Advances in Plasma Astrophysics Proceedings IAU Symposium No. 274, 2010 A. Bonanno, E. de Gouveia Dal Pino & A.G. Kosovichev, eds. © International Astronomical Union 2011 doi:10.1017/S1743921311006867 Modeling circumstellar envelope with advanced numerical codes P. Procopio 1 , A. De Rosa 1 , C. Burigana 1 , G. Umana 2 , and C. Trigilio 2 1 INAF - IASF Bologna, Via P. Gobetti 101, 40129 Bologna 2 INAF - OACt, Via S. Sofia 78, Catania Abstract. We propose a modeling study on the formation and evolution of the Circumstellar Envelopes (CSEs) of a sample of selected radio-loud objects, based on an innovative interaction between two codes widely used by the scientific community, but in different fields. CLOUDY† (Ferland et al. 1998) is a widely used code to model the spectral energy distribution (SED) of the several objects characterized by clouds of gas heated and ionized by a central object. CosmoMC‡ (Lewis & Bridle 2002) instead is usually used for exploring cosmological parameter space. We investigate here on the exploitation of the sampling performance of the Markov-Chain Monte- Carlo (MCMC) engine of CosmoMC to search for a best fit model of the considered objects through the spectral synthesis capacity of CLOUDY. Keywords. circumstellar matter, planetary nebulae, MCMC 1. Introduction Detailed observations of (CSE) are of crucial importance in determining fine details of different aspects related to the physical properties of plasma and dust around various classes of stars in their late evolution stages. The modeling and characterization of the CSEs are of extreme relevance for understanding the formation and evolution of relatively fast evolving objects, like e.g., Planetary Nebulae (PN), on which this contribution is focused. On the other side, the enrichment of the Interstellar Medium (ISM) depends on the chemistry and the composition of gas and dust that are coming out from PNs and Supernovae, through stellar winds or shockwaves. In this study, the spectral emission is predicted through CLOUDY, a performing public C++ based code, while the core of the optimization of the model parameters is CosmoMC, a FORTRAN90 MCMC engine, supplied with additional codes to analyze specific output data of the sampler. 2. The Data-set The sample of PNs has been extracted from the Condon & Kaplan catalogue (1998). Only objects characterized by a flux density higher than 100 mJy at 1.4 GHz were selected (in order to guarantee a good detection with the Noto radiotelescope). Some observations has been already performed at 8.4 and 43 GHz (Umana et al. 2008). To consider the dust emission associated to the PNs, data from near (2 µm) to far (100 µm) infrared were retrieved as well: photometric measurements have been extracted from IRAS, 2MASS, and MSX archives. † CLOUDY is available for free download at http://www.nublado.org ‡ ComoMC is available for free download at http://cosmologist.info/cosmomc/ 175