NSV 19431 and YY Centauri--Two Mira Variables

Volume 38 number 1 (2010)

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Peter F. Williams

3 McAuley Close, Heathcote NSW 2233, Australia;

Abstract

Visual observations of NSV 19431 and YY Cen spanning the twenty- eight years 1980 through 2007 are discussed. These show NSV 19431 is a Mira star of mean period of 298.1 days and visual brightness range of 10.8 to fainter than 15.0. Elements for determining the dates of maximum brightness are JD 2447700 ± 298.1 days (±10 days). The O–C diagram shows what appear to be random cycle- to-cycle fluctuations with a current mean cycle of 298.1 days, evident from the maximum of JD 2447700 (1989). 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.