Observations and interpretation of the infrared emission from supernova SN1987A

Infrared spectrophotometric observations of SN1987A from the Kuiper Airborne Observatory are presented for the wavelength range 1.5 to 12.5 microns for five epochs at about 60, 260, 415, 615, and 777 days after the explosion. These data are combined with the ultraviolet, optical, infrared (UVOIR) measurements from ESO/CTIO and SAAO in order to characterize the continuum by three components: a photospheric contribution, free-free radiation, and the infrared emission from dust characterized by greybody radiation. Line flux measurements from the continuum substracted spectra are given, including the Brackett, Pfund, and Humphreys series of hydrogen and neutral and singly-ionized nickel and argon from the core ejecta. Carbon monoxide and silicon monoxide vibration bands are identified in the spectra. A simple analysis of the hydrogen line and free-free emission is presented. Dust radiative equilibrium calculations are performed. At 415 days, excess infrared emission, not accountable by circumstellar dust, was observed. At 615 and 777 days, this new component dominated the infrared continuum and is evidence for dust condensation in the ejecta of SN1987A. The shape of the infrared emission from newly formed dust is well characterized by the Planck curve, i.e., by a greybody, and therefore the grains which formed in the ejecta are either large or their emission arises from optically thick clumps. The radiative equilibrium temperature of the observed greybody emission indicates that the dust is in the metal-rich volume of the ejected core