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Star in the constellation Lepus From Wikipedia, the free encyclopedia
Gliese 229 (also written as Gl 229 or GJ 229) is a multiple system composed of a red dwarf and two brown dwarfs,[3][10] located 18.8 light years away in the constellation Lepus. The primary component has 58% of the mass of the Sun,[4] 55% of the Sun's radius,[7] and a very low projected rotation velocity of 1 km/s at the stellar equator.[9]
Gliese 229 A and B | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Lepus |
| Right ascension | 06h 10m 34.61494s[1] |
| Declination | −21° 51′ 52.6564″[1] |
| Apparent magnitude (V) | 8.14 |
| Characteristics | |
| Evolutionary stage | Main sequence / Brown dwarf |
| Spectral type | M1Ve [2]+T7+T8[3] |
| U−B color index | +1.222[2] |
| B−V color index | +1.478[2] |
| Variable type | Flare star |
| Astrometry | |
| Radial velocity (Rv) | 4.23±0.12[1] km/s |
| Proper motion (μ) | RA: −135.692(11) mas/yr[1] Dec.: −719.178(17) mas/yr[1] |
| Parallax (π) | 173.5740 ± 0.0170 mas[1] |
| Distance | 18.791 ± 0.002 ly (5.7612 ± 0.0006 pc) |
| Absolute magnitude (MV) | 9.326[4] |
| Absolute bolometric magnitude (Mbol) | 7.96[5] |
| Orbit[4][6] | |
| 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[3] | |
| 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[4] M☉ |
| Radius | 0.549±0.043[7] R☉ |
| Luminosity (bolometric) | 0.0430[4] L☉ |
| Luminosity (visual, LV) | 0.0158[nb 1] L☉ |
| Surface gravity (log g) | 4.695±0.035[7] cgs |
| Temperature | 3,700[5] K |
| Rotation | 27.3±0.2 d[8] |
| Rotational velocity (v sin i) | 1[9] km/s |
| Ba | |
| Mass | 38.1±1.0[3] MJup |
| Radius | 0.089 ± 0.006[3][lower-alpha 1] R☉ |
| Radius | 0.884 RJup |
| Radius | 61,800 ± 4,050 km |
| Luminosity (bolometric) | 3.890+0.375 −0.342×10−6 L☉ |
| Surface gravity (log g) | 5.11±0.01[3] cgs |
| Temperature | 860±20[3] K |
| Age | 2.45±0.20[3] Gyr |
| Bb | |
| Mass | 34.4±1.5[3] MJup |
| Radius | 0.091 ± 0.006[3][lower-alpha 1] R☉ |
| Radius | 0.907 RJup |
| Radius | 63,400 ± 4,400 km |
| Luminosity (bolometric) | 2.630+0.254 −0.231×10−6[3] L☉ |
| Surface gravity (log g) | 5.03±0.01[3] cgs |
| Temperature | 770±20[3] K |
| Age | 2.45±0.20[3] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | A |
| B | |
  Gliese 229 Location of Gliese 229 in the constellation Lepus | |
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]
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] It was the first brown dwarf 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),[6][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.[17]
Gliese 229B is the prototype of the T-dwarfs, due to the detection of methane in its spectrum.[18] It also shows other molecules in its atmosphere, namely water vapor,[19] carbon monoxide[20] and probably ammonia.[21] Atomic absorption lines of caesium,[22] sodium and potassium are also detected.[23]
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.[6]
Inconsistencies between the measured mass and luminosity of Gliese 229 B suggested that it may in fact be an unresolved binary brown dwarf.[4][24] Further evidence that Gliese 229B is an equal-mass binary comes from high-resolution spectroscopy from the Subaru Telescope.[25] The binary was resolved in 2024 with VLT/GRAVITY and VLT/CRIRES+. The components are called Gliese 229 Ba (38.1±1.0 MJ) and Gliese 229 Bb (34.4±1.5 MJ). 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.[3] Additional radial velocity changes between two epochs were detected in Gliese 229B with Keck NIRSPEC. This team independently discovered the binarity of Gliese 229B.[10]
In March 2014, a super-Neptune mass planet candidate was announced in a much closer-in orbit around GJ 229.[26] 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.[27] As of 2022[update], most sources consider both planets to be confirmed.[6][28][29][30]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| c | ≥7.268±1.256 M🜨 | 0.339±0.011 | 121.995±0.161 | 0.19±0.08 | — | — |
| b | ≥8.478±2.033 M🜨 | 0.898±0.031 | 526.115±4.300 | 0.10±0.06 | — | — |
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.[nb 2]
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