PROBING THE INTERSTELLAR-MEDIUM OF THE SUPERBUBBLE LMC2 IN THE LARGE MAGELLANIC CLOUD .1. TI-II AND CA-II ABSORPTION-LINES

The optical interstellar absorption lines of Ti II and Ca II have been observed at high resolution toward seven OB supergiant stars in the L arge Magellanic Cloud. The star lines of sight sample the disks and ha los of both the Galaxy and the LMC, H I clouds in the LMC, and the fil amentary superstructure of ionized gas known as the Superbubble LMC2 n ear the 30 Doradus nebula. We have measured the velocities, equivalent widths, column densities, and Doppler widths of Ca II and Ti II absor ption lines detected over the whole range of velocities from -30 to +3 60 km s(-1) between the Galaxy and the LMC. There is interstellar abso rption at velocities measured for the Ha emission-line gas of the supe rbubble and its surrounding giant H II regions and for the H I gas com ponents toward this region of the LMC. Absorbing gas is also found at intermediate velocities between 150 and 220 km s(-1), possibly identif ied with superbubble gas expanding into the LMC halo. The velocities a bove 150 km s(-1) can be interpreted as three-dimensional motions of s uperbubble gas expanding in the surrounding medium in the framework of two existing representations of the large-scale distribution of H I L MC gas. The first picture consists of overlapping H I sheets at separa te velocities; the interpretation of velocity components follows our p revious kinematical study of the H alpha LMC2 filaments. The second pi cture consists of two main components, the rotating LMC disk (D) and a lower velocity H I component (L); the correlations between H alpha, H I, and absorption velocities suggest that LMC2 is expanding into the H I component L; perhaps its origin comes from cloud collisions betwee n the components L and D. The remarkable extended absorption wings fou nd between 150 and 220 km s(-1) and the high-velocity absorption compo nents at similar to 300 km s(-1) are located in front of the H I compo nents L and D; they prove the existence of upward and downward motions within the three-dimensional superbubble. Therefore, LMC2 is an examp le in which galactic fountains, superwinds, and falling high-velocity clouds participate in the complex dynamics of superbubbles.