Slow irregular variableA slow irregular variable (ascribed the GCVS types L, LB and LC) is a variable star that exhibit no or very poorly defined periodicity in their slowly changing light emissions. These stars have often been little-studied, and once more is learnt about them, they are reclassified into other categories such as semiregular variables. NomenclatureIrregular variable stars were first given acronyms based on the letter "I": Ia, Ib. and Ic.[1] These were later refined so that the I codes were used "nebular" or "rapidly irregular" variable stars such as T Tauri and Orion variables. The remaining irregular stars, cool slowly varying giants and supergiants of type Ib or Ic were reassigned to Lb and Lc.[2] When the General Catalogue of Variable Stars standardised its acronyms to be all uppercase, the codes LB and LC were used.[3] Type LbSlow irregular variables of late spectral types (K, M, C, S); as a rule, they are giants[3] The GCVS also claims to give this type to slow irregular red variables where the luminosity or spectral type is not known, although it also uses the type L for slow irregular red stars where the spectral type or luminosity is unclear. The K5 star CO Cygni is given as a representative example.[3] Type LcIrregular variable supergiants of late spectral types having amplitudes of about 1 mag in V[3] The M2 supergiant TZ Cassiopeiae is given as a representative example.[3] List
Other irregular variablesThere are a number of other types of variable stars lacking clearly detectable periods, and which are sometimes referred to as irregular variables:[4]
In addition, many types of eruptive or cataclysmic variable are highly unpredictable.[4] References
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