2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/8632Under the assumption of a specific nonminimal coupling of torsion to Under the assumption of a specific nonminimal coupling of torsion to electromagnetism, spacetime is birefringent in the presence of a gravitational field leading to depolarization of light emitted from extended astrophysical sources. We use polarimetric data of the magnetic white dwarf RE J0317-853 to set for the very first time constraints on the essential coupling constant for this effect, giving k^2 <22 m^2. electromagnetism, spacetime is birefringent in the presence of a gravitational field leading to depolarization of light emitted from extended astrophysical sources. We use polarimetric data of the magnetic white dwarf RE J0317-853 to set for the very first time constraints on the essential coupling constant for this effect, giving k^2 <22 m^2.4 pages, 1 Figure, to appear in the proceedings of the 14th European Workshop on White Dwarfs, eds. D. Koester and S. Moehler, ASP Conf. SeriesAstrophysicstext