Classification of Red Variables

Red variables are traditionally loosely classified into Mira, semiregular (SR), and slow irregular (L) variables. The Mira variables are the best-defined subgroup, but the SR and L stars are more numerous. The SRs show significant inhomogeneities in their division into SRa (regular variability but smaller pulsation amplitudes than Miras), SRb (less regular variability), SRc (more luminous), and SRd (warmer) variables. Relationships within each group are not clear. To obtain useful P-L relations, and to relate stars to distinct evolutionary states, requires clear classification criteria. We report here on an analysis of longterm AAVSO light curves. We find that Mira-type variables are so clearly different from semiregular variables as to remove all doubt as to their distinction. M-type Miras and C-type Miras are likewise dramatically different in their light curve properties. The M-Miras show a large number of interesting relationships, and appear to form a homogeneous group. The pulsations of SR variables are extremely unstable. Perhaps of greatest interest, most SR variables are multiperiodic, showing two periods P_1 and P_2 whose ratio falls in the narrow range 1.7 =< P_1/P_2 =< 1.95. We are now poised to combine the best available astrometry data with the best available periodicity data.