Radiative transfer in spherical circumstellar dust envelopes. V. Theoretical circumstellar graphite and silicate emission spectra

Models of infrared emission from graphite and silicate dust surrounding a 3000 K star have been constructed for a wide variety of envelope sizes and optical depths. The Feautrier method was employed for solution of the transfer equation, and the Lucy temperature-correction procedure for spherical geometry was used to achieve flux constancy through the model envelopes.The effects of changes in various parameters such as shell size and optical depth are evaluated for both silicates and graphite. From the calculated emission spectra it is seen that typical envelope sizes for cool stars with moderate to large infrared excesses are 102 to 103 stellar radii. The 10 μ silicate opacity feature is given strong focus with a view toward ascertaining when the feature should appear in absorption and when in emission. It is found that compact, hot dust envelopes are more likely to show the feature in emission than cool, distant ones, and this effect is analyzed physically