Microlensing of circumstellar envelopes

III. Line profiles from stellar winds in homologous expansion

¹ Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK e-mail: martin@astro.gla.ac.uk
² Department of Physics, Astronomy and Geology, Box 70652, East Tennessee State University, Johnson City, Tennessee 37614, USA
³ Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, Wisconsin 53706, USA

Received: 25 October 2005
Accepted: 12 December 2005

Abstract

This paper examines line profile evolution due to the linear expansion of circumstellar material obsverved during a microlensing event. This work extends our previous papers on emission line profile evolution from radial and azimuthal flow during point mass lens events and fold caustic crossings. Both “flavours” of microlensing were shown to provide effective diagnostics of bulk motion in circumstellar envelopes. In this work a different genre of flow is studied, namely linear homologous expansion, for both point mass lenses and fold caustic crossings. Linear expansion is of particular relevance to the effects of microlensing on supernovae at cosmological distances. We derive line profiles and equivalent widths for the illustrative cases of pure resonance and pure recombination lines, modelled under the Sobolev approximation. The efficacy of microlensing as a diagnostic probe of the stellar environs is demonstrated and discussed.