Eta Draconis

Eta Draconis (η Draconis, abbreviated Eta Dra, η Dra) is a binary star in the northern circumpolar constellation of Draco. Despite having an apparent visual magnitude of only +2.73,[2] it is the second-brightest star in this generally faint constellation. Based upon parallax measurements collected during the Hipparcos mission, this star is located at a distance of about 92.1 light-years (28.2 parsecs) from the Sun.[1]

η Draconis
Location of η Draconis (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Draco
Right ascension 16h 23m 59.48594s[1]
Declination +61° 30′ 51.1699″[1]
Apparent magnitude (V) +2.73[2]
Characteristics
Spectral type G8 III[2]
U−B color index +0.70[3]
B−V color index +0.91[3]
Astrometry
Radial velocity (Rv)–14.3[4] km/s
Proper motion (μ) RA: –17.02[1] mas/yr
Dec.: +56.95[1] mas/yr
Parallax (π)35.42 ± 0.09[1] mas
Distance92.1 ± 0.2 ly
(28.23 ± 0.07 pc)
Absolute magnitude (MV)+0.58[5]
Details
Mass2.55[2] M☉
Radius11[6] R☉
Luminosity60[2] L☉
Surface gravity (log g)2.82[2] cgs
Temperature5,055[2] K
Metallicity [Fe/H]–0.04[2] dex
Rotational velocity (v sin i)8[7] km/s
Age550[2] Myr
Other designations
Aldibain, Athebyne, 14 Draconis, BD+61 1591, FK5 822, HD 148387, HIP 80331, HR 6132, NSV 7713, SAO 17074, WDS 16240+6131.[8]
Database references
SIMBADdata

The two components are designated Eta Draconis A (also named Athebyne /ˈæθɪbaɪn/[9]) and B.

Nomenclature

η Draconis (Latinised to Eta Draconis) is the system's Bayer designation. The designations of the two components as Eta Draconis A and B derives from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[10]

Eta Draconis, together with Zeta Draconis, bore the traditional Arabic name الذئبين al-dhiʼbayn, "the (two) wolves" (the Duo Lupi), lying in wait for the camel's foal, the little star Al Rubaʽ, protected by the Mother Camels.[11]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[12] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[13] It approved the name Athebyne (a rendering of adh-dhiʼbayn) for the component Eta Draconis A on 5 September 2017. It approved the name Aldhibah (the female wolf) for Zeta Draconis A on the same date. Both are now so included in the List of IAU-approved Star Names.[9]

In Chinese, 紫微左垣 (Zǐ Wēi Zuǒ Yuán), meaning Left Wall of Purple Forbidden Enclosure, refers to an asterism consisting of Eta Draconis, Iota Draconis, Theta Draconis, Zeta Draconis, Upsilon Draconis, 73 Draconis, Gamma Cephei and 23 Cassiopeiae.[14] Consequently, the Chinese name for Eta Draconis itself is 紫微左垣三 (Zǐ Wēi Zuǒ Yuán sān, English: the Third Star of Left Wall of Purple Forbidden Enclosure),[15] representing 少宰 (Shàozǎi), meaning The Second Premier.[16] Possibly, 少宰 (Shàozǎi) is westernized into Hea Tsae by R.H. Allen with meaning "the Lowest Steward" but it was for Theta Draconis.[17]

Properties

Eta Draconis A is a star with 2.55[2] times the mass of the Sun. The spectrum matches a stellar classification of G8 III,[2] with the luminosity class III indicating this is an evolved giant star that has exhausted the supply of hydrogen at its core. It reached this stage in only 550[2] million years because higher mass stars such as this consume the supply of hydrogen more rapidly than the Sun. The measured angular diameter of this star, after correction for limb darkening, is 3.72 ± 0.07 mas.[18] At the estimated distance of Eta Draconis,[1] this yields a physical size of about 11 times the radius of the Sun.[6] From its extended envelope, it is radiating around 60 times the luminosity of the Sun at an effective temperature of 5,055 K,[2] giving it the yellow glow of a G-type star.[19]

Eta Draconis B is located at an angular separation of 5.1 arcseconds from the primary. This is an 8.8 magnitude K-type main sequence star with a stellar classification of K2 V.[20] At the estimated distance of this star system, the two stars are separated by a physical distance of at least 140 AU and require at least a millennium to complete an orbit.[21]

References
  1. van Leeuwen, F. (November 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. Takeda, Yoichi; Sato, Bun'ei; Murata, Daisuke (August 2008), "Stellar parameters and elemental abundances of late-G giants", Publications of the Astronomical Society of Japan, 60 (4): 781–802, arXiv:0805.2434, Bibcode:2008PASJ...60..781T, doi:10.1093/pasj/60.4.781
  3. Nicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System". Astronomy and Astrophysics Supplement Series. 34: 1–49. Bibcode:1978A&AS...34....1N.
  4. Wilson, Ralph Elmer (1953). General Catalogue of Stellar Radial Velocities. Washington: Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W.
  5. Pizzolato, N.; Maggio, A.; Sciortino, S. (September 2000), "Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases", Astronomy and Astrophysics, 361: 614–628, Bibcode:2000A&A...361..614P
  6. 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:
  7. Bernacca, P. L.; Perinotto, M. (1970). "A catalogue of stellar rotational velocities". Contributi Osservatorio Astronomico di Padova in Asiago. 239 (1). Bibcode:1970CoAsi.239....1B.
  8. "eta Dra". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-02-20.
  9. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  10. Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  11. Star Name - R.H Allen p. 202
  12. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  13. "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  14. (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  15. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 10 日
  16. (in Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name Archived August 10, 2010, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  17. Star Name - R.H. Allen p. 210
  18. Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039
  19. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-10, retrieved 2012-01-16
  20. Eggleton, P. P.; Tokovinin, A. A. (September 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.
  21. Kaler, James B., "AL DHIBAIN "PRIOR" (Eta Draconis)", Stars, University of Illinois, retrieved 2012-02-20
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