Pi Cephei
Star in the constellation Cepheus
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Pi Cephei is a trinary star system located in the northern constellation Cepheus.[7] 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,[3] 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.
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cepheus[1] |
| Right ascension | 23h 07m 53.854s[2] |
| Declination | +75° 23′ 15.00″[2] |
| Apparent magnitude (V) | 4.419[3] (4.61[4] + 6.75[5]) |
| Characteristics | |
| Spectral type | G7III[6] + F5V[6] + A7V-A9V[7] |
| U−B color index | −0.46[citation needed] |
| B−V color index | +0.8[citation needed] |
| Astrometry | |
| Radial velocity (Rv) | −27.33±0.01[8] km/s |
| Proper motion (μ) | RA: +6.81±1.05 mas/yr[2] Dec.: −34.06±0.88 mas/yr[2] |
| Parallax (π) | 13.8±0.41 mas[7] |
| Distance | 236 ± 7 ly (72 ± 2 pc) |
| Absolute magnitude (MV) | 0.24 |
| Orbit[6] | |
| Primary | π Cep Aa |
| Name | π Cep Ab |
| Period (P) | 556.72±0.05 d |
| Semi-major axis (a) | 39.0±3.9 mas[7] |
| Eccentricity (e) | 0.297±0.006 |
| Inclination (i) | 99.0±2.5[7]° |
| Longitude of the node (Ω) | 109.2±3.5[7]° |
| 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[9] | |
| 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[7] | |
| π Cep Aa | |
| Mass | 3.63±0.53 M☉ |
| Surface gravity (log g) | 3.05±0.11[10] cgs |
| Temperature | 5,226±92[10] K |
| Metallicity [Fe/H] | 0.29±0.05[10] dex |
| Age | 100[10] 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[11] | |
| Database references | |
| SIMBAD | data |
| Pi Cep A | |
| Pi Cep B | |
Pi Cephei was found to have a visual companion star by Otto Wilhelm von Struve in 1843.[7] 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.[12] The inner pair of stars orbit with a period of 1.5 years while the outer companion completes an orbit in about 160 years.[7]
The primary component has a stellar classification of G7III,[6] presenting as an aging G-type giant star. At the age of 100 million years,[10] it has an estimated 3–4 times the mass of the Sun.[7] The lower mass components have classes of F5V[6] and A7V-A9V,[7] thus appearing to be main sequence stars.