Novo cronômetro estelar a partir da análise de curvas de luz TESS de estrelas gêmeas solares

• Ano de defesa: 2020
• Autor(a) principal: Ponte, Geisa Teixeira da
• Orientador(a): Valio, Adriana Benetti Marques
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Presbiteriana Mackenzie
• Palavras-chave em Português: estrelas; atividade; tipo solar; técnicas; fotometria
• Área do conhecimento CNPq: CNPQ::ENGENHARIAS::ENGENHARIA AEROESPACIAL
• Link de acesso: https://dspace.mackenzie.br/handle/10899/28426

The variability seen in the brightness of stars on timescale of days is often attributed to the crossing of dark spots on the surface as the star rotates. Stellar activity, known to be associated with the occurrence of spots, depends on the age of the star. Younger stars tend to be much more active and this activity decreases as the stars age. To explore a possible new stellar age indicator, we analyzed the photometric variability of 30 solar twins using 2min cadence light curves of the TESS/NASA space mission. This valuable dataset may help to understand the implications of the variability of magnetic activity in exoplanet research and the concept of habitability. For that, we built a photometric amplitude index ATESS directly correlated with the average index of chromospheric activity logR0 HK, analyzed via precise atmospheric parameters derived from HARPS/ESO spectra. These relations use the rotational modulation observed in TESS light curves due to active regions on the stellar surfaces, consisting of stellar spots and faculae, as a function of activity levels. We built a new tool in Python that optimizes the removal of TESS instrumental systematics, maximizing the analysis of the amplitude of the photometric variability due to the passage of active regions on the star surface. We also analyzed the Sun using 22 years of TSI observations by VIRGO/SOHO. Our results show that the photometric amplitudes are strongly correlated with the levels of chromospheric activity of the solar twin stars in our sample, showing a very clear relationship also with their ages. We demonstrate that the Sun is an ordinary star within this scenario, presenting a behavior as expected due to its activity level and well-established age. This result is in agreement with the literature which established a very robust relationship between age and activity of solar twins. Finally, we understand that the ATESS can be used as an index of chromospheric activity, as well as a stellar chronometer for solar twin stars observed by TESS.