Multi-wavelength observing has been particularly fruitful in cool star research. There have been some well-observed examples, eg AB Dor, though ambiguity remains. This raises issues of data information content and model parameter determinacy, which are examined firstly in an optical context. We then widen the discussion to show how multi-site and multi-wavelength data can be combined to point to better constrained models. Particular cases, involving near-simultaneous radiometry and photometry, are discussed to clarify such modelling.

• E. BUDDING(Central Institute of Technology)
• D. ALLEN(Central Institute of Technology)
• D. L. CRAWFORD(Kitt Peak National Observatory)
• K. M. JONES(Department of Physics, The University of Queensland)
• O. B. SLEE(Australia Telescope National Facility)
• M. ZEILIK(Institute for Astrophysics, Department of Physics and Astronomy, Universtiy of New Mexico)