Evolutionary sequences for H and He atmosphere massive white dwarf stars

• Main Author: Ramos, Gabriel Lauffer
• Other Authors: Romero, Alejandra Daniela
• Format: Others
• Language: English
• Published: 2018
• Subjects: Anãs brancas; Evolucao estelar; Métodos numéricos; Star evolution; Numerical methods; White dwarf
• Online Access: http://hdl.handle.net/10183/181005

White dwarf stars are the most common final stage of stellar evolution, corresponding to 99% of all stars in the Galaxy. White dwarf models can be used to obtain the age of stellar populations, to build an initial to final mass relation to understand the connection between the properties of white dwarfs and their progenitors, determine the upper mass limit that separates white dwarfs progenitors from Type II supernovae, enhance the comprehension of the physical properties of high density matter and derive ages and masses for observed white dwarfs from the cooling tracks. The literature is populated with low mass and intermediate mass white dwarf models, however the massive white dwarfs are often forgotten and the evolutionary sequences are incomplete. In this dissertation, we compute full evolutionary sequences for massive white dwarfs, exploring the evolution of hydrogen-rich and hydrogen-deficient white dwarfs stars with masses between 1.012 and 1.307 M , and initial metallicity of Z = 0.02. These sequences are the result of main sequence stars with masses between 8.8 and 11.8 M . The simulations were performed with the Modules for Experiments in Stellar Astrophysics - MESA code, starting at the zero-age main sequence, through thermally pulsing and mass-loss phases, ending as the white dwarfs at the cooling sequence. Our simulations are full evolutionary, in which we consider the entire evolutionary history of the progenitors. We present reliable nuclear chemical profiles for the whole mass range considered, covering the different expected central compositions, i.e. C/O, O/Ne and Ne/O/Mg, and their dependence with the stellar mass. In addition, we present detailed chemical profiles of hybrid C/O-O/Ne core white dwarfs, found in the mass range between 1.024 and 1.150 M . We present the initial-to-final mass relation, mass-radius relation, and cooling times with improved crystallization limits, considering the effects of atmosphere and core composition.