Sigma Aquilae

Sigma Aquilae, Latinized from σ Aquilae, is the Bayer designation for a binary star system in the equatorial constellation of Aquila. The baseline apparent magnitude of the pair is +5.17,[2] which, according to the Bortle Dark-Sky Scale, is bright enough to be seen with the naked eye from suburban skies. Because of the Earth's orbit about the Sun, this system has an annual parallax shift of 4.18 mas.[1] This provides a distance estimate of approximately 780 light-years (240 parsecs).

Sigma Aquilae
Location of σ Aquilae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension 19h 39m 11.64246s[1]
Declination +05° 23′ 51.9797″[1]
Apparent magnitude (V) +5.17[2]
Characteristics
Spectral type B3 V + B3 V:[3]
U−B color index –0.60[2]
B−V color index +0.03[2]
Variable type β Lyr[4]
Astrometry
Radial velocity (Rv)–4.8[5] km/s
Proper motion (μ) RA: +3.97[1] mas/yr
Dec.: –4.26[1] mas/yr
Parallax (π)4.18 ± 0.40[1] mas
Distance780 ± 70 ly
(240 ± 20 pc)
Absolute magnitude (MV)−1.69[6]
Orbit[7]
Primaryσ Aql A
Companionσ Aql B
Period (P)1.95022 ± 0.0001 d
Eccentricity (e)0
Periastron epoch (T)2420054.331 ± 0.0031 JD
Semi-amplitude (K1)
(primary)		163.52 ± 1.35 km/s
Semi-amplitude (K2)
(secondary)		199 ± 4.1 km/s
Details
σ Aql A
Mass6.8 ± 0.1[8] M☉
Radius4.22 ± 0.06[8] R☉
Luminosity1,862[8] L☉
Temperature18,493[8] K
Rotational velocity (v sin i)36.1 ± 8.9[9] km/s
Age140[10] Myr
σ Aql B
Mass5.4 ± 0.1[8] M☉
Radius3.05 ± 0.11[8] R☉
Luminosity524[8] L☉
Temperature15,848[8] K
Rotational velocity (v sin i)120[3] km/s
Other designations
σ Aql, 44 Aquilae, BD+05 4225, HD 185507, HIP 96665, HR 7474, SAO 124903.[11]
Database references
SIMBADdata

Sigma Aquilae is a double-lined[12] spectroscopic binary system consisting of two massive B-type main sequence stars; each has a stellar classification of B3 V.[3] They are detached components,[10] which means the two stars are sufficiently distant from each other that neither fills its Roche lobe.

Because the orbital plane lies close to the line of sight with the Earth, they form a Beta Lyrae-type eclipsing binary variable star system.[4] The brightness of the pair decreases during each eclipse, which occurs with a frequency determined by their orbital period of 1.95026 days. During the eclipse of the primary component the net magnitude decreases by 0.20; the eclipse of the secondary component results in a magnitude decrease of 0.10.[13]

References
  1. 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. Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Astronomy and Astrophysics Supplement Series, 34: 1–49, Bibcode:1978A&AS...34....1N.
  3. 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.
  4. Lefèvre, L.; et al. (November 2009), "A systematic study of variability among OB-stars based on HIPPARCOS photometry", Astronomy and Astrophysics, 507 (2): 1141–1201, Bibcode:2009A&A...507.1141L, doi:10.1051/0004-6361/200912304.
  5. Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W. Cite journal requires |journal= (help)
  6. 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.
  7. Jordan, Frank Craig (1916). "The orbit and spectrum of [sigma] Aquilae". Publications of the Allegheny Observatory of the University of Pittsburgh. 3 (22): 189–196. Bibcode:1916PAllO...3..189J.
  8. Malkov, O. Yu. (December 2007), "Mass-luminosity relation of intermediate-mass stars", Monthly Notices of the Royal Astronomical Society, 382 (3): 1073–1086, Bibcode:2007MNRAS.382.1073M, doi:10.1111/j.1365-2966.2007.12086.x.
  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:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x.
  10. Pan, Kaike; Tan, Huisong; Shan, Hongguang (July 1998), "Orbital circularization in detached binaries with early-type primaries", Astronomy and Astrophysics, 335: 179–182, Bibcode:1998A&A...335..179P.
  11. "* sig Aql". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-07-20.
  12. van Rensbergen, W.; De Loore, C.; Jansen, K. (February 2006), "Evolution of interacting binaries with a B type primary at birth", Astronomy and Astrophysics, 446 (3): 1071–1079, Bibcode:2006A&A...446.1071V, doi:10.1051/0004-6361:20053543.
  13. Zasche, P.; et al. (August 2009), "A Catalog of Visual Double and Multiple Stars With Eclipsing Components", The Astronomical Journal, 138 (2): 664–679, arXiv:0907.5172, Bibcode:2009AJ....138..664Z, doi:10.1088/0004-6256/138/2/664.
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