SRc variable stars
SRa variable stars
Late-type giant stars
SRd variable stars
SRS variable stars
SRb variable stars
Betelgeuse
Semi-regular variable stars
Long period variable stars
Semiregular variable stars
A type of giant or supergiant pulsating variable star, with intermediate or late spectra, showing noticeable periodicity in its light changes, accompanied or sometimes interrupted by various irregularities. Periods lie in the range from 20 to more than 2000 days, while the shapes of the light curve may be rather different and variable with each cycle. The amplitudes may be from several hundredths to several magnitudes (usually 1-2 magnitudes in the V filter). Examples are Betelgeuse, Antares, and Rasalgethi. Semiregular variables are classified in several subtypes: SRA, SRB, SRC, and SRD.