We present the first ultraviolet spectrum of the peculiar, magnetic Of?p star HD 108 obtained in its spectroscopic low state. The new data, obtained with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope, reveal significant changes compared to IUE spectra obtained in the high state: N Vλ1240, Si IVλ1400 and C IVλ1550

Context. Recent near-infrared data have contributed to the discovery of new (obscured) massive stellar clusters and massive stellar populations in previously known clusters in our Galaxy. These discoveries lead us to view the Milky Way as an active star-forming machine. Aims: The main purpose of this work is to determine physically the main

A detailed study of the blue supergiant UIT 005 (B2-2.5Ia+) in M 33 is presented. The results of our quantitative spectral analysis indicate that the star is a very luminous (log L/L sun ~ 5.9 dex) and massive (M ~ 50 M sun) object, showing a very high nitrogen-to-oxygen ratio in its surface (N/O~8, by mass). Based on the derived Mg and Si

For the large population of massive stars lying behind dust, among which are the youngests and potentially the most massive of our Galaxy, none of the commonly used wind diagnostics can be applied. As an alternative, a few observable infrared hydrogen lines are strong enough to hold wind diagnostics similarly to Hα. Using current state-of-the-art

The spectra of O and B supergiants (Sgs) are known to be affected by a significant form of extra line broadening (usually referred to as macroturbulence) in addition to that produced by stellar rotation. Recent analyses of high-resolution spectra have shown that the interpretation of this line broadening as a consequence of large-scale turbulent

The spectrum of O and B Supergiants is known to be affected by an important extra line-broadening (usually called macroturbulence) that adds to stellar rotation. Recent analysis of high resolution spectra has shown that the interpretation of this line-broadening as a consequence of large-scale turbulent motions would imply highly super-sonic

A significant fraction of massive stars in the Milky Way and other galaxies are located far from star clusters and star-forming regions. It is known that some of these stars are runaways, i.e. possess high space velocities (determined through the proper motion and/or radial velocity measurements), and therefore most likely were formed in embedded

Nonionizing stellar continua are a potential source of photons for continuum pumping in the hydrogen Lyman transitions. In the environments where these transitions are optically thick, de-excitation occurs through higher series lines. As a result, the emitted flux in the affected lines has a fluorescent contribution in addition to the usual

The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020-1800 Å wavelength range with unprecedented sensitivity. Previous observatories operating in the 1150-2000 Å range (such as IUE and HST-STIS) have proved extremely useful to study the winds of OB type stars, which leave their most prominent imprints in the

Context. To understand the structure and evolution of massive stars, systematic surveys of the Local Group galaxies have been undertaken, to find these objects in environments of different chemical abundances. We focus on the metal-poor irregular galaxy IC 1613 to analyze the stellar and wind structure of its low-metallicity massive stars. We

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

The VLT-FLAMES Tarantula Survey (VFTS) is an ESO Large Programme that has obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). Here we introduce our scientific motivations and give an overview of the survey targets, including optical and near-infrared photometry and

Context. Very few examples of luminous blue variable (LBV) stars or LBV candidates (LBVc) are known, particularly at metallicities below that of the Small Magellanic Cloud (SMC). The LBV phase is known to be crucial for the evolution of massive stars, and its behavior with metallicity is very poorly known. Variable star V39 in IC 1613 is a well

Aims: This is the first paper of a series devoted to studying the population of blue massive stars in NGC 55, a galaxy of the Sculptor group at a distance of about 2 Mpc. Methods: We have obtained optical (3300{-}6210 Å), low-resolution spectra of approximately 200 blue massive stars with VLT-FORS2, which we have classified with the aid of Milky

Context. The quantitative study of the physical properties and chemical abundances of large samples of massive blue stars at different metallicities is a powerful tool to understand the nature and evolution of these objects. Their analysis beyond the Milky Way is challenging, nonetheless it is doable and the best way to investigate their behavior

The Local Group galaxies enable us to study the impact of metallicity on the structure and evolution of massive stars through spectroscopic analyses. However, color-based target selection for spectroscopy (in absence of known spectral types), though relatively successful, usually produces lists dominated by B-type modest-mass stars. We have

Context. Luminous blue variables (LBVs) are a class of highly unstable stars that have been proposed to play a critical role in massive stellar evolution as well as being the progenitors of some of the most luminous supernovae known. However the physical processes underlying their characteristic instabilities are currently unknown. Aims: In order

Context. Results from the theory of radiatively driven winds are nowadays incorporated in stellar evolutionary and population synthesis models, and are used in our interpretation of the observations of the deep Universe. Yet, the theory has been confirmed only until Small Magellanic Cloud metallicities. Observations and analyses of O-stars at lower

HH 110 is a rather peculiar HerbigHaro object in Orion that originates due to the deflection of another jet (HH 270) by a dense molecular clump, instead of being directly ejected from a young stellar object. Here we present new results on the kinematics and physical conditions of HH 110 based on Integral Field Spectroscopy. The 3D spectral data

HH 223 is the optical counterpart of a larger scale H2 outflow, driven by the protostellar source VLA 2A, in L723. Its poorly collimated and rather chaotic morphology suggested Integral Field Spectroscopy (IFS) as an appropriate option to map the emission in order to derive the physical conditions and kinematics. Here we present new results based