Supernova Remnants in OB Associations

We use the sample of supernova remnants (SNRs) in OB associations in the Large Magellanic Cloud (LMC) to study how interstellar environments affect the physical properties of SNRs. Some of these SNRs have been identified by the three classical SNR signatures-bright x-ray emission, nonthermal radio emission, and enhanced [S II]/Hα ratio; the others have been diagnosed by bright x-ray emission from superbubbles. We have obtained long-slit echelle observations of these 14 SNRs and their surroundings to search for high-velocity shocked gas in the SNRs and to examine the structure of the ambient interstellar medium. Not all SNRs show detectable high-velocity (ΔV≥100 km s^-1) gas. SNRs in H II regions all show classical SNR signatures and high-velocity gas, while SNRs in superbubbles often show only diffuse x-ray emission but not the other SNR signatures. Using ROSAT x-ray observations of two superbubbles, N51D and N44, we illustrate quantitatively that SNR shocks in the interiors of superbubbles can produce bright, detectable x-ray emission for ROSAT and Einstein detectors, but not enough Hα emission for echelle observations using a 4 m class telescope. The wide variety of SNR properties can be explained by the differences in their interstellar environments.