A novel method to bracket the corotation radius in galaxy disks: vertex
  deviation maps
  We map the kinematics of stars in simulated galaxy disks with spiral arms
using the velocity ellipsoid vertex deviation (l$_v$). We use test particle
simulations, and for the first time, fully self-consistent high resolution
N-body models. We compare our maps with the Tight Winding Approximation model
analytical predictions. We see that for all barred models spiral arms rotate
closely to a rigid body manner and the vertex deviation values correlate with
the density peaks position bounded by overdense and underdense regions. In such
cases, vertex deviation sign changes from negative to positive when crossing
the spiral arms in the direction of disk rotation, in regions where the spiral
arms are in between corotation (CR) and the Outer Lindblad Resonance (OLR). By
contrast, when the arm sections are inside the CR and outside the OLR, l$_v$
changes from negative to positive.We propose that measurements of the vertex
deviations pattern can be used to trace the position of the main resonances of
the spiral arms. We propose that this technique might exploit future data from
Gaia and APOGEE surveys. For unbarred N-body simulations with spiral arms
corotating with disk material at all radii, our analysis suggests that no clear
correlation exists between l$_v$ and density structures.
