Pi Centauri

Pi Centauri, Latinized from π Centauri, is a binary star system in the southern constellation of Centaurus. It has a blue-white hue and is visible to the naked eye with a combined apparent visual magnitude of +3.90.[2] The system is located at a distance of approximately 360 light years from the Sun based on parallax,[1] and is drifting further away with a radial velocity of around +9 km/s.[2] It is a member of the Lower Centaurus-Crux subgroup of the Scorpius–Centaurus Association.[10]

Pi Centauri
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Centaurus
Right ascension  11h 21m 00.41s[1]
Declination −54° 29′ 27.7″[1]
Apparent magnitude (V) +3.90[2] (4.08 + 5.65)[3]
Characteristics
Spectral type B5Vn[4] + B6V[5]
B−V color index −0.157±0.015[2]
Astrometry
Radial velocity (Rv)+9.4±3.7[2] km/s
Proper motion (μ) RA: −35.85±0.34[1] mas/yr
Dec.: −1.72±0.27[1] mas/yr
Parallax (π)9.12 ± 0.34[1] mas
Distance360 ± 10 ly
(110 ± 4 pc)
Absolute magnitude (MV)−1.30[2]
Orbit[6]
Period (P)39.0±0.19 yr
Semi-major axis (a)0.2263±0.0011″
Eccentricity (e)0.8530±0.0040
Inclination (i)19.4±4.9°
Longitude of the node (Ω)327.8±3.9°
Periastron epoch (T)2010.410±0.037
Argument of periastron (ω)
(secondary)		340.3±4.0°
Details
A
Mass6.43[6] M☉
Temperature16,760[7] K
Rotational velocity (v sin i)340[8] km/s
B
Mass3.68[6] M☉
Other designations
π Cen, BD−53°4498, FK5 428, GC 15601, HD 98718, HIP 55425, HR 4390, SAO 238986, CCDM J11210-5429[9]
Database references
SIMBADdata

The magnitude +4.08[3] primary, designated component A, is a B-type main-sequence star with a stellar classification of B5Vn,[4] where the 'n' suffix indicates broad, diffuse (nebulous) lines due to rapid rotation. This star is spinning with a projected rotational velocity of 340 km/s, giving it an equatorial bulge that is 22% larger than the polar radius.[8] It has 6.4[6] times the mass of the Sun and is radiating 783[2] times the Sun's luminosity from its photosphere at an effective temperature of 16,760 K.[7]

The secondary companion, component B, is magnitude +5.65[3] with a class of B6V[5] and 3.7[6] times the Sun's mass. The pair orbit around their common barycentre once every 39 years with an eccentricity of 0.8530. The semi-major axis of the companion is 0.23 arcseconds at an inclination of 19.4°.[6]

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.Vizier catalog entry
  2. 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.
  3. Mason, Brian D.; et al. (2001), "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog", The Astronomical Journal, 122 (6): 3466, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
  4. Hiltner, W. A.; et al. (July 1969), "MK Spectral Types for Bright Southern OB Stars", Astrophysical Journal, 157: 313–326, Bibcode:1969ApJ...157..313H, doi:10.1086/150069.
  5. Edwards, T. W. (1976), MK classification for visual binary components, 81, pp. 245–249, Bibcode:1976AJ.....81..245E, doi:10.1086/111879.
  6. Tokovinin, Andrei (2012), "Speckle Interferometry and Orbits of "Fast" Visual Binaries", The Astronomical Journal, 144 (2), 56, arXiv:1206.1882, Bibcode:2012AJ....144...56T, doi:10.1088/0004-6256/144/2/56.
  7. Zorec, J.; et al. (July 2009), "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff", Astronomy and Astrophysics, 501 (1): 297–320, arXiv:0903.5134, Bibcode:2009A&A...501..297Z, doi:10.1051/0004-6361/200811147.
  8. van Belle, Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2.
  9. "pi Cen". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-10-10.
  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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