Iota Aurigae

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

Location of ι Aurigae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Auriga
Right ascension 04h 56m 59.62109s[1]
Declination +33° 09′ 57.9585″[1]
Apparent magnitude (V) 2.69[2]
Spectral type K3 II[3]
U−B color index +1.78[2]
B−V color index +1.53[2]
R−I color index 0.82[citation needed]
Variable type Suspected[4]
Radial velocity (Rv) +17.78[5] km/s
Proper motion (μ) RA: +6.79[1] mas/yr
Dec.: -14.88[1] mas/yr
Parallax (π) 6.61 ± 0.38[1] mas
Distance 490 ± 30 ly
(151 ± 9 pc)
Mass 7.1 ± 0.7[6] M
Radius 127[7] R
Surface gravity (log g) 1.74[8] cgs
Temperature 4,160[8] K
Metallicity [Fe/H] –0.11[8] dex
Rotational velocity (v sin i) 8[9] km/s
Age 39.8 ± 4.9[6] Myr
Other designations
Hassaleh, Kabdhilinan, 3 Aurigae, HR 1577, HD 31398, BD+32° 855, FK5 181, HIP 23015, SAO 57522, GC 6029.[10]
Database references

Iota Aurigae (ι Aur, ι Aurigae) is a star in the northern constellation of Auriga. It has the traditional name Al Kab,[11] short for Kabdhilinan, from the Arabic الكعب ذي العنان al-kacb ðīl-cinān[12] "the shoulder of the rein holder (charioteer)".[11] Under the name Alkab, this star is a marker on the astrolabe described by Geoffrey Chaucer in his Treatise on the Astrolabe in 1391. In Antonín Bečvář's atlas it has the traditional name Hassaleh. It is known as 五車一 (the First Star of the Five Chariots) in Chinese.[citation needed]

This star has an apparent visual magnitude of 2.7,[2] which is bright enough to be readily visible to the naked eye. Parallax measurements give a distance estimate of roughly 490 light-years (150 parsecs) from the Earth. At this distance, extinction from interstellar dust is causing a magnitude reduction of about 0.6.[11] Examination of the spectrum yields a stellar classification of K3 II,[3] with the luminosity class of 'II' indicating this is a category of evolved star known as a bright giant. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[13] The effective temperature of the outer envelope is 4,160 K,[8] which is cooler than the Sun's effective temperature and gives Iota Aurigae the orange hue of a K-type star.[14]

This star is a weak X-ray emitter with an X-ray luminosity of about 1.8 × 1027 ergs s−1. This emission is most likely coming from transient loops of plasma in Iota Aurigae's outer atmosphere, which have a temperature of around 3 million K.[15] This is a suspected variable star, although this variability remains unconfirmed.[4]

Unconfirmed substellar companions[edit]

During the Extreme Solar Systems conference held on June 25–29, 2007, in Santorini, Greece, Reffert et al. announced the detection of two substellar objects orbiting Iota Aurigae in 2:1 resonance. Such companions would be brown dwarfs with orbital periods of approximately 2 and 4 years. No minimum mass for the candidates was provided. So far the detection has not been confirmed, though Hekker et al. (2008) listed significant radial velocity variations at periods of 767 and 1586 days.[16][17]


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J 
  3. ^ 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. ^ a b Strassmeier, K. G. (January 2008), "Stellar Activity with BRITE: the ``Aurigae field", Communications in Asteroseismology, 152: 124–130, Bibcode:2008CoAst.152..124S, doi:10.1553/cia152s124 
  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, Bibcode:2005A&A...430..165F, arXiv:astro-ph/0409579Freely accessible, doi:10.1051/0004-6361:20041272 
  6. ^ a b Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, Bibcode:2011MNRAS.410..190T, arXiv:1007.4883Freely accessible, doi:10.1111/j.1365-2966.2010.17434.x 
  7. ^ Harper, G. M. (1992), "The outer atmospheres of the 'hybrid' bright giants - The chromospheres of Alpha TrA (K4 II), IOTA AUR (K3 II), Gamma AQL (K3 II) and Theta HER (K1 II)", Monthly Notices of the Royal Astronomical Society, 256 (1): 37–64, Bibcode:1992MNRAS.256...37H, arXiv:0809.0359Freely accessible, doi:10.1093/mnras/256.1.37 
  8. ^ a b c d McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants", Astrophysical Journal Supplement Series, 74: 1075–1128, Bibcode:1990ApJS...74.1075M, ISSN 0067-0049, doi:10.1086/191527 
  9. ^ Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago, 239 (1), Bibcode:1970CoAsi.239....1B 
  10. ^ "iot Aur -- Variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-19 
  11. ^ a b c Kaler, James B., "Al Kab", Stars, University of Illinois at Urbana-Champaign, retrieved 2012-01-18 
  12. ^ Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 91 
  13. ^ Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society, 25: 1319, Bibcode:1993AAS...183.1710G, retrieved 2012-02-04 
  14. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 10, 2012, retrieved 2012-01-16 
  15. ^ Kashyap, V.; et al. (August 1994), "X-ray emission on hybird stars: ROSAT observations of alpha Trianguli Australis and IOTA Aurigae", The Astrophysical Journal, 431 (1): 402–415, Bibcode:1994ApJ...431..402K, doi:10.1086/174494 
  16. ^ Hekker, S.; et al. (2008), "Precise radial velocities of giant stars. IV. A correlation between surface gravity and radial velocity variation and a statistical investigation of companion properties", Astronomy and Astrophysics, 480 (1): 215–222, Bibcode:2008A&A...480..215H, arXiv:0801.0741Freely accessible, doi:10.1051/0004-6361:20078321 
  17. ^ Reffert, S.; et al. (2008), "Two brown dwarfs in resonance around a K3II giant", Extreme Solar Systems, ASP Conference Series, Vol. 398, proceedings of the conference held 25–29 June 2007, at Santorini Island, Greece (PDF), p. 115 

External links[edit]