Deacon, John Richard; (1992) An infrared study of mass loss from hot stars. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The aim of this thesis has been to model the infrared excesses from a large number of early stars to derive velocity laws and mass loss rates. The data used to do this consists of ground-based photometry, obtained mainly at UKIRT and CTIO, which has been combined with IRAS photometry to yield coverage from 1.2μm to 60μm. The photometry of approximately 140 stars has been reduced to a homogenous data set and then dereddened using standard star calibrations tied directly to IRAS photometry and an IR extinction law based on the work of Rieke & Lebofsky and Draine. To derive the IR excesses, the underlying photospheric energy distributions have been represented by intrinsic UBVRI and IR colours which have been calculated for all the models in the Kurucz model atmosphere grid and its Fitzpatrick low log g extension. The IR excess fluxes thus derived have then been modelled assuming spherically symmetric winds parameterised by Castor and Lamers velocity laws of index β. The code used to model the excesses includes a full treatment of electron scattering and free-free and bound-free opacity. It has also been modified to include exact f-f and b-f Gaunt factor routines and a radial dependence of the wind electron temperature due to the net cooling effect produced by heavy element lines beyond ~1.2 stellar radii as predicted by the work of Drew. The code was later modified further to allow density fluctuations at the base of the wind, predicted by the work of Owocki and Rybicki and of Owocki et al., to be included. The effects of the cool wind temperature and of the density fluctuations on the IR emission from the wind is discussed and the velocity laws derived for those stars with known mass loss rates are compared to the current theoretical predictions and to the results of other observational studies. Some of the models have been re-examined following a literature search to obtain all the available infrared photometry for the stars in question. This additional photometry and the new models are described in an Addendum along with a brief discussion of an investigation of how varying the base velocity of the wind affects the predicted wind emission.

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