25 Orionis, ψ1 Orionis
25 Orionis location.png

25 Orionis is located roughly between δ Ori and γ Ori.
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Right ascension 05h 24m 44.82664s[1]
Declination 01° 50′ 47.2039″[1]
Apparent magnitude (V) 4.92 - 4.96[2]
Spectral type B1Vn[3]
U−B color index -0.92[4]
B−V color index -0.20[4]
Variable type γ Cas[2]
Radial velocity (Rv)19.3 ± 2[5] km/s
Proper motion (μ) RA: 0.21[1] mas/yr
Dec.: -0.21[1] mas/yr
Parallax (π)3.14 ± 0.83 mas[1]
Distanceapprox. 1,000 ly
(approx. 320 pc)
Mass10.5[6] M
Radius6.4[7] R
Luminosity10,500[6] L
Surface gravity (log g)4.0[7] cgs
Temperature24,661 ± 339[7] K
Rotational velocity (v sin i)316[8] km/s
Age~100[6] Myr
Other designations
ψ1 Ori, 25 Ori, V1086 Ori, BD+01 1005, FK5 2406, HD 35439, HIP 25302, HR 1789, SAO 112734, CCDM J05247+0150A[3]
Database references

25 Orionis, less commonly known by its Bayer designation Psi1 Orionis (ψ1 Orionis, ψ1 Ori) is a fifth-magnitude star in the constellation Orion. It lies among a dense cluster of low-mass pre-main-sequence stars in the Orion OB1a.

Stellar group

25 Orionis is the dominant member of a rich low-mass star region,[9] first identified in 2005 in a statistical analysis of 2.5 million stars.[10] It is one of several sub-associations within Orion OB1a, all thought to lie at around the same distance of 338 parsecs. Over 200 members of the 25 Orionis stellar group have been found, mostly T Tauri stars with spectral types of K and M and masses less than half the sun's. There are also around 60 hotter stars in the region, including the eruptive variable V346 Tauri.[11]


Like the star Pleione in the Pleiades open cluster, 25 Ori is a Be star with a gaseous circumstellar disk. The SIMBAD astronomical database lists its spectral class as B1Vn.[3]

25 Orionis is a fast rotator, clocking a rotational velocity of 316 km/s, significantly faster than Achernar's speed of 251 km/s in the constellation Eridanus.[8][12] Having a radius of 6 R, the star rotates on its axis roughly once every 23 hours. With a mass in excess of 10 M, the star is expected to explode as a supernova.[6]

See also


  1. ^ a b c d e van Leeuwen, F.; et al. (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.
  2. ^ a b Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  3. ^ a b c "* 25 Ori". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-11-07.
  4. ^ a b Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars" (PDF). Communications of the Lunar and Planetary Laboratory. 4 (Part 1): 99–110. Bibcode:1966CoLPL...4...99J. Archived from the original (PDF) on 2021-01-25.
  5. ^ Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Washington. Bibcode:1953GCRV..C......0W.
  6. ^ a b c d Kaler, James B., "25 ORI (25 Orionis)", Stars, University of Illinois, retrieved 2010-11-07
  7. ^ a b c Underhill, A. B.; et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society, 189 (3): 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601
  8. ^ a b "Bright Star Catalogue (Hoffleit+, 1991)", VizieR (5th Revised ed.), Centre de Données astronomiques de Strasbourg, retrieved 2010-11-07
  9. ^ Briceño, César; et al. (June 2007). "25 Orionis: A Kinematically Distinct 10 Myr Old Group in Orion OB1a". The Astronomical Journal. 661 (2): 1119–1128. arXiv:astro-ph/0701710. Bibcode:2007ApJ...661.1119B. doi:10.1086/513087. S2CID 118950935.
  10. ^ Kharchenko, N. V.; Piskunov, A. E.; Röser, S.; Schilbach, E.; Scholz, R.-D. (2005). "109 new Galactic open clusters". Astronomy and Astrophysics. 440 (1): 403–408. arXiv:astro-ph/0505019. Bibcode:2005A&A...440..403K. doi:10.1051/0004-6361:20052740. S2CID 56292154.
  11. ^ Suárez, Genaro; José Downes, Juan; Román-Zúñiga, Carlos; Covey, Kevin R.; Tapia, Mauricio; Hernández, Jesús; Petr-Gotzens, Monika G.; Stassun, Keivan G.; Briceño, César (2017). "New Low-mass Stars in the 25 Orionis Stellar Group and Orion OB1a Sub-association from SDSS-III/BOSS Spectroscopy". The Astronomical Journal. 154 (1): 14. arXiv:1705.02722. Bibcode:2017AJ....154...14S. doi:10.3847/1538-3881/aa733a. S2CID 119087968.
  12. ^ "Bright Star Catalogue (Hoffleit+, 1991)". VizieR (5th Revised ed.). Centre de Données astronomiques de Strasbourg. Retrieved 2010-11-08.

Coordinates: Sky map 05h 24m 44.80s, +01° 50′ 47.0″