In thisstarfield showing many stars of Aquila constellation, δ Aquilae is visible at the right of theasterismα,β andγ Aquilae.
The binary nature of this system was first reported byH. L. Alden atYale Observatory in 1936. It is anastrometric binary where the two components orbit each other with a period of 3.422 years and aneccentricity (ovalness) of about 0.36.[9] This is a type ofbinary star system where the presence of the secondary component is revealed by itsgravitational perturbation of the primary. The individual components have not been resolved with a telescope.
The secondary, component Ab, is a smaller star with about 67% of the Sun's mass and an estimated 61% of the radius of the Sun.[5] It may be aK-type star.[5]
This star, along withη Aql andθ Aql wereAl Mizān (ألميزان), the Scale-beam.[15] According to the catalogue of stars in theTechnical Memorandum 33-507 – A Reduced Star Catalog Containing 537 Named Stars,Al Mizān were the title for three stars: δ Aql asAl Mizān I, η Aql asl Mizān II and θ Aql asAl Mizān III.[16] Being the westernmost star of theasterism,Jim Kaler has suggested the nameAlmizan Occidental.[17]
On the other hand,Antonín Bečvář includes, with no further explanation,Deneb Okab in hiscatalogue,[18] meaningthe tail of eagle inArabic; however, the star is situated in the centre of the constellation, which is usually identified with the chest, while the starsε Aql andζ Aql have been collectively known as Deneb al Okab by Arabian medieval astronomers,[15] which might suggest that Bečvář's assumption was a misnomer.
In the catalogue of stars in theCalendarium ofAl Achsasi al Mouakket, this star was designatedDjenubi Menkib al Nesr (منكب ألنسر ألخنوبي –mankib al-nasr al-janúbii), which was translated intoLatin asAustralior Humerus Vulturis, meaning the southern shoulder of the eagle.[19]
^abcdCousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards",South African Astronomical Observatory Circulars,8: 59,Bibcode:1984SAAOC...8...59C
^abCowley, Anne; Fraquelli, Dorothy (February 1974), "MK Spectral Types for Some Bright F Stars",Publications of the Astronomical Society of the Pacific,86 (509): 70,Bibcode:1974PASP...86...70C,doi:10.1086/129562
^abMantegazza, L.; Poretti, E. (June 2005), "Projected rotational velocities of some Delta Scuti and Gamma Doradus stars",Communications in Asteroseismology,146:37–39,Bibcode:2005CoAst.146...37M,doi:10.1553/cia146s37
^abEvans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick (eds.), "The Revision of the General Catalogue of Radial Velocities",Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, vol. 30, University of Toronto:International Astronomical Union, p. 57,Bibcode:1967IAUS...30...57E
^abKamper, Karl W.; et al. (August 1989), "Astrometric-spectroscopic binary star orbits. III - Alpha Ophiuchi and Delta Aquilae",Astronomical Journal,98:686–691,Bibcode:1989AJ.....98..686K,doi:10.1086/115169
^abSchröder, C.; et al. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo",Astronomy and Astrophysics,493 (3):1099–1107,Bibcode:2009A&A...493.1099S,doi:10.1051/0004-6361:200810377
