Psi Aquarii

91 Aquarii is a triple star system. The primary component, 91 Aqr A, is a giant star with a stellar classification of K1 III. This is an evolved star with 138% of the Sun's mass that has expanded to over 10 times the size of the Sun. It is radiating 54 times the Sun's luminosity from its outer envelope at an effective temperature of 4,730 K. This gives it the orange-hued glow of a K-type star. The primary shares a common proper motion with two others stars, 91 Aqr B and C, suggesting that they are physically connected. The latter pair form a binary system located at an angular separation of 52 arcseconds from the primary. They are 10th magnitude stars separated by 0.3 arcseconds from each other.

Psi2 Aquarii, Latinized from ψ2 Aquarii, is the Bayer designation for a star in the equatorial constellation of Aquarius. It is visible to the naked eye with an apparent visual magnitude of 4.4. Based upon parallax measurements made during the Hipparcos mission, the distance to this star is roughly 400 light-years (120 parsecs). This is a B-type main sequence star with a stellar classification of B5 Vn. The 'n' suffix indicates that the absorption lines in the spectrum are being broadened by Doppler shift from the star's rapid rotation rate. The projected rotational velocity of the star is 341 km/s. Psi2 Aquarii is 4.6 times as large as the Sun with an effective temperature of 15,212 K in its outer envelope. It is a λ Eridani variable, or periodic Be star, with a pulsation cycle lasting 1.073 days. The amplitude of the variation is 0.024 in magnitude.

Psi3 Aquarii, Latinized from ψ3 Aquarii, is the Bayer designation for a visual binary star system in the constellation of Aquarius. It has an apparent visual magnitude of 4.98, which is bright enough to be seen with the naked eye. Parallax measurements give a distance estimate of roughly 262 light-years (80 parsecs). The main component of this system is an A-type main sequence star with a stellar classification of A0 V. Its companion is an 11th magnitude star 1.5 arcseconds from the primary. This system is an X-ray source with a luminosity of 8.34 × 1029 erg s−1. This radiation most likely comes from the companion star.