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), "The Revision of the General Catalogue of Radial Velocities", in Batten, John Frederick; Heard, 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) 30: 57–63, Bibcode:1967IAUS...30...57E.  Unknown parameter |DUPLICATE_editor1-first= ignored (help)
  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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