Confidence limits of evolutionary synthesis models

III. On time-integrated quantities

¹ UMR CNRS 5572, Observatoire Midi-Pyrénées, 14 avenue Édouard Belin, 31400 Toulouse, France
² Centre d'Études Spatiales des Rayonnements, CNRS/UPS, BP 4346, 31028 Toulouse Cedex 4, France
³ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
⁴ Observatoire de Genève, 1290 Sauverny, Switzerland
⁵ Yale University, PO Box 208101, New Haven, CT 06520-8101, USA
⁶ Universidad de Chile, Casilla 36-D, Santiago, Chile
⁷ Departamento de Física Teórica C-XI, Universidad Autónoma de Madrid, 28049 Madrid, Spain
⁸ Instituto de Astronomía, UNAM, Apdo. Postal 70-264, 04510 México D.F., Mexico
⁹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany

Corresponding author: M. Cerviño, mcs@laeff.esa.es

Received: 8 June 2001
Accepted: 9 July 2001

Abstract

Evolutionary synthesis models are a fundamental tool to interpret the properties of observed stellar systems. In order to achieve a meaningful comparison between models and real data, it is necessary to calibrate the models themselves, i.e. to evaluate the dispersion due to the discreteness of star formation as well as the possible model errors. In this paper we show that linear interpolations in the plane, that are customary in the evaluation of isochrones in evolutionary synthesis codes, produce unphysical results. We also show that some of the methods used in the calculation of time-integrated quantities (kinetic energy, and total ejected masses of different elements) may produce unrealistic results. We propose alternative solutions to solve both problems. Moreover, we have quantified the expected dispersion of these quantities due to stochastic effects in stellar populations. As a particular result, we show that the dispersion in the ratio increases with time.