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The past 20 years have seen remarkable advances in spectropolarimetric instrumentation that have allowed us, for the first time, to identify some magnetic stars in most major stages of stellar evolution. We are beginning to see the broad outline of how such fields change during stellar evolution, to confront theoretical hypotheses and models of magnetic field structure and evolution with detailed data, and to understand more of the ways in which the presence of a field in turn affects stellar structure and evolution. [ABSTRACT FROM PUBLISHER]

Many astronomical sources of radiation emit polarised radiation, for example because of the presence of a disk which produces linear polarisation by scattering some photospheric radiation, or because of the presence of a magnetic field, which leads to circular and sometimes linear polarisation of spectral line profiles. Measuring the wavelength dependence of the polarisation of radiation from such sources can reveal valuable and interesting constraints on the nature of the objects observed. This paper summarises the basic ideas of spectropolarimetry and describes some of the information it can provide. [ABSTRACT FROM PUBLISHER]

Stars in various parts of the HR diagram often have atmospheres in which the departure from the simplest kind of plane-parallel model is largely dominated by a single physical effect. For example, massive stars and giants exhibit symptoms of strong winds and lower Main Sequence stars are very strongly influenced by the presence of deep and energetic envelope convection. Main Sequence A stars, in contrast, appear to display the competing effects of several physical effects of comparable magnitude. The effects which can be detected by observation include large and relatively simple magnetic fields, strong surface convection, pulsation (often in multiple modes), diffusion of specific species under the competing influences of gravity and radiative acceleration, and (more indirectly) internal turbulent mixing, weak winds, and non-thermal heating. This situation makes these stars extremely useful as laboratories to explore and to understand the physics of these various phenomena, and how these effects interact with each other. This review will summarize some of the interconnections that are gradually being understood and emphasize some of the major remaining problems.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html [ABSTRACT FROM PUBLISHER]