GCIRS 16SW

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

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]

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]

  1. ^ a b Cite error: The named reference yz2014 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference paumard2006 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference blum2003 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference blum1996 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Gillessen2017 was invoked but never defined (see the help page).
  6. ^ a b c d e Cite error: The named reference Peeples2007 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  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.