New observations of RV Tau stars.

New photoelectric and spectroscopic observations of RV Tauri stars have been obtained, and mean visual magnitudes and characteristics of the light and color curves have been derived. Most RV Tauri stars show rather irregular light curves, with successive cycles showing deviations up to several tenths of a magnitude. An analysis of the color excesses in (V - R) indicates the existence of reddening due to circumstellar material. Revised periods are suggested in a number of cases. Attempts were made to determine absolute magnitudes of RV Tauri stars by the following methods: (i) globular-cluster RV Tauri stars; (ii) mean secular and statistical parallaxes; (iii) the application of Wesselink's method (which was unsuccessful); and (iv) luminosity classification spectrograms. A period-luminosity relation is evident. Absolute magnitude methods which depend on observations of apparent magnitudes yield results averaging about 1.5 mag fainter than those methods based on other arguments. This difference is attributed to mostly nonselective absorption in circumstellar material and leads to visual absolute magnitudes of -5 to -6 inside the circumstellar shells. Subject headings: circumstellar shells - luminosities - RY Tauri stars