Spectropolarimetry of SN 1987A: observations up to 1987 July 8

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Abstract
We present spectropolarimetric observations of SN 1987A in the LMC. These are the first such observations of a supernova with a signal-to-noise ratio sufficient to show polarization variations across the spectral lines. Observations have been made at several epochs and cover a number of spectral regions; in most cases these include the region around Hα. In general the polarization through the lines is double peaked above a continuum value. We discuss in some detail the interstellar component in order to investigate its effect on the polarization profile. The presence of polarization shows that the supernova explosion was asymmetric. The axis and degree of asymmetry is dependent on wavelength. We interpret our observations in terms of existing models but more detailed modelling will be needed to obtain full agreement with the observed polarization spectrum. We also investigate whether the position angle of the polarization may be related to the position of the companion source observed using speckle interferometry. The principal symmetry axis of the supernova envelope appears to be aligned with the angle to the speckle companion. We also describe the modifications made to the existing spectropolarimetry on the Anglo-Australian Telescope in order to obtain the high signal-to-noise ratios required for the observations.

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