Delta Cephei

For the variable star type, see Delta Cephei variable. For the general class of variable stars, see Cepheid variable.
Delta Cephei
Location of δ Cep (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cepheus
δ Cep A
Right ascension 22h 29m 10.26502s[1]
Declination +58° 24′ 54.7139″[1]
Apparent magnitude (V) 4.07 (3.48–4.37) / 7.5
δ Cep C
Right ascension 22h 29m 09.248s[1]
Declination +58° 24′ 14.76″[1]
Apparent magnitude (V) 6.3
Characteristics
Spectral type F5Ib-G1Ib[2] + B7-8[3]
U−B color index 0.36
B−V color index 0.60
Variable type Cepheid
Astrometry
Radial velocity (Rv)-16.8[4] km/s
Proper motion (μ) RA: +15.35[1] mas/yr
Dec.: +3.52[1] mas/yr
Parallax (π)3.66+0.09
−0.10 mas[5]
Distance887 ± 26 ly
(272 ± 8[6][7] pc)
Absolute magnitude (MV)–3.47 ± 0.10 (–3.94 - –3.05)[6]
Details
δ Cep A
Mass5.26+1.26
−1.4[5] M☉
Radius46.1+1.9
−2.1[8] R☉
Luminosity1,949±107[9] L☉
Surface gravity (log g)1.65[8] cgs
Temperature5,905±29[9] K
Metallicity [Fe/H]+0.08[10] dex
Rotational velocity (v sin i)9[11] km/s
δ Cep B
Mass0.72±0.11[5] M☉
δ Cep C
Luminosity500 L☉
Temperature8,800[12] K
Orbit[5]
Primaryδ Cep A
Companionδ Cep B
Period (P)9.32+0.03
−0.04 yr
Semi-major axis (a)0.029+0.002
−0.003″
Eccentricity (e)0.71±0.02
Inclination (i)124+17
−12°
Longitude of the node (Ω)78+56
−50°
Periastron epoch (T)1982.294+0.111
−0.101 yr
Argument of periastron (ω)
(secondary)		230+4
−3°
Semi-amplitude (K1)
(primary)		1.509 ± 0.2[4] km/s
Other designations
27 Cephei, BD+57 2548, FK5 847, HD 213306, HIP 110991, HR 8571, SAO 34508.
Database references
SIMBADdata

Delta Cephei (δ Cep, δ Cephei) is a quadruple star system[4] located approximately 887 light-years away in the northern constellation of Cepheus, the King. At this distance, the visual magnitude of the star is diminished by 0.23 as a result of extinction caused by gas and dust along the line of sight.[6] It is the prototype of the Cepheid variable stars that undergo periodic changes in luminosity.

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