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Gliese 229B

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Gliese 229B

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
Spectral typeM1Ve/T7[2]
U−B color index+1.222[2]
B−V color index+1.478[2]
Variable typeFlare star
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)173.19 ± 1.12[1] mas
Distance18.8 ± 0.1 ly
(5.77 ± 0.04 pc)
Absolute magnitude (MV)9.33[4]
Mass0.58/0.002[5] M
Radius0.69/0.047[6] R
Luminosity.02/0.00032 L
Temperature3,700[7] K
Rotational velocity (v sin i)1[8] km/s
Other designations
BD-21°1377, HD 42581, HIP 29295, LHS 1827, NSV 2863, SAO 171334, TYC 5945- 765-1

Gliese 229 (also written as Gl 229 or GJ 229) is a red dwarf star about 19 light years away in the constellation Lepus. It has 58% of the mass of the Sun,[5] 69% of the Sun's radius,[6] 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.[9] 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.[10] The orbit of this star through the Milky Way galaxy has an eccentricity of 0.07 and an orbital inclination of 0.005.[2]

Substellar companion

In 1994 a substellar companion was discovered in 1994 and confirmed in 1995 as Gliese 229B,[11] 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 20 to 50 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.[12] This object now has a surface temperature of 950 K.[13]


External links

  • Brown dwarfs (NASA)
  • Extrasolar Visions – Gliese 229
  • Extrasolar Visions – Gliese 229 b
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