Structure and Kinematics of the Interstellar Medium in front of SN1987A
  High resolution (10 km/s) [N II] echelle spectra, sampled every 13 arcsec in a 6 arcmin by 6 arcmin region around SN1987A were obtained on the CTIO 4m telescope. The map shows a complicated velocity structure consistent with that reported previously for the interstellar medium. Three components, heliocentric velocity V_hel=265, 277 and 285 km/s are identified as N157C. The radius of this large superbubble was found to expand at 10 km/s, with a lifetime of 6 million years and a total energy of 3x10^51 ergs determined from its radius and velocity according to superbubble theory. The V_hel=235 km/s component corresponds to the near side of 600 pc giant superbubble reported earlier. This bubble is over 10 million years old, and has blown out of the LMC disk. Two other components, V_hel=255 and 245 km/s are identified as the inner major light echo ring (a double-shell structure) at about 130 pc in front of SN1987A. There are also two high velocity components, 300 and 313 km/s, which are possibly the far side of a superbubble in which SN1987A exploded. We also notice that there are two components at 269 and 301 km/s within 20 arcsec of SN1987A. These structures are probably due to the emission from the progenitor star's red supergiant wind. We find that the time it took the SN1987A progenitor to move to the current location 300 pc behind N157C is comparable to the age of N157C as well as that of the progenitor itself. 
J. Xu, and A.P.S. Crotts (Columbia University)