Deriving instrumental point spread functions from partially occulted images.

The point spread function (PSF) of an imaging system describes the response of the system to a point source. Accurately determining the PSF enables one to correct for the combined effects of focusing and scattering within the imaging system and, thereby, enhance the spatial resolution and dynamic contrast of the resulting images. We present a semi-empirical semi-blind methodology to derive a PSF from partially occulted images.

H3+ cooling in primordial gas.

Simulations of the thermal and dynamical evolution of primordial gas typically focus on the role played by H2 cooling. H2 is the dominant coolant in low-density primordial gas and it is usually assumed that it remains dominant at high densities. However, H2 is not an effective coolant at high densities, owing to the low critical density at which it reaches local thermodynamic equilibrium and to the large opacities that develop in its emission lines.