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Gliese 229

Gliese 229 A and B
Observation data Epoch J2000      Equinox J2000
Constellation	Lepus
Right ascension	06 10 34.61494
Declination	−21° 51′ 52.6564″
Apparent magnitude (V)	8.14
Characteristics
Evolutionary stage	Main sequence / Brown dwarf
Spectral type	M1Ve +T7+T8
U−B color index	+1.222
B−V color index	+1.478
Variable type	Flare star
Astrometry
Radial velocity (Rv)	4.23±0.12 km/s
Proper motion (μ)	RA: −135.692(11) mas/yr Dec.: −719.178(17) mas/yr
Parallax (π)	173.5740 ± 0.0170 mas
Distance	18.791 ± 0.002 ly (5.7612 ± 0.0006 pc)
Absolute magnitude (MV)	9.326
Absolute bolometric magnitude (Mbol)	7.96
Orbit
Primary	Gliese 229 A
Companion	Gliese 229 B
Period (P)	216.925+10.604 −10.352 yr
Semi-major axis (a)	28.933+1.008 −1.000 AU
Eccentricity (e)	0.853±0.002
Inclination (i)	5.497+0.153 −0.162°
Longitude of the node (Ω)	145.946+0.306 −0.294°
Periastron epoch (T)	2466912+97 −63
Argument of periastron (ω) (secondary)	358.285+0.836 −0.846°
Semi-amplitude (K1) (primary)	0.081674+0.001688 −0.001680 km/s
Orbit
Primary	Gliese 229 Ba
Companion	Gliese 229 Bb
Period (P)	12.134±0.003 d
Semi-major axis (a)	0.0424±0.0004 AU
Eccentricity (e)	0.234±0.004
Inclination (i)	31.4±0.3°
Longitude of the node (Ω)	213±2°
Periastron epoch (T)	2460378.38±0.04
Argument of periastron (ω) (secondary)	0.7±1.2°
Details
A
Mass	0.579 M☉
Radius	0.549±0.043 R☉
Luminosity (bolometric)	0.0430 L☉
Luminosity (visual, LV)	0.0158 L☉
Surface gravity (log g)	4.695±0.035 cgs
Temperature	3,700 K
Metallicity	−0.02±0.06
Rotation	27.3±0.2 d
Rotational velocity (v sin i)	1 km/s
Ba
Mass	38.1±1.0 MJup
Radius	0.81+0.05 −0.12 RJup
Luminosity (bolometric)	3.890+0.375 −0.342×10 L☉
Surface gravity (log g)	5.15±0.04 cgs
Temperature	900+78 −29 K
Metallicity	0.00+0.04 −0.03
Age	2.45±0.20 Gyr
Bb
Mass	34.4±1.5 MJup
Radius	0.85+0.12 −0.05 RJup
Luminosity (bolometric)	2.630+0.254 −0.231×10 L☉
Surface gravity (log g)	5.07+0.04 −0.011 cgs
Temperature	775+20 −33 K
Metallicity	0.00+0.04 −0.03
Age	2.45±0.20 Gyr
Other designations
NSV 2863, BD−21°1377, GJ 229, HD 42581, HIP 29295, SAO 171334, LHS 1827, TYC 5945-765-1
Database references
SIMBAD	A
	B
Gliese 229Location of Gliese 229 in the constellation Lepus

Gliese 229 (also written as Gl 229 or GJ 229) is a multiple system composed of a red dwarf and two brown dwarfs, located 18.8 light years away in the constellation Lepus. The primary component has 58% of the mass of the Sun, 55% of the Sun's radius, and a very low projected rotation velocity of 1 km/s at the stellar equator.

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.

Companions

Brown dwarf

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, It was one of the first two brown dwarfs to be confirmed. Although too small to sustain hydrogen-burning nuclear fusion as in a main sequence star, with a mass of around 40 to 60 times that of Jupiter (0.06 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 has a surface temperature of 950 K.

Gliese 229B is the prototype of the T-dwarfs, due to the detection of methane in its spectrum. It also shows other molecules in its atmosphere, namely water vapor, carbon monoxide and ammonia. Atomic absorption lines of caesium, sodium and potassium are also detected.

The most recent parameters for Gliese 229 B as of 2022 come from a combination of data from radial velocity, astrometry, and imaging, showing that it is about 60.4 times the mass of Jupiter, and on an eccentric orbit with a semi-major axis of about 28.9 AU and an orbital period of about 217 years.

Inconsistencies between the measured mass and luminosity of Gliese 229 B suggested that it may in fact be an unresolved binary brown dwarf. Further evidence that Gliese 229B is an equal-mass binary comes from high-resolution spectroscopy from the Subaru Telescope. The binary was resolved in 2024 with VLT/GRAVITY and VLT/CRIRES+. The components are called Gliese 229 Ba (38.1±1.0 M_J) and Gliese 229 Bb (34.4±1.5 M_J). The pair is a tight binary with an orbital period of 12.1 days and a semi-major axis of 0.042 astronomical units (about 16 Earth-Moon distances). The changes in radial velocity extracted from CRIRES+ helped to resolve the orbit of Gliese 229B. The binary has an inclination of 31.4 ±0.3° and an eccentricity of 0.234 ±0.004. The inclination of the binary is misaligned by 37+7
−10° in respect to the orbit of Gliese 229B around Gliese 229A. Additional radial velocity changes between two epochs were detected in Gliese 229B with Keck NIRSPEC. This team independently discovered the binarity of Gliese 229B.

Gliese 229B was observed with JWST MIRI low resolution spectroscopy. Previous works showed a difference in abundances between host star and companion in Gliese 229 from near-infrared spectra. This new study using mid-infrared data showed that the pair has abundances consistent with the host star. The metallicities were measured to be C/O = 0.65 ±0.05 and =0.00+0.04
−0.03 and are equal for each brown dwarf in the pair. The host star has C/O = 0.68 ± 0.12 and = −0.02 ± 0.06.

Planetary system

In March 2014, a super-Neptune mass planet candidate was announced in a much closer-in orbit around GJ 229. Given the proximity of the Gliese 229 system 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. While considering GJ 229 Ab unconfirmed, the study estimated a significantly lower minimum mass for it. As of 2022, most sources consider both planets to be confirmed.

If the planets Gliese 229 Ab & c orbit in the same plane as the brown dwarf Gliese 229 B, their true masses would be significantly greater than their minimum masses, making them both nearly as massive as Saturn.

See also

• List of exoplanets discovered in 2014 - Gliese 229 Ab
• List of exoplanets discovered in 2020 - Gliese 229 Ac
• Epsilon Indi

Notes

1. Using the absolute visual magnitude of Gliese 229 A ${\displaystyle \scriptstyle M_{V_{\ast }}=9.33}$ and the absolute visual magnitude of the Sun ${\displaystyle \scriptstyle M_{V_{\odot }}=4.83}$, the visual luminosity can be calculated by ${\displaystyle \scriptstyle {\frac {L_{V_{\ast }}}{L_{V_{\odot }}}}=10^{0.4\left(M_{V_{\odot }}-M_{V_{\ast }}\right)}}$
2. 7.268 M_E/sin(5.497°) = 75.87 M_E
   8.478 M_E/sin(5.497°) = 88.50 M_E

References

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External links

• Brown dwarfs (NASA)
• It's Twins! Mystery of Famed Brown Dwarf Solved press release by Caltech

v t e Constellation of Lepus
Lepus in Chinese astronomy List of star names in Lepus List of stars in Lepus
Stars	Bayer α (Arneb) β (Nihal) γ δ ε ζ η θ ι κ λ μ ν Flamsteed 1 8 10 12 17 19 4 Mon Variable R T RX AF AK HR 1621 1762 HD 31527 32450 32667 33142 33283 Other 2MASS J0523−1403 Gliese 229 WASP-49 WASP-61
Exoplanets HD 33283 b
Star clusters Messier 79
Nebulae Abell 7 IC 418
Galaxies	NGC 1964 1979 1993 2139 Other IRAS 06076-2139 PKS 0454-234
Category

• Binary stars
• Flare stars
• Gliese and GJ objects
• Lepus (constellation)
• M-type main-sequence stars
• T-type brown dwarfs
• Henry Draper Catalogue objects
• Astronomical objects discovered in 1994
• Durchmusterung objects
• Hipparcos objects
• Planetary systems with two confirmed planets
• TIC objects