Iota Draconis

From Wikipedia, the free encyclopedia
Jump to: navigation, search
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
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
Age 10.015[8] Gyr
Other designations
Edasich, Eldsich,[9] 12 Draconis, BD+59 1654, FK5 425, FK5 571, HD 137759, HIP 75458, HR 5744, SAO 29520.[10]

Iota Draconis (ι Draconis, abbreviated Iota Dra, ι Dra), also named Edasich,[11] is a star in the northern circumpolar constellation of Draco. A visually unremarkable star of apparent magnitude 3.3,[2] in 2002 it was discovered to have a planet orbiting it[12] (designated Iota Draconis b, later named Hypatia). From parallax measurements, this star is located at a distance of about 101.2 light-years (31.0 parsecs) from the Sun.[1]


ι Draconis (Latinised to Iota Draconis) is the star's Bayer designation. On discovery the planet was designated Iota Draconis b (or Edasich b).

It bore the traditional name Edasich, derived 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.[9] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[14] included a table of the first two batches of names approved by the WGSN; which included Edasich for this star.

In July 2014 the International Astronomical Union launched a process for giving proper names to certain exoplanets and their host stars.[15] The process involved public nomination and voting for the new names.[16] In December 2015, the IAU announced the winning name was Hypatia for this planet.[17] The winning name was submitted by Hypatia, a student society of the Physics Faculty of the Universidad Complutense de Madrid, Spain. Hypatia was a famous Greek astronomer, mathematician, and philosopher.[18]

In Chinese, 紫微左垣 (Zǐ Wēi Zuǒ Yuán), meaning Left Wall of Purple Forbidden Enclosure, refers to an asterism consisting of Iota Draconis, Theta Draconis, Eta Draconis, Zeta Draconis, Upsilon Draconis, 73 Draconis, Gamma Draconis and 23 Cassiopeiae.[19] Consequently, Iota 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.),[20] representing 左樞 (Zuǒshū), meaning Left Pivot.[21] 左樞 (Zuǒshū) is westernized into Tsao Choo by R.H. Allen with the same meaning [22]


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.[23] It is rotating at a leisurely rate, with a period of around 434 days.[4] It is about 10.015 billion years old.[8]

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.[24]

Planetary system[edit]

The planetary companion discovered in 2002 was the first planet known to orbit a giant star.[12] 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][25]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b (Hypatia) 8.82 ± 0.72 MJ 1.27 510.72 ± 0.07 0.713 ± 0.008


  1. ^ 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:0708.1752free to read, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ 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 (3): 667–679, Bibcode:1975MNRAS.172..667J, doi:10.1093/mnras/172.3.667 
  3. ^ a b Morgan, W. W.; Keenan, P. C. (1973). "Spectral Classification". Annual Review of Astronomy and Astrophysics. 11: 29–50. Bibcode:1973ARA&A..11...29M. doi:10.1146/annurev.aa.11.090173.000333. 
  4. ^ 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:1007.3501free to read, Bibcode:2010ApJ...720.1644K, doi:10.1088/0004-637X/720/2/1644 
  5. ^ 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/0409579free to read, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272 
  6. ^ 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:1109.4950free to read, Bibcode:2011ApJ...743..130B, doi:10.1088/0004-637X/743/2/130 
  7. ^ 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..209M, doi:10.1088/0004-6256/135/1/209 
  8. ^ a b Safonova, M.; Murthy, J.; Shchekinov, Yu. A. (2014). "Age Aspects of Habitability". International Journal of Astrobiology. 15 (2): 93–105. arXiv:1404.0641free to read. doi:10.1017/S1473550415000208. 
  9. ^ a b Allen, Richard Hinckley (1899), Star-names and Their Meanings, New York: G. E. Stechert, p. 210 
  10. ^ "iot Dra -- Variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-11 
  11. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  12. ^ 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..478F, doi:10.1086/341629 
  13. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. 
  14. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016. 
  15. ^ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. 9 July 2014
  16. ^ NameExoWorlds The Process
  17. ^ Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
  18. ^ NameExoWorlds The Approved Names
  19. ^ (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.
  20. ^ (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.
  21. ^ (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010.
  22. ^ Star Name - R.H. Allen p. 210
  23. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16 
  24. ^ Kóspál, Ágnes; et al. (August 2009), "On the Relationship Between Debris Disks and Planets", The Astrophysical Journal Letters, 700 (2): L73–L77, arXiv:0907.0028free to read, Bibcode:2009ApJ...700L..73K, doi:10.1088/0004-637X/700/2/L73 
  25. ^ Kane, Stephen R.; et al. (2010), "On the Transit Potential of the Planet Orbiting Iota Draconis", The Astrophysical Journal, 720 (2): 1644–1649, arXiv:1007.3501free to read, Bibcode:2010ApJ...720.1644K, doi:10.1088/0004-637X/720/2/1644 

External links[edit]

Coordinates: Sky map 15h 24m 55.7747s, +58° 57′ 57.836″