  About 30% to 40% of classical novae produce dust 20-100 days after the
outburst, but no presolar stardust grains from classical novae have been
unambiguously identified yet. Although several studies claimed a nova paternity
for certain grains, the measured and simulated isotopic ratios could only be
reconciled assuming that the grains condensed after the nova ejecta mixed with
a much larger amount of close-to-solar matter. However, the source and
mechanism of this potential post-explosion dilution of the ejecta remains a
mystery. A major problem with previous studies is the small number of
simulations performed and the implied poor exploration of the large nova
parameter space. We report the results of a different strategy, based on a
Monte Carlo technique, that involves the random sampling over the most
important nova model parameters: the white dwarf composition; the mixing of the
outer white dwarf layers with the accreted material before the explosion; the
peak temperature and density; the explosion time scales; and the possible
dilution of the ejecta after the outburst. We discuss and take into account the
systematic uncertainties for both the presolar grain measurements and the
simulation results. Only those simulations that are consistent with all
measured isotopic ratios of a given grain are accepted for further analysis. We
also present the numerical results of the model parameters. We identify 18
presolar grains with measured isotopic signatures consistent with a CO nova
origin, without assuming any dilution of the ejecta. Among these, the grains
G270 2, M11-334-2, G278, M11-347-4, M11-151-4, and Ag2 6 have the highest
probability of a CO nova paternity.
