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Decretion disks and outflows around fast-spinning stars

Abstract

This project aims at strengthening the collaborative ties between Prof. Alex Carciofi's group at the Universidade de São Paulo, and Prof. Michel Curé's group at Universidad de Valparaíso. Both groups share many interests in common and, most importantly, possess quite complementary competences. The applicants have already collaborated in the past, and with the present project this collaboration will increase both in scope and depth, including the exchange of undergraduate and graduate students. The main focus of the project is on detailed modeling of disk-like distributions of gas that surround certain types of massive stars. Two different kinds of objects will be studied. On the one hand, Prof. Curé's hydrodynamical models for radiative outflows will be employed to study disks around B[e] stars. These rare and poorly understood stars are one of the phases of massive star evolution, but their exact evolutionary status is unknown. Yet more mysterious is how these stars form their dense circumstellar envelope. Prof. Carciofi's expertise on radiative transfer will allow for detailed theoretical predictions from Prof. Curé's model to be obtained. The comparison between these predictions and observations (line profiles, polarization, etc.) will bring new constraints to the model, and provide the basis for which it can be improved. The other kind of object are the classical Be stars (CBes). These objects are main sequence stars that are also surrounded by a circumstellar disk. However, contrary to B[e]s, it is a quite well established fact that CBe disks are driven by viscosity, and not radiation pressure. However, recent results in the literature point to the fact that radiative forces act on top of viscosity to drive away disk material, a process known as disk ablation. We propose to combine the experience of both applicants to build a disk model around CBes that include both the effects of viscosity and ablation. The results of this project will be of paramount importance to other researchers in this field and will firmly establish the groups in São Paulo and Valparaíso, along with their collaborators, as world leaders in the study of circumstellar disks around hot stars. (AU)

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