Probing the wind interaction in the massive binary system HD149404 wtith XMM-Newton

Abstract

This work is based on the XMM-Newton observations of the massive binary system HD 149 404 made of a type O7.5 If primary star and a type ON9.7 I secondary star. In 2018, XMM-Newton observed this system at three distinct phases, the two conjunctions and a quadrature, in order to investigate the hydrodynamic shock resulting from the collision of the stellar winds under different angles. In this work, we will start by a brief explanation of HD 149 404 making use of the available scientific literature to understand its peculiarities and interest for the scientific world. Since this binary system harbors two massive stars and an hydrodynamic shock, the properties of those stars will be discussed as well as the physics behind such a shock, notably by establishing the Rankine-Hugoniot relations. At that point, the reason behind the necessity of an X-ray observation of the system will be made clear by detailing the different physical processes that happen in such binaries and are responsible for the emission of X-ray photons. Starting with the full description of the XMM-Newton data transmitted by the European Space Agency, we will see how raw data can be turned into scientifically usable ones by the reduction process specific to the high energy astrophysics. The question of the background during the observations will be tackled and, among others, the impact of the filter used by XMM-Newton will be discussed. The source of interest, HD 149 404, will be clearly identified within all the sources in the field of view and, via background and source regions, an observational spectrum will be extracted. This observational spectrum will serve, in the Xspec software, to create a spectral fitting model. First, a very simple model will be discussed and used as a basis to understand the process of modeling an X-ray spectrum. Then, we improve this spectral model making use of the results of previous studies of this system and testing various hypotheses. Once in possession of our best fit model, we will extract relevant properties of the binary system such as the X-ray fluxes or the Lx/Lbol ratio and compare them with expected behavior from colliding wind binaries. Finally, the Canto formalism will be used to model the collision between the stellar winds and extract properties of the binary system such as the orbital inclination.