A new analytical thin-dusty-shell model to interpret interferometric data

High angular resolution techniques allow the determination of physical and geometrical parameters characterizing the circumstellar dusty environment of late-type stars. The resolution of the radiative transfer equation under the thin-shell approximation provides an analytical expression for the interferometric visibility profile, which can then be compared to simple ad-hoc geometrical models and to physical models based on radiative transfer. Using the DUSTY numerical code to calculate theoretical visibilities of the S star π1 Gru, in agreement with spectrophotometric measurements from the near to the far infrared, we compared the validity of the output parameters found by the least-square analysis of the visibility, given with the thin-shell model and with a simple disk+ring geometrical model of the envelope. The results are discussed in terms of fitting the shape of the intensity profile and of the number of free parameters to be considered.