# Astronomy:Sigma Arae

Short description
Star in the constellation Ara
Observation dataEquinox J2000.0]] (ICRS) Constellation The location of σ Arae (circled) Ara 17h 35m 39.58957s[1] –46° 30′ 20.4618″[1] +4.575[2] A0 V[3] –0.064[2] –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 Distance 380 ± 10 ly (116 ± 3 pc) Absolute magnitude (MV) 1.40[4] Luminosity (bolometric) 26.4[4] L☉ Temperature 9,790[4] K CD–46 11661, HD 159217, HIP 86092, HR 6537, SAO 228162.[5] SIMBAD data

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]

## References

1. 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. 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, Bibcode1973MmRAS..77..223C.
3. Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 2, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode1978mcts.book.....H.
4. 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, doi:10.1086/590423, Bibcode2008ApJ...685..478N
5. 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, doi:10.1051/0004-6361:20078963, Bibcode2008A&A...484..479S