Delta Aquilae

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Delta Aquilae
Diagram showing star positions and boundaries of the Aquila constellation and its surroundings
Cercle rouge 100%.svg

Location of δ Aquilae (circled) near the center
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension 19h 25m 29.90139s[1]
Declination +03° 06′ 53.2061″[1]
Apparent magnitude (V) 3.365[2]
Spectral type F0 IV[3] + K[4]
U−B color index +0.031[2]
B−V color index +0.319[2]
R−I color index +0.16
Variable type δ Sct[5]
Radial velocity (Rv) –30.1[6] km/s
Proper motion (μ) RA: +254.54[1] mas/yr
Dec.: +82.51[1] mas/yr
Parallax (π) 64.41 ± 1.00[1] mas
Distance 50.6 ± 0.8 ly
(15.5 ± 0.2 pc)
Absolute magnitude (MV) 2.46[7]
Period (P) 3.426 ± 0.006 yr
Semi-major axis (a) 0.0539 ± 0.0040"
Eccentricity (e) 0.36 ± 0.07
Inclination (i) 150 ± 11°
Longitude of the node (Ω) 337 ± 9°
Periastron epoch (T) 1954.58 ± 0.13
Argument of periastron (ω)
191 ± 14°
δ Aql A
Mass 1.65[4] M
Radius 2.04[4] R
Luminosity 6.8[9]–7.9[10] L
Surface gravity (log g) 4.03[11] cgs
Temperature 7,016[7] K
Metallicity [Fe/H] –0.04[11] dex
Rotational velocity (v sin i) 87.3[12] km/s
δ Aql B
Mass 0.67[4] M
Radius 0.61[4] R
Other designations
30 Aql, del Aql, BD+02 3879, FK5 730, GJ 760, HD 182640, HIP 95501, HR 7377, NLTT 47775, SAO 124603.[13]
Database references
Data sources:
Hipparcos Catalogue,
CCDM (2002),
Bright Star Catalogue (5th rev. ed.)

Delta Aquilae (δ Aql, δ Aquilae) is a binary star system in the equatorial constellation of Aquila. The traditional name for this star is Denebokab. It has an apparent visual magnitude of 3.4[2] and, based upon parallax measurements, is located about 50.6 light-years (15.5 parsecs) from Earth.


Delta Aquilae is an astrometric binary where the two components orbit each other with a period of 3.422 years and an eccentricity of about 0.36.[8] This is a type of binary star system where the presence of the secondary component is revealed by its gravitational perturbation of the primary. The individual components have not been resolved with a telescope.

The primary component, Delta Aquilae A, is a subgiant star with a stellar classification of F0 IV,[3] where the luminosity class of IV indicates it is in the process of exhausting the supply of hydrogen at its core and evolving into a giant star. The mass of the star is 65% greater than the Sun and it has expanded to more than double the Sun's radius.[4] It is radiating around 7–8 times the luminosity of the Sun from its outer atmosphere at an effective temperature of 7,016 K,[7] giving it the yellow-white hue of an F-type star. Delta Aquilae A is a Delta Scuti variable that exhibits variations in luminosity caused by pulsations in its outer envelope.[5] It is spinning rapidly with a projected rotational velocity of about 87 km s−1. This is a lower bound on the azimuthal velocity along the star's equator.[12]

The secondary component, Delta Aquilae B, is a smaller star with about 67% of the Sun's mass and an estimated 61% of the radius of the Sun.[4] It may be a K-type star.[4]


This star is sometimes called by the name Denebokab, meaning the tail of eagle in Arabic. In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Djenubi Menkib al Nesr (منكب ألنسر ألخنوبي - mankib al-nasr al-janúbii), which was translated into Latin as Australior Humerus Vulturis, meaning the southern shoulder of the eagle.[14]

In Chinese, 右旗 (Yòu Qí), meaning Right Flag, refers to an asterism consisting of δ Aquilae, μ Aquilae, σ Aquilae, ν Aquilae, ι Aquilae, 42 Aquilae, HD 184701, κ Aquilae and 56 Aquilae.[15] Consequently, δ Aquilae itself is known as 右旗三 (Yòu Qí sān, English: the Third Star of Right Flag.)[16]

This star, along with η Aql and θ Aql (Tseen Foo) and, were Al Mizān (ألميزان), the Scale-beam.[17] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Mizān were the title for three stars :δ Aql as Al Mizān I, η Aql as l Mizān II and θ Aql as Al Mizān III.[18]


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752free to read, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars, 8: 59, Bibcode:1984SAAOC...8...59C 
  3. ^ a b Cowley, 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 
  4. ^ a b c d e f g h Fuhrmann, Klaus (February 2008), "Nearby stars of the Galactic disc and halo - IV", Monthly Notices of the Royal Astronomical Society, 384 (1): 173–224, Bibcode:2008MNRAS.384..173F, doi:10.1111/j.1365-2966.2007.12671.x 
  5. ^ a b Mantegazza, 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 
  6. ^ Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, eds., The Revision of the General Catalogue of Radial Velocities, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E 
  7. ^ a b c Reiners, A. (January 2006), "Rotation- and temperature-dependence of stellar latitudinal differential rotation", Astronomy and Astrophysics, 446 (1): 267–277, arXiv:astro-ph/0509399free to read, Bibcode:2006A&A...446..267R, doi:10.1051/0004-6361:20053911 
  8. ^ a b Kamper, Karl W.; Legget, David; McCarthy, Donald W., Jr. (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 
  9. ^ Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series, 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M 
  10. ^ do Nascimento, J. D., Jr.; et al. (July 2003), "On the link between rotation, chromospheric activity and Li abundance in subgiant stars", Astronomy and Astrophysics, 405: 723–731, arXiv:astro-ph/0307196free to read, Bibcode:2003A&A...405..723D, doi:10.1051/0004-6361:20030633 
  11. ^ a b Soubiran, C.; Le Campion, J.-F.; Cayrel de Strobel, G.; Caillo, A. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, arXiv:1004.1069free to read, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247 
  12. ^ a b Schröder, C.; Reiners, A.; Schmitt, J. H. M. M. (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 
  13. ^ "del Aql -- Variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-02-06 
  14. ^ Knobel, E. B. (June 1895), "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket", Monthly Notices of the Royal Astronomical Society, 55: 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429 
  15. ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  16. ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
  17. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 61. ISBN 0-486-21079-0. Retrieved 2010-12-12. 
  18. ^ Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), Jet Propulsion Laboratory, California Institute of Technology, retrieved 2012-02-06 

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