Interferometric and spectroscopic monitoring of emission lines: detection of CIRs in hot star winds

Abstract

We present a theoretical study of hot star wind emissivity in the presence of hypothetical large scale wind structures. Contrary to previous investigations that have focused on the resulting P-Cygni profile variability, we investigate the impact on observable optical and near-infrared emission lines. Our working hypothesis assumes, that such extended wind over-densities are formed via a rotationaly modulated stellar mass loss rate, that gives rise to the so-called co-rotating interaction regions (CIR). Within this context, we find that the variability of emission lines traces an un-equivocal S-shape in the frequency-time space, i.e., a spiraling pattern with positive and negative accelerations towards the line-of-sight over one stellar rotation period. Further, we demonstrate how lines forming at different heights can then be used to provide dynamical and geometrical constraints on the wind structures. Complementary to this spectroscopic approach, we also present theoretical expectations for forthcoming VLT-amber observations of a perturbed hot star outflow presenting such CIRs. The spectrally dispersed visibility and fringe phase output by the Differential Interferometry (DI) method show clearly-defined signatures of the presence of these CIRs. Extrapolating the adequacy of DI beyond the detection of CIRs, we speculate that this method provides very fruitful information on putative large scale structures in hot star environments.