Slow irregular variable#Type Lb

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.

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.

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.

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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.

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

{{cite journal|bibcode=1959SvA.....3..291K|title=A Revised List of T-Associations and Their Members|journal=Soviet Astronomy|volume=3|pages=291|last1=Kholopov|first1=P. N.|year=1959}}

{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|pages=02025|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009|display-authors=etal}}

{{cite web|url=http://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt|access-date=2016-09-04|title=GCVS Variability Types}}

{{cite journal|bibcode=1964JRASC..58..283M|title=Variable Star Notes- from the XII General Assembly, I.A.U.; 043274 X Camelopardalis|journal=Journal of the Royal Astronomical Society of Canada|volume=58|pages=283|last1=Mayall|first1=Margaret W.|year=1964}}

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• [https://www.assa.org.au/sig/variables/classifications Classifying variable stars] - Astronomical Society of South Australia
• [http://www.britastro.org/vss/holland.pdf Why observe variable stars] - British Astronomical Association

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