HD 164922
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Hercules |
| Right ascension | 18h 02m 30.86s[1] |
| Declination | +26° 18′ 46.81″[1] |
| Apparent magnitude (V) | +7.01 |
| Characteristics | |
| Spectral type | G9V[2] |
| U−B color index | 0.47 |
| B−V color index | 0.80 |
| V−R color index | 0.42 |
| R−I color index | 0.36 |
| Variable type | suspected |
| Astrometry | |
| Radial velocity (Rv) | +22.8 km/s |
| Proper motion (μ) | RA: 389.772±0.013[3] mas/yr Dec.: -602.431±0.017[3] mas/yr |
| Parallax (π) | 45.4954 ± 0.0167[3] mas |
| Distance | 71.69 ± 0.03 ly (21.980 ± 0.008 pc) |
| Absolute magnitude (MV) | 5.31 |
| Details | |
| Mass | 0.874 ± 0.012[2] M☉ |
| Radius | 0.999 ± 0.017[2] R☉ |
| Luminosity | 0.703 ± 0.017[2] L☉ |
| Surface gravity (log g) | 4.387 ± 0.014[2] cgs |
| Temperature | 5293 ± 32[2] K |
| Metallicity [Fe/H] | 0.16 ± 0.05[2] dex |
| Rotation | ~58.7 d |
| Age | 13.4 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
HD 164922 is a seventh magnitude G-type main sequence star in the constellation of Hercules. To view it, binoculars or a telescope are necessary, as it is too faint to be visible to the naked eye. It is 72 light years distant from the Earth.[1] At an age of 13.4 billion years, it will soon evolve away from the main-sequence and expand to become a red giant. It is one of the oldest known stars in the Universe and one of the most ancient multiplanetary systems known in the Milky Way.
Nomenclature[]
The designation b derive from the order of discovery. The designation of b is given to the first planet orbiting a given star, followed by the other lowercase letters of the alphabet.[4] In the case of HD 164922, only one was discovered, which was designated b, then a more inner planet, which was designated c.[2] The name HD 164922 derives directly from the fact that the star is the 164,922nd star discovered in the Henry Draper catalog.
Stellar characteristics[]
HD 164922 is a G-type main sequence star that is approximately 87% the mass of and 99% the radius of the Sun. It has a temperature of 5293 K and is 13.4 billion years old. In comparison, the Sun is about 4.6 billion years old[5] and has a temperature of 5778 K.[6]
The star is metal-rich, with a metallicity ([Fe/H]) of 0.16, or 144% the solar amount. This is particularly odd for a star as old as HD 164922. Its luminosity (L☉) is 70% of the solar luminosity.[2]
Planetary system[]
On 15 July 2006, a long period Saturn-mass exoplanet was announced orbiting around HD 164922. This planet orbits at 2.11 AU from the star with a low eccentricity value of 0.05.[7]
Almost exactly ten years later in 2016, another exoplanet, though less massive then the first planet, was discovered orbiting farther in from the star. This planet has a minimum mass of nearly 13 times that of Earth, meaning it is possibly a Neptune-like planet.
A third exoplanet, a hot super-Earth, was discovered in 2020,[8] and fourth, Neptune-sized, in 2021.[9]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| d | ≥4±1 M
|