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Xi Aquarii (ξ Aqr, ξ Aquarii) is the Bayer designation for a binary star system in the equatorial constellation of Aquarius. It has the traditional name Bunda and is visible to the naked eye with an apparent visual magnitude of 4.7. Based upon parallax measurements made during the Hipparcos mission, this system lies at a distance of around 179 light-years (55 parsecs) from Earth.
This is a single-lined spectroscopic binary system, which means that the presence of an unseen orbiting companion can be inferred from Doppler shifts in the spectral absorption lines. The two bodies orbit each other with a period of 8,016 days (22 y) and an eccentricity of 0.54. The primary component is an A-type main sequence star with a stellar classification of A7 V. It has about 1.9 times the mass of the Sun and is rotating rapidly with a projected rotational velocity of 170 km/s. The orbital data is consistent with the secondary component being either a red dwarf or a white dwarf star.
In culture
In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Thanih Saad al Saaoud (تاني سعد السعود - taanii sa‘d al-su‘ūd), which was translated into Latin as Secunda Fortunæ Fortunarum, meaning the second of luck of lucks. This star, along with β Aqr (Sadalsuud) and c Cet, were Saʽd al Suʽud (سعد السعود), the Luck of Lucks.
In Chinese, 天壘城 (Tiān Lěi Chéng), meaning Celestial Ramparts, refers to an asterism consisting of ξ Aquarii, 46 Capricorni, 47 Capricorni, λ Capricorni, 50 Capricorni, 18 Aquarii, 29 Capricorni, 9 Aquarii, 8 Aquarii, ν Aquarii, 14 Aquarii, 17 Aquarii and 19 Aquarii. Consequently, ξ Aquarii itself is known as 天壘城一 (Tiān Lěi Chéng yī, English: the First Star of Celestial Ramparts.)