= Solution
To distinguish the companion, measure the host's <radial velocity> reflex motion to infer a <mass>; a low-mass <star> generally produces a much larger signal than a planet. Also test for a detectable secondary eclipse, colour-dependent dilution, doubled spectral lines and out-of-eclipse ellipsoidal variation. High angular-resolution imaging and shifts of the image <centroid> can identify a blended background <eclipsing binary>. A Jupiter-sized <radius> alone is not decisive because low-mass stars and brown dwarfs can have comparable radii. The three labelled effects on the transit are treated individually below.
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