Most of the visible light coming from the Sun originates in the solar photosphere. Numerical simulations are a common tool to study the solar atmosphere starting from the basic laws of physics and few additional assumptions. This thesis presents results of three-dimensional radiative magnetohydrodynamic simulations of the quiet-sun, plage and

We study the coupling of magneto-acoustic waves to Alvén waves using 2.5D numerical simulations. In our experiment, a fast magnetoacoustic wave of a given frequency and wavenumber is generated below the surface. The magnetic field in the domain is assumed homogeneous and inclined. The efficiency of the conversion to Alfvén waves near the layer of

We present a near-IR and optical spectrophotometric characterization of the stellar population of Sh2-152, as part of our MASGOMAS project. Using new broad band photometry (J, H and K_S) for the cluster and a control field, we have constructed CMD in order to select OB-candidates for H and K spectroscopy. Also, we have obtained the cluster mass

Since the detection of the asymptotic properties of the dipole gravity modes in the Sun, the quest to find individual gravity modes has continued. An extensive and deeper analysis of 14 years of continuous GOLF/SoHO observational data, unveils the presence of a pattern of peaks that could be interpreted as individual dipole gravity modes in the

Context. Recently, unanticipated magnetic activity in ultracool dwarfs (UCDs, spectral classes later than M7) has emerged from a number of radio observations. The highly (up to 100%) circularly polarized nature and high brightness temperature of the emission have been interpreted as requiring an effective amplification mechanism of the high

We analyze more than 5000 days of Sun-as-a-star radial velocity GOLF and intensity VIRGO observations to measure the visibilities of the I = 0, 1, 2, and 3 modes and the m-amplitude ratios of the I = 2 and 3 modes in the solar acoustic spectrum. We provide observational values that we compare to theoretical predictions.