Gliese 86 (13 G. Eridani, HD 13445) is a

K-type main-sequence star A K-type main-sequence star, also referred to as a K-type dwarf or an orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ...

approximately 35

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s away in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

of Eridanus. It has been confirmed that a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fro ...

orbits the primary star. In 1998 the

European Southern Observatory The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental organization, intergovernmental research organisation made up of 16 mem ...

announced that an extrasolar planet was orbiting the star.

Stellar components

The primary companion (Gliese 86 A) is a K-type main-sequence

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

of spectral type K1V. The characteristics in comparison to the Sun are 83% the mass, 79% the radius, and 50% the luminosity. The star has a close-orbiting massive

Jovian planet The giant planets constitute a diverse type of planet much larger than Earth. They are usually primarily composed of low-boiling-point materials (volatiles), rather than rock or other solid matter, but massive solid planets can also exist. Ther ...

. Gliese 86 B is a

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 dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

, but high contrast observations in 2005 suggested that the object is probably a white dwarf, 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 In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the longe ...

of 18.42 AU and an eccentricity of 0.3974. When both stars were on the main sequence, the separation between the two stars was closer, at around 9 AU. More precise measurements for the white dwarf give it a mass of 55% the mass of the Sun and a temperature of around 8200 K.

Planetary system

The preliminary

astrometric Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. Histor ...

measurements made with the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

space probe suggest the planet has an orbital

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...

of 164.0° and a mass 15 times Jupiter, which would make the object a

. 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 Leonhard Euler Telescope, or the Swiss EULER Telescope, is a national, fully automatic reflecting telescope, built and operated by the Geneva Observatory. It is located at an altitude of at ESO's La Silla Observatory site in the Chilean Norte ...

operated by the Geneva Observatory. Such an object was formed from a protoplanetary disk that was truncated at 2 AU from the parent star. 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.

References

External links

* {{DEFAULTSORT:Gliese 86 K-type main-sequence stars White dwarfs Gliese, 0086 Planetary systems with one confirmed planet ? Eridani, 13 010138 013445 Durchmusterung objects 0086 0637 TIC objects

Stellar components

Planetary system

See also

References

External links