Phi Sagittarii

Phi Sagittarii, Latinized from φ Sagittarii, is an interferometric binary star in the southern constellation of Sagittarius. With an apparent visual magnitude of 3.17,[2] it is the ninth-brightest star in the constellation and is readily visible to the naked eye. Parallax measurements place it at a distance of roughly 239 light-years (73 parsecs) from the Earth.[1] It is receding with a radial velocity of +21.5 km/s.[2]

Phi Sagittarii
Location of φ Sagittarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Sagittarius
Right ascension 18h 45m 39.38610s[1]
Declination −26° 59′ 26.7944″[1]
Apparent magnitude (V) 3.17[2]
Characteristics
Spectral type B8.5 III[3]
U−B color index −0.36[4]
B−V color index −0.11[4]
Astrometry
Radial velocity (Rv)+21.5[2] km/s
Proper motion (μ) RA: +50.61[1] mas/yr
Dec.: +1.22[1] mas/yr
Parallax (π)13.63 ± 0.19 mas[1]
Distance239 ± 3 ly
(73 ± 1 pc)
Absolute magnitude (MV)−1.16[5]
Details
Mass3.41[6] M☉
Radius4.8[7] R☉
Luminosity475[7] L☉
Surface gravity (log g)3.73[6] cgs
Temperature12,487±425[6] K
Rotational velocity (v sin i)46[6] km/s
Age152[6] Myr
Other designations
Namalsadirah 1, Awal al Sadira, φ Sgr, Phi Sgr, 27 Sagittarii, CPD−27  5241, FK5 1487, GC 25661, HD 173300, HIP 92041, HR 7039, SAO 268859, PPM 297231[8]
Database references
SIMBADdata

The stellar classification of this star has been rated at B8.5 III,[3] with the luminosity class of III indicating it is a giant star evolved away from the main sequence after it has exhausted the hydrogen at its core. This energy is being radiated from the star's outer envelope at an effective temperature of 12487 K,[6] which produces the blue-white hue typical of B-type stars.[9]

This star has been catalogued as a spectroscopic binary[10] and a companion was apparently detected through lunar occultation.[11] However, the latter was pointed out as spurious.[7][12] Interferometric observations taken in 2017 finally revealed that Phi Sgr is indeed a binary by resolving a companion with a near-infrared K band flux ratio of 6% (corresponding to a mass of 1.6 M☉) at a separation of 17.7 mas (1.3 au).[13]

Name and etymology

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Aoul al Sadirah, which was translated into Latin as Prima τού al Sadirah, meaning first returning ostrich.[14]

In Chinese, 斗 (Dǒu), meaning Dipper, refers to an asterism consisting of φ Sagittarii, λ Sagittarii, μ Sagittarii, σ Sagittarii, τ Sagittarii and ζ Sagittarii. Consequently, the Chinese name for φ Sagittarii itself is 斗宿一 (Dǒu Xiù yī, English: the First Star of Dipper.)[15]

This star, together with γ Sgr, δ Sgr, ε Sgr, ζ Sgr, λ Sgr, σ Sgr and τ Sgr comprising the Teapot asterism.[16] φ Sgr, σ Sgr, ζ Sgr, χ Sgr and τ Sgr were Al Naʽām al Ṣādirah (النعم السادرة), the Returning Ostriches.[17] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Naʽām al Ṣādirah or Namalsadirah was originally the title for four stars: φ Sgr as Namalsadirah I, τ Sgr as Namalsadirah II, χ1 Sgr as Namalsadirah III and χ2 Sgr as Namalsadirah IV (except σ Sgr and ζ Sgr) .[18]

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, S2CID 18759600
  2. Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg, Astronomisches Rechen-Institut Heidelberg, 35 (35): 1, Bibcode:1999VeARI..35....1W
  3. Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 3, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1982mcts.book.....H
  4. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J
  5. 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.
  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. Kaler, James B., "PHI SGR (Phi Sagittarii)", Stars, University of Illinois, retrieved 2012-01-15
  8. "phi Sgr -- Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-15
  9. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 18, 2012, retrieved 2012-01-16
  10. Lee, O. J. (1910-11-01). "Measures on nineteen new spectroscopic binaries". The Astrophysical Journal. 32: 300–308. Bibcode:1910ApJ....32..300L. doi:10.1086/141806. ISSN 0004-637X.
  11. Finsen, W. S. (April 1951), "The duplicity of phi Sgr", Astronomical Journal, 56: 56, Bibcode:1951AJ.....56Q..56F, doi:10.1086/106589
  12. 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
  13. Waisberg, Idel; Klein, Ygal; Katz, Boaz (2023-05-16). "Hidden Companions to Intermediate-mass Stars. III. Discovery of a 1.6M ⊙ , 1.3 au Companion to HIP 92041 = ϕ Sagittarii*". Research Notes of the AAS. 7 (5): 95. Bibcode:2023RNAAS...7...95W. doi:10.3847/2515-5172/acd4bf. ISSN 2515-5172.
  14. Knobel, E. B. (June 1895), "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket", Monthly Notices of the Royal Astronomical Society, 55: 430, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429.
  15. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日
  16. Teapot, constellation-guide.com, retrieved 2017-05-13.
  17. Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 355, ISBN 0-486-21079-0, retrieved 2012-09-04.
  18. Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), Jet Propulsion Laboratory, California Institute of Technology.{{citation}}: CS1 maint: location missing publisher (link)
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