Pi Cephei
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 23h 07m 53.854s |
| Declination | +75° 23′ 15.00″ |
| Apparent magnitude (V) | 4.419 4.61 + 6.75) |
| Characteristics | |
| Spectral type | G7III / F5V / A7V-A9V |
| 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 mas/yr Dec.: −34.06±0.88 mas/yr |
| Parallax (π) | 13.8±0.41 mas |
| Distance | 236 ± 7 ly (72 ± 2 pc) |
| Absolute magnitude (MV) | 0.24 |
| Orbit | |
| Primary | π Cep Aa |
| Companion | π Cep Ab |
| Period (P) | 556.72±0.05 d |
| Semi-major axis (a) | 39.0±3.9 mas |
| Eccentricity (e) | 0.297±0.006 |
| Inclination (i) | 99.0±2.5° |
| Longitude of the node (Ω) | 109.2±3.5° |
| 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 | |
| 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 | |
| π Cep Aa | |
| Mass | 3.63±0.53 M☉ |
| Surface gravity (log g) | 3.05±0.11 cgs |
| Temperature | 5,226±92 K |
| Metallicity [Fe/H] | 0.29±0.05 dex |
| Age | 100 Myr |
| 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 | |
| Database references | |
| SIMBAD | data |
Pi Cephei (π Cephei) is a trinary star located in the constellation Cepheus. With a combined apparent magnitude of about 4.4, 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.
Pi Cephei was found to have a visual companion star by Otto Wilhelm von Struve in 1843. That the primary is itself a spectroscopic binary was first noticed by William Wallace Campbell in 1901 using photographic plates taken at Lick Observatory.