A 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.

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 (K, M, C, S); 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

+ List of Slow Irregular VariablesDesignation (name)ConstellationDiscoveryApparent magnitude (Maximum)Apparent magnitude (Minimum)Range of magnitudeSpectral typeSubtypeComment U Antliae Antlia   8m.1 (p) 9m.7 (p) N:v Lb   Beta Pegasi (Scheat) Pegasus Schmidt, 1847 2m.31 2m.74 M2.3 II-III Lb   Epsilon Pegasi (Enif) Pegasus 2m.37 2m.45 K2 Ib Lc   TX Piscium Pisces   4m.79 5m.20 C5 III Lb   Alpha Scorpii (Antares) Scorpius   0m.88 1m.16 M1.5 Iab-b Lc   Alpha Tauri (Aldebaran) Taurus   0m.75 0m.95 K5 III Lb   Mu Geminorum (Tejat) Gemini   2m.75 3m.02 M3 III Lb   BE Camelopardalis (Custos) Camelopardalis   4m.35 4m.48 M2 II Lc   Tau4 Eridani Eridanus   3m.57 3m.72 M3 III Lb   13 Boötis Bootes   5m.29 5m.38 M2 IIIab Lb   Psi Virginis Virgo   4m.73 4m.96 M3 III Lb   V854 Arae Ara   5m.84 5m.99 M1.5 III Lb   62 Sagittarii Sagittarius   4m.45 4m.62 M4 III Lb   CQ Camelopardalis Camelopardalis   5m.15 5m.27 M0 II Lc   Pi Aurigae Auriga   4m.24 4m.34 M3.5 II Lc   NO Aurigae Auriga   6m.06 6m.44 M2 Iab Lc   Omicron1 Canis Majoris Canis Major   3m.78 3m.99 M2.5 Iab Lc   Sigma Canis Majoris (Nganurganity) Canis Major   3m.43 3m.51 M1.5 Iab Lc   NS Puppis Puppis   4m.4 4m.5 K3 Ib Lc   Lambda Velorum (Suhail) Vela   2m.14 2m.30 K4 Ib-IIa Lc   V337 Carinae Carina   3m.36 3m.44 K3 II Lc   GZ Velorum Vela   3m.43 3m.81 K3 II Lc   RX Telescopii Telescopium   6m.6 7m.4 M3 Iab Lc   45 G. Volantis Volans 5m.89 5m.90 M1III Lb AF Columbae Columba Perryman et al., 1997 5m.60 5m.71

M2 II/III Lb

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: γ Cassiopeiae variables, eruptive shell stars Orion variables, pre-main-sequence stars, including T Tauri stars and YY Orionis stars Rapid irregular variables, possibly similar to Orion variables with shorter period Poorly-defined irregular variable stars, of unknown type

In addition, many types of eruptive or cataclysmic variable are highly unpredictable.

References

External links Classifying variable stars - Astronomical Society of South Australia Why observe variable stars - British Astronomical Association