W Tau Type: SRB AAVSO lightcurve (2020 ) AAVSO lightcurve (index) Semi-regular late-type (M, C, S or Me, Ce, Se) giants with poorly defined periodicity (mean cycles in the range of 20 to 2300 days) or with alternating intervals of periodic and slow irregular changes, and even with light constancy intervals. Every star of this type may usually be assigned a certain mean period (cycle), which is the value given in the catalog. In a number of cases, the simultaneous presence of two or more periods of light variation is observed. AAVSO Legacy Long Period Variable Programme