The topic of magnetism finds its way into discussions of all stages of stellar evolution. Magnetic fields are thought to play a role in the fragmentation of gas clouds, to couple a young star to its protostellar disk, to be a major energy source for solar-type activity, and are dramatically manifest in the distorted spectra and exotic emission mechanisms of compact remnants, such as white dwarfs. White dwarfs are the end products of the vast majority of stars and display the conditions in a stellar interior. Magnetic fields from 10,000 to one billion Gauss have been detected on about 5 dozen white dwarfs. Thus, the study of white dwarfs may have as much to offer to our understanding of the effects of magnetism on stellar evolution as any other avenue of study. This project is a comprehensive study of the new magnetic white dwarfs emerging from the Sloan Digital Sky Survey. A few hundred of the expected 10,000 white dwarfs will exhibit magnetic fields above one million Gauss and be selectable from the survey spectroscopy and will contain many new hydrogen- and helium-atmosphere objects as well as stars portraying atomic and molecular species whose spectra have not yet been computed in strong magnetic fields. Follow-up polarization observations will allow a search for rotational modulation of the features and/or polarization as well as detailed modeling to assess the magnetic field structure over the stellar surface. When complete, the large catalog of magnetic white dwarfs will permit us to evaluate questions of the distribution of magnetic white dwarfs as a function of field strength, of the coupling efficiency of a (magnetic) stellar core to its envelope during the giant stage, and of potential correlations between field strength and white dwarf mass, age, composition, and Galactic population.
Broader Impact: This work is of broad and fundamental importance to physics as well as astrophysics, since these objects are our only laboratories in which the behavior of atomic and molecular species can be empirically studied in very strong magnetic fields. For both hydrogen and neutral helium, observations of magnetic white dwarfs have provided the critical impetus for new calculations of atomic structures and transition probabilities in very strong fields, an activity that has led to a deeper understanding of atomic physics as well as the development of new computational techniques. Correlations between the level of magnetism and rotation rate, cooling age, or atmospheric composition would be important clues to the influence of magnetic fields in previous phases.
