θ Draconis
Location of θ Draconis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Right ascension 16h 01m 53.34636s[1]
Declination +58° 33′ 54.9056″[1]
Apparent magnitude (V) 4.1190[1]
Characteristics
Spectral type F9 V[2] or F8IV-V[3][4]
U−B color index +0.11[5]
B−V color index +0.528±0.013[6]
Astrometry
Radial velocity (Rv)−8.23±0.20[6] km/s
Proper motion (μ) RA: −319.51[1] mas/yr
Dec.: 334.97[1] mas/yr
Parallax (π)47.54 ± 0.12 mas[1]
Distance68.6 ± 0.2 ly
(21.03 ± 0.05 pc)
Absolute magnitude (MV)2.39[7]
Orbit[8]
Period (P)3.0708216±0.0000069 d
Semi-major axis (a)~0.048 AU (10 R☉)[9]
Eccentricity (e)0.039±0.012
Periastron epoch (T)5,971.98±0.13
Argument of periastron (ω)
(secondary)		63±15°
Semi-amplitude (K1)
(primary)		25.10±0.31 km/s
Semi-amplitude (K2)
(secondary)		66.0±2.2 km/s
Details[7]
A
Mass1.53 M☉[7]
1.2±0.1 M☉[8]
1.18[3] M☉
Radius2.83+0.12
−0.05[10] R☉
Luminosity9.998±0.137[10] L☉
Surface gravity (log g)3.79 cgs
Temperature6,105+53
−129[10] K
Metallicity [Fe/H]+0.19 dex
Rotational velocity (v sin i)30.7 km/s
Age2.03 Gyr
B
Mass0.46±0.04 M☉[8]
0.21[3] M☉
Other designations
θ Dra, 13 Her, BD+58°1608, FK5 598, HD 144284, HIP 78527, HR 5986, SAO 29765[11]
Database references
SIMBADdata

Theta Draconis, a name Latinized from θ Draconis, is a binary star system in the northern circumpolar constellation of Draco. It is faintly visible to the naked eye at night with an apparent visual magnitude of 4.12.[1] Parallax measurements place it at an estimated distance of 68.6 light-years (21.0 parsecs) from the Sun,[1] and it is drifting closer with a radial velocity of −8 km/s.[6] It has a relatively high proper motion, traversing the celestial sphere at the rate of 0.464″ per year.[12] O. J. Eggen included this star as a member of the NGC 1901 supercluster based on its space motion.[13]

The binary nature of this system was discovered by W. W. Campbell in 1899, and the first set of orbital elements was published by H. D. Curtis in 1907.[14] It is a single-lined spectroscopic binary in a close orbit with a period of 3.07 days and an eccentricity (ovalness) of 0.04.[2] The secondary component has been resolved in the infrared H band, allowing an estimation of the mass ratio as 0.38±0.03.[8] Some velocity variation of K1 was observed by M. Mayor and T. Mazeh in 1987, which is suggestive of a tertiary component to the system.[15]

The primary component is a solar-type star[4] that at various times has been assigned stellar classifications of F9 V[2] and F8IV-V.[3] The star is about two billion years old and is spinning with a projected rotational velocity of 31 km/s.[7] It has a high metallicity (heavy element abundances) with around 20%[8] more mass than the Sun and nearly three[10] times the Sun's radius. The star displays no chromospheric emission and may be on or entering the subgiant stage. Because of the close orbit, it could be filling up to 60% of its Roche lobe.[16] The star is radiating ten times the luminosity of the Sun from its photosphere at an effective temperature of 6,105 K.[10]

Chinese name

In Chinese, 紫微左垣 (Zǐ Wēi Zuǒ Yuán), meaning Left Wall of Purple Forbidden Enclosure, refers to an asterism consisting of θ Draconis, ι Draconis, η Draconis, ζ Draconis, υ Draconis, 73 Draconis, γ Cephei and 23 Cassiopeiae.[17] Consequently, the Chinese name for θ Draconis itself is 紫微左垣二 (Zǐ Wēi Zuǒ Yuán èr, English: the Second Star of Left Wall of Purple Forbidden Enclosure.),[18] representing 上宰 (Shǎngzǎi), meaning The First Premier.[19] 上宰 (Shǎngzǎi) is westernized into Shang Tsae by R.H. Allen with meaning "the Minor Steward" but it was for η Dra (Aldibain).[20]

References

  1. 1 2 3 4 5 6 7 8 van Leeuwen, F. (November 2007). "Hipparcos, the New Reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600. Retrieved 2010-11-21.
  2. 1 2 3 Abt, Helmut A. (2009). "MK Classifications of Spectroscopic Binaries". The Astrophysical Journal Supplement. 180 (1): 117–18. Bibcode:2009ApJS..180..117A. doi:10.1088/0067-0049/180/1/117. S2CID 122811461.
  3. 1 2 3 4 Tokovinin, A.; et al. (May 2006). "Tertiary companions to close spectroscopic binaries". Astronomy and Astrophysics. 450 (2): 6811–693. arXiv:astro-ph/0601518. Bibcode:2006A&A...450..681T. doi:10.1051/0004-6361:20054427. S2CID 8899546.
  4. 1 2 Mazeh, Tsevi; et al. (December 1992). "On the Mass-Ratio Distribution of Spectroscopic Binaries with Solar-Type Primaries". Astrophysical Journal. 401: 265. Bibcode:1992ApJ...401..265M. doi:10.1086/172058.
  5. ↑ Mermilliod, J. -C (1986). "Compilation of Eggen's UBV data, transformed to UBV (Unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  6. 1 2 3 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. S2CID 119257644.
  7. 1 2 3 4 Luck, R. Earle (January 2017). "Abundances in the Local Region II: F, G, and K Dwarfs and Subgiants". The Astronomical Journal. 153 (1): 19. arXiv:1611.02897. Bibcode:2017AJ....153...21L. doi:10.3847/1538-3881/153/1/21. S2CID 119511744. 21.
  8. 1 2 3 4 5 Mazeh, Tsevi; et al. (January 2002). "Infrared Detection of Low-Mass Secondaries in Spectroscopic Binaries". The Astrophysical Journal. 564 (2): 1007–1014. arXiv:astro-ph/0110536. Bibcode:2002ApJ...564.1007M. doi:10.1086/324404. S2CID 12431948.
  9. ↑ Heacox, William D. (December 1999). "On the Nature of Low-Mass Companions to Solar-like Stars". The Astrophysical Journal. 526 (2): 928–936. Bibcode:1999ApJ...526..928H. doi:10.1086/308033.
  10. 1 2 3 4 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.
  11. ↑ "tet Dra". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-01-10.
  12. ↑ Lépine, Sébastien; Shara, Michael M. (March 2005). "A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)". The Astronomical Journal. 129 (3): 1483–1522. arXiv:astro-ph/0412070. Bibcode:2005AJ....129.1483L. doi:10.1086/427854. S2CID 2603568.
  13. ↑ Eggen, Olin J. (1996). "The Stellar Content of Star Stream I". Astronomical Journal. 111: 1615. Bibcode:1996AJ....111.1615E. doi:10.1086/117901.
  14. ↑ Curtis, H. D. (November 1907). "Orbit of the spectroscopic binary theta Draconis". Astrophysical Journal. 26: 263−267. Bibcode:1907ApJ....26..263C. doi:10.1086/141500. S2CID 222445276.
  15. ↑ Mayor, M.; Mazeh, T. (January 1987). "The frequency of triple and multiple stellar systems". Astronomy and Astrophysics. 171: 157–177. Bibcode:1987A&A...171..157M.
  16. ↑ Young, A.; Koniges, A. (February 1977). "A study of the occurrence of singly ionized calcium emission in late-type spectroscopic binary stars". Astrophysical Journal. 211: 836–843. Bibcode:1977ApJ...211..836Y. doi:10.1086/154992.
  17. ↑ (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.
  18. ↑ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 10 日
  19. ↑ (in Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name Archived 2008-09-24 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  20. ↑ Allen, R. H. (1963). "Draco, the Dragon". Star Names, their Lore and Meaning (Dover ed.). p. 210. Retrieved 2021-01-11.
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