It has the traditional nameDeneb el Okab/ˈdɛnɛbɛlˈoʊkæb/, from anArabic term ذنب العقابðanab al-ʽuqāb "the tail of the eagle", and theMandarin namesWoo/ˈwuː/ andYuë/ˈjuːeɪ/, derived from and represent the stateWú (吳), an old state was located at the mouth of theYangtze River, andYuè (越), an old state inZhejiang province[13] (together with19 Capricorni inTwelve States asterism). According to the R.H. Allen's works, it shares names withζ Aquilae.[14] Epsilon Aquilae could be more precisely calledDeneb el Okab Borealis, because is situated to the north of Zeta Aquilae, which can therefore be calledDeneb el Okab Australis.[15]
The binary nature of this system was reported by German astronomerF. Kustner in 1914, but it was not confirmed until 1974. It is a single-linedspectroscopic binary system;[7] the pair orbit each other over aperiod of 1,271 days (3.5 years) with aneccentricity (ovalness) of 0.27.[6] There are twovisual companions to Epsilon Aquilae, both reported by German astronomerR. Engelmann in 1887. Component B is a magnitude 10.56 star at anangular separation of122.00″ along aposition angle (PA) of 184° relative to the primary, as of 2014. At magnitude 11.25, component C is at a separation of142.90″ with a PA of 159°, as of 2015.[16]
The primary component of this system is anevolvedgiant star with astellar classification ofK1-III CN0.5,[3] showing a mild overabundance of theCN molecule in thespectrum. The chemical abundances of the star suggest it has gone through firstdredge-up.[17] It has more than double the mass of the Sun[7] and has expanded to ten times the Sun's radius.[8] The star shines with 54 times the Sun's luminosity, which is being radiated from itsouter envelope at aneffective temperature of 4,760 K.[9] At this heat, it glows with the orange-hue of aK-type star.[18]
This has been designated abarium star, meaning its atmosphere is extremely enriched withbarium and other heavy elements. However, this is disputed, with astronomerAndrew McWilliam (1990) finding normal abundances from ans-process.[7]
^abcdJohnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars",Communications of the Lunar and Planetary Laboratory,4 (99): 99,Bibcode:1966CoLPL...4...99J.
^abKeenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars",Astrophysical Journal Supplement Series,71: 245,Bibcode:1989ApJS...71..245K,doi:10.1086/191373.
^abGriffin, R. F. (June 1982), "Spectroscopic binary orbits from photoelectric radial velocities. Paper 44: epsilon Aquilae",The Observatory,102:82–85,Bibcode:1982Obs...102...82G.
^Mishenina, T. V.; et al. (October 1995), "Chemical composition of five giants with positive CN-indices",Astronomy and Astrophysics Supplement,113: 333,Bibcode:1995A&AS..113..333M.
