Beta Aquilae

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Beta Aquilae
Location of β Aquilae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension 19h 55m 18.79256s[1]
Declination +06° 24′ 24.3425″[1]
Apparent magnitude (V) 3.87 + 12.0[2]
Spectral type G9.5 IV[3] + M2.5 V[4]
U−B color index 0.48[5]
B−V color index 0.86[5]
R−I color index 0.49
Variable type Suspected
Radial velocity (Rv)−40.3±0.09[6] km/s
Proper motion (μ) RA: 45.27[1] mas/yr
Dec.: −481.91[1] mas/yr
Parallax (π)73.00 ± 0.20 mas[1]
Distance44.7 ± 0.1 ly
(13.70 ± 0.04 pc)
Absolute magnitude (MV)+3.03[7]
Mass1.26±0.18[9] M
Radius3.064±0.020 R
Luminosity5.60±0.17 L
Surface gravity (log g)3.54±0.14 cgs
Temperature5,071±37 K
Metallicity [Fe/H]−0.19±0.05 dex
Rotation5.08697±0.00031 d[10]
Rotational velocity (v sin i)22.28 km/s
Age9.6–11.4[11] Gyr
Other designations
Alshain, Alschairn, β Aql, 60 Aquilae, BD+06° 4357, FK5 749, GJ 771, HD 188512, HIP 98036, HR 7602, SAO 125235, WDS 19553+0624, LHS 5350a, LTT 15822
Database references

Beta Aquilae, Latinized from β Aquilae, is a triple star[12] system in the equatorial constellation of Aquila. It is visible to the naked eye as a point-like source with an apparent visual magnitude of 3.87.[2] Based on parallax measurements obtained during the Hipparcos mission, it is located at a distance of approximately 44.7 light-years from the Sun.[1] It is drifting closer to the Sun with a radial velocity of −40 km/s.[6]

Its two components are designated Beta Aquilae A (formally named Alshain /ælˈʃn/, the traditional name for the system)[13][14] and B.


In this starfield showing many stars of Aquila constellation, the asterism α, β and γ Aquilae can be easily recognized on the left portion of the image.

β Aquilae (Latinised to Beta Aquilae) is the system's Bayer designation. The designations of the two components as Beta Aquilae A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[15]

The system bore the traditional name Alshain derived from the Perso-Arabic term الشاهين, aš-šāhīn, meaning "the (peregrine) falcon", perhaps by folk etymology from the Persian šāhīn tarāzū (or possibly šāhīn tara zed; see Gamma Aquilae), the Persian name for the asterism α, β and γ Aquilae.[citation needed] In 2016, the IAU organized a Working Group on Star Names (WGSN)[16] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[17] It approved the name Alshain for the component Beta Aquilae A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[14]

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Unuk al Ghyrab (عنق ألغراب - únuq al-ghuraab), which was translated into Latin as Collum Corvi, meaning the crow's neck.[18]

In Chinese, 河鼓 (Hé Gŭ), meaning River Drum, refers to an asterism consisting of Beta Aquilae, Altair and Gamma Aquilae.[19] Consequently, the Chinese name for Beta Aquilae itself is 河鼓一 (Hé Gŭ yī, English: the First Star of River Drum).[20]


USS Alshain (AKA-55) was a United States navy ship.


The primary, component A, is of magnitude 3.71 and spectral class G8IV. It has a very low level of surface magnetic activity and may be in a state similar to a Maunder minimum.[21] The activity shows a cycle of 969±27 d.[10] Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[22] This is an aging subgiant star that has exhausted the supply of hydrogen at its core and is evolving into a giant.[10] It has a mass 26% greater than the Sun's,[9] a luminosity six times that of the Sun, and a radius about thrice solar.[8]

The 12th magnitude secondary companion, designated component B, is a double-lined spectroscopic binary[23] which is 13 arcseconds away in the sky. It has a stellar classification of M2.5 V,[4] matching a class M red dwarf.

In culture[edit]

In the Chinese folk tale The Cowherd and the Weaver Girl, Beta and Gamma Aquilae are children of Niulang (牛郎, The Cowherd, Altair) and Zhinü (織女, The Princess, Vega).

The Koori people of Victoria knew Beta and Gamma Aquilae as the black swan wives of Bunjil (Altair), the wedge-tailed eagle.[24]


  1. ^ a b c d e f van Leeuwen, F. (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, S2CID 18759600.
  2. ^ a b Eggleton, P. P.; Tokovinin, A. A. (2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  3. ^ Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637, S2CID 119476992.
  4. ^ a b Montes, D.; et al. (September 2018), "Calibrating the metallicity of M dwarfs in wide physical binaries with F-, G-, and K-primaries - I: High-resolution spectroscopy with HERMES: stellar parameters, abundances, and kinematics", Monthly Notices of the Royal Astronomical Society, 479 (1): 1332–1382, arXiv:1805.05394, Bibcode:2018MNRAS.479.1332M, doi:10.1093/mnras/sty1295.
  5. ^ a b Oja, T. (August 1986), "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series, 65 (2): 405–4, Bibcode:1986A&AS...65..405O.
  6. ^ a b Jofré, E.; et al. (February 2015), "Stellar parameters and chemical abundances of 223 evolved stars with and without planets", Astronomy & Astrophysics, 574: 46, arXiv:1410.6422, Bibcode:2015A&A...574A..50J, doi:10.1051/0004-6361/201424474, S2CID 53666931, A50.
  7. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  8. ^ a b Rains, Adam D.; et al. (April 2020), "Precision angular diameters for 16 southern stars with VLTI/PIONIER", Monthly Notices of the Royal Astronomical Society, 493 (2): 2377–2394, arXiv:2004.02343, Bibcode:2020MNRAS.493.2377R, doi:10.1093/mnras/staa282, S2CID 214802418
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  10. ^ a b c Butkovskaya, Varvara; et al. (February 2018), "Long-term stellar magnetic field study at the Crimean Astrophysical Observatory", Long-term Datasets for the Understanding of Solar and Stellar Magnetic Cycles, Proceedings of the International Astronomical Union, IAU Symposium, vol. 340, pp. 35–38, Bibcode:2018IAUS..340...35B, doi:10.1017/S1743921318001035, S2CID 125610540.
  11. ^ Mamajek, Eric E.; Hillenbrand, Lynne A. (November 2008), "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics", The Astrophysical Journal, 687 (2): 1264–1293, arXiv:0807.1686, Bibcode:2008ApJ...687.1264M, doi:10.1086/591785, S2CID 27151456
  12. ^ Fuhrmann, K.; et al. (February 2017), "Multiplicity among Solar-type Stars", The Astrophysical Journal, 836 (1): 23, Bibcode:2017ApJ...836..139F, doi:10.3847/1538-4357/836/1/139, 139.
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  14. ^ a b "Naming Stars". Retrieved 3 March 2018.
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  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.
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External links[edit]