Gliese 86
Encyclopedia
Gliese 86 is a K-type dwarf star
approximately 35 light-year
s away in the constellation
of Eridanus
. It has been confirmed that a white dwarf
orbits the primary star. In 2000, an extrasolar planet
was confirmed to be orbiting the star.
of spectral type K1V. The characteristics in comparison to our Sun
are 79% the mass, 86% the radius, and 35% the luminosity. The star has a close-orbiting massive Jovian planet.
Gliese 86 B is a white dwarf
star located around 21 AU from the primary star, making the Gliese 86 system one of the tightest binaries known to host an extrasolar planet. It was discovered in 2001 and initially suspected to be a brown dwarf
, but high contrast observations in 2005 suggested that the object is probably a white dwarf star, as its spectrum does not exhibit molecular absorption features which are typical of brown dwarfs. Assuming the white dwarf has a mass about half that of our Sun and that the linear trend observed in radial velocity measurements is due to Gliese 86 B, a plausible orbit for this star around Gliese 86 A has a semimajor axis of 18.42 AU and an eccentricity of 0.3974.
measurements made with the Hipparcos
space probe suggest the planet has an orbital inclination
of 164.0° and a mass 15 times Jupiter, which would make the object a brown dwarf
. However, further analysis suggests the Hipparcos measurements are not precise enough to reliably determine astrometric orbits of substellar companions, thus the orbital inclination and true mass
of the candidate planet remain unknown. It was discovered by the Swiss 1.2 m Leonhard Euler Telescope
operated by the Geneva Observatory.
The radial velocity measurements of Gliese 86 show a linear trend once the motion due to this planet are taken out. This may be associated with the orbital motion of the white dwarf companion 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...
approximately 35 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s 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....
of Eridanus
Eridanus (constellation)
Eridanus is a constellation. It is represented as a river; its name is the Ancient Greek name for the Po River. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations. It is the sixth largest of the modern...
. It has been confirmed that a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
orbits the primary star. In 2000, an extrasolar planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
was confirmed to be orbiting the star.
Stellar components
The primary companion (Gliese 86 A) is a K-type dwarf starStar
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...
of spectral type K1V. The characteristics in comparison to our Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
are 79% the mass, 86% the radius, and 35% the luminosity. The star has a close-orbiting massive Jovian planet.
Gliese 86 B is a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
star located around 21 AU from the primary star, making the Gliese 86 system one of the tightest binaries known to host an extrasolar planet. It was discovered in 2001 and initially suspected to be 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...
, but high contrast observations in 2005 suggested that the object is probably a white dwarf star, as its spectrum does not exhibit molecular absorption features which are typical of brown dwarfs. Assuming the white dwarf has a mass about half that of our Sun and that the linear trend observed in radial velocity measurements is due to Gliese 86 B, a plausible orbit for this star around Gliese 86 A has a semimajor axis of 18.42 AU and an eccentricity of 0.3974.
Planetary system
The preliminary astrometricAstrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
measurements made with the Hipparcos
Hipparcos
Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
space probe suggest the planet has 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 164.0° and a mass 15 times Jupiter, which would make the object 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...
. However, further analysis suggests the Hipparcos measurements are not precise enough to reliably determine astrometric orbits of substellar companions, thus the orbital inclination and true mass
True mass
The term true mass is synonymous with the term mass, but is used in astronomy to differentiate the measured mass of a planet from the lower limit of mass usually obtained from radial velocity techniques...
of the candidate planet remain unknown. It was discovered by the Swiss 1.2 m Leonhard Euler Telescope
Leonhard Euler Telescope
Leonhard Euler Telescope, or Swiss 1.2-m Leonhard Euler Telescope, is a diameter aperture reflecting telescope at the Geneva Observatory at La Silla Observatory. It is use for astronomy, and runs the CORALIE echelle spectrograph to search for planets. Its first planet discovery was of one in orbit...
operated by the Geneva Observatory.
The radial velocity measurements of Gliese 86 show a linear trend once the motion due to this planet are taken out. This may be associated with the orbital motion of the white dwarf companion star.