Astrometry with Mirrors and Lenses

Abstract

view Abstract Citations (8) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Astrometry with Mirrors and Lenses Ross, Frank E. Abstract As part of the development work for the proposed 200-inCh reflecting telescope of the California Institute of Technology, a lens has been designed by the writer, to be placed near the focus of the mirror with the object of correcting the large outstanding aberra- tion of coma, which is serious in a mirror of the high speed ratio proposed. A trial lens has been made and applied to the Mount Wilson 6o-inch telescope. The present paper is concerned primarily with the astrometric characteristics of the correcting lens and mirror system, as compared with those of the usual mirror systems, but has developed into a comparative study of all the telescopes available, ten in all. The two types of astrometric problems are outlined: (a) that in which errors of differ- ential co-ordinates are of importance; (b) that in which changes in these errors, from epoch to epoch, are of importance. Problem (b) has been given the more attention, be- cause of its bearing on the determination of the parallaxes and relative proper motions of stars. It is shown that the equalization of magnitudes customarily employed in the determination of relative positions is not so essential as is usually considered to be the case and that accurate relative positions of a field of stars ranging widely in magnitude and in relative position can be obtained with the instruments now used in astrometric problems. It is demonstrated that the correcting lens greatly enlarges the field over which accurate positions can be obtained; for example, with a field of stars io' from the axis the average error in position is reduced by three-fourths (Table VIa). It is also demonstrated that great accuracy may be obtained in the measurement of star images with a diameter as large as 0.90 mm, and that the relative positions in a field of stars ranging over 6 mag. in brightness may be precisely determined-a matter of the great- est importance in connecting the Boss system of proper motions with the motions of faint stars and spiral nebulae. The R-L discordance in the measurement of star images has been given some attention. An attempt to correlate it with space perception gave no correlation and indicates that bisecting a star image is probably a matter of equating magnitudes. I. INTRODUCTIO Publication: The Astrophysical Journal Pub Date: May 1933 DOI: 10.1086/143466 Bibcode: 1933ApJ....77..243R full text sources ADS | Related Materials (1) Reprint: 1933CMWCI.467....1R