Epsilon Cephei
Star in the constellation Cepheus
From Wikipedia, the free encyclopedia
Epsilon Cephei is a star in the northern constellation of Cepheus. Its name is a Bayer designation that is Latinized from ε Cephei, and abbreviated Epsilon Cep or ε Cep. Based upon an annual parallax shift of 38.16 mas as seen from the Earth,[14] it is located about 85.5 light-years (26.2 pc) from the Sun. The star is visible to the naked eye with an apparent visual magnitude that varies around 4.18.[7]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cepheus[1] |
| Right ascension | 22h 15m 02.197s[2] |
| Declination | +57° 02′ 36.85″[2] |
| Apparent magnitude (V) | 4.15 to 4.21[3] |
| Characteristics | |
| Evolutionary stage | main sequence[2][4] |
| Spectral type | F0 V (Sr II)[5] or F0 IV[6] |
| U−B color index | +0.073[7] |
| B−V color index | +0.277[7] |
| Variable type | δ Sct[3] |
| Astrometry | |
| Radial velocity (Rv) | −4.7±0.8[8] km/s |
| Proper motion (μ) | RA: +423.159 mas/yr[2] Dec.: +52.691 mas/yr[2] |
| Parallax (π) | 38.1598±0.2432 mas[2] |
| Distance | 85.5 ± 0.5 ly (26.2 ± 0.2 pc) |
| Absolute magnitude (MV) | +2.13[1] |
| Details | |
| ε Cep Aa | |
| Mass | 1.64[9] M☉ |
| Radius | 1.86[10] R☉ |
| Luminosity | 11.65[1] L☉ |
| Surface gravity (log g) | 4.11±0.14[9] cgs |
| Temperature | 7,514±255[9] K |
| Metallicity [Fe/H] | +0.08[1] dex |
| Rotational velocity (v sin i) | 91[11] km/s |
| Age | 1.097[9] Gyr |
| ε Cep Ab | |
| Mass | 0.57[12] M☉ |
| Other designations | |
| ε Cephei, 23 Cephei, BD+56 2741, HD 211336, HIP 109857, HR 8494, SAO 34227[13] | |
| Database references | |
| SIMBAD | data |
Properties
Physical characteristics
This is a yellow-white hued, F-type star with a stellar classification of F0 V (Sr II)[5] or F0 IV.[6] Thus it may either be an F-type main sequence star showing an abundance excess of strontium, or it could be a more evolved subgiant star. It is a Delta Scuti variable star that cycles between magnitudes 4.15 and 4.21 every 59.388 minutes.[3] The star displays an infrared excess, indicating the presence of a debris disk with a temperature of 65 K orbiting at a radius of 62 AU. This dust has a combined mass equal to 6.6% of the Earth's mass.[10]
Binary
There is a faint companion star at an angular separation of 330±50 mas along a position angle of 90°±10°. This corresponds to a projected physical separation of 8.6±1.4 AU. The probability of a random star being situated this close to Epsilon Cephei is about one in a million, so it is most likely physically associated. If so, then the debris disk is probably circumbinary. The fact that this companion was not detected during the Hipparcos mission may indicate its orbit has a high eccentricity. The companion star has a K-band magnitude of 7.8 and is probably of class K8–M2.[6]
Naming
In Chinese, 螣蛇 (Téng Shé), meaning Flying Serpent, refers to an asterism consisting of ε Cephei, α Lacertae, 4 Lacertae, π2 Cygni, π1 Cygni, HD 206267, β Lacertae, σ Cassiopeiae, ρ Cassiopeiae, τ Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, λ Andromedae, κ Andromedae, ι Andromedae, and ψ Andromedae. Consequently, the Chinese name for ε Cephei itself is 螣蛇九 (Téng Shé jiǔ, English: the Ninth Star of Flying Serpent).[16]