  We present a 3D study of the formation of refractory-rich exospheres around
the rocky planets HD219134b and c. These exospheres are formed by surface
particles that have been sputtered by the wind of the host star. The stellar
wind properties are derived from magnetohydrodynamic simulations, which are
driven by observationally-derived stellar magnetic field maps, and constrained
by Ly-alpha observations of wind mass-loss rates, making this one of the most
well constrained model of winds of low-mass stars. The proximity of the planets
to their host star implies a high flux of incident stellar wind particles, thus
the sputtering process is sufficiently effective to build up relatively dense,
refractory-rich exospheres. The sputtering releases refractory elements from
the entire dayside surfaces of the planets, with elements such as O and Mg
creating an extended neutral exosphere with densities larger than 10/cm3,
extending to several planetary radii. For planet b, the column density of OI
along the line of sight reaches 10^{13}/cm2, with the highest values found
ahead of its orbital motion. This asymmetry would create asymmetric transit
profiles. To assess its observability, we use a ray tracing technique to
compute the expected transit depth of the OI exosphere of planet b. We find
that the transit depth in the OI 1302.2A line is 0.042%, which is a small
increase relative to the continuum transit (0.036%). This implies that the
sputtered exosphere of HD219134b is unlikely to be detectable with our current
UV instruments.
