Acknowledgements

We thank the referee for helpful suggestions which have improved the presentation of this work. We wish to thank Dr. Harry Ferguson for helpful discussions and for providing the STIS profile. This material is based upon work supported by the National Science Foundation under Grant No. 9970884. Part of the work reported here was done at the Institute of Geophysics and Planetary Physics, under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. MJD acknowledges support from an Australian Research Council Large Grant.

© Copyright Astronomical Society of Australia 1997