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

¹ Departamento de Astrofísica, Facultad de Físicas, Universidad Complutense, 28040 Madrid, Spain
² Instituto de Astronomía, U.N.A.M., Apdo. Postal 70-264, 04510 México D.F., México

Received: 24 April 1997
Accepted: 17 June 1997

Abstract

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.