4 Aquilae

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4 Aquilae
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension  18h 44m 49.93813s[1]
Declination +02° 03′ 36.1381″[1]
Apparent magnitude (V) 5.02[2]
Spectral type B9 V[3]
B−V color index −0.055±0.016[2]
Radial velocity (Rv)−13.0±4.2[4] km/s
Proper motion (μ) RA: +9.347[1] mas/yr
Dec.: −14.719[1] mas/yr
Parallax (π)6.7299 ± 0.2433[1] mas
Distance480 ± 20 ly
(149 ± 5 pc)
Absolute magnitude (MV)−0.75[2]
Mass3.60±0.06[5] M
Radius3.00[6] R
[5] L
Surface gravity (log g)3.46±0.10[7] cgs
[5] K
Rotational velocity (v sin i)259[5] km/s
Other designations
4 Aql, BD+01° 3766, GC 25652, HD 173370, HIP 91975, HR 7040, SAO 123879[8]
Database references

4 Aquilae, abbreviated 4 Aql, is a single,[9] white-hued star in the equatorial constellation of Aquila. 4 Aquilae is the Flamsteed designation. It has an apparent visual magnitude of 5.02,[2] making it a faint star visible to the naked eye. The distance to 4 Aql can be estimated from its annual parallax shift of 6.7 mas,[1] yielding an estimated range of around 480 light years. It is moving closer to the Earth with a heliocentric radial velocity of −13 km/s.[4]

This is a B-type main-sequence star with a stellar classification of B9 V,[3] it was classed as a Be star by Arne Sletteback in 1982, indicating it has ionized circumstellar gas.[6] The star is spinning rapidly, showing a projected rotational velocity of 259 km/s,[5] and is being viewed almost equator-on,[7] it has 3.6[5] times the mass of the Sun and 3[6] times the Sun's radius. The star is radiating 294[5] times the Sun's luminosity from its photosphere at an effective temperature of 10,965 K.[5]


  1. ^ a b c d e f Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051.
  2. ^ a b c d 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.
  3. ^ a b Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Bibcode:1999MSS...C05....0H.
  4. ^ a b Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065.
  5. ^ a b c d e f g h Zorec, J.; Royer, F. (2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691.
  6. ^ a b c Silaj, J.; et al. (November 2014), "The Hα Profiles of Be Shell Stars", The Astrophysical Journal, 795 (1): 12, Bibcode:2014ApJ...795...82S, doi:10.1088/0004-637X/795/1/82, 82.
  7. ^ a b Lefever, K.; et al. (June 2010), "Spectroscopic determination of the fundamental parameters of 66 B-type stars in the field-of-view of the CoRoT satellite", Astronomy and Astrophysics, 515: A74, arXiv:0910.2851, Bibcode:2010A&A...515A..74L, doi:10.1051/0004-6361/200911956.
  8. ^ "4 Aql". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved October 27, 2018.
  9. ^ Chini, R.; et al. (2012), "A spectroscopic survey on the multiplicity of high-mass stars", Monthly Notices of the Royal Astronomical Society, 424 (3): 1925–1929, arXiv:1205.5238, Bibcode:2012MNRAS.424.1925C, doi:10.1111/j.1365-2966.2012.21317.x.