High Mass-loss Rate Research Articles

Effect of Combining Fungal and Flame-Retardant Coatings on the Thermal Degradation of Spruce and Beech Wood Under Flame Loading

Compliance with fire safety standards for wood is crucial for its application in the internal applications of buildings. This article focuses on monitoring the quality of protective coatings for wood under thermal loading conditions. The examined samples of spruce (Picea abies L. Karst.) and beech wood (Fagus sylvatica L.) were treated with selected fungicidal coatings based on dimethylbenzyl ammonium chloride. Following this, they were soaked in a ferric phosphate-based flame-retardant solution. Additionally, a portion of the samples was treated solely with the flame retardant. The effectiveness of the protective coatings was assessed through experimental thermal loading of the prepared samples. The testing method adhered to according to selected standards, which evaluate the ignitability of building materials when subjected to a small flame source. The experimental results, including the mass loss, mass loss rate, and time–temperature curves of the thermally loaded samples, demonstrated a significant influence of the selected coatings on thermal degradation. Notably, the fungicidal coating exhibited protective properties. Samples treated only with the flame retardant showed higher mass losses compared to those treated first with the fungicidal coating followed by the retardant. Additionally, differences were observed between the wood types, with beech samples exhibiting greater mass losses and higher mass loss rates than spruce.

Parametric investigation of acetone liquid pool fire experiments on fire characteristics

Acetone is best known as the primary ingredient in various industrial and domestic settings, the fire characteristics of acetone pool fire are relatively unknown, thus raising safety concerns about the thermal radiation emission to humans and surroundings. This research focuses on parametric investigations of acetone liquid pool fire in a square-shaped stainless-steel pan with diameters of 10, 20, and 30cm. A series of experimental works was employed to investigate the effect of different pan sizes of acetone pool fire on the structure of the flame, flame height, flame temperature, heat release rate, mass loss rate, and thermal radiation intensities with various combinations parameters. The outcome of the experimental work has proven that acetone pool fire exhibited luminous and yellow colour with turbulent flame structure. It was discovered that the combustion of larger acetone pool fire consistently resulted in higher flame height, higher temperature, higher mass loss rate, and higher heat release rate. The thermal radiation intensity of acetone liquid pool fire indicated an inversely proportional relation where the intensity reduced with increasing heat flux gauge distance and height from the flame base but increased with increasing pan size. Overall, the outcomes of this research hold potential significance in advancing the formulation of improved fire protection strategies and fostering safer practices in handling acetone.

Study on sewage erosion resistance of nano titanium modified coral concrete

Sewage environments can significantly erode and degrade coral concrete, impacting its structural longevity. Moreover, the curing water environment greatly influences coral concrete's resistance to sewage erosion. This study investigated the modification of coral concrete with nano TiO2 to enhance its sewage erosion resistance. Concrete specimens with four different mass fractions of nano TiO2 were prepared and cured in three environments. Tests for compressive strength, flexural strength, and mass loss were conducted before and after 180 days of sewage exposure, and a corrosion coefficient was defined to evaluate resistance to sewage corrosion. While nano TiO2 significantly improved the mechanical properties and sewage erosion resistance of coral concrete, oxalic acid and seawater environments had adverse effects. Furthermore, increasing the nano TiO2 mass fraction initially enhanced and then reduced strength and resistance, while mass loss rates first decreased and then increased. The optimal nano TiO2 dosage of 4% resulted in a maximum increase of 22.2% in compressive strength, 33.2% in flexural strength, a 0.06 increase in the compressive corrosion resistance coefficient, and a 0.1 increase in the flexural corrosion resistance coefficient. At this dosage, compressive strengths of coral concrete cured in oxalic acid and seawater were 97.8% and 93.9% of those in freshwater, while flexural strengths were 97.8% and 94.4%, respectively, with slight decreases in corrosion resistance coefficients, accompanied by higher mass loss rates. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that nano TiO2 promotes cement hydration, forming a dense structure by filling matrix pores. However, oxalic acid reacts with Ca(OH)2 to form calcium oxalate, slowing cement hydration, while MgCl2 in seawater reacts with Ca(OH)2, forming expansive Mg(OH)2, which increases internal concrete pores.

Effect of shrinkage-induced initial damage on the frost resistance of concrete in cold regions

The shrinkage-induced initial damage poses a threat to the frost resistance of concrete in cold regions with low relative humidity (RH). However, the progression of freeze–thaw damage in concrete affected by this initial damage, along with the quantitative relationships among RH, freeze–thaw damage, and the number of freeze–thaw cycles (FTCs), remains unexplored. This study employed combination of experimental and numerical simulation approaches to address these challenges. Experimentally, the freeze–thaw damage of concrete cured at low RH (40 ± 5 %) was compared with that cured at standard RH (95 ± 5 %) after varying FTCs. Results indicated that the former experienced more severe freeze–thaw damage, characterized by increased surface peeling, higher mass loss rate, and greater compressive strength attenuation. For the simulation aspect, a numerical model incorporating cohesive elements was firstly proposed to study the evolution of freeze–thaw damage in concrete cured at different RH under FTCs, of which the rationality was confirmed through experimental data. Additionally, the effect of FTCs and curing RH on freeze–thaw damage was investigated, revealing a negative correlation between freeze–thaw damage and curing RH, resulting in opposite evolution trend for residual mechanical properties of concrete. Finally, the freeze–thaw damage prediction model was proposed based on simulation results, and the error between the predicted and actual values was only 2.1 %, which confirmed that this model can be adopted to accurately assess the freeze–thaw damage degree of concrete cured by different RH after different FTCs. In conclusion, this study aims to better understand the freeze–thaw damage evolution of concrete cured under low RH, which provides a feasible scheme for the frost resistant design of concrete construction in cold regions.

Influence of Graphite and Zirconia Addition on the Tribological Properties of Plasma-Sprayed Alumina Coatings

Al2O3, Al2O3-graphite and Al2O3-ZrO2 coatings were formed on the C45 steel rolls using atmospheric plasma spraying. The influence of graphite and zirconia addition on the surface morphology, phase composition and tribological properties under dry sliding conditions using 30 N load were analyzed. It was found that the addition of graphite or ZrO2 slightly affected the fraction of the α-Al2O3 and γ-Al2O3 phases in the alumina coatings. The highest mass loss rate (~8.84 × 10−4 g/s) was obtained for the friction pair of C45 steel roll and steel plate. The friction coefficient of the Al2O3-graphite coating was slightly lower (up to 7%) compared to the coating of Al2O3-ZrO2. However, the friction pair of Al2O3-ZrO2 coating and steel plate demonstrated the highest wear resistance under dry sliding conditions. The increase in the wear resistance of the Al2O3-graphite and Al2O3-ZrO2 coatings is due to the formation of tribofilm in the sliding contact zone.

The maximum black hole mass at solar metallicity

We analyse the current knowledge and uncertainties in detailed stellar evolution and wind modelling to evaluate the mass of the most massive stellar black hole (BH) at solar metallicity. Contrary to common expectations that it is the most massive stars that produce the most massive BHs, we find that the maximum $M_ BH Max is found in the canonical intermediate range between ZAMS $ simeq 30 and 50 instead. The prime reason for this seemingly counter-intuitive finding is that very massive stars (VMS) have increasingly high mass-loss rates that lead to substantial mass evaporation before they expire as stars and end as lighter BHs than their canonical O-star counterparts.

Kaleidoscope of irradiated disks: MUSE observations of proplyds in the Orion Nebula Cluster

In the Orion Nebula Cluster (ONC), protoplanetary disks exhibit ionized gas clouds in the form of a striking teardrop shape as massive stars irradiate the disk material. We present the first spatially and spectrally resolved observations of 12 such objects, known as proplyds, using integral field spectroscopy observations performed with the Multi-Unit Spectroscopic Explorer (MUSE) instrument in Narrow Field Mode (NFM) on the Very Large Telescope (VLT). We present the morphology of the proplyds in seven emission lines and measure the radius of the ionization front (I-front) of the targets in four tracers, covering transitions of different ionization states for the same element. We also derive stellar masses for the targets. The measurements follow a consistent trend of increasing I-front radius for a decreasing strength of the far-UV radiation as expected from photoevaporation models. By analyzing the ratios of the I-front radii as measured in the emission lines of Hα, [O I] 6300 A, [O II] 7330 A, and [O III] 5007 A, we observe the ionization stratification, that is, the most ionized part of the flow being the furthest from the disk (and closest to the UV source). The ratios of ionization front radii scale in the same way for all proplyds in our sample regardless of the incident radiation. We show that the stratification can help constrain the densities near the I-front by using a 1D photoionization model. We derive the upper limits of photoevaporative mass-loss rates (Ṁloss) by assuming ionization equilibrium, and estimate values in the range 1.07–94.5 × 10−7 M⊙ yr−1, with Ṁloss values decreasing towards lower impinging radiation. We do not find a correlation between the mass-loss rate and stellar mass. The highest mass-loss rate is for the giant proplyd 244–440. These values of Ṁloss, combined with recent estimates of the disk mass with ALMA, confirm previous estimates of the short lifetime of these proplyds. This work demonstrates the potential of this MUSE dataset and offers a new set of observables to be used to test current and future models of external photoevaporation.

The dense and non-homogeneous circumstellar medium revealed in radio wavelengths around the Type Ib SN 2019oys

Context. Mass loss from massive stars, especially towards the end of their lives, plays a key role in their evolution. Radio emission from core-collapse supernovae (SNe) serves as a probe of the interaction of the SN ejecta with the circumstellar medium (CSM) and can reveal the mass-loss history of the progenitor. Aims. We aim to present broadband radio observations of the CSM-interacting SN 2019oys. SN 2019oys was first detected in the optical and was classified as a Type Ib SN. Then, ~100 days after discovery, it showed an optical rebrightening and a spectral transition to a spectrum dominated by strong narrow emission lines, which suggests strong interaction with a distant, dense, CSM shell. Methods. We modelled the broadband, multi-epoch radio spectra, covering 2.2 to 36 GHz and spanning from 22 to 1425 days after optical discovery, as a synchrotron emitting source. Using this modelling, we characterised the shockwave and the mass-loss rate of the progenitor. Results. Our broadband radio observations show strong synchrotron emission. This emission, as observed 201 and 221 days after optical discovery, exhibits signs of free–free absorption from the material in front of the shock travelling in the CSM. In addition, the steep power law of the optically thin regime points towards synchrotron cooling of the radiating electrons. Analysing these spectra in the context of the SN-CSM interaction model gives a shock velocity of 11 000 km s−1 (for a radius evolution of ~∆t0.8, where ∆t is the time since optical discovery) and an electron number density of 4.1 × 105 cm−3 at a distance of 2.6 × 1016 cm. This translates to a high mass-loss rate from the progenitor massive star of 10−3 M⊙ yr−1 for an assumed wind of 100 km s−1 (assuming a constant mass-loss rate in steady winds). The late-time radio spectra, 392 and 557 days after optical discovery, show broad spectral peaks. We show that this can be explained by introducing a non-homogeneous CSM structure.

Establishing a mass-loss rate relation for red supergiants in the Large Magellanic Cloud

Context.The high mass-loss rates of red supergiants (RSGs) drastically affect their evolution and final fate, but their mass-loss mechanism remains poorly understood. Various empirical prescriptions scaled with luminosity have been derived in the literature, yielding results with a dispersion of two to three orders of magnitude.Aims.We determine an accurate mass-loss rate relation with luminosity and other parameters using a large, clean sample of RSGs. In this way, we shed light into the underlying physical mechanism and explain the discrepancy between previous works.Methods.We assembled a sample of 2219 RSG candidates in the Large Magellanic Cloud, with ultraviolet to mid-infrared photometry in up to 49 filters. We determined the luminosity of each RSG by integrating the spectral energy distribution and the mass-loss rate using the radiative transfer codeDUSTY.Results.Our derived RSG mass-loss rates range from approximately 10−9 M⊙yr−1to 10−5 M⊙yr−1, mainly depending on the luminosity. The average mass-loss rate is 9.3 × 10−7 M⊙yr−1for log(L/L⊙) > 4, corresponding to a dust-production rate of ∼3.6 × 10−9 M⊙yr−1. We established a mass-loss rate relation as a function of luminosity and effective temperature. Furthermore, we found a turning point in the relation of mass-loss rate versus luminosity at approximately log(L/L⊙) = 4.4, indicating enhanced rates beyond this limit. We show that this enhancement correlates with photometric variability. We compared our results with prescriptions from the literature, finding an agreement with works assuming steady-state winds. Additionally, we examined the effect of different assumptions on our models and found that radiatively driven winds result in mass-loss rates higher by two to three orders of magnitude, which is unrealistically high for RSGs. For grain sizes < 0.1 μm, the predicted mass-loss rates are higher by a factor of 25−30 than larger grain sizes. Finally, we found that 21% of our sample constitute current binary candidates. This has a minor effect on our mass-loss relation.

The role of heating in the formation and the dynamics of YSO jets

Context. Theoretical arguments as well as observations of young stellar objects (YSOs) support the presence of a diversified circumstellar environment. A stellar jet is thought to account for most of the stellar spin down and disk wind outflow for the observed high mass-loss rate, thus playing a major role in the launching of powerful jets. RY Tau, for instance, is an extensively studied intermediate mass pre-main sequence star. Observational data reveal a small-scale jet called micro-jet. Nevertheless, it is not clear how the micro-jet shapes the jet observed at a large scale. Aims. The goal is to investigate the spatial stability and structure of the central jet at a large scale by mixing the stellar and disk components. Methods. Two existing analytical self-similar models for the disk and the stellar winds to build the initial setups. Instead of using a polytropic equation of state, we mapped the heating and cooling sources from the analytical solutions. The heating exchange rate was controlled by two parameters, its spatial extent and its intensity. Results. The central jet and the surrounding disk are strongly affected by these two parameters. We separate the results into three categories, which show different emissivity, temperature, and velocity maps. We reached this categorization by looking at the opening angle of the stellar solution. For cylindrically, well-collimated jets, we have opening angles as low as 10° between 8 − 10 au, and for the wider jets, we can reach 30° with a morphology closer to radial solar winds. Conclusions. Our parametric study shows that the less heated the outflow is, the more collimated it appears. We also show that recollimation shocks appear consistently with UV observations in terms of temperature but not density.

Failure Mechanism and Thermal Runaway in Batteries during Micro-Overcharge Aging at Different Temperatures.

This paper provides insights into the four key behaviors and mechanisms of the aging to failure of batteries in micro-overcharge cycles at different temperatures, as well as the changes in thermal stability. The test results from a scanning electron microscope (SEM) and an energy-dispersive spectrometer (EDS) indicate that battery failure is primarily associated with the rupture of cathode materials, the fracturing and pulverization of electrode materials on the anode current collector, and the formation of lithium dendrites. Additionally, battery safety is influenced by environmental temperatures and the battery's state of health (SOH), with failed batteries exhibiting the poorest stability and the highest mass loss rates. Under isothermal conditions, micro-overcharge leads to battery failure without thermal runaway. Thus, temperature stands out as the most influential factor in battery safety. These insights hold significant theoretical and practical value for the development of more precise and secure battery management systems.

SN 2015da: late-time observations of a persistent superluminous Type IIn supernova with post-shock dust formation

ABSTRACT We present photometry and spectroscopy of the slowly evolving superluminous Type IIn supernova (SN) 2015da. SN 2015da is extraordinary for its very high peak luminosity, and also for sustaining a high luminosity for several years. Even at 8 yr after explosion, SN 2015da remains as luminous as the peak of a normal SN II-P. The total radiated energy integrated over this time period (with no bolometric correction) is at least $1.6 \times 10^{51}$ erg (or 1.6 FOE). Including a mild bolometric correction, adding kinetic energy of the expanding cold dense shell of swept-up circumstellar material (CSM), and accounting for asymmetry, the total explosion kinetic energy was likely 5–10 FOE. Powering the light curve with CSM interaction requires an energetic explosion and 20 M$_{\odot }$ of H-rich CSM, which in turn implies a massive progenitor system $\gt $30 M$_{\odot }$. Narrow P Cyg features show steady CSM expansion at 90 km s$^{-1}$, requiring a high average mass-loss rate of $\sim$0.1 M$_{\odot }$ yr$^{-1}$ sustained for two centuries before explosion (although ramping up toward explosion time). No current theoretical model for single-star pre-SN mass-loss can account for this. The slow CSM, combined with broad wings of H $\alpha$ indicating H-rich material in the unshocked ejecta, disfavours a pulsational pair instability model for the pre-SN mass-loss. Instead, violent pre-SN binary interaction is a likely culprit. Finally, SN 2015da exhibits the characteristic asymmetric blueshift in its emission lines from shortly after peak until the present epoch, adding another well-studied superluminous SNe IIn with unambiguous evidence of post-shock dust formation.

On the Maximum Black Hole Mass at Solar Metallicity

In high-metallicity environments the mass that black holes (BHs) can reach just after core collapse widely depends on how much mass their progenitor stars lose via winds. On one hand, new theoretical and observational insights suggest that early-stage winds should be weaker than what many canonical models prescribe. On the other hand, the proximity to the Eddington limit should affect the formation of optically thick envelopes already during the earliest stages of stars with initial masses M ZAMS ≳ 100 M ⊙, hence resulting in higher mass-loss rates during the main sequence. We use the evolutionary codes MESA and Genec to calculate a suite of tracks for massive stars at solar metallicity Z ⊙ = 0.014, which incorporate these changes in our wind-mass-loss prescription. In our calculations we employ moderate rotation, high overshooting, and magnetic angular momentum transport. We find a maximum BH mass MBH,max=28.3 M ⊙ at Z ⊙. The most massive BHs are predicted to form from stars with M ZAMS ≳ 250 M ⊙, with the BH mass directly proportional to its progenitor’s M ZAMS. We also find in our models that at Z ⊙ almost any BH progenitor naturally evolves into a Wolf–Rayet star due to the combined effect of internal mixing and wind mass loss. These results are considerably different from most recent studies regarding the final mass of stars before their collapse into BHs. While we acknowledge the inherent uncertainties in stellar evolution modeling, our study underscores the importance of employing the most up-to-date physics in BH mass predictions.

The effect of winds on atmospheric layers of red supergiants II. Modelling VLTI/GRAVITY and MATISSE observations of AH Sco, KW Sgr, V602 Car, CK Car, and V460 Car

Context. Mass loss plays a crucial role in the lives of massive stars, especially as the star leaves the main sequence and evolves to the red supergiant (RSG) phase. Despite its importance, the physical processes that trigger mass-loss events in RSGs are still not well understood. Recently, we showed that adding a semi-empirical wind to atmosphere models can accurately reproduce observed extensions in the atmospheres of RSGs, where the mass-loss events are taking place, particularly in the CO and water lines. Aims. By adding a static wind to a MARCS atmospheric model, we computed synthetic observables that match new interferometric data of the RSGs AH Sco, KW Sgr, V602 Car, CK Car, and V460 Car obtained with the VLTI/MATISSE and VLTI/GRAVITY instruments between August 2022 and February 2023. We also used archival VLTI/AMBER data of KW Sgr and VLTI/GRAVITY data of AH Sco. The MATISSE wavelength range includes the SiO molecule at 4.0 μm with a spectral resolution of R ~ 500. Methods. The model intensities with respect to the line-of-sight angle (μ) as well as the spectra and visibilities were computed using the stellar radiative transfer code TURBOSPECTRUM. We found the best-fit model, mass-loss rate, and best-fit angular Rosseland diameter for the observations. We simultaneously matched our model to the data, covering a wavelength range of 1.8–5.0 μm, which corresponds to the K, L, and M bands. Results. Our models reproduce the spectro-interferometric data over this wide wavelength range, including extended atmospheric layers of CO, H2O, and SiO. We obtain a range of Rosseland angular diameters between 3.0 < θRoss < 5.5 mas and a range of mass-loss rates of −6.5 < log Ṁ/M⊙ yr−1 < −4 for our five targets. In our best-fit models, the partial pressure of SiO relative to the gas pressure, PSiO/Pg, and the SiO 4.0 μm line intensity increase between 2 and 3 stellar radii. The relative intensity depends on the luminosity used for our models, since the more luminous models have a higher mass-loss rate. Conclusions. This work further demonstrates that our MARCS+wind model can reproduce the observed physical extension of RSG atmospheres for several spectral diagnostics spanning a broad wavelength range. We reproduce both spectra and visibilities of newly obtained data as well as provide temperature and density stratifications that are consistent with the observations. With the MATISSE data, we newly include the extension of SiO layers as a precursor of silicate dust.

Characterization of elastomer degradation in O2/Ar plasma via mass and surface morphology changes

The degradation of fluoroelastomer, perfluoroelastomer (FFKM), and fluorosilicone materials were compared between three O2/Ar plasma conditions: full plasma (ions plus radicals), radical only, and ion only. These elastomer materials are used extensively in plasma processing equipment used to manufacture semiconductors, and understanding the plasma environments that enhance degradation will inform material choice and further material development. Langmuir probe measurements were made to quantify the electron temperature and plasma density; radical probe measurements were made to quantify the oxygen radical density. The results suggested that plasma radicals were required to drive significant mass loss rates, with ions speeding up the mass loss rate further in the full plasma case. Additionally, it was determined that plasma radicals were the main driver of surface changes of the elastomer, with similar surface roughening in plasma versus radical only conditions and less significant roughening in ion-only conditions. The O2/Ar plasma discharge had an electron temperature of 4.6 ± 0.1 eV and a plasma density of 2.9 ± 0.07 × 1016 m−3. It was observed that the fluorosilicone material had the lowest mass loss rate, the unfilled FFKM had the highest mass loss rate, and the silica-filled FFKM had the lowest mass loss rate among the FFKMs tested. The presence of oxygen radicals during exposure conditions significantly changed surface roughness.

Solving the Mystery of Extreme Light Variability in the Massive Eccentric System MACHO 80.7443.1718

The evolution of massive stars is heavily influenced by their binarity, and the massive eccentric binary system MACHO 80.7443.1718 (ExtEV) serves as a prime example. This study explores whether the light variability of ExtEV, observed near the periastron during its 32.8-day orbit, can be explained by a wind–wind collision (WWC) model and reviews other potential explanations. Using broadband photometry, TESS data, ground-based UBV time-series photometry, and high- resolution spectroscopy, we analysed the system’s parameters. We ruled out the presence of a Keplerian disk and periodic Roche-lobe overflow. Our analysis suggests the primary component has a radius of about 30 R⊙, luminosity of ∼6.6×105 L⊙, and mass between 25 and 45 M⊙, with a high wind mass-loss rate of 4.5×10−5 M⊙ yr−1, likely enhanced by tidal interactions, rotation, and tidally excited oscillations. We successfully modelled ExtEV’s light curve, identifying atmospheric eclipse and light scattering in the WWC cone as key contributors. The system’s mass-loss rate exceeds theoretical predictions, indicating that ExtEV is in a rare evolutionary phase, offering insights into enhanced mass loss in massive binary systems.

Effect of Spruce Wood Density on Selected Fire-Technical Parameters during Thermal Loading

The paper evaluates the effect of spruce wood density on the parameters of mass loss and mass loss rate during exposure to thermal load. The intention was to determine whether the effect of density is still evident after the application of flame retardants to the test samples. Groups of samples with different densities under the same retardant treatment were compared. The differences in densities of the compared groups of samples were different for each flame retardant. Water-soluble flame retardants based on inorganic salts were used. For testing, a simple test method was used in which the samples were exposed to direct flame from a Bunsen burner. The results of the study are the findings of how wood density affects the burning process of the samples treated with flame retardants. Statistical evaluation of the experimental results shows a significant effect of wood density on the monitored parameters even when flame retardants are used. For a difference in sample densities of 244 kg·m−3, there was a density dependence of the mass loss rate, with the lower density samples having a higher mass loss rate (0.158%·s−1) over the whole experimental period compared to the higher density samples (0.077%·s−1). The ANOVA test also demonstrated the influence of density on the mass loss of the samples at the above density difference. At lower density differences (51 kg·m−3 and below), the effect of sample density on the observed parameters was no longer evident. The fire spread rate parameter was also investigated. Here, a linear correlation between the difference in sample densities and the difference in the values of the above parameter at high and low densities is observed with a reliability coefficient R2 = 0.99.

Investigation on the physico-chemical properties of soil and mineralization of three selected tropical tree leaf litter

Plant leaf litter has a major role in the structure and function of soil ecosystems as it is associated with nutrient release and cycling. The present study is aimed to understand how well the decomposing leaf litter kept soil organic carbon and nitrogen levels stable during an incubation experiment that was carried out in a lab setting under controlled conditions and the results were compared to those from a natural plantation. In natural site soil samples, Anacardium. occidentale showed a higher value of organic carbon at surface (1.14%) and subsurface (0.93%) and Azadirachta. indica exhibited a higher value of total nitrogen at surface (0.28%) and subsurface sample (0.14%). In the incubation experiment, Acacia auriculiformis had the highest organic carbon content initially (5.26%), whereas A. occidentale had the highest nitrogen level on 30th day (0.67%). The overall carbon-nitrogen ratio showed a varied tendency, which may be due to dynamic changes in the complex decomposition cycle. The higher rate of mass loss and decay was observed in A. indica leaf litter, the range of the decay constant is 1.26–2.22. The morphological and chemical changes of soil sample and the vermicast were substantained using scanning electron microscopy (SEM) and Fourier transmission infrared spectroscopy (FT-IR).

Circumstellar material ejected violently by a massive star immediately before its death

Type II supernovae represent the most common stellar explosions in the Universe, for which the final stage evolution of their hydrogen-rich massive progenitors towards core-collapse explosion are elusive. The recent explosion of SN 2023ixf in a very nearby galaxy, Messier 101, provides a rare opportunity to explore this longstanding issue. With the timely high-cadence flash spectra taken within 1–5 days after the explosion, we can put stringent constraints on the properties of the surrounding circumstellar material around this supernova. Based on the rapid fading of the narrow emission lines and luminosity/profile of Hα emission at very early times, we estimate that the progenitor of SN 2023ixf lost material at a mass-loss rate Ṁ≈6×10-4M⊙a-1 over the last 2–3 years before explosion. This close-by material, moving at a velocity vw≈55kms-1, accumulates a compact CSM shell at the radius smaller than 7×1014 cm from the progenitor. Given the high mass-loss rate and relatively large wind velocity presented here, together with the pre-explosion observations made about two decades ago, the progenitor of SN 2023ixf could be a short-lived yellow hypergiant that evolved from a red supergiant shortly before the explosion.

Activity of the Young Solar Analog HD 109833 and Estimates of the Mass Loss Rate from the Atmospheres of Its Two Planets

We present the results of our analysis of the manifestations of activity in the young solar analog HD 109833 and estimate the mass loss rate from the atmospheres of its two planets. HD 109833 probably belongs to the Lower Centaurus Crux (LCC) association with an age of 27 ± 3 Myr, but it is not inconceivable that the star is only spatially associated with the association and may be older, although in any case its age does not exceed 100–200 Myr. Based on data from the TESS archive for HD 109833, we have determined the stellar rotation period P = 5.08 ± 0.30 days and the photometric variability amplitude (about 0.6% of the mean stellar brightness) and estimated the spot areas on its surface, which exceed the maximum sunspot area and are 15 200–17 700 m.s.h. Based on data from the All-Sky Automated Survey archive, we have revealed a stellar activity cycle with a duration 1950 days (5.3 years). Both planets in the HD 109833 system are characterized as sub-Neptunes with radii of 2.9 and 2.6 R⊕ and periods of 9.2 and 13.9 days. The mass loss rates by the planetary atmospheres have been found using an approximate formula corresponding to the energy-limited atmospheric escape model. To estimate the XUV flux, we have applied analytical dependences relating the flux and the parameter logR'HK and information about the distribution of these quantities for G-type stars, suggesting that there are two pronounced peaks with maxima for values -0,5 and -4,5 dex in low-activity and active stars, respectively. In addition, we have used the relation between the X-ray flux from the star and logFXUV . The value found is comparable to the estimate obtained by applying the parameter logR'HK for active stars and exceeds it by a factor of 4. Both exoplanets HD 109833 b and c being considered by us fall into the region on the (M-R) diagram in which the populations of rocky and volatile-rich exoplanets overlap and do not allow their masses to be estimated unambiguously. Our calculations were performed for two cases—rocky exoplanets and volatile-rich exoplanets. The masses of the exoplanets HD 109833 b and c are, respectively, 34.9 and 24 M⊕ for rocky exoplanets and 9.3 and 7.8 M⊕ for volatile-rich exoplanets. We present the results of our calculations of the atmospheric mass loss rates by the planets HD 109833 b and c while varying the parameters related to the estimates of the planetary masses and the UV flux incident on the planets. The parameter M for HD 109833 b and c varies in the ranges from 9.60 ×107 to 1.38 ×1010 g s-1 and from 4.56 ×107 to 5.28 ×109 g s-1, respectively. The high mass loss rates found can be a consequence of a fairly high XUV flux from the solar-type star (an analog of the young active Sun) and a fairly close location of the planets from the host star.