7 Draconis

7 Draconis, also named Tianyi /tiænˈjiː/,[6] is a single[7] star in the northern circumpolar constellation of Draco. It is visible to the naked eye as a faint orange-hued star with a stellar classification of 5.43.[2] Based upon an annual parallax shift of 4.16 mas as seen from the Earth,[1] the star is located approximately 780 light-years from the Sun.

7 Draconis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Draco
Right ascension  12h 47m 34.34473s[1]
Declination +66° 47′ 25.0977″[1]
Apparent magnitude (V) 5.43[2]
Characteristics
Spectral type K5 III[2]
B−V color index 1.567±0.006[2]
Astrometry
Radial velocity (Rv)+11.33[3] km/s
Proper motion (μ) RA: 6.674[1] mas/yr
Dec.: −6.498[1] mas/yr
Parallax (π)4.1601 ± 0.1056[1] mas
Distance780 ± 20 ly
(240 ± 6 pc)
Absolute magnitude (MV)−1.35[2]
Details
Radius67[4] R☉
Luminosity1,024.45[2] L☉
Temperature3,945[5] K
Other designations
Tianyi, 7 Dra, BD+67°764, FK5 3020, HD 111335, HIP 62423, HR 4863, SAO 15902[3]
Database references
SIMBADdata

This is an evolved giant star with a stellar classification of K5 III.[2] The measured angular diameter of this star, after correction for limb darkening, is 2.61±0.03 mas.[8] At its estimated distance, this yields a physical size of about 67 times the radius of the Sun.[4] It is radiating about 1,024[2] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 3,945 K.[5]

Nomenclature

7 Draconis is the star's Flamsteed designation.

The star bore the traditional Chinese name of Tianyi,[9] from 天乙 (Tiān Yǐ) or 天一 (Tiān Yī, the Celestial Great One), a deity in Taoism. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[10] to catalogue and standardize proper names for stars. The WGSN approved the name Tianyi for this star on 30 June 2017 and it is now so entered on the List of IAU-approved Star Names.[6]

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References
  1. 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.
  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. "6 Dra". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-01-23.
  4. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
  5. McDonald, I.; et al. (2012), "Fundamental parameters and infrared excesses of Hipparcos stars", Monthly Notices of the Royal Astronomical Society, 427: 343, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.
  6. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  7. Eggleton, P. P.; Tokovinin, A. A. (2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  8. Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.
  9. "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 7. Retrieved 2018-07-14.
  10. "International Astronomical Union | IAU". www.iau.org. Retrieved 2018-01-16.
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