  The nature of the Hyades stream, or Hyades moving group, is a long-standing
question of Galactic Astronomy. Is this stream caused by non-axisymmetric
perturbations of the galactic potential, such as transient or quasi-stationary
spiral waves, or by the on-going evaporation of the Hyades cluster? A simple
observational test has been designed to answer that question. Using the
Geneva-Copenhagen survey of F and G dwarfs, we compare the mass distribution
and metallicity of the stream to those of field disk stars. If the Hyades
stream is composed of stars trapped at resonance, its mass distribution should
obey the present-day mass function (PDMF) of the disk, and its metallicity
should reflect its origin in the inner regions of the Galaxy. On the other
hand, if it is an evaporated cluster, we expect a different mass distribution,
depending on the inital mass function (IMF) of the cluster, and on the
proportion of evaporated stars as a function of mass. We find that extreme
conditions have to be adopted for the selective evaporation and IMF of the
cluster to make the observed mass ditribution of the stream only roughly
consistent (at a one-sigma level) with the coeval evaporated cluster scenario.
The observed mass distribution is in much better agreement with the PDMF of the
field. We also note that the peculiar metallicity of the stream is inconsistent
with that of a field population from the solar neighbourhood trapped in the
primordial cluster during its formation process and subsequently evaporated.
These observations thus favour a resonant origin for the Hyades stream.
