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]
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]