http://arxiv.org/abs/1709.07074

In the same way that seismologists study the interior of the earth from the waves generated by earthquakes, heliosismology is the science that is interested in the study of oscillatory waves inside the Sun. Temperature, chemical composition, rotational velocities at different depths are all factors that influence the oscillation frequencies of the waves trapped inside the Sun. The observation and measurement of the frequencies (or velocities) of oscillations of the principal modes on the surface of the Sun allow us to study the internal properties of the star. In our study, we use a local helioseismic method, called “Time-Distance”; the latter, after appropriate treatment (remapping, tracking, and filtering) of the data, which carried out from the GONG (Global Oscillation Network Group) observation network, allows us to deduce, by correlation of the observed signals, the relationship between the time of the wave path and its crossed distance (hence the name of the method) between different points on the surface as a function of the different solar sub-surface parameters, via the dispersion relation. Once the travel times have been established by approximation of the correlation function by a Gaussian wave packet and based on the Fermat principle dealing with acoustic waves, we find the relationship between these times and the internal parameters of the crossed medium. Two models are considered in this study. The first does not include the effects of the magnetic field and takes into account the flow velocity and the sound speed. The second, on the other hand, includes the magnetic effects, by means of the Alfven velocity (magnetic field perturbation velocity), in addition to the parameters mentioned above. The last part of this paper was devoted to the inversion of the obtained times, which allows us to go back to the solar internal parameters.

Read this paper on arXiv…

M. Hadjara

Fri, 22 Sep 17

75/75

Comments: Master’s thesis (2006), University of Sciences and Technology Houari Boumediene, Algeria. in French

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