2000A&A...353..264M

Analysis of visual observations of the Mira-type variable star S Sex showed that the period of pulsation has decreased strongly since 1984 from 264.8 days to 249.4 days. The cycle length variations were tested by the method of contingency tables and by the span test, so that random or accumulative errors in the period variation were excluded. Our results are in good agreement with the theoretical models that suggest period decreases due to a flash in the helium-burning shell. The great rate of period change shown by S Sex suggests that this Mira star may now be in an immediate post primary helium-shell flash state.