Beta Aquilae

Beta Aquilae
Location of β Aquilae (circled)
Observation data
Epoch J2000      Equinox ICRS
Constellation Aquila
Right ascension 19h 55m 18.793s
Declination +06° 24′ 24.35″
Apparent magnitude (V) 3.87 + 12.0
Characteristics
Spectral type G9.5 IV + M2.5 V
U−B color index 0.48
B−V color index 0.86
R−I color index 0.49
Variable type Suspected
Astrometry
Radial velocity (Rv)−40.3±0.09 km/s
Proper motion (μ) RA: +45.944 mas/yr
Dec.: −480.965 mas/yr
Parallax (π)73.5249±0.1415 mas
Distance44.36 ± 0.09 ly
(13.60 ± 0.03 pc)
Absolute magnitude (MV)+3.03
Details
A
Mass1.24±0.02 M☉
Radius3.123±0.033 R☉
Luminosity6.18±0.26 L☉
Surface gravity (log g)3.66±0.03 cgs
Temperature5,163±17 K
Metallicity [Fe/H]−0.20±0.04 dex
Rotation5.08697±0.00031 days
Rotational velocity (v sin i)22.28 km/s
Age4.77±0.50 Gyr
Other designations
Alshain, Alschairn, β Aql, 60 Aquilae, BD+06°4357, FK5 749, GC 27587, GJ 771, HD 188512, HIP 98036, HR 7602, SAO 125235, PPM 168947, WDS 19553+0624, LHS 5350a, LTT 15822
Database references
SIMBADdata
ARICNSdata

Beta Aquilae is a triple star system in the equatorial constellation of Aquila. Its name is a Bayer designation that is Latinized from β Aquilae, and abbreviated Beta Aql or β Aql. This system is visible to the naked eye as a point-like source with an apparent visual magnitude of 3.87. Based on parallax measurements, it is located at a distance of 44.4 light-years. It is drifting closer to the Sun with a radial velocity of −40 km/s, and is predicted to approach to within 27 light-years (8.4 pc) in roughly 207,000 years.

Its two visible components are designated Beta Aquilae A and B. The former is formally named Alshain /ælˈʃeɪn/, the traditional name for the system.

Nomenclature

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).

The system bore the traditional name Alshain, derived from the Persian shāhīn-i tarazu "the scale beam", the Persian name for the asterism of α, β and γ Aquilae, itself a translation of the Arabic al-mizan "the balance". The name Tarazed for γ Aquilae is derived from the same Persian term. In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. 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.

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.

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

Properties

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. The activity shows a cycle of 969±27 d. The star displays solar-like oscillations. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.

This is an aging subgiant star that has exhausted the supply of hydrogen at its core and is evolving into a giant. Its angular diameter has been precisely determined using interferometry at the CHARA array, which combined with its estimated distance, result in a radius 3.123 times the radius of the Sun. It has a mass 24% greater than the Sun's, a luminosity 6.2 times that of the Sun, and an effective temperature of 5,163 K.

The 12th magnitude secondary companion, designated component B, is a double-lined spectroscopic binary, which is at an angular separation of 13 arcseconds from the primary. It has a stellar classification of M2.5 V, matching a class M red dwarf.

In culture

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.

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

References

  1. 1 2 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.
  2. 1 2 3 4 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. 1 2 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.
  4. ↑ 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.
  5. 1 2 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.
  6. 1 2 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.
  7. 1 2 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.
  8. 1 2 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.
  9. 1 2 3 Kjeldsen, Hans; et al. (2025). "Asteroseismology of the G8 subgiant β Aquilae with SONG-Tenerife, SONG-Australia and TESS". Astronomy & Astrophysics. 700: A39. arXiv:2506.00493. Bibcode:2025A&A...700A..39K. doi:10.1051/0004-6361/202554633.
  10. 1 2 3 4 5 6 Bustos, Romina V. Ibañez; Mourard, Denis; Nardetto, Nicolas; Jones, Jeremy; Ebrahimkutty, Nayeem; Jonák, Juraj; Nowacki, Hugo; Vrard, Mathieu; Berio, Philippe (2026-08-31), "Interferometric Survey of Stellar Parameters: Towards homogeneous FGK stars parameters and surface-brightness color relation in the context of PLATO space mission", arXiv:2608.30557 [astro-ph.SR].
  11. ↑ Karovicova, I.; et al. (February 2022), "Fundamental stellar parameters of benchmark stars from CHARA interferometry -- III. Giant and subgiant stars", Astronomy & Astrophysics, 658: A48, arXiv:2109.13258, Bibcode:2022A&A...658A..48K, doi:10.1051/0004-6361/202142100, ISSN 0004-6361
  12. 1 2 3 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.
  13. ↑ 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
  14. ↑ "bet Aql". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2025-04-13.
  15. ↑ 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.
  16. ↑ Bailer-Jones, C. A. L. (March 2015), "Close encounters of the stellar kind", Astronomy & Astrophysics, 575: 13, arXiv:1412.3648, Bibcode:2015A&A...575A..35B, doi:10.1051/0004-6361/201425221, S2CID 59039482, A35.
  17. 1 2 Kunitzsch, Paul; Smart, Tim (2006), A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.), Cambridge, Massachusetts: Sky Pub, ISBN 978-1-931559-44-7.
  18. 1 2 3 "IAU Catalog of Star Names". Retrieved 16 August 2026.
  19. ↑ Hessman, F. V.; et al. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  20. ↑ IAU Working Group on Star Names (WGSN), International Astronomical Union, archived from the original on 10 June 2016, retrieved 22 May 2016.
  21. ↑ WG Triennial Report (2015-2018) - Star Names (PDF), p. 5, archived from the original (PDF) on 2019-08-23, retrieved 2018-07-14.
  22. ↑ 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: 429–438, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429.
  23. ↑ (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.
  24. ↑ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 26, 2008.
  25. ↑ Andretta, V.; et al. (February 2005), "The Ca II Infrared Triplet as a stellar activity diagnostic . I. Non-LTE photospheric profiles and definition of the RIRT indicator", Astronomy and Astrophysics, 430 (2): 669–677, Bibcode:2005A&A...430..669A, doi:10.1051/0004-6361:20041745.
  26. ↑ Corsaro, E.; et al. (January 2012), "Solar-like oscillations in the G9.5 subgiant β Aquilae", Astronomy & Astrophysics, 537, id. A9, arXiv:1110.2772, Bibcode:2012A&A...537A...9C, doi:10.1051/0004-6361/201117158.
  27. ↑ Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society, 25: 1319, Bibcode:1993AAS...183.1710G, archived from the original on 2019-06-25, retrieved 2012-02-04
  28. ↑ Bonfils, Xavier; et al. (2005), "Metallicity of M dwarfs. I. A photometric calibration and the impact on the mass-luminosity relation at the bottom of the main sequence", Astronomy and Astrophysics, 442 (2): 635–642, arXiv:astro-ph/0503260, Bibcode:2005A&A...442..635B, doi:10.1051/0004-6361:20053046, S2CID 13900901.
  29. ↑ Ridpath, Ian. "Star Tales – Aquila". Retrieved 18 August 2026.
  30. ↑ 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.