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 | |
| 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
edit- ^ "Light Curve". Hipparcos ESA. ESA. Retrieved 17 February 2022.
- ^ a b c d e f g h Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ a b c d "BL Her". The International Variable Star Index. AAVSO. Retrieved 23 August 2022.
- ^ Diethelm, R. (November 1990). "Physical parameters of pulsating variables with periods between one and three days. II. Fundamental parameters". Astronomy and Astrophysics. 239: 186. Bibcode:1990A&A...239..186D.
- ^ Galazutdinov, G. A. (1996). "A Spectroscopic Study of the Pulsating Star BL Her". Astronomy Letters. 22 (3): 364–371. Bibcode:1996AstL...22..326G.
- ^ a b c d e Alexander, A. L.; Joner, M. D.; McNamara, D. H. (July 1987). "A photometric study of BL Herculis". Publications of the Astronomical Society of the Pacific. 99: 645–653. Bibcode:1987PASP...99..645A. doi:10.1086/132028. S2CID 123076764.
- ^ a b Maas, Thomas; Giridhar, Sunetra; Lambert, David L. (September 2007). "The Chemical Compositions of the Type II Cepheids-The BL Herculis and W Virginis Variables". The Astrophysical Journal. 666 (1): 378–392. arXiv:0706.2029. Bibcode:2007ApJ...666..378M. doi:10.1086/520081. S2CID 18862838.
- ^ a b Kovtyukh, V.; Wallerstein, G.; Yegorova, I.; Andrievsky, S.; Korotin, S.; Saviane, I.; Belik, S.; Davis, C. E.; Farrell, E. M. (May 2018). "Metal-poor Type II Cepheids with Periods Less Than Three Days". Publications of the Astronomical Society of the Pacific. 130 (987): 054201. arXiv:1803.05041. Bibcode:2018PASP..130e4201K. doi:10.1088/1538-3873/aaacf7. S2CID 59486927.
- ^ "BL Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2022-08-22.
- ^ Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institute Washington D.C. Publication. Bibcode:1953GCRV..C......0W.
- ^ Hoffmeister, Cuno (September 1929). "354 neue Veränderliche". Astronomische Nachrichten. 236 (15): 233. Bibcode:1929AN....236..233H. doi:10.1002/asna.19292361502.
- ^ Joy, Alfred H. (November 1937). "Radial Velocities of Cepheid Variable Stars". Astrophysical Journal. 86: 363. Bibcode:1937ApJ....86..363J. doi:10.1086/143874.
- ^ Parenago, Pavel (1940). "The Cepheid BL Herculis with an Abnormal Period". IAU Circular. 801.
- ^ Buchler, J. R.; Moskalik, Pawel (June 1992). "Pulsational Study of BL Herculis Models. I. Radial Velocities". Astrophysical Journal. 391: 736. Bibcode:1992ApJ...391..736B. doi:10.1086/171384.
- ^ Carson, Richard; Stothers, Richard (August 1982). "BL HER stars : theoretical models for field variables". Astrophysical Journal. 259: 740–748. Bibcode:1982ApJ...259..740C. doi:10.1086/160210.