Epoch J2000 Equinox J2000
|Right ascension||22h 10m 51.277s|
|Declination||+58° 12′ 04.55″|
|Apparent magnitude (V)||3.35|
|Spectral type||K1.5 Ib|
|B−V color index||+1.55|
|Variable type||Eclipsing binary?|
|Proper motion (μ)||RA: 13.52 ± 0.10 mas/yr
Dec.: 5.24 ± 0.09 mas/yr
|Parallax (π)||3.90 ± 0.10 mas|
|Distance||840 ± 20 ly
(256 ± 7 pc)
|Absolute magnitude (MV)||−4.7|
|Surface gravity (log g)||0.75 cgs|
|Metallicity [Fe/H]||+0.22 dex|
|Rotational velocity (v sin i)||10.64 km/s|
Zeta Cephei (ζ Cep, ζ Cephei) is a star in the constellation of Cepheus. Zeta Cephei marks the left shoulder of Cepheus, the King of Joppa (Ethiopia).[clarification needed] It is one of the fundamental stars of the MK spectral sequence, defined as type K1.5 Ib.
Zeta Cephei is an orange supergiant star with a surface temperature of 3,853 K and eight times more massive than the Sun. The luminosity of Zeta Cephei is approximately 3,600 times that of the Sun. At a distance of about 840 light-years, Zeta Cephei has an apparent magnitude (m) of 3.4 and an absolute magnitude (M) of -4.7. The star has a metallicity approximately 1.6 times that of the Sun; i.e., it contains 1.6 times as much heavy-element material as the Sun.
Hekker et al. (2008) have detected a periodicity of 533 days, hinting at the possible presence of an as yet unseen companion. It is listed as a possible eclipsing binary with a very small amplitude.
At the edge of the 8 to 10 solar mass (M☉) limit at which stars develop iron cores and then explode as supernovae, Zeta Cephei's most likely fate is to produce a very massive white dwarf near the Chandrasekhar limit (1.4 M☉) at which such dense remnants can survive. If Zeta Cephei is a binary star; i.e., if there is a stellar companion, and it is close enough to feed sufficient matter to the white-dwarf-to-be, it is marginally possible that the limit could be overflowed, resulting in the white dwarf's collapse and a Type Ia supernova explosion.
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