We present multidimensional simulations of the early convective phase
preceding ignition in a Type I X-ray burst using the low Mach number
hydrodynamics code, MAESTRO. A low Mach number approach is necessary in order
to perform long-time integration required to study such phenomena. Using
MAESTRO, we are able to capture the expansion of the atmosphere due to
large-scale heating while capturing local compressibility effects such as those
due to reactions and thermal diffusion. We also discuss the preparation of
one-dimensional initial models and the subsequent mapping into our
multidimensional framework. Our method of initial model generation differs from
that used in previous multidimensional studies, which evolved a system through
multiple bursts in one dimension before mapping onto a multidimensional grid.
In our multidimensional simulations, we find that the resolution necessary to
properly resolve the burning layer is an order of magnitude greater than that
used in the earlier studies mentioned above. We characterize the convective
patterns that form and discuss their resulting influence on the state of the
convective region, which is important in modeling the outburst itself.Comment: 47 pages including 18 figures; submitted to ApJ; A version with
higher resolution figures can be found at
http://astro.sunysb.edu/cmalone/research/pure_he4_xrb/ms.pd