Английская Википедия:Eta2 Hydri

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Eta² Hydri is a star in the southern constellation of Hydrus. The name is latinized from η² Hydri and often catalogued as HD 11977. It is visible to the naked eye with an apparent visual magnitude of +4.68, and is one of the least variable stars known. The distance to Eta² Hydri is approximately 221 light-years based on parallax measurements, but it is drifting closer to the Sun with a radial velocity of −18 km/s.

The stellar classification of Eta² Hydri is G8IIIb, which indicates this is a evolved giant star. It is located in the clump zone of the HR diagram, which means it has already ascended the red giant branch and is now generating energy by core helium fusion surrounded by a hydrogen fusing shell. Based on its mass, it was probably a class A star (similar to Vega or Fomalhaut) when it was on the main sequence. It is estimated to be around 1.3 billion years old and has expanded to 10 times the Sun's diameter, though is only around 1.9 times as massive as the Sun. The star has a leisurely rotation, with a period of no more than 230–270 days. As of 2005, an extrasolar planet was confirmed to be orbiting the star.

Planetary system

In 2005, the giant planet Eta² Hydri b was found in orbit around Eta² Hydri by measuring radial velocity variations. This object has at least 6.3 times the mass of Jupiter and is orbiting with a period of Шаблон:Convert. It is the first giant planet to be found in orbit around an intermediate-mass giant star.

See also

• HD 11964

External links

• Шаблон:Cite encyclopedia