Article · Wikipedia archive · Last revised Jun 19, 2026

9 Persei

9 Persei is a single variable star in the northern constellation Perseus, located around 4,300 light years away from the Sun. It has the Bayer designation i Persei; 9 Persei is the Flamsteed designation. This body is visible to the naked eye as a faint, white-hued star with an apparent visual magnitude of about 5.2. It is moving closer to the Sun with a heliocentric radial velocity of −15.2 km/s. The star is a member of the Perseus OB1 association of co-moving stars.

Last revised
Jun 19, 2026
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9 Persei
Location of 9 Persei (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Perseus
Right ascension 02h 22m 21.43482s1
Declination +55° 50′ 44.3518″1
Apparent magnitude (V) 5.15 - 5.252
Characteristics
Spectral type A2 Ia3
U−B color index −0.114
B−V color index +0.374
Variable type α Cyg2
Astrometry
Radial velocity (Rv)−15.205 km/s
Proper motion (μ) RA: +0.3741 mas/yr
Dec.: −1.7981 mas/yr
Parallax (π)0.7603±0.1139 mas1
Distanceapprox. 4,300 ly
(approx. 1,300 pc)
Absolute magnitude (MV)−4.736
Details
Mass10.57 M☉
Radius88.9+3.8
−2.81 R☉
Luminosity12,331±2,1891 L☉
Surface gravity (log g)1.748 cgs
Temperature9,8409 K
Metallicity [Fe/H]+0.268 dex
Rotational velocity (v sin i)253 km/s
Other designations
i Persei, 9 Per, V474 Per, BD+55°598, FK5 2159, GC 2836, HD 14489, HIP 11060, HR 685, SAO 23256, CCDM J02224+5551A, WDS J02224+5551A10
Database references
SIMBADdata
The Double Cluster. 9 Persei is the brightest star on right side of the image. North is to the left. source ↗

9 Persei is a single11 variable star in the northern constellation Perseus, located around 4,300 light years away from the Sun. It has the Bayer designation i Persei; 9 Persei is the Flamsteed designation. This body is visible to the naked eye as a faint, white-hued star with an apparent visual magnitude of about 5.2. It is moving closer to the Sun with a heliocentric radial velocity of −15.2 km/s.5 The star is a member of the Perseus OB1 association of co-moving stars.12

A light curve for V474 Persei. The main plot shows the variation over a year, and the inset plot shows the same data folded over the best-fit period. The data was published by Burggraaff et al. (2018)13 source ↗

This is a blue supergiant with a stellar classification of A2 Ia,3 a massive star that has used up its core hydrogen and is now fusing heavier elements. It is an Alpha Cygni variable (designated V474 Persei), a type of non-radial pulsating variable. It ranges in magnitude from 5.15 down to 5.25.14 The star has 10.57 times the mass of the Sun and has expanded to 891 times the Sun's radius. It is radiating over 12,0001 times the luminosity of the Sun from its swollen photosphere at an effective temperature of 9,840 K.9

9 Persei has one visual companion, designated component B, at an angular separation of 12.3″ and magnitude 12.0.15

References

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. 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. Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H. 5050. Bibcode:1995yCat.5050....0H.
  4. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  5. Wilson, R. E. (1953). "General Catalogue of Stellar Radial Velocities". Carnegie Institute Washington D.C. Publication. Carnegie Institution for Science. Bibcode:1953GCRV..C......0W. ISBN 9780598216885. LCCN 54001336. {{cite journal}}: ISBN / Date incompatibility (help)
  6. Huang, W.; et al. (2012), "A catalogue of Paschen-line profiles in standard stars", Astronomy & Astrophysics, 547: A62, arXiv:1210.7893, Bibcode:2012A&A...547A..62H, doi:10.1051/0004-6361/201219804, S2CID 119286159.
  7. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. S2CID 118629873. Vizier catalog entry
  8. Wu, Yue; Singh, H. P.; Prugniel, P.; Gupta, R.; Koleva, M. (2010). "Coudé-feed stellar spectral library – atmospheric parameters". Astronomy & Astrophysics. 525: A71. arXiv:1009.1491. Bibcode:2011A&A...525A..71W. doi:10.1051/0004-6361/201015014. S2CID 53480665.
  9. Zorec, J.; Cidale, L.; Arias, M. L.; Frémat, Y.; Muratore, M. F.; Torres, A. F.; Martayan, C. (2009). "Fundamental parameters of B supergiants from the BCD system". Astronomy and Astrophysics. 501 (1): 297–320. arXiv:0903.5134. Bibcode:2009A&A...501..297Z. doi:10.1051/0004-6361/200811147. S2CID 14969137.
  10. "9 Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved April 26, 2019.
  11. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  12. Lee, Hsu-Tai; Lim, Jeremy (June 2008). "On the Formation of Perseus OB1 at High Galactic Latitudes". The Astrophysical Journal. 679 (2): 1352–1363. arXiv:0804.4520. Bibcode:2008ApJ...679.1352L. doi:10.1086/587801. S2CID 14252530.
  13. Burggraaff, O.; Talens, G. J. J.; Spronck, J.; Lesage, A. L.; Stuik, R.; Otten, G. P. P. L.; Van Eylen, V.; Pollacco, D.; Snellen, I. A. G. (September 2018). "Studying bright variable stars with the Multi-site All-Sky CAmeRA (MASCARA)". Astronomy and Astrophysics. 617: A32. arXiv:1806.02247. Bibcode:2018A&A...617A..32B. doi:10.1051/0004-6361/201833142.
  14. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  15. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (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. Vizier catalog entry