Modelling spectra of pre-main sequence and magnetic sequence stars

天文学家现在了解了恒星是如何形成的，它们在一生中是如何变化的，以及当它们耗尽燃料、坍塌或爆炸时会发生什么。然而，人们对这个人生故事中的重要步骤仍然知之甚少。 增加我们对恒星的了解的最重要的工具之一是研究恒星光谱，恒星光谱是通过棱镜或其他设备将星光扩散成彩虹而产生的。当我们仔细观察这道彩虹时，我们发现一些特定的颜色比紧邻的颜色相对更亮或更暗。这些特定的减弱或加强的颜色被称为吸收或发射线，它们携带着关于发射光线的恒星的惊人数量的信息：我们可以推断出恒星的表面温度和化学成分，并分辨出这颗恒星是在旋转、脉冲还是磁性的，或者实际上是彼此绕着轨道运行的两颗恒星。 这项提议有两个目标。一种是研究比太阳大几倍的恒星的光谱线，这些恒星具有强大的磁场，并且是疏散星团的成员(像昂宿星团这样的恒星群，它们一起形成，有一个已知的共同年龄)。这些磁性恒星的表面化学成分与普通的非磁性恒星非常不同，通过研究几到10亿年之间不同年龄的疏散星团中的此类恒星，我们希望找到一些线索，了解将不寻常的元素混合带到这些恒星表面的各种过程。 第二个目标是研究恒星的光谱线，这些恒星是最近形成的，它们仍然被一个圆盘包围，其中包含一些气体和尘埃，这些气体和尘埃最终将落到中央恒星上。将气体并入新恒星的实际过程涉及气体和尘埃盘的中介，但这种盘中的条件仍然没有被很好地理解。我们希望通过对盘中产生的光谱发射线的详细研究，阐明气体和尘埃是如何通过盘中到达恒星的。

Astronomers now understand the broad outlines of how stars form, how they change through their lives, and what happens to them when they run out of fuel and collapse or explode. However, important steps in this life story are still poorly or hardly understood. One of the most important tools for increasing our understanding of stars is the study of stellar spectra, which are produced by spreading starlight out into a rainbow of colour with a prism or other device. When we look closely at this rainbow, we find that some specific colours are relatively brighter or fainter than the immediately neighbouring colours. These specific weakened or strengthened colours are called absorption or emission lines, and they carry an astonishing amount of information about the star that emitted the light: we can deduce the surface temperature and the chemical composition, and tell whether the star is rotating or pulsing or magnetic, or is actually two stars in orbit around each other. This proposal has two goals. One is to study spectral lines in stars a few times more massive than the Sun, that have strong magnetic fields, and are members of open clusters (groups of stars like the Pleiades that formed together and have a known common age). These magnetic stars have very different surface chemical composition than commoner, non-magnetic stars, and by studying such stars in open clusters of various ages between a few and a thousand million years, we hope to find some clues to the various processes that bring unusual mixes of elements to the surface of these stars. A second goal is to study spectral lines in stars that have formed so recently that they are still surrounded by a disk containing some of the gas and dust that will eventually fall onto the central star. The actual process of incorporating gas into the new star involves the intermediary of the disk of gas and dust, but conditions in such disks are still not well understood. We hope to clarify how gas and dust move through the disk to the star by detailed study of spectral emission lines produced in the disk.