  A new technique to detect protoplanets is by observing the kinematics of the
surrounding gas. Gravitational perturbations from a planet produce peculiar
`kinks' in channel maps of different gas species. In this paper, we show that
such kinks can be reproduced using semi-analytic models for the velocity
perturbation induced by a planet. In doing so we i) confirm that the observed
kinks are consistent with the planet-induced wake; ii) show how to quantify the
planet mass from the kink amplitude; in particular, we show that the kink
amplitude scales with the square root of the planet mass for channels far from
the planet velocity, steepening to linear as the channels approach the planet;
iii) show how to extend the theory to include the effect of damping, which may
be needed in order to have localized kinks.
