Cygnus OB2-9

The correct title of this article is Cygnus OB2 #9. The omission of the # is due to technical restrictions.

Cygnus OB2-9

Artistic Representation of Cygnus OB2 #9
Observation data Epoch J2000.0       Equinox J2000.0
Constellation	Cygnus [1]
Right ascension	20h 33m 10.74s [2]
Declination	+41° 15′ 8.2″ [2]
Apparent magnitude  (V)	11.0 [3]
Characteristics
Evolutionary stage	Blue Supergiant + Blue Giant [4]
Spectral type	O5I+O4III [5]
Astrometry
Radial velocity (Rv)	−36.9±5.2 [2] km/s
Proper motion (μ)	RA: −2.766 [2] mas/yr Dec.: −4.687 [2] mas/yr
Parallax (π)	0.5214±0.0196  mas [2]
Distance	6,300 ± 200  ly (1,920 ± 70  pc)
Details [6]
A
Mass	~34  M☉
B
Mass	~30  M☉
Other designations
Cygnus OB2 #12, Schulte 9, 2MASS J20331074+4115081, HIP 101419, 3XMM J203310.7+411508, Gaia DR3 2067783623515353728 [7]
Database references
SIMBAD	data

Cygnus OB2 #9 (also known as Cyg OB2-9) is a massive O-type binary star system located in the Cygnus OB2 association, a young and massive OB association in the constellation of Cygnus. It consists of two hot, luminous supergiant and giant stars with strong stellar winds that collide, producing detectable non-thermal radio and X-ray emission. The system is notable for its eccentric orbit and has been the subject of multi-wavelength monitoring campaigns to study wind-wind interactions in massive binaries. ^{[4] [8] [9] [6]}

Characteristics

Short narrated video about Cygnus OB2 #9

Cygnus OB2 #9 is a close spectroscopic with an orbital period of 2.35 years and high eccentricity of approximately 0.75–0.8. The semi-major axis is about 18–20 astronomical units (AU), with periastron distances as small as 4.5 AU, leading to intensified wind interactions during closest approach. The binary nature was confirmed through radial velocity variations observed in optical spectroscopy. ^[4]

Observations

The colliding stellar winds produce thermal X-ray emission from shocks in the wind-wind collision region (WWCR), with luminosities of 10³²–10³³ ergs/second. Dedicated campaigns using Swift, XMM-Newton, and Chandra during the 2011 periastron passage revealed flux peaks following a 1/D dependence on separation, with spectral softening at closest approach. No evidence of radiative cooling is observed, distinguishing it from systems like Eta Carinae. ^{[10] [4] [11]}

References

1. Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific . 99 (617): 695. Bibcode:1987PASP...99..695R. doi: 10.1086/132034 . Constellation record for this object at VizieR.
2. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv: 2208.00211 . Bibcode:2023A&A...674A...1G. doi: 10.1051/0004-6361/202243940 . S2CID   244398875. Gaia DR3 record for this source at VizieR.
3. 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.
4. Nazé, Y.; Mahy, L.; Damerdji, Y.; Kobulnicky, H. A.; Pittard, J. M.; Parkin, E. R.; Absil, O.; Blomme, R. (2012-10-01). "The 2.35 year itch of Cygnus OB2 #9 - I. Optical and X-ray monitoring". Astronomy & Astrophysics. 546: A37. arXiv: 1209.5622 . Bibcode:2012A&A...546A..37N. doi:10.1051/0004-6361/201219442. ISSN   0004-6361.
5. Kobulnicky, Henry A.; Kiminki, Daniel C.; Lundquist, Michael J.; Burke, Jamison; Chapman, James; Keller, Erica; Lester, Kathryn; Rolen, Emily K.; Topel, Eric; Bhattacharjee, Anirban; Smullen, Rachel A.; Vargas Álvarez, Carlos A.; Runnoe, Jessie C.; Dale, Daniel A.; Brotherton, Michael M. (2014). "Toward Complete Statistics of Massive Binary Stars: Penultimate Results from the Cygnus OB2 Radial Velocity Survey". The Astrophysical Journal Supplement Series. 213 (2): 34. arXiv: 1406.6655 . Bibcode:2014ApJS..213...34K. doi:10.1088/0067-0049/213/2/34.
6. Kiminki, Daniel C.; Kobulnicky, Henry A.; Ewing, Ian; Bagley Kiminki, Megan M.; Lundquist, Michael; Alexander, Michael; Vargas-Alvarez, Carlos; Choi, Heather; Henderson, C. B. (2012-03-01). "Additional Massive Binaries in the Cygnus Ob2 Association". The Astrophysical Journal. 747 (1): 41. arXiv: 1112.3383 . Bibcode:2012ApJ...747...41K. doi:10.1088/0004-637X/747/1/41. ISSN   0004-637X.
7. "Simbad - Object view". simbad.cds.unistra.fr. Retrieved 2025-12-17.
8. "Cygnus OB2 #9". www.esa.int. Retrieved 2025-12-23.
9. Giudici Michilini, F. N.; Gamen, R.; Ferrero, G.; Morrell, N.; Barbá, R. (2025-11-01). "The Atlas of Massive Galactic O-type Spectral Standards (MaGOSS) in the Near-infrared". The Astrophysical Journal Supplement Series. 281 (1): 18. Bibcode:2025ApJS..281...18G. doi: 10.3847/1538-4365/ae0a51 . ISSN   0067-0049.
10. "NASA - X-ray Satellites Monitor the Clashing Winds of a Colossal Binary". www3.nasa.gov. Retrieved 2025-12-23.
11. Wiessinger, Scott (2012-10-12). "NASA Scientific Visualization Studio | X-ray Satellites Monitor the Clashing Winds of a Colossal Binary". NASA Scientific Visualization Studio. Retrieved 2025-12-23.