  We present optical identification and high-resolution spectroscopy of ROSAT
sources in the field of the old open cluster M 67. For the first time it is
possible to analyze coronal and chromospheric activity of active stars in a
solar-age cluster, and to compare it with field stars. ROSAT observed the high
X-ray luminosity tail of the cluster sources. In agreement with what expected
from studies of field stars, most of the detected X-ray sources are binaries,
preferably with short periods and eccentric orbits. In addition, several of the
M 67 ROSAT sources have peculiar locations in the cluster colour-magnitude
diagram. This is most likely due to rather complex evolutionary histories,
involving the presence of mass transfer or large mass losses. The X-ray
luminosity of the sources does not scale with the stellar parameters in an
obvious way. In particular, no relationship is found between coronal emission
and stellar magnitude or binary period. The Ca II K chromospheric flux from
most of the counterparts is in excess to that of single stars in the cluster by
one order of magnitude. The X-ray luminosity of the sources in the old M 67 is
one order of magnitude lower than the most active active binaries in the field,
but comparable to that of the much younger binaries in the Hyades.
