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A&A Supplement series, Vol. 127, February I 1998, 597-605

Received April 24; accepted June 17, 1997

Reliable random error estimation in the measurement of line-strength indices

N. Cardieltex2html_wrap1885, J. Gorgastex2html_wrap1885, J. Cenarrotex2html_wrap1885, and J.J. Gonzáleztex2html_wrap1891

tex2html_wrap1885 Departamento de Astrofısica, Facultad de Fısicas, Universidad Complutense, 28040 Madrid, Spain
tex2html_wrap1891 Instituto de Astronomıa, U.N.A.M., Apdo. Postal 70-264, 04510 México D.F., México


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

Copyright by the European Southern Observatory (ESO)