Observations and theory both point out that the magnetic photosphere is not smooth but irregular at optically-thin scales. The relevance of these irregularities for a proper magnetic field diagnostics depends upon the not yet known structure of the magnetic field fluctuations (and, of course, on the purpose of our determination). Sánchez Almeida &

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At least 60% of stars appear to be binary and about half of these are close enough to interact. Because of the enormous expansion on the AGB, many of these interactions will involve an AGB star and a relatively compact companion, anything from a low-mass main-sequence star to a degenerate remnant. Mass loss plays the dominant role in determining

Physical processes in the Sun give rise to an ample variety of structures on different spatial scales that in many cases are very small, with sizes probably below the resolution limit of existing solar telescopes (see Sánchez Almeida, 1997; Sánchez Almeida and Bonet, 1997). Thus, the interpretation of solar phenomena requires the study of these

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