Estudo espectroscópico de estrelas T Tauri no aglomerado NGC 2264

• Ano de defesa: 2020
• Autor(a) principal: Silva, Marcus Vinicius Grilo da
• Orientador(a): Souto, Diogo Martins
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Programa de Pós-Graduação: Pós-Graduação em Física
• Palavras-chave em Português: Astrofísica; Formação estelar; Estrelas T Tauri; Acreção; NGC 2264; Periodicidade; Variabilidade; Linha Hα; T Tauri Stars; Accretion; Periodicity; Variability; Line Hα
• Área do conhecimento CNPq: CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: https://ri.ufs.br/jspui/handle/riufs/14726

We present a spectroscopic study of two classical T Tauri stars, Mon-667 and Mon-996, belonging to the young open cluster NGC 2264. These stars were observed during the CSI 2264 campaign of the FLAMES spectrograph in 2011. From the analysis of the light curves obtained in this campaign, these stars were classified as aperiodic. Using a periodicity study, we find that these stars presented periodicity in the Hα line (Sousa et al., 2016). This is an unusual behavior as aperiodic objects on the light curve are not expected to be periodic on the Hα line. The unexpected feature of these objects motivated the development of this work. To analyze the periodicity of these stars, we used the periodogram analysis for unevenly spaced data described by Scargle (1982). With this method we can verify if the objects continued to present periodicity in the Hα line in 2013, if the velocity intervals that presented periodicity in 2013 remained the same as in 2011, and if periods remained unchanged from the previous observations. From the comparison between the Hα line profiles of 2011 and 2013, we find that the Mon-996 Hα profile in 2013 maintained the same morphology of 2011. However, its periodogram changed considerably, having periodicity in non-periodic regions in 2011. The periodicity observed in the red wing of ~ 8 days remained less pronounced. Also, the blue wing started presenting periodicity, which may have been generated by the wind. We observed that the star Mon-667 showed a drastic change in its profile of the Hα line from 2011 to 2013, no longer in emission and showing absorption in that line. The periodic velocity range and the period of the spectral region have been modified. The absorption spectral region presented a periodicity of ~ 3 days. We examined the correlation of the Hα line profile variability of the studied objects using the correlation matrix calculation method. In 2013, the blue and red wings of the Hα profile of the star Mon-996 showed a good correlation with themselves. However, there was no good correlation between one wing and another. Also, we realize that there is an anticorrelation region between these wings at velocity ranges of ~ -50 to ~ -200 km/s and ~ 100 to ~ 200 km/s. These regions correspond to emission in blue and red wings, which vary anti-phase. Consequently, this results in anticorrelated variability between the wings. In Mon-667, there was a good correlation between the blue and red wings with themselves for velocities in the range of ~ -100 to ~ 0 km/s and ~ 0 to ~ 200 km/s. In addition, there was also a good correlation between the wings at these intervals. In the Hα line, we found that these velocity ranges correspond to the absorption region of the profile in the spectrum of some nights, which indicates that there is a single process causing the absorption in the Hα line of this star. In 2013, the absence of Hα in emission in the observed period indicates that the magnetospheric accretion decreased significantly, indicating that there was no emission in Mon-667. Although no emission occurred, we observed that the spectra of particular nights, the absorption was filled. Figuring out what may have caused a significant change in the Hα line profile for the Mon-667 case is hard to understand and is still an open question.