Pi Cephei

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π Cephei
Observation data
Epoch J2000      Equinox J2000
Constellation Cepheus
Right ascension 23h 07m 53.854s[1]
Declination +75° 23′ 15.00″[1]
Apparent magnitude (V) 4.419[2] 4.61[3] + 6.75[4])
Spectral type G7III[5] / F5V[5] / A7V-A9V[6]
U−B color index -0.46
B−V color index 0.8
Radial velocity (Rv)-18.6 ± 0.9 km/s
Proper motion (μ) RA: 6.81 ± 1.05[1] mas/yr
Dec.: -34.06 ± 0.88[1] mas/yr
Parallax (π)13.8 ± 0.41[6] mas
Distance236 ± 7 ly
(72 ± 2 pc)
Absolute magnitude (MV)0.24
Primaryπ Cep Aa
Companionπ Cep Ab
Period (P)556.72 ± 0.05 d
Semi-major axis (a)39.0 ± 3.9 mas[6]
Eccentricity (e)0.297 ± 0.006
Inclination (i)99.0 ± 2.5[6]°
Longitude of the node (Ω)109.2 ± 3.5[6]°
Periastron epoch (T)2,439,172.9 ± 1.6
Argument of periastron (ω)
7.6 ± 1.2°
Semi-amplitude (K1)
24.18 ± 0.15 km/s
Primaryπ Cephei A (Aa + Ab)
Companionπ Cephei B
Period (P)162.8 ± 2.8 yr
Semi-major axis (a)0.810 ± 0.050″
Eccentricity (e)0.5968 ± 0.0067
Inclination (i)30.0 ± 3.0°
Longitude of the node (Ω)90.3 ± 4.9°
Periastron epoch (T)B 1934.573 ± 0.35
Argument of periastron (ω)
90.0 ± 4.4°
π Cep Aa
Mass3.63 ± 0.53 M
Surface gravity (log g)3.05±0.11[8] cgs
Temperature5,226±92[8] K
Metallicity [Fe/H]0.29±0.05[8] dex
Age100[8] Myr
π Cep Ab
Mass3.27 ± 0.48 M
π Cep B
Mass1.93 ± 0.23 M
Other designations
HD 218658, HR 8819, 33 Cephei, BD+74° 1006, SAO 10629, HIP 114222[9]
Database references

Pi Cephei (π Cephei) is a trinary star located in the constellation Cepheus.[6] With a combined apparent magnitude of about 4.4,[2] the system is faintly visible to the naked eye. The inner pair of stars orbits in 1.5 years while the outer companion completes one orbit in about 160 years.[6]

Stellar system[edit]

Pi Cephei was found to have a visual companion star by Otto Wilhelm von Struve in 1843.[6] That the primary is itself a spectroscopic binary was first noticed by William Wallace Campbell in 1901 using photographic plates taken at Lick Observatory.[10]


  1. 1.0 1.1 1.2 1.3 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. http://www.aanda.org/index.php?option=com_article&access=bibcode&Itemid=129&bibcode=2007A%2526A...474..653VFUL. Vizier catalog entry
  2. 2.0 2.1 Hauck, B.; Mermilliod, M. (1998). "Uvbybeta photoelectric photometric catalogue". Astronomy and Astrophysics Supplement 129 (3): 431–433. Bibcode 1998A&AS..129..431H. doi:10.1051/aas:1998195. http://aas.aanda.org/articles/aas/full/1998/09/ds1467/ds1467.html.Vizier catalog entry
  3. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P. et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics 355: L27. Bibcode 2000A&A...355L..27H.
  4. Fabricius, C.; Høg, E.; Makarov, V. V.; Mason, B. D.; Wycoff, G. L.; Urban, S. E. (2002). "The Tycho double star catalogue". Astronomy and Astrophysics 384: 180–189. Bibcode 2002A&A...384..180F. doi:10.1051/0004-6361:20011822.
  5. 5.0 5.1 5.2 Scarfe, C. D. et al. (1983). "Revised orbits for 105 Herculis and Pi Cephei A and a model for the Pi Cephei system". Monthly Notices of the Royal Astronomical Society 203: 103–116. Bibcode 1983MNRAS.203..103S. doi:10.1093/mnras/203.1.103. http://articles.adsabs.harvard.edu/full/1983MNRAS.203..103S.
  6. 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 Gatewood, George et al. (2001). "Hipparcos and MAP Studies of the Triple Star π Cephei". The Astrophysical Journal 549 (2): 1145–1150. Bibcode 2001ApJ...549.1145G. doi:10.1086/319458. http://iopscience.iop.org/0004-637X/549/2/1145/fulltext/.
  7. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  8. 8.0 8.1 8.2 8.3 Feuillet, Diane K.; Bovy, Jo; Holtzman, Jon; Girardi, Léo; MacDonald, Nick; Majewski, Steven R.; Nidever, David L. (2016). "Determining Ages of APOGEE Giants with Known Distances". The Astrophysical Journal 817 (1): 40. Bibcode 2016ApJ...817...40F.
  9. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  10. Campbell, William Wallace (1901). "Some recent results secured with the Mills spectrograph". Lick Observatory Bulletin 1 (4): 22–25. Bibcode 1901LicOB...1...22C. doi:10.5479/ADS/bib/1901LicOB.1.22C. http://articles.adsabs.harvard.edu/full/1901LicOB...1...22C.

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