Tesis postgrado Astrofísica

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Examinando Tesis postgrado Astrofísica por Autor "Concha Astorga, David"

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    Characterization of the disk and line-profile variability of the Be star π Aquarii
    (Universidad de Valparaíso, 2023) Concha Astorga, David; Supervisor: Arcos, Catalian; Internal reviewer: Curé, Michel; External reviewer: Cochetti, Yanina
    Massive stars have masses roughly greater than 8 M⊙ and temperatures bigger tan 10000 K, with a luminosity of 104 − 105 L⊙. These stars are very important because they end their lives with core-collapse events as supernovae, enriching the interstellar medium, that activates the formation of new stars. They are also important to study stellar and galaxy evolution, the multiplicity and rotation of stars, and the effects of the magnetic field on stars. They can provide studies of evolution at various redshifts and metallicities covering the vast cosmic history, etc. Classical Be stars have thin circumstellar disks at the stellar equator with a flaring shape, confirmed by spectroscopic and interferometric observations. They are rapidly rotating B-type stars, expelling material from their photosphere under a process that to date is not fully understood. Their disks rotate in a quasi-Keplerian motion. They can be detected via Hydrogen lines in emission and infrared excess in the spectral energy distribution, which is attributed to the presence of ionized gas. Several mechanisms are proposed to explain how the material is placed from the star to the disk with these mentioned characteristics. Some possibilities are binarity, rapid rotation, non-radial pulsation, winds, or a combination of these mechanisms. The main purpose of this thesis is to add new knowledge of Be stars, with a characterization of the variable Be star named π Aquarii. It’s a bright, rapidly rotat- ing classical Be star observed more than 100 years, presenting mid- and long-term variability over 50 years in the profile of Hα and Hγ. This star is in a binary system, and over the years, the disk has been active and quiet with respect to the formation and dissipation of the disk. We use spectroscopic data recollected from the BeSS and BeSOS databases to obtain different measurements on the spectral lines. We studied the disk parameters in five phases over the course of 21 years with a 3D NLTE Montecarlo transfer radiative code-named HDUST . The parameters of the disk for the first three phases with low uncertainty, where for the first, second, four, and fifth phases the range of inclination is between 50-70◦ , but for the third phase the inclination is lower, around 25-45◦ which can be the reason for the sudden apparition of FeII emission lines. Some Helium and other lines are also in emission, in different epochs of the star. We were able to confirm the phase-locked V/R variation of 81.14 days, which is the period of the binary star found in the literature. The method applied in this thesis can help analyze this kind of shape profile, usu- ally observed in Be stars. These results and discussion contribute to the knowledge of the variability observed in Be disks and the connection with the companion.