Stellar spectropolarimetry: basic principles, observing strategies, and diagnostics of magnetic fields

Abstract

A large fraction of night-time astronomical polarimetric measurements is aimed at the detection of stellar magnetic fields. These kinds of measurements are often performed at the limit of instrumental capabilities, and it is of paramount importance to employ observational and data-reduction techniques that allow one to reach the highest possible precision. This chapter is a review of these techniques ranging from the basic principles to the presentation of recent results. I will start with the definition of the Stokes parameters and with an analytical characterization of the optical devices that are most commonly used to measure the polarization of light for objects of astrophysical interest. I will then discuss the observational and data-reduction techniques that help minimize the instrumental effects, allowing one at the same time to perform basic quality checks of the measured signals. Next, I will recapitulate the Zeeman effect and show how analyses of Stokes-parameter profiles can be exploited for the detection and modeling of stellar magnetic fields. Lastly, I will describe a method for field detection based on high-resolution spectropolarimetry and a method based on low-resolution spectropolarimetry. © Springer Science+Business Media B.V. 2011.