16 Sagittarii

16 Sagittarii is a multiple[6] star system in the southern zodiac constellation of Sagittarius. It is near the lower limit of brightness for stars that can be seen with the naked eye, having an apparent visual magnitude of 6.02.[2] The estimated distance to this system is about 4,600 light years.[4] It is a member of the Sgr OB7 cluster.[4] Along with the O-type star 15 Sgr, it is ionizing an H II region along the western edge of the molecular cloud L291.[10]

16 Sagittarii
Observation data
Epoch J2000      Equinox J2000
Constellation Sagittarius
Right ascension  18h 15m 12.96915s[1]
Declination −20° 23′ 16.7021″[1]
Apparent magnitude (V) 6.02[2]
Characteristics
Spectral type O9.5 III[3]
B−V color index 0.02[4]
Astrometry
Radial velocity (Rv)−11.0±1.3[5] km/s
Proper motion (μ) RA: +1.60[1] mas/yr
Dec.: −1.51[1] mas/yr
Distance4,600 ly
(1,400[4] pc)
Orbit[6]
Period (P)12.76123±0.00022 d
Eccentricity (e)0.181±0.060
Periastron epoch (T)54005.3 ± 0.7
Argument of periastron (ω)
(secondary)		156±19°
Semi-amplitude (K1)
(primary)		22.1±2.8 km/s
Details
16 Sgr Aa
Mass50[7] M☉
Luminosity7×109[8] L☉
Temperature11,683[8] K
Rotational velocity (v sin i)51[7] km/s
16 Sgr Ab
Mass3.72[7] M☉
Other designations
16 Sgr, BD−20° 5055, HD 167263, HIP 89440, HR 6823, SAO 186544, WDS J18152-2023A[9]
Database references
SIMBADdata

Mason et al. (1998) found this to be a member of a speckle binary with an estimated orbital period of roughly 130 years and a magnitude difference of 0.4. Both components show indications of a variable radial velocity, suggesting that they are spectroscopic binaries – making it a candidate quadruple star system.[6] However, Tokovinin (2008) considers it a triple star system.[7]

Orbital elements for the main spectroscopic binary, components Aa and Ab,[4] were published by Mayer et al. (2014), giving an orbital period of 12.76 days and an eccentricity of 0.18.[6] This system displays a merged stellar classification of O9.5 III,[3] matching an blue-hued O-type giant star. It shows a longitudinal magnetic field strength of −74±44 G and a projected rotational velocity of 51 km/s.[11] Tokovinin (2008) gives an estimated mass of 50 times the mass of the Sun for the primary, and 3.72 for the secondary. The tertiary member, component B, has 2.54 times the Sun's mass.[7]

References
  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.
  2. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  3. Sota, A.; Maíz Apellániz, J.; Morrell, N. I.; Barbá, R. H.; Walborn, N. R.; Gamen, R. C.; Arias, J. I.; Alfaro, E. J. (2014). "The Galactic O-Star Spectroscopic Survey (GOSSS). II. Bright Southern Stars". The Astrophysical Journal Supplement. 211: 10. arXiv:1312.6222. Bibcode:2014ApJS..211...10S. doi:10.1088/0067-0049/211/1/10.
  4. Aldoretta, E. J.; et al. (January 2015). "The Multiplicity of Massive Stars: a High Angular Resolution Survey With the Guidance Sensor". The Astronomical Journal. 149 (1): 14. arXiv:1410.0021. Bibcode:2015AJ....149...26A. doi:10.1088/0004-6256/149/1/26. 26.
  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.
  6. Mayer, Pavel; Drechsel, Horst; Irrgang, Andreas (May 2014). "New and revised parameters for several southern OB binaries". Astronomy & Astrophysics. 565: 9. arXiv:1404.1686. Bibcode:2014A&A...565A..86M. doi:10.1051/0004-6361/201423455. A86.
  7. Tokovinin, A. (September 2008). "Comparative statistics and origin of triple and quadruple stars". Monthly Notices of the Royal Astronomical Society. 389 (2): 925–938. arXiv:0806.3263. Bibcode:2008MNRAS.389..925T. doi:10.1111/j.1365-2966.2008.13613.x.
  8. McDonald, I.; et al. (2012), "Fundamental parameters and infrared excesses of Hipparcos stars", Monthly Notices of the Royal Astronomical Society, 427: 343, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.
  9. "16 Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-03-16.
  10. Marti, J.; et al. (October 1993), "HH 80-81: A Highly Collimated Herbig-Haro Complex Powered by a Massive Young Star", Astrophysical Journal, 416: 208, Bibcode:1993ApJ...416..208M, doi:10.1086/173227
  11. Grunhut, J. H.; Wade, G. A.; Neiner, C.; Oksala, M. E.; Petit, V.; Alecian, E.; Bohlender, D. A.; Bouret, J. -C.; Henrichs, H. F.; Hussain, G. A. J.; Kochukhov, O.; MiMeS Collaboration (February 2017). "The MiMeS survey of Magnetism in Massive Stars: magnetic analysis of the O-type stars". Monthly Notices of the Royal Astronomical Society. 465 (2): 2432–2470. arXiv:1610.07895. Bibcode:2017MNRAS.465.2432G. doi:10.1093/mnras/stw2743.
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