BL Herculis variable
BL Herculis variables are a type of variable star with low luminosity and mass that have a period of less than eight days.[1][2] They are pulsating stars making up a subclass of Type II Cepheids with light curves that frequently show a bump on the descending side for stars of the shortest periods and on the ascending side for longer period stars.[2] Like other Type II Cepheids, they are very old population II stars found in the galaxy’s halo and globular clusters.[3] Also, compared to other Type II Cepheids, BL Her variables have shorter periods and are fainter than W Virginis variables. Pulsating stars vary in spectral class as they vary in brightness and BL Herculis variables are normally class A at brightest and class F when most dim.[4] When plotted on the Hertzsprung–Russell diagram they fall in-between W Virginis and RR Lyrae variables.[3]
The prototype star, BL Herculis, varies between magnitude 9.7 and 10.6 in a period of 1.3 days. The brightest BL Herculis variables are: VY Pyxidis (7.7 mag max), V553 Centauri(8.2), SW Tauri (9.3), RT Trianguli Australis (9.4), V351 Cephei (9.5), BL Herculis (9.7), BD Cassiopeiae (10.8), and UY Eridani (10.9).
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