7_Sagittarii

7 Sagittarii

7 Sagittarii

Star in the constellation Sagittarius

7 Sagittarii is a massive star in the southern zodiac constellation of Sagittarius which is located in the Lagoon Nebula (NGC 6530),[9] although multiple sources have considered it a foreground star.[10] It is a dim star but visible to the naked eye with an apparent visual magnitude of 5.37.[2] The distance to this star can be determined from the annual parallax shift of 3.02±0.28 mas,[1] yielding a value of roughly 1,100 light years. It is moving closer to the Sun with a heliocentric radial velocity of −11 km/s.[5]

Quick Facts Observation data Epoch J2000 Equinox J2000, Constellation ...
7 Sagittarii is the brightest star in the region of the Lagoon Nebula, towards the right edge.

Gray and Garrison (1989) listed a stellar classification of F2 II/III[3] for this star, suggesting it is a K-type star with a spectrum showing mixed traits of a giant/bright giant. Houk and Smith-Moore (1978) had a similar classification of F2/3 II/III.[11] This may indicate it is not a member of NGC 6530, since it should not have evolved to this class from the O-type stars that still populate this cluster, and hasn't had time to evolve from a less massive cluster star.[10]

It is a suspected chemically peculiar star.[4][5] The spectral class from the calcium K line has been given as A8 while the class determined from other metallic lines was F4, making it an Am star.[12] This peculiarity is now considered doubtful.[4]

7 Sagittarii has an estimated 18[6] times the Sun's radius and is radiating 658[2] times the Sun's luminosity from its photosphere at an effective temperature of around 6,800 K.[5]

References

  1. [1]
    van Leeuwen, F. (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, S2CID 18759600.
  2. [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. [3]
    Gray, R. O.; Garrison, R. F. (February 1989), "The early F-type stars: refined classification, confrontation with Stroemgren photometry, and the effects of rotation", Astrophysical Journal Supplement, 69: 301, Bibcode:1989ApJS...69..301G, doi:10.1086/191315.
  4. [4]
    Renson, P.; Manfroid, J. (May 2009), "Catalogue of Ap, HgMn and Am stars", Astronomy and Astrophysics, 498 (3): 961–966, Bibcode:2009A&A...498..961R, doi:10.1051/0004-6361/200810788
  5. [5]
    Khalack, V.; LeBlanc, F. (July 2015), "Project VeSElkA: Analysis of Balmer Line Profiles of Slowly Rotating Chemically Peculiar Stars", The Astronomical Journal, 150 (1): 10, arXiv:1505.08158, Bibcode:2015AJ....150....2K, doi:10.1088/0004-6256/150/1/2, S2CID 118283214, 2.
  6. [6]
    Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics, 367 (Third ed.): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754.
  7. [7]
    Rutten, R. G. M.; Pylyser, E. (February 1988), "Magnetic structure in cool stars. XV. The evolution of rotation rates and chromospheric activity of giants", Astronomy and Astrophysics, 191: 227−236, Bibcode:1988A&A...191..227R.
  8. [8]
    "7 Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-03-14.
  9. [9]
    Damiani, F.; et al. (August 2017), "The Gaia-ESO Survey: dynamics of ionized and neutral gas in the Lagoon nebula (M 8)", Astronomy & Astrophysics, 604: 25, arXiv:1705.08194, Bibcode:2017A&A...604A.135D, doi:10.1051/0004-6361/201730986, S2CID 119488696, A135.
  10. [10]
    Sowell, James R. (May 1987), "Yellow evolved stars in open clusters", Astrophysical Journal Supplement Series, 64: 241−267, Bibcode:1987ApJS...64..241S, doi:10.1086/191196. See NGC 6530 on p. 257.
  11. [11]
    Houk, Nancy; Smith-Moore, M. (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988mcts.book.....H.
  12. [12]
    Hauck, B. (June 1973), "Catalogue of AM stars with known spectral types", Astronomy and Astrophysics Supplement, 10: 385, Bibcode:1973A&AS...10..385H.
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