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Iota Draconis

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Iota Draconis

Iota Draconis
Diagram showing star positions and boundaries of the Draco constellation and its surroundings

Location of ι Draconis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Right ascension 15h 24m 55.77463s[1]
Declination +58° 57′ 57.8344″[1]
Apparent magnitude (V) 3.290[2]
Spectral type K2 III[3]
U−B color index +1.230[2]
B−V color index +1.160[2]
Variable type Suspected[4]
Radial velocity (Rv) –10.71[5] km/s
Proper motion (μ) RA: –8.36[1] mas/yr
Dec.: +17.08[1] mas/yr
Parallax (π) 32.23 ± 0.10[1] mas
Distance 101.2 ± 0.3 ly
(31.03 ± 0.10 pc)
Mass 1.82 ± 0.23[6] M
Radius 11.99 ± 0.06[6] R
Luminosity 55.3 ± 5.3[6] L
Surface gravity (log g) 2.5[7] cgs
Temperature 4,545 ± 110[6] K
Metallicity [Fe/H] +0.14[6] dex
Rotation 434 days[4]
Rotational velocity (v sin i) 1.5[4] km/s
Other designations
Edasich, Eldsich,[8] 12 Draconis, BD+59 1654, FK5 425, FK5 571, HD 137759, HIP 75458, HR 5744, SAO 29520.[9]

Iota Draconis (ι Dra, ι Draconis) is a star in the northern circumpolar constellation of Draco. It has the traditional name Edasich, a name that comes from the Arabic Al Ḍhiba' of Ulug Beg and the Dresden Globe, or Al dhīlī 'Male hyena' by Kazwini, with Eldsich being recorded in the Century Cyclopedia.[8] A visually unremarkable star of apparent magnitude 3.3,[2] in 2002 it was discovered to have a planet.[10] From parallax measurements, this star is located at a distance of about 101.2 light-years (31.0 parsecs) from Earth.[1]


  • Properties 1
  • Planetary system 2
  • In culture 3
  • References 4
  • External links 5


Edasich is larger and more massive than the Sun, with 1.8 times the mass and nearly 12 times the radius.[6] The spectrum matches a stellar classification of K2 III,[3] indicating this is an evolved star that has exhausted the supply of hydrogen at its core and left the main sequence of stars like the Sun. With an expanded outer envelope, this giant star is radiating over 55 times the luminosity of the Sun at an effective temperature of 4,545 K.[6] This temperature gives it an orange hue that is a characteristic of K-type stars.[11] It is rotating at a leisurely rate, with a period of around 434 days.[4]

In the past Iota Draconis has been suspected of variability. However, the star has been found to have a constant luminosity to within about 0.004 magnitudes. Hence, as of 2010, the variability remains unconfirmed.[4] An excess emission of infrared radiation at a wavelength of 70μm suggests the presence of a circumstellar disk of dust; what astronomers term a debris disk.[12]

Planetary system

The planetary companion discovered in 2002 was the first planet known to orbit a giant star.[10] The habitable zone for this star lies in the range of 6.8–13.5 Astronomical Units, placing this planet well inside.[6] The alignment of this planet's orbit may make it directly detectable via the transit method.[4]

The Iota Draconis planetary system[6][13]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b ≥12.6 ± 1.1 MJ 1.27 510.72 ± 0.07 0.713 ± 0.008

The planet is one of those selected by the International Astronomical Union as part of their public process for giving proper names to exoplanets.[14][15] The process involves public nomination and voting for the new name, and the IAU plans to announce the new name in mid-November 2015.[16]

In culture

In Chinese, 紫微左垣 (Zǐ Wēi Zuǒ Yuán), meaning Left Wall of Purple Forbidden Enclosure, refers to an asterism consisting of ι Draconis, θ Draconis, η Draconis, ζ Draconis, υ Draconis, 73 Draconis, γ Cephei and 23 Cassiopeiae.[17] Consequently, ι Draconis itself is known as 紫微左垣一 (Zǐ Wēi Zuǒ Yuán yī, English: the First Star of Left Wall of Purple Forbidden Enclosure.),[18] representing 左樞 (Zuǒshū), meaning Left Pivot.[19] 左樞 (Zuǒshū) is westernized into Tsao Choo by R.H. Allen with the same meaning [20]


  1. ^ a b c d e f
  2. ^ a b c d
  3. ^ a b
  4. ^ a b c d e f
  5. ^
  6. ^ a b c d e f g h i
  7. ^
  8. ^ a b
  9. ^
  10. ^ a b
  11. ^
  12. ^
  13. ^
  14. ^ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. 9 July 2014
  15. ^ NameExoWorlds.
  16. ^ NameExoWorlds.
  17. ^ (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. ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
  19. ^ (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010.
  20. ^ Star Name - R.H. Allen p. 210

External links

  • : HD 137759 -- Variable StarSIMBAD
  • : Notes for star HIP 75458Extrasolar Planets Encyclopaedia
  • : Edasich/Iota DraconisSolStation

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