Epsilon Piscis Austrini

Epsilon Piscis Austrini, Latinized from ε Piscis Austrini, is a blue-white hued star in the southern constellation of Piscis Austrinus. It is visible to the naked eye with an apparent visual magnitude of +4.17.^[2] Based upon an annual parallax shift of 5.92mas as seen from the Gaia satellite, the system is located at a distance of roughly 550 light years.^[1]

Epsilon Piscis Austrini

Location of ε Piscis Austrini (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Piscis Austrinus
Right ascension	22h 40m 39.34826s[1]
Declination	−27° 02′ 37.0151″[1]
Apparent magnitude (V)	+4.17[2]
Characteristics
Spectral type	B8 Ve[3] or B8 IVe[4]
U−B color index	−0.31[2]
B−V color index	−0.11[2]
Astrometry
Radial velocity (Rv)	+1.1±2.8[5] km/s
Proper motion (μ)	RA: +21.839 mas/yr[1] Dec.: −1.588 mas/yr[1]
Parallax (π)	5.9219±0.2931 mas[1]
Distance	550 ± 30 ly (169 ± 8 pc)
Absolute magnitude (MV)	−1.66[4]
Details
Mass	5.95±0.30[6] M☉
Radius	7.51±0.38[6] R☉
Luminosity	661[7] L☉
Surface gravity (log g)	3.93[8] cgs
Temperature	11,066[7] K
Rotational velocity (v sin i)	216[7] km/s
Other designations
ε PsA, 18 Piscis Austrini, CD−27°16010, FK5 854, HD 214748, HIP 111954, HR 8628, SAO 191318[9]
Database references
SIMBAD	data

Characteristics

This is a B-type main sequence star with a stellar classification of B8 Ve.^[3] It is a Be star that is spinning rapidly with a projected rotational velocity of 216 km/s,^[7] compared to an equatorial critical velocity of 301 km/s.^[8] The star has 6.0 times the mass of the Sun, 7.5 times the Sun's radius,^[6] and is radiating 661 times the solar luminosity from its photosphere at an effective temperature of 11,066 K.^[7]

Epsilon Piscis Austrini is part of a wide binary star system, the companion is likely a low-mass red dwarf with a projected separation of 11,700 astronomical units. It also exhibits a strong discrepancy between proper motion measurements taken by the Hipparcos and Gaia satellites, hinting the presence of an astrometric companion, possibly a solar-mass star, with a separation between 6 and 30 au.^[6]

The star is moving through the Galaxy at 18.7 km/s relative to the Sun. Its projected Galactic orbit carries it between 23,917 and 28,138 light-years from the center of the Galaxy.^[10]

Naming

In Chinese, 羽林軍 (Yǔ Lín Jūn), meaning Palace Guard, refers to an asterism consisting of:

• ε Piscis Austrini
• 29 Aquarii
• 35 Aquarii
• 41 Aquarii
• 47 Aquarii
• 49 Aquarii
• λ Piscis Austrini
• HD 212448
• 21 Piscis Austrini
• 20 Piscis Austrini
• υ Aquarii
• 68 Aquarii
• 66 Aquarii
• 61 Aquarii
• 53 Aquarii
• 50 Aquarii
• 56 Aquarii
• 45 Aquarii
• 58 Aquarii
• 64 Aquarii
• 65 Aquarii
• 70 Aquarii
• 74 Aquarii
• τ² Aquarii
• τ¹ Aquarii
• δ Aquarii
• 77 Aquarii
• 88 Aquarii
• 89 Aquarii
• 86 Aquarii
• 101 Aquarii
• 100 Aquarii
• 99 Aquarii
• 98 Aquarii
• 97 Aquarii
• 94 Aquarii
• ψ³Aquarii
• ψ²Aquarii
• ψ¹Aquarii
• 87 Aquarii
• 85 Aquarii
• 83 Aquarii
• χ Aquarii
• ω¹ Aquarii
• ω² Aquarii

Consequently, the Chinese name for ε Piscis Austrini itself is 羽林軍八 (Yǔ Lín Jūn bā, English: the Eighth Sixth Star of Palace Guard.)^[11]