Gliese 229

Gliese 229

Gliese 229 A and B.
Observation data Epoch J2000      Equinox J2000
Constellation	Lepus
Right ascension	06h 10m 34.6154s[1]
Declination	−21° 51′ 52.715″[1]
Apparent magnitude (V)	8.14
Characteristics
Evolutionary stage	Main sequence / Brown dwarf
Spectral type	M1Ve / T7[2]
U−B color index	+1.222[2]
B−V color index	+1.478[2]
Variable type	Flare star
Astrometry
Radial velocity (Rv)	+3.9[3] km/s
Proper motion (μ)	RA: –137.01[1] mas/yr Dec.: –714.05[1] mas/yr
Parallax (π)	173.5740 ± 0.0170[4] mas
Distance	18.791 ± 0.002 ly (5.7612 ± 0.0006 pc)
Absolute magnitude (MV)	9.326[5]
Absolute bolometric magnitude (Mbol)	7.96[6]
Orbit[5]
Companion	Gliese 229 B
Period (P)	237.9+5.1 −4.6 yr
Semi-major axis (a)	33.3+0.4 −0.3 AU
Eccentricity (e)	0.851+0.002 −0.008
Inclination (i)	7.7+7.6 −4.4°
Longitude of the node (Ω)	−29+13 −140°
Periastron epoch (T)	2466912+97 −63
Argument of periastron (ω) (secondary)	−9+140 −13°
Details
A
Mass	0.579[5] M☉
Radius	0.69[7] R☉
Luminosity (bolometric)	0.0430[5] L☉
Luminosity (visual, LV)	0.0158[nb 1] L☉
Temperature	3,700[6] K
Rotational velocity (v sin i)	1[8] km/s
B
Mass	71.4±0.6[5] MJup
Radius	~1.1[9] RJup
Luminosity (bolometric)	~0.000011 L☉
Temperature	950[10] K
Other designations
BD-21°1377, HD 42581, HIP 29295, LHS 1827, NSV 2863, SAO 171334, TYC 5945- 765-1
Database references
SIMBAD	A
	B

Gliese 229 (also written as Gl 229 or GJ 229) is a binary system composed of a red dwarf and the first brown dwarf seen by astronomers, about 19 light years away in the constellation Lepus. The primary component has 58% of the mass of the Sun,^[5] 69% of the Sun's radius,^[7] and a very low projected rotation velocity of 1 km/s at the stellar equator.^[8]

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.^[11] 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.^[2]

The space velocity components of this star are U = +12, V = –11 and W = –12 km/s.^[12] The orbit of this star through the Milky Way galaxy has an eccentricity of 0.07 and an orbital inclination of 0.005.^[2]

Planetary system[]

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,^[13][14] 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 70 times that of Jupiter (0.07 solar masses),^[15] 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.^[16] This object has a surface temperature of 950 K.^[10]

In March 2014, a super-Neptune mass planet candidate was announced in a much closer-in orbit around GJ 229.^[17] Given the proximity to the Sun, the orbit of GJ 229 Ab 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. GJ 229 Ac orbits the star closer in than GJ 229 Ab, located towards the outer edge but still well inside the star's habitable zone and in that sense similar to Mars in our own Solar System. GJ 229 Ab was not confirmed, but its estimated minimum mass was reduced.^[18]