Slow irregular variable

Last updated November 24, 2025

A light curve for Lambda Velorum, plotted from Hipparcos data LambdaVelLightCurve.png — A light curve for Lambda Velorum, plotted from *Hipparcos* data

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.^[2] 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.^[3] When the General Catalogue of Variable Stars standardised its acronyms to be all uppercase, the codes LB and LC were used.^[4]

Type Lb

Slow irregular variables of late spectral types (K, M, C, S); as a rule, they are giants^[4]

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.^[4]

Type Lc

Irregular variable supergiants of late spectral types having amplitudes of about 1 mag in V^[4]

The M2 supergiant TZ Cassiopeiae is given as a representative example.^[4]

List

List of Slow Irregular Variables^[5]
Designation (name)	Constellation	Discovery	Apparent magnitude (Maximum)^[a]	Apparent magnitude (Minimum)^[a]	Range of magnitude	Spectral type	Subtype
U Antliae	Antlia		8^m.1 (p)	9^m.7 (p)	1.6	N:v	Lb
Beta Pegasi	Pegasus	Schmidt, 1847	2^m.31	2^m.74	0.43	M2.3 II-III	Lb
Epsilon Pegasi (Enif)	Pegasus		2^m.37	2^m.45	0.07	K2 Ib	Lc
TX Piscium	Pisces		4^m.79	5^m.20	0.42	C5 III	Lb
Alpha Scorpii (Antares)	Scorpius		0^m.88	1^m.16	0.28	M1.5 Iab-b	Lc
Alpha Tauri (Aldebaran)	Taurus		0^m.75	0^m.95	0.20	K5 III	Lb
Mu Geminorum	Gemini		2^m.75	3^m.02	0.28	M3 III	Lb
BE Camelopardalis	Camelopardalis		4^m.35	4^m.48	0.13	M2 II	Lc
Tau⁴ Eridani	Eridanus		3^m.57	3^m.72	0.15	M3 III	Lb
13 Boötis	Bootes		5^m.29	5^m.38	0.09	M2 IIIab	Lb
Psi Virginis	Virgo		4^m.73	4^m.96	0.23	M3 III	Lb
V854 Arae	Ara		5^m.84	5^m.99	0.12	M1.5 III	Lb
62 Sagittarii	Sagittarius		4^m.45	4^m.62	0.17	M4 III	Lb
CQ Camelopardalis	Camelopardalis		5^m.15	5^m.27	0.12	M0 II	Lc
Pi Aurigae	Auriga		4^m.24	4^m.34	0.10	M3.5 II	Lc
NO Aurigae	Auriga		6^m.06	6^m.44	0.58	M2 Iab	Lc
Omicron1 Canis Majoris	Canis Major		3^m.78	3^m.99	0.21	M2.5 Iab	Lc
Sigma Canis Majoris	Canis Major		3^m.43	3^m.51	0.08	M1.5 Iab	Lc
NS Puppis	Puppis		4^m.4	4^m.5	0.1	K3 Ib	Lc
Lambda Velorum	Vela		2^m.14	2^m.30	0.16	K4 Ib-IIa	Lc
V337 Carinae	Carina		3^m.36	3^m.44	0.08	K3 II	Lc
GZ Velorum	Vela		3^m.43	3^m.81	0.38	K3 II	Lc
RX Telescopii	Telescopium		6^m.6	7^m.4	0.8	M3 Iab	Lc
45 G. Volantis	Volans		5^m.89	5^m.90	0.01	M1III	Lb
AF Columbae	Columba	Perryman et al., 1997	5^m.60	5^m.71	0.11	M2 II/III	Lb

1 2 (visual magnitude, unless marked (B) (= blue) or (p) (= photographic))

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:^[5]

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.^[5]

References

↑ "Hipparcos Tools Interactive Data Access". Hipparcos. ESA. Retrieved 8 December 2021.
↑ Kholopov, P. N. (1959). "A Revised List of T-Associations and Their Members". Soviet Astronomy. 3: 291. Bibcode:1959SvA.....3..291K.
↑ Mayall, Margaret W. (1964). "Variable Star Notes- from the XII General Assembly, I.A.U.; 043274 X Camelopardalis". Journal of the Royal Astronomical Society of Canada. 58: 283. Bibcode:1964JRASC..58..283M.
1 2 3 4 5 "GCVS Variability Types" . Retrieved 2016-09-04.
1 2 3 Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: 02025. Bibcode:2009yCat....102025S.

External links

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

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[ReferenceA-6] 1 2 (visual magnitude, unless marked (B) (= blue) or (p) (= photographic))

[HipDataAccess-1] "Hipparcos Tools Interactive Data Access". Hipparcos. ESA. Retrieved 8 December 2021.

[kholopov-2] Kholopov, P. N. (1959). "A Revised List of T-Associations and Their Members". Soviet Astronomy. 3: 291. Bibcode:1959SvA.....3..291K.

[mayall-3] Mayall, Margaret W. (1964). "Variable Star Notes- from the XII General Assembly, I.A.U.; 043274 X Camelopardalis". Journal of the Royal Astronomical Society of Canada. 58: 283. Bibcode:1964JRASC..58..283M.

[gcvs_vartype-4] 1 2 3 4 5 "GCVS Variability Types" . Retrieved 2016-09-04.

[gcvs-5] 1 2 3 Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: 02025. Bibcode:2009yCat....102025S.

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