Adaptive Mesh Refinement (AMR) Codes

The FLASH Adaptive Mesh Refinement Hydrodynamics Code

We seek to study the dynamics of mixing and transport processes in the presolar cloud and in the solar nebula, in the context of isotopic heterogeneity introduced either by shock-triggered collapse of the presolar cloud or by infall from an x-wind outflow, the two leading explanations for the widespread evidence of short-lived radioactivities in chondritic refractory inclusions and, much more rarely, in chondrules. We have developed a new hydrodynamical code for studying these problems, using the FLASH adaptive mesh refinement code. FLASH allows the problem of shock-wave triggering and injection to be studied with an unprecedented degree of high spatial resolution, which is likely to be critical to the question of simultaneous triggering and injection when nonisothermal shock front thermodynamics is employed. The FLASH code will permit extending these investigations down to the scale of the solar nebula, where nebular transport and mixing processes can be studied in general terms, applicable to isotopically heterogeneous grains falling onto the nebular surface as a result of either shock-triggered collapse or x-wind outflows. We will seek in part to learn whether spatial and temporal heterogeneity inherited from such sources can survive subsequent nebular mixing processes and can help to explain certain isotopic abundance patterns seen in the inner Solar System and the asteroid belt. The development of the FLASH code should also prove useful for Boss's studies of the formation of giant planets by the disk instability mechanism.

The ENZO Adaptive Mesh Refinement Hydrodynamics Code

We seek to improve our understanding of the star formation process, through detailed models of the collapse and fragmentation of magnetized, molecular cloud cores. The theoretical models should result in an improved understanding of binary and multiple protostar formation, as well as of the minimum mass of a newly-formed protostellar fragment. The initial conditions for the models will be based on observations of dense molecular cloud cores on the verge of collapse, i.e., dense cores without embedded protostellar objects, with a range of initial masses, rotation rates, and magnetic field strengths. We are using the ENZO adaptive mesh refinement code to study these problems. ENZO allows 3D MHD calculations to be performed, as well as flux-limited radiative transfer. The significanse of this work lies in the fact that the majority of pre-main-sequence and main-sequence stars are known to be members of binary or multiple systems. Thus, we cannot claim to understand the formation of stars until we understand the processes through which binary stars form. The main question to be addressed by this research is whether or not magnetic fields are able to stifle fragmentation during the dynamic, gravitational collapse of dense molecular cloud cores. While considerable theoretical effort has already been expended on the fragmentation of 3D magnetic molecular clouds, none of this has been achieved with a full treatment of radiative transfer. Observations have shown the importance of magnetic fields for the dynamics of molecular cloud complexes, and theoretical work on star-forming regions implies that we are close to confirming protostellar fragmentation as the process responsible for forming the great majority of binary stars, and possibly for the formation of brown dwarfs and sub-brown dwarfs as well.

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