21 Aquilae

21 Aquilae is a solitary[9] variable star in the equatorial constellation of Aquila. It has the variable star designation V1288 Aql; 21 Aquilae is its Flamsteed designation. This object is visible to the naked eye as a dim, blue-white hued star with a baseline apparent visual magnitude of 5.14.[2] The star is located at a distance of around 740 light-years (230 parsecs) from Earth, give or take a 30 light-year margin of error.[10] It is moving closer to the Earth with a heliocentric radial velocity of –5 km/s.[5]

21 Aquilae
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension  19h 13m 42.70079s[1]
Declination +02° 17′ 37.2921″[1]
Apparent magnitude (V) 5.140[2]
Characteristics
Spectral type B8 II-III[3]
U−B color index –0.399[2]
B−V color index –0.065[2]
Variable type α2 CVn[4]
Astrometry
Radial velocity (Rv)–5.2[5] km/s
Proper motion (μ) RA: +10.537[1] mas/yr
Dec.: +0.375[1] mas/yr
Parallax (π)4.3902 ± 0.1945[1] mas
Distance740 ± 30 ly
(230 ± 10 pc)
Absolute magnitude (MV)−2.12[6]
Details
Radius4.3[7] R☉
Luminosity913.05[6] L☉
Surface gravity (log g)3.27[3] cgs
Temperature13,175[3] K
Metallicity [Fe/H]–0.14[3] dex
Other designations
21 Aql, V1288 Aql, BD+02°3824, FK5 3537, HD 179761, HIP 94477, HR 7287, SAO 124408, WDS J19137+0218A[8]
Database references
SIMBADdata

The stellar classification of this star is B8 II-III,[3] with the luminosity class of II-III suggesting that the spectrum displays elements of both a giant star and a bright giant. It is a chemically peculiar star of the Mercury-Manganese type (CP3).[11] This is a probable Alpha2 Canum Venaticorum variable that ranges in visual magnitude from 5.06 down to 5.16.[4] The star is radiating 913[6] times the luminosity of the Sun from its photosphere at an effective temperature of 13,175 K;[3] this searing heat gives it the blue-white glow of a B-type star.[12]

21 Aquilae is catalogued as an optical double star, having a 12th magnitude companion 37″ away as of 2010. It was first identified as a double star by John Herschel.[13] The companion is a distant background object.[14]

References
  1. 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. Gaia DR2 record for this source at VizieR.
  2. Stepien, K. (December 1968), "Photometric behavior of magnetic stars", Astrophysical Journal, 154: 945, Bibcode:1968ApJ...154..945S, doi:10.1086/149815.
  3. Cenarro, A. J.; et al. (January 2007), "Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters", Monthly Notices of the Royal Astronomical Society, 374 (2): 664–690, arXiv:astro-ph/0611618, Bibcode:2007MNRAS.374..664C, doi:10.1111/j.1365-2966.2006.11196.x.
  4. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S.
  5. Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick (eds.), Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E.
  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. Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics", Astronomy and Astrophysics, 367 (2): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451.
  8. "21 Aql". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-06-05.
  9. 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.
  10. 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.
  11. Ghazaryan, S.; et al. (November 2018), "New catalogue of chemically peculiar stars, and statistical analysis", Monthly Notices of the Royal Astronomical Society, 480 (3): 2953–2962, arXiv:1807.06902, Bibcode:2018MNRAS.480.2953G, doi:10.1093/mnras/sty1912.
  12. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 10, 2012, retrieved 2012-01-16
  13. Mason, B. D.; et al. (2014). "The Washington Visual Double Star Catalog". The Astronomical Journal. 122: 3466–3471. Bibcode:2001AJ....122.3466M. doi:10.1086/323920. Retrieved 2015-07-22.
  14. 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. Gaia DR2 record for this source at VizieR.
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