Eta Piscis Austrini (η Piscis Austrini) is binary star 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, 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, 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. 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.
The magnitude 5.7 primary, component A, is a blue-white hued Be star with a stellar classification B6 III. At 115 million years old, the star is spinning rapidly with a projected rotational velocity of 265. 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. The secondary, component B, has a visual magnitude of 6.8 and a spectral class of B8.5 V.
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.[1]