Bow-shock chemistry in the interstellar medium

Abstract

Stars are bad neighbors: they often disturb their surroundings. They sometimes travel very fast through the interstellar medium (ISM). They frequently undergo violent ejection events which leave an imprint on their neighborhood (jets, winds, supernovae). These supersonic flows generate shocks both in the ejected material (bow shock) and in the stellar environment (termination shock). The global purpose of this thesis is to link the properties of stars and the ISM by studying these shocks. We model them with the Paris-Durham planar shock code, which incorporates a wealth of micro-physics and chemical processes relevant to the magnetized ISM. In the first part, we model 3D magnetized axis-symmetric bow shock by a statistical distribution of 1D planar shocks computed with the Paris-Durham model. For the first time, we examine systematically the effect of the geometry, age, and various other parameters on the H2 excitation diagram and emission line profiles. Then, we will show that this 3D bow shock model unprecedentedly improves interpretations of the H2 observations inOrion BN-KL and BHR71, and show how spectral resolved H2 line emission profiles on the Herbig-Haro objects HH54 can be used to extract a wealth of dynamical information. In the second part, we model 1D steady stellar winds from AGB stars, which trigger the termination shock, by including relevant physical and chemical ingredients in the Paris-Durham code. For the first time, we examine the time-dependent conversion of atomic to molecular hydrogen along the wind trajectories of "hot" and "cold" AGB stars. We suggest that the low abundance of HI inferred from observations is due to hydrogen locked in its molecular form. Then, we try to reproduce HI 21-cm line profile in a "hot" AGB (called Y CVn) and a "cold" AGB (called CW Leo).