bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intrinsic polarization of Wolf-Rayet stars due to the rotational modulation of the stellar wind
Authors: Abdellaoui Slah , Krtička Jiří , Kurfürst Petr 
Published: August 2024

AbstractWolf-Rayet stars are regarded as candidates for progenitors of core-collapse supernovae, and they are expected to be progenitors of long gamma-ray bursts. These types of stars are considered to be fast rotators. Their high rotation speed breaks the sphericity of the star and leads to an axisymmetric wind density structure. In such a case, the electron scattering takes place in a nonspherical environment, and as a result, we might expect an intrinsic polarization. We present a 2.5D radiation hydrodynamic stellar wind model of these stars. The model simulations account for the deformation of the stellar surface due to rotation, gravity darkening, and nonradial forces. We computed the polarization from the density variable of the hydrodynamic model, derived the upper limit of rotational velocities, and found no conflict with the previous studies of Wolf-Rayet stars.
The clumped winds of the most massive stars
Authors: Brands Sarah A. , de Koter Alex , Bestenlehner Joachim M. , Crowther Paul A. , Sundqvist Jon O. , Puls Joachim , Caballero-Nieves Saida M. , Abdul-Masih Michael , Driessen Florian A. , García Miriam , Geen Sam , Gräfener Götz , Hawcroft Calum , Kaper Lex , Keszthelyi Zsolt , Langer Norbert , Sana Hugues , Schneider Fabian R. N. , Shenar Tomer , Vink Jorick S. 
Published: August 2024

AbstractThe core of the cluster R136 in the Large Magellanic Cloud hosts the most massive stars known. The high mass-loss rates of these stars strongly impact their surroundings, as well as the evolution of the stars themselves. To quantify this impact accurate mass-loss rates are needed, however, uncertainty about the degree of inhomogeneity of the winds (‘wind clumping’), makes mass-loss measurements uncertain. We combine optical and ultraviolet HST/STIS spectroscopy of 56 stars in the core of R136 in order to put constraints on the wind structure, improving the accuracy of the mass-loss rate measurements. We find that the winds are highly clumped, and use our measured mass-loss rates to test theoretical predictions. Furthermore we find, for the first time, tentative trends in the wind-structure parameters as a function of mass-loss rate, suggesting that the winds of stars with higher mass-loss rates are less clumped than those with lower mass-loss rates.
An exploration of Cygnus OB2 and perspectives for the upcoming WEAVE High-Resolution Cygnus Survey
Authors: Berlanas Sara R. , Herrero Artemio 
Published: August 2024

AbstractDuring the last years we have carried out different studies in the Cygnus OB2 association based on new spectroscopic data and benefiting from the unprecedented Gaia astrometry. They include membership, chemical and structure studies, that allowed us to discern for the first time ever between two stellar groups separated by several hundred parsecs within the association and find at least two star-forming bursts at ∼3 and ∼5 Myr. Using these studies as a template and combining upcoming spectroscopic WEAVE data and the expected accuracy that Gaia will reach in the Cygnus-X area (DR3 and forthcoming releases), we will be able to perform the deepest multi-dimensional study ever done before in a massive star-forming complex. The results of this project will lead to an important improvement of our knowledge of star formation and evolution of star-forming regions and clusters, including our understanding of the dynamics and kinematics of OB associations and stellar groups.
Massive stars in metal-poor dwarf galaxies are often extreme rotators
Authors: Schootemeijer Abel , Lennon Danny J. , Garcia Miriam , Langer Norbert , Hastings Ben , Schürmann Christoph 
Published: August 2024

AbstractWe probe how common extremely rapid rotation is among massive stars in the early universe by measuring the OBe star fraction in nearby metal-poor dwarf galaxies. We apply a new method that uses broad-band photometry to measure the galaxy-wide OBe star fractions in the Magellanic Clouds and three more distant, more metal-poor dwarf galaxies. We find OBe star fractions of ∼20% in the Large Magallanic Cloud (0.5Zȯ), and ∼30% in the Small Magellanic Cloud (0.2Zȯ) as well as in the so-far unexplored metallicity range 0.1 Z/Zȯ < 0.2 occupied by the other three dwarf galaxies. Our results imply that extremely rapid rotation is common among massive stars in metal-poor environments such as the early universe.
Formation of Supermassive Stars and the Direct Collapse to Black Holes
Authors: Regan John A. 
Published: August 2024

AbstractSupermassive stars represent a promising avenue for seeding the (super-)massive black holes observed in the centres of massive galaxies. In these proceedings I review the motivation on the need for supermassive stars as a progenitor pathway for seeding massive black holes. I discuss the currently understood limitations of seeds produced by less massive stars (i.e. remnants from the first generation of stars) and advocate that more massive stars - with masses up to M∗ ∼ 105Mȯ - formed under the conditions of hierarchical structure formation, in rare haloes, are the favoured pathway. Finally, I discuss some recent high resolution simulations demonstrating the formation of supermassive stars in early galaxies.
New self-consistent wind parameters to fit optical spectra of O-type stars
Authors: Gormaz-Matamala Alex Camilo 
Published: August 2024

AbstractWe perform spectral fittings for O-type stars based on self-consistent wind solutions, providing Ṁ and ν(r directly derived from the initial stellar parameters. We introduce our two methods: m-CAK prescription and Lambert-procedure.The Lambert-procedure allows the calculation of consistent v(r) that reduce the number of free parameters when a spectral fitting using CMFGEN is performed, even without recalculation of the Ṁ. Spectra calculated from our Lambert-solutions show significant differences compared to the initial β-law CMFGEN models. For m-CAK prescription, self-consistent solutions provide values for theoretical Ṁ on the order of the most recent predictions from other studies. Later, we find a global fit with the RT code FASTWIND. This is an important step towards the determination of stellar and wind parameters without using β-law. Our m-CAK prescription is valid for the O-type stars with Teff ≥ 30 kK and log g ≥ 3.2.We expect that solutions introduced here to be extended to numerous studies about massive stars in future.
Fundamental Properties of O and B Stars with Optical Interferometry
Authors: Gordon Kathryn D. , Gies Douglas R. , Schaefer Gail H. 
Published: August 2024

AbstractWe used interferometric observations made with the CHARA Array of 25 B-type stars and 6 O-type stars to obtain precise measurements of angular size, radius, and effective temperature to test stellar atmospheric models for massive stars. Our measured angular diameters range from 1.09 milli-arcseconds (mas) for β Tau down to 0.11 mas for 10 Lac, the smallest star yet resolved with the CHARA Array. The rotational oblateness of the rapidly rotating star ζ Oph is directly measured for the first time. We collected ultraviolet to infrared spectrophotometry for all sample stars and derived temperatures, angular diameters, and reddening estimates that best fit the spectra. There is generally good agreement between the observed and spectral fit angular diameters for the O and B stars, indicating that the fluxes predicted from model atmospheres are reliable. The derived and model temperatures for the O stars are also in fair agreement, however the sample size is small and several of the O stars results we consider to be preliminary. On the other hand, the temperatures derived from angular diameters and fluxes tend to be larger (by ≈ 4%) for the B stars than those from published results based on analysis of the line spectrum (Gordon et al. 2018, 2019).
Magnetic massive stars from stellar mergers
Authors: Schneider Fabian R. N. , Ohlmann Sebastian T. , Podsiadlowski Philipp , Röpke Friedrich K. , Balbus Steven A. , Pakmor Rüdiger , Springel Volker 
Published: August 2024

AbstractThe first magnetic field in a star other than the Sun was detected in 1947 in the star 78 Vir. Today, we know that about 10% of these intermediate-mass and high-mass stars have strong, large-scale surface magnetic fields whose origin has remained a mystery till today. It has been suggested that merging of main-sequence and pre-main-sequence stars could produce such strong fields. The massive star τ Sco is a well-known member of the group of magnetic stars and is a blue straggler given its apparently young age compared to that of other members of the Upper Scorpius association. Here, we present 3D magnetohydrodynamic simulations of the coalescence of two massive main-sequence stars and 1D stellar evolution computations of the subsequent evolution of the merger product that can explain τ Sco’s magnetic field, apparent youth and other observed characteristics. We argue that field amplification in stellar mergers is a general mechanism to form strongly-magnetised massive stars. Such stars are promising progenitors of magnetars, which may give rise to some of the enigmatic fast radio bursts, and their supernova explosions may be affected by the strong magnetic fields.
Mass loss and the Eddington parameter
Authors: Bestenlehner Joachim M. 
Published: August 2024

AbstractMass loss through stellar winds plays a dominant role in the evolution of massive stars. Very massive stars (VMSs, > 100Mȯ) display Wolf-Rayet spectral morphologies (WNh) whilst on the main-sequence. Bestenlehner (2020) extended the elegant and widely used stellar wind theory by Castor, Abbott & Klein (1975) from the optically thin (O star) to the optically thick main-sequence (WNh) wind regime. The new mass-loss description is able to explain the empirical mass-loss dependence on the Eddington parameter and is suitable for incorporation into stellar evolution models for massive and very massive stars. The prescription can be calibrated with the transition mass-loss rate defined in Vink & Gräfener (2012). Based on the stellar sample presented in Bestenlehner et al. (2014) we derive a mass-loss recipe for the Large Magellanic Cloud using the new theoretical mass-loss prescription of Bestenlehner (2020).
Wind line variability and intrinsic errors in observational mass loss rates
Authors: Massa Derck , Prinja Raman 
Published: August 2024

AbstractUV wind line variability in OB stars appears to be universal. We review the evidence that the variability is due to large, dense, optically thick structures rooted in or near the photosphere. Using repeated observations and a simple model we translate observed profile variations into optical depth variations and, consequently, variations in measured mass loss rates. Although global rates may be stable, measured rates vary. Consequently, profile variations infer how mass loss rates determined from UV wind lines vary. These variations quantify the intrinsic error inherent in any mass loss rate derived from a single observation. These derived rates can differ by factors of 3 or more. Our results also imply that rates from non-simultaneous observations (such as UV and ground based data) need not agree. Finally, we use our results to examine the nature of the structures responsible for the variability.
Formation of black holes in the pair-instability mass gap: Hydrodynamical simulation of a massive star collision & evolution of a post-collision star
Authors: Costa Guglielmo , Ballone Alessandro , Mapelli Michela , Bressan Alessandro , MacLeod Morgan 
Published: August 2024

AbstractIn this work, we study in detail the collision formation scenario of black holes (BHs) which lie in the pair-instability (PI) mass gap. We study the collision scenario of two massive stars by means of a smoothed-particle hydrodynamics (SPH) simulation and the post-collision evolution with detailed stellar evolutionary codes. We find that the stellar collision scenario is a suitable formation channel to populate the BHs’ PI mass gap.
Study of the Be/X-ray binary IGR J21343+4738 physical parameters based on the 15-years monitoring
Authors: Nikolaeva Evgeniia , Bikmaev Ilfan 
Published: August 2024

AbstractWe present the results of our long-term RTT-150 photometric and spectroscopic observations Be optical counterpart of the High-mass X-ray binary IGR J21343+4738.
Luminous red supergiants in the Magellanic Clouds
Authors: De Wit S. , Bonanos A. Z. , Tramper F. , Yang M. , Maravelias G. , Boutsia K. , Britavskiy N. , Zapartas M. 
Published: August 2024

AbstractThere is evidence that some red supergiants (RSGs) experience phases of episodic mass-loss. These episodes yield more extreme mass-loss rates, further stripping the envelope of the RSG, significantly affecting the further evolution towards the final collapse of the star. Mass lost through RSG outbursts/superwinds will flow outwards and form dust further out from the surface and this dust may be detected and modelled. Here, we aim to derive the surface properties and estimate the global properties of Mid-IR bright RSGs in the Magellanic Clouds. These properties will then be compared to evolutionary predictions and used for future spectral energy distribution fitting studies to measure the mass-loss rates from present circumstellar dust.
Access platform to our database of CMFGEN spectra for atmospheric studies of massive stars
Authors: Payen-Sandoval A. , Arias L. , Zargó J. , Arrieta A. , Fierro-Santillán C. R. , Klapp J. 
Published: August 2024

AbstractWe have collected a database of more than 43,000 spectra of atmospheres of massive stars. These spectra have been generated with the CMFGEN code of Hillier & Miller (1998) by systematically varying stellar parameters: effective temperature, luminosity, metallicity and mass loss rate for stars from 9 to 120 solar masses (Zsargó et al. 2020) In this work we present a web-based platform for accessing the database. The platform allows an online comparison between an observed and a synthetic spectrum to quickly assess the stellar and wind parameters. The platform will be available without cost to the astronomical community and will be hosted on servers shared between Mexican Universities.
Double Vision: Combining X-ray and Spectropolarimetric Observations of WR Binaries
Authors: Johnson R. A. , Nazé Y. , Panzera T. , Fullard A. G. , Lomax J. R. , Hoffman J. L. , Nordsieck K. H. 
Published: August 2024

AbstractWe present X-ray and spectropolarimetric observations of the WN+O binaries WR71 and WR97, which are analogs of the well-studied V444 Cygni. The combined results have the potential to constrain the locations and properties of wind interaction regions in these binaries, give clues to their subsequent evolution, and address the commonalities among WR+O systems.
Nuclear proteasomes buffer cytoplasmic proteins during autophagy compromise
Authors: Park So Jung , Son Sung Min , Barbosa Antonio Daniel , Wrobel Lidia , Stamatakou Eleanna , Squitieri Ferdinando , Balmus Gabriel , Rubinsztein David C. 
Published: August 2024

AbstractAutophagy is a conserved pathway where cytoplasmic contents are engulfed by autophagosomes, which then fuse with lysosomes enabling their degradation. Mutations in core autophagy genes cause neurological conditions, and autophagy defects are seen in neurodegenerative diseases such as Parkinson’s disease and Huntington’s disease. Thus, we have sought to understand the cellular pathway perturbations that autophagy-perturbed cells are vulnerable to by seeking negative genetic interactions such as synthetic lethality in autophagy-null human cells using available data from yeast screens. These revealed that loss of proteasome and nuclear pore complex components cause synergistic viability changes akin to synthetic fitness loss in autophagy-null cells. This can be attributed to the cytoplasm-to-nuclear transport of proteins during autophagy deficiency and subsequent degradation of these erstwhile cytoplasmic proteins by nuclear proteasomes. As both autophagy and cytoplasm-to-nuclear transport are defective in Huntington’s disease, such cells are more vulnerable to perturbations of proteostasis due to these synthetic interactions.
Innovative voltammetric techniques for bumadizone analysis in pharmaceutical and biological samples: emphasizing green, white, and blue analytical approaches
Authors: Kelani Khadiga M. , Said Ragab A. , El-Dosoky Mohammad A. , Mohamed Ahmed R. 
Published: August 2024

AbstractThere are no documented electroanalytical methods for quantifying the anti-inflammatory drug bumadizone (BUM) in pharmaceutical or biological matrices. So, a new voltammetric method was developed to determine BUM at nano concentrations in pharmaceutical forms, in the presence of its alkaline degradant, and in biological fluids. Five electrodes were tested, including three nano-reduced graphene oxide (nRGO) electrodes (5%, 15%, and 20%), a carbon paste electrode (CPE), and a 10% nRGO-modified CPE. The 10% nRGO-modified electrode showed the best performance, offering high selectivity and low detection limits, with good linearity in the concentration range of 0.9 × 102 to 15 × 102 ng mL−1. Differential pulse voltammetry successfully applied this electrode for BUM determination in various samples, achieving excellent recovery without preliminary separation. The method was validated according to ICH guidelines and compared favorably to the reference method. Its environmental impact was assessed using AGREE and Eco-scale metrics in addition to the RGB algorithm, showing superior greenness and whiteness profiles due to safer solvents and lower energy consumption, along with high practical effectiveness using the BAGI metric.
Interplay of FXN expression and lipolysis in white adipocytes plays a critical role in insulin sensitivity in Friedreich’s ataxia mouse model
Authors: Wu Lin , Huang Fei , Yang Lu , Yang Liu , Sun Zichen , Zhang Jinghua , Xia Siyu , Zhao Hongting , Ding Yibing , Bian Dezhi , Li Kuanyu 
Published: August 2024

AbstractFrataxin (FXN) is required for iron-sulfur cluster biogenesis, and its loss causes the early-onset neurodegenerative disease Friedreich ataxia (FRDA). Loss of FXN is a susceptibility factor in the development of diabetes, a common metabolic complication after myocardial hypertrophy in patients with FRDA. The underlying mechanism of FXN deficient-induced hyperglycemia in FRDA is, however, poorly understood. In this study, we confirmed that the FXN deficiency mouse model YG8R develops insulin resistance in elder individuals by disturbing lipid metabolic homeostasis in adipose tissues. Evaluation of lipolysis, lipogenesis, and fatty acid β-oxidation showed that lipolysis is most severely affected in white adipose tissues. Consistently, FXN deficiency significantly decreased expression of lipolytic genes encoding adipose triglyceride lipase (Atgl) and hormone-sensitive lipase (Hsl) resulting in adipocyte enlargement and inflammation. Lipolysis induction by fasting or cold exposure remarkably upregulated FXN expression, though FXN deficiency lessened the competency of lipolysis compared with the control or wild type mice. Moreover, we found that the impairment of lipolysis was present at a young age, a few months earlier than hyperglycemia and insulin resistance. Forskolin, an activator of lipolysis, or pioglitazone, an agonist of PPARγ, improved insulin sensitivity in FXN-deficient adipocytes or mice. We uncovered the interplay between FXN expression and lipolysis and found that impairment of lipolysis, particularly the white adipocytes, is an early event, likely, as a primary cause for insulin resistance in FRDA patients at later age.
When the liver is in poor condition, so is the heart – cardiac remodelling in MASH mouse models
Authors: Bott Sebastian , Lallement Justine , Marino Alice , Daskalopoulos Evangelos-Panagiotis , Beauloye Christophe , Esfahani Hrag , Dessy Chantal , Leclercq Isabelle Anne 
Published: August 2024

Abstract
Metabolic dysfunction-associated steatohepatitis (MASH) confers a risk for cardiovascular diseases in patients. Animal models may help exploring the mechanisms linking liver and heart diseases. Hence, we explored the cardiac phenotype in two MASH mouse models: foz/foz mice fed a high-fat diet (HFD) for 24 or 60 weeks and C57BL/6J mice fed a high-fat-, high-cholesterol-, and high-fructose diet for 60 weeks. Angiotensin II (AngII) was used as an additional cardiovascular stressor for 4 weeks in 10 weeks HFD-fed foz/foz mice. Foz/foz mice with fibrosing MASH developed cardiac hypertrophy with adverse cardiac remodelling not seen in WT similarly fed the HFD. AngII caused hypertension and up-regulated the expression of genes contributing to pathological cardiac hypertrophy (Nppa, Myh7) more severely so in foz/foz mice than in controls. After 60 weeks of HFD, while liver disease had progressed to burn-out non steatotic MASH with hepatocellular carcinoma in 50% of the animals, the cardiomyopathy did not. In an independent model (C57BL/6J mice fed a fat-, cholesterol- and fructose-rich diet), moderate fibrosing MASH is associated with cardiac fibrosis and dysregulation of genes involved in pathological remodelling (Col1a1, Col3a1, Vim, Myh6, Slc2a1). Thus, animals with MASH present consistent adverse structural changes in the heart with no patent alteration of cardiac function even when stressed with exogenous AngII. Liver disease, and likely not overfeeding or aging alone, is associated with this cardiac phenotype. Our findings support foz/foz mice as suitable for studying links between MASH and heart structural changes ahead of heart failure.
Microcapsule preparation process research and current status of oilfield application
Authors: Wang Sicai , Zhang Qun , Xiu Jianlong , Ma Yuandong , Huang Lixin , Yi Lina , Fu Haowei 
Published: August 2024

AbstractTraditional tertiary oil recovery methods are fraught with challenges such as significant reagent adsorption, voluminous injection requirements, limited sweep efficiency, and inadequate intelligent targeting. These issues lead to suboptimal displacement of residual oil, resulting in the inability to mobilize substantial crude oil resources and thus yielding low recovery rates. Microcapsules—spherical particles with micron or nanometer scale diameters—have been extensively utilized across various sectors, including food storage, targeted drug encapsulation, and fragrance containment, owing to their distinct advantages in controlled release, isolation, and targeted delivery. These applications have successfully achieved industrialization and commercialization. In recent years, numerous researchers have explored the application of microcapsule preparation processes to diverse facets of oil extraction, with the aim of further enhancing oil recovery (EOR). This article elucidates the mechanism of action of microcapsules, their preparation methods (encompassing in situ polymerization, interfacial polymerization, spray drying, solvent evaporation, phase separation, and supercritical CO2‐assisted techniques), characterization and evaluation methodologies, among other aspects. It encapsulates the current status and principal challenges associated with the application of microcapsule preparation processes in oilfield development and probes the potential and pivotal research directions for their oilfield applications.