Transformation equations and other aids for VRI photometry

Abstract

Transformations among VRI systems are commonly beset by Paschen-jump effects, for which fully satisfactory allowance has not previously been made. This paper describes two new techniques which are based on the work of Gutierrez-Moreno, and which allow fully for the effects of the Paschen jump. Values of E(V-R)/E(B-V) and E(R-I)/E(B-V) are also given for the Cousins system for a wide range of temperatures. These and the new techniques contribute to a set of new transformation relations which apply for most VRI systems; the status of the remaining systems is reviewed, and future work needed for them is described. Two major sources of Cousins VRI data underlie the new relations; the consistency of these sources is reviewed and found to be generally satisfactory, although more work on this question is needed. Finally, three tables of transformed standard-star and other data are given for the Cousins and Johnson systems, and a description of ways to reproduce the latter is presented.