HD 125823

HD 125823, also known as V761 Centauri or a Centauri, is a variable star in the constellation Centaurus. It is a blue-white star that is visible to the naked eye with a mean apparent visual magnitude of +4.41. The distance to this star is approximately 460 light years based on parallax measurements.[2] It is a member of the Upper Centaurus–Lupus subgroup of the Scorpius–Centaurus association.[10]

This article is about "a Centauri". For "A Centauri", see HD 100673. Not to be confused with α (alpha) Centauri.
HD 125823

A light curve V761 Centauri, plotted from Hipparcos data[1]
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Centaurus
Right ascension 14h 23m 02.24s[2]
Declination −39° 30′ 42.5″[2]
Apparent magnitude (V) +4.41[3]
Characteristics
Spectral type B2V[4]
U−B color index −0.75
B−V color index −0.185±0.019[3]
Variable type SX Ari[5]
Astrometry
Radial velocity (Rv)+7.13±0.16[6] km/s
Proper motion (μ) RA: −24.15±0.13[2] mas/yr
Dec.: −21.90±0.13[2] mas/yr
Parallax (π)7.13 ± 0.16 mas[2]
Distance460 ± 10 ly
(140 ± 3 pc)
Absolute magnitude (MV)−1.27[7]
Details
Mass5.69±0.30[7] M☉
Radius3.7±0.5[7] R☉
Luminosity1,175[7] L☉
Surface gravity (log g)4.20±0.12[7] cgs
Temperature17,700[7] K
Rotation8.817744 days[7][8]
Other designations
a Centauri, V761 Centauri, CD−38 9329, HD 125823, HIP 70300, HR 5378, SAO 205497[9]
Database references
SIMBADdata

In 1965, W. P. Bidelman discovered that the intensities of the star's neutral helium lines had varied on photographic plates taken over the period 1908 to 1911. This variation was confirmed by A. D. Thackeray in 1966.[11] The star ranges from a helium-strong B2 class to a helium-weak B8 with a period of 8.82 days.[12] Radial velocity measurements during the 1970s showed differing velocity variations for helium and other elements.[13] The magnetic field strength peaks at a negative maximum in phase with the maximum helium line strength.[12] Weak emission has been detected in the singly-ionized lines of silicon, magnesium, and iron, but not in the neutral lines of hydrogen and helium.[12]

This is a magnetic peculiar Bp star that shows periodic variation in the strength of its neutral helium lines. It is classified as an SX Arietis type variable star and its brightness varies from magnitude +4.38 to +4.43 with a period of 8.82 days.[5] The star displays very different helium abundances between the two hemispheres, and, unusually, helium-3 has been detected in the weaker southern hemisphere. Latitudinal abundance concentrations have been found for iron, nitrogen, and oxygen.[8] The variation in helium concentration effects the density scale height of the atmosphere, causing helium rich regions to have a lower luminosity in the visual band but emitting stronger levels of far ultraviolet.[14]

References
  1. "Hipparcos Tools Interactive Data Access". Hipparcos. ESA. Retrieved 8 December 2021.
  2. 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. S2CID 18759600. Vizier catalog entry
  3. 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. S2CID 119257644.
  4. Houk, Nancy (1979). Michigan catalogue of two-dimensional spectral types for the HD stars. Vol. 3. Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan. Bibcode:1982mcts.book.....H.
  5. Samus, N. N.; et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. GCVS 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869. Retrieved 2021-10-10.
  6. Soubiran, C.; et al. (2018). "Gaia Data Release 2. The catalogue of radial velocity standard stars". Astronomy and Astrophysics. 616: A7. arXiv:1804.09370. Bibcode:2018A&A...616A...7S. doi:10.1051/0004-6361/201832795. S2CID 52952408.
  7. North, P. (June 1998), "Do SI stars undergo any rotational braking?", Astronomy and Astrophysics, 334: 181–187, arXiv:astro-ph/9802286, Bibcode:1998A&A...334..181N
  8. Bohlender, D. A.; et al. (September 2010). "Doppler imaging of the helium-variable star a Centauri". Astronomy and Astrophysics. 520: 9. arXiv:1007.0977. Bibcode:2010A&A...520A..44B. doi:10.1051/0004-6361/201014157. S2CID 118374769. A44.
  9. "HD 125823". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-10-08.
  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. S2CID 15785349.
  11. Jaschek, C.; et al. (August 1968). "On the Spectrum of Bidelman's Helium Variable Star HD 125823". Astrophysical Journal. 153: L87. Bibcode:1968ApJ...153L..87J. doi:10.1086/180227.
  12. Hubrig, S.; González, J. F. (May 2007). "Detection of variable Si II, Mn II, and Fe II emission lines in the magnetic Bp star a Centauri". Astronomy and Astrophysics. 466 (3): 1083–1087. arXiv:astro-ph/0703229. Bibcode:2007A&A...466.1083H. doi:10.1051/0004-6361:20066738. S2CID 15414222.
  13. Underhill, A. B.; et al. (May 1973). "The radial velocity variations of HD 125823 a Centauri". Astronomy and Astrophysics. 25: 141. Bibcode:1973A&A....25..141U.
  14. Krtička, J.; et al. (April 2020). "Distorted surfaces of magnetic helium-peculiar stars: an application to a Cen". Monthly Notices of the Royal Astronomical Society. 493 (2): 2140–2148. arXiv:2002.01385. Bibcode:2020MNRAS.493.2140K. doi:10.1093/mnras/staa378.
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