An ultraviolet and visible spectroscopic study of a pulsational cycle of RY Sagittarii

Geoffrey C. Clayton, University of Colorado Boulder
W. A. Lawson, University of New South Wales at Australian Defence Force Academy
P. L. Cottrell, University of Canterbury Mount John Observatory
Barbara A. Whitney, Harvard-Smithsonian Center for Astrophysics
S. Adam Stanford, Infrared Processing & Analysis Center
Frank De Ruyter, University of Canterbury Mount John Observatory


High-dispersion visible and ultraviolet spectra and UBVRI photometry, covering a complete pulsation of the R Coronae Borealis star RY Sgr, have been obtained. The UV spectra were the first high-dispersion data ever obtained for the star. Together these observations comprise the most complete data set covering an RCB star pulsation cycle. The cycle observed was somewhat anomalous as it was affected by a second 55 day pulsation period as well as the primary 38 day period. Howevever, the visible spectra showed the typical line splitting and radial velocity variations which have been observed previously. The simultaneous UV spectra showed much smaller, and phase-shifted, velocity variations than those seen in the visible. No evidence was seen of shock-induced emission at Mg II. These observations provide some support for the models of pulsating hydrogen deficient stars developed by Saio & Wheeler.