X-ray emission from massive stars in CYG OB2

Wright

Abstract

We report on the analysis of the Chandra-ACIS data of O, B, and WR stars in the young association Cyg OB2. X-ray spectra of 49 O-stars, 54 B-stars, and 3 WR-stars are analyzed and for the brighter sources, the epoch dependence of the X-ray fluxes is investigated. The O-stars in Cyg OB2 follow a well-defined scaling relation between their X-ray and bolometric luminosities: $\mathrm{log}\;\frac{{L}_{{\rm{X}}}}{{L}_{\mathrm{bol}}}=-7.2\pm 0.2$. This relation is in excellent agreement with the one previously derived for the Carina OB1 association. Except for the brightest O-star binaries, there is no general X-ray overluminosity due to colliding winds in O-star binaries. Roughly half of the known B-stars in the surveyed field are detected, but they fail to display a clear relationship between LX and Lbol. Out of the three WR stars in Cyg OB2, probably only WR 144 is itself responsible for the observed level of X-ray emission, at a very low $\mathrm{log}\;\frac{{L}_{{\rm{X}}}}{{L}_{\mathrm{bol}}}=-8.8\pm 0.2$. The X-ray emission of the other two WR-stars (WR 145 and 146) is most probably due to their O-type companion along with a moderate contribution from a wind–wind interaction zone.

Citation

Wright. (2015). X-ray emission from massive stars in CYG OB2. Astrophysical Journal Supplement, https://doi.org/10.1088/0067-0049/221/1/1

• Acceptance Date: Jan 28, 2014
• Publication Date: Oct 6, 2015
• Journal: Astrophysical Journal Supplement
• Print ISSN: 0067-0049
• Publisher: American Astronomical Society
• DOI: https://doi.org/10.1088/0067-0049/221/1/1
• Keywords: open clusters and associations, individual (Cyg OB2), stars, early-type, Wolf–Rayet, x-rays
• Publisher URL: http://dx.doi.org/10.1088/0067-0049/221/1/1