Astronomy:Rho1 Arae

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Short description: Star in the constellation Ara

Rho1 Arae
Diagram showing star positions and boundaries of the Ara constellation and its surroundings
Cercle rouge 100%.svg
The location of ρ1 Arae (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Ara
Right ascension  16h 56m 08.8405s[1]
Declination –50° 40′ 29.244″[1]
Apparent magnitude (V) 6.275[2]
Spectral type B3 Vnpe
U−B color index –0.691[2]
B−V color index +0.008[2]
Radial velocity (Rv)+19[3] km/s
Proper motion (μ) RA: –7.66[1] mas/yr
Dec.: –9.79[1] mas/yr
Parallax (π)5.06 ± 0.39[1] mas
Distance640 ± 50 ly
(200 ± 20 pc)
Absolute magnitude (MV)−0.16[4]
Mass6.3 ± 0.1[5] M
Luminosity1,418[6] L
Surface gravity (log g)3.75[7] cgs
Temperature19,800[7] K
Rotational velocity (v sin i)370 ± 10[8] km/s
Age18.4 ± 1.5[5] Myr
Other designations
ρ1 Ara, V846 Arae, CD–50 10905, GC 22790, HD 152478, HIP 82868, HR 6274, NSV 8047, SAO 244280.[9]
Database references

Rho1 Arae is the Bayer designation for a star in the southern constellation of Ara. Unusually for a star with a Bayer designation, it was not catalogued by Bayer in his Uranometria. It was instead first catalogued by Nicolas Lacaille, in his Coelum Australe Stelliferum published in 1763. This star gained the Bayer designation of Rho1 Arae in Bode's Uranographia, published in 1801. Rho1 Arae is one of the dimmest stars with a Bayer designation, having an apparent visual magnitude of just +6.275[2] According to the Bortle Dark-Sky Scale, this means the star is just barely visible to the naked eye in dark rural skies. Based upon parallax measurements, it is about 640 light-years (200 parsecs) distant from the Sun, give or take a 50 light-year margin of error.[1]

This is a spectroscopic binary system, which means that the presence of an orbiting companion is indicated by shifts in the spectrum. However, because the primary component is spinning rapidly with a projected rotational velocity of 370 ± 10, it is difficult to obtain reliable orbital elements. The orbital period has been estimated at 0.439 days. The spectrum of this system matches a stellar classification of B3 Vnpe, which may indicate the primary is a B-type main sequence star. The 'e' suffix indicates the presence of emission lines, indicating this is a Be star. For Rho1 Arae, the emission lines are prominent and variable.[8]

Rho1 Arae has a peculiar velocity of 27.4 ± 4.9 km/s relative to its neighbors,[5] making it a runaway star system. A scenario that it was ejected from the Scorpius-Centaurus OB association as a result of a past supernova explosion seems unlikely because of its binarity.[8]


  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 Kozok, J. R. (September 1985), "Photometric observations of emission B-stars in the southern Milky Way", Astronomy and Astrophysics Supplement Series 61: 387–405, Bibcode1985A&AS...61..387K. 
  3. Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, 30, University of Toronto: International Astronomical Union, p. 57, Bibcode1967IAUS...30...57E. 
  4. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode2012AstL...38..331A. 
  5. 5.0 5.1 5.2 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. 
  6. Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten 331 (4): 349, doi:10.1002/asna.200911355, Bibcode2010AN....331..349H. 
  7. 7.0 7.1 Soubiran, C.; Le Campion, J.-F.; Cayrel de Strobel, G.; Caillo, A. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics 515: A111, doi:10.1051/0004-6361/201014247, Bibcode2010A&A...515A.111S. 
  8. 8.0 8.1 8.2 Jilinski, E. et al. (September 2010), "A Dynamical Study of Suspected Runaway Stars as Traces of Past Supernova Explosions in the Region of the Scorpius-Centaurus OB Association", The Astrophysical Journal 721 (1): 469–477, doi:10.1088/0004-637X/721/1/469, Bibcode2010ApJ...721..469J. 
  9. "rho01 Ara". SIMBAD. Centre de données astronomiques de Strasbourg. 

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