Is it bigger than a breadbox? Probing stellar secrets by modelling spectra of magnetic and other stars

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The most obvious astronomical object in the sky, our Sun, is a typical star. At night most of what we see in the sky is other stars, bodies much like our Sun except that they come in a wide variety of sizes, surface temperatures, distance, etc. For much of the past century, many astronomers have been actively trying to obtain information about individual stars (such as how much mass each has), to understand what stars are like below their glowing surfaces (How hot and how dense is the interior? Is the material gaseous?), and particularly to understand how stars form and change, and eventually collapse to huge hot cinders.***Learning about stars requires us to squeeze as much information as possible from the faint light they send to us. This light contains an astonishing amount of information. By studying the light in detail, we can often discover how large the star is, how hot, how far away, and how massive. We can also get more detailed information about the surface layer (the star's "atmosphere''), for example how dense the gas is, what the chemical composition of the gas is, and whether the gas is quiet or is bubbling and blowing like a windy day. ***My overall research programme focusses on using starlight to try to answer specific questions about specific kinds of stars. For example, some stars are observed to be permeated by strong magnetic fields. I am looking at the fields of a number of stars that are in environments which allow us to estimate their ages, and searching for evidence of how the average magnetism of these stars changes with age, from young stars to older ones. Answering this question should help us to understand how magnetic fields grow and change in stars. ***Another aspect of my programme involves looking for very weak magnetism in white dwarf stars. These are the hot stellar corpses that result when a star like the Sun runs out of fuel and collapses to become a "tiny'' body, about as large as the earth, that simply cools through the ages. Again this should help us to understand magnetic fields in stars better. ***I am also looking at the light from stars that are so young that they still have around them some of the gas that gravity pulled together to form the new star. The gas that is close to the star but has not yet fallen onto the surface is heated by the light from the new star, and glows. This glow can be analysed to find out more about that gas - how much material is there, how hot it is, and so on. ***Each of these aspects of my research digs into a very small, specific question about stars, but the results are like pieces of a huge jigsaw puzzle - putting them all together allows us to understand better the big story of how stars form and change through their lives.**