L Slow irregular variable stars

-The light variations of these stars show no evidence of periodicity, or any periodicity present is very poorly defined and appears only occasionally. As for type L, stars are often attributed to this type because of insufficient study. Many type L variables are really semiregulars or other types. LB (subtype) - Slow irregular variables of late spectral type (K, M, C, S); as

Observation

•jf Mixed stars gg Mixed amplitudes

J\ Mixed periods

a rule, these are giants. This type is also ascribed in the GCVS to slow red irregular variables in the case of unknown spectral types and luminosities. LC (subtype) -Irregular variable supergiants of late spectral type having amplitudes of about 1 mag in V. GCVS

Irregular variable stars are slowly varying stars with no evidence of periodicity. Variable stars are frequently assigned to this class when their variability has been noted but not well-studied. This class of variable star is another excellent group deserving study by amateur astronomers.

One of the interesting aspects of studying these stars is that some semiregular (SR) variables experience periods of irregular variations so it is not entirely clear whether the irregular classification represents a fundamentally different type of variability.

As described within the GCVS, this group is composed of stars with spectral types K, M, C and S. The K-, M- and C-type have already been introduced (RCB stars). The S-type stars are presented here. An S-type star is a late-type giant, usually K5-M, that shows distinct bands of ZrO (zirconium oxide) in the blue and visual spectral regions. If these ZrO bands are weak or can be seen only at high levels of dispersion, the star is classed as MS so that a classification such as M4 S describes an M4 star with ZrO bands. Emission lines are seen within the spectra of those S-type stars that are variable. In general, S-type stars are rare; they are less abundant than C-type stars.

Observation Key

^ Bright stars ¡¿ft Mixed amplitudes

Mixed periods <3> CCD or PEP

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