Joint spectral-polarimetric analysis of accelerated hot star wind transient

Description

Transient stellar mass loss has already been studied as an inverse problem by Brown and Wood (1994) and by Calvini, Bertero and Brown (1995), in the hypothesis of a uniform flow speed nu (r)= nu 0. Here we consider a generalization of this inverse problem to an accelerated wind profile based on an empirical form for nu (r) with an adjustable acceleration parameter c0. We deduce the two generalized convolution equations linking the time ( tau ) evolution of the equatorial mass loss rate m( tau ) and the asphericity 'shape function' u( tau ) to the observed polarization and absorption line strength variations in time. In order to perform the regularized inversion of these equations, we introduce an iterative algorithm which allows us to take into account the positivity constraint on the solutions. This method is tested on simulated data for various choices of hypothetical, m( tau ) and a( tau ) and the results are compared with those provided by Fourier deconvolution, for several values of the parameter c0. It is found that the iterative algorithm is more efficient than the Fourier one and that, for both techniques, recoveries are less good for finite c0 (accelerating wind) than for c0 to infinity (impulsive acceleration at the stellar surface and then steady wind speed) due to slower sampling of the important inner-wind region.

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