Line profile variability from tidal interactions in binary systems

Abstract

We present the results of ab initio calculations of the photospheric line-profile variability produced by the tidal deformations in binary systems. We use the one-layer approximation to compute the effects produced on a primary star's equatorial region by its companion in the general case of arbitrary rotational velocity (Veq), eccentricity and viscosity, ν. For an eccentric binary such as ϵ Per, the computed absorption lines display bumps that are superposed on the rotationally broadened profile and that travel from the blue side of the line towards the red, qualitatively similar to the observations. The strength and multiplicity of the bumps depend on orbital phase. In the case of binaries with circular orbits, non-synchronous rotation leads to strong profile variability which can be described in terms of inverted “S”-shape patterns in grey-scale representations of the variability. The radial velocity curves obtained by measuring the centroid of the varying line-profiles are distorted with respect to the true radial velocity curves. This effect may introduce significant uncertainties in the mass determination of unseen companions. The line-profile variability is produced almost entirely by the azimuthal component of the velocity perturbations, . We put forth the hypothesis that the differentially-rotating external layers that develop in non-synchronous binary systems may lead to the generation of magnetic activity near the stellar surface. The possibility of constraining the values of ν near the stellar surface through the use of line-profile variability is also suggested.