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The physical mechanism responsible for high mass-loss in luminous blue variable stars (LBVs) is still poorly understood. The possibility that it is independent of metallicity is of paramount importance to LBVs in the metal-poor Universe. Our approach to investigate this possibility is to study LBVs in different environments and to use multiwavelength observations to resolve their nebulae. These contain the fingerprints of their mass-loss, as shown here by the galactic example G79.29+0.46. I also present our pilot study of objects in the Magellanic Clouds (MCs), where a paucity of data existed so far. [ABSTRACT FROM AUTHOR]

We describe the evolution of the carbon dust shells around Very Late Thermal Pulse (VLTP) objects as seen at infrared wavelengths. This includes a 20-year overview of the evolution of the dust around Sakurai's object (to which Olivier made a seminal contribution) and FG Sge. VLTPs may occur during the endpoint of as many as 25% of solar mass stars, and may therefore provide a glimpse of the possible fate of the Sun. [ABSTRACT FROM AUTHOR]

The majority of close binaries undergo episodes of mass transfer between their components, which completely change their further evolution. Simulations and observations agree that the mass transfer has two phases: i) short and rapid one, and ii) long and slow one. The bulk of the mass is likely exchanged during the rapid phase, but due to its shortness, systems undergoing this phase are rare, but they hold the key to understanding of the process. One system that is either undergoing the rapid mass transfer phase or is in a transient phase between the two phases is β Lyrae. Our goal is to map the distribution of circumstellar gas in the system. To achieve it, a series of spectro-interferometric observations acquired with the optical instrument VEGA/CHARA are investigated. Here we present our tools and preliminary results of our analysis. [ABSTRACT FROM AUTHOR]

FSCMa type stars is a group of ~70 objects formerly known as unclassified stars with the B[e] phenomenon. Their very strong emission-line spectra in combination with a nearly main-sequence luminosity suggest the binary nature for them. They possess strong IR excesses due to radiation of circumstellar dust that implies a compact distribution probably in a circumbinary disk. Our long-term spectroscopic monitoring revealed neutral metal lines, which always include that of Li I 6708 Å, in the spectra of some FSCMa objects indicating the presence of a cool star. We present a summary of our results with a first overview of FSCMa type binaries and review possible implications for the nature and evolutionary status of the entire group. [ABSTRACT FROM AUTHOR]

We present a model of inner dust regions around the cool Mira component of the two symbiotic novae, RR Tel and HM Sge, based on the near-IR photometry, ISO spectra and mid-IR interferometry. The dust properties were determined using the DUSTY code. A compact circumstellar silicate dust shell with inner dust shell temperatures between 900K and 1300K and of moderate optical depth can explain all the observations. RR Tel shows the presence of an equatorially enhanced dust density during minimum obscuration. Obscuration events are explained by an increase in optical depth caused by the newly condensed dust. The mass loss rates are significantly higher than in intermediate-period single Miras but in agreement with longer-period O-rich AGB stars. [ABSTRACT FROM AUTHOR]

Olivier Chesneau challenged several fields of observational stellar astrophysics with bright ideas and an impressive amount of work to make them real in the span of his career, from his first paper on P Cygni in 2000, up to his last one on V838 Mon in 2014. He was using all the so-called high-angular resolution techniques since it helped his science to be made, namely study in details the inner structure of the environments around stars, be it small mass (AGBs), more massive (supergiant stars), or explosives (Novae). I will focus here on his work on massive stars. [ABSTRACT FROM AUTHOR]

During his too short career, Olivier Chesneau pioneered the study of the circumstellar environments of low mass evolved stars using very high angular resolution techniques. He applied state of the art high angular resolution techniques, such as optical interferometry and adaptive optics imaging, to the the study of a variety of objects, from AGB stars to Planetary Nebulae, via e.g. Born Again stars, RCB stars and Novae. I present here an overview of this work and most important results by focusing on the paths he followed and key encounters he made to reach these results. Olivier liked to work in teams and was very strong at linking people with complementary expertises to whom he would communicate his enthusiasm and sharp ideas. His legacy will live on through the many people he inspired. [ABSTRACT FROM AUTHOR]

This paper provides a summary of binary star research conducted at the CHARA Array. The high angular resolution provided by the longest baselines of the interferometer can resolve binaries down to sub-milli-arcsecond separations. Combining the visual orbit of a binary with spectroscopic radial velocity variations of the components provides a measurement of the stellar masses and distance to the system. This paper provides an overview of interferometric methods used to resolve binaries and a table of orbits that have been resolved spatially using the CHARA Array. In addition to mapping the orbits of binary stars, the six telescopes in the array provide excellent coverage on the sky for studying the circumstellar environments within binary systems and investigating tidal effects within interacting binaries. [ABSTRACT FROM AUTHOR]

Traces of heavy metal in cool DZ white dwarfs may be attributed to the accretion of circumstellar dust. This dust is thought to originate from the tidal disruption of some rocky material, they provide a unique opportunity to study the composition of extra-solar planetary systems. The determinations of precise atmospheric parameters and abundances require accurate description of the line profiles of the identified features. We present absorption spectra of Na-He and Ca+-He for the conditions prevailing in cool white dwarfs. [ABSTRACT FROM AUTHOR]

Classical T Tauri stars are low mass young forming stars that are surrounded by a circumstellar accretion disc from which they gain mass. Despite this accretion and their own contraction that should both lead to their spin up, these stars seem to conserve instead an almost constant rotational period as long as the disc is maintained. Several scenarios have been proposed in the literature in order to explain this puzzling "disc-locking" situation: either deposition in the disc of the stellar angular momentum by the stellar magnetosphere or its ejection through winds, providing thereby an explanation of jets from Young Stellar Objects. In this lecture, these various mechanisms will be critically detailed, from the physics of the star-disc interaction to the launching of self-confined jets (disc winds, stellar winds, X-winds, conical winds). It will be shown that no simple model can account alone for the whole bulk of observational data and that "disc locking" requires a combination of some of them. [ABSTRACT FROM AUTHOR]

We present, for the first time, three dimensional (3D) adaptive mesh refinement simulations of a GRB jet crossing a pre-SN progenitor (with resolutions comparable to the resolutions of 2D simulations) (Lopez-Camara et al. 2012). The morphology, Lorentz factor, and symmetries, will be discussed in this presentation. Basically the evolution is divided into three main phases: the jet moving inside the progenitor; the jet just about break out of the progenitor; and the phase where the jet has broken out of the star and is now moving through the circumstellar medium. The resolution and 3D effects are also discussed. Still, as with all numerical work, the current investigation lacks in several aspects and needs improvement as well as further investigations. [ABSTRACT FROM AUTHOR]

The formation of inorganic dust in circumstellar environments of evolved stars is poorly understood. Spectra of molecules thought to be most important for the nucleation, i.e. A10, TiO, and TiO2, have been recently detected in the red supergiant VYCMa. These molecules are effectively formed in VY CMa and the observations suggest that non-equilibrium chemistry must be involved in their formation and nucleation into dust. In addition to exploring the recent observations of VY CMa, we briefly discuss the possibility of detecting these molecules in the "dust-poor" circumstellar environment of Betelgeuse. [ABSTRACT FROM AUTHOR]

The VLTI (Very Large Telescope Interferometer) makes available milli-arcsecond-seale observations in the infrared. It offers new possibilities for constraining stellar structures such as polar jets, equatorial disks and rotationally-flattened photospheres of Be stars. Such constraints allows us to better estimate the stellar fundamental parameters and refine the mechanisms such as mass loss, pulsation and magnetism that govern the variability and evolution of these stars. In this paper we present a chromatic semi-analytical model of fast rotators, which allows us to study the dynamics and the interaction between the photosphere and the wind of fast rotating stars of O, B, A and F spectral types. Our simple analytical model addresses the oblateness, inclination and position angle of the rotation axis of the star. It produces iso-velocity maps and intensity maps. It includes line profiles, limb-darkening and the von Zeipel effect and the non-radial pulsations. SCIROCCOq-: Simulation Code of Interferometric-observations for ROtators and CirCumstellar Objects including Non-Radial Pulsations, includes all the parameters cited above in order to be fast, powerful and light simulation tool in high angular resolution of rotating objects. [ABSTRACT FROM AUTHOR]

Carbonaceous cosmic dust is mainly observed through infrared spectroscopy either in absorption or in emission. Laboratory soot analogues of this interstellar or circumstellar dust were produced in fuel-rich, low-pressure, premixed and flat, flames. The particles were investigated by infrared absorption spectroscopy in the 2-15 µm spectral region. The details of the spectral features shed some light on the structure of the material and enable the study of its life cycle. In particular, the 8 µm band position is tentatively attributed to defects at the edge or in the polyaromatic units of the materials, revealing these structural changes in astrophysical dust. [ABSTRACT FROM AUTHOR]

The accretion and desorption processes of gas molecules on cold grains play an important role in the evolution of dense clouds and circumstellar regions around YSOs. Given the low temperatures in dark cloud interiors (10-20 K), thermal desorption is negligible and most molecules are expected to stick to grains leading to depletion in the gas phase. Laboratory simulations of these processes under astrophysically relevant conditions are required for their understanding. The use of ultra-high-vacuum conditions minimalizes contamination by background water accretion. This introduces a radical improvement, allowing the study of photodesorption and the detection of products at very low abundances in a water-free ice matrix. We studied UV-photoprocessing of pure NH3 and N2 ices under ultra-high-vacuum conditions using the Interstellar Astrochemistry Chamber. The photodesorbed molecules, and the volatile products released upon photolysis and warm-up, were detected in situ by quadrupole mass spectroscopy. [ABSTRACT FROM AUTHOR]

Ice desorption affects the evolution of the gas-phase chemistry during the protostellar stage, and also determines the ice composition of comets forming in circumstellar disks. Prom observations, most volatile species, including CO2, are found in H2O-dominated ices. In this study, the desorption of CO2 mixed in H2O ice and the impact of ice thickness, mixture ratio and heating rate are experimentally determined. The results are used to parametrize an extended three-phase model (gas, ice surface and ice mantle) which describes ice mixture desorption using rate equations and a minimum number of free parameters. The model can be used to predict the evolution in thickness and concentration of volatile-rich H2O ice during infall of icy grains around protostars. [ABSTRACT FROM AUTHOR]

Outflows and jets are intimately related to the formation of stars, and play a central role in redistributing mass, energy and angular momentum within the core, disk and parent cloud. The interplay between magnetic field and rotation is widely thought to be responsible for launching and collimating these outflows. Shear induced by differential rotation along initially poloidal field lines results in an azimuthal component of the magnetic field being generated; the magnetic pressure gradient then accelerates the plasma, and inflates bipolar magnetic cavities within the circumstellar matter. However, the resulting winding of the magnetic field can be potentially disrupted by magneto-hydrodynamic instabilities. To better understand the role of magnetic fields in shaping these oufiows, a series of experiments on pulsed-power z-pinch machines have been developed. In this talk I will present results related to the formation of jets in young stellar objects and in the laboratory, and draw a parallel between the two systems. [ABSTRACT FROM AUTHOR]

We discuss the role of Configuration Interaction (Cl) and the influence of the number of configurations taken into account in the calculations of nickel and iron spectral opacities provided by the OPAC international collaboration, including statistical approaches (SCO, CASSANDRA, STA), detailed accounting (OPAS, LEDCOP, OP, HULL AC-v9) or hybrid method (SCO-RCG). Opacity calculations are presented for a temperature T of 27.3 eV and a density of 3.4 mg/cm³, conditions relevant for pulsating stellar envelopes. [ABSTRACT FROM AUTHOR]

In this lecture, we briefly present the main models currently proposed to describe the collapse of prestellar dense cores and the formation of young Class 0 protostars. An empirical evolutionary sequence for the formation of low-mass stars is described. Then, the typical properties of Class 0 protostars are reviewed and the question of their structure at small scales is adressed through the question of circumstellar disks. [ABSTRACT FROM AUTHOR]

The formation of Polycyclic Aromatic Hydrocarbons in the circumstellar outflows of evolved stars is reviewed, with an emphasis on carbon stars on the Asymptotic Giant Branch. Evidence for PAHs present in their winds is provided by meteoritic studies and recent observations of the Unidentified Infrared bands. We detail the chemical processes leading to the closure of the first aromatic ring as well as the growth mechanisms leading to amorphous carbon grains. Existing studies on PAH formation in evolved stellar envelopes are reviewed and new results for the modelling of the inner wind of the archetype carbon star IRC+10216 are presented. Benzene, C6H6, forms close to the star, as well as water, H2O, as a result of non-equilibrium chemistry induced by the periodic passage of shocks. The growth process of aromatic rings may thus resemble that active in sooting flames due to the presence of radicals like hydroxyl, OH. Finally, we discuss possible formation processes for PAHs and aromatic compounds in the hydrogen-rich R CrB star, V854 Cen, and their implication for the carriers of the Red Emission and the Diffuse Interstellar Bands. [ABSTRACT FROM AUTHOR]

Studies of dust analogs formed from hydrocarbon (CH4, C2H2, C2H4, C2H6) and PAH precursors have been performed using a new facility that we have developed to simulate interstellar and circumstellar processes. The species formed in a plasma are detected, characterized and monitored in situ with high-sensitivity techniques, which provide both spectroscopic and ion mass information. From these measurements we derive information on the nature, the size and the structure of dust particles, as well as a better understanding of the growth and destruction processes of extraterrestrial dust. [ABSTRACT FROM AUTHOR]

The mechanisms of nucleation and growth of carbon dust particles in circumstellar envelopes of carbon-rich stars in the red giant and AGB phases of their evolution are poorly understood. It has been proposed that the transition of gas phase species to solid particles, is achieved by the formation of a critical nucleus composed of two PAHs held together by van der Waals forces. Some insights into the validity of the nucleation of PAH molecules in the envelope can be gained through the investigation of the thermodynamics of dimers, representing the first stage towards condensation. We have performed experiments to identify the temperature range over which small PAH clusters form in saturated uniform supersonic flows. The kinetics of the formation has also been investigated. The experimental data have been combined with theoretical calculations. We unambiguously demonstrate that the association of small PAHs such as pyrene (C16H10) is slower than the destruction of the dimer in warm and hot environments such as IRC +10216. Our findings challenge a formation model based on the physical stacking of small PAH units in circumstellar shells of carbon rich stars. [ABSTRACT FROM AUTHOR]

The discovery that the short-lived radionucleide 60Fe was present in the oldest meteorites suggests that the formation of the Earth closely followed the death of a massive star. I discuss three astrophysical origins: winds from an AGB star, injection of supernova ejecta into circumstellar disks, and induced star formation on the boundaries of HII regions. I show that the first two fail to match the solar system 60Fe abundance in the vast majority of star forming systems. The cores and pillars on the edges of HII regions are spectacular but rare sites of star formation and larger clumps with masses 103-4M.. at tens of parsec from a supernova are a more likely birth environment for our Sun. I also examine γ-ray observations of 60Fe decay and show that the Galactic background could account for the low end of the range of meteoritic measurements if the massive star formation rate was at least a factor of 2 higher 4.6Gyr ago. [ABSTRACT FROM AUTHOR]

We present a model for the dispersal of protoplanetary disks by winds from either the central star or the inner disk. These winds obliquely strike the flaring disk surface and strip away disk material by entraining it in an outward radial-moving flow at the disk-wind interface. This interface lies several disk scale heights above the mid plane. The disk dispersal time depends on the velocity at which disk material flows into the mixing layer. If this velocity is ~10% of the sound speed, the disk dispersal time at ~-1-10AU is ~5Myr for a 0.01M⊙ disk around a solar mass star, with a spherical wind launched from the inner disk or central star with a typical mass loss rate of 10-8 M⊙yr-1 and terminal velocity of vw = 100 km s-1. We conclude that wind stripping is not a dominant disk dispersal mechanism compared with viscous accretion and photoevaporation. Nevertheless, wind stripping may affect the evolution of the intermediate disk regions. [ABSTRACT FROM AUTHOR]

The magnetorotational instability (MRI) is the most likely source of MHD turbulence in accretion disks. Recently, it has been realized that microscopic diffusion coefficients (viscosity and resistivity) are important in determining the saturated state of the turbulence and thereby the rate of angular momentum transport. In this paper, we use a set of numerical simulations performed with a variety of numerical methods to investigate the dependance of α, the rate of angular momentum transport, on these coefficients. We show that α is an increasing function of the magnetic Prandtl number Pm, the ratio of viscosity over resistivity. In the absence of a mean field, we also find that MRI--induced MHD turbulence decays at low Pm. [ABSTRACT FROM AUTHOR]

Circumstellar disks surrounding young forming stars, are likely the location where planets form. While the gaseous phase rep- resents up to ~99% of the disk mass and control the dynamics, most of disk properties relies on dust analyses. The main constituent of the gaseous component, molecular hydrogen (H2), remains nearly out of reach and the gas disk is probed through emission lines of minor tracers, such as CO. In this lecture, we will first recall how H2 symmetric molecular structure makes its detection difficult. We will then review the most significant results achieved so far, thanks to new generation of ground and space-based telescopes, with a special emphasize given to Herbig Ae/be, which are pre-main sequence stars of intermediate mass. Though the first direct estimates of circumstellar disk mass have been reported, observation of H2 is still challenging detection. [ABSTRACT FROM AUTHOR]

We have modelled a detailed physical structure of protoplanetary disks, taking into account X-ray and UV irradiation from a central star, as well as dust size growth and settling towards the disk midplane. In addition, we have calculated the level populations and line emission of molecular hydrogen in the disks. As a result, we reproduce the observed strong H2 line flux if the disks are influenced by strong UV and X-ray irradiation. Also, the dust evolution changes the physical properties of the disk, and thus the H2 line ratios. [ABSTRACT FROM AUTHOR]

We have studied the effect of the gas accretion flow on the distribution of molecules in hot inner regions of young circumstellar disks. The gas-phase reactions initiated by evaporation of icy mantle on dust grains are calculated along the accretion flow, and the molecular line emission is simulated using the obtained abundance profiles. Our results have shown that some evaporated molecules keep high abundances and emit strong transition lines only when the accretion velocity is high enough. [ABSTRACT FROM AUTHOR]

Debris disks are dusty and/or gasous disk that are viewed in scattered light and thermal emission around stars around 107-108 yr. It is well known that the dust in these system is not primodial. It is short lived and must be continuously replenished by colliding planetesimals. Most of them appear distorted by the gravitational pertubations by inner planets or stellar companions. This is why these systems are viewed today as young planetary systems. Debris disks are collisional systems. Thanks to collisional cascade towards smaller size, the dust particles are transported outwards by radiation or stellar wind pressure. Below a given blow-off size they escape the system. This model explains the radial density profiles observed. The various asymmetries, clumps and other dynamical structures such as spiral arms are though to originate in gravitational perturbations by planets and/or companions. Planets usually create gaps in disks, but they also sculpt disks via their mean-motion resonances. Clumpy structures are often invoked as resulting from such an interaction. Stellar companions usually truncate the disk, sometimes confining them to thin annular structures. They also help creating spiral patterns, either tidally or by secular interaction. In this context, the situation is different whether the perturbing companions are bound or just passing stars. In any case, dynamical studies (often specific to each system) can greatly help constraining the configuration and the past history of these systems. [ABSTRACT FROM AUTHOR]

This pedagogical review covers an unsolved problem in the theory of protoplanetary disks: the growth of dust grains into planetesimals, solids at least a kilometer in size. I summarize timescale constraints imposed on planetesimal formation by circumstellar disk observations, analysis of meteorites, and aerodynamic radial migration. The infall of ... meter-sized solids in a hundred years is the most stringent constraint. I review proposed mechanisms for plan- etesimal formation. Collisional coagulation models are informed by laboratory studies of microgravity collisions. The gravitational collapse (or Safronov-Goldreich-Ward) hypothesis involves detailed study of the interaction between solid particles and turbulent gas. I cover the basics of aerodynamic drag in protoplanetary disks, including radial drift and vertical sedimentation. I describe various mechanisms for particle concentration in gas disks -- including turbulent pressure maxima, drag instabilities and long-lived anticylonic vortices. I derive a general result for the minimum size for a vortex to trap particles in a sub-Keplerian disk. Recent numerical simulations demonstrate that particle clumping in turbulent protoplanetary disks can trigger gravitational collapse. I discuss several outstanding issues in the field. [ABSTRACT FROM AUTHOR]

For stars with ages ≥ 10 Myr, circumstellar disks are dominated by a population of optically thin dust grains most likely associated with the erosion of a planetesimal population in a system that may have also formed planets. The key goal of this chapter is to provide a core introduction to circumstellar debris disks that will allow the reader to more easily grasp the vast literature. We review key concepts involving the thermal and scattered light detection of debris disks, stellar age determinations, dust destruction mechanisms, and the connection between debris disks and exosolar planets. The material is presented at a level suitable for the non-astronomy graduate students attending the Les Houches winter school, but also includes tables and previously unpublished figures that will interest advanced astronomers. [ABSTRACT FROM AUTHOR]

Long hypothesized to be the origin of planetary systems, disks around newly formed stars have been studied in detail in the last twenty years. Most, if not all stars form surrounded by a disk, with typical masses of 0.001-0.3M⊙ and up to several hundred AU. Molecular emission lines show the gas to be in Keplerian rotation, with most species (but not H2) frozen out onto dust grains in the cold and dense disk interior. The fraction of stars with disks decreases from > 80% at <1Myr to <10% at 10Myr. The disk "half-life" is 2-3Myr, with the inner and outer disks disappearing nearly simultaneously. There is a small but distinct populations of disks with cleared-out inner regions, so-called cold or transitional disks, explained by photoevaporation, planet formation, or binarity. Inside the disks, planet formation begins, with clear observational evidence for the growth of dust grains to sizes of a few cm at least. [ABSTRACT FROM AUTHOR]

Near-infrared spectro-photometry, at a spectral resolution of ~100, allows to characterize a great variety of stellar sources, from late-type giants to emission line stars. Various components of the interstellar medium, including circumstellar environments and Planetary Nebulae, can also be traced. We propose AIFU, a fiber-fed nearinfrared low-resolution spectrograph. With a 1′×1′ field of view and a 2″ sampling, AIFU will be well suited to survey spectroscopically stellar populations in large areas of the Galaxy and of the Magellanic Clouds, as e.g. star-forming regions, as well as to image extended sources, like circumstellar shells around nearby evolved stars, PDRs, simultaneously in many different emission lines. [ABSTRACT FROM AUTHOR]

This contribution focuses on the current state-of-play in multi-dimensional continuum radiative transfer modeling of gaseous astrophysical media containing dust. The fundamentals of the radiative transfer problem are briefly reviewed. The different solution methods are discussed in terms of applicability, advantages, and error control. To illustrate the problems and requirements for future analysis making use of dust data, two recent transfer models for prominent sources are shown: (i) the silhouette structure SO-1 in M17 turned out to be the largest circumstellar disk known sofar; (ii) with inverse multiwavelengths continuum radiative transfer modeling, the full 3D density and temperature structure of the molecular cloud core ρ? Oph D could be determined. [ABSTRACT FROM AUTHOR]

Good knowledge of the far-infrared and millimeter emission from dust in the interstellar medium is important to get reliable estimates of the dust mass, to trace and understand the evolution of prestellar structures, and to accurately subtract the foreground emission in the cosmological background anisotropy measurements. Up to now the modeled dust emission profile in FIR and millimeter wavelength range is deduced from the wings of some mid-infrared fundamental latticeresonances inside the silicate material, which is known to be the dominant constituent of this dust component. However recent astronomical observations have shown that the dust emission profile could be significantly more complicated than expected. In addition, spectroscopic studies in the laboratory on analogues of amorphous interstellar grains have revealed that additional processes can occur in that spectral range, which are strongly temperature-dependent. We propose a new model for far-infrared and millimeter dust emission which takes into account results from the solid state physics, used to interpret these laboratory data. This model explicitly incorporates the effect of the disorder in the internal structure of the dust grain. We show that this model can give a satisfactory interpretation for the astronomical observations. It opens new perspectives to derive some new dust characteristics from the shape of the dust emission spectrum. [ABSTRACT FROM AUTHOR]

Polycyclic Aromatic Hydrocarbons (PAHs) are the most likely carriers proposed to account for the Aromatic Infrared Bands observed in emission between 3.3 and 12.7 μm, fulfilling both the chemical (presence of CC and CH aromatic bonds) and excitation constraints. We explain here how the emission spectrum of such species in astronomical environments can be modelled, to obtain for each infrared band both its intensity and its detailed profile. The PAH model suffers from the lack of identification of individual species. Two strategies are described here that are currently being used to progress in this identification process. The first idea is that features in the far-IR are much more specific to the exact molecular identity. Therefore their search with the coming Herschel Space Observatory will provide an unambiguous way to identify these molecules through their IR emission. Second, a reflection on where interstellar PAHs come from and how they evolve due to environmental conditions (UV irradiation, gas and dust interactions) is also necessary to get more insights into the nature of interstellar PAH candidates. In particular, recent studies have emphasized a chemical link between PAHs and very small grains in photodissociation regions. Finally, we illustrate in this paper how progress in this field can only be attained by a synergy between astronomical observations, fundamental studies, both theoretical and experimental, and models. [ABSTRACT FROM AUTHOR]

Laboratory measurements aimed at studying the properties of carbonaceous materials and their evolution under simulated space conditions support the idea that interstellar carbon dust evolves through exposure to UV and cosmic rays, gas and heat. After summarizing the principal aspects of the laboratory approach to the problem of cosmic carbon dust, we discuss recent laboratory results showing how carbon grains influence the properties and evolution of ices mantles and the formation of molecular hydrogen. [ABSTRACT FROM AUTHOR]

The observational constraints on interstellar dust are summarized. A dust model, consisting of a mixture of amorphous silicate, graphite, and PAH material that reproduces the observed interstellar extinction, is described. It is used to calculate the infrared emission expected when such dust is heated by radiation with the spectrum of interstellar starlight with various intensities. By adopting a suitable size distribution for the smallest carbonaceous grains (PAHs), and a distribution of starlight intensities, one can reproduce the observed global emission spectrum of galaxies. This allows the total dust mass, and the PAH abundance, to be estimated for any galaxy with a spectral energy distribution measured by the IRAC and MIPS cameras on Spitzer Space Telescope. For the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample, galaxies with metallicities Z > 0.3Z⊚ tend to have a major fraction of their refractory elements in dust grains, just as in the Milky Way. For lower metallicity galaxies with extended H I envelopes, the overall dust-to-metals ratio remains uncertain. The PAH abundance index qPAH (the fraction of the total dust mass in PAH particles with NC < 103 C atoms) is dependent on metallicity: galaxies with Z < 0.3Z⊚ have median qPAH = 1.1%, whereas galaxies with Z > 0.3Z⊚ have median qPAH = 3.5%. The reasons for the pronounced dependence of qPAH on metallicity remain unclear. [ABSTRACT FROM AUTHOR]

All stars end through a phase where they form copious amounts of dust either in a stellar outflow or following explosive events. The most efficient dust factories seem to be stars that evolve through the Red Giant stage and form for several 105 yrs, dust in a cool stellar wind. The dust returned by them triggers the interstellar dust cycle and therefore is vital for the matter cycling in space. We discuss the theoretical basis for calculating the dust production by such stars. First, some elements of the theory of chemical equilibrium condensation calculations are presented and it is then discussed how the concept of activities can be used to also study non-equilibrium condensation. Then we discuss how dust particle growth in stellar winds can be calculated and which kind of input data are required for such calculations. Finally some results for dust production by AGB stars are discussed. [ABSTRACT FROM AUTHOR]

Irradiation is one of the main processes which influences the evolution of dust in astrophysical environments. This article reviews the basics of particle-matter interactions and gives an introduction to the induced modifications including phase transformation, sputtering, implantation, charging effects and transmutation. We also discuss the role of the nature of the incident particle (energetic photons, electrons and ions) as a function of its energy. Finally, we briefly review the main results obtained by irradiation studies on ices, carbonaceous matter and silicates. [ABSTRACT FROM AUTHOR]

Silicates form a major component of cosmic dust. This paper summarizes the main structural and spectroscopic properties of amorphous and crystalline silicates. Furthermore, it reviews our knowledge of cosmic silicates in the Galaxy. Recent in-situ studies of presolar silicates extracted from primitive meteorites and anhydrous interplanetary dust grains will be discussed. [ABSTRACT FROM AUTHOR]

When the most primitive types of meteorite (chondrites) and interplanetary dust particles (IDPs) formed in the solar protoplanetary disk (solar nebula), all of them incorporated at least two types of presolar material: interstellar organic matter and circumstellar grains. The organic matter probably formed in the protosolar molecular cloud. To date, 10 types of circumstellar grain have been found and their isotopic compositions show that they formed around RGB/AGB stars, supernovae and, possibly, novae and WR stars. It has been proposed that interstellar silicates are also present in IDPs, but the evidence for this is less compelling. The range of isotopic compositions exhibited by the circumstellar grains require a minimum of 35-40 stellar sources, suggesting that they are a fairly representative sample of circumstellar dust production in the Galaxy. In general, the relative abundances of circumstellar grains from different sources are similar to what is expected from astronomical estimates provided that the contribution from supernovae is relatively small. The one exception is graphite grains from AGB stars that are highly depleted. Collisional erosion, radiation damage and sputtering are all expected to affect grains in the ISM on relatively short timescales. Yet, for reasons that are unclear, examination of the circumstellar grains has found little evidence for any of these processes. The circumstellar grains also provide information about grain nucleation and growth in stellar winds. For instance, only graphite grains from AGB stars seem to have formed by heterogeneous nucleation. Graphite and SiC grains from AGB stars as large as 10-20 μm have been found in meteorites, probably requiring regions of high gas density rather than the usual assumption of uniformly expanding outflows. However, few graphite and SiC grains have similar C isotopic compositions, suggesting that they tend to form at different stages of AGB evolution. [ABSTRACT FROM AUTHOR]

Dust is present in almost every astrophysical environment, ranging from circumstellar shells and disks to spiral, elliptical, starburst, and active galaxies, and to pre-galactic objects such as QSO absorption-line and damped Lyα systems. Dust leaves its imprint on interstellar extinction curves, IR spectra, and the elemental depletion patterns in the ISM of galaxies. Understanding the origin and the complex evolutionary cycle of dust is therefore an important goal in astrophysics. In this contribution, we present models to describe the evolutionary history of interstellar dust in a diverse set of astrophysical environments, ranging from normal star-forming galaxies like the Milky Way to high-redshift galaxies undergoing extreme rates of star formation. In particular, we show how the chemical evolution models can explain the correlations of dust abundances with galactic metallicities, and the presence of large amounts of dust in young dusty hyperluminous infrared galaxies in which supernovae are the only source of newly-condensed dust. [ABSTRACT FROM AUTHOR]

IR spectroscopy is the premier tool to study the composition of interstellar dust. Broad absorption and emission bands provide direct identification of the solid compounds present in space and allow measurement of accurate abundances. Systematic studies of large samples of sources allow then inferences on the origin and evolution of dust in space. Overall, the observed infrared spectra of interstellar and circumstellar dust reveals an incredibly rich and varied composition. This chapter briefly reviews the principles of infrared spectroscopy. This is then applied to the composition of circumstellar oxides and minerals and interstellar Polycyclic Aromatic Hydrocarbon molecules. [ABSTRACT FROM AUTHOR]

This introductory article aims to give a brief overview of our current view of interstellar dust studies with a particular emphasis on the properties of dust at low temperatures and long wavelengths. An understanding of these dust properties will be key in unravelling the wealth of data that will be forthcoming from the imminent, space-based Herschel and Planck missions, and from the ALMA telescopes. [ABSTRACT FROM AUTHOR]

Active hot stars are hot stars (Teff ≥ 8000 K) exhibiting emission lines (namely hydrogen lines) and IR excess which both originate in a circumstellar environment. In this paper we present in details the SIMECA (SImulation pour Etoiles Chaudes Actives) code which is the only code freely available to model the gaseous environment of active hot stars. It computes line profiles, Spectral Energy Distributions (SED) and intensity maps, which can be directly compared to high angular resolution observations. [ABSTRACT FROM AUTHOR]

Thanks to the development of long baseline facilities, near infrared interferometry is becoming an important tool to study the innermost regions of circumstellar proto-planetary disks around close-by pre-main sequence stars. Providing a milli arcsecond spatial resolution and spectroscopic capabilities, the existing interferometers can, for the first time, spatially resolve and separate the gas and dust emission arising form the disk regions where planets are supposed to form, namely inside few Astronomical Units from the central star. The observational limitations and the complexity of the resulting data require however to perform the data analysis in the Fourier space by the comparison with theoretical disk models. To this purpose a number of self consistent radiative transfer models have been recently developed. In this chapter I will first review some of the most recent observational and theoretical results and then, discuss some important future challenges. [ABSTRACT FROM AUTHOR]

Continuum radiative transfer is a physical process that must be taken into account in almost all astrophysical situations. Indeed, many astrophysical objects of different natures show continuum dust grain emission: circumstellar discs around young stellar objects, evolved stars, active galactic nuclei. I will focus the present discussion on (dust) continuum radiative transfer and more precisely on the Monte Carlo approach to the solution of the problem (but not only). [ABSTRACT FROM AUTHOR]

Recent years have seen a major contribution of infrared interferometry to studies on the circumstellar environment of cool evolved stars. Particularly, two interferometric instruments at ESO's Very Large Telescope Interferometer (VLTI) - AMBER and MIDI - offer the community a novel opportunity to carry out high-angular resolution observations. In the mid-infrared, where thermal emission from the circumstellar gas and/or dust is remarkable, MIDI has proven to be a powerful tool to derive the physical properties of the molecule and dust formation zone close to the star, particularly when combined with radiative transfer modeling. AMBER is also expected to shed more light on the circumstellar material closer to the star and the photosphere itself. In this paper, we present recent results on cool evolved stars obtained with VLTI as well as future prospects for interferometric observations and radiative transfer modeling for cool evolved stars. [ABSTRACT FROM AUTHOR]

Near-infrared and mid-infrared broad band interferometric observations of young stellar objects trace the inner part of the warm dusty circumstellar environment (smaller than a few AUs) and can be used to constrain its physical properties, in particular to characterize the size, location and composition of the emitting region. Because the spatial frequency coverage of current instruments remain sparse, modeling, including detailed radiative transfer (RT), is necessary to get a precise estimate of these properties. [ABSTRACT FROM AUTHOR]