The Young Stellar Population of IC 1613 I . A New Catalogue of OB Associations ⋆ ⋆ ⋆

Context. Determining the parameters of massive stars is crucial to understand many processes in galaxies and the Universe, since these objects are important sources of ionization, chemical enrichment and momentum. 10m class telescopes enable us to perform detailed quantitative spectroscopic analyses of massive stars in other galaxies, sampling areas of different metallicity. Relating the stars to their environment is crucial to understand the physical processes ruling their formation and evolution. Aims. In preparation for the new instrumentation coming up on the GTC, our goal is to build a list of massive star candidates in the metal-poor irregular galaxy IC 1613. The catalogue must have very high astrometric accuracy, apt for the current generation of multi-object spectrographs. A census of OB associations in this galaxy is also needed, to provide important additional information about age and environment of the candidate OB stars. Methods. From INT-WFC observations, we have built an astrometric and photometric catalogue of stars in IC 1613. Candidate blue massive stars are preselected from their colors. A friends-of-friends algorithm is developed to find their clustering in the galaxy. While a common physical origin for all the members of the associations cannot be ensured, this is a necessary first step to place candidate OB stars in a population context. Results. We have produced a deep catalogue of targets in IC 1613 that covers a large field of view. To achieve high astrometric accuracy a new astrometric procedure is developed for the INT-WFC data. We have also built a catalogue of OB associations in IC 1613. We have found that they concentrate in the central regions, specially in the H ii bubbles. The study of extinction confirms that it is patchy, with local values of color-excess above the foreground value. Conclusions.