Radiative transfer in spherical circumstellar dust envelopes. IV - The infrared emissivity profile and composition of the dust in NGC 7027

Abstract

Using radiative transfer methods described in the previous papers of this series, dust-emission models of the bright planetary nebula NGC 7027 have been calculated. An analysis of the infrared continuum of NGC 7027 based upon these calculations shows the following: If the spatial dust distribution coincides with the ionized gas distribution as given by Scott in 1973 (within approx.3.2'' from the center), the infrared continuum may be produced by an unknown substance whose infrared emissivity declines with increasing wavelength to about 50 $mu$ and then rises. If there exists a cool outer dust shell beyond 5''-6'' from the central source, the observed infrared continuum may be produced by iron grains of radius 1 $mu$ or by a mixture of smaller iron and graphite grains. (AIP)