Studies Of Circumstellar Envelope Models And Line Emission Of AGB Stars

Studying AGB stars is of great significance to stellar evolution and interstellar medium researches. Due to the influence of circumsteller envelope, most parameters of AGB stars can't be directly derived. Because the circumstellar envelope (CSE), cre-ated by stellar wind, contains elements produced by internal nuclear synthesis, and dust grains formed in the inner part of the wind near the photosphere, the physical and chem-ical properties of the CSEs (density structure, temperature structure, velocity structure,abundances of molecules) are essential to the studies of AGB stars. Therefore, many researchers use spectrophotometric measurements and molecular emission line observa-tions to study the properties of AGB stars, with different kinds of modeling approaches(dust radiative transfer modeling, gas radiative transfer modeling and hydrodynamic modeling). The first part of this paper reviews the numerical models and calculation methods of circumsteller envelopes around AGB stars, and the future development of the field.Plentiful observations are essential to the modeling studies of AGB stars. Radio observations of gas phase materials are helpful to understand the overall properties of the stellar winds. Particularly, molecular line survey is a powerful tool for analyzing both physical and chemical parameters of astronomical objects. In the second part of this paper, the results of a spectral line survey of IRC +10216, a typical carbon rich AGB star, between 13.3 and 18.5 GHz are presented. The spectral line survey of IRC+ 10216 is carried out using the Shanghai Tian Ma 65 m Radio Telescope (TMRT-65m)with a sensitivity of < 7 mK. Forty-one spectral lines of 15 different molecules and rad-icals are detected in total. Except for SiS, the detected molecules are all carbon-chain molecules,including HC3N,HC5N, HC7N, HC9N,C6H,C6H-,C8H,SiC2, SiC4, c?C3H2 and 1-C5H. The presence of rich carbon-bearing molecules is consistent with the identity of IRC +10216 as a carbon-rich AGB star. The excitation temperatures and col-umn densities of the observed species are derived by assuming a local thermodynamic equilibrium and homogeneous conditions. Comparing with previous works, it is clear that the high-J transitions of the molecules in the circumstellar envelope of IRC +10216 trace the warmer molecular regions.