Prof Patrick Roche

Abstract:

Spectra of SN1987A in the 10-micron region taken on days 257 and 366-371 after core collapse are presented. The hydrogen/helium envelope is partially ionized at the few percent level and this provides the free-free continuum and hydrogenic lines. There is relative transparency in the midinfrared, while the bound electrons provide the X-ray opacity which is still considerable at day 370. The continuum appears to have become optically thin from about 6 months, and there may be a contribution from low ionization middle mass elements and the iron group. Apart from an excess between 8-9 microns which has been tentatively attributed to molecular SiO, there is no evidence of departure from the emission expected from an optically thin plasma, and no sign of any emission from dust.

Abstract:

Low-resolution spectra of the 3 micron water-ice features of 22 stars and the 10 micron silicate dust features of 16 stars are presented for stars in the direction of the extensive dark cloud complex in Taurus, including both dust-embedded objects and background field stars seen through the cloud. A very close linear correlation is found between the peak optical depth in the 3 micron feature and visual extinction, A(v), for field stars. The detection of ice in all cases where A(v) exceeds a threshold value of 3.3 + or - 0.1 mag serves as a basis for models of volatile mantle growth on grains in the dark cloud environment. The silicate feature is poorly correlated with A(v), and its relative weakness per unit A(v) in the spectra of field stars with strong ice bands may reflect the dilution of silicates as a fraction of total grain mass as mantles accrete in the dark cloud.

Abstract:

The authors present spectra of SN 1987A in the 10 μm region; at these wavelengths the photometric flux is much weaker than in the visible and near infrared, and emission from the lower density regions of the expanding envelope becomes correspondingly more important. On days 54, 86 and 164, 8 - 13 μm spectra have revealed a free-free emission component from the expanding envelope, along with emission lines of hydrogen and lines tentatively identified with [S IV] and [Ne II]. While all the lines increased in strength during this period, those of the fine structure lines did so dramatically. The authors attribute the appearance of [S IV], its rapid increase in strength, and the flattening of the continuum slope, to early signs of a developing nebular or coronal phase. There was no evidence by day 164 for dust emission either as an echo from pre-existing material, or from condensation in the supernova ejecta.