Interferometric and spectroscopic monitoring of emission lines

Detection of CIRs in hot star winds

¹ N&S Sterrenkunde Universiteit Utrecht, Princetonplein 5, 3584 CC Utrecht, The Netherlands e-mail: l.dessart@phys.uu.nl
² Max-Planck-Institut für Astronomie Königstuhl 17, 69117 Heidelberg, Germany e-mail: chesneau@mpia-hd.mpg.de

Corresponding author: L. Dessart, l.dessart@phys.uu.nl

Received: 30 April 2002
Accepted: 31 July 2002

Abstract

We present a theoretical study of hot star wind variability in the presence of hypothetical large scale wind structures. Contrary to previous investigations that have focused on P-Cygni profiles, we investigate the impact on observable optical and near-infrared emission lines. Our working hypotheses assume that such extended wind structures are formed via a rotationally modulated stellar wind mass loss rate that gives rise to the so-called co-rotating interaction regions and that the modelled wind emissivity suffers from no opacity effect. Within this context, we find that the variability of emission lines traces an unambiguous S-shape in the frequency–time space, i.e. a spiralling 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 be used to provide dynamical and geometrical constraints on wind structures. Complementary to this spectroscopic approach, we also present theoretical expectations for VLT-AMBER interferometric observations of such a perturbed hot star outflow. For a fixed baseline orientation and length (space-based interferometer), the spectrally dispersed visibility and fringe phase output by the Differential Interferometry (DI) method show strong variable signatures, over a rotation period, of the same nature as those determined from spectroscopy. In the realistic case of both variable length and baseline orientation (ground-based interferometer), the DI method still yields a high detection sensitivity and geometrical characterisation of large scale wind structures.