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 |
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]
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.
RV Tauri variables are luminous variable stars that have distinctive light variations with alternating deep and shallow minima.
RT Aurigae is a yellow supergiant variable star in the constellation Auriga, about 1,500 light years from Earth.
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.
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.
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.
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.
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.
Kappa Pavonis is a variable star in the constellation Pavo. It is the brightest W Virginis variable in the sky.
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.
S Vulpeculae is a variable star located in the constellation Vulpecula. A supergiant star, it is around 382 times the diameter of the Sun.
SV Vulpeculae is a classical Cepheid variable star in the constellation Vulpecula. It is a supergiant at a distance of 8,700 light years.
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.
RT Trianguli Australis, or RT TrA, is a BL Herculis variable in the constellation of Triangulum Australe.
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.
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.
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.
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.
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.
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.