Linear spectropolarimetry in stars different than the Sun: what can we learn?

Polarimetry is considered as an important searching tool in Astronomy and it deserves to be a standard observational technique for a variety of astrophysical contexts: from stellar photospheric inhomogeneities to protoplanetary nebulae, as well as in the exoplanet research field. Despite this, however, the difficulties involved in the measurements and in the theoretical interpretation made this technique not as widespread as it deserves. In this talk I will review the results of my research about the diagnostic potential of optical high resolution linear spectropolarimetry in stars different than the Sun.  At this purpose, after an introduction on the observational technique, I will focus on the polarised spectrum of the post-AGB binary system 89 Herculis: from the very inner regions of the stellar envelope to the first observational evidence of a micro-Gauss level magnetic field. Finally, I will discuss on the applicability and future prospect of this technique in the more general context of stellar physics.