Infrared emission towards SN 1987A, 11 years after outburst: Properties of the circumstellar dust
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69115 Heidelberg, Germany
Corresponding author: Jg. Fischera, Joerg.Fischera@mpi-hd.mpg.de
Accepted: 28 August 2002
Detailed models are presented for the late epoch mid infrared (MIR) emission from collisionally heated grains in the shocked circumstellar gas around SN 1987A. Thermal dust emission from a region of moderate density interior to the thick inner ring seen with the Hubble Space Telescope (HST) is found to be a natural explanation for the MIR spectral energy distribution measured by ISOCAM. The MIR-spectrum can be reproduced by a mixture of silicate-iron or silicate-graphite grains or by a composition of pure graphite grains. A composition of pure iron grains on the other hand can be excluded and a pure silicate composition does not seem to be very likely. The dust-to-gas ratio in the interaction zone is ~, an order of magnitude lower than estimates for dust abundances in the winds of red supergiant (RSG) stars in the LMC. This low dust abundance can be accounted for by a combination of evaporation through the UV-flash from the supernova outburst and subsequent sputtering in the shocked gas. For this explanation to hold, dust in the pre-supernova circumstellar medium (CSM) would have to have been predominantly composed of grains other than graphite, with a maximum size smaller than ~.
Key words: stars: supernovae: individual: SN 1987A / infrared: ISM / stars: circumstellar matter
© ESO, 2002