  Results. We found that gas-phase silicon was present throughout the Rosetta
mission. Furthermore, the presence of sodium and iron atoms near the comet's
perihelion confirms that sputtering cannot be the sole release process for
refractory elements into the gas phase. Nickel was found to be below the
detection limit. The search for parent species of any of the identified gas
phase refractories has not been successful. Upper limits for a suite of
possible fragment species (SiH, SiC, NaH, etc.) of larger parent and daughter
species have been obtained. Furthermore, Si did not exhibit the same drop in
signal as do common cometary gases when the spacecraft is pointed away from the
nucleus. The combined results suggest that a direct release of elemental
species from small grains on the surface of the nucleus or from small grains in
the surrounding coma is a more likely explanation than the previous assumption
of release via the dissociation of gaseous parent molecules.
