NSV 19431 and YY Centauri—Two Mira Variables
Peter F. Williams
Received September 28, 2009; revised February 22, 2010; accepted February 22, 2010
YY Cen is a Mira star of mean period 371.3 days and brightness range 10.6 to fainter than 15.0. On at least three occasions during this twenty-eight years YY Cen has experienced individual cycles that are significantly longer or shorter than the 371.3-day mean period. Subsequent cycles remain close to the mean period but there is a resulting clear shift in the O–C values. Elements for predicting the dates of maximum brightness are JD2446897 ± 371.3 days (±10 days), but they should be treated with some caution due to the random instances of long/short cycles observed thus far and which may prove to be a long term characteristic of YY Cen.