HD 81817

HD 81817 is a binary star[8] system in the northern circumpolar constellation of Draco. It has an orange hue and is visible to the naked eye with an apparent visual magnitude of 4.28.[2] The system is located at a distance of approximately 990 light years from the Sun based on parallax,[1] and is drifting closer with a radial velocity of −7 km/s.[2] It is a member of the IC 2391 moving group.[9]

HD 81817
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Draco
Right ascension  09h 37m 05.28778s[1]
Declination +81° 19′ 34.9711″[1]
Apparent magnitude (V) 4.28[2]
Characteristics
Spectral type K3III + DA2.8[3]
B−V color index +1.488±0.001[2]
Astrometry
Radial velocity (Rv)−6.98±0.10[2] km/s
Proper motion (μ) RA: −16.62[1] mas/yr
Dec.: −16.41[1] mas/yr
Parallax (π)3.28 ± 0.15[1] mas
Distance990 ± 50 ly
(300 ± 10 pc)
Absolute magnitude (MV)−3.14[2]
Details
A
Mass8.5±0.4[4] M☉
Radius109.46+1.09
−2.99[5] R☉
Luminosity2,885±252[5] L☉
Temperature4,043+65
−20[5] K
Metallicity [Fe/H]0.18±0.06[2] dex
Age31.9±2.7[4] Myr
B
Temperature~20,000[6] K
Other designations
BD+81°302, FK5 910, HD 81817, HIP 47193, HR 3751, SAO 1551, WD 0930+815[7]
Database references
SIMBADdata

The primary component of this system is an aging giant star with a stellar classification of K3III.[3] The star's chromosphere is of the type called "hybrid", displaying a cool stellar wind in combination with hot emission lines.[10] It appears to be the source for the X-ray emission coming from this system.[6] The star is 32[4] million years old with 8.5[4] times the mass of the Sun. With the supply of hydrogen at its core exhausted, the star has expanded to 109[5] times the Sun's radius. It is radiating 2,885 times the luminosity of the Sun from its photosphere at an effective temperature of 4,043.[5]

The companion star was discovered in 1984 based upon its ultraviolet spectrum. The distribution of the far ultraviolet flux matches that of a white dwarf star of class DA.[8]

References
  1. van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015.
  3. Holberg, J. B.; et al. (2013). "Where are all the Sirius-like binary systems?". Monthly Notices of the Royal Astronomical Society. 435 (3): 2077. arXiv:1307.8047. Bibcode:2013MNRAS.435.2077H. doi:10.1093/mnras/stt1433.
  4. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x.
  5. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  6. Bilíková, Jana; et al. (November 2010). "Hard X-ray Emission Associated with White Dwarfs. III". The Astronomical Journal. 140 (5): 1433–1443. Bibcode:2010AJ....140.1433B. doi:10.1088/0004-6256/140/5/1433.
  7. "HD 90264". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-01-26.
  8. Reimers, D. (July 1984). "Discovery of a white dwarf companion of the "hybrid" K giant HD 81817". Astronomy and Astrophysics. 136: L5–L6. Bibcode:1984A&A...136L...5R.
  9. Montes, D.; et al. (November 2001). "Late-type members of young stellar kinematic groups - I. Single stars". Monthly Notices of the Royal Astronomical Society. 328 (1): 45–63. arXiv:astro-ph/0106537. Bibcode:2001MNRAS.328...45M. doi:10.1046/j.1365-8711.2001.04781.x.
  10. Ayres, Thomas R. (January 2005). "X-Rays from Hybrid Stars". The Astrophysical Journal. 618 (1): 493–501. Bibcode:2005ApJ...618..493A. doi:10.1086/425891.
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