Be discs in binary systems – II. Misaligned orbits

Abstract

We use a smoothed particle hydrodynamics (SPH) code to examine the effects of\nmisaligned binary companions on Be star discs. We systematically vary the\ndegree of misalignment between the disc and the binary orbit, as well as the\ndisc viscosity and orbital period to study their effects on the density in the\ninner and outer parts of the disc. We find that varying the degree of\nmisalignment, the viscosity, and the orbital period affects both the truncation\nradius and the density structure of the outer disc, while the inner disc\nremains mostly unaffected. We also investigate the tilting of the disc in the\ninnermost part of the disc and find the tilt increases with radius until\nreaching a maximum around 5 stellar radii. The direction of the line of nodes,\nwith respect to the equator of the central star, is found to be offset compared\nto the orbital line of nodes, and to vary periodically in time, with a period\nof half a orbital phase. We also compare the scale height of our discs with the\nanalytical scale height of an isothermal disc, which increases with radius as\n$r^{1.5}$. We find that this formula reproduces the scale height well for both\naligned and misaligned systems but underestimates the scale height in regions\nof the disc where density enhancements develop.\n