AAVSO: American Association of Variable Star Observers

Long-term Secular Changes in the Period of Mira Stars

Volume 42 number 2 (2014)

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Thomas Karlsson
Almers väg 19, 432 51 Varberg, Sweden; tkn@seaside.se


A possible secular change of the period is investigated for 362 Mira stars. Mean periods and the proportion of stars with increasing and decreasing period were calculated using all available maxima found. The state as it was known in 1938 is compared year by year up until 2013. Analysis of O-C diagrams for the stars shows a rate of change of +6.8 • 10-6 days/day, standard error 3.8 • 10-6. The mean period over 75 years shows an increase by 0.15 day for the investigated stars, and by 2013 58% of them had an increasing period.