We analyze the production of the element Cr in galactic chemical evolution ( GCE ) models using the NuGrid nucleosynthesis yields set .
We show that the unusually large [ Cr/Fe ] abundance at [ Fe/H ] \approx 0 reported by previous studies using those yields and predicted by our Milky Way model originates from the merging of convective Si-burning and C-burning shells in a 20 M _ { \sun } model at metallicity Z = 0.01 , about an hour before the star explodes .
This merger mixes the incomplete burning material in the Si shell , including ^ { 51 } V and ^ { 52 } Cr , out to the edge of the carbon/oxygen ( CO ) core .
The adopted supernova model ejects the outer 2 M _ { \sun } of the CO core , which includes a significant fraction of the Cr-rich material .
When including this 20 M _ { \odot } model at Z = 0.01 in the yields interpolation scheme of our GCE model for stars in between 15 and 25 M _ { \sun } , we overestimate [ Cr/Fe ] by an order of magnitude at [ Fe/H ] \approx 0 relative to observations in the Galactic disk .
This raises a number of questions regarding the occurrence of Si-C shell mergers in nature , the accuracy of different simulation approaches , and the impact of such mergers on the pre-supernova structure and explosion dynamics .
According to the conditions in this 1D stellar model , the substantial penetration of C-shell material into the Si-shell could launch a convective-reactive global oscillation , if a merger does take place .
In any case , GCE provides stringent constraints on the outcome of this stellar evolution phase .