Gliese 229
Encyclopedia
Gliese 229 is a red dwarf
star
about 19 light years away in the constellation
Lepus
. It 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.
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-ray
s 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.
In 1994 a substellar companion was imaged and it was confirmed in 1995. Gliese 229B is a brown dwarf
orbiting the star; although it is too small to sustain hydrogen
-burning nuclear fusion
, 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
. Gliese 229B was the first confirmed substellar-mass object. This object has a surface temperature of 950 K.
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.
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
about 19 light years away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Lepus
Lepus (constellation)
Lepus is a constellation lying just south of the celestial equator, immediately south of Orion. Its name is Latin for hare. Although the hare does not represent any particular figure in Greek mythology, Lepus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it...
. It has 58% of the mass of the Sun
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
, 69% of the Sun's radius, and a very low projected rotation velocity
Stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface....
of 1 km/s at the stellar equator.
The star is known to be a low activity flare star
Flare star
A flare star is a variable star that can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to solar flares in that they are due to magnetic reconnection in the atmospheres of the stars. The brightness increase is...
, which means it undergoes random increases in luminosity because of magnetic activity
Stellar magnetic field
A stellar magnetic field is a magnetic field generated by the motion of conductive plasma inside a star. This motion is created through convection, which is a form of energy transport involving the physical movement of material. A localized magnetic field exerts a force on the plasma, effectively...
at the surface. The spectrum shows emission lines of calcium in the H and K bands. The emission of X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s has been detected from the corona
Corona
A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...
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.
In 1994 a substellar companion was imaged and it was confirmed in 1995. Gliese 229B is a brown dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
orbiting the star; although it is too small to sustain hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
-burning nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
, with a mass of 20 to 50 times that of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
(0.02 to 0.05 solar masses) it is still too massive to be a planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
. Gliese 229B was the first confirmed substellar-mass object. This object has a surface temperature of 950 K.
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
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
galaxy has an eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
of 0.07 and an orbital inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
of 0.005.
External links
- Astronomers Announce First Clear Evidence of a Brown Dwarf – STScISpace Telescope Science InstituteThe Space Telescope Science Institute is the science operations center for the Hubble Space Telescope and for the James Webb Space Telescope...
news release STScI-1995-48 (November 29, 1995) - Brown dwarfs (NASA)
- Extrasolar Visions – Gliese 229
- Extrasolar Visions – Gliese 229 b