21 Vulpeculae

21 Vulpeculae is a single,[11] white-hued star in the northern constellation of Vulpecula. Its distance can be estimated from the annual parallax shift of 10.4302±0.0696 mas,[1] yielding a separation of 313 light years. The star is faintly visible to the naked eye at night, having an apparent visual magnitude of 5.19.[2] It is moving further away with a heliocentric radial velocity of about +7 km/s,[2] having come within 243 ly (74.53 pc) around 4.2 million years ago.[2]

21 Vulpeculae
Observation data
Epoch J2000      Equinox J2000
Constellation Vulpecula
Right ascension 20h 14m 14.5295s[1]
Declination +28° 41′ 41.342″[1]
Apparent magnitude (V) 5.19[2]
Characteristics
Spectral type A7 IVn[3] or A5 Vn[4]
B−V color index 0.191±0.003[2]
Variable type δ Sct[5]
Astrometry
Radial velocity (Rv)+7.0±4.2[2] km/s
Proper motion (μ) RA: 12.541±0.050[1] mas/yr
Dec.: −19.117±0.068[1] mas/yr
Parallax (π)10.4302 ± 0.0696[1] mas
Distance313 ± 2 ly
(95.9 ± 0.6 pc)
Absolute magnitude (MV)0.39[2]
Details
Mass1.61[6] or 2.36±0.03[7] M☉
Radius1.5[8] R☉
Luminosity67.4+3.2
−3.1[7] L☉
Surface gravity (log g)3.34±0.14[6] cgs
Temperature7,739±263[6] K
Rotational velocity (v sin i)222[7][9] km/s
Age356[6] Myr
Other designations
21 Vul, NU Vul, BD+28° 3675, HD 192518, HIP 99738, HR 7731, SAO 88391[10]
Database references
SIMBADdata

There is some disagreement about the class of this star. Cowley et al. (1969) listed it as an A-type subgiant star with a stellar classification of A7 IVn,[3] where the 'n' notation indicates "nebulous" lines due to rapid rotation. The luminosity class of IV suggests the star has exhausted the supply of hydrogen at its core and is evolving away from the main sequence. Slettebak (1982) classified it as an A5 IV shell star[12] and it was so regarded by Hauck & Jaschek (2000),[13] while Abt & Morrell (1995) listed it with a class of A5 Vn,[4] indicating a rapidly-rotating A-type main-sequence star. It is a Delta Scuti type variable star,[5] with a dominant pulsation period of 0.1881 days and an amplitude of 0.016 in magnitude.[9]

David and Hillenbrand (2015) found an average mass for this star of 1.61 times the mass of the Sun,[6] whereas Zorec and Royer (2012) list a much higher mass estimate of 2.36±0.03 M☉.[7] It is about 356[6] million years old with a projected rotational velocity of 222 km/s.[9] This rapid rotation is giving the star an oblate shape with an equatorial bulge that is an estimated 16% larger than the polar radius.[14] Observations since 1997 suggest 21 Vul has an orbiting disk of gaseous material that is too equatorially confined to make it a shell star. The line strengths from this disk have been decreasing over time.[15]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics (in press). arXiv:2012.01533. doi:10.1051/0004-6361/202039657. S2CID 227254300. Gaia EDR3 record for this source at VizieR.
  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.
  3. Cowley, A.; Cowley, C.; Jaschek, M.; Jaschek, C. (1969), "A study of the bright a stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375, Bibcode:1969AJ.....74..375C, doi:10.1086/110819
  4. Abt, Helmut A.; Morrell, Nidia I. (1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", Astrophysical Journal Supplement, 99: 135, Bibcode:1995ApJS...99..135A, doi:10.1086/192182.
  5. Garrido, R.; Saez, M. (1979), "21 VUL - A new luminous long period Delta Scuti star", Astronomy and Astrophysics, 79: 347–349, Bibcode:1979A&A....79..347G
  6. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
  7. 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, S2CID 55586789.
  8. Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics (3rd ed.), 367 (2): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754.
  9. Chang, S.-W.; et al. (2013), "Statistical Properties of Galactic δ Scuti Stars: Revisited", The Astronomical Journal, 145 (5): 132, arXiv:1303.1031, Bibcode:2013AJ....145..132C, doi:10.1088/0004-6256/145/5/132, S2CID 118900730.
  10. "21 Vul". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-04-21.
  11. 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:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  12. Slettebak, A. (September 1982), "Spectral types and rotational velocities of the brighter Be stars and A-F type shell stars", Astrophysical Journal Supplement Series, 50: 55−83, Bibcode:1982ApJS...50...55S, doi:10.1086/190820
  13. Hauck, B.; Jaschek, C. (February 2000), "A-shell stars in the Geneva system", Astronomy and Astrophysics, 354: 157–162, Bibcode:2000A&A...354..157H.
  14. Belle, G. T. (2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2, S2CID 119273474.
  15. Abt, Helmut A. (February 2008), "New Data on A-Type Disk Stars", The Astrophysical Journal Supplement Series, 174 (2): 499–503, Bibcode:2008ApJS..174..499A, doi:10.1086/522698, 499–503
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