Modelling spectra of pre-main sequence and magnetic sequence stars

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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.