Uncertainties in theoretical HeI emissivities: HII regions, primordial abundance and cosmological recombination

Abstract

A number of recent works in astronomy and cosmology have relied upon theoretical He I emissivities, but we know of no effort to quantify the uncertainties in the atomic data. We analyse and assign uncertainties to all relevant atomic data, perform Monte Carlo analyses, and report standard deviations in the line emissivities. We consider two sets of errors, which we call 'optimistic' and 'pessimistic'. We also consider three different conditions, corresponding to prototypical Galactic and extragalactic H II regions and the epoch of cosmo-logical recombination. In the extragalactic H II case, the errors we obtain are comparable to or larger than the errors in some recent Yp calculations, including those derived from cosmic microwave background observations. We demonstrate a systematic effect on primordial abundance calculations; this effect cannot be reduced by observing a large number of objects. In the cosmological recombination case, the errors are comparable to many of the effects considered in recent calculations. © 2008 The Authors. Journal compilation © 2008 RAS.