BL Herculis variables are a type of variable star with low luminosity and mass that have a period of less than eight days. [1 ] They are pulsating stars making up a subclass of [2 ] 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. Like other Type II Cepheids, they are very old [2 ] population II stars found in the galaxy’s halo and globular clusters. Also, compared to other Type II Cepheids, BL Her variables have shorter periods and are fainter than [3 ] 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. When plotted on the [4 ] 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), V0553 Centauri (8.2), SW Tauri (9.3), RT Trianguli Australis (9.4), V0351 Cephei (9.5), BL Herculis (9.7), BD Cassiopeiae (10.8), and UY Eridani (10.9). [4 ]
References [ edit ]
^ Wallerstein, George (2002). "The Cepheids of Population II and Related Stars". The Publications of the Astronomical Society of the Pacific 114 (797): 689. Bibcode: 2002PASP..114..689W. doi: 10.1086/341698.
^ a b Soszyński, I.; Udalski, A.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Wyrzykowski, Ł.; Szewczyk, O.; Ulaczyk, K.; Poleski, R. (2008). "The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. II.Type II Cepheids and Anomalous Cepheids in the Large Magellanic Cloud". Acta Astronomica 58: 293. arXiv: 0811.3636. Bibcode: 2008AcA....58..293S.
^ a b "The Masses and Pulsations of BL Herculis Variables" (PDF). Information Bridge. US Department of Energy, Office of Scientific and Technical Information . Retrieved . 30 May 2013
^ a b "General Catalogue of Variable Stars". GCVS. Institute of Astronomy of Russian Academy of Sciences and Sternberg State Astronomical Institute . Retrieved . 31 May 2013
External links [ edit ]