Irregular variable

Irregular variable stars are giants or supergiants with mid to late spectral type and show in contrast to semi-regular variable stars little or no signs of periodic light changes.

Definition

This class is defined as a slow variable stars, in the light of change, at best, minor signs of periodicity are observed. The stars of this group are usually only assigned because the observational material covers a short period of time and / or in comparison to the amplitude has a large scatter. In case of intensive investigation of the light change, the star would be allocated among semi- regular variable stars. In addition to the light curves of the two Mutable classes differ not systematically in other properties.

Subgroups

There are two subgroups of irregular variable stars:

• Lb: Slow irregular stars with late spectral type (K, M, C, S), where it is mostly red giants. This subgroup is also attributed to red variable stars in the General Catalogue of Variable Stars, whose spectral and light changes is not known.
• Lc: irregular light variation of late supergiants with an amplitude of more than 1 like in V. The cause of the irregular light variation large convection cells are accepted. This assumption is supported by the observation that the light curves of the Lc - stars often show a cyclic moiety of low amplitude in addition to the irregular light change.