Cygnus OB2-8A

Cygnus OB2 #8A is a double-lined spectroscopic binary located near the centre of the Cygnus OB2 association located 5,500 light years away.

Cygnus OB2 #8A

Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension  20h 33m 15.07905s[1]
Declination +41° 18′ 50.4762″[1]
Apparent magnitude (V) 9.06[2]
Characteristics
Spectral type O6If + O5.5III(f)[3]
U−B color index +0.15[4]
B−V color index +1.29[4]
Astrometry
Radial velocity (Rv)-27.7 km/s
Proper motion (μ) RA: -0.91[1] mas/yr
Dec.: -6.02[1] mas/yr
Parallax (π)-3.91 ± 1.76[1] mas
Distance1,700[5] pc
Absolute magnitude (MV)−6.78[6]
Orbit[7]
Period (P)21.9 days
Semi-major axis (a)71 R☉[5]
Eccentricity (e)0.24
Semi-amplitude (K1)
(primary)		82.8 km/s
Semi-amplitude (K2)
(secondary)		95.8 km/s
Details[5]
Cyg OB2 #8A1
Mass44.1 M☉
Radius20 R☉
Luminosity650,000 L☉
Surface gravity (log g)3.48 cgs
Temperature36,800 K
Cyg OB2 #8A2
Mass37.4 M☉
Radius14.8 R☉
Luminosity468,000 L☉
Surface gravity (log g)3.67 cgs
Temperature39,200 K
Age2[6] Myr
Other designations
Schulte 8A, 1E 203127+4108.5, TYC 3161-1325-1, ADS 14000 A, 2E 4382, HIP 101425, UBV 17839, AG+41° 1925, 2E 2031.4+4108, IDS 20297+4058, LS III +41 37, Cyg OB2-8A, 1ES 2031+41.1, 2MASS J20331508+4118504, BD+40°4227, GCRV 20036, PPM 60129, CCDM J20332+4119A, 1RXS J203315.8+411848, CGO 605, GOS G080.22+00.79 01, SAO 49781, CSI+40 4227 1, GSC 03161-01325.
Database references
SIMBADdata

Discovery

Until 1951 Cyg OB2 #8 had been known only as an anonymous catalogue entry in the Bonner Durchmusterung. Then it was identified as one of several highly luminous hot stars close together in Cygnus. Despite being commonly referred to as Schulte #8A, the number 8 was first published in an earlier paper.[8] Schulte identified the grouping as a massive stellar association and split star #8 into four components, including #8A.[9]

System

The Cygnus OB2 #8A system contains two massive luminous O class stars in a 21.9 day orbit. The primary is a 44 M☉ supergiant and the secondary is a 37 M☉ giant star.[7] The two stars are not thought to be exchanging mass and their luminosity classes match the main sequence turnoff in the Cyg OB2 association at around O6.[6] The nearby stars Cyg OB2 #8B, #8C, and #8D, originally thought to be a single star, are all massive and luminous class O stars.

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References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. Caballero-Nieves, S. M.; Nelan, E. P.; Gies, D. R.; Wallace, D. J.; Degioia-Eastwood, K.; Herrero, A.; Jao, W.-C.; Mason, B. D.; Massey, P.; Moffat, A. F. J.; Walborn, N. R. (2014). "A High Angular Resolution Survey of Massive Stars in Cygnus OB2: Results from the Hubble Space Telescope Fine Guidance Sensors". The Astronomical Journal. 147 (2): 40. arXiv:1311.5087. Bibcode:2014AJ....147...40C. doi:10.1088/0004-6256/147/2/40.
  3. Cazorla, Constantin; Nazé, Yaël; Rauw, Gregor (2014). "Wind collisions in three massive stars of Cygnus OB2". Astronomy & Astrophysics. 561: A92. arXiv:1312.1871. Bibcode:2014A&A...561A..92C. doi:10.1051/0004-6361/201322539.
  4. 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.
  5. De Becker, M.; Rauw, G.; Sana, H.; Pollock, A. M. T.; Pittard, J. M.; Blomme, R.; Stevens, I. R.; Van Loo, S. (2006). "XMM-Newton observations of the massive colliding wind binary and non-thermal radio emitter CygOB2#8A [O6If + O5.5III(f)]" (PDF). Monthly Notices of the Royal Astronomical Society. 371 (3): 1280. Bibcode:2006MNRAS.371.1280D. doi:10.1111/j.1365-2966.2006.10746.x.
  6. Negueruela, I.; Marco, A.; Herrero, A.; Clark, J. S. (2008). "New very massive stars in Cygnus OB2". Astronomy and Astrophysics. 487 (2): 575. arXiv:0806.2879. Bibcode:2008A&A...487..575N. doi:10.1051/0004-6361:200810094.
  7. De Becker, M.; Rauw, G.; Manfroid, J. (2004). "A Spectroscopic study of the non-thermal radio emitter Cyg OB2 #8A: Discovery of a new binary system". Astronomy and Astrophysics. 424 (3): L39. arXiv:astro-ph/0408027. Bibcode:2004A&A...424L..39D. doi:10.1051/0004-6361:200400049.
  8. Münch, Luis; Morgan, W. W. (1953). "Notes: A Probable Clustering of Blue Giants in Cygnus". Astrophysical Journal. 118: 161. Bibcode:1953ApJ...118..161M. doi:10.1086/145737.
  9. Schulte, D. H. (1956). "New Members of the Association VI Cygni". Astrophysical Journal. 124: 530. Bibcode:1956ApJ...124..530S. doi:10.1086/146256.

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