2 Scorpii

2 Scorpii (A Scorpii) is a double star in the southern zodiac constellation of Scorpius. The brighter component has an apparent visual magnitude of 4.69, which is bright enough to be visible to the naked eye, while the fainter star is of magnitude 6.98.[2] The distance to this pair can be estimated from the annual parallax shift of 6.49±0.51 mas,[1] which places it roughly 500 light years away. It has a peculiar velocity of 16.5±2.4 km/s and is moving closer to the Sun with a heliocentric radial velocity of about −9 km/s,[4] which will bring it to a perihelion distance of 450 ly (139 pc) in about 2.9 million years.[5] This is a probable (73% chance) member of the Lower Centaurus Crux group of the nearby Scorpius-Centaurus association (Sco OB2), or else (27% chance) it is a member of the Gould's Belt.[10]

2 Scorpii
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 15h 53m 36.71880s[1]
Declination −25° 19′ 37.7087″[1]
Apparent magnitude (V) 4.69 + 6.98[2]
Characteristics
Spectral type B2.5 Vn[3]
B−V color index −0.11/+0.07[2]
Astrometry
Radial velocity (Rv)−9.3±1.6[4] km/s
Proper motion (μ) RA: −15.12[1] mas/yr
Dec.: −25.18[1] mas/yr
Parallax (π)6.49 ± 0.51[1] mas
Distance500 ± 40 ly
(150 ± 10 pc)
Absolute magnitude (MV)−1.33[5]
Details
2 Sco A
Mass6.9±0.1[6] M☉
Luminosity457.40[5] L☉
Temperature20,350[7] K
Rotational velocity (v sin i)320[8] km/s
Age30.4±4.6[6] Myr
Other designations
A Sco, 2 Sco, CD−24° 12352, HD 142114, HIP 77840, HR 5904, SAO 183896, WDS J15536-2520[9]
Database references
SIMBADdata

With high likelihood (>95%), this is a binary star system. As of 2014, the pair had an angular separation of 2.061″±0.001″ along a position angle of 268.28°±0.02°.[7] The brighter member, component A, is a B-type main-sequence star with a stellar classification of B2.5 Vn.[3] The 'n' suffix indicates broad (nebulous) absorption lines due to rapid rotation. It is spinning with a projected rotational velocity of 320 km/s, giving the star an oblate shape with an equatorial bulge that is 15% larger than the polar radius.[8] Roughly 30[6] million years old, it has an estimated 6.9[6] times the mass of the Sun and is radiating 457[5] times the Sun's luminosity from its photosphere at an effective temperature of 20,350 K.[7]

References
  1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. Fabricius, C.; et al. (2002), "The Tycho double star catalogue", Astronomy and Astrophysics, 384: 180, Bibcode:2002A&A...384..180F, doi:10.1051/0004-6361:20011822.
  3. Houk, Nancy; Smith-Moore, M. (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988mcts.book.....H.
  4. Bobylev, V. V.; Bajkova, A. T. (August 2013), "Galactic kinematics from a sample of young massive stars", Astronomy Letters, 39 (8): 532–549, arXiv:1307.1677, Bibcode:2013AstL...39..532B, doi:10.1134/S106377371308001X.
  5. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  6. 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, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x.
  7. Lafrenière, David; et al. (April 2014), "An Adaptive Optics Multiplicity Census of Young Stars in Upper Scorpius", The Astrophysical Journal, 785 (1): 18, Bibcode:2014ApJ...785...47L, doi:10.1088/0004-637X/785/1/47, 47.
  8. Belle, G. T. (2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20: 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2.
  9. "2 Sco". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-03-16.
  10. Bobylev, V. V.; Bajkova, A. T. (September 2007), "Kinematics of the Scorpius-Centaurus OB association", Astronomy Letters, 33 (9): 571–583, arXiv:0708.0943, Bibcode:2007AstL...33..571B, doi:10.1134/S1063773707090010.
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