Astronomy & Astrophysics manuscript no. WAql-v6-revision_02_final c ESO 2018 October 5, 2018 Molecular line study of the S-type AGB star W Aquilae ALMA observations of CS, SiS, SiO and HCN M. Brunner1, T. Danilovich2; 3, S. Ramstedt4, I. Marti-Vidal2, E. De Beck2, W.H.T. Vlemmings2, M. Lindqvist2, and F. Kerschbaum1 1 Department for Astrophysics, University of Vienna, Türkenschanzstrasse 17, A-1180 Vienna e-mail:
[email protected] 2 Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden 3 Department of Physics and Astronomy, Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium 4 Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden Received Month nr, YYYY; accepted Month nr, YYYY ABSTRACT Context. With the outstanding spatial resolution and sensitivity of the Atacama Large Millimeter/sub-millimeter Array (ALMA), molecular gas other than the abundant CO can be observed and resolved in circumstellar envelopes (CSEs) around evolved stars, such as the binary S-type Asymptotic Giant Branch (AGB) star W Aquilae. Aims. We aim to constrain the chemical composition of the CSE and determine the radial abundance distribution, the photospheric peak abundance, and isotopic ratios of a selection of chemically important molecular species in the innermost CSE of W Aql. The derived parameters are put into the context of the chemical evolution of AGB stars and are compared with theoretical models. Methods. We employ one-dimensional radiative transfer modeling – with the accelerated lambda iteration (ALI) radiative transfer code – of the radial abundance distribution of a total of five molecular species (CS, SiS, 30SiS, 29SiO and H13CN) and determine the best fitting model parameters based on high-resolution ALMA observations as well as archival single-dish observations.