Radiative Transfer Modeling of the Circumstellar Shell around W Ori: Evidence for Dust pile up at ISM boundary

Asymptotic Giant Branch (AGB) stars are major contributors of cosmic dust to the interstellar medium (ISM). The dust composition of a circumstellar shell is primarily determined by a star’s carbon to oxygen ratio (C/O). Carbon-rich stars are expected to have circumstellar shells dominated by amorphous or graphitic carbon grains. With a C/O > 1, we can refer to W Ori as a carbon-rich giant. Using the radiative transfer code, DUSTY, we tested the effect of using different types of carbon dust, as well as metallic iron dust to generate the dust continuum observed in the spectrum of W Ori. All models required a similar abundance of silicon carbide grains, to account for an infrared spectral feature around 11-micron. We used a wide set of observed parameters, including the light curve, C/O, mass-loss rate and expansion velocity to constrain our model inputs. We produced two-shell models allowing for a compositional change between the innermost dust and that further away from the star. The resulting best fit models suggest that there is a pile-up of dust in the outermost part of the shell where it collides with the ISM. We present these results of this study of W Ori.