Iron-peak Research Articles

Abundance ties: Nephele and the globular cluster population accreted with ω Cen

Context. The peculiar Galactic globular cluster ω Centauri (NGC 5139) has drawn attention for its unique features, such as an unusually high stellar mass compared to other Galactic globular clusters and a broad distribution of chemical elements. These features have led to the hypothesis that ω Centauri might be the nuclear remnant of an ancient dwarf galaxy accreted by the Milky Way, potentially bringing along its own globular cluster system. Aims. In this work, we adopt an innovative approach by examining the individual chemical abundances of Galactic globular clusters to identify shared patterns with ω Centauri. Methods. Applying Gaussian mixture models to globular cluster stars, whose membership is based on the analysis of the Gaia EDR3 release, and whose chemical abundances have been obtained from APOGEE DR17, we depart from traditional kinematic-based procedures and search for globular clusters that are chemically compatible with ω Centauri in an eight-dimensional space defined by [Fe/H], α-elements such as [Mg/Fe], [Si/Fe], and [Ca/Fe], light+odd-Z elements such as [C/Fe], [Al/Fe], and [K/Fe], and an iron-peak element as [Mn/Fe]. With this approach, clusters that are chemically compatible with ω Centauri are clusters whose chemical patterns are contained in the abundance domain defined by ω Centauri stars. Results. Our analysis leads to the identification of six globular clusters – NGC 6752, NGC 6656, NGC 6809, NGC 6273, NGC 6205, and NGC 6254 – that exhibit strong chemical similarities with ω Centauri, and that have metallicities that coincide with those of the two known peaks (primary and secondary) of ω Centauri’s metallicity distribution. They all exhibit non-null intrinsic [Fe/H] dispersions, ranging between 0.07 and 0.12 dex, unless the ASPCAP uncertainties had been severely underestimated, and three of them have statistically significant skewed [Fe/H] distributions. Furthermore, the chemical patterns of these clusters lead to the exclusion that they were formed in progenitor galaxies with chemical enrichment histories similar to those of the Large and Small Magellanic Clouds, Sagittarius, and Fornax. Once placed in kinematic spaces such as the energy – angular momentum plane, these clusters result scatter across an extended region, which is predicted by N-body simulations if their common progenitor was sufficiently massive compared to the Milky Way. Conclusions. Our novel approach suggests a common origin for NGC 6752, NGC 6656, NGC 6809, NGC 6273, NGC 6205, NGC 6254, and ω Centauri, indicating that Nephele, as we propose to call the progenitor in which all these clusters formed, played a substantial role in the Galaxy’s history. The finding that a set of globular clusters can be associated with ω Centauri reinforces the hypothesis that this system is the remnant of a galaxy, and not simply an unusual globular cluster. This study also shows that the spectroscopic data at our disposal have reached the quality needed to compare chemical patterns of stellar systems, to reveal their common origins or exclude their association with specific progenitor galaxies.

Application of low-temperature reduction by hydrogen for enhancing the magnetic characteristics of several iron ores

The conversion of non-magnetic or weakly magnetic constituents of iron ores into the magnetic ‘magnetite’ phase was investigated using partial reduction by hydrogen at temperatures below 400 °C. The examined four commercial iron ores from Russian and Chinese deposits have significant differences in their compositions and morphologies. All ore samples were crushed using mechanical abrasion in a stamp and sieved with a mesh size of 1.5 mm. Reduction was carried out in a tube furnace under isothermal conditions at 375 and 400 °C for one hour. To study the kinetics of the reduction process, non-isothermal studies of selected ores were сonducted using a thermogravimetric analyzer with heating to 800 °C at a heating rate of 10 °C/min in hydrogen flow. The authors made a detailed characterization of the annealed products using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy to determine the magnetic characteristics of initial and partially reduced ores. X-ray diffraction patterns showed hematite peaks in the initial samples; both magnetite and metallic iron peaks were detected in the samples reduced at 375 and 400 °C. Such behavior was observed for all four samples under investigation. The most important result of the study is the confirmation of an order of magnitude increase in saturation magnetization for hematite ores, in addition the reduced ore samples show soft magnetic properties with average coercive force values ​​of approximately 20 kA/m. Application of the low-temperature reduction by hydrogen to iron-containing ores is very promising for production of the materials that could later be subjected to enrichment using magnetic separation methods.

X-Ray Photoelectron Spectroscopy of Compounds Simultaneously Containing Zinc and Iron: Alert on Fe 2p Region

Many interesting materials in a broad range of applications have in their composition the coexistence of zinc and iron. Their characterization by XPS should identify and quantify both elements. The most intense regions for these elements Zn 2p and Fe 2p are, therefore, used to accomplish that purpose. By using sphalerite as an example of a material where Zn and Fe may coexist and using XPS with two different X radiation sources to study them, it is demonstrated that the Fe 2p region, when the iron is the minor component, may be seriously affected by the Auger Zn L3M1M23 structure. The sphalerite (Zn1−xFexS) here studied has x ≈ 0 and is a good example to show how an XPS spectrum obtained with the X-ray Al Kα, the most used radiation in monochromatic equipment, leads to a wrong assignment of the structures existing in the binding energy region of Fe 2p. The simultaneous use of Mg Kα radiation showed that the Fe 2p is below the XPS detection in this specific sample of sphalerite. Its attested absence reveals that the structure detected, when using Al Kα in the “Fe 2p” region, is assigned to a zinc Auger multiple peak and not to the expected 2p photoelectron doublet peak of iron.

Synchrotron Radiation Study of Fe-N-C Catalysts for Dissemination of Fuel Cells

Fuel cells are attracting worldwide attention as a technology for achieving carbon neutrality. However, existing fuel cells use large amounts of precious metals, which limits their widespread use. In our laboratory, we are studying fuel cells that do not use precious metals. We have synthesized iron-based complex catalysts using the method reported by Plamen Atanassov1 et al. Iron nitrate nonahydrate is mixed in aqueous solution with glucose, 2-methylimidazole, and zinc nitrate hexahydrate, followed by hydrothermal synthesis at 200°C for 24 hours. Hydrogen heat treatment is performed at 950 °C, followed by acid treatment with nitric acid to dissolve excess metallic iron. Then, ammonia heat treatment is performed at 950 °C to complete the Fe-N-C catalyst. In our laboratory, we have been working on various process improvements to reduce the amount of metallic iron to make the four-electron oxygen reduction reaction proceed more seamlessly. What is particularly noteworthy is that we have dramatically reduced the amount of iron nitrate dihydrate, a catalyst raw material, by 1/40.The results of the XAFS measurement of the reduced catalyst at SPring-8 BL14B1 showed that the prepared Fe-N-C catalyst formed a good complex, since the peak was like that of iron phthalocyanine (II), an iron complex, which was very different from the peak of metallic iron (Fe foil) (Figure 1). Through these process improvements, we succeeded in creating a catalyst that exceeds the performance of current platinum catalysts. The structure of the catalyst changes the ease of oxygen adsorption. The prepared catalysts were used to determine the catalyst fine structure by High-Energy-Resolution-Fluorescence-Detected (HERFD-XAFS)2 and Kβ X-ray emission spectroscopy (XES) measurements using synchrotron radiation at BL-11XU in SPring-8, where the spectral broadening due to the inner-shell lifetime width is suppressed.Using a half-cell with only a cathode, the prepared Fe-N-C catalyst was sprayed onto carbon paper, and a potentiostat was manipulated to measure the adsorbed species on the Fe surface at a specific potential.We used N2 and O2 gases and discussed the structure and valence of the catalyst by the peak transitions, focusing on Fe in the Fe-N-C catalyst, The structure of Fe was discussed based on the energy position transition for each potential.The structure of Fe-N-C oxide was discussed based on the energy of the Fe K-edge (7115eV) in high-resolution XAFS (Fig. 2).The catalysts were measured on Fe-N-C catalysts prepared in the laboratory and were a mixture of planar 4- and 6-coordinated catalysts. From these results, it was considered that the highly active iron complex catalyst we prepared was a hybrid of multiple complex structures. The structure and activity will be discussed in an oral presentation.References 1 R. Gokhale, L-K. Tsui, K. Roach, Y. Chen, M. M. Hossen, K. Artyushkova, F. Garzon, P. Atanassov, “Hydrothermal synthesis of platinum-Group-Metal-Free Catalysts: Structural Elucidation and Oxygen Reduction Catalysis”, ChemElectroChem, 5, 14, (2017), 1848-1853 2N. Yamamoto, D.Matsumura, Y. Hagihara, K.Tanaka, Y. Hasegawa, K. Ishii, H. Tanaka, “Investigation of hydrogen superoxide adsorption during ORR on Pt/C catalyst in acidic solution for PEFC by in-situ high energy resolution XAFS”, Jounal of Power Sources, 557, 15, (2023), 232508AcknowledgmentsThe authors would like to express their sincere appreciation and celebration to Professor Dr. P. Atanassov of University of California, Irvine for his contribution to the fuel cell research. The authors would like to acknowledge Dr. S. Kusano and Emeritus Professor Dr. J. Mizuki of Kwansei Gakuin University for their cooperation in establishing the in-situ XAFS measurement method. And they also thank Dr. H. Kishi, Dr. T. Sakamoto and Dr. K. Asazawa of Daihatsu Motor Co., Ltd. for development of electrochemical cells.The synchrotron radiation experiments were performed at the BL11XU in the SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal Numbers of 2022B-H08,2023A-H06,2023B-H08,2024A-H10)The SPring-8 experiment was also supported by the Advanced Research Infrastructure for Materials and Nanotechnology in Japan (ARIM Japan) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan (Grant No. JPMXP1222QSO108, JPMXP1223QS0006, JPMXP1223QS0108, JPMXP1224QS0010)This work was supported by JSPS KAKENHI Grant Number JP22H02188) Figure 1

Contribution of astrophysical events to the chemical evolution of a dwarf irregular galaxy

ABSTRACT We study the contribution of various astrophysical events asymptotic giant branch (AGB stars, core collapse and thermonuclear supernovae, neutron star mergers, and collapsars) to the abundances of elements both up to and heavier than the iron peak in a Local Group dwarf irregular galaxy, Wolf–Lundmark–Melotte (WLM). Its star formation history has been recently determined by observations with the JWST, and we use it to estimate the occurrence of the astrophysical sources. The rates of the gas accretion and the outflow are roughly determined based on the stellar metallicity distribution, the oxygen abundance of H ii regions, and the gas fraction. As discussed in the literature, the difference in time-scales on which the astrophysical events release the nucleosynthesis products is seen in the occurrence of the events and the evolution of abundance ratios. WLM has an extended star formation history and massive stars are recently and currently formed. Thus, the contribution of rotating massive stars through the weak s-process appears in the abundance ratios of light trans-iron elements to iron at later time of the evolution.

Morphological and Structural Characterization of Algae-Based Nanoformulation

In the present study, confirmation of Spirulina platensis-mediated TiO2NPs formation was indicated by a noticeable shift in hue from white to light yellow. TEM analysis revealed the presence of irregularly distributed nanoparticles with sizes between 50 and 60 nm, while TEM analysis further disclosed a hexagonal structure. EDAX analysis identified elemental composition, with titanium peaks appearing at 4.5 to 5 keV, carbon peaks at 0.5 keV, oxygen peaks at 0.4 to 1.0 keV, silica peaks at 1.7 to 2.0 keV, zinc peaks at 8.0 keV, copper peaks at 7 keV, potassium peaks at 4 keV, phosphorus peaks at 3 keV, and iron peaks at 6 keV. These comprehensive findings confirm the successful synthesis of well-defined Spirulina platensis-mediated TiO2 nanoparticles and provide valuable insights into their structural and elemental characteristics.

Cosmic Type Ia supernova rate and constraints on supernova Ia progenitors

Type Ia supernovae play a key role in the evolution of galaxies by polluting the interstellar medium with a fraction of iron peak elements larger than that released in the core-collapse supernova events. Their light curve, moreover, is widely used in cosmological studies as it constitutes a reliable distance indicator on extragalactic scales. Among the mechanisms proposed to explain the Type Ia supernovae (SNe), the single- and double-degenerate channels are thought to be the dominant ones, which implies a different distribution of time delays between the progenitor formation and the explosion. In this paper, we aim to determine the dominant mechanism by comparing a compilation of Type Ia SN rates with those computed from various cosmic star-formation histories coupled with different delay-time distribution functions. We also evaluate the relative contributions of both channels. By using a least-squares fitting procedure, we modeled the observations of Type Ia SN rates assuming different combinations of three recent cosmic star-formation rates and seven delay-time distributions. The goodness of these fits are statistically quantified by the $ test. For two of the three cosmic star-formation rates, the single degenerate scenario provides the most accurate explanation for the observations, while a combination of 34<!PCT!> single-degenerate- and 66<!PCT!> double-degenerate delay-time distributions is more plausible for the remaining tested cosmic star-formation rates. Though dependent on the assumed cosmic star-formation rate, we find arguments in favor of the single-degenerate model. From the theoretic point of view, at least sim 34<!PCT!> of the Type Ia SN must have been produced through the single-degenerate channel to account for the observations. The wide, double-degenerate mechanism slightly under-predicts the observations at redshift $z 1$, unless the cosmic SFR flattens in that regime. On the contrary, although the purely close double-degenerate scenario can be ruled out, we cannot rule out a mixed scenario with single- and double-degenerate progenitors.

One-Pot Phyto-Mediated Synthesis of Fe2O3/Fe3O4 Binary Mixed Nanocomposite Efficiently Applied in Wastewater Remediation by Photo-Fenton Reaction

A binary Fe2O3/Fe3O4 mixed nanocomposite was prepared by phyto-mediated avenue to be suited in the photo-Fenton photodegradation of methylene blue (MB) in the presence of H2O2. XRD and SEM analyses illustrated that Fe2O3 nanoparticles of average crystallite size 8.43 nm were successfully mixed with plate-like aggregates of Fe3O4 with a 15.1 nm average crystallite size. Moreover, SEM images showed a porous morphology for the binary Fe2O3/Fe3O4 mixed nanocomposite that is favorable for a photocatalyst. EDX and elemental mapping showed intense iron and oxygen peaks, confirming composite purity and symmetrical distribution. FTIR analysis displayed the distinct Fe-O assignments. Moreover, the isotherm of the developed nanocomposite showed slit-shaped pores in loose particulates within plate-like aggregates and a mesoporous pore-size distribution. Thermal gravimetric analysis (TGA) indicated the high thermal stability of the prepared Fe2O3/Fe3O4 binary nanocomposite. The optical properties illustrated a narrowing in the band gab (Eg = 2.92 eV) that enabled considerable absorption in the visible region of solar light. Suiting the developed binary Fe2O3/Fe3O4 nanocomposite in the photo-Fenton reaction along with H2O2 supplied higher productivity of active oxidizing species and accordingly a higher degradation efficacy of MB. The solar-driven photodegradation reactions were conducted and the estimated rate constants were 0.002, 0.0047, and 0.0143 min−1 when using the Fe2O3/Fe3O4 nanocomposite, pure H2O2, and the Fe2O3/Fe3O4/H2O2 hybrid catalyst, respectively. Therefore, suiting the developed binary Fe2O3/Fe3O4 nanocomposite and H2O2 in photo-Fenton reaction supplied higher productivity of active oxidizing species and accordingly a higher degradation efficacy of MB. After being subjected to four photo-Fenton degradation cycles, the Fe2O3/Fe3O4 nanocomposite catalyst still functioned admirably. Further evaluation of Fe2O3/Fe3O4 nanocomposite in photocatalytic remediation of contaminated water using a mixture of MB and pyronine Y (PY) dyestuffs revealed substantial dye photodegradation efficiencies.

PROJECT OLVE (OBSERVATORY OF HIGH-ENERGY COSMICRAYS): OBJECTIVES AND DESIGN FORM

The High Energy Cosmic Ray Observatory (HERO) is an experimental design for the direct study of cosmicrays based on the use of an ultra-heavy ionization calorimeter. The effective geometric factor of the facilitywill be at least 12 2sr for cosmic-ray protons and at least 16–20 2sr for nuclei and electrons. During 5–7 years of exposure, this mission will make it possible to measure the energy spectra of all common andrare cosmic-ray nuclei in the energy region 1012–1016 eV/particle with element-by-element resolution ofthe charge of nuclei and with sufficiently high energy resolution. It is planned to study not only the chargerange of cosmic-ray nuclei Z=1−26, but also the detection of super-heavy nuclei beyond the iron peak,as well as high-energy electrons, positrons and gamma rays. The main objectives, design appearance andcharacteristics of the space mission are discussed.

Extremely metal-poor stars in the Fornax and Carina dwarf spheroidal galaxies

We present our analysis of VLT/UVES and X-shooter observations of six very metal-poor stars, including four stars at [Fe/H] ≈ −3 in the Fornax and Carina dwarf spheroidal (dSph) galaxies. To date, this metallicity range in these two galaxies has not yet been investigated fully, or at all in some cases. The chemical abundances of 25 elements are presented, based on 1D and local thermodynamic equilibrium (LTE) model atmospheres. We discuss the different elemental groups, and find thatα- and iron-peak elements in these two systems are generally in good agreement with the Milky Way halo at the same metallicity. Our analysis reveals that none of the six stars we studied exhibits carbon enhancement, which is noteworthy given the prevalence of carbon-enhanced metal-poor stars withouts-process enhancement (CEMP-no) in the Galaxy at similarly low metallicities. Our compilation of literature data shows that the fraction of CEMP-no stars in dSph galaxies is significantly lower than in the Milky Way, and than in ultra-faint dwarf galaxies. Furthermore, we report the discovery of the lowest metallicity, [Fe/H] = −2.92,r-process rich (r-I) star in a dSph galaxy. This star, fnx_06_019, has [Eu/Fe] = +0.8, and also shows enhancement of La, Nd, and Dy, [X/Fe] > +0.5. Our new data in Carina and Fornax help populate the extremely low metallicity range in dSph galaxies, and add to the evidence of a low fraction of CEMP-no stars in these systems.

Age Analysis of Extrasolar Planets: Insight from Stellar Isochrone Models

There is growing evidence from stellar kinematics and galactic chemical evolution suggesting that giant planets (M P ≥ 0.3M J ) are relatively young compared to the most commonly occurring population of small planets (M P < 0.3M J ). To further test the validity of these results, we analyzed the ages for a large number of 2336 exoplanet hosting stars determined using three different but well-established isochrone fitting models, namely, PARSEC, MIST, and Yonsei Yale. As input parameters, we used Gaia DR3 parallaxes, magnitudes, and photometric temperature, as well as spectroscopically determined more accurate temperatures and metallicities from the Sweet Catalog. Our analysis suggests that ∼50%–70% of stars with planets are younger than the Sun. We also find that, among the confirmed exoplanetary systems, stars hosting giant planets are even younger compared to small planet hosts. The median age of ∼2.61–3.48 Gyr estimated for the giant planet-hosting stars (depending on the model input parameters) suggests that the later chemical enrichment of the galaxy by the iron-peak elements, largely produced from Type Ia supernovae, may have paved the way for the formation of gas giants. Furthermore, within the giant planet population itself, stars hosting hot Jupiters (orbital period ≤10 days) are found to be younger compared to the stellar hosts of cool and warm Jupiters (orbital period >10 days), implying that hot Jupiters could be the youngest systems to emerge in the progression of planet formation.

The GALAH survey: tracing the Milky Way’s formation and evolution through RR Lyrae stars

ABSTRACT Stellar mergers and accretion events have been crucial in shaping the evolution of the Milky Way (MW). These events have been dynamically identified and chemically characterized using red giants and main-sequence stars. RR Lyrae (RRL) variables can play a crucial role in tracing the early formation of the MW since they are ubiquitous, old (t ≥ 10 Gyr) low-mass stars and accurate distance indicators. We exploited Data Release 3 of the GALAH survey to identify 78 field RRLs suitable for chemical analysis. Using synthetic spectra calculations, we determined atmospheric parameters and abundances of Fe, Mg, Ca, Y, and Ba. Most of our stars exhibit halo-like chemical compositions, with an iron peak around [Fe/H] ≈ −1.40, and enhanced Ca and Mg content. Notably, we discovered a metal-rich tail, with [Fe/H] values ranging from −1 to approximately solar metallicity. This sub-group includes almost 1/4 of the sample, it is characterized by thin disc kinematics and displays sub-solar α-element abundances, marginally consistent with the majority of the MW stars. Surprisingly, they differ distinctly from typical MW disc stars in terms of the s-process elements Y and Ba. We took advantage of similar data available in the literature and built a total sample of 535 field RRLs for which we estimated kinematical and dynamical properties. We found that metal-rich RRLs (1/3 of the sample) likely represent an old component of the MW thin disc. We also detected RRLs with retrograde orbits and provided preliminary associations with the Gaia–Sausage–Enceladus, Helmi, Sequoia, Sagittarius, and Thamnos stellar streams.

SN 2022joj: A Potential Double Detonation with a Thin Helium Shell

We present photometric and spectroscopic data for SN 2022joj, a nearby peculiar Type Ia supernova (SN Ia) with a fast decline rate (Δm 15,B = 1.4 mag). SN 2022joj shows exceedingly red colors, with a value of approximately B − V ≈ 1.1 mag during its initial stages, beginning from 11 days before maximum brightness. As it evolves, the flux shifts toward the blue end of the spectrum, approaching B − V ≈ 0 mag around maximum light. Furthermore, at maximum light and beyond, the photometry is consistent with that of typical SNe Ia. This unusual behavior extends to its spectral characteristics, which initially displayed a red spectrum and later evolved to exhibit greater consistency with typical SNe Ia. Spectroscopically, we find strong agreement between SN 2022joj and double detonation models with white dwarf masses of around 1 M ⊙ and a thin He shell between 0.01 and 0.05 M ⊙. Moreover, the early red colors are explained by line-blanketing absorption from iron peak elements created by the double detonation scenario in similar mass ranges. The nebular spectra in SN 2022joj deviate from expectations for double detonation, as we observe strong [Fe iii] emission instead of [Ca ii] lines as anticipated, though this is not as robust a prediction as early red colors and spectra. The fact that as He shells get thinner these SNe start to look more like normal SNe Ia raises the possibility that this is the triggering mechanism for the majority of SNe Ia, though evidence would be missed if the SNe are not observed early enough.

A Facile Method for Synthesis of α-Fe2O3 Nanoparticles and Assessment of Their Characterization

Recently, magnetic nanomaterials have gained much attention from researchers because of their various unique physical and chemical properties and usage in a wide range of technological aspects. In this study, the synthesis of α-Fe2O3 nanoparticles was performed by a simple co-precipitation method. The synthesis of α-Fe2O3 nanoparticles was carried out by mixing ferric nitrate and oxalic acid in an aqueous solution followed by evaporation, resulting in the solution’s dried form. The synthesized nanoparticles were analyzed by XRD, FTIR, Raman spectra, SEM-EDX, DSC, BET, and Zeta potential for detailed examination of the morphology, structure, and other physicochemical characteristics. The XRD results confirmed that the nanoparticles formed were Hematite (α-Fe2O3) after the evaluation of obtained spectra compared to the Joint Committee on Powder Diffraction Standards Database (JCPDS). The FTIR spectra showed various bonds among functional groups, O-H bending, Fe-O group, and within-vibration bonds. The phase study of the α-Fe2O3 nanoparticles was performed by using Raman spectroscopy. SEM depicted a sphere-like or rhombohedral (hexagonal) structure, and the EDX spectrum confirmed the peaks of iron and oxygen.

Type Ia supernovae from chemically segregated white dwarfs

Type Ia supernovae are the outcome of the explosion of a carbon–oxygen white dwarf in a close binary system. They are thought to be the main contributors to the galactic nucleosynthesis of iron-peak elements, with important contributions to the yields of intermediate-mass elements. Recent analyses of the phase diagram of carbon and oxygen containing impurities such as 22Ne and 56Fe in conditions relevant to white dwarf interiors suggest that both isotopes can partially separate when the temperature of the star is low enough to start solidifying. The purpose of the present paper is to examine the impact of this separation on the yields of the different chemical species synthesized during explosions. We used a one-dimensional supernova code to evaluate the impact of the sedimentation assuming different degrees of chemical separation. We find that the main properties of the ejecta, the kinetic energy, and the ejected mass of 56Ni only vary slightly when the separation is taken into account. However, the yields of important isotopes that are used as diagnostic tools, such as manganese, can be strongly modified. Furthermore, the chemical separation studied here is able to change several indicators related to the metallicity of the progenitor (such as the mass ratio of calcium to sulphur in the ejecta or the UV flux of the supernova) and to its mass, whether it is a Chandrasekhar-mass white dwarf or a substantially lighter one (such as the imprint of stable nickel on late-time infrared spectra or that related to the presence of radioactive nickel at the center of the ejecta).

Abundances of iron-peak elements in accreted and in situ born Galactic halo stars

Context. Studies of the element abundances and kinematics of stars belonging to the Galactic halo have revealed the existence of two distinct populations: accreted stars with a low [α/Fe] ratio and in situ born stars with a higher ratio. Aims. Previous work on the abundances of C, O, Na, Mg, Si, Ca, Ti, Cr, Mn, Fe, Ni, Cu, and Zn in high-α and low-α halo stars is extended to include the abundances of Sc, V, and Co, enabling us to study the nucleosynthesis of all iron-peak elements along with the lighter elements. Methods. The Sc, V, and Co abundances were determined from a 1D MARCS model-atmosphere analysis of equivalent widths of atomic lines in high signal-to-noise, high resolution spectra assuming local thermodynamic equilibrium (LTE). In addition, new 3D and/or non-LTE calculations were used to correct the 1D LTE abundances for several elements including consistent 3D non-LTE calculations for Mg. Results. The two populations of accreted and in situ born stars are well separated in diagrams showing [Sc/Fe], [V/Fe], and [Co/Fe] as a function of [Fe/H]. The [X/Mg] versus [Mg/H] trends for high-α and low-α stars were used to determine the yields of core-collapse and Type Ia supernovae. The largest Type Ia contribution occurs for Cr, Mn, and Fe, whereas Cu is a pure core-collapse element. Sc, Ti, V, Co, Ni, and Zn represent intermediate cases. A comparison with yields calculated for supernova models shows poor agreement for the core-collapse yields. The Ia yields suggest that sub-Chandrasekhar-mass Type Ia supernovae provide a dominant contribution to the chemical evolution of the host galaxies of the low-α stars. A substructure in the abundances and kinematics of the low-α stars suggests that they arise from at least two different satellite accretion events, Gaia-Sausage-Enceladus and Thamnos.

Mechano-thermic reduction of low-grade titanium ore for high-grade TiO2 synthesis

A systematic study on the mechano-thermic reduction of low-grade ilmenite concentrate for the production of high-grade TiO2 powder used in the production of non-oxide ceramics for cutting tool applications has been successfully carried out. Samples were prepared via planetary ball milling and carbothermic reduction processes, and the as-reduced product was subsequently leached in order to improve the synthesized TiO2 by removing the metallic iron in it and other minor soluble impurities dissolved in the iron. The mechano-thermic reduction was achieved by milling a representative mixture of ilmenite and carbon in a molar ratio of 1:1, followed by carbothermic reduction at 1000 °C in a laboratory high-temperature furnace for 60 min. The as-reduced product was subsequently leached at 80 °C for 6 h in a hydrochloric acid solution. It was found that there was a complete reduction of ilmenite to metallic iron and TiO2 at 1000 °C. The results of the FESEM showed there were only two distinct regions of metallic iron (bright region) and titanium dioxide (grey region) with minor traces of unreacted carbon (dark spots), although there was clear regional demarcation between these regions. However, the iron dissolution during the acid treatment was almost 100% as there were no peaks of iron in the as-leached powder. The results of these analyses confirmed the synthesis of high-grade TiO2, which finds application in cutting tool applications and other areas such as in reflective pigment production.

Stationary neutron star envelopes at high accretion rates

ABSTRACT In this work we model stationary neutron star envelopes accreting under various conditions and describe our new code for such studies, which we plan to couple to a full thermal evolution code. We put special emphasis on the rp-process, resulting in the synthesis of heavy elements, and study its dependence on the mass accretion rate and the chemical composition of the accreted matter. We show that at $\dot{M} \sim 0.01 \dot{M}_{\text{Edd}}$, mostly low mass ($A\le$ 24) elements are synthesized with a few heavier ones below the $^{40}$Ca bottleneck. Once $\dot{M}$ is above ${\buildrel\sim \over \gt } 0.1 \dot{M}_{\text{Edd}}$ this bottleneck is surpassed and nuclei in the iron peak region ($A\sim$ 56) are abundantly produced. This synthesis of heavy elements reaches $A \sim 70$ at $\dot{M}_{\text{Edd}}$ and $A \sim 90$ at $5 \dot{M}_{\text{Edd}}$. Their density profiles of the energy generation rate are discussed, particularly at high density beyond the hydrogen exhaustion point. We explored the efficiency of the rp-process under variations of the relative abundances of H and He. We find that when the rp-process is efficient, the nucleosynthesis it generates is independent of the accreted abundance of CNO elements as these are directly and copiously generated once the $3\alpha$-reaction is operating. Our results are of importance for the study of neutron stars mostly in systems in which X-ray bursts are absent, but they are also relevant for describing the low density region of other systems, mostly below $10^6$ g cm$^{-3}$, in-between bursts.

Green Synthesis of Iron Nanozymes Using Eucalyptus grandis Extract and Their Application as Peroxidase-Like Catalysts for H2O2 Quantification

In this work, iron nanoparticles were synthesized by a green and bio-inspired process, using Eucalyptus grandis extract as a reducing and stabilizing agent. The functional groups from the extract were incorporated into the structure of the nanoparticles, as confirmed by infrared spectroscopy. Characteristic peaks of zero-valence iron were observed by X-ray diffraction analysis, besides hematite and goethite. The nanoparticles showed spherical morphology and an average size of 96.4 nm. The zeta potential (|35| mV) indicated good stability. The nanoparticles were used as catalysts for o-phenylenediamine oxidation by H2O2, exhibiting optimal catalytic activity. The kinetic assays were performed, and the Michaelis-Menten model was adjusted to the data (maximum rate reached (Vmax) = 2.0 µmol L-1 s-1 and Michaelis-Menten constant (Km) = 307 µmol L-1). A spectrophotometric method was developed for H2O2 quantification. The analytical curve (18.3-112.6 µmol L-1) showed a good linear fit and limits of detection and quantification of 5.48 and 18.3 µmol L-1, respectively. Thus, the method is very promising, adhering to the principles of green chemistry.

Tracing Population III supernovae with extreme energies through the Sculptor dwarf spheroidal galaxy

The Sculptor dwarf spheroidal galaxy is old and metal-poor, making it ideal to study the earliest chemical enrichment in the Local Group. We followed up on the most metal-poor star known in this (or any external) galaxy, AS0039, with high-resolution ESO VLT/UVES spectra. Our new analysis confirmed its low metallicity, [Fe/H]LTE = −3.90 ± 0.15, and that it is extremely C-poor, with A(C) = + 3.60, which corresponds to [C/Fe]LTE = −0.33 ± 0.17 (accounting for internal mixing). This adds to the evidence of Sculptor being intrinsically C-poor at low [Fe/H] ≲ −3. However, here we also report a new discovery of a carbon-enhanced metal-poor (CEMP-no) star in Sculptor, DR20080, with no enhancement of Ba, indicative of enrichment by zero-metallicity low-energy supernovae, ESN &lt; 1 × 1051. This is the first piece of evidence of a dual population of CEMP-no and C-normal stars in Sculptor at [Fe/H] ≤ −3. The fraction of CEMP-no stars is still low, fCEMPScl = 9−8+11% at −4 ≤ [Fe/H] ≤ −3, compared to the significantly higher fraction in the Milky Way halo, fCEMPMW ≈ 40%. To further investigate the early chemical enrichment of Sculptor, we re-derived chemical abundances of light, α, iron-peak, and neutron-capture elements in all Sculptor stars at [Fe/H] ≤ −2.8, with available high-resolution spectra. Our results show that at these low [Fe/H], Sculptor is deficient in light elements (e.g. C, Na, Al, Mg) relative to both the Milky Way halo, and ultra-faint dwarf galaxies, pointing towards a significant contribution from high-energy supernovae. Furthermore, the abundance pattern of the star AS0039 is best fitted with a zero-metallicity hypernova progenitor, ESN = 10 × 1051, with a mass of M = 20 M⊙. Our results in Sculptor, at [Fe/H] ≤ −3, therefore suggest significant enrichment by both very low-energy supernovae and hypernovae, solidifying this galaxy as one of the benchmarks for understanding the energy distribution of the first supernova in the Universe.