Asteroseismology in action: a test of spin-orbit synchronism in the close binary system Feige 48

Aims. In this paper, we provide a test of spin-orbit synchronism in the close binary system Feige 48. This system is made of a rapidly pulsating subdwarf B (sdB) star with an unseen companion, most likely a white dwarf. The presence of nonradial oscillations offers the opportunity to infer the inner profile and period of rotation of the primary star through asteroseismology. This constitutes the key element for testing spin-orbit synchronism in depth, since stellar internal layers are inaccessible to traditional techniques.