Astronomy:Iota Arae

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Short description: Star in the constellation Ara
Iota Arae
Diagram showing star positions and boundaries of the Ara constellation and its surroundings
Cercle rouge 100%.svg
The location of ι Arae (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Ara
Right ascension  17h 23m 16.07715s[1]
Declination –47° 28′ 05.5073″[1]
Apparent magnitude (V) 5.245[2]
Spectral type B2 IIIne[3]
U−B color index –0.82[4]
B−V color index –0.11[4]
R−I color index –0.08
Variable type BE[5]
Radial velocity (Rv)–19[6] km/s
Proper motion (μ) RA: –4.35[1] mas/yr
Dec.: –17.59[1] mas/yr
Parallax (π)3.49 ± 0.26[1] mas
Distance930 ± 70 ly
(290 ± 20 pc)
Absolute magnitude (MV)−2.06[7]
Mass8.3 ± 0.4[8] M
Luminosity (bolometric)5,740[9] L
Surface gravity (log g)4.10[2] cgs
Temperature21,380[2] K
Rotational velocity (v sin i)375[10] km/s
Age30.0 ± 7.4[8] Myr
Other designations
ι Ara, CD –47° 11484, FK5 3379, HD 157042, HIP 85079, HR 6451, NSV 8566, SAO 227886.[11]
Database references

Iota Arae, Latinized from ι Arae, is the Bayer designation for a star in the southern constellation of Ara. It is approximately 930 light-years (290 parsecs)[1] from Earth, give or take a 70 light-year margin of error, and has an apparent visual magnitude of 5.25.[4] Based upon the Bortle Dark-Sky Scale, this means the star is visible to the naked eye from suburban skies.

This is an evolved giant star with a stellar classification of B2 IIIne.[3] The 'e' notation indicates the spectrum displays emission lines, which means this is a Be star that is surrounded by hot, circumstellar gas. It is spinning rapidly with a projected rotational velocity of 375 km/s.[10] The Doppler effect from this rotation is causing the absorption lines to widen and become nebulous, as indicated by the 'n' notation in the stellar class.

Iota Arae has around 8.3[8] times the mass of the Sun and is shining brightly with 5,740[9] times the Sun's luminosity. This energy is being radiated into space from the outer atmosphere at an effective temperature of 21,380 K,[2] giving it the characteristic blue-white hue of a B-type star.[12] It has been detected to vary in brightness by 0.054 in magnitude with no clear period.[13]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode2007A&A...474..653V. 
  2. 2.0 2.1 2.2 2.3 Soubiran, C.; Le Campion, J.-F.; Cayrel de Strobel, G.; Caillo, A. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics 515: A111, doi:10.1051/0004-6361/201014247, Bibcode2010A&A...515A.111S. 
  3. 3.0 3.1 Hiltner, W. A.; Garrison, R. F.; Schild, R. E. (July 1969), "MK Spectral Types for Bright Southern OB Stars", Astrophysical Journal 157: 313, doi:10.1086/150069, Bibcode1969ApJ...157..313H. 
  4. 4.0 4.1 4.2 Kozok, J. R. (September 1985), "Photometric observations of emission B-stars in the southern Milky Way", Astronomy and Astrophysics Supplement Series 61: 387–405, Bibcode1985A&AS...61..387K. 
  5. Samus, N. N. et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S 1. Bibcode2009yCat....102025S. 
  6. Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Alan Henry, Batten; John Frederick, Heard, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, 30, University of Toronto: International Astronomical Union, p. 57, Bibcode1967IAUS...30...57E. 
  7. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode2012AstL...38..331A. 
  8. 8.0 8.1 8.2 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, doi:10.1111/j.1365-2966.2010.17434.x, Bibcode2011MNRAS.410..190T. 
  9. 9.0 9.1 Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten 331 (4): 349, doi:10.1002/asna.200911355, Bibcode2010AN....331..349H. 
  10. 10.0 10.1 Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago 239 (1): 1, Bibcode1970CoAsi.239....1B. 
  11. "iot Ara". SIMBAD. Centre de données astronomiques de Strasbourg. 
  12. "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004,, retrieved 2012-01-16 
  13. Lefèvre, L. et al. (November 2009), "A systematic study of variability among OB-stars based on HIPPARCOS photometry", Astronomy and Astrophysics 507 (2): 11411201, doi:10.1051/0004-6361/200912304, Bibcode2009A&A...507.1141L 

External links