Cygnus OB2

Cygnus OB2 is an OB association that is home to some of the most massive and most luminous stars known, including suspected Luminous blue variable Cyg OB2 #12. It also includes one of the largest known stars, NML Cygni.[3] The region is embedded within a wider one of star formation known as Cygnus X, which is one of the most luminous objects in the sky at radio wavelengths. The region is approximately 1,570 parsecs from Earth in the constellation of Cygnus.[4]

Cygnus OB2
Cygnus OB2 in the light of H-Alpha; 3.5° view
Credit: IPHAS
Observation data (J2000.0 epoch)
ConstellationCygnus
Right ascension20h 33m 12s[1]
Declination41° 19′ 00″
Distance5.12 kly (1,570+80
−70 pc[2])
Apparent magnitude (V)6.1
Apparent dimensions (V)60.0′
Physical characteristics
Estimated age1 to 7 million years
Notable features–

The young cluster is one of the largest known and the largest in the northern hemisphere with some authors formerly classifying it as a young globular cluster similar to those in the Large Magellanic Cloud.[5] Today, however, it is considered a massive, low-density stellar association.[6]

Although it is over ten times more massive than the Orion Nebula, which is easily seen with the naked eye, Cygnus OB2 is hidden behind a massive dust cloud known as the Cygnus Rift, which obscures many of the stars in it. This means that despite its large size, it is hard to determine its actual properties. The estimated number of massive stars range from 50[7] to 100[5] of spectral type O and its total mass having been calculated as (4–10)×104[5] or 3×104 solar masses according to other investigations.[7]

Despite this, recent surveys ranging from radio to X-ray wavelengths have observed the region to great depths to gain a better understanding of how the processes of star and planet formation occur on such a large scale. These studies include observations with the Chandra X-ray Observatory, Spitzer Space Telescope, the Herschel Space Observatory and the Gran Telescopio Canarias. As for recent observations, the final stages of the process of photoablation is taking place, where the biggest stars formed and cleared the ambient material from the region.[8]

Prominent stars
Schulte number[9] MT number[9] Other name/CPR number[10] Spectral type[10][11] Luminosity[10](L☉) Mass[10][11](M☉)
HD 195213[12] O7 180300 43.3
WR 144 WC4 97000 >20
WR 145 WN7o/CE+O7V((f)) 371000 >25
WR 146 WC6+O8III 114000 >25
WR 147[13] WN8h+B0.5V 2000000 51
NML Cyg[14][15][16] M4.5–M7.9Ia–III 229000 50
V1827 Cyg/B17[12] Ofpe 242100 57
BD+40°4210[12][17] B1III:e 630000 54
BD+40 4223[12] B0Ia 539500 48.3
#1 59 O8.5V12000026
#2 83[18] B1I4000014
#3 O6IV+O9III346000>17 + >8
#4 217 O7III((f))15800029
#5 V729[19][20]O7I+O6I+O9V158400031 + 27 + 9
#6 317 O8V10900025
#7 457 O3If42600047
#8A 465[21] O6If+O5.5III(f)50100044 + 37
#8B 462 O6.5III(f)30100035
#8C 483 O5If37100042
#8D 473[22] O8.5V4800020
#9 431[20][23] O5–5.5I+O3–4III707000>34 + >30
#10 632 O9.5I47800037
#11 734[18] O5If53700044
#12 304[24] B3-4Ia+1230000110
#14 227 O9V 45000 19
#15 258 O8V 61000 22
#16 299 O8V 83000 23
#17 339 O8.5V 61000 21
#18 556 B1Ib33800029
#19 601 B0Iab 186000 26
#20 145 O9III 26000 17
#21 259 B0.5V 15000 13
#22 417 O3If+O6V(f)66000050
#23 470 O9.5V 26000 17
#24 480 O7.5V 104000 25
#25 531 O8.5V 97000 24
#26 642 B1III 69000 16
#27 696 O9.5V+B0V 30000 17
#29 745 O7V 87000 25
#30 793 B1.5III 33000 13
#37 358 B3V 3000 7
#41 378 B0V 44000 18
#51 425 B0V 27000 16
#54 395 B1V 7000 10
#64 488 B2Ve 23000 12
#66 515 B1V 10000 11
#70 588 B0V 48000 18
#71 646 B1.5V 6000 9
#73 O8III+O8III 41000 20
#74 555 O8V 109000 25
#75 736 O9V 31000 18
138[12] O8I 88700 26
267 A11[12] O7.5III 323000 35
448 O6V 107000 29
516[18] O5.5V((f))70700052
716 O9V 28000 18
771 O7V15100029
A12[12] B0Ia 373300 36
A15 O7I 263000 32
A20 O8II 380000 35
A23 B0.7Ib 263000 26
A24 O6.5III 154000 30
A25[12] O8III 88700 28
A27 B0Ia 426000 35
A29[12] O9.7Iab 167500 29.1
A32[12] O9.5IV 106700 26.1
A36 B0Ib+B0III 173000 26
A37[12] O5V((f)) 66100 34.8
A46[12] O7V((f)) 46600 25.6
E47 B0Ia 676000 42
IRAS 20321+4009[12] O9 278000 32
TYC 3156-998-1[12] OC9.7Ia 516000 34.2

The progenitor of BD+43°3654 might be a member in Cygnus OB2 before. Two stars of each binary would collide and merge forming BD+43°3654, that would be ejected from the stellar association along with two other stars. Prominent members of the association are often referred to by their Schulte numbers: for example Schulte 12, VI Cygni 12, or Cygnus OB2 #12. The numbers were first used in the 1953 discovery paper where 11 "blue giants" were numbered.[25] A 12th star (Cyg OB2 #12) was added in 1954,[26] and eight more shortly after.[27] Schulte himself maintained the already-published numbers and added many more when studying the association which he called VI Cygni.[9]

References
  1. "Ass Cyg OB 2". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2009-12-06.
  2. Parker, Richard J.; Crowther, Paul A.; Rate, Gemma (2020). "Unlocking Galactic Wolf–Rayet stars with Gaia DR2 – II. Cluster and association membership". Monthly Notices of the Royal Astronomical Society. 495 (1): 1209–1226. arXiv:2005.02533. Bibcode:2020MNRAS.495.1209R. doi:10.1093/mnras/staa1290. S2CID 218516882.
  3. Schuster, M. T.; Marengo, M.; Hora, J. L.; Fazio, G. G.; Humphreys, R. M.; Gehrz, R. D.; Hinz, P. M.; Kenworthy, M. A.; Hoffmann, W. F. (2009). "Imaging the Cool Hypergiant NML Cygni's Dusty Circumstellar Envelope with Adaptive Optics". The Astrophysical Journal. 699 (2): 1423–1432. arXiv:0904.4690. Bibcode:2009ApJ...699.1423S. doi:10.1088/0004-637X/699/2/1423. S2CID 17699562.
  4. Rygl, K.; Brunthaler, A.; Sanna, A.; Menten, K. M.; Reid, M. J.; van Langevelde, H. J.; Honma, M.; Torstensson, K. J. E.; Fujisawa, K. (March 2012). "Parallaxes and proper motions of interstellar masers toward the Cygnus X star-forming complex. I. Membership of the Cygnus X region". Astronomy and Astrophysics. 539: A79. arXiv:1111.7023. Bibcode:2012A&A...539A..79R. doi:10.1051/0004-6361/201118211. S2CID 54647474.
  5. Knödlseder, J. (2000). "Cygnus OB2—a young globular cluster in the Milky Way". Astronomy and Astrophysics. 360: 539. arXiv:astro-ph/0007442. Bibcode:2000A&A...360..539K.
  6. Wright, Nicholas J.; Parker, Richard J.; Goodwin, Simon P.; Drake, Jeremy J. (2014). "Constraints on massive star formation: Cygnus OB2 was always an association". Monthly Notices of the Royal Astronomical Society. 438 (1): 639–646. arXiv:1311.4537. Bibcode:2014MNRAS.438..639W. doi:10.1093/mnras/stt2232. S2CID 16957082.
  7. Wright, N. J.; Drake, J. J.; Drew, J. E.; Vink, J. S. (2010). "The Massive Star-Forming Region Cygnus OB2. II. Integrated Stellar Properties and the Star Formation History". The Astrophysical Journal. 713 (2): 871–882. arXiv:1003.2463. Bibcode:2010ApJ...713..871W. doi:10.1088/0004-637X/713/2/871. S2CID 118590238.
  8. Hartigan, P.; Palmer, J.; Cleeves, L.I. (2012). "Irradiated interfaces in the Ara OB1, Carina, Eagle Nebula, and Cyg OB2 massive star formation regions". High Energy Density Physics. 8 (4): 313. arXiv:1304.3930. Bibcode:2012HEDP....8..313H. doi:10.1016/j.hedp.2012.08.002. S2CID 118863688.
  9. Massey, P.; Thompson, A. B. (1991). "Massive stars in CYG OB2". The Astronomical Journal. 101: 1408. Bibcode:1991AJ....101.1408M. doi:10.1086/115774.
  10. Wright, Nicholas J.; Drew, Janet E.; Mohr-Smith, Michael (2015). "The massive star population of Cygnus OB2". Monthly Notices of the Royal Astronomical Society. 449 (1): 741–760. arXiv:1502.05718. Bibcode:2015MNRAS.449..741W. doi:10.1093/mnras/stv323. S2CID 119268358.
  11. Massey, P.; Degioia-Eastwood, K.; Waterhouse, E. (2001). "The Progenitor Masses of Wolf-Rayet Stars and Luminous Blue Variables Determined from Cluster Turnoffs. II. Results from 12 Galactic Clusters and OB Associations". The Astronomical Journal. 121 (2): 1050–1070. arXiv:astro-ph/0010654. Bibcode:2001AJ....121.1050M. doi:10.1086/318769. S2CID 53345173.
  12. Comerón, F.; Pasquali, A. (2012). "New members of the massive stellar population in Cygnus". Astronomy & Astrophysics. 110: 2715. Bibcode:2012A&A...543A.101C. doi:10.1051/0004-6361/201219022.
  13. Sota, A.; Maíz Apellániz, J.; Morrell, N. I.; Barbá, R. H.; Walborn, N. R.; Gamen, R. C.; Arias, J. I.; Alfaro, E. J.; Oskinova, L. M. (2019). "The Galactic WN stars revisited. Impact of Gaia distances on fundamental stellar parameters". Astronomy & Astrophysics. A57: 625. arXiv:1904.04687. Bibcode:2019A&A...625A..57H. doi:10.1051/0004-6361/201834850. S2CID 104292503.
  14. "GCVS Query=V1489 Cyg". Sternberg Astronomical Institute. General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. Retrieved 2018-09-21.
  15. Davies, Ben; Beasor, Emma R. (March 2020). "The 'red supergiant problem': the upper luminosity boundary of Type II supernova progenitors". MNRAS. 493 (1): 468–476. arXiv:2001.06020. Bibcode:2020MNRAS.493..468D. doi:10.1093/mnras/staa174. S2CID 210714093.
  16. Morris, M.; Jura, M. (1983). "The nature of NML Cygnus". Astrophysical Journal. 267: 179. Bibcode:1983ApJ...267..179M. doi:10.1086/160856.
  17. http://www.sciops.esa.int/SD/ESACFACULTY/docs/seminars/160212_Comeron.pdf Archived 2016-03-03 at the Wayback Machine In and around the rich association Cygnus OB2
  18. Herrero, A.; Puls, J.; Najarro, F. (2002). "Fundamental parameters of Galactic luminous OB stars VI. Temperatures, masses and WLR of Cyg OB2 supergiants". Astronomy and Astrophysics. 396 (3): 949–966. arXiv:astro-ph/0210469. Bibcode:2002A&A...396..949H. doi:10.1051/0004-6361:20021432. S2CID 16917437.
  19. Rauw, G.; Vreux, J. ‐M.; Bohannan, B. (1999). "The Interacting Early‐Type Binary BD +40°4220 (V729 Cyg): Modeling the Colliding Winds Region". The Astrophysical Journal. 517 (1): 416–430. Bibcode:1999ApJ...517..416R. doi:10.1086/307185.
  20. Kiminki, D. C.; Kobulnicky, H. A.; Ewing, I.; Bagley Kiminki, M. M.; Lundquist, M.; Alexander, M.; Vargas-Alvarez, C.; Choi, H.; Henderson, C. B. (2012). "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. S2CID 119203797.
  21. 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): 1280–1294. Bibcode:2006MNRAS.371.1280D. doi:10.1111/j.1365-2966.2006.10746.x.
  22. 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 Alvarez, 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. S2CID 118543368.
  23. Nazé, Y.; Mahy, L.; Damerdji, Y.; Kobulnicky, H. A.; Pittard, J. M.; Parkin, E. R.; Absil, O.; Blomme, R. (2012). "The 2.35 year itch of Cygnus OB2 #9". Astronomy & Astrophysics. 546: A37. arXiv:1209.5622. Bibcode:2012A&A...546A..37N. doi:10.1051/0004-6361/201219442. S2CID 119187102.
  24. Clark, J. S.; Najarro, F.; Negueruela, I.; Ritchie, B. W.; Urbaneja, M. A.; Howarth, I. D. (2012). "On the nature of the galactic early-B hypergiants". Astronomy & Astrophysics. 541: A145. arXiv:1202.3991. Bibcode:2012A&A...541A.145C. doi:10.1051/0004-6361/201117472. S2CID 11978733.
  25. 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.
  26. Morgan, W. W.; Johnson, H. L.; Roman, Nancy G. (1954). "A Very Red Star of Early Type in Cygnus". Publications of the Astronomical Society of the Pacific. 66 (389): 85. Bibcode:1954PASP...66...85M. doi:10.1086/126660.
  27. Morgan, W. W.; Meinel, A. B.; Johnson, Hugh M. (1954). "Spectral Classification with Exceedingly Low Dispersion". Astrophysical Journal. 120: 506. Bibcode:1954ApJ...120..506M. doi:10.1086/145938.
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