  We present the results of our 600 ks RGS observation as part of the
multiwavelength campaign on Mrk 509. The very high quality of the spectrum
allows us to investigate the ionized outflow with an unprecedented accuracy due
to the long exposure and the use of the RGS multipointing mode. We detect
multiple absorption lines from the interstellar medium and from the ionized
absorber in Mrk 509. A number of emission components are also detected,
including broad emission lines consistent with an origin in the broad line
region, the narrow OVII forbidden emission line and also (narrow) radiative
recombination continua. The ionized absorber consists of two velocity
components (v = -13 \pm 11 km/s and v = -319 \pm 14 km/s), which both are
consistent with earlier results, including UV data. There is another tentative
component outflowing at high velocity, -770 \pm 109 km/s, which is only seen in
a few highly ionized absorption lines. The outflow shows discrete ionization
components, spanning four orders of magnitude in ionization parameter. Due to
the excellent statistics of our spectrum, we demonstrate for the first time
that the outflow in Mrk 509 in the important range of log xi between 1-3 cannot
be described by a smooth, continuous absorption measure distribution, but
instead shows two strong, discrete peaks. At the highest and lowest ionization
parameters we cannot differentiate smooth and discrete components.
