Convection during the Late Stages of Simmering in Type Ia Supernovae

Following the unstable ignition of carbon, but prior to explosion, a white dwarf (WD) in a Type Ia supernova (SN Ia) undergoes a simmering phase. During this time, a central convective region grows and encompasses ~1 M_☉ of the WD over a timescale of ~10³ yr, which sets the thermal and turbulent profile for the subsequent explosion. We study this time-dependent convection and summarize some of the key features that differ from the traditional, steady-state case. We show that the long conductive timescale above the convective zone and the extraction of energy to heat the WD core lead to a decrease of the convective luminosity and the characteristic velocities near the convective zone's top boundary. In addition, differences in the composition between the convective core and the conductive exterior will significantly alter the location of this boundary. In this respect, we find the biggest effect to be due to complete ²²Ne sedimentation prior to carbon ignition. These effects add diversity to the possible WD models, which may alter the properties of SN Ia explosions.