Magnetospheres around High Mass Stars revealed by Polarimetry

• Ano de defesa: 2022
• Autor(a) principal: Oliveira, Matheus Zaghi de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Campo magnético; Magnetic field; magnetosfera; magnetosphere; polarimetria; polarimetry; radiative transfer; transporte radiativo
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/14/14131/tde-14022023-162404/

About 10% of the known massive stars have a magnetic field of relevant strength. Combined with the star\'s fast rotation, the magnetic field may be able to trap the expelled material, forcing it to corotate with the star, creating the so-called magnetospheres. The Rigidly Rotating Magnetosphere (RRM) model was created for the case of strong magnetic fields and high rotation velocity. However, it is not able to simultaneously reproduce the photometry and polarimetry of the archetype star sigma Ori E\'s magnetosphere. An alternative model, named Dumbbell plus Disk (D+D) was proposed, which allows a good fit of the data and the determination of basic parameters of the magnetosphere. We present the results of a polarimetric survey of massive magnetic stars at Pico dos Dias Observatory (OPD), where observations of 18 stars were carried out int the V and R filters. We improved the fitting method of the D+D model, coupling the original routine to the emcee algorithm of the Monte Carlo Markov Chain method, making possible a more robust statistical analysis of the data. The objective of the project is to obtain linear polarization data of massive magnetic stars throughout their rotation period, and thus apply the D+D model to study their magnetospheres. We report the detection of four new magnetospheres by polarimetry, in the stars OriE, HD 35502, HD 142990, HR 7355, and HR 5907. We applied the model to observational data and improved the results of sigma Ori E. Of the new detections, two stars, HD 35502 and HD 142990 had good fits, making it possible to determine the parameters of their magnetospheres. HR 7355 and HR 5907 had marginal fits, which can be caused by the low modulation of the intrinsic polarization, or by the inadequacy of the D+D for these objects. An analysis was also made to investigate existing relations between the properties of the magnetosphere and its host star. We found that the mass of the magnetosphere increases with the strength of the magnetic field.