Gamma Aquilae

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

Location of γ Aquilae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension 19h 46m 15.58029s[1]
Declination +10° 36′ 47.7408″[1]
Apparent magnitude (V) 2.712[2]
Spectral type K3 II[3]
U−B color index +1.720[2]
B−V color index +1.500[2]
Radial velocity (Rv) -2.79[4] km/s
Proper motion (μ) RA: +16.99[1] mas/yr
Dec.: -2.98[1] mas/yr
Parallax (π) 8.26 ± 0.17[1] mas
Distance 395 ± 8 ly
(121 ± 2 pc)
Absolute magnitude (MV) 3.38+0.24
Mass 5.66±0.66[6] M
Radius 95[7] R
Luminosity 2538[6] L
Surface gravity (log g) 1.63[8] cgs
Temperature 4210[8] K
Metallicity [Fe/H] –0.29[8] dex
Rotational velocity (v sin i) 8[9] km/s
Other designations
Tarazed, Reda, 50 Aql, gam Aql, BD+10 4043, FK5 741, HD 186791, HIP 97278, HR 7525, SAO 105223.[10]
Database references
Database references

Gamma Aquilae (γ Aql, γ Aquilae) is a star in the constellation Aquila. It has the traditional name Tarazed.[11] This star has an apparent visual magnitude of 2.712,[2] so it is readily visible to the naked eye at night. Parallax measurements place it at a distance of 395 light-years (121 parsecs) from Earth.[1]


Position of Tarazed relative to Altair (center)

Gamma Aquilae is a relatively young star with an age of about 100 million years. Nevertheless, it has reached a stage of its evolution where it has consumed the hydrogen at its core and expanded into what is termed a bright giant star, with a stellar classification of K3 II.[3] The star is now burning helium into carbon in its core. After it has finished generating energy through nuclear fusion, Gamma Aquilae will become a white dwarf.[11]

The interferometry-measured angular diameter of Gamma Aquilae is 7.271±0.073 mas,[12] which, at its estimated distance, equates to a physical radius of about 95 times the radius of the Sun.[7] With almost six times the Sun's mass, this is an enormous star that is radiating over 2500 times the luminosity of the Sun.[6] An effective temperature of 4210 K in its outer envelope gives it the orange hue typical of K-type stars.[8][13]

In culture[edit]

The traditional name Tarazed may derive from Persian شاهين ترازو šāhin tarāzu "the beam of the scale", referring to an asterism of the Scale, α, β and γ Aquillae. Persian šāhīn means "royal falcon", "beam", and "pointer", and gave its name (as "falcon") to Beta Aquilae. In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Menkib al Nesr (منكب ألنسر - mankib al-nasr), which was translated into Latin as Humerus Vulturis, meaning the eagle's shoulder.[14]

In Chinese, 河鼓 (Hé Gŭ), meaning River Drum, refers to an asterism consisting of γ Aquilae, β Aquilae and Altair.[15] Consequently, γ Aquilae itself is known as 河鼓三 (Hé Gŭ sān, English: the Third Star of River Drum.)[16] In Chinese mythology, The Princess and the Cowherd, this star and β Aql, are children of Niulang (牛郎, The Cowherd, Altair) and Zhinü (織女, The Princess, Vega).

The Koori people of Victoria knew β and γ Aquilae as the black swan wives of Bunjil (Altair), the wedge-tailed eagle.[17]


  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 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 Morgan, W. W.; Keenan, P. C. (1973), "Spectral Classification", Annual Review of Astronomy and Astrophysics 11 (1): 29, Bibcode:1973ARA&A..11...29M, doi:10.1146/annurev.aa.11.090173.000333 
  4. ^ Famaey, B. et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics 430 (1): 165–186, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272 
  5. ^ Carney, Bruce W. et al. (March 2008), "Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars", The Astronomical Journal 135 (3): 892–906, arXiv:0711.4984, Bibcode:2008AJ....135..892C, doi:10.1088/0004-6256/135/3/892 
  6. ^ a b c Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten 331 (4): 349, arXiv:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355 
  7. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1 . The radius (R*) is given by:
    \begin{align} 2\cdot R_*
 & = \frac{(10^{-3}\cdot 121\cdot 7.271)\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\
 & \approx 189.2\cdot R_{\bigodot}
  8. ^ a b c d McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances", Astrophysical Journal Supplement Series 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527 
  9. ^ Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago 239 (1), Bibcode:1970CoAsi.239....1B 
  10. ^ "TARAZED -- Star in double system", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2012-01-09 
  11. ^ a b Kaler, James B., "TARAZED (Gamma Aquilae)", Stars (University of Illinois), retrieved 2012-01-10 
  12. ^ Mozurkewich, D. et al. (November 2003), "Angular Diameters of Stars from the Mark III Optical Interferometer", The Astronomical Journal 126 (5): 2502–2520, Bibcode:2003AJ....126.2502M, doi:10.1086/378596 
  13. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16 
  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. ^ Mudrooroo (1994). Aboriginal mythology : an A-Z spanning the history of aboriginal mythology from the earliest legends to the present day. London: HarperCollins. p. 4. ISBN 1-85538-306-3. 

External links[edit]