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]
Characteristics
Spectral type G7III[3] / F5V[3] / A7V-A9V[4]
U−B color index -0.46
B−V color index 0.8
Astrometry
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[4] mas
Distance 236 ± 7 ly
(72 ± 2 pc)
Absolute magnitude (MV) 0.24
Orbit[3]
Primary π Cep Aa
Companion π Cep Ab
Period (P) 556.72 ± 0.05 d
Semi-major axis (a) 39.0 ± 3.9 mas[4]
Eccentricity (e) 0.297 ± 0.006
Inclination (i) 99.0 ± 2.5[4]°
Longitude of the node (Ω) 109.2 ± 3.5[4]°
Periastron epoch (T) 2,439,172.9 ± 1.6
Argument of periastron (ω)
(secondary)
7.6 ± 1.2°
Semi-amplitude (K1)
(primary)
24.18 ± 0.15 km/s
Orbit[5]
Primary π Cephei A (Aa + Ab)
Companion π 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)
(secondary)
90.0 ± 4.4°
Details[4]
π Cep Aa
Mass 3.63 ± 0.53 M
π Cep Ab
Mass 3.27 ± 0.48 M
π Cep B
Mass 1.93 ± 0.23 M
Other designations
HD 218658, HR 8819, 33 Cephei, BD+74° 1006, SAO 10629, HIP 114222[6]
Database references
SIMBAD data

Pi Cephei (π Cephei) is a trinary star located in the constellation Cepheus.[4] With an 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.[4]

Stellar system[edit]

Pi Cephei was found to have a visual companion star by Otto Wilhelm von Struve in 1843.[4] That the primary is itself a spectroscopic binary was first noticed by William Wallace Campbell in 1901 using photographic plates taken at Lick Observatory.[7]

References[edit]

  1. ^ a b c d van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. Bibcode:2007A&A...474..653V. arXiv:0708.1752Freely accessible. doi:10.1051/0004-6361:20078357.  Vizier catalog entry
  2. ^ a b Hauck, B.; Mermilliod, M. (1998). "Uvbybeta photoelectric photometric catalogue". Astronomy and Astrophysics Supplement. 129: 431–433. Bibcode:1998A&AS..129..431H. doi:10.1051/aas:1998195. Vizier catalog entry
  3. ^ a b c 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. 
  4. ^ a b c d e f g h i 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. 
  5. ^ "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Retrieved 3 June 2017. 
  6. ^ "* pi. Cep". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2013-09-01. 
  7. ^ 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.