Sigma Arae

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Sigma Arae
Diagram showing star positions and boundaries of the Ara constellation and its surroundings
Cercle rouge 100%.svg
The location of σ Arae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ara
Right ascension  17h 35m 39.58957s[1]
Declination –46° 30′ 20.4618″[1]
Apparent magnitude (V) +4.575[2]
Spectral type A0 V[3]
U−B color index –0.064[2]
B−V color index –0.027[2]
Proper motion (μ) RA: –25.78[1] mas/yr
Dec.: –38.30[1] mas/yr
Parallax (π)8.62 ± 0.26[1] mas
Distance380 ± 10 ly
(116 ± 3 pc)
Absolute magnitude (MV)1.40[4]
Luminosity (bolometric)26.4[4] L
Temperature9,790[4] K
Other designations
CD–46 11661, HD 159217, HIP 86092, HR 6537, SAO 228162.[5]
Database references

Sigma Arae (σ Ara, σ Arae) is the Bayer designation for a star in the southern constellation of Ara. It is visible to the naked eye with an apparent visual magnitude of +4.575.[2] The distance to this star, based upon an annual parallax shift of 8.62 mas,[1] is around 380 light-years (120 parsecs).

This is an A-type main sequence star with a stellar classification of A0 V.[3] Unusually for an A-type star, X-ray emissions with a luminosity of 4.6 × 1029 erg s−1 have been detected from Sigma Arae. Normally this is explained by the presence of a lower mass orbiting companion star. However, such a scenario does not appear to hold true for this star. Instead, the signature of a surface magnetic field has been detected with a strength of roughly 128 ± 73 Gauss, indicating the source of the X-rays may be surface magnetic activity.[6]


  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:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. ^ a b c d Cousins, A. W. J. (1973), "Revised zero points and UBV photometry of stars in the Harvard E and F regions", Memoirs of the Royal Astronomical Society, 77: 223–236, Bibcode:1973MmRAS..77..223C.
  3. ^ a b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 2, Ann Arbor: Dept. of Astronomy, University of Michigan,
  4. ^ a b c Neff, James E.; Simon, Theodore (September 2008), "O VI Observations of the Onset of Convection Zones in Main-Sequence A Stars", The Astrophysical Journal, 685 (1): 478–488, arXiv:0805.4459, Bibcode:2008ApJ...685..478N, doi:10.1086/590423
  5. ^ "* sig Ara". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-08-02.
  6. ^ Schröder, C.; Hubrig, S.; Schmitt, J. H. M. M. (June 2008), "Magnetic fields in A-type stars associated with X-ray emission", Astronomy and Astrophysics, 484 (2): 479–486, Bibcode:2008A&A...484..479S, doi:10.1051/0004-6361:20078963

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