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BL Herculis
Variable star in the constellation Hercules From Wikipedia, the free encyclopedia
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BL Herculis is a variable star in the northern constellation of Hercules. Its apparent visual magnitude ranges from 9.70 to 10.62,[3] so it is never bright enough to be seen with the naked eye, even with ideal observing conditions. Its distance from the Sun is about 3,850 light-years,[2] and it is moving away from us at 18 km/sec.[10] It is the prototype of the BL Herculis class of variable star, a short-period subset of the pulsating Cepheid variables.
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The variability of BL Herculis was discovered by Cuno Hoffmeister, and announced in 1929.[11] Early observations of the star produced a very inaccurate period of 4.2 days, which resulted in peculiar light and radial velocity curves.[12] The first accurate period, 1.3 days, was published by Pavel Parenago in 1940.[13] and a far more precise period of 1.30744185 days was derived from photometric observations in 1983.[6] The descending portion of the star's light curve shows a "bump" (near phase=0.3, with peak brightness phase defined as 0), which models suggest arises from a 2:1 resonance between the fundamental and second overtone pulsation modes.[14] This bump is considered the primary characteristic of BL Her stars, although its position relative to peak brightness varies as a function of the star's period.[6][15]
The mass of BL Herculis is estimated to be about 0.75 solar masses, just slightly greater than the mass of a typical RR Lyrae variable.[6]
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References
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