A&A Supplement series, Vol. 127, February I 1998, 597-605
Received April 24; accepted June 17, 1997
N. Cardiel, J. Gorgas, J. Cenarro, and J.J. GonzálezDepartamento de Astrofısica, Facultad de Fısicas, Universidad Complutense, 28040 Madrid, Spain
We present a new set of accurate formulae for the computation of random errors in the measurement of atomic and molecular line-strength indices. The new expressions are in excellent agreement with numerical simulations. We have found that, in some cases, the use of approximated equations can give misleading line-strength index errors. It is important to note that accurate errors can only be achieved after a full control of the error propagation throughout the data reduction with a parallel processing of data and error images. Finally, simple recipes for the estimation of the required signal-to-noise ratio to achieve a fixed index error are presented.
keywords: methods: data analysis -- methods:
analytical -- methods: statistical