  Nine metal-polluted white dwarfs are observed with medium-resolution optical
spectroscopy,where photospheric abundances are determined and interpreted
through comparison against solar system objects. An improved method of making
such comparisons is presented that overcomes potential weaknesses of prior
analyses, with the numerous sources of error considered to highlight the
limitations on interpretation. The stars are inferred to be accreting rocky,
volatile-poor asteroidal materials with origins in differentiated bodies, in
line with the consensus model. The most heavily polluted star in the sample has
14 metals detected, and appears to be accreting material from a rocky
planetesimal, whose composition is mantle-like with a small Fe-Ni core
component. Some unusual abundances are present: one star is strongly depleted
in Ca, while two others show Na abundances elevated above bulk Earth,
speculated either to reflect diversity in the formation conditions of the
source material, or to be traces of past accretion events. Another star shows
clear signs that accretion ceased around 5 Myr ago,causing Mg to dominate the
photospheric abundances, as it has the longest diffusion time of the observed
elements. Observing such post-accretion systems allows constraints to be placed
on models of the accretion process.
