Variability among M Giants
Víctor Manuel Blanco, L. Plaut · Publications of the Astronomical Society of the Pacific · 1965
In the years 1926 to 1929 Stebbins and Hufïer observed 178 late-type giant stars for light variability.1 On the average, the stars were observed 6 to 7 times throughout this period.Stars were regarded as variable if their brightness showed average deviations from the mean larger than 0"25, twice the deviation expected from observational errors.From their photoelectric data, Stebbins and Hufïer concluded that no red giant "is really constant in light over an interval of a few months or years."Their published measurements may now be subjected to a modern variance ratio test. 2 The results are presented in Table I, the last row of which gives the percentage of variables at the 95% confidence level.