Epsilon Cephei

Epsilon Cephei, Latinized from ε Cephei, is a star in the northern constellation of Cepheus. Based upon an annual parallax shift of 38.17 mas as seen from the Earth,^[2] it is located about 85 light years from the Sun. The star is visible to the naked eye with an apparent visual magnitude of 4.18.^[6]

Epsilon Cephei

A visual band light curve for Epsilon Cephei, adapted from Bruntt et al. (2007)[1]
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Cepheus
Right ascension	22h 15m 02.19530s[2]
Declination	+57° 02′ 36.8771″[2]
Apparent magnitude (V)	4.15 - 4.21[3]
Characteristics
Spectral type	F0 V (Sr II)[4] or F0 IV[5]
U−B color index	+0.073[6]
B−V color index	+0.277[6]
Variable type	δ Sct[3]
Astrometry
Radial velocity (Rv)	−4.7±0.8[7] km/s
Proper motion (μ)	RA: +481.53[2] mas/yr Dec.: +46.04[2] mas/yr
Parallax (π)	38.17±0.97 mas[2]
Distance	85 ± 2 ly (26.2 ± 0.7 pc)
Absolute magnitude (MV)	+2.13[8]
Details
ε Cep Aa
Mass	1.64[9] M☉
Radius	1.86[10] R☉
Luminosity	11.65[8] L☉
Surface gravity (log g)	4.11±0.14[9] cgs
Temperature	7,514±255[9] K
Metallicity [Fe/H]	+0.08[8] 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)^[4] or F0 IV.^[5] 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.^[5]

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)^[14]