V901 Orionis

V901 Orionis
Location of V901 Orionis (circled in red) just north of Alnitak in Orion's Belt
Observation data
Epoch J2000.0      Equinox ICRS
Constellation Orion
Right ascension 23h 57m 58.477s
Declination +15° 57′ 10.09″
Apparent magnitude (V) 6.97 to 7.02
Characteristics
Evolutionary stage main sequence
Spectral type B2V
B−V color index −0.139±0.007
Variable type SX Ari
Astrometry
Radial velocity (Rv)14.66±0.25 km/s
Proper motion (μ) RA: 2.743 mas/yr
Dec.: 1.671 mas/yr
Parallax (π)2.5463±0.0524 mas
Distance1,280 ± 30 ly
(393 ± 8 pc)
Absolute magnitude (MV)−0.77
Details
Mass8.3±0.3 M☉
Radius3.2 R☉
Luminosity1,995+823
−583 L☉
Surface gravity (log g)4.04±0.01 cgs
Temperature22,000±1,000 K
Rotation1.539 days
Rotational velocity (v sin i)101 km/s
Age3.98 Myr
Other designations
Landstreet's star, V901 Ori, BD−01°1005, HD 37776, HIP 26742, SAO 132446, PPM 175998
Database references
SIMBADdata

V901 Orionis is a variable star in the equatorial constellation of Orion. It is sometimes known as Landstreet's Star and has the designation HD 37776 from the Henry Draper Catalogue; V901 Ori is the variable star designation. With an apparent visual magnitude that varies around seven, it is a challenge to view with the naked eye. Based on parallax measurements from Earth, it is located at a distance of 1,280 ± 30 light-years (393 ± 8 pc). The star is drifting further away from the Sun with a radial velocity of 15 km/s.

Properties

A light curve for V901 Orionis, plotted from TESS data. The 1.5385 day period is marked in red.

This object was found to be a helium-rich variable star in 1976. It was shown to have a high rotation rate and display an infrared excess. Magnetic field measurements showed a multipole distribution and a period of 1.5 days. This was the first star discovered in which a quadrupole-like geometry of the magnetic field dominated over the dipole field found in most stars.

In 2007, HD 37776 was discovered to undergo change in rotation, probably due to loss of angular momentum from a magnetically-confined stellar wind. The rotational braking in this star is 0.54±0.02 s per year, a record level for magnetic chemically-peculiar stars. Surprisingly, a long-term study of the rotation period showed a steady increase until 2003, after which the period began to decrease. This may be the result of an interaction between a thin, magnetically-confined outer envelope and a faster rotating inner body.

This is a massive, helium-strong, magnetic chemically peculiar star with a stellar classification of B2V. It is classified as an SX Arietis variable that ranges in visual magnitude from 6.97 to 7.02 with a period of 1.5385 days. The light variation is believed due to uneven surface distribution of helium and silicon. The topology of the magnetic field is the most complex ever found for an early-type star (i.e. a higher mass main sequence star).

Stellar models paint this as a young star with an estimated age of four million years, that is spinning with a projected rotational velocity of 101 km/s. It has an estimated 8.3 times the mass of the Sun and 3.2 times the Sun's radius. The star is radiating nearly 2,000 times the luminosity of the Sun from its photosphere at an effective temperature of around 22,000 

HD 37776 is a member of the Orion OB1 association of co-moving stars and is embedded in the emission nebula IC 432. It is a candidate member of the Orion B Complex star forming region.

References

  1. 1 2 3 4 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. XHIP record for this object at VizieR.
  2. 1 2 3 4 5 Vallenari, A.; et al. (Gaia collaboration) (2023), "Gaia Data Release 3. Summary of the content and survey properties", Astronomy and Astrophysics, 674: A1, arXiv:2208.00211, Bibcode:2023A&A...674A...1G, doi:10.1051/0004-6361/202243940, S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. 1 2 3 4 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. V901 Ori data
  4. 1 2 3 Shultz, M. E.; et al. (2019), "The magnetic early B-type stars - III. A main-sequence magnetic, rotational, and magnetospheric biography", Monthly Notices of the Royal Astronomical Society, 490 (1): 274, arXiv:1909.02530, Bibcode:2019MNRAS.490..274S, doi:10.1093/mnras/stz2551.
  5. 1 2 Houk, N.; Smith-Moore, M. (1988), Declinations -26°.0 to -12°.0, Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars, vol. 4, Bibcode:1988mcts.book.....H.
  6. 1 2 Jönsson, Henrik; et al. (August 17, 2020), "APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South", The Astronomical Journal, 160 (3), American Astronomical Society: 120, arXiv:2007.05537, Bibcode:2020AJ....160..120J, doi:10.3847/1538-3881/aba592, ISSN 0004-6256.
  7. 1 2 3 4 5 6 7 8 Shultz, M. E.; et al. (June 2022), "MOBSTER - VI. The crucial influence of rotation on the radio magnetospheres of hot stars", Monthly Notices of the Royal Astronomical Society, 513 (1): 1429–1448, arXiv:2201.05512, Bibcode:2022MNRAS.513.1429S, doi:10.1093/mnras/stac136.
  8. 1 2 Yu, Jie; et al. (2023), "Revised Extinctions and Radii for 1.5 Million Stars Observed by APOGEE, GALAH, and RAVE", The Astrophysical Journal Supplement Series, 264 (2): 41, arXiv:2206.00046, Bibcode:2023ApJS..264...41Y, doi:10.3847/1538-4365/acabc8.
  9. 1 2 Román-Zúñiga, Carlos G.; et al. (February 2023), "Stellar Properties for a Comprehensive Collection of Star-forming Regions in the SDSS APOGEE-2 Survey", The Astronomical Journal, 165 (2), id. 51, arXiv:2211.09217, Bibcode:2023AJ....165...51R, doi:10.3847/1538-3881/aca3a4.
  10. 1 2 3 4 Mikulášek, Z.; et al. (November 2020), "What's New with Landstreet's Star HD 37776 (V901 Ori)?", in Wade, Gregg; et al. (eds.), Stellar Magnetism: A Workshop in Honour of the Career and Contributions of John D. Landstreet, held 8-11 July 2019 in London, Canada, Proceedings of the Polish Astronomical Society, vol. 11, pp. 46–53, arXiv:1912.04121, Bibcode:2020pase.conf...46M, ISBN 978-83-950430-9-3.
  11. ↑ "V901 Ori", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2025-11-03.
  12. ↑ MAST: Barbara A. Mikulski Archive for Space Telescopes, Space Telescope Science Institute, retrieved 6 November 2025.
  13. ↑ Groote, D.; Kaufmann, J. P. (1981), "The helium-rich variable star HD 37776", Chemically peculiar stars of the upper main sequence; International Conference on Astrophysics, 23rd, Liege, Belgium, June 23–26, 1981, Reports. (A82-37717 18-39), vol. 23, Liege: Universite de Liege, pp. 435–438, Bibcode:1981LIACo..23..435G.
  14. ↑ Thompson, I. B.; Landstreet, J. D. (February 1985), "The extraordinary magnetic variation of the helium-strong star HD 37776 : a quadrupole field configuration.", Astrophysical Journal, 289: L9–L13, Bibcode:1985ApJ...289L...9T, doi:10.1086/184424.
  15. ↑ Krtička, J.; et al. (March 2007), Stefl, S.; et al. (eds.), "The Nature of Light Variations of the Helium Strong Chemically Peculiar Star HD 37776", Active OB-Stars: Laboratories for Stellar and Circumstellar Physics. Proceedings of the conference held 29 August - 2 September 2005 at Hokkai-Gakuen University, Sapporo, Japan, ASP Conference Series, vol. 361, San Francisco: Astronomical Society of the Pacific, p. 454, arXiv:astro-ph/0509751, Bibcode:2007ASPC..361..454K.
  16. ↑ Mikulášek, Z.; et al. (April 2008), "The record-breaking rotational deceleration of the He strong CP star HD 37776 (V901 Ori)", Contributions of the Astronomical Observatory Skalnaté Pleso, 38 (2): 429−430, arXiv:0712.0524, Bibcode:2008CoSka..38..429M.
  17. ↑ Mikulášek, Z.; et al. (October 2011), "Surprising variations in the rotation of the chemically peculiar stars CU Virginis and V901 Orionis", Astronomy & Astrophysics, 534, id. L5, arXiv:1110.1104, Bibcode:2011A&A...534L...5M, doi:10.1051/0004-6361/201117784.
  18. 1 2 Semenko, Eugene; et al. (September 2022), "Spectropolarimetry of magnetic Chemically Peculiar stars in the Orion OB1 association", Monthly Notices of the Royal Astronomical Society, 515 (1): 998–1011, arXiv:2207.00337, Bibcode:2022MNRAS.515..998S, doi:10.1093/mnras/stac1864.
  19. ↑ Krtička, J.; et al. (2007), Romanyuk, I. I.; Kudryavtsev, D. O. (eds.), "The light variations of HD 37776 as a result of the uneven surface distribution of helium and silicon", Physics of Magnetic Stars. Proceedings of the International Conference, held in the Special Astrophysical Observatory of the Russian AS, August 28–31, 2006, pp. 310–314, arXiv:astro-ph/0703396, Bibcode:2007pms..conf..310K.
  20. ↑ Krtička, J.; et al. (August 2007), "The light variability of the helium strong star HD 37776 as a result of its inhomogeneous elemental surface distribution", Astronomy and Astrophysics, 470 (3): 1089–1098, arXiv:0706.2338, Bibcode:2007A&A...470.1089K, doi:10.1051/0004-6361:20066627.
  21. ↑ Kochukhov, Oleg; et al. (January 2011), "The Extraordinary Complex Magnetic Field of the Helium-strong Star HD 37776", The Astrophysical Journal, 726 (1), id. 24, arXiv:1010.5500, Bibcode:2011ApJ...726...24K, doi:10.1088/0004-637X/726/1/24.

Further reading

  • Monier, Richard (May 2023), "The Behavior of Bp He-strong Stars in the far UV-Paper I: HD 37776", Research Notes of the AAS, 7 (5), id. 89, Bibcode:2023RNAAS...7...89M, doi:10.3847/2515-5172/acd253.
  • Mikulášek, Z.; et al. (July 2008), "The extremely rapid rotational braking of the magnetic helium-strong star HD 37776", Astronomy and Astrophysics, 485 (2): 585–597, Bibcode:2008A&A...485..585M, doi:10.1051/0004-6361:20077794.
  • Mikulášek, Z.; et al. (March 2007), Stefl, S.; et al. (eds.), "Light Variations and Angular Momentum Loss from the He-Strong Magnetic Chemically Peculiar Star HD 37776", Active OB-Stars: Laboratories for Stellar and Circumstellar Physics. Proceedings of the conference held 29 August - 2 September 2005 at Hokkai-Gakuen University, Sapporo, Japan., ASP Conference Series, vol. 361, San Francisco: Astronomical Society of the Pacific, p. 466, arXiv:astro-ph/0509751, Bibcode:2007ASPC..361..466M.
  • Glagolevskij, Yu. V.; Gerth, E. (2001), "The Magnetic Model of HD 37776", in Mathys, G.; et al. (eds.), Magnetic Fields Across the Hertzsprung-Russell Diagram, ASP Conference Proceedings, vol. 248, San Francisco: Astronomical Society of the Pacific, p. 337, Bibcode:2001ASPC..248..337G, ISBN 1-58381-088-9.
  • Khokhlova, V. L.; et al. (March 2000), "Doppler-Zeeman Mapping of the Rapidly Rotating Magnetic CP Star HD37776", Astronomy Letters, 26 (3): 177–191, Bibcode:2000AstL...26..177K, doi:10.1134/1.20380.
  • Romanyuk, I. I.; et al. (1998), "Spectrum and magnetic variations of the remarkable helium-strong star HD 37776 I. Observations and data reduction.", Bulletin of the Special Astrophysical Observatory, 45: 93–104, Bibcode:1998BSAO...45...93R.
  • Adelman, S. J. (October 1997), "UVBY photometry of the magnetic chemically peculiar stars HD 37776, HR 2258, HR 6958, and 108 Aquarii", Astronomy & Astrophysics Supplement Series, 125: 65–70, Bibcode:1997A&AS..125...65A, doi:10.1051/aas:1997211.
  • Bohlender, D. A.; Landstreet, J. D. (September 1989), "The Magnetic Field Geometry of the Helium-Strong Star HD 37776", Bulletin of the American Astronomical Society, 21: 1198, Bibcode:1989BAAS...21.1198B.
  • Bohlender, D. A.; Landstreet, J. D. (October 1986), "Spectral variations in the peculiar helium-strong star HD 37776", Journal of the Royal Astronomical Society of Canada, 80 (5): 279–280, Bibcode:1986JRASC..80..279B.
  • Adelman, S. J.; Pyper, D. M. (November 1985), "Spectrophotometry of peculiar B and A stars. XVIII. The helium rich variable stars HR 1890, sigma Orionis E and HD 37776.", Astronomy and Astrophysics, Supplement Series, 62: 279–290, Bibcode:1985A&AS...62..279A.