BL Herculis
{{Short description|Variable star in the constellation Hercules}}
{{Starbox begin}}
{{Starbox image
| image = 250px
| caption = A light curve for BL Herculis, plotted from Hipparcos data
}}
{{Starbox observe
| epoch = J2000
| constell = Hercules
| appmag_v = {{val|9.70|to|10.62}}
}}
{{Starbox character
| class =
| variable = BL Her
}}
{{Starbox astrometry
| radial_v =
| prop_mo_ra = −4.051
| prop_mo_dec = −11.847
| parallax = 0.8469
| p_error = 0.0179
}}
{{Starbox detail
| rotational_velocity =
}}
{{Starbox catalog
| names = {{odlist | V=BL Her | HD=347827 | HIP=88242| 2MASS=J18010922+1914567}}
}}
{{Starbox reference
| Simbad = BL+Her
}}
{{Starbox end}}
BL Herculis is a variable star in the northern constellation of Hercules. Its apparent visual magnitude ranges from 9.70 to 10.62, 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, and it is moving away from us at 18 km/sec. 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. Early observations of the star produced a very inaccurate period of 4.2 days, which resulted in peculiar light and radial velocity curves. The first accurate period, 1.3 days, was published by Pavel Parenago in 1940. and a far more precise period of 1.30744185 days was derived from photometric observations in 1983. 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. 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.
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.
References
{{reflist|refs=
| last1=Carson | first1=Richard | last2=Stothers | first2=Richard
| title=BL HER stars : theoretical models for field variables
| journal=Astrophysical Journal |date=August 1982 |volume=259 |pages=740–748
| doi=10.1086/160210 | bibcode=1982ApJ...259..740C| doi-access=free }}
| last1=Alexander | first1=A. L. | last2=Joner | first2=M. D. | last3=McNamara | first3=D. H.
| title=A photometric study of BL Herculis
| journal=Publications of the Astronomical Society of the Pacific
| date=July 1987 | volume=99 | pages=645–653 | doi=10.1086/132028 | bibcode=1987PASP...99..645A| s2cid=123076764 | doi-access=free }}
| last1=Buchler | first1=J. R. | last2=Moskalik | first2=Pawel
| title=Pulsational Study of BL Herculis Models. I. Radial Velocities
| journal=Astrophysical Journal | date=June 1992 | volume=391 | page=736
| doi=10.1086/171384 | bibcode=1992ApJ...391..736B}}
| last1=Diethelm | first1=R. | bibcode=1990A&A...239..186D
| title=Physical parameters of pulsating variables with periods between one and three days. II. Fundamental parameters
| journal=Astronomy and Astrophysics |date=November 1990 | volume=239 | page=186}}
| last1=Maas | first1=Thomas | last2=Giridhar | first2=Sunetra
| last3=Lambert | first3=David L.
| title=The Chemical Compositions of the Type II Cepheids-The BL Herculis and W Virginis Variables
| journal=The Astrophysical Journal | date=September 2007 | volume=666 | issue=1 | pages=378–392
| doi=10.1086/520081 | arxiv=0706.2029 | bibcode=2007ApJ...666..378M| s2cid=18862838 }}
| last1=Kovtyukh | first1=V. | last2=Wallerstein | first2=G.
| last3=Yegorova | first3=I. | last4=Andrievsky | first4=S.
| last5=Korotin | first5=S. | last6=Saviane | first6=I.
| last7=Belik | first7=S. | last8=Davis | first8=C. E.
| last9=Farrell | first9=E. M.
| title=Metal-poor Type II Cepheids with Periods Less Than Three Days
| journal=Publications of the Astronomical Society of the Pacific | bibcode=2018PASP..130e4201K
| date=May 2018 |volume=130 |issue=987 | page=054201 |doi=10.1088/1538-3873/aaacf7| s2cid=59486927 | arxiv=1803.05041 }}
| last1=Parenago | first1=Pavel
| title=The Cepheid BL Herculis with an Abnormal Period
| journal=IAU Circular |date=1940 |volume=801}}
| last1=Galazutdinov | first1=G. A.
| title=A Spectroscopic Study of the Pulsating Star BL Her
| journal=Astronomy Letters | date=1996 | volume=22 | issue=3
| pages=364–371 | bibcode=1996AstL...22..326G }}
| last1=Joy | first1=Alfred H.
| title=Radial Velocities of Cepheid Variable Stars
| journal=Astrophysical Journal |date=November 1937 |volume=86
| page=363 |doi=10.1086/143874 | bibcode=1937ApJ....86..363J}}
| last1=Hoffmeister |first1=Cuno
| title=354 neue Veränderliche
| journal=Astronomische Nachrichten |date=September 1929 |volume=236 |issue=15
|page=233
| doi=10.1002/asna.19292361502 | bibcode=1929AN....236..233H}}
| last1=Wilson | first1=Ralph Elmer | bibcode=1953GCRV..C......0W
| title=General catalogue of stellar radial velocities
| journal=Carnegie Institute Washington D.C. Publication| year=1953 }}
{{cite simbad | title=BL Her | access-date=2022-08-22 }}
| title=BL Her |url=https://www.aavso.org/vsx/index.php?view=detail.top&oid=14900
| website=The International Variable Star Index | publisher=AAVSO | access-date=23 August 2022}}
{{Cite Gaia DR3|4527596850906132352}}
| title=Light Curve
| url=https://www.cosmos.esa.int/web/hipparcos/java-tools/light-curve
| website=Hipparcos ESA | publisher=ESA | access-date=17 February 2022}}
}}
{{Stars of Hercules}}
{{DEFAULTSORT:BL Herculis}}