HD 164922

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HD 164922
Hercules HD 164922.png
Position of star HD 164922 in the constellation Hercules
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
Distance71.69 ± 0.03 ly
(21.980 ± 0.008 pc)
Absolute magnitude (MV)5.31
Details
Mass0.874 ± 0.012[2] M
Radius0.999 ± 0.017[2] R
Luminosity0.703 ± 0.017[2] L
Surface gravity (log g)4.387 ± 0.014[2] cgs
Temperature5293 ± 32[2] K
Metallicity [Fe/H]0.16 ± 0.05[2] dex
Rotation~58.7 d
Age13.4 Gyr
Other designations
BD +26°3151, GJ 700.2, LFT 1388, SAO 85678, HIP 88348, 2MASS J18023085+2618471
Database references
SIMBADdata

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]

The HD 164922 planetary system[7][2][8][9]
Companion
(in order from star)
Mass Semimajor axis
(AU)
Orbital period
(days)
Eccentricity Inclination Radius
d ≥4±M
WIKI