Massive stars are key agents in the chemical and dynamical evolution of the Universe. Not only for millions of years do they continously deliver radiative and mechanical energy to their surroundings together with newly formed elements. They also explode as different kinds of Supernovae when they reach their final moment, injecting comparable amounts of energy in a few seconds and polluting the medium with heavy elements. In spite of its small number, its impact is enormeous. Our research on massive stars will focus in the present subproject in three areas:

(i) the exploitation of the large, high quality multiepoch and multiwavelength spectroscopic database set up during the previous AYA project, the IAC database of OB stars, IACOB. This database will be used to dissentangle the role of the different physical processes that determine the evolution and fate of massive stars by analyzing the large number of spectra with our automatic tools, whose accuracy we have tested. Processes presently demanding attention are angular momentum transfer and loss, multiplicity, pulsations, stellar winds and magnetic fields. To optimize our results we will extend our database and combine it with those of our collaborators (OWN, CAFE-BEANS, GOSSS), will participate in international efforts (VFTS, WEAVE, BOB, GES, Gaia) and will compare with stellar evolutionary models calculated by international experts collaborating in our project. Telescopes of all sizes, from the 1.2 m MERCATOR to the 10.4m GTC will be used to achieve our aim, together with the distributed computing tool Condor.

(ii) use nearby galaxies as stellar laboratories and explore the dependency of massive stars physics on metallicity and environment by observing them spectroscopically at distances d<10 Mpc. The results of the analyses will be incorporated into population synthesis models. This will allow us to assess the reliability of its extrapolation to the early Universe. The use of large telescopes and their multiobject instruments, particularly OSIRIS and MEGARA in the GTC, combined with our participation in the above mentioned internacional surveys and LEGUS (at HST, from which we will set up catalogs of candidate massive stars) will be of fundamental importance here. In a larger temporal scale, HARMONI@E-ELT will be the required instrument to continue this research line.

(iii) Identify the massive stellar clusters population in the Milky Way by exploiting our optimized search tools and upgraded stellar models in the near IR. Use the NIR spectra to reveal stellar structure details not accessible from the optical spectra (particularly, wind clumping close to the photosphere). At the same time, check the capabilities of the NIR to obtain reliable stellar parameters solely from this wavelength range. Key here will be the use of multiobject spectrographs in the NIR, specially EMIR@GTC and KMOS@VLT.