Saturday, 18 April 2015


Iota Draconis

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Iota Draconis
Diagram showing star positions and boundaries of the Draco constellation and its surroundings
Cercle rouge 100%.svg

Location of ι Draconis (circled)
Observation data
Epoch J2000      Equinox J2000
Right ascension15h 24m 55.77463s[1]
Declination+58° 57′ 57.8344″[1]
Apparent magnitude (V)3.290[2]
Spectral typeK2 III[3]
U−B color index+1.230[2]
B−V color index+1.160[2]
Variable typeSuspected[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
Distance101.2 ± 0.3 ly
(31.03 ± 0.10 pc)
Mass1.82 ± 0.23[6] M
Radius11.99 ± 0.06[6] R
Luminosity55.3 ± 5.3[6] L
Surface gravity (log g)2.5[7] cgs
Temperature4,545 ± 110[6] K
Metallicity [Fe/H]+0.14[6] dex
Rotation434 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 theArabic 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]


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[edit]

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)
MassSemimajor axis
Orbital period
b≥12.6 ± 1.1 MJ1.27510.72 ± 0.070.713 ± 0.008

In culture[edit]

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 Draconisη Draconis,ζ Draconisυ Draconis73 Draconisγ Cephei and 23 Cassiopeiae.[14] 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.),[15] representing 左樞 (Zuǒshū), meaning Left Pivot.[16] 左樞 (Zuǒshū) is westernized into Tsao Choo by R.H. Allen with the same meaning [17]


  1. Jump up to:a b c d e f 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..653Vdoi:10.1051/0004-6361:20078357
  2. Jump up to:a b c d Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants.", Monthly Notices of the Royal Astronomical Society 172: 667–679,Bibcode:1975MNRAS.172..667J
  3. Jump up to:a b Morgan, W. W.; Keenan, P. C. (1973). "Spectral Classification". Annual Review of Astronomy and Astrophysics 11: 29. Bibcode:1973ARA&A..11...29M.doi:10.1146/annurev.aa.11.090173.000333.
  4. Jump up to:a b c d e f Kane, Stephen R. et al. (September 2010), "On the Transit Potential of the Planet Orbiting Iota Draconis", The Astrophysical Journal 720 (2): 1644–1649,arXiv:1007.3501Bibcode:2010ApJ...720.1644Kdoi:10.1088/0004-637X/720/2/1644
  5. Jump up^ Famaey, B. et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters",Astronomy and Astrophysics 430 (1): 165–186, arXiv:astro-ph/0409579,Bibcode:2005A&A...430..165Fdoi:10.1051/0004-6361:20041272
  6. Jump up to:a b c d e f g h i Baines, Ellyn K. et al. (December 2011), "Fundamental Parameters of the Exoplanet Host K Giant Star ι Draconis from the CHARA Array", The Astrophysical Journal 743 (2): 130, arXiv:1109.4950,Bibcode:2011ApJ...743..130Bdoi:10.1088/0004-637X/743/2/130
  7. Jump up^ Massarotti, Alessandro et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal 135 (1): 209–231, Bibcode:2008AJ....135..209Mdoi:10.1088/0004-6256/135/1/209
  8. Jump up to:a b Allen, Richard Hinckley (1899), Star-names and Their Meanings, New York: G. E. Stechert, p. 210
  9. Jump up^ "iot Dra -- Variable Star"SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2012-01-11
  10. Jump up to:a b Frink, Sabine et al. (2002), "Discovery of a Substellar Companion to the K2 III Giant Iota Draconis", The Astrophysical Journal 576 (1): 478–484,Bibcode:2002ApJ...576..478Fdoi:10.1086/341629
  11. Jump up^ "The Colour of Stars"Australia Telescope, Outreach and Education(Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16
  12. Jump up^ Kóspál, Ágnes et al. (August 2009), "On the Relationship Between Debris Disks and Planets", The Astrophysical Journal Letters 700 (2): L73–L77,arXiv:0907.0028Bibcode:2009ApJ...700L..73Kdoi:10.1088/0004-637X/700/2/L73
  13. Jump up^ Kane, Stephen R. et al. (2010), "On the Transit Potential of the Planet Orbiting Iota Draconis", The Astrophysical Journal 720 (2): 1644–1649, arXiv:1007.3501,Bibcode:2010ApJ...720.1644Kdoi:10.1088/0004-637X/720/2/1644
  14. Jump up^ (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. Jump up^ (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.
  16. Jump up^ (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010.
  17. Jump up^ Star Name - R.H. Allen p. 210

External links[edit]


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