1_Aquarii
1 Aquarii
Binary star in the constellation Aquarius
1 Aquarii is a binary star[5] system in the zodiac constellation of Aquarius, about 263 light years away from the Sun.[1] 1 Aquarii is the Flamsteed designation. It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 5.151,[2] located a degree north of the celestial equator.[5] The system is moving closer to the Earth with a heliocentric radial velocity of −41 km/s.[5]
Systematic observation for determining the orbit of this system began in 2002, some eighty years following the first radial velocity measurements. It is a single-lined spectroscopic binary with an orbital period of 5.385 yr and an eccentricity of 0.368.[5] The visible component is an aging giant star with a stellar classification of K1III.[4] At the age of 1.26[7] billion years old it is a red clump giant, which indicates it is on the horizontal branch and is generating energy through helium fusion at its core.[3] The star has 1.5[7] times the mass of the Sun and has expanded to 11[8] times the Sun's radius. It is radiating 53.7[8] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,715 K.[9]
The mass of the companion appears small, suggesting a red dwarf no higher than class M5.[5] In addition to the spectroscopic companion there are two faint optical companions that have no physical relation to 1 Aqr.[11]