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In the past decade, space missions, such the CoRoT, Kepler and TESS, have provided the asteroseismic community with a vast amount of observations, of unprecedented quality. This gave the opportunity to stellar astrophysicists, to study the stellar interiors of a large variety of pulsating stars. Amongst them, are the solar-like stars, that are low-mass main-sequence stars, reaching up to 2.3 Solar Masses. 
During the main-sequence phase, the solar-like stars are stable, and they present frequencies that are very regular, which is most obvious in a power spectrum. Nevertheless, there are some departures from that equidistance, to which we refer as the smooth part, and one of the reasons for that, are the glitches. The glitches are due to sharp variations, on the internal structure of the stars, which introduce an oscillatory feature, as a function of the frequency, in the oscillation spectrum. Solar-like stars experience mostly two glitches, the helium glitch, for which our study is about, and the convection zone glitch. The former is located in the second ionization zone of helium, quite close to the stellar surface, and the latter, is located in the transition region between the convective envelope and the radiation zone. The study of those glitches is important, because they provide information about their respective regions, which further helps constrain the internal structure of a star. The amplitude of the helium glitch, is directly linked to the helium abundance, in that area and, since that area is very close to the surface, and convection dominates there, it provides information about the surface helium abundance. This is the only way to obtain that value, because the stellar surface of solar-like stars, does not have the required temperature for the excitation of helium, and thus, few or no emission lines can be obtained spectroscopically. 
There exists a number of methods that use the observed frequencies, and derive seismic constraints, which are used to derive information about the stellar structure, through stellar modeling. The one that we used for our analysis, is the Whole Spectrum and Glitches Adjustment (WhoSGlAd). It uses both the smooth part of the spectrum, along with the glitches part, to derive seismic indicators, as little correlated as possible. The accuracy of those indicators, allows them to be used as constraints by minimization techniques, in order to retrieve precise values about global quantities, as is the mass, the age and the chemical composition. 
In the case of WhoSGlAd, one of the constraints that is used is the helium glitch amplitude, but for its value we need to know the helium acoustic depth. When we work with observations this value is not available and so, we have to derive it by a model, to estimate the helium acoustic depth, which takes time and it is inconvenient, since it makes the results model dependent. In this study, we propose a method, that uses a linear relation, in order to derive this acoustic depth, which uses only observed quantities and so, makes the procedure much faster. We prove the efficiency and the accuracy of that method, by using both models and observations. This means that it does not make any sacrifices in the precision of WhoSGlAd. Moreover, since this method is linear, and uses only observables, it can be implemented in already existing codes, and provide results much faster. The method, as a result of the assumed linear formulation, does not apply to cases that are not linear. This occurs in cases beyond the main sequence, or with convective cores. This can happen for example, for the case of stars ≥1.2 solar masses, for some chemical compositions.

Physique, chimie, mathématiques & sciences de la terre > Aérospatiale, astronomie & astrophysique

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The aurora on Jupiter is a remarkable phenomenon in our solar system. After having
been observed for the first time by the Voyager 1 spacecraft in 1979, many spectral
observations of these polar lights have been conducted on a continuous basis. Since
2016, the Juno spacecraft, in polar orbit around Jupiter, is gathering images and
spectroscopic data that allow us to unravel the complex interplay between Jupiter’s
magnetosphere and atmosphere.
In this work, we use data from the UVS spectrograph onboard Juno to construct
northern and southern spectral cubes for perijoves 1 to 48. From these spectral cubes,
we derive H2 brightness maps, emission angle maps and color ratio maps. We then
use use a relation between color ratio, emission angle of the photons and energy of the
precipitating electrons to compute energy maps for each of Juno’s orbits, considering
both monoenergetic and kappa energy flux distribution of electrons. These maps give
an interesting overview of the evolution of several characteristics of the auroral regions
over time.
We then perform a statistical analysis of the energy of the precipitating electrons as
a function of time. We divide each auroral region into three sub regions: the polar,
main and outer emission regions. We compare the energy of the electrons falling into
these three sub regions and the energy of the electrons falling into their counterpart
in the other hemisphere.
We also study the correlation between the H2 auroral brightness and the energy of
the precipitating electrons for the whole auroral emission region and for each sub re-
gion. We find that the H2 auroral brightness is not correlated with the energy of the
impinging photons by studying correlation plots as well as correlation coefficients for
each perijove.
In the last part, we identify zones of the auroral emission where the color ratio seems
to call into question the validity of the atmospheric model that we used. We then use
TransPlanet to model synthetic spectra produced by populations of electrons falling
into the atmospheric model that we use. We attempt to fit the modeled spectra to the
observed ones by adjusting the energy of the impinging electrons that we computed
as well as the amount of hydrocarbons in the model atmosphere. We find that the
observed spectra for some of the selected zones can be fit by tuning the energy of the
electrons while for others, changing the atmospheric composition is necessary. This
raises the question of the consistency of the atmospheric composition across the entire
auroral emission region.

Jupiter --- Juno --- UVS --- Aurora --- Spectral modelling --- Physique, chimie, mathématiques & sciences de la terre > Aérospatiale, astronomie & astrophysique

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Le but de ce travail de mémoire est de développer une méthode d'ajustement du glitch causé par la seconde zone d'ionisation partielle de l'hélium au sein des étoiles de type solaire. Nous l'appellerons l'algorithme 'HeFi' pour 'Helium Fit'. Notre méthode prend pour point de départ la méthode C développée par Verma et al. (2014, ApJ, 790 138). L'intérêt nouveau de celle que nous développons est que nous visons à utiliser des informations indépendantes lors de nos ajustements afin de garantir la robustesse et la fiabilité de nos résultats. Ce n'était pas le cas des méthodes proposées jusqu'ici. Ceci passe par la redéfinition d'une fonction coût unique ainsi que des paramètres ajustés afin d'empêcher toute corrélation entre ceux-ci. Notre algorithme s'inscrit dans la catégorie des méthodes astérosismologiques directes. Nous l'appliquerons à l'analyse du signal du glitch de l'analogue solaire 16 Cygni A (HD 186408).

Astrophysics --- Asteroseismology --- Helium Glitch --- Astrophysique --- Astérosismologie --- Glitch d'hélium --- Physique, chimie, mathématiques & sciences de la terre > Aérospatiale, astronomie & astrophysique