Excesso infravermelho e discos de detritos em estrelas do aglomerado M67

• Ano de defesa: 2021
• Autor(a) principal: Brito, Francisco de Assis Chaves de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Rio Grande do Norte; Brasil; UFRN; PROGRAMA DE PÓS-GRADUAÇÃO EM FÍSICA
• Palavras-chave em Português: Física; Excesso no infravermelho; Discos de detrito; Aglomerado M67; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: https://repositorio.ufrn.br/handle/123456789/49900

The search for circumstellar material orbiting different star families is one of the most studied topics in Stellar Astronomy, mainly because the presence of this material indicates the existence of exoplanets. In addition, their physical properties can tell us how much a planetary system may resemble the Solar System, indicating how this system may evolve. Current studies show the presence of circumstellar material with temperatures close to those found in the asteroid belt of the Solar System, but with widely varying dimensions and compositions. Although most studies of circumstellar dust and disks reveal that this material tends to disappear for stellar ages exceeding 300-400 million years, there are research showing that debris disks can be found orbiting stars with ages on the order of the solar age, i.e., 4 to 5 billion years. The main objective of this doctoral thesis is to search for debris disks that orbit stars of the Open Cluster M67, which is close to the age of the Sun. From this point of view M67 Cluster may contain stars at different evolutionary stages and may offer unique conditions to search for debris disks. It should be noted that this aspect offers conditions to better understand how circumstellar debris disks evolve with age. This study adopted the strategy of searching for infrared excess in M67 stars, using observations collected by the WISE Mission, which provides fluxes at wavelengths corresponding to the bands 3.3, 4.7, 12 and 22 µm. The diagnostics to identify the excess in M67 stars compared the spectral distributions of energy, built from theoretical models, and observational fluxes obtained at different wavelengths, extending from about 0.5 to 22 µm, covering observations made by the Gaia Mission, 2MASS Project and WISE Mission. From an initial sample of 1520 stars, members of M67, 1380 stars were identified, presenting observations at WISE wavelengths 3.3, 4.7, 12 and 22 µm, defined as bands W1, W2, W3 and W4 respectively. These stars with WISE measurements also showed observations in the G, GRP and GBP bands of Gaia, as well as in the J, H and K bands of 2MASS. From the sample of 1380 stars, three objects designated J085103.24+114547.3, J085202.94+105932.7 and J085116.70+114529.6 show excesses with physical meaning (SNR > 3), absence of contamination by other sources or artifacts and circular images. These results point to a fraction of 0.2% of M67 stars with an excess at 22 µm, a value far below that cited in the literature for stars on the order of or with greater ages than the solar age, which is about 4%. Considering that this excess is associated with the presence of circumstellar material, defined as debris disk, we used standard models to estimate the physical parameters associated with the disks: luminosity fraction, radius, mass and temperature. Although the temperatures of the material, between 225 and 300 K, are on the order of the temperatures known for the solar Zodiacal Cloud, the values obtained for the luminosity fraction and the mass, respectively 104 and 105 times higher than the Zodiacal Cloud values, show that the material around the stars J085103.24+114547.3, J085202.94+105932.7 and J085116.70+114529.6 is brighter and denser than what is expected at the age of M67. Such material must also be composed of second-generation dust and debris and no longer be composed of material from the planetary formation phase. This unusual characteristic, that is, brighter and denser material, seems to indicate the presence of one or more replenishment mechanisms in these regions, through violent collisions between asteroids, planetesimals and planets.