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Master's Dissertation
DOI
10.11606/D.14.2013.tde-10092014-144416
Document
Author
Full name
Felipe Donizeti Teston Navarete
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2013
Supervisor
Committee
Damineli Neto, Augusto (President)
Diaz, Marcos Perez
Jablonski, Francisco Jose
Title in Portuguese
Procura de Estrelas de Alta Massa em Formação
Keywords in Portuguese
estrelas de alta massa
formação estelar
infravermelho
jatos moleculares
levantamento
Abstract in Portuguese
O mecanismo de formação de estrelas de alta massa é um dos problemas fundamentais em Astrofísica e um dos menos compreendidos. Duas teorias predizem a formação destes objetos, que se formariam via i) colisão de estrelas de baixa massa, ou ii) acreção por disco circunstelar. Atualmente, ambas as teorias carecem de testes observacionais críticos. Não obstante, o número de estrelas de alta massa jovens já identificadas na Galáxia corresponde a uma fração muito menor do que o esperado pela função de massa inicial. Este trabalho apresenta um estudo observacional de candidatos a MYSOs, selecionados a partir do levantamento Red MSX Source. Observações de 376 objetos nos filtros estreitos do H2 em 2.12 mícrons e num contínuo adjacente foram realizadas para identificar jatos moleculares colimados e 296 delas são apresentadas nesse trabalho. As observações do hemisfério Norte foram realizadas com o telescópio CFHT (Havaí) enquanto os objetos do hemisfério Sul, foram observados com o telescópio SOAR (Chile). A análise dos mapas de emissão em H2 permitiu concluir que 150 dos 296 objetos (51%) estão associados a emissões extensas em H2, e 62 delas foram classificadas como emissões polares. A análise da razão de aspecto das estruturas identificadas mostra que as emissões associadas a fontes com maior luminosidade apresentam baixo grau de colimação, tal como sugere o cenário de geração dos jatos a partir de ventos emanados pela pressão de radiação do disco circunstelar. A baixa fração de emissões polares (apenas 21% da amostra) indica que o tempo de vida dessas estruturas devem ser curtos. As evidências observacionais encontradas nesse trabalho corroboram o cenário de acreção via disco circunstelar e invalidam o modelo formação via coalescência de estrelas de baixa massa, que requer ambientes relativamente densos e não é capaz de produzir jatos colimados.
Title in English
Search for Massive Stars in Early Stages of Formation
Keywords in English
infrared
massive stars
molecular jets
star formation
survey
Abstract in English
Very few massive stars in early formation stages were clearly identified in our Galaxy. The formation process of these objects is still unclear and two theories predict the formation of massive stars: i) by merging of low mass stars or ii) by an accretion disk. There are no critical observational evidences to choose between them. The lack of observational evidences combined with the small number of known massive stars in formation in our Galaxy does not allow us to choose between these scenarios. We present a near-infrared survey of MYSOs candidates selected from the Red MSX Source survey. Such catalog is based on an accurate revision of distances and luminosities, overcoming the limitations and failures in previous searches of this kind. 376 targets were observed through the H2 narrow-band filter at 2.12 microns and in the continuum to identify collimated molecular jets. 296 targets were successfully processed using the THELI pipeline and are presented. Observations in the Northern Hemisphere were carried at the CFHT telescope (Hawaii) while the Southern targets were observed with the Soar Telescope (Chile). The results show that 150 of the 296 sources display extended H2 emission and 62 of them are polar. The analysis of the aspect ratio of the structures indicates that emissions associated with higher luminosity sources have low degree of collimation. This is in agreement with the scenario of the radiation pressure-driven outflows from the circunstellar discs. The low fraction of sources associated with polar jets (21%) indicates a short timescale of such structures. The observational evidences found on this work support the accretion scenario and show that coalescence of low-mass stars (which may require relatively dense environments and is not expected to produce jet-like structures) is not likely to explain most of the studied MYSOs candidates.
 
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Publishing Date
2014-11-26
 
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