Long-term Secular Changes in the Period of Mira Stars
Almers väg 19, 432 51 Varberg, Sweden
Received June 3, 2014; revised October 8, 2014; accepted October 24, 2014
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.