HD 81799

HD 81799
Observation data
Epoch J2000      Equinox J2000
Constellation Hydra
Right ascension 09h 27m 18.43258s[1]
Declination −22° 20′ 37.4967″[1]
Apparent magnitude (V) 4.69[2]
Characteristics
Spectral type K2+ IIIb[3]
B−V color index 1.154[4]
Astrometry
Radial velocity (Rv)29.05±0.28[1] km/s
Proper motion (μ) RA: +160.160[1] mas/yr
Dec.: −173.131[1] mas/yr
Parallax (π)19.8887 ± 0.3128 mas[1]
Distance164 ± 3 ly
(50.3 ± 0.8 pc)
Absolute magnitude (MV)1.32[5]
Details
Radius10.6[6] R☉
Luminosity41.97[5] L☉
Surface gravity (log g)2.43[2] cgs
Temperature4,490[2] K
Metallicity [Fe/H]−0.01[2] dex
Other designations
G Hya, BD−21° 2802, HD 81799, HIP 46371, HR 3749, SAO 177469, LTT 3479[7]
Database references
SIMBADdata

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]

  1. ^ a b c d e f g h Cite error: The named reference GaiaDR2 was invoked but never defined (see the help page).
  2. ^ a b c d e f Cite error: The named reference Soubiran2010 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference Keenan1989 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference Alves2000 was invoked but never defined (see the help page).
  5. ^ a b c Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference lang2006 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Eggleton2008 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Wroblewski1998 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Richichi2005 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Haakonsen2009 was invoked but never defined (see the help page).