Investigation of the dust formation and violent mass loss of evolved stars

演化恒星是我们银河系中恒星尘埃的主要来源，将物质返回星际介质，并为新恒星和行星的形成提供物质。因此，他们的暴力质量损失过程正在接受严密的调查。该项目的主要动机是研究恒星演化后期发生的强烈质量损失，这一点仍然知之甚少。特别是，我们想要重点回答以下问题：渐近巨星分支(AGB)上的恒星脉动与尘埃凝聚序列，从而与质量损失有什么关系？AGB恒星和质量更大的红超巨星(RGs)之间的主要区别是什么？富氧星和富碳星的质量损失有何不同？为了回答这些问题，该项目的重点是利用甚大望远镜干涉仪(VLTI)上的琥珀和MIDI仪器，研究以最高可用角分辨率观察到的不同质量和化学成分的演化恒星。这些数据将通过使用不同的理论代码来利用：辐射传输代码、图像重建代码和多维流体动力学代码。这项建议中的科学项目是基于对安装在VLTI的第一代干涉仪器Amber和MIDI的观测。然而，该项目的一部分也致力于下一代中红外干涉仪器马蒂斯。马蒂斯将在L和M波段打开两个新的观察窗口。它将首次将4个望远镜的光束组合在一起，允许在中红外波段成像。该项目这一部分的重点是协助编写便于用户使用的图像重建代码，以及实施第二代条纹跟踪器。这些任务非常重要，因为马蒂斯预计将于2016年迎来第一缕曙光。

Evolved stars are the major source of stellar dust in our Galaxy, returning matter to the interstellarmedium and providing material for new star and planet formation. As such, their violent mass loss process is under intense investigation. The main motivation of the project is to study the strong mass loss occurring during the late stages of stellar evolution, which is still poorly understood. In particular, we want to focus on answering the following questions: How is the pulsation of stars on the Asymptotic Giant Branch (AGB) related to the dust condensation sequence and thus to the mass loss? What are the main differences between AGB stars and the more massive Red SuperGiant stars (RSGs)? How does the mass loss of oxygen-rich stars differ from that of carbon-rich stars? To answer these questions, the project focuses on studying evolved stars of different masses and chemical compositions observed with the highest available angular resolution, using the AMBER and MIDI instrument at the Very Large Telescope Interferometer (VLTI). The data will be exploited by using different theoretical codes: radiative transfer codes, an image reconstruction code, and a multidimensional hydrodynamical code. The scientific projects in this proposal are based on observations with AMBER and MIDI, the first generation interferometric instruments installed at the VLTI. However, part of the project is also dedicated to the next generation mid-infrared interferometric instrument MATISSE. MATISSE will open two new observing windows in the L and M bands. For the very first time, it will combine beams of 4 telescopes, allowing imaging in the mid-infrared band. This part of the project focuses on assisting with the preparation of user-friendly image reconstruction code, and on the implementation of the second generationfringe tracker. These tasks are of high importance since the first light from MATISSE is expected in 2016.