Beta Cephei
Star in the constellation Cepheus / From Wikipedia, the free encyclopedia
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Beta Cephei (β Cephei, abbreviated Beta Cep, β Cep) is a triple star system of the third magnitude in the constellation of Cepheus. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 690 light-years distant from the Sun. It is the prototype of the Beta Cephei variable stars.
Quick Facts Observation data Epoch J2000 Equinox J2000, Constellation ...
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Cepheus |
Right ascension | 21h 28m 39.59685s[1] |
Declination | +70° 33′ 38.5747″[1] |
Apparent magnitude (V) | 3.16 – 3.27[2] |
Characteristics | |
Spectral type | B1 IV[3] |
U−B color index | –0.95[4] |
B−V color index | –0.22[4] |
Variable type | β Cep[2] |
Astrometry | |
Radial velocity (Rv) | –8.2[5] km/s |
Proper motion (μ) | RA: +12.54[1] mas/yr Dec.: +8.39[1] mas/yr |
Parallax (π) | 4.76 ± 0.30 mas[1] |
Distance | 690 ± 40 ly (210 ± 10 pc) |
Absolute magnitude (MV) | –3.03[3] |
Orbit[6] | |
Primary | β Cep Aa |
Companion | β Cep Ab |
Period (P) | 29616.54 ± 1.36 d |
Semi-major axis (a) | 206.96 ± 0.53 mas |
Eccentricity (e) | 0.7478 ± 0.0005 |
Inclination (i) | 88.80 ± 0.07° |
Longitude of the node (Ω) | 227.83 ± 0.14° |
Periastron epoch (T) | 2450944.5 ± 24.2 |
Argument of periastron (ω) (secondary) | 202.43 ± 0.31° |
Semi-amplitude (K1) (primary) | 9.63 ± 0.26 km/s |
Details | |
β Cep Aa | |
Mass | 7.4[6] M☉ |
Radius | 7.22±0.42[7] R☉ |
Luminosity | 15,100[3] L☉ |
Surface gravity (log g) | 4.12±0.07[7] cgs |
Temperature | 23,600±1,000[7] K |
Metallicity [Fe/H] | –0.23[8] dex |
Rotational velocity (v sin i) | 28[9] km/s |
Age | 8.7[3] Myr |
β Cep Ab | |
Mass | 5.0[6] M☉ |
Other designations | |
Database references | |
SIMBAD | data |
Close
It consists of a binary pair (designated Beta Cephei A) together with a third companion (B). The binary's two components are themselves designated Beta Cephei Aa (officially named Alfirk /ˈælfərk/, the traditional name for the system)[10][11] and Ab.