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Irregular eruptive 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). So-called IN (irregular nebulous) variables, 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 stars, 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.
Irregular pulsating giants or supergiants, all of late spectral types (K, M, C, or S), are 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= http://books.google.com/books?vid=ISBN1852334983&id=k9ViYKvKRz0C&pg=PA8&lpg=PA8&ots=AojoVu3Lpn&dq=%22Irregular+variable%22&ie=ISO-8859-1&output=html&sig=hIF3ZDs-Rh3XGKVECqONh7aKAYM|id=ISBN 1852334983}}</ref>
==References==
<references/>
[[Category:Irregular variables| ]]
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