Gliese 777 (Gl 777) is a 6th magnitude star in the constellation Cygnus. The system is a binary. The primary component is a yellow subgiant and the secondary component is a red dwarf. The primary component is visible to the unaided eye under very good conditions.

Gliese 777 A

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Gliese 777 A is a yellow subgiant, a Sun-like star that is ceasing fusing hydrogen in its core. The star is much older than the Sun being about 6700 million years old. It is 4% less massive than the Sun. It is also rather metal-rich having about 70% more "metals" (elements heavier than helium) than the Sun, which is typical to stars with extrasolar planets.

As of 2005 two extrasolar planets are known to be orbiting Gliese 777 A.

Planets of Gliese 777 A

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Gliese 777 Ac

Gliese 777 Ac is one of the smallest extrasolar planets discovered to date with a minimum mass just 18 times that of the Earth. It is likely a "hot Neptune", a small gas giant, or possibly a rocky "super-Earth".

Gliese 777 Ab

Gliese 777 Ab is a planet orbiting star Gliese 777 A. It was discovered in 2002 by the Geneva Extrasolar Planet Search Team using the radial velocity method that has been used to detect most of the planets found so far. The planet is at least one third more massive than Jupiter. Because the inclination of the planet's orbit is not known, the true mass is unknown. But it is unlikely to be much more than the given minimum mass.

The planet has one of the longest orbits currently known for an extrasolar planet. The planet's mean distance from the star is close to the distance between Jupiter and the Sun. However, unlike Jupiter it has a eccentric orbit. At periastron the distance between the planet and the star is only 2.50 AU and at apoastron the distance is as much as 5.34 AU (compared to our Solar system, distance from Sun to the inner asteroid belt and from Sun to just beyond the orbit of Jupiter). The gravitational influence of the red dwarf companion may have caused the eccentricity of the planet.

The signal produced by the planet is very weak and the eccentricity was originally supposed to be very circular which led to speculations of a very Jupiter-like planet. Fortunately, the inner system should be stable for Earth-like planets.

Gliese 777 B

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Gliese 777 B is a distant, dim red dwarf star orbiting the primary at a distance of 3000 AU. One orbit takes at least tens of thousands of years to complete. The star itself may be a binary, the secondary being a very dim red dwarf. Not much information is available on the star system.

See also

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• 51 Pegasi
• Gliese 229

References

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External links

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• SIMBAD: HD 190360 --High proper-motion Star (Gl 777 A) + LHS 3509 (Gl 777 B)
• Extrasolar Planets Encyclopaedia: HD 190360
• Extrasolar Visions: Gliese 777 A + Gliese 777 Ac + Gliese 777 Ab

Binary stars | Cygnus constellation | Planetary systems | HD and HDE objects | HIP objects | Yellow subgiants | Red dwarfs