Our recent work demonstrates a correlation between the high-velocity blue edge , v _ { edge } , of the iron-peak Fe/Co/Ni H -band emission feature and the optical light curve shape of normal , transitional and sub-luminous type Ia Supernovae ( SNe Ia ) .
We explain this correlation in terms of SN Ia physics . v _ { edge } corresponds to the sharp transition between the complete and incomplete silicon burning regions in the ejecta .
It measures the point in velocity space where the outer ^ { 56 } Ni mass fraction , X _ { Ni } , falls to the order of 0.03-0.10 .
For a given ^ { 56 } Ni mass , M ( ^ { 56 } Ni ) , v _ { edge } is sensitive to the specific kinetic energy E _ { kin } ( M ( ^ { 56 } Ni ) / M _ { WD } ) of the corresponding region .
Combining v _ { edge } with light curve parameters ( i.e. , s _ { BV } , \Delta m _ { 15 ,s } in B and V ) allows us to distinguish between explosion scenarios .
The correlation between v _ { edge } and light-curve shape is consistent with explosion models near the Chandrasekhar limit .
However , the available sub- M _ { Ch } WD explosion model based on SN 1999by exhibits velocities which are too large to explain the observations .
Finally , the sub-luminous SN 2015bo exhibits signatures of a dynamical merger of two WDs demonstrating diversity among explosion scenarios at the faint end of the SNe Ia population .