  We have found that individual presolar silicon carbide (SiC) dust grains from
supernovae show a positive correlation between 49Ti and 28Si excesses, which is
attributed to the radioactive decay of the short-lived (t1/2=330 day) 49V to
49Ti in the inner highly 28Si-rich Si/S zone. The 49V-49Ti chronometer
constrains that these supernova SiC dust grains formed at least two years after
their parent stars exploded. This result supports recent dust condensation
calculations that predict a delayed formation of carbonaceous and SiC grains in
supernovae. The astronomical observation of continuous buildup of dust in
supernovae over several years can, therefore, be interpreted as a growing
addition of C-rich dust to the dust reservoir in supernovae.
