Estudos de eventos de acresção de matéria em estrelas pré-sequência principal Ae/Be de Herbig

• Ano de defesa: 2004
• Autor(a) principal: Marcelo Medeiros Guimaraes
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Herbig; Física
• Link de acesso: http://hdl.handle.net/1843/ESCZ-692HEH

Herbig Ae/Be objects are pre-main sequence stars with intermediate mass (2 to 10 M) that show high spectroscopic and photometric variability. Most of this variability is due to the circunstellar environment, in the form of a disc and/or an envelope. In this work we looked for evidences of ejection and/or accretion of matter in a sample of Herbig Ae/Be stars that were observed using high resolution spectroscopy. To do this search a synthetic photospheric spectrum was subtracted from the observed one in order to obtain the circumstellar component. Where such patterns were found we did a kinematic analysis and tried to distinguish if these phenomena might be originated by the accretion of a remnant gaseous structure from the primordial cloud (rich in Hydrogen) or a metal rich body (like comets in our Solar System). Evidences of accretion were found for three stars: PDS069N (Hen 3-949), PDS076 (HD142666) and PDS080 (HD145718). To PDS069N we have determined the following physical parameters: Tef = 17000 ± 2000 K, log g = 4.0 ± 0.2, v sin i = 90 ± 10 kms1 and vrad = 7± 2 kms1. We have also found redshifted absorption components in the Balmer lines, Na i D, He i, Si ii and Oi, and that they are correlated to each other. The chemical composition of the infalling matter seems to be richer than the solar one.The physical parameters determined to PDS076 were: Tef = 7300 ± 200 K, log g = 4.0 ± 0.2, v sin i = 66 ± 3 kms1 and vrad = 6± 2 kms1. The possibility that the infalling material have been produced by the evaporation of a cometary body can be excluded based on the presence and value of the circumstellar absorption depth in the Balmer lines. A kinematic analysis of the redshifted absorption components led us to believe that the material is in free fall towards the star. To PDS080 the physical parameters are: Tef = 7300 ± 200 K, log g = 3.8 ± 0.4, v sin i = 115 ± 4 km/s and vrad = 7± 2 kms1. The high values of ¿ in the Balmer lines led us to think that the infalling material was not produced by the evaporation of cometary bodies. The kinematic behaviour of the redshifted absorption components suggest that the material is falling onto the star through the stars magnetic field lines (magnetospheric accretion), similar to what happens in T Tauri stars.