Published online by Cambridge University Press: 30 March 2016
(1) Mira variables define the tip of the AGB for low mass stars (cf. Feast and Whitelock 1987 fig. 1).
(2) The kinematics of Mira variables are a function of period (e.g. Feast 1989 and earlier references) and for Miras in globular clusters the period is a function of metallicity (e.g. Feast 1981). Hence the Mira period sequence is not an evolutionary sequence but represents the sequence of AGB tips for stars of different initial mass and/or chemical composition and/or age.
(3) Mira are surrounded by circumstellar dust shells. The mass loss rates are a function of period and light amplitude (Whitelock et al. 1987, Whitelock et al. 1991, Whitelock 1990). The results suggest evolution with increasing pulsation amplitude and mass loss but little change in log P ((2) and (3) do not preclude some (small) change in log P during evolution nor possible phases of decreasing light amplitude and mass loss).