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Radio astrophysics --- Congresses.

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Interstellar hydrogen. --- Hydrogen --- Galaxies. --- Radio astrophysics. --- Spectra. --- Milky Way.

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Massive stars can be characterized by various properties. Two of them are their winds and
their multiplicity. Since massive stars are more likely to be part of a binary system, their
winds may collide and interact. These systems are called colliding-wind binaries (CWB).
CWBs in which some charged particles in the wind collisions region are accelerated to rel-
ativistic velocities are called particle-accelerating colliding-wind binaries (PACWB). This
master thesis focuses on one of them, WR 147. The physics and properties of these objects
are discussed in Chap. 1.
In Chap. 2 the radiative processes are presented. Indeed, two types of radio emission can
be observed in these PACWB systems. On the one hand, the thermal emission, also called
Bremsstrahlung, comes from the ionized wind of the stars. On the other hand, the non-
thermal emission, or synchrotron emission, is produced by relativistic electrons accelerated
by the Diffusive Shock Acceleration process (DSA). The low frequency part of the spec-
trum is likely to be affected by so-called turnover processes, leading to a severe drop of the
synchrotron flux. Among these processes, free-free absorption is the most likely to affect
the radio spectrum of PACWBs.
This master thesis includes the analysis of the radio emission of WR 147 in two radio fre-
quency bands. More precisely, it aims at achieving a deeper understanding of the WR 147
behavior at these frequencies through a detailed intra-band investigation. In particular,
it focuses on low frequencies where the synchrotron emission is stronger but also more
susceptible of being affected by turnover processes that are often difficult to constrain.
Data from the Jansky Very Large Array (JVLA) are used for this purpose. After processing
the radio data, including flagging, calibrating, and imaging steps, the flux density of the
source is obtained in both bands but also in each sub-band. All these steps are described in
Chap. 3. With these flux densities, several fits are proposed, in Chap. 4, notably based on
the foreground absorption model. Several parameters are determined such as the thermal
and non-thermal spectral indices. However, it is observed that this model is not adapted
to the behavior of WR 147 at low frequencies. Thus a new model, the internal absorption
model, is proposed. It consists in the absorption of the synchrotron radio emission by ther-
mal electrons located in the emission region, and not by material surrounding the emission
region. It seems that this new model better represents the behavior of WR 147, although
it does not lead to a perfect fit.
Then, in Chap. 5, several elements of discussion are addressed based on the parameters
and fits of the different models. These include the value of the compression ratio, the
justification of the turnover process at play being free-free absorption, and the possible
influence of a third star in the system. The relevance of the internal absorption model is
also discussed in detail. Finally, a more general model combining the foreground absorp-
tion model and the internal absorption model is proposed to generalize the behavior of
PACWBs. In Chap. 6 several perspectives for future observations are considered, notably
based on the internal absorption model and on the general model.

radio astrophysics --- PACWB --- WR 147 --- Physique, chimie, mathématiques & sciences de la terre > Aérospatiale, astronomie & astrophysique

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Radio astrophysics --- Radio sources (Astronomy) --- Stars --- Congresses. --- Radiation --- Sterren. Radiatie. (Congres) --- Radio-sources stellaires. (Congrès) --- Etoiles. Radiations. (Congrès) --- Radiobronnen (Sterre-). (Congres)

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METHODS OF EXPERIMENTAL PHYSICS V.12C

Astrophysics --- Methodology. --- Methodology --- Radio astrophysics. --- Astrophysics. --- Astronomical physics --- Astronomy --- Cosmic physics --- Physics --- Radio astronomy --- Radio telescopes. --- Radio telescope --- Radiotelescopes --- Telescopes --- Radar telescopes --- 520.8 --- 520.8 Techniques of observation, measurement, analysis --- Techniques of observation, measurement, analysis --- Astrophysics - Methodology --- ASTROPHYSICS --- METHODOLOGY