2000ApJ...532.1006H

A model to calculate the circumstellar dust emission of an evolved carbon star is developed, and the relations between the infrared flux densities at 2.2, 12, 25, and 60 µm and the dust properties are described. The model is combined with a preexisting model for CO emission, keeping physical quantities consistent between the two models. The results are used to analyze the infrared and CO data of a sample of 17 evolved carbon stars. The dust-shell opacity determined from the 60 µm flux density correlates well with that determined from the [25]-[2.2], [60]-[12], and [25]-[12] colors over a range of almost 4 orders of magnitude within the sample. The scaled mass-loss rate M{dot} is revealed through the CO line profile observational parameter z^†=(M{dot}/1.5x10^–6 M_☉.yr^–1){cubl0}([CO]/[H₂])/6.4x10^–4{cubr0}[(L_*/L_☉)/10⁴]^–0.5, which ranges from 0.2 to 30 and averages 4.3. The envelope dust-to-gas mass ratio, f, is found to be ≲10^–3 on the assumption of usual values of [CO]/[H₂] and dust absorption efficiency. Typical grain radii a are found to be very small, with a geometric mean of ≲2 nm. It does not appear that the dust properties, such as f and a, have a direct, strong influence on the mass-loss rate, but the selected sample is, admittedly, small.