Spectroscopy of supernova 1987A at 1 - 4  m - II. Days 377 to 1114

Abstract

Infrared spectroscopy of SN 1987A has continued through the second and third years of its existence, allowing unprecedented coverage of the late-time behaviour of a supernova. We present the data and their analysis. The continuum emission in the L window is interpreted in terms of dust condensation which had commenced by day 3 50. The mass of dust formed exceeded 3 x 10(-4) M., possibly by a large factor, and it probably had a clumped distribution. Forbidden lines increased in prominence, especially those of [Fe II]. The similarity of linewidths for a wide range of elements confirms extensive mixing of the ejecta. Up to day approximately 500, most lines were redshifted with respect to the supernova centre of mass, possibly due to a spatially biased, clumped distribution of material. After day approximately 500 most lines exhibited a shift to the blue, probably due to inhomogeneous, localized cooling and dust condensation. By the end of year 3, the decline rate of lines and of the JHK continuum roughly matched the radioactive decay rate. This may also be an indication of strong clumping. The ejecta of SN 1987A were extensively mixed and yet highly inhomogeneous; high-excitation emission zones co-existed with localized, cold concentrations of dust and molecules.