X-ray grating and optical image of Cyg OB2
Credit: X-ray: Wayne Waldron et al., 2004, The Astrophysical Journal, Vol. 616, pg. 542; optical: Digitized Sky Survey

Hot Association

One major finding of the Einstein X-ray Observatory was the discovery of X-rays from the massive stars in the Cygnus OB2 stellar association. This discovery immediately spawned a controversy about how the X-rays were made, via magnetic processes near the star as in the case of the Sun, or from strong shocks far from the star. Now a new observations of Cyg OB2 with the High Energy Transmission Grating on the Chandra X-ray Observatory has clarified some areas but deepened some mysteries. The image at the very top shows a "true color" image of the field around the star Cygnus OB2 #8a (the locations of stars #8a, 9, 12, & 5 are indicated) along with dispersed X-ray spectra from a number of these sources, where color indicates the energy of the X-ray photon. Notice that spectra from different sources can cross, or can intersect the locations of stars, complicating the analysis. The middle panel shows an X-ray image of this field with identified X-ray sources indicated. Finally the bottom panel shows the locations of the identified sources on an optical image. These X-ray spectra allow astronomers to study the motion of the X-ray emitting plasma and to determine how deeply the X-ray gas is embedded in the winds which continually blow from these stars.

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Page Author: Dr. Michael F. Corcoran
Last modified Friday, 20-Apr-2012 15:27:16 EDT