2014MNRAS.440.3532L

We study the interactions between a protostar and circumstellar disc under the influence of a binary companion to determine the evolution of the mutual misalignment between the stellar spin and disc angular momentum axes. Significant misalignments can be generated as the star-disc system evolves in time such that the frequency of disc precession (driven by the binary companion) and that of stellar precession (driven by the disc) cross each other. This resonance behaviour can be understood in a geometric way from the precession dynamics of spin and disc angular momenta. We show that such resonance crossing can occur under reasonable protostar-disc-binary conditions. The star-disc inclination is also affected by mass accretion and by magnetic star-disc interaction torques, which can either promote or reduce star-disc misalignment. In general, a variety of star-disc misalignment angles are produced within the lifetimes of protoplanetary discs. We discuss the implications of our results for stellar spin orientations in binaries, for the alignments/misalignments of protostellar and debris discs, and for the stellar obliquities in exoplanetary systems. In particular, even for systems where the Kozai effect is absent or suppressed, misaligned planets and hot Jupiters may still be produced during the protoplanetary disc phase.