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The Thermally Pulsing- (Super) Asymptotic Giant Branch is a late stage in the evolution of low- and intermediate-mass stars. These stars undergo strong wind mass-loss and diverse nucleosynthesis. Third dredge-up events, that occur following thermal pulses, are responsible for enriching the surfaces of Asymptotic Giant Branch stars, hence an understanding of this process is crucial for constraining galactic chemical evolution. Using a custom numerical scheme, we investigate the temporal and spatial resolution required to resolve the third dredge-up in the 1D stellar evolution code mesa. With mesa 's default controls, the third dredge-up efficiency is underestimated by as much as |$\approx 76~{{\ \rm per\ cent}}$|⁠. In stars that undergo hot third dredge-up (M ≳ 6 M⊙), the third dredge-up efficiency is overestimated by |$\approx 55~{{\ \rm per\ cent}}$|⁠. The Thermally Pulsing- (Super) Asymptotic Giant Branch (TP-(S)AGB) evolution is computed for models with initial masses 1 ≤ M i/M⊙ ≤ 8 at Solar metallicity (Z = 0.014). The minimum initial mass for carbon stars falls in the range 1.5–1.75 M⊙, compatible with observations. The use of mesa for TP-(S)AGB evolution is validated by comparison to the widely used monash models which show good agreement in the maximum third dredge-up efficiency at initial masses M i > 2 M⊙. We also compare the third dredge-up efficiency in models produced using two independent stellar evolution codes, fruity and aton , which were computed with various differences in input physics including mass-loss, and which exhibit weaker third dredge-up episodes. [ABSTRACT FROM AUTHOR]

There is evidence that some red supergiants (RSGs) experience phases of episodic mass-loss. These episodes yield more extreme mass-loss rates, further stripping the envelope of the RSG, significantly affecting the further evolution towards the final collapse of the star. Mass lost through RSG outbursts/superwinds will flow outwards and form dust further out from the surface and this dust may be detected and modelled. Here, we aim to derive the surface properties and estimate the global properties of Mid-IR bright RSGs in the Magellanic Clouds. These properties will then be compared to evolutionary predictions and used for future spectral energy distribution fitting studies to measure the mass-loss rates from present circumstellar dust. [ABSTRACT FROM AUTHOR]

Many asymptotic giant branch (AGB) and supergiant stars exhibit extended detached shells in the far-infrared, resembling rings or arcs. These structures have long been interpreted as the bow shock formed in the interface between the stellar wind and the interstellar medium (ISM), the astrosphere. To date, only a few AGB stars have been observed showing an extended shell in the ultraviolet (UV): the cometary tail drifting away from o Ceti, and a bubble around IRC+10216, CIT6, and U Hya. This paper describes a search of UV extended shells around AGB stars using archival Galaxy Evolution Explorer (GALEX) far-UV images. After inspecting visually 282 GALEX images, we identified the fourth discovery of a UV bubble around the AGB star R Dor. The bubble is seen as a 26 arcmin × 29 arcmin ring, corresponding to an actual diameter of 0.41 × 0.46 parsec2. The mass of the thin UV bubble is estimated to be ≃0.003 M⊙. The morphological asymmetry (less than ∼20 per cent) and brightness variations of this shell are uncorrelated with the stellar proper motion and thus they can rather be ascribed to inhomogeneities in the ISM. Archival Infrared Astronomical Satellite 60 and 100 μm images reveal that the bubble is filled with cold (i.e. |${\lesssim} 32$|  K) dust. All UV bubbles known to date are limited to be within a distance |${\lesssim} 350$| pc and at high Galactic latitudes (⁠|$|b| \gtrsim 35^{\circ }$|⁠), which suggests that their detection is hampered in most cases by the strong UV interstellar extinction. [ABSTRACT FROM AUTHOR]

Computer modeling of the outflow from Be stars is performed. In our approach, processes of turbulence excitation and turbulent viscosity are added to the conventional model of the radiation driven winds. The objective of our study is to reproduce from the first principles the main features of the outflow from Be stars: a fast polar wind and a slow viscous Keplerian disk at the equator. At sub-critical velocity of rotation up to 0.999 of the critical velocity, our model reproduces the formation of the fast polar wind together with a slow highly turbulent outflow at the equatorial region. This outflow, however, does not reassemble a Keplerian disk. We link this to the absence of the angular moment transfer from the star to the disk. This process provides an increase of the angular momentum of the disk matter with radius. We consider a star with super critical rotation as the simplest way to supply the angular momentum to the disk. In this case, the star surface has a higher azimuthal speed than the matter at the inner edge of the disk. The angular momentum transfer becomes unavoidable. Already at rotation velocity 0.5% above the critical one, a quasi Keplerian disk at the equator is formed with size ∼10 stellar radius. At rotation 1% higher than the critical speed, the disk reaches ∼15 stellar radius. The main conclusion following from our work is that the conventional model of the radiation driven winds is able to reproduce the main features of the outflow from Be stars provided that the process of turbulence excitation and a process of angular momentum supply of the disk from the central source are added in to this model. [ABSTRACT FROM AUTHOR]

A significant fraction of the stars near the tip of the AGB phase become regular or semi-regular (Mira-type, SRs) pulsators. However, some of these light curves have shown intriguing secondary minima or sharp dips with much longer periods. Although this phenomenon shows some resemblance with the R CrB variables, the light curve is generally symmetric before and after the dip, whereas in R CrB the luminosity recovers slower after its minimum. More recently, high-resolution ALMA CO observations revealed a spiral structure around some of these stars, which suggests the presence of a stellar or sub-stellar companion. In these cases, the long-term light curve minima could be caused by periodic eclipses of the primary by a spiral circumstellar structure, and the long-period would be related to the orbital period. In this paper we discuss the pros and cons of the various proposed scenarios for the long-term minima of pulsating AGB stars. [ABSTRACT FROM AUTHOR]

We present interferometric continuum and molecular line emission maps obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) of OH231.8+4.2, a well studied bipolar nebula around an asymptotic giant branch (AGB) star that is key to understand the remarkable changes in nebular morphology and kinematics during the short transition from the AGB to the Planetary Nebula (PN) phase. The excellent angular resolution of our maps (∼20 mas ∼30 AU) allows us to scrutinize the central nebular regions of OH231.8+4.2, which hold the clues to understanding how this iconic object assembled its complex nebular architecture. We report, for the first time in this object and others of its kind (i.e. pre-PNe with massive bipolar outflows), the discovery of a rotating circumbinary disk of radius ∼30 AU traced by NaCl, KCl, and H2O emission lines. The disk lies at the base of a young bipolar wind with signs of rotation as well. A compact spatially resolved dust disk is found perpendicular to the bipolar outflow. We also identify a point-like continuum source, which likely represents the central Mira star enshrouded by a ∼3 R * shell or disk of hot (∼1400 K) freshly formed dust. The point source is slightly off-centre from the disk centroid, enabling us for the first time to place constraints to the orbital separation of the central binary system. [ABSTRACT FROM AUTHOR]

The mass‐loss, polarization tests, and electrochemical impedance spectroscopic strategies were applied to assess the inhibition performance of the environmentally friendly inhibitor Araucaria heterophylla leaves extract (AHLE) for soft‐cast steel corrosion safety in 1 M HCl at 300 ± 1 K. The environmentally friendly inhibitor creates a protective coat on soft‐cast steel that decelerates the corrosion process in acidic environments. The percentage inhibition effectiveness, corrosion current density, corrosion potential, cathodic and anodic Tafel slopes are being assessed. The outcomes of chemical and electrochemical research are almost similar. The inhibitor's inhibition activity was well illustrated by the AHLE adsorption on soft‐cast steel follows the Langmuir adsorption isotherm. According to the study, AHLE is a mixed kind of inhibitor. Experiments were conducted with varying inhibitor amounts and temperatures. The calculated ΔGadso$\Delta G_{{\rm{ads}}}^o$ values were in the range of −33.75 to −34.40 kJ/mol, which discloses the corrosion inhibitory action is exothermic and spontaneous. Scanning electron microscopy, Fourier transform infrared spectroscopy, and contact angle techniques were used to determine the association of the AHLE on the metal surface. [ABSTRACT FROM AUTHOR]

Abradable coatings are essentially sealing materials and are deposited by thermal spray techniques. The main function of these coatings is to control the clearance of the gas path of the gas turbine engines. The abradable coating prevents turbine blade damage by abrading itself when there is an offset or vibration during turbine operation. Since the coating is meant to abrade, the preferred coating material is relatively softer than the turbine blade material. As these coatings are prone to solid particle erosion at high temperatures, the erosion response of these coatings at elevated temperatures needs to be investigated. In order to achieve this objective, MCrAlY boron nitride polymer coating was deposited employing an air plasma spraying technique on a Ni-base alloy substrate. The important features of the microstructure and mechanical properties of the coating were examined, and the coating was subjected to erosion at various temperatures under different erosion conditions. The results indicate a ductile erosion behaviour for an abradable top coat. The erosion rate increases with the temperature of the coating. The detailed results of the investigation are presented, and the erosion mechanisms are studied.

Ancient ceramic artefacts attracted the attention of scientists as being a chronological indicator within the archaeological context; however, they can also provide information about the tech-nology and provenance. A series of brick samples from an ancient nomadic town at Karabal-gasun (Mongolia) have been analyzed using X-ray fluorescence (XRF) spectroscopy, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric (TG) analysis in order to obtain information on the performance of the kilns used and on the technological skills of ancient pot-ters.

The objective of this work is to reproduce the formation of the fast polar wind and viscous disk outflow from Be stars in a unified physical picture. Numerical modeling of the plasma outflow from fast rotating stars was performed taking into account the acceleration of the plasma due to scattering of the radiation of the star in lines of plasma ions and excitation of the hydrodynamic turbulence in the outflow. The fast polar wind naturally arises in this picture with an expected flow rate. For the first time, it is shown that a disk-like outflow with a relatively high level of turbulence is formed at the equator of fast rotating stars emitting radiation-driven wind. However, the level of turbulent viscosity is well below the level necessary for the formation of a Keplerian disk. [ABSTRACT FROM AUTHOR]

Computer modeling of the outflow from Be stars is performed. In our approach, processes of turbulence excitation and turbulent viscosity are added to the conventional model of the radiation driven winds. The objective of our study is to reproduce from the first principles the main features of the outflow from Be stars: a fast polar wind and a slow viscous Keplerian disk at the equator. At sub-critical velocity of rotation up to 0.999 of the critical velocity, our model reproduces the formation of the fast polar wind together with a slow highly turbulent outflow at the equatorial region. This outflow, however, does not reassemble a Keplerian disk. We link this to the absence of the angular moment transfer from the star to the disk. This process provides an increase of the angular momentum of the disk matter with radius. We consider a star with super critical rotation as the simplest way to supply the angular momentum to the disk. In this case, the star surface has a higher azimuthal speed than the matter at the inner edge of the disk. The angular momentum transfer becomes unavoidable. Already at rotation velocity 0.5% above the critical one, a quasi Keplerian disk at the equator is formed with size ∼10 stellar radius. At rotation 1% higher than the critical speed, the disk reaches ∼15 stellar radius. The main conclusion following from our work is that the conventional model of the radiation driven winds is able to reproduce the main features of the outflow from Be stars provided that the process of turbulence excitation and a process of angular momentum supply of the disk from the central source are added in to this model.

We present our observations of SN 2010mb, a Type Ic supernova (SN) lacking spectroscopic signatures of H and He. SN 2010mb has a slowly declining light curve (LC) (600 days) that cannot be powered by 56Ni/56Co radioactivity, the common energy source for Type Ic SNe. We detect signatures of interaction with hydrogen-free circumstellar material including a blue quasi-continuum and, uniquely, narrow oxygen emission lines that require high densities (109 cm-3). From the observed spectra and LC, we estimate that the amount of material involved in the interaction was 3 M . Our observations are in agreement with models of pulsational pair-instability SNe described in the literature. © 2014. The American Astronomical Society. All rights reserved..

Yttria-stabilized zirconia (YSZ) is used extensively as a ceramic top coat of thermal barrier coating (TBC) system in land-based gas turbines and aero engines. TBC enables modern engines to operate at significantly higher gas temperatures. TBCs are subjected to solid particle erosion at elevated temperature, especially during the operation of aero engines in sandy terrain. Thus, the objective of the present investigation is to evaluate the impact erosion response of these coatings as a function of various eroding conditions. Toward that purpose, YSZ TBC was deposited on Ni base alloy using air plasma spraying technique. The microstructural features of the coating are evaluated, and coated samples are subjected to erosion test employing a high-temperature air jet erosion testing machine at various temperatures, at different impact velocities, and at different impact angles. The results show a brittle erosion response of TBC at all temperatures. The erosion rate of TBC is generally independent of temperature under the normal impact, and it increases with temperature under oblique impact at high impact velocity. Intersplat adhesion governs the erosion mechanism. [ABSTRACT FROM AUTHOR]

There is evidence that some red supergiants (RSGs) experience phases of episodic mass-loss. These episodes yield more extreme mass-loss rates, further stripping the envelope of the RSG, significantly affecting the further evolution towards the final collapse of the star. Mass lost through RSG outbursts/superwinds will flow outwards and form dust further out from the surface and this dust may be detected and modelled. Here, we aim to derive the surface properties and estimate the global properties of Mid-IR bright RSGs in the Magellanic Clouds. These properties will then be compared to evolutionary predictions and used for future spectral energy distribution fitting studies to measure the mass-loss rates from present circumstellar dust. [ABSTRACT FROM AUTHOR]

Ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques, over different time periods, and at various levels of spatial detail. Considerable disparity remains between these estimates due to the inherent uncertainties of each method, the lack of detailed comparison between independent estimates, and the effect of temporal modulations in ice sheet surface mass balance. Here, we present a consistent record of mass balance for the Greenland and Antarctic ice sheets over the past two decades, validated by the comparison of two independent techniques over the last 8 years: one differencing perimeter loss from net accumulation, and one using a dense time series of time-variable gravity. We find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss. In 2006, the Greenland and Antarctic ice sheets experienced a combined mass loss of 475 ± 158 Gt/yr, equivalent to 1.3 ± 0.4 mm/yr sea level rise. Notably, the acceleration in ice sheet loss over the last 18 years was 21.9 ± 1 Gt/yr2 for Greenland and 14.5 ± 2 Gt/yr2 for Antarctica, for a combined total of 36.3 ± 2 Gt/yr2. This acceleration is 3 times larger than for mountain glaciers and ice caps (12 ± 6 Gt/yr2). If this trend continues, ice sheets will be the dominant contributor to sea level rise in the 21st century.

We review the observational properties and possible carriers of the 21 and 30 μm features seen in the spectra of evolved carbon-rich objects. The 30 μm feature is generally taken to be due to MgS, possibly in combination with other sulfides. It is commonly assumed that the sulfides coat grains of SiC or amorphous carbon, but it remains unclear if coated grains can produce the observed feature given the low relative abundance of sulfur and the optical constraints on the thickness of the coating and size of the grains. The lack of optical constants for MgS at wavelengths below 1 μm hampers attempts to model the dust shells of these objects. A small number of alternative carriers have been proposed, but these have not been investigated thoroughly. The situation for the 21 μm feature is more ambiguous. Many carriers have been proposed, but each has issues, and none have gained broad support. The feature only appears in carbon-rich objects which have evolved off of the asymptotic giant branch but have not yet become planetary nebulae. The spectral class of the central star is typically F or G. The transient nature of the 21 μm feature is an important clue to the nature of its carrier. It appears with a variety of other infrared emission features related to complex hydrocarbons, including aliphatic species and polycyclic aromatic hydrocarbons, but correlations with specific features have proven difficult to quantify. [ABSTRACT FROM AUTHOR]

In latest years, the high sensitivity of the instruments on-board the XMM-Newton and Chandra satellites allowed us to explore the properties of the X-ray emission from hot subdwarf stars. The small but growing sample of X-ray detected hot subdwarfs includes binary systems, in which the X-ray emission is due to wind accretion onto a compact companion (white dwarf or neutron star), as well as isolated sdO stars, in which X-rays are probably due to shock instabilities in the wind. X-ray observations of these low-mass stars provide information which can be useful for our understanding of the weak winds of this type of stars and can lead to the discovery of particularly interesting binary systems. Here we report the most recent results we have recently obtained in this research area.

The objective of this work is to reproduce the formation of the fast polar wind and viscous disk outflow from Be stars in a unified physical picture. Numerical modeling of the plasma outflow from fast rotating stars was performed taking into account the acceleration of the plasma due to scattering of the radiation of the star in lines of plasma ions and excitation of the hydrodynamic turbulence in the outflow. The fast polar wind naturally arises in this picture with an expected flow rate. For the first time, it is shown that a disk-like outflow with a relatively high level of turbulence is formed at the equator of fast rotating stars emitting radiation-driven wind. However, the level of turbulent viscosity is well below the level necessary for the formation of a Keplerian disk.

A computational study has been carried out to investigate smoldering ignition and propagation in polyurethane foam. The one-dimensional, transient, governing equations for smoldering combustion in a porous fuel are solved accounting for improved solid-phase chemical kinetics. A systematic methodology for the determination of solid-phase kinetics suitable for numerical models has been developed and applied to the simulation of smoldering combustion. This methodology consists in the correlation of a mathematical representation of a reaction mechanism with data from previous thermogravimetric experiments. Genetic-algorithm and trail-and-error techniques are used as the optimization procedure. The corresponding kinetic parameters for two different mechanisms of polyurethane foam smoldering kinetics are quantified: a previously proposed 3-step mechanism and a new 5-step mechanism. These kinetic mechanisms are used to model one-dimensional smoldering combustion, numerically solving for the solid-phase and gas-phase conservation equations in microgravity with a forced flow of oxidizer gas. The results from previously conducted microgravity experiments with flexible polyurethane foam are used for calibration and testing of the model predictive capabilities. Both forward and opposed smoldering configurations are examined. The model describes well both opposed and forward propagation. Specifically, the model predicts the reaction-front thermal and species structure, the onset of smoldering ignition, and the propagation rate. The model results reproduce the most important features of the smolder process and represent a significant step forward in smoldering combustion modeling.

This is a non-comprehensive review of observations of pre-Planetary Nebulae (pPNe) and young Planetary Nebulae (yPNe) at (sub)mm-wavelengths, a valuable window for probing multi-phased gas and dust in these objects. This contribution focuses on observations of molecular lines (from carbon monoxide—CO—and other species), and briefly at the end, on hydrogen radio recombination lines from the emerging H ii regions at the center of yPNe. The main goal of this contribution is to show the potential of (sub)mm-wavelength observations of pPNe/yPNe to help the community to devise and develop new observational projects that will bring us closer to a better understanding of these latest stages of the evolution of low-to-intermediate (∼0.8−8 M ⊙ ) mass stars.

High-mass X-ray binaries belong to the brightest objects in the X-ray sky. They usually consist of a massive O or B star or a blue supergiant while the compact X-ray emitting component is a neutron star (NS) or a black hole. Intensive matter accretion onto the compact object can take place through different mechanisms: wind accretion, Roche-lobe overflow, or circumstellar disk. In our multi-dimensional models we perform numerical simulations of the accretion of matter onto a compact companion in case of Be/X-ray binaries. Using Bondi-Hoyle-Littleton approximation, we estimate the NS accretion rate. We determine the Be/X-ray binary disk hydrodynamic structure and compare its deviation from isolated Be stars' disk. From the rate and morphology of the accretion flow and the X-ray luminosity we improve the estimate of the disk mass-loss rate. We also study the behavior of a binary system undergoing a supernova explosion, assuming a blue supergiant progenitor with an aspherical circumstellar environment. [ABSTRACT FROM AUTHOR]

The massive outflows of gas and dust which characterize giant stars on the Asymptotic Giant Branch (AGB), build cool circumstellar envelopes readily observed at infrared (IR) and sub-millimeter wavelengths. The observations will give the amount of matter lost by the star, the wind velocity (in the case of spectral line observations), and, when the spatial resolution is sufficient, the wind evolution over time. To gain detailed insight into the mass-loss process, we study the nearby (closer than 1 kpc) stars. Through these investigations we aim to determine the best constrained wind properties available. By combining this with theoretical results, mass-loss estimates for more distant sources can also be significantly improved. ALMA has opened up new opportunities to study the winds of AGB stars. The DEATHSTAR project (www.astro.uu.se/deathstar) has mapped the circumstellar CO emission from so far ∼50 nearby M- and C-type AGB stars. The data will initially be used to give a definitive mass-loss prescription for the sample sources, but the large-bandwidth observations opens for many different legacy projects. The current status and results are presented. [ABSTRACT FROM AUTHOR]

The first four gravitational wave events detected by LIGO were all interpreted as merging black hole binaries (BHBs), opening a new perspective on the study of such systems. Here we use our new population-synthesis code MOBSE, an upgraded version of BSE, to investigate the demography of merging BHBs. MOBSE includes metallicity-dependent prescriptions for mass-loss of massive hot stars. It also accounts for the impact of the electron-scattering Eddington factor on mass-loss. We perform >108 simulations of isolated massive binaries, with 12 different metallicities, to study the impact of mass-loss, core-collapse supernovae and common envelope on merging BHBs. Accounting for the dependence of stellar winds on the Eddington factor leads to the formation of black holes (BHs) with mass up to 65 M⊙ at metallicity Z ~ 0.0002. However, most BHs in merging BHBs have masses ≲ 40 M⊙. We find merging BHBs with mass ratios in the 0.1-1.0 range, even if mass ratios >0.6 are more likely. We predict that systems like GW150914, GW170814 and GW170104 can form only from progenitors with metallicity Z ≤ 0.006, Z ≤ 0.008 and Z ≤ 0.012, respectively. Most merging BHBs have gone through a common envelope phase, but up to ~17 per cent merging BHBs at low metallicity did not undergo any common envelope phase.We find a much higher number of mergers from metal-poor progenitors than from metal-rich ones: the number of BHB mergers per unit mass is ~10-4 M-1⊙ at low metallicity (Z = 0.0002-0.002) and drops to ~10-7 M-1⊙ at high metallicity (Z ~ 0.02). [ABSTRACT FROM AUTHOR]

Core-collapse Supernovae (CCSNe) are the most powerful explosions that occur at the last stage of a massive star's (MZAMS > 8MO) life cycle marking their endpoint. The type of supernova that a star will undergo at the end of its life cycle depends on the mass-loss history of the star. Stars with similar initial mass might end up having different types of end evolution phases and dying by different types of supemovae (SNe) processes. Particularly, red and yellow supergiant stars (RSG & YSG) begin their lives with identical masses, but at some point, in their evolution, their paths to endpoint diverge. A recent work on the nested dust shells around the Wolf-Rayet WR 140 observed with JWST shows the presence of interstellar molecules and carbonaceous dust grains around the star. The work establishes a precedent for studying the effects of dust shells on massive stars which can be optimized for the analysis of mass-loss in these stars. Here we present high spatial resolution observation of seven CCSNe progenitors using Very Large Telescopes, SPHERE/IRDIS to study the mass-loss effect due to dust and wind profile of the circumstellar materials. These coronagraphic fits images are processed using Vortex Image Processing pipeline to get the flux, angular differential image, signal-to-noise ratio, and other characteristics of the annuli of these stars. [ABSTRACT FROM AUTHOR]