Slow irregular variable

{{Short description|Type of variable star}} [[File:LambdaVelLightCurve.png|thumb|upright=1.25|A light curve for Lambda Velorum, plotted from ''Hipparcos'' data<ref name=HipDataAccess/>]] 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''.<ref name=kholopov/> 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.<ref name=mayall/> When the General Catalogue of Variable Stars standardised its acronyms to be all uppercase, the codes LB and LC were used.<ref name=gcvs_vartype/>

===Type Lb=== ''Slow irregular variables of late spectral types (K, M, C, S); as a rule, they are giants''<ref name=gcvs_vartype/>

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.<ref name=gcvs_vartype/>

===Type Lc=== ''Irregular variable supergiants of late spectral types having amplitudes of about 1 mag in V''<ref name=gcvs_vartype/>

The M2 supergiant TZ Cassiopeiae is given as a representative example.<ref name=gcvs_vartype/>

==List== {{dynamic list}} {| class="wikitable sortable" style="font-size:90%;" |+ List of Slow Irregular Variables<ref name=gcvs/> |- bgcolor="#efefef" ! width="15%"|'''Designation (name)''' ! width="10%"|'''Constellation''' ! width="15%"|'''Discovery''' ! width="8%"|''Apparent magnitude'' (Maximum){{efn|name=ReferenceA}} ! width="8%"|''Apparent magnitude'' (Minimum){{efn|name=ReferenceA}} ! width="8%"|''Range of magnitude'' ! width="15%"|'''Spectral type''' ! width="6%"|'''Subtype''' ! width="15%"|'''Comment''' |--- | U Antliae | Antlia | &nbsp; | {{ntsh|8.1}}8^m.1 (p) | {{ntsh|9.7}}9^m.7 (p) | {{nts|1.6}} | N:v | Lb | &nbsp; |--- | Beta Pegasi | Pegasus | Schmidt, 1847 | {{ntsh|2.31}}2^m.31 | {{ntsh|2.74}}2^m.74 | {{nts|0.43}} | M2.3 II-III | Lb | &nbsp; |--- | Epsilon Pegasi (Enif) | Pegasus | | {{ntsh|2.37}}2^m.37 | {{ntsh|2.45}}2^m.45 | {{nts|0.07}} | K2 Ib | Lc | &nbsp; |--- | TX Piscium | Pisces | &nbsp; | {{ntsh|4.79}}4^m.79 | {{ntsh|5.20}}5^m.20 | {{nts|0.42}} | C5 III | Lb | &nbsp; |--- | Alpha Scorpii (Antares) | Scorpius | &nbsp; | {{ntsh|0.88}}0^m.88 | {{ntsh|1.16}}1^m.16 | {{nts|0.28}} | M1.5 Iab-b | Lc | &nbsp; |--- | Alpha Tauri (Aldebaran) | Taurus | &nbsp; | {{ntsh|0.75}}0^m.75 | {{ntsh|0.95}}0^m.95 | {{nts|0.20}} | K5 III | Lb | &nbsp; |--- | Mu Geminorum | Gemini | &nbsp; | {{ntsh|2.75}}2^m.75 | {{ntsh|3.02}}3^m.02 | {{nts|0.28}} | M3 III | Lb | &nbsp; |--- | BE Camelopardalis | Camelopardalis | &nbsp; | {{ntsh|4.35}}4^m.35 | {{ntsh|4.48}}4^m.48 | {{nts|0.13}} | M2 II | Lc | &nbsp; |--- | Tau⁴ Eridani | Eridanus | &nbsp; | {{ntsh|3.57}}3^m.57 | {{ntsh|3.72}}3^m.72 | {{nts|0.15}} | M3 III | Lb | &nbsp; |--- | 13 Boötis | Bootes | &nbsp; | {{ntsh|5.29}}5^m.29 | {{ntsh|5.38}}5^m.38 | {{nts|0.09}} | M2 IIIab | Lb | &nbsp; |--- | Psi Virginis | Virgo | &nbsp; | {{ntsh|4.73}}4^m.73 | {{ntsh|4.96}}4^m.96 | {{nts|0.23}} | M3 III | Lb | &nbsp; |--- | V854 Arae | Ara | &nbsp; | {{ntsh|5.87}}5^m.84 | {{ntsh|5.99}}5^m.99 | {{nts|0.12}} | M1.5 III | Lb | &nbsp; |--- | 62 Sagittarii | Sagittarius | &nbsp; | {{ntsh|4.45}}4^m.45 | {{ntsh|4.62}}4^m.62 | {{nts|0.17}} | M4 III | Lb | &nbsp; |--- | CQ Camelopardalis | Camelopardalis | &nbsp; | {{ntsh|5.15}}5^m.15 | {{ntsh|5.27}}5^m.27 | {{nts|0.12}} | M0 II | Lc | &nbsp; |--- | Pi Aurigae | Auriga | &nbsp; | {{ntsh|4.24}}4^m.24 | {{ntsh|4.34}}4^m.34 | {{nts|0.10}} | M3.5 II | Lc | &nbsp; |--- | NO Aurigae | Auriga | &nbsp; | {{ntsh|6.06}}6^m.06 | {{ntsh|6.44}}6^m.44 | {{nts|0.58}} | M2 Iab | Lc | &nbsp; |--- | Omicron1 Canis Majoris | Canis Major | &nbsp; | {{ntsh|3.78}}3^m.78 | {{ntsh|3.99}}3^m.99 | {{nts|0.21}} | M2.5 Iab | Lc | &nbsp; |--- | Sigma Canis Majoris | Canis Major | &nbsp; | {{ntsh|3.43}}3^m.43 | {{ntsh|3.51}}3^m.51 | {{nts|0.08}} | M1.5 Iab | Lc | &nbsp; |--- | NS Puppis | Puppis | &nbsp; | {{ntsh|4.4}}4^m.4 | {{ntsh|4.5}}4^m.5 | {{nts|0.1}} | K3 Ib | Lc | &nbsp; |--- | Lambda Velorum | Vela | &nbsp; | {{ntsh|2.14}}2^m.14 | {{ntsh|2.30}}2^m.30 | {{nts|0.16}} | K4 Ib-IIa | Lc | &nbsp; |--- | V337 Carinae | Carina | &nbsp; | {{ntsh|3.36}}3^m.36 | {{ntsh|3.44}}3^m.44 | {{nts|0.08}} | K3 II | Lc | &nbsp; |--- | GZ Velorum | Vela | &nbsp; | {{ntsh|3.43}}3^m.43 | {{ntsh|3.81}}3^m.81 | {{nts|0.38}} | K3 II | Lc | &nbsp; |--- | RX Telescopii | Telescopium | &nbsp; | {{ntsh|6.6}}6^m.6 | {{ntsh|7.4}}7^m.4 | {{nts|0.8}} | M3 Iab | Lc | &nbsp; |--- | 45 G. Volantis | Volans | | {{ntsh|5.89}}5^m.89 | {{ntsh|5.9}}5^m.90 | {{nts|0.01}} | M1III | Lb | |--- | AF Columbae | Columba | Perryman et al., 1997 | {{ntsh|5.6}}5^m.60 | {{ntsh|5.71}}5^m.71 | {{nts|0.11}} | M2 II/III | Lb | |} {{notelist|refs= {{efn|name=ReferenceA|1=''(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:<ref name=gcvs/> *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.<ref name=gcvs/>

==References== {{Reflist|refs=

<ref name=HipDataAccess>{{cite web |title=Hipparcos Tools Interactive Data Access |url=https://www.cosmos.esa.int/web/hipparcos/interactive-data-access |website=Hipparcos |publisher=ESA |access-date=8 December 2021}}</ref>

<ref name=kholopov>{{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}}</ref>

<ref name=gcvs>{{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}}</ref>

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

<ref name=mayall>{{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}}</ref>

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==External links== *[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

{{Variable star topics}}

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