On measuring the deuterium abundance in QSO absorption systems

We describe the results of numerical simulations aimed at evaluating techniques for potential measurements of the deuterium abundance in extragalactic absorption clouds. The calculations provide a guide to the precision with which we may hope to measure D/H using existing observational facilities. The measurement error can be small enough to provide valuable cosmological constraints, even if the deuterium absorption cannot be seen as a separate feature in the wing of the hydrogen lines and instead is only seen as an extension in the blue wing of one or more of the hydrogen lines. (author)