Eta Piscis Austrini

Eta Piscis Austrini (η Piscis Austrini) is binary star[2] system in the southern constellation of Piscis Austrinus. As of 2000, the two components had an angular separation of 1.818 arc seconds along a position angle of 113.4°. The pair have a combined apparent visual magnitude of +5.43,[5] which is bright enough to be seen with the naked eye. Based upon an annual parallax shift of 3.99 mas as seen from the Earth,[13] the system is located roughly 820 light years from the Sun.

η Piscis Austrini

Location of η Piscis Austrini (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Piscis Austrinus
A
Right ascension	22h 00m 50.22454s[1]
Declination	−28° 27′ 13.4587″[1]
Apparent magnitude (V)	5.742[2]
B
Right ascension	22h 00m 50.34936s[3]
Declination	−28° 27′ 14.1460″[3]
Apparent magnitude (V)	6.825[2]
Characteristics
Spectral type	B6 III shell + B8.5 V[4]
U−B color index	−0.30[5]
B−V color index	−0.10[5]
Variable type	suspected[6]
Astrometry
Absolute magnitude (MV)	−1.53[7]
A
Proper motion (μ)	RA: +15.289[1] mas/yr Dec.: −0.096[1] mas/yr
Parallax (π)	3.8087 ± 0.0932 mas[1]
Distance	860 ± 20 ly (263 ± 6 pc)
B
Proper motion (μ)	RA: +17.554[3] mas/yr Dec.: −1.229[3] mas/yr
Parallax (π)	4.5342 ± 0.3306 mas[3]
Distance	720 ± 50 ly (220 ± 20 pc)
Details
η PsA A
Mass	4.01±0.18[8] M☉
Luminosity	881[9] L☉
Surface gravity (log g)	3.48[9] cgs
Temperature	12,310[9] K
Rotational velocity (v sin i)	320[9] km/s
Age	115[10] Myr
η PsA B
Mass	3.6[11] M☉
Surface gravity (log g)	4.17[11] cgs
Temperature	14,144[11] K
Metallicity [Fe/H]	−0.21[11] dex
Other designations
η PsA, 12 Piscis Austrini, CPD−29° 6659, HD 209014, HIP 108661, HR 8386, SAO 190822, WDS J22008-2827AB[12]
Database references
SIMBAD	data

Although not catalogued formally as a variable star, brightness changes between magnitude 5,33 and 5.44 have been widely reported.[6][14] The type of variability is thought to be related to its rapid rotation and a surrounding shell, and is tentatively given as a combination of a Be star and Maia variable.[15]

The magnitude 5.7 primary, component A,[2] is a blue-white hued Be star[10] with a stellar classification B6 III.[4] At 115 million years old,[10] the star is spinning rapidly with a projected rotational velocity of 265.[8] It has an estimated four times the mass of the Sun and is radiating 604 times the solar luminosity at an effective temperature of 11,272 K.[8] The secondary, component B, has a visual magnitude of 6.8[2] and a spectral class of B8.5 V.[4]

Eta Piscis Austrini is moving through the Galaxy at a speed of 11.3 km/s relative to the Sun. Its projected Galactic orbit carries it between 23,600 and 30,800 light years from the center of the Galaxy.[16]