Prior to the explosive burning of a white dwarf (WD) that makes a Type Ia
supernova (SN Ia), the star "simmers" for ~10^3 yrs in a convecting, carbon
burning region. I estimate the excitation of g-modes by convection during this
phase and explore their possible affect on the WD. As these modes propagate
from the core of the WD toward its surface, their amplitudes grow with
decreasing density. Once the modes reach nonlinear amplitudes, they break and
deposit their energy into a shell of mass ~10^{-4}M_\odot. This raises the
surface temperature by 6*10^8 K, which is sufficient to ignite a layer of
helium, as is expected to exist for some SN Ia scenarios. This predominantly
synthesizes 28Si, 32S, 40Ca, and some 44Ti. These ashes are expanded out with
the subsequent explosion up to velocities of ~20,000 km/s, which may explain
the high velocity features (HVFs) seen in many SNe Ia. The appearance of HVFs
would therefore be a useful discriminant for determining between progenitors,
since a flammable helium-rich layer will not be present for accretion from a
C/O WD as in a merger scenario. I also discuss the implications of 44Ti
production.Comment: Submitted for publication in The Astrophysical Journal Letters, 5
pages, 1 figure
