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Session 61 - New Views of the Magellanic Clouds.
Display session, Wednesday, June 12
LMC2 is the most spectacular supergiant shell in the Large Magellanic Cloud, having the most coherent filamentary structure and the highest X-ray surface brightness. We have obtained high-dispersion echelle data to study its dynamics, and analyzed its X-ray emission to examine the hot gas content.
The echelle observations reveal two dominant H\alpha velocity components (V_hel \sim 250 km/s and 275 km/s) across LMC2, corresponding to two observed HI velocities over an area much more extended than LMC2. Therefore, we conclude that LMC2, instead of being a simple expanding shell as previously suggested, is blown between two sheets of HI gas.
ROSAT PSPC images of LMC2 show excellent correspondence between the boundary of X-ray emission and the H\alpha filaments, implying the association of hot (10^6 K) plasma with the LMC2 interior. Two prominent features are seen in the X-ray images: a region of low surface brightness caused by the shadow of a foreground HI cloud, and an arc of enhanced emission extending eastward from the active star formation regions N158/N160/N159.
High-velocity (with \DeltaV > 50 km/s) gas is detected at the aforementioned X-ray arc as well as the northeastern rim of LMC2. This indicates that interstellar shocks are responsible for heating the X-ray-emitting plasma. The origin of the shocks and the formation of the supergiant shell will be discussed.
Program listing for Wednesday