The period shortening of RY Sagittarii

Using 10,000 visual estimates taken from the literature and obtained between 1897 and 1977, the 39-day period, 0.6-mag amplitude cycle of RY Sgr is analyzed. 2800 averages were made with these estimates and 460 dates of maxima and an equal number of minima were determined. A secular period change is found analyzing these dates. In the time interval studied the period change is from 39.4 to 38.2 days. Superimposed on this variation is a sinusoidal phase change suggesting a periodicity of about half a century. On top of these two phenomena there are phase shifts of about 10 days that happen rather randomly. These phase shifts seem to be associated with the deep minima of this R CrB-type variable. The meaning of the secular period change is discussed and alternatively explained as mass loss or rapid evolution changes. A possible explanation of the random phase shifts is given.