From November 2019 to April 2020, the prototypical red supergiant Betelgeuse experienced an unexpected and historic dimming. This event was observed worldwide by astrophysicists, and also by the general public with the naked eye. We present here the results of our observing campaign with ESO’s VLT and VLTI in the visible and infrared domains. The observations with VLT/SPHERE-ZIMPOL, VLT/SPHERE-IRDIS, VLTI/GRAVITY and VLTI/MATISSE provide spatially resolved diagnostics of this event. Using PHOENIX atmosphere models and RADMC3D dust radiative transfer simulations, we built a consistent model reproducing the images and the photometry.

Carbon-rich dust is known to form in the atmosphere of the semiregular variable star R Sculptoris. Such stardust, as well as the molecules and gas produced during the lifetime of the star, will be spread into the Galaxy via the mass-loss process. Probing this process is crucial to understand the chemical enrichment of the Galaxy. R Scl was observed using the ESO/VLTI MATISSE instrument in December 2018. Here we show the first images of the star between 3 and 10 R*. Using the complementary MIRA 3D image reconstruction and the RHAPSODY 1D intensity profile reconstruction code, we reveal the location of molecules and dust in the close environment of the star. Indeed, the C2H2 and HCN molecules are spatially located between 1 and 3.4 R* which is much closer to the star than the location of the dust. The R Scl spectrum is fitted by molecules and a dust mixture of 90% of amorphous carbon and 10% of silicone carbide. The inner boundary of the dust envelope is estimated by DUSTY at about 4.6 R*. We derive a mass-loss rate of 1.2 ± 0.4 × 10−6M⊙ yr−1however no clear SiC forming region has been detected in the MATISSE data.

The surface brightness colors (SBC) relation is a very important tool to derive the distance of extragalactic eclipsing binaries. However, for early-type stars, this SBC relation is critically affected by the stellar environment (wind, circumstellar disk, etc...) and/or by the fast rotation. We calculated 6 models based on the code of Domiciano de Souza et al. (2012) considering different inclinations and rotational velocities. Using these results, we quantify for the first time the impact of the rotation on the SBC relation.

The Working Group on Active B-type Stars (formerly known as the Working Group on Be Stars) was re-established under IAU Commission 29 at the IAU General Assembly in Montreal, Quebec (Canada) in 1979, and has been continuously active to the present. Its main goal is to promote and stimulate research and international collaboration on the field of the active early-type (OB) stars.

We present high spatial resolution observations of the mid-infrared core of the dusty symbiotic system HM Sge. The MIDI interferometer was used with the VLT Unit Telescopes and Auxiliary Telescopes providing baselines oriented from PA=42° to 105°. The MIDI visibilities are compared with the ones predicted in the frame of various spherical dust shells published in the literature involving single or double dusty shells intended to account for the influence of the hot White Dwarf. The mid-IR environment is unresolved by a 8m telescope and the MIDI spectrum exhibits a level similar to the ISO spectra recorded 10 yr ago. The discrepancies between the HWHM at different angle orientations suggest an increasing level of asymmetry from 13 to 8 μm. The observations are surprisingly well fitted by the densest (optically thick in the N band) and smallest spherical model published in the literature based on the ISO data, although such a model does not account for the variations of near-IR photometry due to the Mira pulsation cycle suggesting a much smaller optical thickness. These observations also discard the two shells models, developed in an attempt to take into account the effect of the White Dwarf illumination onto the dusty wind of the Mira. These models are too extended, and lead to a level of asymmetry of the dusty environment tightly constrained by the MIDI visibilities. These observations show that a high rate of dust formation is occurring in the vicinity of the Mira which seems to be not highly perturbed by the hot companion.

New 2D dynamical models for carbon-rich and oxygen-rich AGB stars, and red supergiants are presented which include hydrodynamics with gravity and radiation pressure on dust, equilibrium chemistry, time-dependent dust formation, and coupled frequency-dependent Monte Carlo radiative transfer. The simulations reveal a much more complicated picture of the dust formation and wind acceleration of red giants as compared to 1D spherical models. Triggered by non-spherical pulsations or large-scale convective motions, dust forms event-like in the cooler regions above the stellar surface which temporarily receive less radiation from the star, followed by the radial ejection of dust arcs and clumps. These simulations can possible explain recent high angular resolution interferometric IR observations of red giants, which show an often non-symmetric and highly time-variable innermost dust formation and wind acceleration zone. The new wind models are intended to harvest the results of future interferometric mission like Chara, AMBER on the Vlti, and Alma, aiming to provide the physical answers of the scientific questions arising from these new instruments.

The radiative transfer equation can be solved analytically for optically thin shells. The solution leads to a semi-analytical expression of the visibility function, which can be compared to the numerical solution given by the DUSTY code. Best-fit model parameters are given using real measurements of ISO fluxes, ISI and VLTI-MIDI visibilities for 3 late-type stars.


Miras and Semi-Regular variables are, among Red Giants, cool objects which are difficult to understand. This paper presents an adaptation of the spectral synthesis code SYNSPEC to cool objects. Some examples of application of this code to static and dynamical structures are presented.


AMBER is the near I.R. focal instrument of the VLTI. It recombines 3 beams simultaneously and has spectral resolution capability allowing simultaneous spectrum, visibilities, differential visibilities, closure phase and differential phases measurements on the observed sources. We present here the general formalism used on AMBER in order to compute differential phases and differential visibilities, in complement to the article of Tatulli et al. (2006). We show that these differential observables have precisions close to the fundamental noises and we present an illustration of model-fitting using them on the binary star γ2 Velorum where we made a precise measurment of the astrometry of the 2 components (3.65±0.1 mas). 


The aim of this work is to help for choosing the optimal configuration of the VLTI for the observation of dust shell inner boundary of the S star π1 Gru. We show that this depends on the choice of the used geometrical model. The visibility curves produced by different models are compared to that predicted by the DUSTY spherical transfer radiative numerical code fitting real wide-band spectrophotometric data. The JMMC-ASPRO software is used to calculate the visibility points from the DUSTY code. The optimal configuration of the VLTI with 2 and 3 auxiliary telescopes, depending on the used geometrical model, minimizes the error on the inner shell radius.

This is a review of methods for the solution of non-LTE radiativetransfer equations in long cylinders. The principal goal of thesemethods is the modelling of elongated structuresimbedded in the solar corona, such as loops or prominence threads.These objects are submitted to the solar radiation, which determinesthe boundary conditions of the problem. Different cases areexamined. Concerning the geometry, one-dimension and two-dimensioncases are treated. The two-dimension case itself is subdivided into(radius, altitude) and (radius, azimuth) problems, which are treated byquite different methods. Another distinction concerns the method ofresolution: semi-analytical, Monte-Carlo and finite-differencemethods are examined. Some methods are restricted to a two-levelatom, others allow the treatment of realistic multilevel cases. Somerecent results, obtained with finite-difference, acceleratedΛ-iteration methods, are presented.

ASAP is a project initiated at the MPIfR which aims at providing a new generation of scientific analysis tools to extract the physical information from the high dynamical range data of current and future instruments. It was motivated by the ALMA project but the concepts and their implementations are applicable to all wavelengths. This presentation is focused on DALIA (Direct Aproach to spectral Line Analysis), a prototype software for forward modeling. It consists of a JAVA graphical user interface through which the user can fit models to observations. The models are stored as binaries and are described by XML files according to a schema. New models developed in any language can thus be easily added to the model database by the user. The different steps of the fit (simulation, evaluation, parameter change) can be executed manually or automatically through an optimization engine. The interface allows the user to have a direct control on the model parameters which can be fixed or constrained. The data to be modeled can be of any type (1D, 2D, 3D, specral, spatial, temporal...) and associations of datasets of different types are supported as long as the axes are identical to those of the model output. In this prototype the FITS format is supported. For spectral synthesis, the spectroscopic data from the molecular databases (Cologne, JPL) are used. This approach is very generic and uses concepts similar to those of the Virtual Observatory. Its integration into the VO would allow astronomers to use the data archives to constrain a model and would permit to store model solutions for each source. These model solutions could thus be easily shared and be improved with the aquisition of new data.

Despite their important luminosity, massive stars keep unveiledmost of their formation mainly because they are deeply embedded withintheir native cloud. This difficulty is accentuated by their small numberand by their larger distances compared to low mass stars.This explains why models for the various stages oftheir formation are still in their infancy.We briefly present here the initial conditions andthe most common models for the formation of massive stars. Also, we focus onto a family of self-similar modelsthat allow accretion and outflows around massive protostars.Finally, we try to sketch the temporal evolution of massive star formation.

A brief account is given of the advanced evolutionary stagesof massive stars, from central C-burning up to the final supernova explosion.We describe the role of neutrino losses, the phases of C, Ne, O and Si burning,the Fe core collapse, current ideas on the supernova explosion, as well as theexplosive nucleosynthesis resulting from the passage of the shock wave.

Contrary to what is assumed in building standard stellar models, all stars undergo some mild mixing in their radiation zones. This mixingis due mainly to a slow thermally driven meridional circulation, andshear turbulence presumably contributes to it.It is the rotation of the star which isresponsible for these motions, and therefore the transport of angular momentum must be described in time and space when modeling stellar evolution. This rotational mixing plays an important role in the evolution of massive stars; in particular it determines the late, pre-supernova phases. We review the present state of the problem and discuss briefly the open questions.

Astronomy and astrophysics can today produce a lot of discoveries and syntheses, driven by the convergence of sophisticated technology (advanced detectors and instrumentation, and supercomputers) with new observation platforms (VLT, Keck) and a revitalised satellite program. These advances will decisively affect many of the fundamental studies of origins, dynamics, and emission for all scales of astrophysical phenomena. Traditionally astrophysical research has been divided into observations and theoretical modelling or a combination of both. But scientists have discovered that existing models did not explain their observations of the great supernova of 1987. Since is born a closed collaboration between astrophysicists and plasma scientists leading to perform laboratory experiments motivated by the astrophysics. Start many collaborations is essential in order to progress in this new field and together astro/plasma physicists and laser bench scientists are pushing the frontiers of recreating the Universe's most exotic phenomena. The goal is to create in the laboratory a sample plasma similar to what would be found in the astronomical body, then to study its properties (radiation or thermodynamical state).

In the present review we summarize direct and indirect evidence that the massive close binary frequency is very large. Wethen discuss the binary evolutionary processes and we present a general massive close binary evolutionary scheme. Finally,we highlight the importance of massive close binaries for population number synthesis and the chemical evolution ofgalaxies.

We discuss the determination of fundamental parameters of "normal" hot, massive OB-type stars, namelytemperatures, luminosities, masses, gravities and surface abundances. We also present methods used to derive properties of stellar winds - mass-loss rates and wind velocities from early-type stars.

Hot luminous stars are characterized by their fast, dense and persistent outflows.Here, we analyze the unambiguous spectroscopic signatures of the presence of these winds. We then present various observational elements that suggest that hot star winds are not smoothly expanding outflows.The unstable nature of line-driving could be at the origin of these propertiesof radiatively-driven outflows and we investigate here its ability to explainthe Line Profile Variability (LPV) observed in hot star spectra. Such variabilityfeatures profile sub-peaks migrating away from line center, and with characteristic velocity scales increasing from50 to 100-200 km s-1 (from center to edge). Based on radiation-hydrodynamics simulations, we compute the average and temporal evolution of the emissivity of a hot star wind, and compare with LPV datasets of Wolf-Rayet (WR) spectra.The inferred inadequacy of the spherically-symmetric assumption suggests a globally asymmetrical wind structure, which we model by mapping the 3D wind volume with closely-packed star-centered cones. We find that the cone-angle α, which represents the lateral extent of wind structures, controls the sub-peak width at line center. Given the absence of an explicit lateral velocity in our simulations, the best match to observations suggest an upper limit of ca. 1-3 deg to these structures. At line edge, syntheticsub-peaks are narrower than observed by a factor 2-3, suggesting the lack of radial velocity dispersion of computed wind structures, a likely artifact of our 1D simulations.Additionally, assuming that sub-peak lifetimes in LPV time-series represents the crossing-time of the Line Emission Region (LER), we determine the wind acceleration in the LER. Contrary to previous findings, we find no firm evidence for very extended acceleration of WR winds, which would require usingspectral diagnostics with LER located distinctly below v∞.Although the best candidates, WR objects and their optically thick outflows constitute a big challenge for constraining observationally the velocity law of radiatively-driven winds.

In the present paper we review some basic facts regarding the similarities and differences between Galactic planetary nebulae (PN) and Galactic Wolf-Rayet (WR) nebulae within the scope of stellar mass-loss history and its subsequent impact on the nebular dynamics and morphology. The case of planetary nebulae with [WR] nucleus, which allows one to perform a more direct comparison with WR nebulae, is emphasized.In particular, we reviewselected studies on the PN NGC 40 and on the WR nebula M 1-67.We describe the apparently ubiquitous turbulent-like phenomena originating in WR/[WR] stellar atmospheres and the surrounding nebulae, and discuss the possible impact of turbulence on ejected nebula studies. The properties of turbulence observed in ejectednebulae (apparently supersonic) are at odds with the ones related toKolmogorov's subsonic, incompressibleturbulence. The large compressibility of the nebular gases and the possiblemultiplicity of turbulence energy sources are likely the main explanationsfor that difference. The Universal Multifractal approach ofLovejoy & Schertzer is presented and constitutes a physically realistic and natural way of modeling andquantifyingnebular turbulence data with only three independent parameters, includingthe key C1 intermittence parameter.