Advanced evolutionary stages of lower mass stars

在我职业生涯的大部分时间里，我研究的主要方向是建立尽可能满足观测限制的恒星模型--主要集中在主序星和巨型分支恒星上。事实上，近期将就这些阶段开展更多工作。例如，将与B·古斯塔夫松的Uppsala小组合作，研究使用模型大气作为恒星内部模型的边界条件对预测温度范围的影响。此外，还将与蒙特利尔大学的同事合作，计算适用于考虑扩散过程的贫金属恒星的等时线。然而，在接下来的几年里，我研究的主要目标是将已发表的网格扩展到包括水平分支(HB)和渐近-巨分支(AGB)阶段，以便维多利亚大学的恒星模型可以用于研究复杂的恒星群。最初，这些模型将应用于球状星团，以试图更好地理解所谓的“第二参数问题”(具有非常相似的金属丰度的星团所包含的Hb形态广泛多样性的未知原因)，并改进目前对星团氦丰度的估计。此外，模型的脉动特性将使用G.Fontaine提供的代码来计算，以便利用由簇RR Lyrae变量提供的约束。为了比现有程序更有效地生成AGB模型(大约是现有程序的5倍)，将建立一个混合程序，该程序具有拉格朗日模式和非拉格朗日模式(即，求解P.Eggleton开发的恒星结构方程的方法)，以跟踪在连续壳闪之间薄核燃烧壳的演化。有了这样的代码，就有可能比迄今为止更全面地探索参数空间，从而提高我们对这一演化阶段的理解，这一阶段在星系的化学演化中发挥着特别重要的作用。

The main thrust of my research over much of my career has been to produce stellar models that satisfy observational constraints as tightly as possible - focusing primarily on main-sequence and giant-branch stars. Indeed, additional work on these phases will be carried out in the near term. For instance, the impact on the predicted temperature scale of using model atmospheres as boundary conditions for the stellar interior models will be examined in collaboration with B. Gustafsson's Uppsala group. In addition, isochrones applicable to metal-poor stars that take diffusive processes into account will be computed in collaboration with colleagues at the U. of Montreal. However, the main goal of my research over the next several years is to extend the published grids to include the horizontal-branch (HB) and asymptotic-giant-branch (AGB) phases, so that University of Victoria stellar models may be used to study complex stellar populations. Initially these models will be applied to globular star clusters to try to obtain an improved understanding of the so-called "second-parameter problem" (the unknown cause of the wide diversity in HB morphology encompassed by clusters having very similar metallicities), and to refine current estimates of the cluster helium abundances. Moreover, the pulsational characteristics of the models will be computed using a code provided by G. Fontaine, in order to make use of the constraints provided by the cluster RR Lyrae variables. To generate AGB models much more efficiently than existing programs (by about a factor of 5), a hybrid code will be set up having a Lagrangian mode to follow the evolution, nucleosynthesis, and mixing during He shell flashes in considerable detail (using techniques developed by F. Herwig), as well as a non-Lagrangian mode (i.e., the method of solving the stellar structure equations developed by P. Eggleton) to follow the evolution of thin nuclear-burning shells between consective shell flashes. With such a code, it will be possible to explore parameter space much more fully than has been possible to date, and thereby to improve our understanding of this evolutionary phase, which plays an especially important role in the chemical evolution of galaxies.