GCIRS 16SW, also known as S97, is a contact binary star located in the Galactic Center. It is composed of two hot massive stars of equal size that orbit each other with a period of 19.5 days. The stars are so close that their atmospheres overlap, and the two stars form an eclipsing binary varying in brightness by 0.35 magnitudes at infrared wavelengths.[6]

GCIRS 16SW
The location of GCIRS 16SW (circled in red)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagittarius
Right ascension 17h 45m 40.124s[1]
Declination −29° 00′ 29.02″[1]
Characteristics
Evolutionary stage Slash star
Spectral type Ofpe/WN9[2]
Apparent magnitude (J) 14.75[3]
Apparent magnitude (H) 11.6[3]
Apparent magnitude (K) 9.34[4]
Orbit[5]
PrimarySagittarius A*
CompanionGCIRS 16SW
Period (P)1270±309 yr
Semi-major axis (a)2.32±0.46
Eccentricity (e)0.35±0.11
Inclination (i)113.0±1.3°
Longitude of the node (Ω)113.2±1.4°
Periastron epoch (T)2132±29
Argument of periastron (ω)
(secondary)
28±14°
Orbit[6]
Period (P)19.4513±0.0011 d
Semi-major axis (a)140.6±4.7 R
Inclination (i)70.85±0.6°
Periastron epoch (T)2451775.102±0.032
Details[6]
A
Mass~50 M
Radius54.5±1.8 × 58.2±1.9 × 62.7±2.1 R
Luminosity1,100,000 L
Surface gravity (log g)3.0 cgs
Temperature24,400 K
B
Mass~50 M
Radius54.5±1.8 × 58.2±1.9 × 62.7±2.1 R
Luminosity1,100,000 L
Surface gravity (log g)3.0 cgs
Temperature23,500 K
Other designations
GCIRS 16SW, S97, S1-16[7]
Database references
SIMBADdata
Artist's impression of GCIRS 16SW

GCIRS 16SW orbits Sagittarius A* at approximately 19,000 AU, with a period of approximately 1,270 years.[5] At the stars' estimated mass of about 50 solar masses, they are predicted to have a lifespan of about 4 million years, indicating that the system formed within 0.1 parsecs (0.33 ly; 21,000 AU) of Sagittarius A*, instead of having migrated inward from a greater distance.[6]

GCIRS 16SW was classified as a candidate luminous blue variable on the basis of its spectrum and physical properties.[8] This was before it was identified as an eclipsing binary, but it is still treated as a candidate LBV.[9]

Each star is strongly distorted by the gravity of the other star. The polar radius is calculated to be 54.5 R, while the radius along the direction of orbital motion is 58.2 R. The radius along the line joining the two stars is 62.7 R, while the separation of the centres of the two stars is 132.8 R. A calculation of properties treating the binary as a single star gave an effective temperature of 24,400 K.[8] The secondary component is found to have a temperature 96% of that of the primary. However, these temperatures yield a luminosity over a million times that of the sun, uncomfortably close to the Eddington luminosity for each star, and it is suspected the actual temperatures are slightly lower.[6]

References

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  1. ^ a b Miho N. Ishigaki; Nozomu Tominaga; Chiaki Kobayashi; Ken'ichi Nomoto (2014). "Faint Population III Supernovae as the Origin of the Most Iron-Poor Stars". The Astrophysical Journal Letters. 792 (2): L32. arXiv:1404.4817. Bibcode:2014ApJ...792L..32I. doi:10.1088/2041-8205/792/2/L32. S2CID 119012372.
  2. ^ Paumard, T.; Genzel, R.; Martins, F.; Nayakshin, S.; Beloborodov, A.M.; Levin, Y.; Trippe, S.; Eisenhauer, F.; Ott, T.; Gillessen, S.; Abuter, R.; Cuadra, J.; Alexander, T.; Sternberg, A. (2006). "The two young star disks in the central parsec of the galaxy: Properties, dynamics, and formation". The Astrophysical Journal. 643 (2): 1011–1035. arXiv:astro-ph/0601268. Bibcode:2006ApJ...643.1011P. doi:10.1086/503273. S2CID 14440768.
  3. ^ a b Blum, R. D.; Ramírez, Solange V.; Sellgren, K.; Olsen, K. (2003). "Really Cool Stars and the Star Formation History at the Galactic Center". The Astrophysical Journal. 597 (1): 323–346. arXiv:astro-ph/0307291. Bibcode:2003ApJ...597..323B. doi:10.1086/378380. S2CID 5664467.
  4. ^ Blum, R. D.; Sellgren, K.; Depoy, D. L. (1996). "JHKL Photometry and the K-Band Luminosity Function at the Galactic Center". The Astrophysical Journal. 470: 864. arXiv:astro-ph/9604109. Bibcode:1996ApJ...470..864B. doi:10.1086/177917. S2CID 2730271.
  5. ^ a b Gillessen, S.; Plewa, P. M.; Eisenhauer, F.; Sari, R.; Waisberg, I.; Habibi, M.; Pfuhl, O.; George, E.; Dexter, J. (2017). "An Update on Monitoring Stellar Orbits in the Galactic Center". The Astrophysical Journal. 837 (1): 30. arXiv:1611.09144. Bibcode:2017ApJ...837...30G. doi:10.3847/1538-4357/aa5c41. ISSN 0004-637X. S2CID 119087402.
  6. ^ a b c d e Peeples, Molly S.; et al. (January 2007). "The Nature of the Variable Galactic Center Source GCIRS 16SW Revisited: A Massive Eclipsing Binary". The Astrophysical Journal. 654 (1): L61–L64. arXiv:astro-ph/0610212. Bibcode:2007ApJ...654L..61P. doi:10.1086/510720. S2CID 14242573.
  7. ^ "GCIRS 16SW -- Wolf-Rayet Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 30 June 2020.
  8. ^ a b Najarro, F.; Krabbe, A.; Genzel, R.; Lutz, D.; Kudritzki, R. P.; Hillier, D. J. (1997). "Quantitative spectroscopy of the HeI cluster in the Galactic center". Astronomy and Astrophysics. 325: 700. Bibcode:1997A&A...325..700N.
  9. ^ Smith, Nathan; Aghakhanloo, Mojgan; Murphy, Jeremiah W.; Drout, Maria R.; Stassun, Keivan G.; Groh, Jose H. (2019). "On the Gaia DR2 distances for Galactic luminous blue variables". Monthly Notices of the Royal Astronomical Society. 488 (2): 1760. arXiv:1805.03298. Bibcode:2019MNRAS.488.1760S. doi:10.1093/mnras/stz1712. S2CID 119267371.