CU Virginis

CU Virginis is a single[10] star in the equatorial constellation of Virgo.[11] It has an apparent visual magnitude of 4.99,[2] which is bright enough to be faintly visible to the naked eye. The distance to this star can be estimated from its annual parallax shift of 13.9 mas,[1] yielding a separation of 234 light years.

CU Virginis
Observation data
Epoch J2000      Equinox J2000
Constellation Virgo
Right ascension  14h 12m 15.80569s[1]
Declination +02° 24′ 33.9342″[1]
Apparent magnitude (V) 4.99[2] (4.92–5.07)[3]
Characteristics
Spectral type ApSi[4] or B8.5 Vp Si[5]
B−V color index −0.118±0.006[2]
Variable type α2 CVn[3]
Astrometry
Radial velocity (Rv)−2.0±7.4[6] km/s
Proper motion (μ) RA: −43.049[1] mas/yr
Dec.: +26.081[1] mas/yr
Parallax (π)13.9366 ± 0.2601[1] mas
Distance234 ± 4 ly
(72 ± 1 pc)
Absolute magnitude (MV)0.50[2]
Details[7]
Mass3.06±0.06 M☉
Radius2.06±0.14 R☉
Luminosity100±11 L☉
Surface gravity (log g)4.30±0.06 cgs
Temperature12,750±250 K
Rotation0.5207137±0.0000010 d[8]
Rotational velocity (v sin i)145±3 km/s
Other designations
CU Vir, BD+03° 2867, FK5 3127, HD 124224, HIP 69389, HR 5313, SAO 120339, ADS 9152 A, WDS J14123+0225A[9]
Database references
SIMBADdata

This is one of the best studied Ap stars.[12] It has a stellar classification of Ap Si[4] with strong lines of silicon and weak helium lines. The star is a fast rotator with a period of 0.52 days and an axis that is inclined by 46.5°±4.1° to the line of sight from the Earth.[7] Both the spectrum and luminosity of the star vary with the rotation,[12] and it is classified as a α2 Canum Venaticorum variable with the designation CU Virginis (CU Vir).[3] There is some evidence that the rotation period may vary slightly over a timescale measured in decades.[13] Such changes have been observed to occur in glitches, rather than varying constantly.[12]

CU Virginis has three times the mass of the Sun and double the Sun's radius. It is radiating 100 times the Sun's luminosity from its photosphere at an effective temperature of 12,750 K.[7] The star has a strong magnetic field, placing it in the class of magnetic chemically peculiar stars. The polar magnetic field has a strength of about 3 kT.[12] The magnetic pole may be displaced by 87° from the axis of rotation, and the effective magnetic field is seen to vary over the course of a rotation.[12] The mean surface magnetic field varies over the range 1.2–3.2 kT.[14]

This star is a radio emitter, with the emission being modulated by the rotational phase. This emission is believed to be "gyrosynchrotron radiation emitted by mildly relativistic (Lorentz factor of γ ≤ 2) electrons trapped in the magnetosphere". Two pulses of 100% circularly polarized radio energy are detected each rotation, which may be produced via an electron cyclotron maser process. These polarized beams are then refracted as they pass through cold plasma in the star's magnetosphere.[12]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  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. Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017), "General catalogue of variable stars: Version GCVS 5.1", Astronomy Reports, 61: 80, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085.
  4. Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Bibcode:1999MSS...C05....0H.
  5. Abt, Helmut A.; Morrell, Nidia I. (1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", Astrophysical Journal Supplement, 95: 135, Bibcode:1995ApJS...99..135A, doi:10.1086/192182.
  6. Kharchenko, N. V.; et al. (2007), "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations", Astronomische Nachrichten, 328 (9): 889, arXiv:0705.0878, Bibcode:2007AN....328..889K, doi:10.1002/asna.200710776.
  7. Kochukhov, O.; et al. (May 2014), "Magnetic field topology of the unique chemically peculiar star CU Virginis", Astronomy & Astrophysics, 565: 14, arXiv:1404.2645, Bibcode:2014A&A...565A..83K, doi:10.1051/0004-6361/201423472, A83.
  8. Pyper, Diane M.; et al. (May 2013), "An update on the rotational period of the magnetic chemically peculiar star CU Virginis", Monthly Notices of the Royal Astronomical Society, 431 (3): 2106–2110, Bibcode:2013MNRAS.431.2106P, doi:10.1093/mnras/stt256.
  9. "HD 124224". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 16 August 2018.
  10. Eggleton, P. P.; Tokovinin, A. A. (2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  11. Kaler, James B. (May 23, 2014), "CU Virginis", Stars, University of Illinois, retrieved 2018-08-18.
  12. Lo, K. K.; et al. (April 2012), "Observations and modelling of pulsed radio emission from CU Virginis", Monthly Notices of the Royal Astronomical Society, 421 (4): 3316–3324, arXiv:1201.3678, Bibcode:2012MNRAS.421.3316L, doi:10.1111/j.1365-2966.2012.20555.x.
  13. Mikulášek, Z.; et al. (October 2011), "Surprising variations in the rotation of the chemically peculiar stars CU Virginis and V901 Orionis", Astronomy & Astrophysics, 534: 5, arXiv:1110.1104, Bibcode:2011A&A...534L...5M, doi:10.1051/0004-6361/201117784, L5.
  14. Glagolevskij, Yu. V.; Gerth, E. (February 2002), "Comments on the magnetic field structure of the star CU Virginis", Astronomy and Astrophysics, 382: 935–938, Bibcode:2002A&A...382..935G, doi:10.1051/0004-6361:20011629.
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