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.
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][unreliable source?]