In this contribution we present the results from a 1 homogeneous quantitative spectroscopic analysis of ∼400 Galactic O-type stars targeted by the IACOB and OWN surveys. The ultimate objective is to perform a modern reassessment of one of the long-standing problems in the field of massive stars: the elusive detection of mid O-type stars close to

Since massive stars form preferentially as members of close binary systems, we use dense grids of detailed binary evolution models to explore how binary evolution shapes the main-sequence morphology of young star clusters. We propose that binary mergers might be the origin of the blue main sequence stars in young star clusters. Our results imply

The Instrumentation Division of the Instituto de Astrofísica de Canarias (IAC) is involved since several years in upgrading its capacities to design and manufacture optical components. To this end, we have created a new laboratory (Centre for Advanced Optical Systems, CSOA) which will be capable to design, fabricate and qualify large optical