BL Herculis
Variable star in the constellation Hercules From Wikipedia, the free encyclopedia
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.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hercules |
| Right ascension | 18h 01m 09.224s[2] |
| Declination | 19° 14′ 56.696″[2] |
| Apparent magnitude (V) | 9.70 to 10.62[3] |
| Characteristics | |
| Evolutionary stage | F0-F6II-III[3] |
| B−V color index | 0.05[4] |
| Variable type | BL Her[3] |
| Astrometry | |
| Proper motion (μ) | RA: −4.051 mas/yr[2] Dec.: −11.847 mas/yr[2] |
| Parallax (π) | 0.8469±0.0179 mas[2] |
| Distance | 3,850 ± 80 ly (1,180 ± 20 pc) |
| Absolute magnitude (MV) | −0.3[5] |
| Details | |
| Mass | 0.75[6] M☉ |
| Radius | 8.6[2] R☉ |
| Luminosity | 101[2] L☉ |
| Surface gravity (log g) | 2.53[6] cgs |
| Temperature | 6,500 - 7,000[7][8] K |
| Metallicity [Fe/H] | −0.1 - −0.2[7][8] dex |
| Age | 377[2] Myr |
| Other designations | |
| BL Her, HD 347827, HIP 88242, 2MASS J18010922+1914567[9] | |
| Database references | |
| SIMBAD | data |
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]
References
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