Slow irregular variable


A slow irregular variable 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.

Nomenclature

Irregular variable stars were first given acronyms based on the letter "I": Ia, Ib. and Ic. 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. When the General Catalogue of Variable Stars standardised its acronyms to be all uppercase, the codes LB and LC were used.

Type Lb

Slow irregular variables of late spectral types ; as a rule, they are giants
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.

Type Lc

Irregular variable supergiants of late spectral types having amplitudes of about 1 mag in V
The M2 supergiant TZ Cassiopeiae is given as a representative example.

List

Designation ConstellationDiscoveryApparent magnitude Apparent magnitude Range of magnitudeSpectral typeSubtypeComment
U AntliaeAntlia 8m.1 9m.7 N:vLb
Beta PegasiPegasusSchmidt, 18472m.312m.74M2.3 II-IIILb
Epsilon Pegasi Pegasus0m.73m.5K2 IbLc
TX PisciumPisces 4m.795m.20C5 IIILb
Alpha Scorpii Scorpius 0m.881m.16M1.5 Iab-bLc
Alpha Tauri Taurus 0m.750m.95K5 IIILb
Mu GeminorumGemini 2m.753m.02M3 IIILb
BE CamelopardalisCamelopardalis 4m.354m.48M2 IILc
Tau4 EridaniEridanus 3m.573m.72M3 IIILb
13 BoötisBootes 5m.295m.38M2 IIIabLb
Psi VirginisVirgo 4m.734m.96M3 IIILb
V854 AraeAra 5m.845m.99M1.5 IIILb
62 SagittariiSagittarius 4m.454m.62M4 IIILb
CQ CamelopardalisCamelopardalis 5m.155m.27M0 IILc
Pi AurigaeAuriga 4m.244m.34M3.5 IILc
NO AurigaeAuriga 6m.066m.44M2 IabLc
Omicron1 Canis MajorisCanis Major 3m.783m.99M2.5 IabLc
Sigma Canis MajorisCanis Major 3m.433m.51M1.5 IabLc
NS PuppisPuppis 4m.44m.5K3 IbLc
Lambda VelorumVela 2m.142m.30K4 Ib-IIaLc
V337 CarinaeCarina 3m.363m.44K3 IILc
GZ VelorumVela 3m.433m.81K3 IILc
RX TelescopiiTelescopium 6m.67m.4M3 IabLc

Other irregular variables

There are a number of other types of variable stars lacking clearly detectable periods, and which are sometimes referred to as irregular variables:
In addition, many types of eruptive or cataclysmic variable are highly unpredictable.