  We report on the results of NanoSIMS isotope imaging of low-density supernova
graphite grains from the Orgueil meteorite. 70 nm thick microtomed sections of
three supernova graphite grains were deposited on Si wafers and isotopically
imaged in the NanoSIMS. These sections contain hotspots of excesses in $^{18}O$
and $^{15}N$ which are spatially well correlated, and are likely carried by
internal TiC subgrains. These hotspots are considerably more enriched in
$^{18}O$ and $^{15}N$ than the host graphite grain. Correlations between
$^{18}O$ and $^{15}N$ excesses indicate that the grains incorporated material
from the He/C supernova zone. Isotope images of the surfaces of some grains
show heterogeneities in their N and O isotope compositions, with extreme
excesses in $^{15}N$ and $^{18}O$. In the microtome sections, we also observe
two types of heterogeneities in the grains' C isotopic compositions: smooth,
radial gradients in $^{12}C/^{13}C$, with this ratio trending toward solar with
increasing radius; and highly anomalous pockets up to 2 {\mu}m in size with
$^{12}C/^{13}C$ > solar that are located near the centers of the grain
sections. Partial isotopic equilibration does not likely explain the C isotopic
heterogeneities. These grains and their constituent parts probably formed in a
stellar environment with changing isotopic composition.
