ULTRAVIOLET INTERSTELLAR ABSORPTION-LINES IN THE LMC - SEARCHING FOR HIDDEN SNRS

Strong x-ray emission detected in Large Magellanic Cloud (LMC) superbu bbles has been explained as the result of interior supernova remnants (SNRs) hitting the dense superbubble shell. Such SNRs cannot be found using conventional criteria. We thus investigate the possibility of us ing the interstellar absorption properties in the UV as a diagnostic o f hidden SNR shocks. The IUE archives provide the database for this pi lot study. They contain high-dispersion spectra of several stars in x- ray bright superbubbles. To distinguish the effects of SNR shocks from those of local stellar winds and a global hot halo around the LMC, we included control objects in different environments. We find that almo st all interstellar absorption properties can be explained by the inte rstellar environment associated with the objects. Summarizing the two most important results of this study: (1) a large velocity shift betwe en the high-ionization species (C IV and Si IV) and the low-ionization species (S II, Si II, and C II) is a diagnostic of hidden SNR shocks ; however, the absence of a velocity shift does not preclude the exist ence of SNR shocks; (2) there is no evidence that the LMC is uniformly surrounded by hot gas; hot gas is preferentially found associated wit h large interstellar structures like superbubbles and supergiant shell s, which may extend to large distances from the plane.