It forms the primary or 'A' component of adouble star designated WDS J22058-0019; the secondary or 'B' component is UCAC2 31789179.[16] However, the pair is only an optical binary, with UCAC2 31789179 being a background star.[16]
It bore the traditional nameSadalmelik, which derived from anArabic expression سعد الملك (sa‘d al-malik), meaning "Luck of the king" or “arm/support of God”. The nameRucbah had also been applied to this star; though it shared that name withDelta Cassiopeiae.[14] It is only one of two stars with ancient proper names to lie within a degree of thecelestial equator. The origin of the Arabic name is lost to history.[17] In 2016, theInternational Astronomical Union organized aWorking Group on Star Names (WGSN)[18] to catalogue and standardize proper names for stars. The WGSN approved the nameSadalmelik for Alpha Aquarii (WDS J22058-0019 A) on 21 August 2016, and it is now so included in the List of IAU-approved Star Names (Delta Cassiopeiae was given the nameRuchbah).[15]
There is some uncertainty about Alpha Aquarii's distance. The originalHipparcos catalog gave aparallax of4.3±0.83 mas, which translates to a distance of233±45 parsecs, or 760light-years.[22] However, the 2007 Hipparcos reduction give a parallax that implies a distance of161±5 pc, or 520 light-years.[23] The third Gaia data release (Gaia DR3) give a parallax of4.94±0.43 mas, translating to a distance of202±17 pc, or 660light-years.[1]
^abcdeCousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards",South African Astronomical Observatory Circulars,8: 59,Bibcode:1984SAAOC...8...59C
^abWielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions",Veröff. Astron. Rechen-Inst. Heidelb,35 (35), Astronomisches Rechen-Institut Heidelberg: 1,Bibcode:1999VeARI..35....1W
^abAyres, Thomas R.; Brown, Alexander; Harper, Graham M. (July 2005), "Chandra Observations of Coronal Emission from the Early G Supergiants α and β Aquarii",The Astrophysical Journal,627 (1):L53 –L56,Bibcode:2005ApJ...627L..53A,doi:10.1086/431977,S2CID122519436
^HR 8414, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr.,CDS IDV/50. Accessed on line October 3, 2008.
^Dupree, A. K.; et al. (December 1993), "HST/GHRS Spectroscopy of the Hybrid Star Alpha Aquarii",Bulletin of the American Astronomical Society,25, American Astronomical Society, 183rd AAS Meeting: 1321,Bibcode:1993AAS...183.1807D, 18.07.
