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Hot stars are the main source of ionization of the interstellar medium and its enrichment due to heavy elements. Constraining the physical conditions of their environments is crucial to understand how these stars evolve and their impact on the evolution of galaxies. The objective of my thesis was to investigate the physical properties of the photosphere and circumstellar environment of massive hot stars confronting multi-band spectroscopic or spectro-interferometric observations and sophisticated non-LTE radiative transfer codes. My work was focused on two main lines of research. The first concerns radiative line-driven winds. Using UV and visible spectroscopic data and the radiative transfer code CMFGEN, I investigated the weak wind phenomenon on a sample of nine Galactic O stars. This study shows for the first time that the weak wind phenomenon, originally found for O dwarfs, also exists on more evolved O stars and that future studies must evaluate its impact on the evolution of massive stars. My other line of research concerns the study of classical Be stars, the fastest rotators among the non-degenerated stars, and which are surrounded by rotating equatorial disks. I studied the Be star $omicron$ Aquarii using H$alpha$ (CHARA/VEGA) and Br$gamma$ (VLTI/AMBER) spectro-interferometric observations, the radiative transfer code HDUST, and developing new automatic procedures to better constrain the kinematics of the disk. This multi-band study allowed to draw the most detailed picture of this object and its environment, to test the limits of the current generation of radiative transfer models, and paved the way to my future work on a large samples of Be stars observed with VEGA, AMBER, and the newly available VLTI mid-infrared combiner MATISSE.
We calculate the emission of protoplanetary disks threaded by a poloidal magnetic field and irradiated by the central star. The radial structure of these disks was studied by Shu and collaborators and the vertical structure was studied by Lizano and
The disks around Herbig Ae/Be stars are commonly divided into group I and group II based on their far-infrared spectral energy distribution, and the common interpretation for that is flared and flat disks. Recent observations suggest that many flarin
With increasingly accurate data on RR Lyrae stars we find that the Blazhko effect may be a rule rather than an exception. However, we still do not know what is the cause of this mysterious amplitude and phase modulation. In my talk, I intended to giv
The presence of debris disks around young main sequence stars hints at the existence and structure of planetary systems. Millimeter-wavelength observations probe large grains that trace the location of planetesimal belts. The FEPS (Formation and Evol
Extreme ultraviolet (EUV, 13.6 eV $< h u lta 100$ eV) and X-rays in the 0.1-2 keV band can heat the surfaces of disks around young, low mass stars to thousands of degrees and ionize species with ionization potentials greater than 13.6 eV. Shocks gene