A theoretical and observational spectroscopic study of white dwarf stars

白矮星代表着包括太阳在内的银河系中超过95%的恒星演化的终点。在中心耗尽核燃料后，白矮星只是在数十亿年的时间里悄悄冷却下来。虽然它们的质量与太阳相当，但它们的体积更接近地球，这使得它们非常致密(大约是太阳密度的100万倍)。对这些垂死恒星的研究和它们的基本参数，如温度、质量和化学成分的确定，不仅为我们提供了关于这些恒星的性质的关键信息，而且还提供了关于它们与其直接祖先的进化联系的关键信息。用于测量白矮星基本参数的最准确方法是所谓的光谱技术，即将光谱观测，即恒星流量随波长的分布，与详细恒星大气的预测进行比较，这是蒙特雷亚尔大学最初开发并不断改进的一种方法。恒星大气对应于恒星周围的薄薄的表层，所有的辐射都来自该层。我们项目的目标是通过测量大样本天体的基本参数，并借助适用于这些恒星的合成光谱的改进计算，来提高我们对白矮星的理解。从观测角度来看，我们将确保使用位于亚利桑那州斯图尔德天文台和魁北克省蒙特梅根蒂克天文台的光谱仪，对表面丰度由氢(DA型)和氦(DB型)组成的白矮星进行光谱观测。从理论上讲，我们将计算新一代模式大气和合成光谱，包括本构物理方面的一些改进，如谱线加宽、不透明度和对流能量输运。观测光谱和理论光谱之间的比较将为我们提供更好的白矮星大样本参数，这反过来将有助于了解它们的全球性质以及它们的演化。

White dwarf stars represent the endpoint of stellar evolution for more than 95% of the stars in our galaxy, including our Sun. Having exhausted their nuclear fuel at their center, white dwarf stars simply cool off quietly over periods of billions of years. While their mass is comparable to that of the Sun, their volume is closer to that of Earth, which makes them extremely compact objects (about a million times the density of the Sun). The study of these dying stars and the determination of their fundamental parameters such as temperature, mass, and chemical composition, provide us with crucial information not only about the nature of these stars, but also on the evolutionary link with their immediate progenitors. The most accurate method used for measuring the fundamental parameters of white dwarf stars is the so-called spectroscopic technique where spectroscopic observations, i.e. the distribution of the stellar flux with wavelength, are compared with the predictions of detailed stellar atmospheres, a method originally developed and continuously being improved at the Université de Montréal. A stellar atmosphere corresponds to this thin superficial layer surrounding the star where all the radiation comes from. The goal of our project is to improve our understanding of white dwarf stars by measuring the fundamental parameters of a large sample of objects with the help of improved calculations of synthetic spectra appropriate for these stars. From an observational point of view, we will secure spectroscopic observations of white dwarf stars with surface abundances composed of hydrogen (DA type) and helium (DB type) using spectrographs located at Steward Observatory in Arizona as well as at Mont Mégantic Observatory in Québec. From a theoretical point of view, we will calculate a new generation of model atmospheres and synthetic spectra, including several improvements in the constitutive physics such as line broadening, opacities, and convective energy transport. The comparison between observed and theoretical spectra will provide us with improved parameters for a large sample of white dwarf stars, which in turn will shed some light on their global properties as well as on their evolution.