars has been carried out entirely at RGO by M. Penston.
Paper I deals with the project and catalog, while a completely independent block adjustment solution will be given in Paper III. This paper (II) describes the astrometric results based on the classical single plate adjustment. The adopted reference star catalog is the Southern Reference Star Catalog SRS, provided by USNO in two versions FK 4/B1950 and FK 5/J2000, together with a preliminary system of proper motions. Plate reductions have been carried out independently with these two catalog versions and results are given in both systems.
For the plate reductions an 8-parameter weighted least squares solution has been adopted, with non orthogonal and plate tilt parameters as common unknowns for both exposures. Weights are based on an adopted constant m.e. of 110 mas for all x, y - measurements and individual catalog accuracies of the reference star positions. A small third order term of optical distortion, has been applied to the x, y - measurements before adjustment. Differential refraction and aberration have been removed from the measurements rigorously using an apparent place computational approach.
From the detailed analysis of the adjustment residuals a small magnitude equation in declination (CPC 2-SRS) has been found in some zones which does not exceed 75 mas in the magnitude range 7-10. No significant color dependent systematic errors were found.
Comparisons with other catalogs as FK 4, FK 5, CAMC 4, Perth 70 and AGK 3 gave no further significant information because these catalogs are inconsistent already on the 100 mas level.
Quality classes have been assigned to the final catalog positions, class 1 contains some 195 600 stars with m.e. =54 mas; class 2 contains some 53 300 stars with m.e. =80 mas and class 3 contains about 27000 stars for identification purposes only, with m.e. ≍ 200 mas. The catalog accuracy is slightly magnitude dependent, the optimal range being 6.5 ≤ V ≤ 9.5.
For the 124000 SAO stars in the catalog, preliminary proper motions have been derived. A final high precision system of proper motions for all catalog stars will be obtained when the results of the recently finished FOCAT-S catalog and the planned new southern hemisphere catalog project of the USNO will be available. Based on these new epoch catalogs and the anticipated results of the HIPPARCOS mission for the first time an optimal, dense system of reference stars for a final reduction of the Astrographic Catalog can be established which will make it possible to determine high precision proper motions (σμ = 2-3 mas yr-1) for some million stars on the southern hemisphere down to magnitude 12 as an unbiased sample for detailed studies of galactic kinematics and dynamics.
de Vegt Ch.
Nicholson W.
Penston Margaret J.
Zacharias Norbert
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