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Epsilon Draconis

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Epsilon Draconis, Latinized from ε Draconis, is a fourth-magnitude star in the constellation Draco. This star along with Delta Draconis (Altais), Pi Draconis and Rho Draconis forms an asterism known as Al Tāis, meaning "the Goat".[10]

Epsilon Draconis
Location of ε Draconis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Right ascension 19h 48m 10.34973s[1]
Declination 70° 16′ 04.5329″[1]
Apparent magnitude (V) 3.9974[2]
Characteristics
Spectral type G7IIIbFe-1[3]
U−B color index +0.48[4]
B−V color index +0.88 [4]
Astrometry
Radial velocity (Rv)+2.69±0.23[5] km/s
Proper motion (μ) RA: +79.702[1] mas/yr
Dec.: +41.078[1] mas/yr
Parallax (π)21.2526 ± 0.3016 mas[1]
Distance153 ± 2 ly
(47.1 ± 0.7 pc)
Absolute magnitude (MV)0.71[2]
Details
Mass2.7[6][7] M☉
Radius11.15+0.47
−0.56[1] R☉
Luminosity69.6±1.12[1] L☉
Temperature4993+129
−103[1] K
Metallicity [Fe/H]-0.31[8] dex
Rotational velocity (v sin i)1.2 [6] km/s
Age500[6] Myr
Other designations
Tyl, ε Dra, 63 Dra, AG+70° 689, BD+69° 1070, GC 27471, HD 188119, HIP 97433, HR 7582, SAO 9540, CCDM J19482+7016AB, PLX 4689, IRAS 19483+7008, 2MASS J19481035+7016045[9]
Database references
SIMBADdata

In Chinese astronomy, 天廚 (Tiān Chú), meaning the Celestial Kitchen, refers to an asterism consisting of Epsilon Draconis, Delta Draconis, Sigma Draconis, Rho Draconis, 64 Draconis and Pi Draconis.[11] Consequently, the Chinese name for Epsilon Draconis itself is 天廚三 (Tiān Chú sān, English: the Third Star of the Celestial Kitchen.)[12] Most authors do not use a traditional name for this star, using instead the Bayer designation;[13] but Bečvář (1951) listed it as Tyl /ˈtɪl/.[14][15]

Visibility

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With a declination in excess of 70 degrees north, Epsilon Draconis is principally visible in the northern hemisphere, with southern locations north of 20° South able to see it just above the horizon. The star is circumpolar throughout all of Europe, China, most of India and as far south as the tip of the Baja peninsula in North America as well as other locations around the globe having a latitude greater than ± 20° North. Since Epsilon Draconis has an apparent magnitude of almost 4.0, the star is easily observable to the naked eye as long as one's stargazing is not hampered by the light pollution common to most cities.

The best time for observation is in the evening sky during the summer months, when the "Dragon constellation" passes the meridian at midnight, but given its circumpolar nature in the northern hemisphere, it is visible to most of the world's inhabitants throughout the year.

Properties

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Epsilon Draconis is a yellow giant star with a spectral type of G8III. It has a radius that has been estimated at 11 solar radii and a mass of 2.7 solar masses.[6] Compared to most G class stars, Epsilon Draconis is a relatively young star with an estimated age of around 500 million years old.[6] Like the majority of giant stars, Epsilon Draconis rotates slowly on its axis with a rotational velocity of 1.2 km/s, a speed which takes the star approximately 420 days to make one complete revolution.[6]

In 2007, Floor van Leeuwen and his team calibrated the star's apparent magnitude at 3.9974 with an updated parallax of 22.04 ± 0.37 milliarcseconds, yielding a distance of 45.4 parsecs or approximately 148 light years from Earth.[2] Given a surface temperature of 5,068 Kelvin, theoretical calculations would yield a total luminosity for the star of about 60 times the solar luminosity.

Star system

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Epsilon Draconis is resolvable as a double star in telescopes of 10 centimeters aperture or larger. The companion has an apparent brightness of 7.3 at an angular distance of 3.2 arcseconds. It is a giant of spectral class F5,[9] orbiting the yellow giant at about 130 astronomical units.[citation needed]

See also

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References

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  1. ^ a b c d e f g h 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. ^ a b c 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 2010-12-18.
  3. ^ Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
  4. ^ a b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. SIMBAD. Bibcode:1986EgUBV........0M.
  5. ^ Soubiran, C.; et al. (2008). "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants". Astronomy and Astrophysics. 480 (1): 91–101. arXiv:0712.1370. Bibcode:2008A&A...480...91S. doi:10.1051/0004-6361:20078788. S2CID 16602121.
  6. ^ a b c d e f Mallik, Sushma V.; Parthasarathy, M.; Pati, A. K. (October 2003). "Li abundances and velocities in F and G stars". VizieR. Centre de Données astronomiques de Strasbourg. Retrieved 2010-12-18.
  7. ^ Mallik, Sushma V.; Parthasarathy, M.; Pati, A. K. (October 2003). "Lithium and rotation in F and G dwarfs and subgiants". Astronomy and Astrophysics. 409 (1): 251–261. Bibcode:2003A&A...409..251M. doi:10.1051/0004-6361:20031084. Retrieved 2010-12-18.
  8. ^ Soubiran, C.; Bienaymé, O.; Mishenina, T. V.; Kovtyukh, V. V. (2008). "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants". Astronomy and Astrophysics. 480 (1): 91–101. arXiv:0712.1370. Bibcode:2008A&A...480...91S. doi:10.1051/0004-6361:20078788. S2CID 16602121.
  9. ^ a b "* eps Dra". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-12-18.
  10. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 209. ISBN 0-486-21079-0. Retrieved 2010-12-12.
  11. ^ (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.
  12. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived August 19, 2010, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  13. ^ Kaler, Jim. "Epsilon Draconis". Retrieved 2016-11-24.
  14. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  15. ^ Bakich, Michael (1995). The Cambridge Guide to the Constellations. Cambridge University Press. p. 202. ISBN 0521449219. Retrieved 2016-11-24. Tyl.
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