Etude et mise en oeuvre des techniques Temps-Distance en Heliosismologie

TL;DR

This paper explores the application of the Time-Distance helioseismic technique to analyze the Sun's internal structure using GONG data, considering models with and without magnetic effects, and performs inversions to infer subsurface parameters.

Contribution

It demonstrates the implementation of the Time-Distance helioseismic method with magnetic and non-magnetic models, including data processing and inversion techniques for solar interior analysis.

Findings

Successful correlation of wave travel times with subsurface parameters.

Inclusion of magnetic effects improves the model accuracy.

Effective inversion of travel times to deduce internal solar properties.

Abstract

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.