Transients Obscured by Dusty Disks

Dust absorption is invoked in a number of contexts for hiding a star that has survived some sort of transient event from view. Dust formed in a transient is expanding away from the star and, in spherical models, the mass and energy budgets implied by a high optical depth at late times make such models untenable. Concentrating the dust in a disk or torus can in principle hide a source from an equatorial observer using less mass and so delay this problem. However, using axisymmetric dust radiation transfer models with a range of equatorial dust concentrations, we find that this is quite difficult to achieve in practice. The polar optical depth must be either low or high to avoid scattering optical photons to equatorial observers. Most of the emission remains at wavelengths easily observed by JWST, and the equatorial brightness is reduced by at most a factor of ~2 compared to isotropic emission even for equatorial (visual) optical depths of 1000. It is particularly difficult to hide a source with silicate dusts because the absorption feature near 10\ microns frequently leads to the emission being concentrated just bluewards of the feature, near 8 microns.