  Alhena ($\gamma$ Gem) was observed in the frame of the BRITE (BRIght Target
Explorer) spectropolarimetric survey, which gathers high resolution, high
signal-to-noise, high sensitivity, spectropolarimetric observations of all
stars brighter than V=4 to combine seismic and spectropolarimetric studies of
bright stars.
  We present here the discovery of a very weak magnetic field \textbf{on} the
Am star Alhena, thanks to very high signal-to-noise spectropolarimetric data
obtained with Narval at T\'elescope Bernard Lyot (TBL). All previously studied
Am stars show the presence of ultra-weak (sub-Gauss) fields with Zeeman
signatures with an unexpected prominent positive lobe. However, Alhena presents
a slightly stronger (but still very weak, only a few Gauss) field with normal
Zeeman signatures with a positive and negative lobe, as found in stronger field
(hundreds or thousands of Gauss) stars. It is the first detection of a normal
magnetic signature in an Am star.
  Alhena is thus a very interesting object, which might provide the clue to
understanding the peculiar shapes of the magnetic signatures of the other Am
stars.
