A Physical Basis for the H-band Blue-edge Velocity and Light-curve Shape Correlation in Context of Type Ia Supernova Explosion Physics
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2019. The American Astronomical Society. All rights reserved. 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 (LC) shape of normal, transitional and subluminous 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 56Ni mass fraction, X Ni, falls to the order of 0.03-0.10. For a given 56Ni mass, M(56Ni), v edge is sensitive to the specific kinetic energy E kin(M(56Ni)/M WD) of the corresponding region. Combining v edge with LC parameters (i.e., s BV, 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 that are too large to explain the observations. Finally, the subluminous 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.