BL Herculis

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BL Herculis
BLHerLightCurve.png
A light curve for BL Herculis, plotted from Hipparcos data [1]
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
ER Vul, HD  347827, HIP  88242, 2MASS J18010922+1914567 [9]
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]

Related Research Articles

<span class="mw-page-title-main">Cepheid variable</span> Type of variable star that pulsates radially

A Cepheid variable is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.

<span class="mw-page-title-main">RV Tauri variable</span> Class of luminous variable star

RV Tauri variables are luminous variable stars that have distinctive light variations with alternating deep and shallow minima.

<span class="mw-page-title-main">RT Aurigae</span> Star in the constellation Auriga

RT Aurigae is a yellow supergiant variable star in the constellation Auriga, about 1,500 light years from Earth.

<span class="mw-page-title-main">Instability strip</span> Region of an astronomical diagram

The unqualified term instability strip usually refers to a region of the Hertzsprung–Russell diagram largely occupied by several related classes of pulsating variable stars: Delta Scuti variables, SX Phoenicis variables, and rapidly oscillating Ap stars (roAps) near the main sequence; RR Lyrae variables where it intersects the horizontal branch; and the Cepheid variables where it crosses the supergiants.

<span class="mw-page-title-main">AM Herculis</span> Star in the constellation Hercules

AM Herculis is a binary variable star located in the constellation Hercules. This star, along with the star AN Ursae Majoris, is the prototype for a category of cataclysmic variable stars called polars, or AM Her type stars.

<span class="mw-page-title-main">V1401 Aquilae</span> Star in the constellation Aquila

V1401 Aquilae is a single, semi-regular pulsating star in the equatorial constellation of Aquila. It has the designation HD 190390 from the Henry Draper Catalogue, and was formerly designated 64 Sagittarii. The evolutionary status of the star is unclear, and it has been classified as a post-AGB object, a UU Herculis variable, or belonging to the W Virginis variable subclass of the type II Cepheids. It is dimly visible to the naked eye with an apparent visual magnitude that fluctuates around 6.38. Based on parallax measurements, it is located at a distance of approximately 2,380 light years. It lies 21.5° from the galactic plane.

<span class="mw-page-title-main">Classical Cepheid variable</span>

Classical Cepheids are a type of Cepheid variable star. They are population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes from a few tenths of a magnitude to about 2 magnitudes.

<span class="mw-page-title-main">W Virginis</span> Variable star in the constellation Virgo

W Virginis is the prototype W Virginis variable, a subclass of the Cepheid variable stars. It is located in the constellation Virgo, and varies between magnitudes 9.46 and 10.75 over a period of approximately 17 days.

<span class="mw-page-title-main">Kappa Pavonis</span> Variable star in the constellation Pavo

Kappa Pavonis is a variable star in the constellation Pavo. It is the brightest W Virginis variable in the sky.

<span class="mw-page-title-main">BL Herculis variable</span>

BL Herculis variables are a subclass of type II Cepheids with low luminosity and mass, that have a period of less than eight days. They are pulsating stars with light curves that frequently show a bump on the descending side for stars of the shortest periods and on the ascending side for longer period stars. Like other type II Cepheids, they are very old population II stars found in the galaxy’s halo and globular clusters. Also, compared to other type II Cepheids, BL Herculis variables have shorter periods and are fainter than W Virginis variables. Pulsating stars vary in spectral class as they vary in brightness and BL Herculis variables are normally class A at their brightest and class F when most dim. When plotted on the Hertzsprung–Russell diagram they fall in-between W Virginis and RR Lyrae variables.

<span class="mw-page-title-main">S Vulpeculae</span> Variable star in the constellation Vulpecula

S Vulpeculae is a variable star located in the constellation Vulpecula. A supergiant star, it is around 382 times the diameter of the Sun.

<span class="mw-page-title-main">SV Vulpeculae</span> Star in the constellation Vulpecula

SV Vulpeculae is a classical Cepheid variable star in the constellation Vulpecula. It is a supergiant at a distance of 8,700 light years.

<span class="mw-page-title-main">RU Camelopardalis</span> Star in the constellation Camelopardalis

RU Camelopardalis, or RU Cam, is a W Virginis variable in the constellation of Camelopardalis. It is also a Carbon star, which is very unusual for a Cepheid variable.

<span class="mw-page-title-main">RT Trianguli Australis</span> Star in the constellation Triangulum Australe

RT Trianguli Australis, or RT TrA, is a BL Herculis variable in the constellation of Triangulum Australe.

<span class="mw-page-title-main">BL Boötis</span> Star in the constellation Boötes

BL Boötis is a pulsating star in the constellation Boötes. It is the prototype of a class of anomalous Cepheids which is intermediate in the H-R diagram between the type I classical Cepheids and the type II Cepheids.

<span class="mw-page-title-main">R Sagittae</span> Star in the constellation Sagitta

R Sagittae is an RV Tauri variable star in the constellation Sagitta that varies from magnitude 8.0 to 10.5 in 70.77 days. It is a post-AGB low mass yellow supergiant that varies between spectral types G0Ib and G8Ib as it pulsates. Its variable star designation of "R" indicates that it was the first star discovered to be variable in the constellation. It was discovered in 1859 by Joseph Baxendell, though classified as a semi regular variable until RV Tauri variables were identified as a distinct class in 1905.

<span class="mw-page-title-main">DY Pegasi</span> Star in the constellation Pegasus

DY Pegasi, abbreviated DY Peg, is a binary star system in the northern constellation of Pegasus. It is a well-studied SX Phoenicis variable star with a brightness that ranges from an apparent visual magnitude of 9.95 down to 10.62 with a period of 1.75 hours. This system is much too faint to be seen with the naked eye, but can be viewed with large binoculars or a telescope. Based on its high space motion and low abundances of heavier elements, it is a population II star system.

<span class="mw-page-title-main">SZ Tauri</span>

SZ Tauri is a variable star in the equatorial constellation of Taurus. The brightness of this star varies from an apparent visual magnitude of 6.39 down to 6.69 with a period of 3.149 days, which is near the lower limit of visibility to the naked eye. The distance to this star is approximately 2,070 light years based on parallax measurements. There is some indication this may be a binary system, but the evidence is inconclusive.

<span class="mw-page-title-main">EU Tauri</span> Variable star in the constellation Taurus

EU Tauri is a variable star in the equatorial constellation of Taurus. With a brightness that cycles around an apparent visual magnitude of 8.07, it is too faint to be visible to the naked eye. The distance to this star is approximately 3,900 light years based on parallax measurements, but it is drifting closer with a radial velocity of −2.5 km/s. The position of this star near the ecliptic means it is subject to lunar occultations.

<span class="mw-page-title-main">VZ Cancri</span> Variable star in the constellation Cancer

VZ Cancri is a variable star in the constellation Cancer, abbreviated VZ Cnc. It varies in brightness with a period of 0.178364 days, from an apparent visual magnitude of 7.18 down to 7.91, which lies below the typical threshold of visibility for the naked eye. The distance to this star is approximately 724 light years based on parallax measurements, and it is receding from the Sun with a radial velocity of 25 km/s.

References

  1. "Light Curve". Hipparcos ESA. ESA. Retrieved 17 February 2022.
  2. 1 2 3 4 5 6 7 8 9 Vallenari, A.; et al. (Gaia Collaboration) (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics . arXiv: 2208.00211 . doi: 10.1051/0004-6361/202243940 . Gaia DR3 record for this source at VizieR.
  3. 1 2 3 4 "BL Her". The International Variable Star Index. AAVSO. Retrieved 23 August 2022.
  4. 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.
  5. Galazutdinov, G. A. (1996). "A Spectroscopic Study of the Pulsating Star BL Her". Astronomy Letters. 22 (3): 364–371. Bibcode:1996AstL...22..326G.
  6. 1 2 3 4 5 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.
  7. 1 2 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.
  8. 1 2 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. Bibcode:2018PASP..130e4201K. doi:10.1088/1538-3873/aaacf7. S2CID   59486927.
  9. "BL Her". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2022-08-22.
  10. Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institute Washington D.C. Publication. Bibcode:1953GCRV..C......0W.
  11. Hoffmeister, Cuno (September 1929). "354 neue Veränderliche". Astronomische Nachrichten. 236 (15): 233. Bibcode:1929AN....236..233H. doi:10.1002/asna.19292361502.
  12. Joy, Alfred H. (November 1937). "Radial Velocities of Cepheid Variable Stars". Astrophysical Journal. 86: 363. Bibcode:1937ApJ....86..363J. doi:10.1086/143874.
  13. Parenago, Pavel (1940). "The Cepheid BL Herculis with an Abnormal Period". IAU Circular. 801.
  14. 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.
  15. 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.