# Irregular variable

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{{Short description|Type of variable star}}
{{Refimprove|date=December 2009}}
An '''irregular variable''' is a type of [variable star](/source/variable_star) in which variations in brightness show no regular [periodicity](/source/Frequency). There are two main sub-types of irregular variable: eruptive and pulsating.

'''Eruptive''' irregular variables are divided into three categories:

* Group I variables are split into subgroups IA (spectral types O to A) and IB (spectral types F through M).
* [Orion variables](/source/Orion_variables), GCVS type IN (irregular and nebulous), indigenous to star-forming regions, may vary by several magnitudes with rapid changes of up to 1 magnitude in 1 to 10 days, are similarly divided by spectral type into subgroups INA and INB, but with the addition of another subgroup, INT, for [T Tauri star](/source/T_Tauri_star)s, or INT(YY) for YY Orionis stars.
* The third category of eruptive irregulars are the IS stars, which show rapid variations of 0.5 to 1 magnitude in a few hours or days; again, these come in subgroups ISA and ISB.

'''Pulsating''' irregular giants or supergiants, called [slow irregular variable](/source/slow_irregular_variable)s, are all of late spectral types (K, M, C, or S), and classed as type L-LB for giants and LC for supergiants. How many of these are actually semi-regular variables that simply need more study, remains unclear.<ref>{{citation|title=Observing Variable Stars |author=Gerry Arlen Good|year= 2003|publisher=Springer Science|url= https://books.google.com/books?id=k9ViYKvKRz0C&q=%22Irregular+variable%22&pg=PA8|isbn=978-1-85233-498-7}}</ref>

== References ==
{{Reflist}}

Category:Irregular variables

{{var-star-stub}}

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Adapted from the Wikipedia article [Irregular variable](https://en.wikipedia.org/wiki/Irregular_variable) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Irregular_variable?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.