Irregular variable

Anirregular variableis a type ofvariable starin which variations in brightness show no regularperiodicity.There are two main sub-types of irregular variable: eruptive and pulsating.

Eruptiveirregular variables are divided into three categories:

• Group I variables are split into subgroups IA (spectral types O to A) and IB (spectral types F through M).
• Orion variables,GCVS type IN (irregular and nebulous), indigenous to star-forming regions, may vary by several magnitudes with rapid changes of up to 1 magnitude in 1 to 10 days, are similarly divided by spectral type into subgroups INA and INB, but with the addition of another subgroup, INT, forT Tauri stars,or INT(YY) for YY Orionis stars.
• The third category of eruptive irregulars are the IS stars, which show rapid variations of 0.5 to 1 magnitude in a few hours or days; again, these come in subgroups ISA and ISB.

Pulsatingirregular giants or supergiants, calledslow irregular variables,are all of late spectral types (K, M, C, or S), and classed as type L-LB for giants and LC for supergiants. How many of these are actually semi-regular variables that simply need more study, remains unclear.