Mass loss from inhomogeneous hot star winds I. Resonance line formation in 2D models
J. O. Sundqvist 1, J. Puls 1, A. Feldmeier 2
2Institut für Physik und Astronomie, Universität Potsdam, Germany
Small-scale clumping in the winds of hot, massive stars is
conventionally included in spectral analyses by assuming optically
thin clumps, a void inter-clump medium, and a smooth velocity
field. To reconcile investigations of different diagnostics within
such models, a highly clumped wind with very low mass-loss rates needs
to be invoked. Particularly, unsaturated UV resonance lines seem to
indicate rates an order of magnitude (or even more) lower than
previously accepted values. We investigate resonance line formation in
inhomogeneous hot star winds with non-monotonic velocity fields by
means of 2D stochastic and pseudo-2D radiation-hydrodynamic wind
models. A Monte-Carlo radiative transfer code is presented and used to
produce synthetic line spectra. Results: The optically thin clumping
limit is only valid for very weak lines. For intermediate strong
lines, the velocity spans of the clumps are of central
importance. Current hydrodynamical models predict spans that are too
large to reproduce observed profiles unless a very low mass-loss rate
is invoked. By simulating lower spans in 2D stochastic models, the
profile strengths become drastically reduced, and are consistent with
higher mass-loss rates. To simultaneously meet the constraints from
strong lines, the inter-clump medium must be non-void. A first
comparison to the observed PV doublet in the O6 supergiant lam Cep
confirms that a stochastic 2D model reproduces observations with a
mass-loss rate roughly ten times higher than that derived from the
same lines but assuming optically thin clumping. Tentatively this may
resolve discrepancies between theoretical predictions, evolutionary
constraints, and recent derived mass-loss rates, and suggests a
re-investigation of the structure predicted by current hydrodynamical
models.
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