Low Mass-loss Rate Research Articles

The mass-loss rates of star clusters with stellar-mass black holes: implications for the globular cluster mass function

ABSTRACT Stellar-mass black holes (BHs) can be retained in globular clusters (GCs) until the present. Simulations of GC evolution find that the relaxation driven mass-loss rate is elevated if BHs are present, especially near dissolution. We capture this behaviour in a parametrized mass-loss rate, bench marked by results from N-body simulations, and use it to evolve an initial GC mass function (GCMF), similar to that of young massive clusters in the Local Universe, to an age of 12 Gyr. Low-metallicity GCs ([Fe/H] ≲ −1.5) have the highest mass-loss rates, because of their relatively high BH masses, which combined with their more radial orbits and stronger tidal field in the past explains the high turnover mass of the GCMF ($\sim 10^5\, {\rm M}_\odot$ ) at large Galactic radii ($\gtrsim 10\, {\rm kpc}$ ). The turnover mass at smaller Galactic radii is similar because of the upper mass truncation of the initial GCMF and the lower mass-loss rate due to the higher metallicities. The density profile in the Galaxy of mass lost from massive GCs ($\gtrsim 10^{5}\, {\rm M}_\odot$ ) resembles that of nitrogen-rich stars in the halo, confirming that these stars originated from GCs. We conclude that two-body relaxation is the dominant effect in shaping the GCMF from a universal initial GCMF, because including the effect of BHs reduces the need for additional disruption mechanisms.

Evolution of rotating massive stars with new hydrodynamic wind models

Context. Mass loss due to radiatively line-driven winds is central to our understanding of the evolution of massive stars in both single and multiple systems. This mass loss plays a key role in modulating the stellar evolution at different metallicities, particularly in the case of massive stars with M* ≥ 25 M⊙. Aims. We extend the evolution models introduced in Paper I, where the mass-loss recipe is based on the simultaneous calculation of the wind hydrodynamics and the line acceleration, by incorporating the effects of stellar rotation. Methods. As in Paper I, we introduce a grid of self-consistent line-force parameters (k, α, δ) for a set of standard evolutionary tracks using GENEC. Based on this grid, we analysed the effects of stellar rotation, CNO abundances, and He/H ratio on the wind solutions to derive additional terms for the recipe with which we predict the self-consistent mass-loss rate, Ṁsc. With this, we generated a new set of evolutionary tracks with rotation for MZAMS = 25, 40, 70, and 120 M⊙, and for metallicities Z = 0.014 (Galactic) and 0.006 (Large Magellanic Cloud). Results. In addition to the expected correction factor due to rotation, the mass-loss rate decreases when the surface becomes more helium rich, especially in the later moments of the main-sequence phase. The self-consistent approach gives lower mass-loss rates than the standard values adopted in previous GENEC evolution models. This decrease strongly affects the tracks of the most massive models. Weaker winds allow the star to retain more mass, but also more angular momentum. As a consequence, weaker wind models rotate faster and show a less efficient mixing in their inner stellar structure at a given age. Conclusions. The self-consistent tracks predict an evolution of the rotational velocities through the main sequence that closely agrees with the range of v sin i values found by recent surveys of Galactic O-type stars. As subsequent implications, the weaker winds from self-consistent models also suggest a reduction of the contribution of the isotope 26Al to the interstellar medium due to stellar winds of massive stars during the MS phase. Moreover, the higher luminosities found for the self-consistent evolutionary models suggest that some populations of massive stars might be less massive than previously thought, as in the case of Ofpe stars at the Galactic centre. Therefore, this study opens a wide range of consequences for further research based on the evolution of massive stars.

Synthetic photometry for carbon-rich giants

Context. The properties and the evolution of asymptotic giant branch (AGB) stars are strongly influenced by their mass loss through a stellar wind. This, in turn, is believed to be caused by radiation pressure due to the absorption and scattering of the stellar radiation by the dust grains formed in the atmosphere. The optical properties of dust are often estimated using the small particle limit (SPL) approximation, and it has been used frequently in modelling AGB stellar winds when performing radiation-hydrodynamics (RHD) simulations. Aims. We aim to investigate the effects of replacing the SPL approximation by detailed Mie calculations of the size-dependent opacities for grains of amorphous carbon forming in C-rich AGB star atmospheres. Methods. We performed RHD simulations for a large grid of carbon star atmosphere+wind models with different effective temperatures, luminosities, stellar masses, carbon excesses, and pulsation properties. Also, a posteriori radiative transfer calculations for many radial structures (snapshots) of these models were done, resulting in spectra and filter magnitudes. Results. We find that, when giving up the SPL approximation, the wind models become more strongly variable and more dominated by gusts, although the average mass-loss rates and outflow speeds do not change significantly; the increased radiative pressure on the dust throughout its formation zone does, however, result in smaller grains and lower condensation fractions (and thus higher gas-to-dust ratios). The photometric K magnitudes are generally brighter, but at V the effects of using size-dependent dust opacities are more complex: brighter for low mass-loss rates and dimmer for massive stellar winds. Conclusions. Given the large effects on spectra and photometric properties, it is necessary to use the detailed dust optical data instead of the simple SPL approximation in stellar atmosphere+wind modelling where dust is formed.

Meandering periods and asymmetries in light curves of Miras: Observational evidence for low mass-loss rates

Context. Some Miras (long-period variables in late evolutionary stages) have meandering pulsation periods and light-curve asymmetries, the causes of which are still unclear. Aims. We aim to better understand the origin of meandering periods and light-curve asymmetries by investigating a sample of Miras in the solar neighbourhood. We characterised this group of stars and related their variability characteristics to other stellar parameters. Methods. We analysed observations from several databases to obtain light curves with maximum time span and temporal coverage for a sample of 548 Miras. We determined their pulsation-period evolution over a time span of many decades, searched for changes in the periods, and determined the amplitude of the period change. We also analysed the Fourier spectra with respect to possible secondary frequency maxima. The sample was divided into two groups with respect to the presence of light-curve asymmetries (‘bumps’). Infrared colours and indicators of the third dredge-up were collected to study the mass loss and deep mixing properties of the stars of our sample. Results. Our analysis reveals one new star, T Lyn, with a continuously changing period. The group of Miras with meandering period changes is exclusively made up of M-type stars. The Fourier spectra of the meandering-period Miras have no prominent additional peaks, suggesting that additional pulsation modes are not the cause of the meandering periods. We confirm that light-curve bumps are more common among S and C Miras and show, for the first time, that Miras with such bumps have lower mass-loss rates than those with regular, symmetric light curves. Also, Miras with meandering period changes have relatively little mass loss. Conclusions. We conclude that Miras with strongly changing periods (including meandering periods) or asymmetries in their light curves have relatively low dust mass-loss rates. Meandering period changes and light-curve asymmetries could be connected to He-shell flashes and third dredge-up episodes.

Effect of recycled coarse aggregate quality on the interfacial property and sulfuric acid resistance of geopolymer concrete at different acidity levels

Geopolymer recycled concrete (GRC) is a green and low-carbon building material which can promote the early achievement of the goals of carbon peak and carbon neutral globalization. This study aims to clarify the effect of recycled coarse aggregate (RA) quality on the interfacial property and sulfuric acid resistance of geopolymer concrete (GPC) at different acidity levels. Specimens with three qualities of coarse aggregates were prepared, which were immersed in sulfuric acid solution of three acidities (pH = 0.5, 1.0, 1.5) for 98 d to evaluate their acid resistance. The results showed that the adhered mortar attached on the surface of RA affected the inhomogeneous distribution of interfacial transition zones (ITZs) and weakened the bond strength between aggregate and paste, threatening the development of concrete strength. Low-quality coarse aggregate accelerated the deterioration of sulfuric acid resistance of GPC. But at the exposure time of 28 d, GRC showed a lower mass loss rate than that of GPC prepared with natural aggregate (GPCNA) regardless of acid environment levels, indicating the presence of RA resulted in the loose ITZ structure in GRC which could provide more space for gypsum generation to some extent. As exposure time goes on, the adhered mortars of RA provided extra calcium source for GPC to generate gypsum. More adhered mortar content caused overmuch gypsum crystals, generating internal stress, thus resulting in spalling of mortar and worsen acid resistance of concrete. In addition, the fracture of Si-O-Al bonds and disappearance of amorphous N-A-S-H gels caused by the dealuminization was another key reason for failure of the GRC in high acid environment (pH = 0.5 and 1.0). At last, based on the carbon emission calculations of raw materials, transportation and production of concrete, more than 20% of total carbon dioxide (CO2) emissions can be reduced using GRC to replace ordinary Portland cement concrete (OPCC).

Effect of Protective Coatings on Wooden Elements Exposed to a Small Ignition Initiator

This paper presents the results of monitoring the behaviour of selected wood species exposed to a small ignition initiator. We specifically aimed to investigate the effect of retardant coating on the combustion process of the wood species spruce (Picea abies), red spruce (Larix decidua), Scots pine (Pinus sylvestris), ash (Fraxinus excelsior L.), beech (Fagus sylvatica), and oak (Quercus robur) when exposed to a small initiator of ignition. At the same time, we studied the effect of different types of fungicidal agents (based on N-(3-aminopropyl)-N-dodecylpropane-1,3-diamine; alkyl (C12–16) dimethylbenzyl ammonium chloride or 3-iodo-prop-2-inylbutylcarbamate) on the effectiveness of a flame retardant (containing ferric phosphate) applied to the selected fungicide-treated wood samples. The experimentally obtained mass-loss and flame-spread results were statistically evaluated using the QtiPlot software program. A significant dependence of mass loss and surface flame spread on wood species was the primary focus. It was only confirmed for the surface-flame-spread variable. The dependence of the effect of fungicide treatment on the effectiveness of the selected retardant was confirmed. Fungicidal coatings with the active ingredient alkyl/benzyl (C12–16) dimethylbenzyl ammonium chloride indicated the lowest mass loss rate and flame spread for all wood samples.

Stripped-envelope stars in different metallicity environments

Stripped-envelope stars can be observed as Wolf-Rayet (WR) stars or as less luminous hydrogen-poor stars with low mass-loss rates and transparent winds. Both types are potential progenitors of Type I core-collapse supernovae (SNe). We used grids of core-collapse models obtained from single helium stars at different metallicities to study the effects of metallicity on the transients and remnants these stars produce. We characterised the surface and core properties of our core-collapse models and investigated their ‘explodability’ using three criteria. In the cases where explosions are predicted, we estimated the ejecta mass, explosion energy, nickel mass, and neutron star (NS) mass. Otherwise, we predicted the mass of the resulting black hole (BH). We constructed a simplified population model and find that the properties of SNe and compact objects depend strongly on metallicity. The ejecta masses and explosion energies for Type Ic SNe are best reproduced by models with Z = 0.04 that exhibit strong winds during core helium burning. This implies that either their mass-loss rates are underestimated or that Type Ic SN progenitors experience mass loss through other mechanisms before exploding. The distributions of ejecta masses, explosion energies, and nickel mass for Type Ib SNe are not well reproduced by progenitor models with WR mass loss, but are better reproduced if we assume no mass loss in progenitors with luminosities below the minimum WR star luminosity. We find that Type Ic SNe become more common as metallicity increases, and that the vast majority of progenitors of Type Ib SNe must be transparent-wind stripped-envelope stars. We find that several models with pre-collapse CO masses of up to ∼30 M⊙ may form ∼3 M⊙ BHs in fallback SNe. This may have important consequences for our understanding of SNe, binary BH and NS systems, X-ray binary systems, and gravitational wave transients.

The sculpting of rectangular and jet-like morphologies in supernova remnants by anisotropic equatorially confined progenitor stellar winds

ABSTRACT Thermonuclear and core-collapse supernova remnants (SNRs) are the nebular leftovers of defunct stars. Their morphology and emission properties provide insights into the evolutionary history of the progenitor star. But while some SNRs are spherical, as expected from a point-like explosion expanding into a roughly uniform medium, many others exhibit complex non-spherical morphologies that are often not easily explained. In this work, we use 3D magnetohydrodynamic simulations to show that rectangular and jet-like morphologies can be explained by supernovae (SNe), either type Ia or type II, expanding within anisotropic, bipolar stellar wind bubbles driven by the progenitor star. The stellar wind has an anisotropic density distribution, which channels the SN ejecta differently depending on the anisotropy characteristics. We compute synthetic thermal (X-ray) and non-thermal (synchrotron) emission maps from our numerical simulations to compare with observations. We find rectangular morphologies are generated when the stellar wind has a high-mass loss rate and forms a dense, narrow disc at the equatorial region. Instead, a jet-like or ear-like morphology is obtained when the stellar wind develops a wide, dense disc. Stellar winds with low mass-loss rates do not strongly influence the SNR morphology. Finally, our synthetic synchrotron and X-ray maps for the high mass-loss rate case qualitatively agree with the observations of the SNRs G332.5-5.6 and G290.1-0.8.

The Time-averaged Mass-loss Rates of Red Supergiants as Revealed by Their Luminosity Functions in M31 and M33

Mass loss in red supergiants (RSGs) is generally recognized to be episodic, but mass-loss prescriptions fail to reflect this. Evolutionary models show that the total amount of mass lost in this phase determines if these stars evolve to warmer temperatures before undergoing core collapse. The current Geneva evolutionary models mimic episodic mass loss by enhancing the quiescent prescription rates whenever the star’s outer layers exceed the Eddington luminosity by a large factor. This results in a 20 M ⊙ model undergoing 10× more mass loss than it would otherwise, but has little effect on models of lower mass. We can test the validity of this approach observationally by measuring the proportion of high-luminosity RSGs to that predicted by the models. To do this, we use our recent luminosity-limited census of RSGs in M31 and M33, making modest improvements to membership, and adopting extinctions based on the recent panchromatic M31 and M33 Hubble surveys. We then compare the proportions of the highest luminosity RSGs found to that predicted by published Geneva models, as well as to a special set of models computed without the enhanced rates. We find good agreement with the models which include the supra-Eddington enhanced mass loss. The models with lower mass-loss rates predict a larger fraction of high-luminosity RSGs than observed, and thus can be ruled out. We also use these improved data to confirm that the upper luminosity limit of RSGs is , regardless of metallicity, using our improved data on M31 and M33 plus previous results on the Magellanic Clouds.

On the Jet Structures of GRB 050820A and GRB 070125

We present the broadband numerical modeling of afterglows for two remarkably bright long gamma-ray bursts (GRBs), GRB 050820A and GRB 070125, with a wide range of observations from the radio band to the X-ray band. In our work, we fit light curves and constrain physical parameters using a standard forward shock model from the afterglowpy Python package, considering different jet structures and the jet lateral expansion. For GRB 050820A, the constrained jet is close to a top-hat jet with an extremely small half opening angle of about 0.015 rad, and the circumburst matter density is as small as 10−7 cm−3, which suggests that this peculiar long GRB might originate from metal-poor stars with low mass-loss rates. To explain the late time optical light curves of GRB 070125, the effects of the lateral expansion and the participation factor of electrons that are accelerated by the shock have to be taken into account. The constrained results for GRB 070125 show that the jet is also close to a top-hat jet with a half opening angle of about 0.1 rad, the viewing angle is about 0.05 rad, the circumburst density is about 10 cm−3, and the participation factor is about 0.1. The jet energy of the two bursts is required to be ∼1051–1052 erg, which can be produced by a millisecond magnetar or a hyper-accreting black hole.

Design and preparation of a novel organic–inorganic hybrid for reducing fire hazards of epoxy

AbstractHerein, a novel type of organic–inorganic hybrid (SiO2‐Co‐BHMTPMPA) with core‐shell structure was designed to reduce the fire risk of epoxy resin (EP). The chemical composition and micro‐morphology of SiO2‐Co‐BHMTPMPA were characterized by XRD, FTIR, TGA, XPS, and SEM. As observed by SEM images, the SiO2‐Co‐BHMTPMPA exhibited spherical morphology while a large amount of SiO2 was attached on the surface to form a covering layer. The SiO2‐Co‐BHMTPMPA hybrids showed better dispersion state within epoxy matrix, in comparison with that of Co‐BHMTPMPA. According to TGA and cone calorimeter test, the thermal stability and fire safety of EP/SiO2‐Co‐BHMTPMPA have been significantly improved. Compared to neat epoxy, the epoxy composites with 2 wt% SiO2‐Co‐BHMTPMPA exhibited a low mass loss rate, increased residual char of 68.4%, reduced 36.0% in peak heat release rate (PHRR) and a drop of 28.5% in peak smoke production rate (PSPR), respectively. The good dispersibility, catalytic carbon formation and smoke inhibition ability of SiO2‐Co‐BHMTPMPA hybrid led to the reduction of fire risk of epoxy composites.

The strong suppression of galactic cosmic rays reaching AU Mic b, c, and Prox Cen b

ABSTRACT The propagation of Galactic cosmic rays is well understood in the context of the Solar system but is poorly studied for M dwarf systems. Quantifying the flux of cosmic rays reaching exoplanets is important since cosmic rays are relevant in the context of life. Here, we calculate the Galactic cosmic ray fluxes in AU Mic and Prox Cen planetary systems. We propagate the Galactic cosmic rays using a 1D cosmic ray transport model. We find for Prox Cen b, AU Mic b, and AU Mic c that the Galactic cosmic ray fluxes are strongly suppressed and are lower than the fluxes reaching Earth. We include in our models, for the first time for a star other than the Sun, the effect of radial particle drift due to gradients and curvatures in the stellar magnetic field. For Prox Cen, we find that the inclusion of particle drift leads to less suppression of Galactic cosmic rays fluxes than when it is excluded from the model. In the case of AU Mic we explore two different wind environments, with a low and high stellar wind mass-loss rate. For AU Mic, the particle drift also leads to less suppression of the Galactic cosmic ray fluxes but it is only significant for the high mass-loss rate scenario. However, both wind scenarios for AU Mic suppress the Galactic cosmic rays strongly. Overall, careful modelling of stellar winds is needed to calculate the Galactic cosmic ray fluxes reaching exoplanets. The results found here can be used to interpret future exoplanet atmosphere observations and in atmospheric models.

Preparation of artificial lightweight aggregate using alkali-activated incinerator bottom ash from urban sewage sludge

The preparation of lightweight aggregates (LWAs) using sewage sludge ash (SSA) by cold bonding technology can reduce the negative impact of SSA on the environment, it is an efficient solution to dispose of SSA. In this study, the granulated blast furnace slag (GBFS) was mixed with SSA to improve the performance of the prepared LWAs, with a dosage of 15% (SSA-G15) and 30% (SSA-G30) SSA by weight. Moreover, the 15% cement and 15% GBFS (SSA-G15C15) were added to the SSA as the third batch for comparison. The physical and mechanical characteristics of the LWAs were investigated, including particle size distribution, density, water absorption, compressive strength, and freeze-thaw resistance. Besides, the mineral composition, bonding type, microstructure, porosity, and heavy metal leaching behavior of the LWAs were evaluated by XRD, FTIR, SEM, MIP, and ICP, respectively. Results showed that all LWAs exhibited a uniform particle size distribution, a bulk density below 700 kg/3, and an acceptable leaching value of harmful metals as recommended by NEN-EN 6966, 2005. The SSA-G15C15 aggregates had higher cylinder compressive strength (1.8 MPa) and lower mass-loss rate (62.06%) under freeze-thaw cycles due to the dense microstructure compared to other batches. The water absorption value of SSA-G15C15 was 24.58%, within the acceptable limits as recommended by ACI-213R. It can be concluded that the application of SSA to produce LWAs is feasible, with a promising potential in sustainable lightweight concrete.

Mass loss of massive helium star supernova progenitors shortly before explosion constrained by supernova radio properties

Abstract Mass loss of massive helium stars is not well understood even though it plays an essential role in determining their remnant neutron-star or black hole masses as well as ejecta mass of Type Ibc supernovae. Radio emission from Type Ibc supernovae is strongly affected by circumstellar matter properties formed by mass loss of their massive helium star progenitors. In this study, we estimate the rise time and peak luminosity distributions of Type Ibc supernovae in radio based on a few massive helium star mass-loss prescriptions and compare them with the observed distribution to constrain the uncertain massive helium star mass-loss rates. We find that massive helium stars in the luminosity range expected for ordinary Type Ibc supernova progenitors (4.6 ≲ log L/L⊙ ≲ 5.2) should generally have large mass-loss rates (≳ 10−6 M⊙ yr−1) in order to account for the observed rise time and peak luminosity distribution. Therefore, mass-loss prescriptions that predict significantly low mass-loss rates for helium stars in this luminosity range is inconsistent with the supernova radio observations. It is also possible that massive helium stars shortly before their explosion generally undergo mass-loss enhancement in a different way from the standard radiation-driven wind mechanism.

Influence of Waste Tire Particles on Freeze–Thaw Resistance and Impermeability Performance of Waste Tires/Sand-Based Autoclaved Aerated Concrete Composites

Waste tires/sand-based autoclaved aerated concrete (SAAC) composites were prepared by mixing waste tires, which have different particle sizes and content. The physical performance, mechanical properties, freeze–thaw resistance, impermeability performance, phase composition, and microstructure of waste tires/sand-based autoclaved aerated concrete composite materials were examined. The results demonstrated that the 750-μm-sized waste tire particles on the surface of the SAAC composite did not agglomerate. Moreover, these particles did not damage the pore structure of the composites. The SAAC composites, with a relatively high compressive strength and low mass-loss rate, were obtained when the contents of waste tire particles ranged from 1.0 to 2.5 wt.%. For composites prepared with 2.0 wt.% of 750-μm-sized waste tire particles, the optimal compressive and flexural strength values were 3.20 and 0.95 MPa, respectively. The increase in the rate of water absorption on SAAC composites was lowest (i.e., 16.3%) when the soaking time was from 24 to 120 h.

Rapid Mass Loss in West Antarctica Revealed by Swarm Gravimetry in the Absence of GRACE

AbstractGRACE observations revealed that rapid mass loss in the West Antarctic Ice Sheet (WAIS) abruptly paused in 2015, followed by a much lower rate of mass loss ( Gt yr−1) until the decommissioning of GRACE in 2017. The critical 1‐year GRACE intermission data gap raises the question of whether the reduced mass loss rate persists. The Swarm gravimetry data, which have a lower resolution, show good agreement with GRACE/GRACE‐FO observations during the overlapping period, i.e., high correlation (0.78) and consistent trend estimates. Swarm data efficiently bridge the GRACE/GRACE‐FO data gap and reveal that WAIS has returned to the rapid mass loss state ( Gt yr−1) that prevailed prior to 2015 during the GRACE intermission data gap. The changes in precipitation patterns, driven by the climate cycles, further explain and confirm the dramatic shifts in the WAIS mass loss regime implied by the Swarm observations.

Morpho-kinematics of the wind of asymptotic giant branch star L2 Pup

ABSTRACT Single-dish observations of asymptotic giant branch star L2 Pup have revealed exceptionally low mass-loss rate and expansion velocity, challenging interpretations in terms of standard wind models. Recent VLT and ALMA observations have drawn a detailed picture of the circumstellar envelope within ∼20 au from the centre of the star: a nearly edge-on rotating disc of gas and dust, probably hosting a planetary companion near the star. However, these observations provide no direct information on the wind escaping the gravity of the star. This article uses ALMA observations of the 12, 13CO(3-2), 29SiO(8-7), 12CO(2-1), and 28SiO(5-4) line emissions to shed new light on this issue. It shows the apparent normality of L2 Pup in terms of the formation of the nascent wind, with important line broadening within 4 au from the centre of the star, but no evidence for a wind flowing along the disc axis. At larger distances, up to some 200 au from the centre of the star, the wind morpho-kinematics is dominated by a disc, or equatorial enhancement, expanding isotropically and radially with a velocity not exceeding some 5 km s−1, inclined in the north-west/south-east direction with respect to the plane of the sky. In addition, outflows of lower density are observed on both sides of the disc, covering large solid angles about the disc axis, contributing about half the flux of the disc. Such morphology is at strong variance with the expectation of a pair of back-to-back outflows collimated by the central gas-and-dust disc.

Lip-height effect in diffusive pool fires

A freeboard, lip height, from the container rim to the fuel surface affects the mass-loss rate of a pool fire. Experiments where heptane was burned in circular containers with diameter 10, 20 and 30 cm have been conducted. The results showed a decrease of up to 36% in the mass-loss rate for lip heights larger than zero. The mass-loss rate per unit area is affected by the lip height enough for it to surpass the effect of the diameter: a large-diameter pool fire with a high lip height may have lower mass-loss rate per unit area than a pool fire with smaller diameter and lower lip height. An analysis of the energy distribution for one experiment, showed that 35% of the received energy was lost to the surroundings; 30% was stored, and 35% was spent on evaporating fuel.

Regulation of the elemental distribution in biomass by the torrefaction pretreatment using different atmospheres and its influence on the subsequent pyrolysis behaviors

In this work, four types of torrefaction atmosphere (N2, 14% O2, CO2, and NH3) were employed during torrefaction pretreatment to regular the element distribution of biomass, then the effect of torrefaction pretreatment on subsequent pyrolysis behaviors was investigated. After torrefaction pretreatment, the content of carbon increased, while the content of oxygen sharply decreased. CO2 atmosphere resulted in highest content of carbon, and NH3 atmosphere resulted in lowest content of oxygen and highest content of nitrogen. The residual mass in TG curve increased after torrefaction pretreatment, resulting in lower mass loss rate at the DTG peaks. Meanwhile, the release amounts of H2O, CH4, CO2, and CO were highly related to the element distribution in torrefied biomass. As the increase of torrefaction temperature, the contents of ketones and acids decreased, while the content of phenols increased. Compared to other three types of torrefaction atmospheres (N2, CO2, and 14%O2), NH3 atmosphere resulted in lowest content of acids because of the Maillard reactions where majority of carbonyl group in the biomass was replaced by the NH2*/NH* radicals. Thus, some nitrogen-containing components was detected after the NH3 torrefaction pretreatment because of the incorporation of nitrogen element in torrefied biomass.

Multifrequency high spectral resolution observations of HCN toward the circumstellar envelope of Y Canum Venaticorum

High spectral resolution observations toward the low mass-loss rate C-rich, J-type asymptotic giant branch (AGB) star Y CVn were carried out at 7.5, 13.1, and 14.0 μm with the Echelon-cross-echelle Spectrograph mounted on the Stratospheric Observatory for Infrared Astronomy and the Texas Echelon-cross-echelle Spectrograph on the Infrared Telescope Facility. Around 130 HCN and H13CN lines of bandsν2, 2ν2, 2ν2−ν2, 3ν2− 2ν2, 3ν2−ν2, and 4ν2− 2ν2were identified involving lower levels with energies up to ≃3900 K. These lines were complemented with the pure rotational linesJ= 1−0 and 3–2 of the vibrational states up to 2ν2acquired with the Institut de Radioastronomie Millimétrique 30 m telescope, and with the continuum taken with Infrared Space Observatory. We analyzed the data in detail by means of a ro-vibrational diagram and with a code written to model the absorption and emission of the circumstellar envelope of an AGB star. The continuum is mostly produced by the star with a small contribution from dust grains comprising warm to hot SiC and cold amorphous carbon. The HCN abundance distribution seems to be anisotropic close to Y CVn and in the outer layers of its envelope. The ejected gas is accelerated up to the terminal velocity (≃8 km s−1) from the photosphere to ≃3R⋆, but there is evidence of higher velocities (≳9–10 km s−1) beyond this region. In the vicinity of the star, the line widths are as high as ≃10 km s−1, which implies a maximum turbulent velocity of 6 km s−1or the existence of other physical mechanisms probably related to matter ejection that involve higher gas expansion velocities than expected. HCN is rotationally and vibrationally out of local thermodynamic equilibrium throughout the whole envelope. It is surprising that a difference of about 1500 K in the rotational temperature at the photosphere is needed to explain the observations at 7.5 and 13–14 μm. Our analysis finds a total HCN column density that ranges from ≃2.1 × 1018to 3.5 × 1018cm−2, an abundance with respect to H2of 3.5 × 10−5to 1.3 × 10−4, and a12C/13C isotopic ratio of ≃2.5 throughout the whole envelope.