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 IIregions and the epoch of cosmological 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.

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Published in Monthly Notices of the Royal Astronomical Society, v. 393, issue 1, p. L36 -L40 .

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2009 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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