Astronomy:BL Herculis
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| 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[2] mas/yr Dec.: −11.847[2] mas/yr |
| Parallax (π) | 0.8469 ± 0.0179[2] mas |
| 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 |
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.
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
- ↑ "Light Curve". ESA. https://www.cosmos.esa.int/web/hipparcos/java-tools/light-curve.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 3.0 3.1 3.2 3.3 "BL Her". AAVSO. https://www.aavso.org/vsx/index.php?view=detail.top&oid=14900.
- ↑ 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.
- ↑ 6.0 6.1 6.2 6.3 6.4 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. doi:10.1086/132028. Bibcode: 1987PASP...99..645A.
- ↑ 7.0 7.1 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. doi:10.1086/520081. Bibcode: 2007ApJ...666..378M.
- ↑ 8.0 8.1 Kovtyukh, V.; Wallerstein, G.; Yegorova, I.; Andrievsky, S.; Korotin, S.; Saviane, I.; Belik, S.; Davis, C. E. et al. (May 2018). "Metal-poor Type II Cepheids with Periods Less Than Three Days". Publications of the Astronomical Society of the Pacific 130 (987): 054201. doi:10.1088/1538-3873/aaacf7. Bibcode: 2018PASP..130e4201K.
- ↑ "BL Her". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=BL+Her.
- ↑ 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. doi:10.1002/asna.19292361502. Bibcode: 1929AN....236..233H.
- ↑ Joy, Alfred H. (November 1937). "Radial Velocities of Cepheid Variable Stars". Astrophysical Journal 86: 363. doi:10.1086/143874. Bibcode: 1937ApJ....86..363J.
- ↑ 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. doi:10.1086/171384. Bibcode: 1992ApJ...391..736B.
- ↑ Carson, Richard; Stothers, Richard (August 1982). "BL HER stars : theoretical models for field variables". Astrophysical Journal 259: 740–748. doi:10.1086/160210. Bibcode: 1982ApJ...259..740C.
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