Symbiotic Stars and Dust

Abstract

New members of the class of very high excitation symbiotic stars, with relatively strong lines of [Fe vII], have been found. The strong unidentified emission band at 6830 Å has been detected in two of these and its identification is discussed. There is a subgroup of high excitation objects which also emit near-infrared thermal radiation from dust grains and are distinguished by the properties of their emission-line spectra. It is proposed that the dust exists in neutral gas and that the optical and infrared spectra of this subgroup of symbiotic stars arise because they are radiation bounded either at their perimeter or around condensations.