Towards a Molecular Inventory of Protostellar Discs

The chemical environment in circumstellar discs is a unique diagnostic of the thermal, physical and chemical environment. In this paper we examine the structure of star formation regions giving rise to low mass stars, and the chemical environment inside them, and the circumstellar discs around the developing stars.Comment: 9 page PDF, 550 kbyte

On the Timescale for the Formation of Protostellar Cores in Magnetic Interstellar Clouds

We revisit the problem of the formation of dense protostellar cores due to ambipolar diffusion within magnetically supported molecular clouds, and derive an analytical expression for the core formation timescale. The resulting expression is similar to the canonical expression = t_{ff}^2/t_{ni} ~ 10 t_{ni} (where t_{ff} is the free-fall time and t_{ni} is the neutral-ion collision time), except that it is multiplied by a numerical factor C(\mu_{c0}), where \mu_{c0} is the initial central mass-to-flux ratio normalized to the critical value for gravitational collapse. C(\mu_{c0}) is typically ~ 1 in highly subcritical clouds (\mu_{c0} << 1), although certain conditions allow C(\mu_{c0}) >> 1. For clouds that are not highly subcritical, C(\mu_{c0}) can be much less than unity, with C(\mu_{c0}) --> 0 for \mu_{c0} --> 1, significantly reducing the time required to form a supercritical core. This, along with recent observations of clouds with mass-to-flux ratios close to the critical value, may reconcile the results of ambipolar diffusion models with statistical analyses of cores and YSO's which suggest an evolutionary timescale \~ 1 Myr for objects of mean density ~ 10^4 cm^{-3}. We compare our analytical relation to the results of numerical simulations, and also discuss the effects of dust grains on the core formation timescale.Comment: 11 pages, 2 figures, accepted for publication in the Astrophysical Journa

Time-Dependent Eddy-Mean Energy Diagrams and Their Application to the Ocean

Insight into the global ocean energy cycle and its relationship to climate variability can be gained by examining the temporal variability of eddy–mean flow interactions. A time-dependent version of the Lorenz energy diagram is formulated and applied to energetic ocean regions from a global, eddying state estimate. The total energy in each snapshot is partitioned into three components: energy in the mean flow, energy in eddies, and energy temporal anomaly residual, whose time mean is zero. These three terms represent, respectively, correlations between mean quantities, correlations between eddy quantities, and eddy-mean correlations. Eddy–mean flow interactions involve energy exchange among these three components. The temporal coherence about energy exchange during eddy–mean flow interactions is assessed. In the Kuroshio and Gulf Stream Extension regions, a suppression relation is manifested by a reduction in the baroclinic energy pathway to the eddy kinetic energy (EKE) reservoir following a strengthening of the barotropic energy pathway to EKE; the baroclinic pathway strengthens when the barotropic pathway weakens. In the subtropical gyre and Southern Ocean, a delay in energy transfer between different reservoirs occurs during baroclinic instability. The delay mechanism is identified using a quasigeostrophic, two-layer model; part of the potential energy in large-scale eddies, gained from the mean flow, cascades to smaller scales through eddy stirring before converting to EKE. The delay time is related to this forward cascade and scales linearly with the eddy turnover time. The relation between temporal variations in wind power input and eddy–mean flow interactions is also assessed

Super Star Clusters in SBS0335-052E

As one of the lowest metallicity star forming galaxies, with a nucleus of several super star clusters, SBS0335-052E is the subject of substantial current study. We present new insights on this galaxy based on new and archival high spatial resolution NICMOS and ACS images. We provide new measurements and limits on the size of several of the SSCs. The images have sufficient resolution to divide the star formation into compact regions and newly discovered extended regions, indicating a bi-modal form of star formation. The star formation regions are dated via the equivalent width of the Pa alpha emission and we find that two of the extended regions of star formation are less than 10 million years old. Our previous finding that stellar winds confine the photo-ionizing flux to small regions around individual stars is consistent with the new observations. This may allow planet formation in what would traditionally be considered a harsh environment and has implications for the number of planets around globular cluster stars. In addition the images pinpoint the regions of H2 emission as located in, but not at the center of the two star forming super star clusters, S1 and S2.Comment: Accepted by the Astrophysical Journa

Indian Country Criminal Justice, the Dual-Sovereignty Doctrine, and Best Practices for Curbing Multiple Prosecutions

The dual-sovereignty doctrine is a significant carve-out to the Fifth Amendment’s Double Jeopardy Clause, allowing individuals to be criminally prosecuted twice for the same alleged conduct, as long as those prosecutions are conducted by different sovereigns. There is much scholarship on the doctrine, most of it critical. The vast majority of this scholarship examines the doctrine’s application in the state-federal context, devoting little attention to its role in the tribal-federal context. Nor is there substantial data on the doctrine’s application in the tribal-federal context. This thesis takes an initial step in filling this knowledge gap. It analyzes how the dual-sovereignty doctrine interacts with the unique framework of criminal law in Indian country, illuminating tribal sovereignty concerns and issues of fairness for defendants that the doctrine creates or exacerbates in the tribal-federal context. It also lays the groundwork for further study of the doctrine’s application in the tribal-federal context, with an eye toward identifying when, why, and with what frequency dual tribal and federal prosecutions arise, as well as the best practices tribal justice systems may already be using that mitigate potential tribal sovereignty concerns and fairness issues

Occasional papers

no.4 (1994