  Using data from the California-Kepler-Survey (CKS) we study trends in
planetary properties with host star metallicity for close-in planets. By
incorporating knowledge of the properties of the planetary radius gap
identified by the CKS survey, we are able to investigate the properties of
planetary cores and their gaseous envelopes separately. Our primary findings
are that the solid core masses of planets are higher around higher metallicity
stars and that these more massive cores were able to accrete larger gas
envelopes. Furthermore, investigating the recently reported result that planets
with radii in the range (2-6Rearth) are more common at short periods around
higher metallicity stars in detail, we find that the average host star
metallicity of H/He atmosphere-hosting planets increases smoothly inside an
orbital period of ~20 days. We interpret the location of the metallicity
increase within the context of atmospheric photoevaporation: higher metallicity
stars are likely to host planets with higher atmospheric metallicity, which
increases the cooling in the photoevaporative outflow, lowering the mass-loss
rates. Therefore, planets with higher metallicity atmospheres are able to
resist photoevaporation at shorter orbital periods. Finally, we find evidence
at 2.8 sigma that planets that do not host H/He atmospheres at long periods are
more commonly found around lower metallicity stars. Such planets are difficult
to explain by photoevaporative stripping of planets which originally accreted
H/He atmospheres. Alternatively, this population of planets could be
representative of planets that formed in a terrestrial-like fashion, after the
gas disc dispersed.
