Π_Aquarii
Pi Aquarii
Star in the constellation Aquarius
Pi Aquarii, Latinized from π Aquarii, is the Bayer designation for a binary star in the equatorial constellation of Aquarius. This system has an apparent visual magnitude of a mean apparent magnitude of +4.57.[4] Based upon parallax measurements, it is located at a distance of roughly 780 light-years (240 parsecs) from Earth.[1] It is drifting further away with a radial velocity of +4 km/s.[5]
This is a binary star system with an orbital period of 84.1 days.[14][15] The primary component is a B1 giant or subgiant star.[3] This is a large star with nearly eleven[8] times the mass and over six times the radius of the Sun.[9] Pi Aquarii shines about 7,300[10] times as brightly as the Sun. This energy is being radiated from its outer atmosphere at an effective temperature of 27,094 K,[9] giving it the blue-hued glow of a B-type star.[16] It is spinning rapidly with a projected rotational velocity of 215 km/s.[11] The nature of the secondary is unknown; some analyses have suggested it is an A- or F-type main-sequence star,[7] but the possibility of a white dwarf has not been ruled out.[17]
Pi Aquarii is notable for having undergone a transition from a Be star (showing hydrogen emission lines) into an ordinary B-type star.[15] It is classified as a Gamma Cassiopeiae type[2] variable star and its brightness varies from magnitude +4.45 to +4.71; a range of 0.28. The dominant variability period, 83.8±0.8 days, is nearly the same as the orbital period.[15] Pi Aquarii has a reasonable chance of becoming a supernova some day.[14]