Iota Aquilae

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

Location of ι Aquilae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension 19h 36m 43.27606s[1]
Declination –01° 17′ 11.7611″[1]
Apparent magnitude (V) 4.364[2]
Spectral type B5 III[3]
U−B color index –0.428[2]
B−V color index –0.083[2]
R−I color index –0.08
Radial velocity (Rv) –21.4[4] km/s
Proper motion (μ) RA: –0.87[1] mas/yr
Dec.: –20.39[1] mas/yr
Parallax (π) 8.34 ± 0.79[1] mas
Distance 390 ± 40 ly
(120 ± 10 pc)
Mass 4.8 ± 0.3[5] M
Radius 5.5 ± 0.5[5] R
Luminosity 851[5] L
Surface gravity (log g) 3.64 ± 0.05[5] cgs
Temperature 14,552[6] K
Rotational velocity (v sin i) 55[7] km/s
Age 100 ± 8[5] Myr
Other designations
Al Thalimain, 41 Aql, BD-01° 3782, HD 184930, HIP 96468, HR 7447, SAO 143597.[8]
Data sources:
Hipparcos Catalogue,
CCDM (2002),
Bright Star Catalogue (5th rev. ed.)

Iota Aquilae (ι Aql, ι Aquilae) is the Bayer designation for a star in the equatorial constellation of Aquila. It has the traditional name Al Thalimain, which it shares with λ Aquilae. The name is derived from the Arabic term الظليمان ath-thalīmain meaning "The Two Ostriches". With an apparent visual magnitude of 4.364,[2] this star is bright enough to be seen with the naked eye. Based upon an annual parallax shift of 8.34 ± 0.79 mas,[1] it is located at a distance of around 390 light-years (120 parsecs) from Earth. At that distance, the visual magnitude of the star is diminished by 0.15[5] from extinction caused by intervening gas and dust.

In Chinese, 右旗 (Yòu Qí), meaning Right Flag, refers to an asterism consisting of ι Aquilae, μ Aquilae, σ Aquilae, δ Aquilae, ν Aquilae, 42 Aquilae, HD 184701, κ Aquilae and 56 Aquilae.[9] Consequently, ι Aquilae itself is known as 右旗五 (Yòu Qí wu, English: the Fifth Star of Right Flag.)[10]

Although Iota Aquilae is listed in star catalogues as a giant star, calculations of its dimension show that in reality it is a main-sequence star.[11] It has nearly five times the mass of the Sun and five to six times the Sun's radius.[5] It is emitting 851[5] times the luminosity of the Sun from its outer atmosphere at an effective temperature of 14,552 K,[6] giving it the blue-white hue of a B-type star. The projected rotational velocity of this star is 55 km/s.[7] Even though it is only around 100 million years old, it has already spent 91% of its allotted lifetime on the main sequence.[5]


  1. ^ a b c d e f 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. ^ a b c d Kozok, J. R. (September 1985), "Photometric observations of emission B-stars in the southern Milky Way", Astronomy and Astrophysics Supplement Series 61: 387–405, Bibcode:1985A&AS...61..387K. 
  3. ^ Lesh, Janet Rountree (December 1968), "The Kinematics of the Gould Belt: an Expanding Group?", Astrophysical Journal Supplement 17: 371, Bibcode:1968ApJS...17..371L, doi:10.1086/190179. 
  4. ^ Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, eds., "The Revision of the General Catalogue of Radial Velocities, in Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30", Determination of Radial Velocities and their Applications (University of Toronto: International Astronomical Union, published 1967) 30: 57–63, Bibcode:1967IAUS...30...57E. 
  5. ^ a b c d e f g h i Lyubimkov, Leonid S.; et al. (June 2002), "Surface abundances of light elements for a large sample of early B-type stars - II. Basic parameters of 107 stars", Monthly Notices of the Royal Astronomical Society 333 (1): 9–26, Bibcode:2002MNRAS.333....9L, doi:10.1046/j.1365-8711.2002.05341.x 
  6. ^ a b Underhill, A. B.; et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society 189 (3): 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601. 
  7. ^ a b Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590. 
  8. ^ "iot Aql -- Star in double system", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2012-07-18. 
  9. ^ (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.
  10. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 3 日
  11. ^ Kaler, James B., Al Thalimain (Iota Aquilae), university of Illinois, retrieved 2012-07-18 

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