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The nature of the Hyades stream, or Hyades moving group, is a long-standingquestion of Galactic Astronomy. Is this stream caused by non-axisymmetricperturbations of the galactic potential, such as transient or quasi-stationaryspiral waves, or by the on-going evaporation of the Hyades cluster? A simpleobservational test has been designed to answer that question. Using theGeneva-Copenhagen survey of F and G dwarfs, we compare the mass distributionand metallicity of the stream to those of field disk stars. If the Hyadesstream is composed of stars trapped at resonance, its mass distribution shouldobey the present-day mass function (PDMF) of the disk, and its metallicityshould reflect its origin in the inner regions of the Galaxy. On the otherhand, if it is an evaporated cluster, we expect a different mass distribution,depending on the inital mass function (IMF) of the cluster, and on theproportion of evaporated stars as a function of mass. We find that extremeconditions have to be adopted for the selective evaporation and IMF of thecluster to make the observed mass ditribution of the stream only roughlyconsistent (at a one-sigma level) with the coeval evaporated cluster scenario.The observed mass distribution is in much better agreement with the PDMF of thefield. We also note that the peculiar metallicity of the stream is inconsistentwith that of a field population from the solar neighbourhood trapped in theprimordial cluster during its formation process and subsequently evaporated.These observations thus favour a resonant origin for the Hyades stream.Comment: 7 pages, 4 figures,, accepted for publication in A&

The Hyades stream: an evaporated cluster or an intrusion from the inner disk?