Cygnus OB2
{{Short description|Cluster of massive and luminous stars}}
{{Technical reasons|Cygnus OB2 #8A|this star|Cygnus OB2-8A}}
{{Technical reasons|Cygnus OB2 #12|this star|Cygnus OB2-12}}
{{Infobox open cluster|
| name = Cygnus OB2
| image=Image:CygOB2 med.jpg
| image_size=250px
| caption=Cygnus OB2 in the light of H-Alpha; 3.5° view
| credit = IPHAS
| epoch = J2000.0
| class =
| ra = {{RA|20|33|12}}{{cite simbad
| title=Ass Cyg OB 2
| access-date=2009-12-06}}
| dec = {{DEC|41|19|00}}
| constellation = Cygnus
| dist_ly = 5.12 kly
| dist_pc = {{val|1570|80|70|fmt=commas|ul=pc}}{{cite journal|arxiv=2005.02533|doi=10.1093/mnras/staa1290|title=Unlocking Galactic Wolf–Rayet stars with Gaia DR2 – II. Cluster and association membership|year=2020|last1=Parker|first1=Richard J.|last2=Crowther|first2=Paul A.|last3=Rate|first3=Gemma|journal=Monthly Notices of the Royal Astronomical Society|volume=495|issue=1|pages=1209–1226|doi-access=free |bibcode=2020MNRAS.495.1209R|s2cid=218516882}}
| appmag_v = 6.1
| size_v = 60.0{{prime}}
| age = 1 to 7 million years
| notes = –
}}
File:X-ray Satellites Monitor the Clashing Winds of a Colossal Binary.ogv
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.{{Cite journal | last1 = Schuster | first1 = M. T. | last2 = Marengo | first2 = M. | last3 = Hora | first3 = J. L. | last4 = Fazio | first4 = G. G. | last5 = Humphreys | first5 = R. M. | last6 = Gehrz | first6 = R. D. | last7 = Hinz | first7 = P. M. | last8 = Kenworthy | first8 = M. A. | last9 = Hoffmann | first9 = W. F. | doi = 10.1088/0004-637X/699/2/1423 | title = Imaging the Cool Hypergiant NML Cygni's Dusty Circumstellar Envelope with Adaptive Optics | journal = The Astrophysical Journal | volume = 699 | issue = 2 | pages = 1423–1432 | year = 2009 |arxiv = 0904.4690 |bibcode = 2009ApJ...699.1423S | s2cid = 17699562 }} 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.{{cite journal
|last=Rygl|first=K.
|author2=Brunthaler, A.
|author3=Sanna, A.
|author4=Menten, K. M.
|author5=Reid, M. J.
|author6=van Langevelde, H. J.
|author7=Honma, M.
|author8=Torstensson, K. J. E.
|author9=Fujisawa, K.
|title=Parallaxes and proper motions of interstellar masers toward the Cygnus X star-forming complex. I. Membership of the Cygnus X region
|journal=Astronomy and Astrophysics|date=March 2012|volume=539|page=A79|doi=10.1051/0004-6361/201118211|bibcode=2012A&A...539A..79R
|arxiv = 1111.7023 |s2cid=54647474
}}
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.{{cite journal|bibcode=2000A&A...360..539K|title=Cygnus OB2—a young globular cluster in the Milky Way|journal=Astronomy and Astrophysics|volume=360|pages=539|last1=Knödlseder|first1=J.|year=2000|arxiv = astro-ph/0007442 }} Today, however, it is considered a massive, low-density stellar association.{{cite journal|bibcode=2014MNRAS.438..639W|title=Constraints on massive star formation: Cygnus OB2 was always an association|journal=Monthly Notices of the Royal Astronomical Society|volume=438|pages=639–646|last1=Wright|first1=Nicholas J.|last2=Parker|first2=Richard J.|last3=Goodwin|first3=Simon P.|last4=Drake|first4=Jeremy J.|year=2014|issue=1|doi=10.1093/mnras/stt2232|doi-access=free |arxiv = 1311.4537 |s2cid=16957082}}
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{{Cite journal | last1 = Wright | first1 = N. J. | last2 = Drake | first2 = J. J. | last3 = Drew | first3 = J. E. | last4 = Vink | first4 = J. S. | title = The Massive Star-Forming Region Cygnus OB2. II. Integrated Stellar Properties and the Star Formation History | doi = 10.1088/0004-637X/713/2/871 | journal = The Astrophysical Journal | volume = 713 | issue = 2 | pages = 871–882 | year = 2010 |arxiv = 1003.2463 |bibcode = 2010ApJ...713..871W | s2cid = 118590238 }} to 100 of spectral type O and its total mass having been calculated as (4–10){{e|4}} or 3{{e|4}} solar masses according to other investigations.
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.{{Cite journal|arxiv=1304.3930|doi=10.1016/j.hedp.2012.08.002|title=Irradiated interfaces in the Ara OB1, Carina, Eagle Nebula, and Cyg OB2 massive star formation regions|journal=High Energy Density Physics|volume=8|issue=4|pages=313|year=2012|last1=Hartigan|first1=P.|last2=Palmer|first2=J.|last3=Cleeves|first3=L.I.|bibcode = 2012HEDP....8..313H |s2cid=118863688}}
class="wikitable sortable"
|+ Prominent stars | |||
style="background:#efefef;" valign="top" width="120" align="center" | Schulte number
! style="background:#efefef;" valign="top" width="120" align="center" | MT number{{Cite journal | last1 = Massey | first1 = P. | last2 = Thompson | first2 = A. B. | doi = 10.1086/115774 | title = Massive stars in CYG OB2 | journal = The Astronomical Journal | volume = 101 | pages = 1408 | year = 1991 |bibcode = 1991AJ....101.1408M }} ! style="background:#efefef;" valign="top" width="190" align="center" | Other name/CPR number{{cite journal|bibcode=2015MNRAS.449..741W|title=The massive star population of Cygnus OB2|journal=Monthly Notices of the Royal Astronomical Society|volume=449|pages=741–760|last1=Wright|first1=Nicholas J.|last2=Drew|first2=Janet E.|last3=Mohr-Smith|first3=Michael|year=2015|issue=1|doi=10.1093/mnras/stv323|doi-access=free |arxiv=1502.05718|s2cid=119268358}} ! style="background:#efefef;" valign="top" width="140" align="center" | Spectral type{{Cite journal | last1 = Massey | first1 = P. | last2 = Degioia-Eastwood | first2 = K.|author2-link=Kathy Eastwood | last3 = Waterhouse | first3 = E. | doi = 10.1086/318769 | title = The Progenitor Masses of Wolf-Rayet Stars and Luminous Blue Variables Determined from Cluster Turnoffs. II. Results from 12 Galactic Clusters and OB Associations | journal = The Astronomical Journal | volume = 121 | issue = 2 | pages = 1050–1070 | year = 2001 |arxiv = astro-ph/0010654 |bibcode = 2001AJ....121.1050M | s2cid = 53345173 }} ! style="background:#efefef;" valign="top" width="120" align="center" | Luminosity ! style="background:#efefef;" valign="top" width="120" align="center" | Mass | |||
---|---|---|---|
|
|O7 | align="center" | 180,300 | align="center" | 43.3 | |||
|
| align="center" | WR 144 |WC4 | align="center" | 158,500 | align="center" | 9.9 | |||
|
| align="center" | WR 145 |WN7o/CE+O7V((f)) | align="center" | 371,000 | align="center" | 18.3 | |||
|
| align="center" | WR 146 |WC6+O8III | align="center" | 115,000 | align="center" | 8?+? | |||
|
| align="center" |WR 147{{cite journal|arxiv=1904.04687|last1=Sota|first1=A.|title=The Galactic WN stars revisited. Impact of Gaia distances on fundamental stellar parameters|journal=Astronomy & Astrophysics|volume=A57|pages=625|last2=Maíz Apellániz|first2=J.|last3=Morrell|first3=N. I.|last4=Barbá|first4=R. H.|last5=Walborn|first5=N. R.|last6=Gamen|first6=R. C.|last7=Arias|first7=J. I.|last8=Alfaro|first8=E. J.|last9=Oskinova|first9=L. M.|year=2019|doi=10.1051/0004-6361/201834850|bibcode=2019A&A...625A..57H|s2cid=104292503}} |WN8h+B0.5V | align="center" |2,000,000 | align="center" |51 | |||
|
| align="center" | NML Cyg{{cite web |title=GCVS Query=V1489 Cyg |publisher=General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia |url=http://www.sai.msu.su/gcvs/cgi-bin/search.cgi?search=V1489+Cyg |access-date=2018-09-21|website=Sternberg Astronomical Institute}}{{Cite journal|last1=Davies|first1=Ben|last2=Beasor|first2=Emma R.|s2cid=210714093|date=March 2020|title=The 'red supergiant problem': the upper luminosity boundary of Type II supernova progenitors|bibcode=2020MNRAS.493..468D|journal=MNRAS|language=en|volume=493|issue=1|pages=468–476|doi=10.1093/mnras/staa174|doi-access=free |arxiv=2001.06020 }}{{cite journal|bibcode=1983ApJ...267..179M|title=The nature of NML Cygnus|journal=Astrophysical Journal|volume=267|pages=179|last1=Morris|first1=M.|last2=Jura|first2=M.|year=1983|doi=10.1086/160856|doi-access=free}} |M4.5–M7.9Ia–III | align="center" | 229,000 | align="center" | 50 | |||
|
| align="center" | V1827 Cyg/B17 |Ofpe | align="center" | 242,100 | align="center" | 57 | |||
|
| align="center" | BD+40°4210{{cite journal| volume = 110| pages = 2715| last1 = Comerón| first1 = F.| last2 = Pasquali| first2 = A.| title = New members of the massive stellar population in Cygnus| journal = Astronomy & Astrophysics| year = 2012|bibcode = 2012A&A...543A.101C| doi = 10.1051/0004-6361/201219022| doi-access = free}}http://www.sciops.esa.int/SD/ESACFACULTY/docs/seminars/160212_Comeron.pdf {{Webarchive|url=https://web.archive.org/web/20160303225600/http://www.sciops.esa.int/SD/ESACFACULTY/docs/seminars/160212_Comeron.pdf |date=2016-03-03 }} In and around the rich association Cygnus OB2 |B1III:e | align="center" | 630,000 | align="center" | 54 | |||
|
|B0Ia | align="center" | 539,500 | align="center" | 48.3 | |||
align="center" | #1
| align="center" | 59 | | O8.5V | align="center" | 120,000 | align="center" | 26 |
align="center" | #2
| | B1I | align="center" | 40,000 | align="center" | 14 |
align="center" | #3
| align="center" | | | O6IV+O9III | align="center" | 346,000 | align="center" | >17 + >8 |
align="center" | #4
| align="center" | 217 | | O7III((f)) | align="center" | 158,000 | align="center" | 29 |
align="center" | #5
| align="center" | | align="center" | V729{{Cite journal|last1=Rauw|first1=G.|last2=Vreux|first2=J. -M.|last3=Bohannan|first3=B.|year=1999|title=The Interacting Early-Type Binary BD +40°4220 (V729 Cyg): Modeling the Colliding Winds Region|journal=The Astrophysical Journal|volume=517|issue=1|pages=416–430|bibcode=1999ApJ...517..416R|doi=10.1086/307185|doi-access=free}}{{Cite journal|last1=Kiminki|first1=D. C.|last2=Kobulnicky|first2=H. A.|last3=Ewing|first3=I.|last4=Bagley Kiminki|first4=M. M.|last5=Lundquist|first5=M.|last6=Alexander|first6=M.|last7=Vargas-Alvarez|first7=C.|last8=Choi|first8=H.|last9=Henderson|first9=C. B.|year=2012|title=Additional Massive Binaries in the Cygnus OB2 Association|journal=The Astrophysical Journal|volume=747|issue=1|pages=41|arxiv=1112.3383|bibcode=2012ApJ...747...41K|doi=10.1088/0004-637X/747/1/41|s2cid=119203797}} | O7I+O6I+O9V | align="center" | 1584000 | align="center" | 31 + 27 + 9 |
align="center" | #6
| align="center" | 317 | | O8V | align="center" | 109,000 | align="center" | 25 |
align="center" | #7
| align="center" | 457 | | O3If | align="center" | 426,000 | align="center" | 47 |
align="center" | #8A
| | O6If+O5.5III(f) | align="center" | 501,000 | align="center" | 44 + 37 |
align="center" | #8B
| align="center" | 462 | | O6.5III(f) | align="center" | 301,000 | align="center" | 35 |
align="center" | #8C
| align="center" | 483 | | O5If | align="center" | 371,000 | align="center" | 42 |
align="center" | #8D
| | O8.5V | align="center" | 48,000 | align="center" | 20 |
align="center" | #9
| align="center" | 431{{Cite journal | last1 = Nazé | first1 = Y. | last2 = Mahy | first2 = L. | last3 = Damerdji | first3 = Y. | last4 = Kobulnicky | first4 = H. A. | last5 = Pittard | first5 = J. M. | last6 = Parkin | first6 = E. R. | last7 = Absil | first7 = O. | last8 = Blomme | first8 = R. | doi = 10.1051/0004-6361/201219442 | title = The 2.35 year itch of Cygnus OB2 #9 | journal = Astronomy & Astrophysics | volume = 546 | pages = A37 | year = 2012 |arxiv = 1209.5622 |bibcode = 2012A&A...546A..37N | s2cid = 119187102 }} | | O5–5.5I+O3–4III | align="center" | 707,000 | align="center" | >34 + >30 |
align="center" | #10
| align="center" | 632 | | O9.5I | align="center" | 478,000 | align="center" | 37 |
align="center" | #11
| | O5If | align="center" | 537,000 | align="center" | 44 |
align="center" | #12
| | B3-4Ia+ | align="center" | 1,230,000 | align="center" | 110 |
align="center" | #14
| align="center" | 227 | |O9V | align="center" | 45,000 | align="center" | 19 | |||
align="center" | #15
| align="center" | 258 | |O8V | align="center" | 61,000 | align="center" | 22 | |||
align="center" | #16
| align="center" | 299 | |O8V | align="center" | 83,000 | align="center" | 23 | |||
align="center" | #17
| align="center" | 339 | |O8.5V | align="center" | 61,000 | align="center" | 21 | |||
align="center" | #18
| align="center" | 556 | | B1Ib | align="center" | 338,000 | align="center" | 29 |
align="center" | #19
| align="center" | 601 | |B0Iab | align="center" | 186,000 | align="center" | 26 | |||
align="center" | #20
| align="center" | 145 | |O9III | align="center" | 26,000 | align="center" | 17 | |||
align="center" | #21
| align="center" | 259 | |B0.5V | align="center" | 15,000 | align="center" | 13 | |||
align="center" | #22
| align="center" | 417 | | O3If+O6V(f) | align="center" | 660,000 | align="center" |50 |
align="center" | #23
| align="center" | 470 | |O9.5V | align="center" | 26,000 | align="center" | 17 | |||
align="center" | #24
| align="center" | 480 | |O7.5V | align="center" | 104,000 | align="center" | 25 | |||
align="center" | #25
| align="center" | 531 | |O8.5V | align="center" | 97,000 | align="center" | 24 | |||
align="center" | #26
| align="center" | 642 | |B1III | align="center" | 69,000 | align="center" | 16 | |||
align="center" | #27
| align="center" | 696 | |O9.5V+B0V | align="center" | 30,000 | align="center" | 17 | |||
align="center" | #29
| align="center" | 745 | |O7V | align="center" | 87,000 | align="center" | 25 | |||
align="center" | #30
| align="center" | 793 | |B1.5III | align="center" | 33,000 | align="center" | 13 | |||
align="center" | #37
| align="center" | 358 | |B3V | align="center" | 3,000 | align="center" | 7 | |||
align="center" | #41
| align="center" | 378 | |B0V | align="center" | 44,000 | align="center" | 18 | |||
align="center" | #51
| align="center" | 425 | |B0V | align="center" | 27,000 | align="center" | 16 | |||
align="center" | #54
| align="center" | 395 | |B1V | align="center" | 7,000 | align="center" | 10 | |||
align="center" | #64
| align="center" | 488 | |B2Ve | align="center" | 23,000 | align="center" | 12 | |||
align="center" | #66
| align="center" | 515 | |B1V | align="center" | 10,000 | align="center" | 11 | |||
align="center" | #70
| align="center" | 588 | |B0V | align="center" | 48,000 | align="center" | 18 | |||
align="center" | #71
| align="center" | 646 | |B1.5V | align="center" | 6,000 | align="center" | 9 | |||
align="center" | #73
| | |O8III+O8III | align="center" | 41,000 | align="center" | 20 | |||
align="center" | #74
| align="center" | 555 | |O8V | align="center" | 109,000 | align="center" | 25 | |||
align="center" | #75
| align="center" | 736 | |O9V | align="center" | 31,000 | align="center" | 18 | |||
| align="center" | 138
| |O8I | align="center" | 88,700 | align="center" | 26 | |||
| align="center" | 267
|O7.5III | align="center" | 323,000 | align="center" | 35 | |||
| align="center" | 448
| |O6V | align="center" | 107,000 | align="center" | 29 | |||
align="center" |
| | O5.5V((f)) | align="center" | 707,000 | align="center" | 52 |
| align="center" | 716
| |O9V | align="center" | 28,000 | align="center" | 18 | |||
align="center" |
| align="center" | 771 | | O7V | align="center" | 151,000 | align="center" | 29 |
|
|B0Ia | align="center" | 373,300 | align="center" | 36 | |||
|
| align="center" | A15 |O7I | align="center" | 263,000 | align="center" | 32 | |||
|
| align="center" | A20 |O8II | align="center" | 380,000 | align="center" | 35 | |||
|
| align="center" | A23 |B0.7Ib | align="center" | 263,000 | align="center" | 26 | |||
|
| align="center" | A24 |O6.5III | align="center" | 154,000 | align="center" | 30 | |||
|
|O8III | align="center" | 88,700 | align="center" | 28 | |||
|
| align="center" | A27 |B0Ia | align="center" | 426,000 | align="center" | 35 | |||
|
|O9.7Iab | align="center" | 167,500 | align="center" | 29.1 | |||
|
|O9.5IV | align="center" | 106,700 | align="center" | 26.1 | |||
|
| align="center" | A36 |B0Ib+B0III | align="center" | 173,000 | align="center" | 26 | |||
|
|O5V((f)) | align="center" | 66,100 | align="center" | 34.8 | |||
|
|O7V((f)) | align="center" | 46,600 | align="center" | 25.6 | |||
|
| align="center" | E47 |B0Ia | align="center" | 676,000 | align="center" | 42 | |||
|
| align="center" | IRAS 20321+4009 |O9 | align="center" | 278,000 | align="center" | 32 | |||
|
| align="center" | TYC 3156-998-1 |OC9.7Ia | align="center" | 516,000 | align="center" | 34.2 |
The progenitor of BD+43°3654 might have been a member of Cygnus OB2. Two stars from two binaries would have collided and merged forming BD+43°3654, which would have then been ejected from the stellar association along with the two remaining stars.
{{cite journal
| volume = 485
| issue = 3
| pages = L29–L32
| last1 = Gvaramadze
| first1 = V. V.
| last2 = Bomans
| first2 = D. J.
| title = BD+43 3654 - a blue straggler?
| journal = Astronomy & Astrophysics
| year = 2008
|bibcode = 2008A&A...485L..29G
| doi = 10.1051/0004-6361:200809860
|arxiv = 0805.3893 | s2cid = 18755032
}}
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.{{cite journal|bibcode=1953ApJ...118..161M|title=Notes: A Probable Clustering of Blue Giants in Cygnus|journal=Astrophysical Journal|volume=118|pages=161|last1=Münch|first1=Luis|last2=Morgan|first2=W. W.|year=1953|doi=10.1086/145737|doi-access=free}} A 12th star (Cyg OB2 #12) was added in 1954,{{cite journal|bibcode=1954PASP...66...85M|title=A Very Red Star of Early Type in Cygnus|journal=Publications of the Astronomical Society of the Pacific|volume=66|pages=85|last1=Morgan|first1=W. W.|last2=Johnson|first2=H. L.|last3=Roman|first3=Nancy G.|year=1954|issue=389|doi=10.1086/126660|doi-access=free}} and eight more shortly after.{{cite journal|bibcode=1954ApJ...120..506M|title=Spectral Classification with Exceedingly Low Dispersion|journal=Astrophysical Journal|volume=120|pages=506|last1=Morgan|first1=W. W.|last2=Meinel|first2=A. B.|last3=Johnson|first3=Hugh M.|year=1954|doi=10.1086/145938}} Schulte himself maintained the already-published numbers and added many more when studying the association which he called VI Cygni.
Cygnus OB2 contains embedded star clusters as well as two open clusters located in the center of Cygnus OB2. The open clusters are called Bica 1 and Bica 2. Both Bica 1 and Bica 2 contain several OB-stars, such as Cygnus OB2 #8A and Cygnus OB2 #22.{{Cite journal |last1=Bica |first1=E. |last2=Bonatto |first2=Ch. |last3=Dutra |first3=C. M. |date=2003-07-01 |title=Does Cyg OB2 harbour any open cluster? |bibcode=2003A&A...405..991B |journal=Astronomy and Astrophysics |volume=405 |issue=3 |pages=991–998 |doi=10.1051/0004-6361:20030700 |issn=0004-6361|hdl=10183/108028 |hdl-access=free }}
{{Multiple image
| image1 = Bica1 HST.jpg
| caption1 = Open cluster Bica 1
| image2 = Bica2 HST.jpg
| caption2 = Part of open cluster Bica 2
| total_width = 700
| direction = horizontal
| align = center
}}
References
{{Reflist|2}}
{{Cygnus (constellation)}}
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