The Hyades stream as a dynamical signature of spiral structure.

The Hyades stream, or Hyades moving group, has long been thought to be a dispersed vestige of the 
Hyades cluster.  Here we review  recent analyses of the parallax distribution, the mass  function,  and the  
action space distribution of stream stars that have  shown  that it was rather composed of orbits trapped at 
a resonance of  a density disturbance. We then present a numerical model where the Hyades stream is 
linked to the 4:1 inner Lindblad resonance of the spiral structure.  The advantage of this model is that it 
reproduces the Sirius stream at the same time. We then note that this resonant scenario for the origin of  
the  stream should leave a clearly different signature in the element  abundances of member stars than the 
dispersed cluster scenario. In view of this, we  studied the element abundances of a random sample of stars 
belonging to  the Hyades stream, and found two different populations inside the stream: a first small 
population of past Hyades cluster stars and a  large second population  compatible with being a normal thin 
disk population, but with an excess in metallicity.