Chandra observations of Cygnus OB2

N.J. Wright, Jeremy J. Drake, J.E. Drew, Jorick S. Vink

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Abstract

Cygnus OB2 is the nearest example of a massive star forming region, containing over 50 O-type stars and hundreds of B-type stars.We have analyzed two Chandra pointings in Cyg OB2, detecting ∼1,700 X-ray sources, of which ∼1,450 are thought to be members of the association. Optical and near-IR photometry has been obtained for ∼90% of these sources from recent deep Galactic plane surveys. We have performed isochrone fits to the near-IR color-magnitude diagram, deriving ages of 3.5-1.0 +0.75 and 5.25-1.0 +0.75 Myrs for sources in the two fields, both with considerable spreads around the pre-MS isochrones. The presence of a second population in the region, somewhat older than the present-day O-type stars, has been suggested by other authors and fits with the ages derived here. The fraction of sources with inner circumstellar disks (as traced by the K-band excess) is found to be very low, but appropriate for a population of age∼5Myrs.We measure the stellar mass functions and find a power-law slope of Γ = -1.09±0.13, in good agreement with the global mean value estimated by Kroupa. A steepening of the mass function at high masses is observed and we suggest this is due to the presence of the previous generation of stars that have lost their most massive members. Finally, combining our mass function and an estimate of the radial density profile of the association suggests a total mass of Cyg OB2 of ∼ 3 × 104M ⊙ similar to that of many of our Galaxy's most massive star forming regions.
Original languageEnglish
Title of host publicationStar Clusters in the Era of Large Surveys
Subtitle of host publicationProceedings of Symposium 5 of JENAM 2010
EditorsA. Moitinho, J. Alves
PublisherSpringer Nature
Pages179-184
Number of pages6
ISBN (Electronic)978-3-642-22113-2
ISBN (Print)978-364222112-5
DOIs
Publication statusPublished - 2012
Event5th JENAM Symposium - Lisbon, Portugal
Duration: 9 Sept 201010 Sept 2010

Publication series

NameAstrophysics and Space Science Proceedings

Conference

Conference5th JENAM Symposium
Country/TerritoryPortugal
Period9/09/1010/09/10

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