Rho2 Arae

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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
Epoch J2000      Equinox J2000
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
Distance 520 ± 30 ly
(159 ± 10 pc)
Mass 3.42 ± 0.10[6] M
Luminosity 238[6] L
Temperature 10,520[6] K
Rotational velocity (v sin i) 302[6] km/s
Other designations
CD–50° 10924, FK5 1444, HD 152824, HIP 83057, HR 6289, SAO 244313.[7]
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.[6]

Rho2 Arae has more than three times the mass of the Sun and shines with 238 times the Sun's luminosity.[6] This energy is being radiated into space from the outer atmosphere at an effective temperature of 10,520 K,[6] giving it the blue-white hue of a B-type star.[8] It is spinning rapidly with a projected rotational velocity of 302 km/s.[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, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c 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, Bibcode:1968MNSSA..27...11C. 
  3. ^ a b Hiltner, W. A.; Garrison, R. F.; Schild, R. E. (July 1969), "MK Spectral Types for Bright Southern OB Stars", Astrophysical Journal, 157: 313, Bibcode:1969ApJ...157..313H, doi:10.1086/150069. 
  4. ^ 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, Bibcode:1978mcts.book.....H. 
  5. ^ Wielen, R.; et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W. 
  6. ^ a b c d e f g h Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, Bibcode:2012A&A...537A.120Z, arXiv:1201.2052Freely accessible, doi:10.1051/0004-6361/201117691 
  7. ^ "HR 6289 -- Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-08-02. 
  8. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16.