Wrigge, M.; Chu, Y.-H.; Magnier, E. A.; Kamata, Y.

Journal: Lecture Notes in Physics, vol.506, The Local Bubble and Beyond. Lyman-Spitzer Colloquium, 1997, XXVII, edited by D. Breitschwerdt, M. J. Freyberg, and J. Truemper, pp. 425-428

Abstract

We present ASCA SIS observations of the wind-blown bubble NGC 6888. Because the ASCA SIS is sensitive to higher energy photons and has a higher spectral resolution compared to the ROSAT PSPC, we are able to detect a T ~ 8 x 10^6 K plasma component besides the T ~ 1.5 x 10^6 K component known from previous PSPC observations. The existence of a high-temperature component, the observed limb-brightened X-ray surface brightness profile, and the observed level of X-ray surface brightness cannot be satisfactorily explained by currently available models. Reducing heat conduction at the contact discontinuity may raise the central temperature and produce a limb-brightening; however, the expected X-ray surface brightness is still considerably higher than the observed surface brightness.