Gliese 229 (also written as Gl 229 or GJ 229) is a binary system composed of red dwarf and brown dwarf about 19 light years away in the constellation Lepus. Primary component has 58% of the mass of the Sun, 69% of the Sun's radius, and a very low projected rotation velocity of 1 km/s at the stellar equator.
Epoch J2000 Equinox J2000
|Right ascension||06h 10m 34.6154s|
|Declination||−21° 51′ 52.715″|
|Apparent magnitude (V)||8.14|
|U−B color index||+1.222|
|B−V color index||+1.478|
|Variable type||Flare star|
|Radial velocity (Rv)||+3.9 km/s|
|Proper motion (μ)|| RA: –137.01 mas/yr |
Dec.: –714.05 mas/yr
|Parallax (π)||173.81 ± 0.99 mas|
|Distance||18.8 ± 0.1 ly |
(5.75 ± 0.03 pc)
|Absolute magnitude (MV)||9.33|
|Luminosity (bolometric)||0.052[nb 1]/~0.000011 L☉|
|Luminosity (visual, LV)||0.0158[nb 2] L☉|
|Rotational velocity (v sin i)||1 km/s|
The star is known to be a low activity flare star, which means it undergoes random increases in luminosity because of magnetic activity at the surface. The spectrum shows emission lines of calcium in the H and K bands. The emission of X-rays has been detected from the corona of this star. These may be caused by magnetic loops interacting with the gas of the star's outer atmosphere. No large-scale star spot activity has been detected.
The space velocity components of this star are U = +12, V = –11 and W = –12 km/s. The orbit of this star through the Milky Way galaxy has an eccentricity of 0.07 and an orbital inclination of 0.005.
A substellar companion was discovered in 1994 by Caltech astronomers Kulkarni, Tadashi Nakajima, Keith Matthews, and Rebecca Oppenheimer, and Johns Hopkins scientists Sam Durrance and David Golimowski. It was confirmed in 1995 as Gliese 229B, one of the first two instances of clear evidence for a brown dwarf, along with Teide 1. Although too small to sustain hydrogen-burning nuclear fusion as in a main sequence star, with a mass of 21 to 52.4 times that of Jupiter (0.02 to 0.05 solar masses), it is still too massive to be a planet. As a brown dwarf, its core temperature is high enough to initiate the fusion of deuterium with a proton to form helium-3, but it is thought that it used up all its deuterium fuel long ago. This object now has a surface temperature of 950 K.
In March 2014, a super-Neptune mass planet candidate was announced in a much closer-in orbit around GJ 229. Given the proximity to the Sun, the orbit of GJ 229Ab might be fully characterized by the Gaia space-astrometry mission or via direct imaging. In 2020, a super-Earth mass planet was discovered around GJ 229. It orbits the star closer in than GJ 229Ab, and is located in the star's habitable zone.
(in order from star)
|GJ 229Ac||≥7.93 M⊕||0.339||122.005||0.29||—||—|
|GJ 229Ab||≥10.02 M⊕||0.896||523.242||0.17||—||—|
|GJ 229B||≥1.62 MJ||19.433||~50000||0.03||—||0.468 RJ|
Note: Minimum mass of GJ 229B as measured by radial velocity measurements is 1.62 Mj. However, observations of GJ 229B suggest, that the system is viewed with a relative face-on orientation with an inclination of 13+10
−12. If that is true and the planetary system is coplanar, then the real masses of all plantes would be at least ~4.5 times more massive than the minimal mass derived from radial velocity measurements (2.6 up to 57 times of minimal mass, depending on exact value of inclination).
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- Brandt, Timothy D.; Dupuy, Trent J.; Bowler, Brendan P.; Gagliuffi, Daniella C. Bardalez; Faherty, Jacqueline; Brandt, G. Mirek; Michalik, Daniel (2019-10-03). "A Dynamical Mass of 70±5 Jupiter Masses for Gliese 229B, the First Imaged T Dwarf". arXiv:1910.01652 [astro-ph.SR].
- Using the absolute bolometric magnitude of Gliese 229 A and the absolute bolometric magnitude of the Sun , the bolometric luminosity can be calculated by
- Using the absolute visual magnitude of Gliese 229 A and the absolute visual magnitude of the Sun , the visual luminosity can be calculated by
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