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Session 61 - New Views of the Magellanic Clouds.
Display session, Wednesday, June 12
Great Hall,

[61.08] Energetics and Hot Gas of the Supergiant Shell LMC2

S. D. Points, Y. -H. Chu, D. J. Bomans (U. Illinois), R. C. Smith (U. Michigan)

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