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Radio Emissions from Substellar Companions of Evolved Cool Stars

A number of substellar companions to evolved cool stars have now been reported. Cool giants are distinct from their progenitor Main Sequence (MS) low-mass stars in a number of ways. First, the mass loss rates of cool giant stars are orders of magnitude greater than for the late-type MS stars. Second, on the cool side of the Linsky-Haisch "dividing line", K and M giant stars are not X-ray sources, although they do show evidence for chromospheres. As a result, cool star winds are largely neutral for those spectral types, suggesting that planetary or brown dwarf magnetospheres will not be effective in standing off the stellar wind. In this case one expects the formation of a bow shock morphology at the companion, deep inside its magnetosphere. We explore radio emissions from substellar companions to giant stars with ionised winds or neutral winds.