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) | −27.33±0.01 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 |
| Name | 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) |
| Name | 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 | |
| π Cep, 33 Cephei, BD+74°1006, GC 32237, HD 218658, HIP 114222, HR 8819, SAO 10629, WDS J23079+7523AB | |
| Database references | |
| SIMBAD | data |
| Pi Cep A | |
| Pi Cep B | |
Pi Cephei is a trinary star system located in the northern constellation Cepheus. Its name is a Bayer designation that is Latinized from π Cephei, and abbreviated Pi Cep or π Cep. With a combined apparent magnitude of about 4.4, the system is faintly visible to the naked eye. It is located at a distance of approximately 236 light-years (72 pc) from the Earth.
Pi Cephei was found to have a visual companion star by Otto Wilhelm von Struve in 1843. The brighter member is itself a spectroscopic binary, which was first noticed by William Wallace Campbell in 1901 using photographic plates taken at Lick Observatory. The inner pair of stars orbit with a period of 1.5 years while the outer companion completes an orbit in about 160 years.
The primary component has a stellar classification of G7III, presenting as an aging G-type giant star. At the age of 100 million years, it has an estimated 3–4 times the mass of the Sun. The lower mass components have classes of F5V and A7V-A9V, thus appearing to be main sequence stars.