Multidimensional Modeling of Type I X-ray Bursts. I. Two-Dimensional Convection Prior to the Outburst of a Pure Helium Accretor

TL;DR

This paper uses multidimensional simulations with a low Mach number hydrodynamics code to study the convective phase before a Type I X-ray burst, revealing the importance of high resolution and convective patterns.

Contribution

It introduces a novel method for initial model generation and demonstrates the need for higher resolution in multidimensional simulations of X-ray burst convection.

Findings

Convective patterns influence the burst ignition conditions.

Higher resolution is required to accurately resolve the burning layer.

Multidimensional effects are significant in modeling X-ray burst precursors.

Abstract

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.