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Diffuse X-Ray Emission in the Cygnus OB2 Association

Albacete-Colombo, J. F.; Drake, J. J.; Flaccomio, E.; Wright, N. J.; Kashyap, V.; Guarcello, M. G.; Briggs, K.; Drew, J. E.; Fenech, D. M.; Micela, G.; McCollough, M.; Prinja, R. K.; Schneider, N.; Sciortino, S.; Vink, J. S.


J. F. Albacete-Colombo

J. J. Drake

E. Flaccomio

V. Kashyap

M. G. Guarcello

K. Briggs

J. E. Drew

D. M. Fenech

G. Micela

M. McCollough

R. K. Prinja

N. Schneider

S. Sciortino

J. S. Vink


We present a large-scale study of diffuse X-ray emission in the nearby massive stellar association Cygnus OB2 as part of the Chandra Cygnus OB2 Legacy Program. We used 40 Chandra X-ray ACIS-I observations covering ∼1.0 deg2. After removing 7924 point sources detected in our survey and applying adaptive smoothing to the background-corrected X-ray emission, the adaptive smoothing reveals large-scale diffuse X-ray emission. Diffuse emission was detected in the subbands soft (0.5−1.2 keV) and medium (1.2−2.5 keV) and marginally in the hard (2.5−7.0 keV) band. From X-ray spectral analysis of stacked spectra we compute a total (0.5–7.0 keV) diffuse X-ray luminosity of LXdiff≈ 4.2 × 1034 erg s−1, characterized by plasma temperature components at kT ≈ 0.11, 0.40, and 1.18 keV, respectively. The H i absorption column density corresponding to these temperatures has a distribution consistent with N H = (0.43, 0.80, 1.39) × 1022 cm−2. The extended medium-band energy emission likely arises from O-type stellar winds thermalized by wind−wind collisions in the most populated regions of the association, while the soft-band emission probably arises from less energetic termination shocks against the surrounding interstellar medium. Supersoft and soft diffuse emission appears more widely dispersed and intense than the medium-band emission. The diffuse X-ray emission is generally spatially coincident with low-extinction regions that we attribute to the ubiquitous influence of powerful stellar winds from massive stars and their interaction with the local interstellar medium. Diffuse X-ray emission is volume filling, rather than edge brightened, oppositely to other star-forming regions. We reveal the first observational evidence of X-ray halos around some evolved massive stars.

Journal Article Type Article
Acceptance Date May 31, 2018
Online Publication Date Oct 25, 2023
Publication Date Nov 1, 2023
Deposit Date Oct 30, 2023
Publicly Available Date Oct 30, 2023
Journal The Astrophysical Journal Supplement Series
Print ISSN 0067-0049
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 269
Issue 1
Article Number 14
Keywords Massive stars, Stellar winds, X-ray stars


Diffuse X-Ray Emission in the Cygnus OB2 Association (16.6 Mb)

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Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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