Delta Aquilae

Delta Aquilae (δ Aquilae, δ Aql) is a binary star system in the equatorial constellation of Aquila. 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
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]
Characteristics
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]
Astrometry
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
Distance50.6 ± 0.8 ly
(15.5 ± 0.2 pc)
Absolute magnitude (MV)2.46[7]
Orbit[8]
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)
(secondary)		191 ± 14°
Details
δ Aql A
Mass1.65[4] M☉
Radius2.04[4] R☉
Luminosity6.8[9]–7.9[10] L☉
Surface gravity (log g)4.03[11] cgs
Temperature7,016[7] K
Metallicity [Fe/H]–0.04[11] dex
Rotational velocity (v sin i)87.3[12] km/s
δ Aql B
Mass0.67[4] M☉
Radius0.61[4] R☉
Other designations
30 Aql, δ Aql, BD+02° 3879, FK5 730, GJ 760, HD 182640, HIP 95501, HR 7377, NLTT 47775, SAO 124603.[13]
Database references
SIMBADdata

Properties
In this starfield showing many stars of Aquila constellation, δ Aquilae is visible at the right of the asterism α, β and γ Aquilae.

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]

Naming

This star, along with η Aql and θ Aql were Al Mizān (ألميزان), the Scale-beam.[14] 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.[15] Being the westernmost star of the asterism, Jim Kaler has suggested the name Almizan Occidental.[16]

On the other hand, Antonín Bečvář includes, with no further explanation, Deneb Okab in his catalogue,[17] meaning the tail of eagle in Arabic; however, the star is situated in the centre of the constellation, which is usually identified with the chest, while the stars ε Aql and ζ Aql have been collectively known as Deneb al Okab by Arabian medieval astronomers,[14] which might suggest that Bečvář's assumption was a misnomer.

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.[18]

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.[19] Consequently, the Chinese name for δ Aquilae itself is 右旗三 (Yòu Qí sān, English: the Third Star of Right Flag.)[20]

This star, together with η Aql, θ Aql, ι Aql, κ Aql and λ Aql were consist Antinous, the obsolete constellation[21].

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References
  1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
  2. Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars, 8: 59, Bibcode:1984SAAOC...8...59C
  3. 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. 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. 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. Reiners, A. (January 2006), "Rotation- and temperature-dependence of stellar latitudinal differential rotation", Astronomy and Astrophysics, 446 (1): 267–277, arXiv:astro-ph/0509399, Bibcode:2006A&A...446..267R, doi:10.1051/0004-6361:20053911
  8. 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/0307196, Bibcode:2003A&A...405..723D, doi:10.1051/0004-6361:20030633
  11. 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:1004.1069, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247
  12. 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" (PDF), 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. 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.
  15. 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
  16. Kaler, Jim. "Delta Aql". Retrieved 2017-03-10.
  17. Bečvář, A. (1951). Atlas Coeli Skalnaté Pleso II - Katalog 1950.0. Přírodovědecké Vydavatelstrí. p. 277. Retrieved 10 March 2017.
  18. 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
  19. (in 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.
  20. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived September 29, 2009, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  21. Ian Ridpath's Star Tales - Antonious
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