The dust envelope of the carbon star RW LMi

On the basis of long-term near-IR photometry and IRAS flux data, we have de veloped a model for the dust envelope of the carbon star RW LMi. The model proposes that the envelope consists of two kinds of grains: amorphous carbo n (AC) and silicon carbide (SiC). The model parameters that best fit the ob servations at intermediate and far infrared;wavelengths are: luminosity of the star 9380 L-., distance 360 pc, effective temperature 2700 K, grain rad ius 0.10 mu m, temperature of the dust at the inner envelope boundary 1300 K, and relative proportion of SiC grains 0.03, with the number of grains pe r unit volume varying as the inverse square of the radial distance. The opt ical depth of the envelope at 11.3 mu m is 0.58. Compared to the model, a l arge excess is observed in the near IR, possibly due to deviations from sph erical symmetry in the envelope. A self-consistent procedure for estimating the mass-loss rate and expansion velocity of the envelope indicates the fo llowing parameters for the stellar wind from RW LMi: ratio of light pressur e on a grain and the gravitational force 3.9, velocity of grain drift relat ive to the surrounding gas 4.1 km/s, mass ratio of dust and gas 0.002, and mass-loss rates for dust 2.1 x 10(-8) M-./yr and for gas 10.4 x 10(-6) M-./ yr. When these parameters are compared with the data for other o Ceti carbo n stars, it is apparent that RW LMi is among those objects with the highest mass-loss rates. The other parameters are close to the average values for the other stars.