Astronomy:Theta Arae

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Short description: Star in the constellation Ara
Theta Arae
Diagram showing star positions and boundaries of the Ara constellation and its surroundings
Cercle rouge 100%.svg
The location of θ Arae (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Ara
Right ascension  18h 06m 37.87129s[1]
Declination –50° 05′ 29.3125″[1]
Apparent magnitude (V) +3.67[2]
Spectral type B2 Ib[3]
U−B color index –0.870[2]
B−V color index –0.109[2]
Radial velocity (Rv)+3.4[4] km/s
Proper motion (μ) RA: –8.27[1] mas/yr
Dec.: –8.70[1] mas/yr
Parallax (π)4.01 ± 0.15[1] mas
Distance810 ± 30 ly
(249 ± 9 pc)
Absolute magnitude (MV)−3.33[5]
Mass8.9 ± 0.1[6] M
Radius20.1[7] R
Luminosity3,450[5] L
Surface gravity (log g)2.70[8] cgs
Temperature17,231 ± 231[7] K
Rotational velocity (v sin i)95[9] km/s
Age28.2 ± 4.7[6] Myr
Other designations
θ Ara, CD−50° 11720, FK5 1471, HD 165024, HIP 88714, HR 6743, SAO 245242.[10]
Database references

Theta Arae, Latinized from θ Arae, is the Bayer designation for a star in the constellation Ara. It has an apparent visual magnitude of +3.67,[2] which is bright enough to be seen with the naked eye. Based upon an annual parallax shift of 4.01 mas,[1] Theta Arae is 810 light-years (250 parsecs) distant from the Earth.

This is a supergiant star with a stellar classification of B2 Ib.[3] It has nearly nine[6] times the mass of the Sun and is over 20[7] times the Sun's radius. The outer atmosphere of this star has an effective temperature of 17,231 K;[7] much hotter than the surface of the Sun. At this heat, the star shines with the characteristic blue-white hue of a B-type star.[11]


  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 Gutierrez-Moreno, Adelina; Moreno, Hugo (June 1968), "A photometric investigation of the Scorpio-Centaurus association", Astrophysical Journal Supplement 15: 459, doi:10.1086/190168, Bibcode1968ApJS...15..459G. 
  3. 3.0 3.1 Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 2, Ann Arbor: Dept. of Astronomy, University of Michigan, 
  4. Wielen, R. et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions, Astronomisches Rechen-Institut Heidelberg, Bibcode1999VeARI..35....1W. 
  5. 5.0 5.1 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode2012AstL...38..331A. 
  6. 6.0 6.1 6.2 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. 
  7. 7.0 7.1 7.2 7.3 Underhill, A. B. et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society 189 (3): 601–605, doi:10.1093/mnras/189.3.601, Bibcode1979MNRAS.189..601U. 
  8. Fraser, M. et al. (May 2010), "Atmospheric parameters and rotational velocities for a sample of Galactic B-type supergiants", Monthly Notices of the Royal Astronomical Society 404 (3): 1306–1320, doi:10.1111/j.1365-2966.2010.16392.x, Bibcode2010MNRAS.404.1306F. 
  9. Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago 239 (1), Bibcode1970CoAsi.239....1B. 
  10. "* tet Ara". SIMBAD. Centre de données astronomiques de Strasbourg. 
  11. "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004,, retrieved 2012-01-16 

External links