Semiregular variable star

The original definitions of the four main groups were formalised in 1958 at the tenth general assembly of the International Astronomical Union (IAU).

The closely related OSARG (OGLE small amplitude red giant) variables pulsate in an unknown mode.

T Cen is listed as the next-brightest SRa example,[2] but it is suggested that it may actually be an RV Tauri variable, which would make it by far the brightest member of that class.

β Gru is a second magnitude star classified as a slow irregular variable by the GCVS, but reported to be of SRb type by later research.

[2] Most SRS variables have been discovered in deep large-scale surveys, but the naked-eye stars V428 And, AV Ari, and EL Psc are also members.