HD_81799
HD 81799
Star and suspected binary system in the constellation Hydra
HD 81799 (G Hydrae) is a suspected astrometric binary[8] star system in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 4.69.[2] The distance to this system, as determined from an annual parallax shift of 19.9 mas,[1] is 164 light years. It is moving further away from the Earth with a heliocentric radial velocity of 29 km/s.[1] The system has a relatively high rate of proper motion, traversing the celestial sphere at the rate of 233±19 mas/yr along a position angle of 136°.[9]
The stellar classification of the visible component is K2+ IIIb,[3] which matches an evolved K-type giant star. It is a red clump star, which indicates it is on the horizontal branch and is generating energy through helium fusion at its core.[4] The interferometry-measured angular diameter of the primary, after correcting for limb darkening, is 1.96±0.03 mas,[10] which, at its estimated distance, equates to a physical radius of about 10.6 times the radius of the Sun.[6] It is radiating 42[5] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,490 K.[2]
The system is a likely (99.4% chance) source of the X-ray emission coming from these coordinates.[11]