Galaxies as references in construction of star catalogues

Abstract

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Galaxies as references in construction of star catalogues Vasilevskis, S. Abstract There are two distinct groups of users of star catalogues: (1) those primarily interested in stellar positions, and (2) those mainly interested in proper motions. Celestial mechanics and geodesy are the principal representatives of fields with a need of precise stellar positions as references. Proper motions serve only for reduction of positions to a desired epoch, and they must be known to a sufficiently small angular value per annum. Systematic errors, for example due to an error in adopted value for precession, are of no interest as long as the sum of all the quantities used for re- duction of position gives a system consistent with the laws of celestial mechanics. In stellar astronomy, on the other hand, "pure" proper motions of high precision must be known, i.e., those which are caused only by space velocities of the sun and of stars. Consequently, the proper motions given in star catalogues must be corrected for systematic errors of constants used in reduction of meridian circle observations, mainly of precession. This fact and the need of data for faint stars not given in catalogues have led to programs designed specially for problems in stellar astronomy, namely, determination of stellar proper motions with reference to galaxies. Only approximate positions are needed in the problem of stellar astronomy. The time is approaching when the proper motions with reference to galaxies will start to become available and it seems not too early to discuss the possible relationship of these proper motions to the star catalogues based on meridian observations. It is obvious that these proper motions cannot be used in catalogues without changing the adopted values of some astronomical constants, mainly of precession. This change would in- convenience greatly the comparison of positions observed at various epochs and it would also create a hybrid system which may be less satisfactory than two distinctly different systems, one consistent in the field of celestial mechanics and the other one in stellar dynamics. Investigations of differences between two systems may lead to new information; a forced combination of both would be a compromise without a strong justifi- cation. The considerations above indicate that two independent systems of proper motions may exist in the future. Common stars for both types of sources will permit correlating both systems and reducing proper motions from one to another as needed, without disturbing either system. Publication: The Astronomical Journal Pub Date: June 1967 DOI: 10.1086/110274 Bibcode: 1967AJ.....72..583V full text sources ADS |