Astronomy:Rho2 Arae

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Short description
Star in the constellation Ara
Diagram showing star positions and boundaries of the Ara constellation and its surroundings
Cercle rouge 100%.svg
The location of ρ2 Arae (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Ara
Right ascension  16h 58m 17.94161s[1]
Declination –50° 38′ 28.2691″[1]
Apparent magnitude (V) 5.54[2]
Spectral type B9 IV[3] or B9 V[4]
B−V color index +0.02[2]
Radial velocity (Rv)–44.0[5] km/s
Proper motion (μ) RA: –8.05[1] mas/yr
Dec.: –38.68[1] mas/yr
Parallax (π)6.28 ± 0.38[1] mas
Distance520 ± 30 ly
(159 ± 10 pc)
Absolute magnitude (MV)−0.47[6]
Mass3.42 ± 0.10[7] M
Luminosity238[7] L
Temperature10,520[7] K
Rotational velocity (v sin i)302[7] km/s
Other designations
ρ2 Ara, CD–50° 10924, FK5 1444, HD 152824, HIP 83057, HR 6289, SAO 244313.[8]
Database references

Rho2 Arae is the Bayer designation for a star in the southern constellation of Ara. It received this designation when the star was catalogued by Bode in his Uranographia. This is a rather dim naked eye star with an apparent visual magnitude of 5.54.[2] Based upon an annual parallax shift of just 6.28 mas, it is around 520 light-years (160 parsecs) distant from the Sun, give or take a 30 light-year margin of error.[1]

The spectrum of this star matches a stellar classification of B9 IV[3] or B9 V.[4] The IV luminosity class would indicate the star is in the subgiant stage, while a V class means it is a main sequence star like the Sun. In the latter case, it is close to entering the subgiant stage at an estimated 93% of the way through its lifespan on the main sequence.[7]

Rho2 Arae has more than three times the mass of the Sun and shines with 238 times the Sun's luminosity.[7] This energy is being radiated into space from the outer atmosphere at an effective temperature of 10,520 K,[7] giving it the blue-white hue of a B-type star.[9] It is spinning rapidly with a projected rotational velocity of 302 km/s.[7]


  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 Corben, P. M.; Stoy, R. H. (1968), "Photoelectric Magnitudes and Colours for Bright Southern Stars", Monthly Notes of the Astronomical Society of Southern Africa 27: 11, Bibcode1968MNSSA..27...11C. 
  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 Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 2, Ann Arbor: Dept. of Astronomy, University of Michigan, 
  5. Wielen, R. et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg (Astronomisches Rechen-Institut Heidelberg) 35 (35): 1, Bibcode1999VeARI..35....1W. 
  6. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode2012AstL...38..331A. 
  7. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics 537: A120, doi:10.1051/0004-6361/201117691, Bibcode2012A&A...537A.120Z 
  8. "rho02 Ara". SIMBAD. Centre de données astronomiques de Strasbourg. 
  9. "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004,, retrieved 2012-01-16.