Calibration of Star Formation Rate Tracers using Evolutionary Synthesis Models H. Ot´ ı-Floranes and J.M. Mas-Hesse Abstract Starburst phenomena can be characterized by their Star Formation Rate, which measures the mass converted to stars per unit time within the starburst re- gion. Many diverse expressions for this magnitude, using the emission of the bursts at different wavelengths, have been suggested in the literature: UV radiation emit- ted by young stars, FIR emission from dust heated by the UV field, recombination lines from the gas nebula surrounding the stars, X-ray emission from X-ray bina- ries, etc... Our objective is to use last generation evolutionary synthesis models to calibrate the different Star Formation Rate (for constant stellar formation bursts), or Star Formation Strength (for instantaneous bursts) tracers in a consistent way. The first step performed has been to derive the calibration of the soft X-ray luminosity as a Star Formation Rate/Strength tracer. In this contribution we present the same kind of analyses performed on several other tracers at lower energies, such as the UV continuum, the production of ionizing photons per unit of time, the total infrared emission, etc. We also compare the expressions yielded by the models with those frequently used in the literature and discuss the ranges of usability of the latter ones. Several results are presented, among which we stress the importance of taking into account both the age of the burst considered, as well as the type of burst (extended or instantaneous) for the sources studied. H. Ot´ ı-Floranes Laboratorio de Astrof´ ısica Espacial y F´ ısica Fundamental, CAB (CSIC–INTA), POB 78, 28691 Villanueva de la Ca˜ nada, Spain, and Dpto. de F´ ısica Moderna, Facultad de Ciencias, Universidad de Cantabria, 39005 Santander, Spain, e-mail: otih@laeff.inta.es J.M. Mas-Hesse Laboratorio de Astrof´ ısica Espacial y F´ ısica Fundamental, CAB (CSIC–INTA), POB 78, 28691 Villanueva de la Ca˜ nada, Spain, e-mail: mm@laeff.inta.es 1