Physics
Scientific paper
Mar 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt.......267c&link_type=abstract
Ph.D. thesis, Imperial College, London, (1994)
Physics
11
Scientific paper
The narrow line emission from supernova (SN) 1987A is believed to originate from circumstellar material which was ejected by the progenitor star and ionised by the extreme ultraviolet (EUV) burst which accompanied the supernova explosion. Imaging has shown that the brightest circumstellar gas is in the form of an elliptical ring about 1 light year from the supernova. Here I report high-resolution optical spectroscopy of the circumstellar medium (CSM), taken with the UCL echelle spectrograph at the Anglo-Australian Telescope between 1990 March and 1992 December. I have used the profiles of the narrow lines to test models of the CSM, thereby providing constraints for models of the mass-loss history and the evolution of the progenitor.
I have constructed model profiles using nebular and kinematic models for the ring, taking into account the observational effects of seeing and finite spectral resolution. The nebular model was supplied by P. Lundqvist. All the lines show a velocity gradient across the nebula which confirms that the ring is intrinsically circular and expanding at 10.3 +/- 0.4 km/s. Comparison of [N II] 6583-Å and 5755-Å profiles has indicated a persistent temperature difference across the ring: the north side is hotter than the south side. This temperature difference can be easily explained if the ring material is less dense in the north than in the south. The later observations show a slight relative brightening of the northern side which is consistent with this picture.
About 10% of the CSM emission comes from gas at higher velocities than the ring. The measured velocities (up to +/- 30 km/s relative to the ring) are consistent with an origin in a homologously-expanding hourglass-shaped shell whose waist is the ring, in agreement with recent hydrodynamic models.
The H-alpha line has shown a transient, extremely narrow component, which is attributed to a cold, dense cloud behind the supernova, at the interface of the fast and slow progenitor winds. The feature's narrowness is extremely hard to explain in terms of standard nebular physics.
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