Astronomy:BL Herculis variable
BL Herculis variables are a subclass of type II Cepheids with low luminosity and mass, that have a period of less than eight days.[2][3] They are pulsating stars 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.[3] Like other type II Cepheids, they are very old population II stars found in the galaxy’s halo and globular clusters.[4] Also, compared to other type II Cepheids, BL Herculis 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 their brightest and class F when most dim.[5] When plotted on the Hertzsprung–Russell diagram they fall in-between W Virginis and RR Lyrae variables.[4]
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, with their maximum magnitudes, are:[5]
- VY Pyxidis, 7.7
- 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
- UY Eridani, 10.9
The BL Herculis stars show a wide variety of light curves, temperatures, and luminosity, and three subdivisions of the class have been defined, with the acronym AHB referring to above horizontal branch:[6][7][8]
- XX Virginis stars (AHB1), with very fast rises to maximum and low metallicity
- CW stars (AHB2), W Virginis variables, longer periods, the bump on the ascending leg
- BL Herculis stars (AHB3), shorter periods, the bump on the descending leg
References
- ↑ "Light Curve". ESA. https://www.cosmos.esa.int/web/hipparcos/java-tools/light-curve.
- ↑ Wallerstein, George (2002). "The Cepheids of Population II and Related Stars". The Publications of the Astronomical Society of the Pacific 114 (797): 689–699. doi:10.1086/341698. Bibcode: 2002PASP..114..689W.
- ↑ 3.0 3.1 Soszyński, I.; Udalski, A.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Wyrzykowski, Ł.; Szewczyk, O.; Ulaczyk, K. et al. (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. Bibcode: 2008AcA....58..293S.
- ↑ 4.0 4.1 "The Masses and Pulsations of BL Herculis Variables". Information Bridge. US Department of Energy, Office of Scientific and Technical Information. http://library.lanl.gov/cgi-bin/getfile?00251594.pdf. Retrieved 30 May 2013.
- ↑ 5.0 5.1 "General Catalogue of Variable Stars". GCVS. Institute of Astronomy of Russian Academy of Sciences and Sternberg State Astronomical Institute. http://vizier.u-strasbg.fr/viz-bin/VizieR-S?V*%20BL%20Her. Retrieved 31 May 2013.
- ↑ McNamara, D. H.; Pyne, M. D. (1994). "A Photometric Study of XX Virginis and V716 Ophiuchi". Publications of the Astronomical Society of the Pacific 106: 472. doi:10.1086/133402. Bibcode: 1994PASP..106..472M.
- ↑ Diethelm, R. (1983). "A photometric classification of pulsating variables with periods between one and three days". Astronomy and Astrophysics 124: 108. Bibcode: 1983A&A...124..108D.
- ↑ Diethelm, R. (1996). "Period changes of AHB1 variables". Astronomy and Astrophysics 307: 803. Bibcode: 1996A&A...307..803D.
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