  Presolar grains constitute remnants of stars that existed before the
formation of the solar system. In addition to providing direct information on
the materials from which the solar system formed, these grains provide
ground-truth information for models of stellar evolution and nucleosynthesis.
Here we report the in-situ identification of two unique presolar graphite
grains from the primitive meteorite LaPaz Icefield 031117. Based on these two
graphite grains, we estimate a bulk presolar graphite abundance of 5(-3)(+7)
ppm in this meteorite. One of the grains (LAP-141) is characterized by an
enrichment in 12C and depletions in 33,34S, and contains a small iron sulfide
subgrain, representing the first unambiguous identification of presolar iron
sulfide. The other grain (LAP-149) is extremely 13C-rich and 15N-poor, with one
of the lowest 12C/13C ratios observed among presolar grains. Comparison of its
isotopic compositions with new stellar nucleosynthesis and dust condensation
models indicates an origin in the ejecta of a low-mass CO nova. Grain LAP-149
is the first putative nova grain that quantitatively best matches nova model
predictions, providing the first strong evidence for graphite condensation in
nova ejecta. Our discovery confirms that CO nova graphite and presolar iron
sulfide contributed to the original building blocks of the solar system.
