18 Aquilae

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18 Aquilae
Aquila constellation map.svg
Red circle.svg
Location of 18 Aquilae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension 19h 06m 58.60289s[1]
Declination +11° 04′ 16.4173″[1]
Apparent magnitude (V) 5.072
Spectral type B8 III[2]
U−B color index -0.44[3]
B−V color index -0.08[3]
Variable type Eclipsing[4]
Radial velocity (Rv) -18.6[5] km/s
Proper motion (μ) RA: -0.89[1] mas/yr
Dec.: -32.11[1] mas/yr
Parallax (π) 6.43 ± 0.79[1] mas
Distance approx. 510 ly
(approx. 160 pc)
Rotational velocity (v sin i) 50[2] km/s
Other designations
Y Aquilae, 18 Aql, BD+10 3787, FK5 3525, HD 178125, HIP 93867, HR 7248, SAO 104488.[6]
Database references

18 Aquilae (abbreviated 18 Aql) is a triple star[7] system in the constellation of Aquila. 18 Aquilae is the Flamsteed designation; it also bears the variable star designation Y Aquilae. It has an apparent visual magnitude of 5.07. The distance to this system can be estimated from the annual parallax shift of 6.43 mas, yielding a value of around 510 light-years (160 parsecs) away from Earth.

The inner pair of stars in this system form a spectroscopic binary with a combined magnitude of 5.44 and an orbital period of 1.302 days. The primary component is a giant star with a stellar classification of B8 III.[2] Because the orbital plane is inclined near the line of sight, two form an eclipsing binary system, the eclipse of the primary component causes a 0.04 drop in magnitude, while the eclipse of the secondary results in a decrease of 0.03.[8] At an angular separation of 0.310 arcseconds is the magnitude 6.39 tertiary component.[7] This system has a high peculiar velocity of 29.7 ± 3.9 km/s relative to the neighboring stars.[9]


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c Levato, H. (January 1975), "Rotational velocities and spectral types for a sample of binary systems", Astronomy and Astrophysics Supplement Series, 19: 91–99, Bibcode:1975A&AS...19...91L. 
  3. ^ a b Osawa, K.; Hata, S. (1962), "Three-color photometry of B8-A2 stars (II).", Annals of the Tokyo Astronomical Observatory, 7: 209, Bibcode:1962AnTok...7..209O. 
  4. ^ Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S. 
  5. ^ Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W. 
  6. ^ "18 Aql". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-07-25. 
  7. ^ a b Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878Freely accessible, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x. 
  8. ^ Malkov, O. Yu.; et al. (February 2006), "A catalogue of eclipsing variables", Astronomy and Astrophysics, 446 (2): 785–789, Bibcode:2006A&A...446..785M, doi:10.1051/0004-6361:20053137. 
  9. ^ Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883Freely accessible, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x. 

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