Notes for Editors

“The 2.35 years itch of Cyg OB2 #9 I. Optical and X-ray monitoring” by Y. Nazé et al., is accepted for publication in Astronomy & Astrophysics.

Animation caption:

Colliding winds at Cyg OB 2 #9
Evidence for colliding stellar winds in the Cyg OB2 #9 binary system was only found as the two stars neared the closest point on their 2.4-year orbit around each other. As the stars approach each other the fierce stellar winds slammed together at speeds of several million kilometres per hour, generating hot plasma at a million degrees which then shone brightly in X-rays. The emission falls away as the two stars move away from each other.

The animation begins by tracing the orbits of the two stars, before presenting X-ray data from ESA’s XMM-Newton and NASA’s Swift space telescopes during observing opportunities of Cyg OB2 #9 in 2011. The corresponding positions of the stars along their orbits are illustrated in the animation inset.

Credits: NASA Goddard Space Flight Center

Colliding winds at WR 22
This computer simulation shows the gas density around a colliding wind binary named WR 22. The star locations are marked by yellow dots, and decreasing gas density is indicated by the sequence of red, white and blue colours. In this simulation, a 26 solar mass O-type star orbits the hotter and more massive 72 solar mass Wolf-Rayet star WR 22. During closest approach, the more massive star's stellar wind is so intense that the collision region is forced back onto the O star. Such a collapse of the wind region does not occur with Cygnus OB2 #9, which makes it a well-behaved and important example of wind-wind interactions.

Credits: University of Liège/Australian National University/E. R. Parkin and E. Gosset

For further information, please contact:

Markus Bauer 

ESA Science and Robotic Exploration Communication Officer

Tel: +31 71 565 6799

Mob: +31 61 594 3 954


Yael Nazé

Université de Liège, Belgium


Norbert Schartel

XMM-Newton Project Scientist

Tel: +34 91 8131 184


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