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Projeto Observacional para 2016A - SO2016A-007
Autor: W.L. Marcolino
Título: Addressing the weak wind problem in massive stars through OSIRIS/near-IR spectroscopy
Resumo: We propose to settle the question regarding the existence of weak winds in O stars through OSIRIS spectroscopy. The weak wind problem has been considered as one of the most urgent issues regarding O stars in the literature (mass-loss rates observed << predicted). Recently, we analyzed 9 late O giants (O8-9III) in the UV region by means of sophisticated atmosphere models. The results indicate that these stars present the weak wind problem, as the late O dwarfs (O8-9V). However, contrary to the case of O dwarfs, our models predicted that not only the UV but near-IR Hydrogen lines (e.g., Pa-alpha), are sensitive to mass-loss rate changes. This can provide a definite test for the reliability of the rates measured from UV diagnostics, which have been a major point of criticism in the literature. The OSIRIS IR spectrometer at SOAR is the ideal instrument to verify our predictions. We propose to observe 6 late O giants. Our observations will have an impact on the mass-loss rates in use in stellar evolution codes as well as in the radiatively driven wind theory.