Remarks on statistical errors in equivalent widths

Equivalent width measurements for rapid line variability in atomic spectral lines are degraded by increasing error bars with shorter exposure times. We derive an expression for the error of the line equivalent width sigma(W-lambda) with respect to pure photon noise statistics and provide a correction value for previous calculations. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.