Epsilon Capricorni
Star in the constellation Capricornus
From Wikipedia, the free encyclopedia
Epsilon Capricorni is a binary star system[10] in the constellation Capricornus. Based upon an annual parallax shift of 3.09 mas as seen from the Earth,[2] the star is located about 1,060 light years from the Sun. It can be seen with the naked eye, having a combined apparent visual magnitude of 4.62.[3]
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Capricornus[1] |
| Right ascension | 21h 37m 04.83068s[2] |
| Declination | −19° 27′ 57.6464″[2] |
| Apparent magnitude (V) | +4.62[3] |
| Characteristics | |
| Spectral type | B2.5 Vpe[4] |
| U−B color index | −0.64[3] |
| B−V color index | −0.19[3] |
| Variable type | γ Cas[5] |
| Astrometry | |
| Proper motion (μ) | RA: +12.79 mas/yr[2] Dec.: +0.28 mas/yr[2] |
| Parallax (π) | 3.09±0.18 mas[2] |
| Distance | 1,060 ± 60 ly (320 ± 20 pc) |
| Absolute magnitude (MV) | −3.03[1] |
| Details | |
| ε Cap A | |
| Mass | 7.6[6] M☉ |
| Radius | 4.80[6] R☉ |
| Luminosity | 4,649[1] L☉ |
| Surface gravity (log g) | 4.0[6] cgs |
| Temperature | 18,800[6] K |
| Metallicity [Fe/H] | −0.08[1] dex |
| Rotational velocity (v sin i) | 225[7] km/s |
| Age | 27.5±4.2[8] Myr |
| Other designations | |
| Castra, ε Cap, 39 Cap, BD−20°6251, FK5 3724, HD 205637, HIP 106723, HR 8260, SAO 164520, WDS J21371-1928A[9] | |
| Database references | |
| SIMBAD | data |
Nomenclature
Epsilon Capricorni is the star's Bayer designation, which is Latinized from ε Capricorni and abbreviated Epsilon Cap or ε Cap. It is sometimes called by the name Castra, meaning "fort" or "military camp" in Latin, usually in an astrological context.[11][12]
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.[13] Consequently, the Chinese name for ε Capricorni itself is 壘壁陣二 (Lěi Bì Zhèn èr, English: the Second Star of Line of Ramparts.)[14]
Observations
In 2006, this was reported as a single-lined spectroscopic binary with an orbital period of 128.5 days. It was confirmed in 2023.[10] The primary, component Aa, is a Be star that is surrounded by ionized gas that is producing the emission lines in the spectrum. This circumstellar shell is inclined by 80° to the line of sight from the Earth.[6] The system is undergoing both short term and long term variations in luminosity, with the short period variations showing a phase cycle of 1.03 days.[5] It is classified as a Gamma Cassiopeiae variable with an amplitude of 0.16 in magnitude.[5]
Epsilon Capricorni Aa is a blue-white hued B-type main sequence star with a stellar classification of B2.5 Vpe[4] and a visual magnitude of +4.62.[3] It has 7.6 times the mass of the Sun and 4.8 times the Sun's radius.[6] The star is spinning rapidly, with a projected rotational velocity of 225 km/s. This is giving it an oblate shape with an equatorial bulge that is 7% larger than the polar radius.[7]
The system has two visual companions. Component B is a visual magnitude 10.11 star at an angular separation of 65.8 arc seconds along a position angle of 46°, as of 2013. Component C with visual magnitude of 14.1 lies at an angular separation of 62.7 arc seconds along a position angle of 164°, as of 1999.[16] Both stars are likely to be unrelated and at different distances to Epsilon Capricorni.[17]