A. A. Nordlund

THE STAR FORMATION RATE OF SUPERSONIC MAGNETOHYDRODYNAMIC TURBULENCE

This work presents a new physical model of the star formation rate (SFR), which is verified with an unprecedented set of large numerical simulations of driven, supersonic, self-gravitating, magneto-hydrodynamic (MHD) turbulence, where collapsing cores are captured with accreting sink particles. The model depends on the relative importance of gravitational, turbulent, magnetic, and thermal energies, expressed through the virial parameter, αvir, the rms sonic Mach number, , and the ratio of mean gas pressure to mean magnetic pressure, β0. The SFR is predicted to decrease with increasing αvir (stronger turbulence relative to gravity), to increase with increasing (for constant values of αvir), and to depend weakly on β0 for values typical of star forming regions (-20 and β0 1-20). In the unrealistic limit of β0 → ∞, that is, in the complete absence of a magnetic field, the SFR increases approximately by a factor of three, which shows the importance of magnetic fields in the star formation process, even when they are relatively weak (super-Alfvenic turbulence). The star-formation simulations used to test the model result in an approximately constant SFR, after an initial transient phase. The dependence of the SFR on the virial parameter is shown to agree very well with the theoretical predictions.

Three-Dimensional Radiative Hydrodynamics for Disk Stability Simulations: A Proposed Testing Standard and New Results

Recent three-dimensional radiative hydrodynamics simulations of protoplanetary disks report disparate disk behaviors, and these differences involve the importance of convection to disk cooling, the dependence of disk cooling on metallicity, and the stability of disks against fragmentation and clump formation. To guarantee trustworthy results, a radiative physics algorithm must demonstrate the capability to handle both the high and low optical depth regimes. We develop a test suite that can be used to demonstrate an algorithms ability to relax to known analytic flux and temperature distributions, to follow a contracting slab, and to inhibit or permit convection appropriately. We then show that the radiative algorithm employed by Mejia and Boley et al. and the algorithm employed by Cai et al. pass these tests with reasonable accuracy. In addition, we discuss a new algorithm that couples flux-limited diffusion with vertical rays, we apply the test suite, and we discuss the results of evolving the Boley et al. disk with this new routine. Although the outcome is significantly different in detail with the new algorithm, we obtain the same qualitative answers. Our disk does not cool fast due to convection, and it is stable to fragmentation. We find an effective α ≈ 10-2. In addition, transport is dominated by low-order modes.

ABUNDANCE OF 26 Al AND 60 Fe IN EVOLVING GIANT MOLECULAR CLOUDS

The nucleosynthesis and ejection of radioactive

THE OBSERVABLE PRESTELLAR PHASE OF THE INITIAL MASS FUNCTION

^{26}

Convection and the Origin of Evershed Flows

Al (t

Magnetic Fields: Modeling And ATST Observations

_{1/2} \sim

Zooming in on Star Formation

0.72\,Myr) and

Supergranule Scale Flux Emergence Simulations

^{60}

The Thermal Relaxation Time

Fe, (t

Solar Magneto-Convection Simulations of Emergin Flux

_{1/2} \sim