ESTUDO DOS MODOS P NO LIMBO SOLAR

Abstract

Helioseismology aims to study the oscillations observed on the surface of the Sun. These oscillations are acoustic and stationary waves called p modes, and penetrate the solar interior and provide information about the internal structure. Because these waves have small amplitudes, they can be dealed with small perturbations in a model in hydrostatic equilibrium. Acoustic waves can be represented by spherical harmonics, characterized by l degree, m order and n order (nodes on radial direction). The p modes are waves whose restoration force are pressure, and g modes are waves whose restoration force are gravity. The data analyzed in this study were obtained from the Helioseismic and Magnetic Imager (HMI) that integrates the SDO mission (Solar Dynamics Observatory). Filtergrams are narrow band wavelength filters very close to some absorption line of the Sun. From the filtergrams obtained by the HMI, a processing pipeline generates the arrays and, describing the limb brightness and displacement as a function of central angle around the limb, respectively. Through a computer program developed in IDL (Interactive Data Language), used to calculate the Fourier transform of the arrays and we obtained the modes, and compared the results of the transform with frequencies of oscillation modes obtained by other authors (in the literature) using data obtained by MDI (Michelson Doppler Imager) and GONG (Global Oscillation Network Group), in order to find the characteristic frequencies of the modes. From this analysis, we obtained the relation between amplitude and frequency for the modes, it has been found that the behavior of the full width at half maximum as a function of the frequency confirm some results found in the literature, it was found larger amplitudes for low frequencies, confirming the theoretical prediction of Toutain’s model (1998) and we found the arise of degeneracy of the modes for different m values. It was also found that the noise presence in data is significant, and probably is the main source of error.