Epsilon Capricorni

ε Capricorni A/B

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Capricornus
Right ascension	21h37m04.8s
Declination	−19°27′58″
Apparent magnitude (V)	+4.51/+9.5
Distance	660 ± 120 ly (203 ± 38 pc)
Spectral type	B2.5Vpe/K1III-IV
Other designations
Kastra, 39 Capricorni, HR 8260, HD 205637, BD−20°6251/BD−20°6253, FK5 3724, HIP 106723, SAO 164520, GC 30252, BDS 11077, CCDM J21371-1928

Epsilon Capricorni (ε Cap, ε Capricorni) is a triple star system in the constellation Capricornus. It also has the traditional star name Castra or Kastra, meaning "fort" or "military camp" in Latin. It is approximately 660 light years from Earth.

In Chinese, 壘壁陣 (Lěi Bì Zhèn), meaning Line of Ramparts, refers to an asterism consisting of ε Capricorni, κ Capricorni, γ Capricorni, δ Capricorni, ι Aquarii, σ Aquarii, λ Aquarii, φ Aquarii, 27 Piscium, 29 Piscium, 33 Piscium and 30 Piscium. Consequently, ε Capricorni itself is known as 壘壁陣二 (Lěi Bì Zhèn èr, English: the Second Star of Line of Ramparts.)

The primary component, ε Capricorni A, is a blue-white B-type main sequence dwarf with a mean apparent magnitude of +4.51. It is classified as a Gamma Cassiopeiae type variable star and its brightness varies from magnitude +4.48 to +4.72. It is a spectroscopic binary, and the two subcomponents have apparent magnitudes of +5.0 and +6.3 and are separated by 0.0047 arcseconds (1 AU).

Further out, 68 arcseconds away, is ε Capricorni B which is at least 13,000 AU, or 0.22 light years away from the close binary. It is an orange K-type giant with an apparent magnitude of +9.5.