Slow irregular variable explained

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 Variables

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

External links

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