Pub Date : 2026-02-04DOI: 10.1051/0004-6361/202556749
Jongchul Chae, Juhyung Kang, Kyoung-Sun Lee, Eun-Kyung Lim, Maria S. Madjarska, Hannah Kwak
On-disk Hα light-absorbing plasma structures such as mottles, fibrils, filaments, and Hα jets are observable magnetohydrodynamic features in the upper solar chromosphere. We attempt to determine their physical parameters by regarding them as optical clouds scattering the Hα-line light incident from below. For this purpose, we developed a new inversion, which we call the three-layer background plus three-component cloud model inversion. This new spectral inversion was found to be applicable to every Hα line profile taken from a quiet-Sun region. We used the model parameters inferred from the fitting to determine the temperature and to construct the velocity distribution function at every point in the observed region. This function was used in turn to calculate the column mass, mass flux, kinetic energy, and kinetic energy flux. Our approach yielded three types of Doppler velocities: the mass flux-associated velocity, the kinetic energy-associated velocity, and the kinetic energy flux-associated velocity. We found that the physical parameters of Hα-absorbing structures in a quiet-Sun region resolve the long-standing discrepancy between the Doppler velocities of mottles observed on the disk and the rising speeds of spicules observed off the limb. We also found that the kinetic energy budget of the upper chromosphere is large enough for the radiative loss in the upper chromosphere and corona. These results support the hypothesis that magnetohydrodynamic waves heat the upper atmosphere of the quiet Sun.
{"title":"Inference of the physical parameters of Hα-absorbing plasma structures in the quiet Sun","authors":"Jongchul Chae, Juhyung Kang, Kyoung-Sun Lee, Eun-Kyung Lim, Maria S. Madjarska, Hannah Kwak","doi":"10.1051/0004-6361/202556749","DOIUrl":"https://doi.org/10.1051/0004-6361/202556749","url":null,"abstract":"On-disk H<i>α<i/> light-absorbing plasma structures such as mottles, fibrils, filaments, and H<i>α<i/> jets are observable magnetohydrodynamic features in the upper solar chromosphere. We attempt to determine their physical parameters by regarding them as optical clouds scattering the H<i>α<i/>-line light incident from below. For this purpose, we developed a new inversion, which we call the three-layer background plus three-component cloud model inversion. This new spectral inversion was found to be applicable to every H<i>α<i/> line profile taken from a quiet-Sun region. We used the model parameters inferred from the fitting to determine the temperature and to construct the velocity distribution function at every point in the observed region. This function was used in turn to calculate the column mass, mass flux, kinetic energy, and kinetic energy flux. Our approach yielded three types of Doppler velocities: the mass flux-associated velocity, the kinetic energy-associated velocity, and the kinetic energy flux-associated velocity. We found that the physical parameters of H<i>α<i/>-absorbing structures in a quiet-Sun region resolve the long-standing discrepancy between the Doppler velocities of mottles observed on the disk and the rising speeds of spicules observed off the limb. We also found that the kinetic energy budget of the upper chromosphere is large enough for the radiative loss in the upper chromosphere and corona. These results support the hypothesis that magnetohydrodynamic waves heat the upper atmosphere of the quiet Sun.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"73 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146115838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-02-02DOI: 10.1051/0004-6361/202555979
Aris Tritsis
Context. The mass-to-magnetic flux ratio of molecular clouds is a parameter of central importance as it quantifies the dynamical significance of the magnetic field with respect to gravitational forces. Therefore, it can provide invaluable information on the fate of clouds and the sites of star formation.Aims. Our objective was to study the accuracy with which we can measure the true mass-to-flux ratio in molecular clouds under various projection angles and identify systematic biases.Methods. We used a 3D nonideal magnetohydrodynamic chemo-dynamical simulation of a turbulent collapsing molecular cloud. We quantified the accuracy with which the mass-to-flux ratio is recovered under various projection angles and dynamical stages by analyzing the magnetic field–gas column density relation, and comparing the “observed” mass-to-flux ratio against the true values.Results. We find that projection effects have a major impact on measurements of the mass-to-flux ratio. Zeeman measurements can overestimate the true mass-to-flux ratio of the cloud by more than an order of magnitude when the magnetic field primarily lies on the plane of the sky. Therefore, measurements of the mass-to-flux ratio based on Zeeman observations should be considered as upper limits. Mass-to-flux ratio estimates inferred from polarization observations do not provide a physically meaningful probe of the true mass-to-flux ratio and can lead to unphysical results as they fail to capture the underlying correlation between the magnetic field and column density.
{"title":"The mass-to-flux ratio in molecular clouds: What are we really measuring?","authors":"Aris Tritsis","doi":"10.1051/0004-6361/202555979","DOIUrl":"https://doi.org/10.1051/0004-6361/202555979","url":null,"abstract":"<i>Context<i/>. The mass-to-magnetic flux ratio of molecular clouds is a parameter of central importance as it quantifies the dynamical significance of the magnetic field with respect to gravitational forces. Therefore, it can provide invaluable information on the fate of clouds and the sites of star formation.<i>Aims<i/>. Our objective was to study the accuracy with which we can measure the true mass-to-flux ratio in molecular clouds under various projection angles and identify systematic biases.<i>Methods<i/>. We used a 3D nonideal magnetohydrodynamic chemo-dynamical simulation of a turbulent collapsing molecular cloud. We quantified the accuracy with which the mass-to-flux ratio is recovered under various projection angles and dynamical stages by analyzing the magnetic field–gas column density relation, and comparing the “observed” mass-to-flux ratio against the true values.<i>Results<i/>. We find that projection effects have a major impact on measurements of the mass-to-flux ratio. Zeeman measurements can overestimate the true mass-to-flux ratio of the cloud by more than an order of magnitude when the magnetic field primarily lies on the plane of the sky. Therefore, measurements of the mass-to-flux ratio based on Zeeman observations should be considered as upper limits. Mass-to-flux ratio estimates inferred from polarization observations do not provide a physically meaningful probe of the true mass-to-flux ratio and can lead to unphysical results as they fail to capture the underlying correlation between the magnetic field and column density.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"19 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146098079","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-02-02DOI: 10.1051/0004-6361/202450483
Myrto Falalaki, Vasiliki Pavlidou
Context. Breaks in the cosmic-ray (CR) flux spectrum encode information on the properties of CR accelerator populations producing the observed flux. Spectral steepenings, known as knees, are generally accompanied by a transition to a higher-mass composition.Aims. We seek generic features of CR source populations that are robustly enough imprinted on knee observables to be discernible even in the presence of significant uncertainties in CR data. We explore how the diversity among population members imprints on the knee phenomenology under the assumption that a knee arises from a fixed-rigidity cutoff in the source spectrum. Our scope is explicitly exclusionary: We did not fit specific datasets, but determined which observed spectral features are incompatible with a single-population fixed-rigidity cutoff picture, which would indicate additional physics.Methods. We used a simple theoretical model for a population of CR accelerators. Each member of the population stochastically accelerated CR to a power-law spectrum up to a cutoff rigidity that resulted from source-confinement requirements. We allowed variance among the members in the cutoff rigidity and in the power-law slope.Results. We found that (a) the slope step of the flux spectrum is ∼0.5 and decreased weakly with increasing spread in either property, (b) composition always broke first, and (c) the difference between the break energies in composition and flux increased with increasing diversity. These trends are robust under our assumptions. Deviations from them in observed data would indicate more complex physics than encoded in our simple model.Conclusions. From comparing these trends with observed CR knees, we conclude that (i) the primary knee at ∼4 × 1015 eV is consistent with a constant-rigidity cutoff according to KASCADE-Grande data processed with post-LHC hadronic models, but not according to other datasets, (ii) the second knee at ∼5 × 1017 eV conclusively requires more complexity than the cutoff of a single CR source population, (iii) the constant-rigidity source cutoff interpretation of the spectral feature identified by Auger at ∼1019 eV cannot be rejected when the cutoff rigidity and slope in the parent source population are substantial. Interestingly, a significant spread in slope would also result in the spectral curvature before the break, which in turn might contribute to the ankle feature.
{"title":"What can cosmic-ray knees reveal about source populations?","authors":"Myrto Falalaki, Vasiliki Pavlidou","doi":"10.1051/0004-6361/202450483","DOIUrl":"https://doi.org/10.1051/0004-6361/202450483","url":null,"abstract":"<i>Context.<i/> Breaks in the cosmic-ray (CR) flux spectrum encode information on the properties of CR accelerator populations producing the observed flux. Spectral steepenings, known as knees, are generally accompanied by a transition to a higher-mass composition.<i>Aims.<i/> We seek generic features of CR source populations that are robustly enough imprinted on knee observables to be discernible even in the presence of significant uncertainties in CR data. We explore how the diversity among population members imprints on the knee phenomenology under the assumption that a knee arises from a fixed-rigidity cutoff in the source spectrum. Our scope is explicitly exclusionary: We did not fit specific datasets, but determined which observed spectral features are incompatible with a single-population fixed-rigidity cutoff picture, which would indicate additional physics.<i>Methods.<i/> We used a simple theoretical model for a population of CR accelerators. Each member of the population stochastically accelerated CR to a power-law spectrum up to a cutoff rigidity that resulted from source-confinement requirements. We allowed variance among the members in the cutoff rigidity and in the power-law slope.<i>Results.<i/> We found that (a) the slope step of the flux spectrum is ∼0.5 and decreased weakly with increasing spread in either property, (b) composition always broke first, and (c) the difference between the break energies in composition and flux increased with increasing diversity. These trends are robust under our assumptions. Deviations from them in observed data would indicate more complex physics than encoded in our simple model.<i>Conclusions.<i/> From comparing these trends with observed CR knees, we conclude that (i) the primary knee at ∼4 × 10<sup>15<sup/> eV is consistent with a constant-rigidity cutoff according to KASCADE-Grande data processed with post-LHC hadronic models, but not according to other datasets, (ii) the second knee at ∼5 × 10<sup>17<sup/> eV conclusively requires more complexity than the cutoff of a single CR source population, (iii) the constant-rigidity source cutoff interpretation of the spectral feature identified by Auger at ∼10<sup>19<sup/> eV cannot be rejected when the cutoff rigidity and slope in the parent source population are substantial. Interestingly, a significant spread in slope would also result in the spectral curvature before the break, which in turn might contribute to the ankle feature.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"58 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146098083","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-02-02DOI: 10.1051/0004-6361/202557659
S. Rendon Restrepo, O. Gressel
Context. The stability of a differentially-rotating fluid subject to its own gravity is a problem with applications across wide areas of astrophysics, from protoplanetary discs to entire galaxies. The shearing box formalism offers a conceptually simple framework for studying differential rotation in the local approximation.Aims. Aimed at self-gravitating, and importantly, vertically stratified protoplanetary discs, we develop two novel methods for solving Poisson’s equation in the framework of the shearing box with vertical vacuum boundary conditions (BCs).Methods. Both approaches naturally make use of multi-dimensional fast Fourier transforms (FFTs) for computational efficiency. While the first one exploits the linearity properties of the Poisson equation, the second, which is slightly more accurate, consists of finding the adequate discrete Green’s function (in Fourier space) adapted to the problem at hand. To this end, we have derived, in Fourier space, an analytical Green’s function satisfying the shear-periodic BCs in the plane as well as vacuum BCs, vertically.Results. Our spectral method demonstrates excellent accuracy, even with a modest number of grid points, and exhibits third-order convergence. It has been implemented in the NIRVANA-III code, where it exhibits good scalability up to 4096 CPU cores, consuming less than 6% of the total runtime. This was achieved through the use of P3DFFT, a fast Fourier Transform library that employs pencil decomposition, overcoming the scalability limitations inherent in libraries using slab decomposition.Conclusions. We have introduced two novel spectral Poisson solvers that guarantee high accuracy, performance, and intrinsically support vertical vacuum BCs in the shearing box framework. Our solvers enable high-resolution local studies involving self-gravity, such as magnetohydrodynamic (MHD) simulations of gravito-turbulence and/or gravitational fragmentation.
{"title":"An efficient spectral Poisson solver for the NIRVANA-III code: The shearing box case with vertical vacuum boundary conditions","authors":"S. Rendon Restrepo, O. Gressel","doi":"10.1051/0004-6361/202557659","DOIUrl":"https://doi.org/10.1051/0004-6361/202557659","url":null,"abstract":"<i>Context<i/>. The stability of a differentially-rotating fluid subject to its own gravity is a problem with applications across wide areas of astrophysics, from protoplanetary discs to entire galaxies. The shearing box formalism offers a conceptually simple framework for studying differential rotation in the local approximation.<i>Aims<i/>. Aimed at self-gravitating, and importantly, vertically stratified protoplanetary discs, we develop two novel methods for solving Poisson’s equation in the framework of the shearing box with vertical vacuum boundary conditions (BCs).<i>Methods<i/>. Both approaches naturally make use of multi-dimensional fast Fourier transforms (FFTs) for computational efficiency. While the first one exploits the linearity properties of the Poisson equation, the second, which is slightly more accurate, consists of finding the adequate discrete Green’s function (in Fourier space) adapted to the problem at hand. To this end, we have derived, in Fourier space, an analytical Green’s function satisfying the shear-periodic BCs in the plane as well as vacuum BCs, vertically.<i>Results<i/>. Our spectral method demonstrates excellent accuracy, even with a modest number of grid points, and exhibits third-order convergence. It has been implemented in the NIRVANA-III code, where it exhibits good scalability up to 4096 CPU cores, consuming less than 6% of the total runtime. This was achieved through the use of P3DFFT, a fast Fourier Transform library that employs pencil decomposition, overcoming the scalability limitations inherent in libraries using slab decomposition.<i>Conclusions<i/>. We have introduced two novel spectral Poisson solvers that guarantee high accuracy, performance, and intrinsically support vertical vacuum BCs in the shearing box framework. Our solvers enable high-resolution local studies involving self-gravity, such as magnetohydrodynamic (MHD) simulations of gravito-turbulence and/or gravitational fragmentation.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"89 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146098081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-30DOI: 10.1051/0004-6361/202557446
D. Galán-Diéguez, S. R. Berlanas, A. Herrero, M. Abdul-Masih, D. J. Lennon, C. Martínez-Sebastián, F. M. Pérez-Toledo
Context. Cygnus OB2, located within the Cygnus X complex – one of the most active star-forming regions of the Galaxy – hosts hundreds of O- and B-type stars at different evolutionary stages. This rich association offers a unique opportunity to study the evolution and dynamic interactions of massive stars. However, despite extensive studies, a notable absence of a fast-rotating group (v sin i > 200 km s−1) among the O-type population of Cygnus OB2 challenges current models of massive star evolution.Aims. Stellar rotation strongly impacts spectral line shapes of O-type stars, with high rotational velocities potentially leading to misclassifications. This study investigates whether some stars in Cygnus OB2, classified at low spectral resolution as B0, are actually rapidly rotating late-O types. Such cases could explain the observed lack of fast rotators in Cygnus OB2.Methods. Considering the effects of rotation, we reclassified the known B0 population in Cygnus OB2, using the MGB tool and both the new and pre-existing optical spectroscopy. Finally, we computed the projected rotational velocities using iacob-broad.Results. We find that approximately 19% of the initial B0 population in Cygnus OB2 are, in fact, late-O types. Further analysis shows that only six stars in the entire dataset have projected rotational velocities above 200 km s−1, with just one new O-type star exceeding this threshold.Conclusions. In our study of Cygnus OB2, we continue to find a notable lack of fast rotators among its O-type population. We propose a combination of three factors as the most likely explanation: (i) the young age of Cygnus OB2 may imply that fast rotators have not been produced yet due to binary interactions; (ii) fast rotators may have been dynamically ejected from the core as runaway stars; and (iii) local star formation conditions may hinder binary formation (reducing spin-up interactions) or result in slower rotational velocities at birth.
上下文。天鹅座OB2位于天鹅座X复合体内，这是银河系中最活跃的恒星形成区域之一，拥有数百颗处于不同进化阶段的O型和b型恒星。这种丰富的联系为研究大质量恒星的演化和动态相互作用提供了一个独特的机会。然而，尽管进行了大量的研究，在天鹅座OB2的o型星群中明显缺乏一个快速旋转的星群（vsin i bbb20 200 km s - 1），这对目前的大质量恒星演化模型提出了挑战。恒星旋转强烈影响o型恒星的谱线形状，高转速可能导致错误分类。这项研究调查了天鹅座OB2中的一些恒星，在低光谱分辨率下被分类为B0，是否实际上是快速旋转的晚o型恒星。这种情况可以解释天鹅座ob2中观察到的缺乏快速旋转体的现象。考虑到旋转的影响，我们使用MGB工具和新的和已有的光学光谱对天鹅座OB2中已知的B0种群进行了重新分类。最后，我们使用iacob-broad计算了投影的旋转速度。我们发现天鹅座OB2中大约19%的初始B0型实际上是晚o型。进一步的分析表明，整个数据集中只有6颗恒星的预计转速超过200 km s - 1，只有一颗新的o型恒星超过了这个阈值。在我们对天鹅座OB2的研究中，我们继续发现在它的o型星群中明显缺乏快速旋转星。我们提出三个因素作为最有可能的解释：(i)天鹅座OB2的年轻年龄可能意味着由于双星相互作用尚未产生快速旋转体；（ii）快速旋转星可能作为逃逸星被动态地从核心抛出；（iii）局部恒星形成条件可能阻碍双星形成（减少自旋向上的相互作用）或导致出生时较慢的旋转速度。
{"title":"The lack of fast rotators in Cyg OB2","authors":"D. Galán-Diéguez, S. R. Berlanas, A. Herrero, M. Abdul-Masih, D. J. Lennon, C. Martínez-Sebastián, F. M. Pérez-Toledo","doi":"10.1051/0004-6361/202557446","DOIUrl":"https://doi.org/10.1051/0004-6361/202557446","url":null,"abstract":"<i>Context.<i/> Cygnus OB2, located within the Cygnus X complex – one of the most active star-forming regions of the Galaxy – hosts hundreds of O- and B-type stars at different evolutionary stages. This rich association offers a unique opportunity to study the evolution and dynamic interactions of massive stars. However, despite extensive studies, a notable absence of a fast-rotating group (<i>v<i/> sin <i>i<i/> > 200 km s<sup>−1<sup/>) among the O-type population of Cygnus OB2 challenges current models of massive star evolution.<i>Aims.<i/> Stellar rotation strongly impacts spectral line shapes of O-type stars, with high rotational velocities potentially leading to misclassifications. This study investigates whether some stars in Cygnus OB2, classified at low spectral resolution as B0, are actually rapidly rotating late-O types. Such cases could explain the observed lack of fast rotators in Cygnus OB2.<i>Methods.<i/> Considering the effects of rotation, we reclassified the known B0 population in Cygnus OB2, using the MGB tool and both the new and pre-existing optical spectroscopy. Finally, we computed the projected rotational velocities using iacob-broad.<i>Results.<i/> We find that approximately 19% of the initial B0 population in Cygnus OB2 are, in fact, late-O types. Further analysis shows that only six stars in the entire dataset have projected rotational velocities above 200 km s<sup>−1<sup/>, with just one new O-type star exceeding this threshold.<i>Conclusions.<i/> In our study of Cygnus OB2, we continue to find a notable lack of fast rotators among its O-type population. We propose a combination of three factors as the most likely explanation: (i) the young age of Cygnus OB2 may imply that fast rotators have not been produced yet due to binary interactions; (ii) fast rotators may have been dynamically ejected from the core as runaway stars; and (iii) local star formation conditions may hinder binary formation (reducing spin-up interactions) or result in slower rotational velocities at birth.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"140 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146098077","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-30DOI: 10.1051/0004-6361/202558173
L. Gonzalez-Rivas, L. Krapp, X. Ramos, P. Benitez-Llambay
Context. A crucial aspect of formation models for the Galilean moons of Jupiter is that the objects survive rapid inward orbital migration.Aims. The primary aim of this study is to investigate the orbital migration of the Galilean moons by incorporating self-consistent solid dynamics in models of circumjovian disks.Methods. We performed two-fluid simulations using the code FARGO3D on a 2D polar grid. The simulations modeled a satellite with the mass of a protomoon, Europa, or Ganymede that interacts with a circumjovian disk. The dust component, coupled to the gas via a drag force, was characterized by the dust-to-gas mass ratio (ϵ) and the Stokes number (Ts).Results. The effect of solids fundamentally alters the evolution of the satellites. We identified a vast parameter space in which migration is slowed, halted, robustly reversed (leading to outward migration), or significantly accelerated inward. The migration rate is dependent on satellite mass. This provides a natural source of differential migration.Conclusions. Solid dynamics provides a robust and self-consistent mechanism that fundamentally alters the migration of the Galilean moons. This might address the long-standing migration catastrophe. This mechanism critically affects the survival of satellites and might offer a viable physical process to explain the establishment of resonances through differential migration. These findings establish that solid torques are a critical non-negligible factor in the shaping of the final architecture of satellite systems.
{"title":"Not just gas: How solids-driven torques shaped the migration of the Galilean moons","authors":"L. Gonzalez-Rivas, L. Krapp, X. Ramos, P. Benitez-Llambay","doi":"10.1051/0004-6361/202558173","DOIUrl":"https://doi.org/10.1051/0004-6361/202558173","url":null,"abstract":"<i>Context.<i/> A crucial aspect of formation models for the Galilean moons of Jupiter is that the objects survive rapid inward orbital migration.<i>Aims.<i/> The primary aim of this study is to investigate the orbital migration of the Galilean moons by incorporating self-consistent solid dynamics in models of circumjovian disks.<i>Methods.<i/> We performed two-fluid simulations using the code FARGO3D on a 2D polar grid. The simulations modeled a satellite with the mass of a protomoon, Europa, or Ganymede that interacts with a circumjovian disk. The dust component, coupled to the gas via a drag force, was characterized by the dust-to-gas mass ratio (<i>ϵ<i/>) and the Stokes number (<i>T<i/><sub><i>s<i/><sub/>).<i>Results.<i/> The effect of solids fundamentally alters the evolution of the satellites. We identified a vast parameter space in which migration is slowed, halted, robustly reversed (leading to outward migration), or significantly accelerated inward. The migration rate is dependent on satellite mass. This provides a natural source of differential migration.<i>Conclusions.<i/> Solid dynamics provides a robust and self-consistent mechanism that fundamentally alters the migration of the Galilean moons. This might address the long-standing migration catastrophe. This mechanism critically affects the survival of satellites and might offer a viable physical process to explain the establishment of resonances through differential migration. These findings establish that solid torques are a critical non-negligible factor in the shaping of the final architecture of satellite systems.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"8 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146097823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-30DOI: 10.1051/0004-6361/202557822
A. R. Offringa, R. J. van Weeren
Context. Processing radio interferometric data often requires storing forward-predicted model data. In direction-dependent calibration, these data may have a volume an order of magnitude larger than the original data. Existing lossy compression techniques work well for observed, noisy data, but cause issues in calibration when applied to forward-predicted model data.Aims. To reduce the volume of forward-predicted model data, we present a lossless compression method called Simulated Signal Compression (Sisco) for noiseless data that integrates seamlessly with existing workflows. We show that Sisco can be combined with baseline-dependent averaging for further size reduction.Methods. Sisco decomposes complex floating-point visibility values and uses polynomial extrapolation in time and frequency to predict values, groups bytes for efficient encoding, and compresses residuals using the DEFLATE algorithm. We evaluated Sisco on diverse LOFAR, MeerKAT, and MWA datasets with various extrapolation functions. Implemented as an open-source Casacore storage manager, it can directly be used by any observatory that makes use of this format.Results. We find that a combination of linear and quadratic prediction yields optimal compression, reducing noiseless forward-predicted model data to 24% of its original volume on average. Compression varies by dataset, ranging from 13% for smooth data to 38% for less predictable data. For pure noise data, compression achieves just a size of 84% due to the unpredictability of such data. With the current implementation, the achieved compression throughput is with 534 MB/s mostly dominated by I/O on our testing platform, but occupies the processor during compression or decompression. Finally, we discuss the extension to a lossy algorithm.
{"title":"Lossless compression of simulated radio interferometric visibilities","authors":"A. R. Offringa, R. J. van Weeren","doi":"10.1051/0004-6361/202557822","DOIUrl":"https://doi.org/10.1051/0004-6361/202557822","url":null,"abstract":"<i>Context<i/>. Processing radio interferometric data often requires storing forward-predicted model data. In direction-dependent calibration, these data may have a volume an order of magnitude larger than the original data. Existing lossy compression techniques work well for observed, noisy data, but cause issues in calibration when applied to forward-predicted model data.<i>Aims<i/>. To reduce the volume of forward-predicted model data, we present a lossless compression method called Simulated Signal Compression (Sisco) for noiseless data that integrates seamlessly with existing workflows. We show that Sisco can be combined with baseline-dependent averaging for further size reduction.<i>Methods<i/>. Sisco decomposes complex floating-point visibility values and uses polynomial extrapolation in time and frequency to predict values, groups bytes for efficient encoding, and compresses residuals using the DEFLATE algorithm. We evaluated Sisco on diverse LOFAR, MeerKAT, and MWA datasets with various extrapolation functions. Implemented as an open-source Casacore storage manager, it can directly be used by any observatory that makes use of this format.<i>Results<i/>. We find that a combination of linear and quadratic prediction yields optimal compression, reducing noiseless forward-predicted model data to 24% of its original volume on average. Compression varies by dataset, ranging from 13% for smooth data to 38% for less predictable data. For pure noise data, compression achieves just a size of 84% due to the unpredictability of such data. With the current implementation, the achieved compression throughput is with 534 MB/s mostly dominated by I/O on our testing platform, but occupies the processor during compression or decompression. Finally, we discuss the extension to a lossy algorithm.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"80 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146098080","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-30DOI: 10.1051/0004-6361/202557649
A. Choplin, L. Siess, S. Goriely, P. Eggenberger, F. D. Moyano
Context. The intermediate neutron-capture process (i-process) can occur during proton ingestion events (PIEs), which may take place in the early evolutionary phases of asymptotic giant branch (AGB) stars.Aims. We investigate the impact of rotational and magnetic mixing on i-process nucleosynthesis in low-metallicity, low-mass AGB stars.Methods. We computed AGB models with [Fe/H] = −2.5 and −1.7 and initial masses of 1 and 1.5 M⊙ using the STAREVOL code, including a network of 1160 nuclei coupled to transport equations. Rotating models incorporate a calibrated Tayler-Spruit (TS) dynamo to account for core rotation rates inferred from asteroseismic observations of solar-metallicity sub-giants and giants. Initial rotation velocities of 0, 30, and 90 km s−1 were considered, along with varying assumptions for magnetic mixing.Results. Rotation without magnetic fields strongly suppresses the i-process due to the production of primary 14N, which is subsequently converted into 22Ne – a potent neutron poison during the PIE. Including magnetic fields via the TS dynamo restores the models close to their non-rotating counterparts: strong core-envelope coupling suppresses shear mixing and prevents primary 14N synthesis, yielding i-process nucleosynthesis similar to non-rotating models. We also find that rotational mixing during the AGB phase is insufficient to affect the occurrence of PIEs.Conclusions. Proton ingestion event-driven nucleosynthesis proceeds similarly in asteroseismic-calibrated magnetic rotating AGB stars and non-rotating stars, producing identical abundance patterns.
上下文。中间中子捕获过程（i-process）可能发生在质子摄取事件（pie）中，这可能发生在渐近巨支（AGB）恒星的早期演化阶段。我们研究了旋转和磁性混合对低金属丰度、低质量AGB星i-过程核合成的影响。我们使用STAREVOL代码计算了[Fe/H] = - 2.5和- 1.7，初始质量为1和1.5 M⊙的AGB模型，包括一个由1160个核组成的网络，耦合到输运方程。旋转模型包括一个校准的泰勒-斯普雷特（TS）发电机，以解释从太阳金属丰度次巨星和巨星的星震观测推断出的核心旋转速率。考虑了0、30和90 km s−1的初始旋转速度，以及对磁混合的不同假设。没有磁场的旋转强烈地抑制了i过程，因为产生了初级14N，随后在PIE过程中转化为22Ne——一种强大的中子毒素。通过TS发电机加入磁场使模型恢复到接近非旋转模型的状态：强核包膜耦合抑制剪切混合并阻止初级14N合成，产生类似于非旋转模型的i-过程核合成。我们还发现，AGB阶段的旋转混合不足以影响pie的发生。质子摄取事件驱动的核合成在星震校准的磁旋转AGB恒星和非旋转恒星中进行类似，产生相同的丰度模式。
{"title":"The intermediate neutron capture process","authors":"A. Choplin, L. Siess, S. Goriely, P. Eggenberger, F. D. Moyano","doi":"10.1051/0004-6361/202557649","DOIUrl":"https://doi.org/10.1051/0004-6361/202557649","url":null,"abstract":"<i>Context.<i/> The intermediate neutron-capture process (i-process) can occur during proton ingestion events (PIEs), which may take place in the early evolutionary phases of asymptotic giant branch (AGB) stars.<i>Aims.<i/> We investigate the impact of rotational and magnetic mixing on i-process nucleosynthesis in low-metallicity, low-mass AGB stars.<i>Methods.<i/> We computed AGB models with [Fe/H] = −2.5 and −1.7 and initial masses of 1 and 1.5 <i>M<i/><sub>⊙<sub/> using the STAREVOL code, including a network of 1160 nuclei coupled to transport equations. Rotating models incorporate a calibrated Tayler-Spruit (TS) dynamo to account for core rotation rates inferred from asteroseismic observations of solar-metallicity sub-giants and giants. Initial rotation velocities of 0, 30, and 90 km s<sup>−1<sup/> were considered, along with varying assumptions for magnetic mixing.<i>Results.<i/> Rotation without magnetic fields strongly suppresses the i-process due to the production of primary <sup>14<sup/>N, which is subsequently converted into <sup>22<sup/>Ne – a potent neutron poison during the PIE. Including magnetic fields via the TS dynamo restores the models close to their non-rotating counterparts: strong core-envelope coupling suppresses shear mixing and prevents primary <sup>14<sup/>N synthesis, yielding i-process nucleosynthesis similar to non-rotating models. We also find that rotational mixing during the AGB phase is insufficient to affect the occurrence of PIEs.<i>Conclusions.<i/> Proton ingestion event-driven nucleosynthesis proceeds similarly in asteroseismic-calibrated magnetic rotating AGB stars and non-rotating stars, producing identical abundance patterns.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"290 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146098082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-30DOI: 10.1051/0004-6361/202558482
Wenjie Zhang
In this Letter, we report the detection of soft X-ray time lags – i.e., variability in the softer photons lagging behind that in the harder photons – in seven XMM–Newton observations of the tidal disruption event (TDE) candidate AT2021ehb. We find correlated variability between the soft (0.3–0.7 keV) and hard (0.9–10 keV) bands on ∼104 s timescales, and measure a soft lag of ∼500 s. This behavior is broadly consistent with the disk–corona reverberation scenario established in active galactic nuclei (AGNs). Together with the previously reported strong hard X-ray emission and broad Fe K line, our results suggest the presence of a compact corona and prominent relativistic disk reflection in AT2021ehb. The unusually high blackbody temperature (peaking at ∼200 eV) is difficult to reconcile with thermal emission from a standard accretion disk around a ∼107M⊙ black hole, and may instead be analogous to the soft excess commonly observed in AGNs, whose physical origin remains debated. Finally, the measured lags offer a possible explanation for the rapid X-ray flux decline that occurred only three days after the peak, pointing to a scenario in which the corona cools following a sudden loss of the magnetic support required to sustain it.
{"title":"Discovery of a soft X-ray lag in the tidal disruption event AT2021ehb","authors":"Wenjie Zhang","doi":"10.1051/0004-6361/202558482","DOIUrl":"https://doi.org/10.1051/0004-6361/202558482","url":null,"abstract":"In this Letter, we report the detection of soft X-ray time lags – i.e., variability in the softer photons lagging behind that in the harder photons – in seven <i>XMM–Newton<i/> observations of the tidal disruption event (TDE) candidate AT2021ehb. We find correlated variability between the soft (0.3–0.7 keV) and hard (0.9–10 keV) bands on ∼10<sup>4<sup/> s timescales, and measure a soft lag of ∼500 s. This behavior is broadly consistent with the disk–corona reverberation scenario established in active galactic nuclei (AGNs). Together with the previously reported strong hard X-ray emission and broad Fe K line, our results suggest the presence of a compact corona and prominent relativistic disk reflection in AT2021ehb. The unusually high blackbody temperature (peaking at ∼200 eV) is difficult to reconcile with thermal emission from a standard accretion disk around a ∼10<sup>7<sup/> <i>M<i/><sub>⊙<sub/> black hole, and may instead be analogous to the soft excess commonly observed in AGNs, whose physical origin remains debated. Finally, the measured lags offer a possible explanation for the rapid X-ray flux decline that occurred only three days after the peak, pointing to a scenario in which the corona cools following a sudden loss of the magnetic support required to sustain it.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"81 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146098078","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-29DOI: 10.1051/0004-6361/202557127
Q. Kral, J. Wang, J. Kammerer, S. Lacour, M. Malin, T. Winterhalder, B. Charnay, C. Perrot, P. Huet, R. Abuter, A. Amorim, W. O. Balmer, M. Benisty, J.-P. Berger, H. Beust, S. Blunt, A. Boccaletti, M. Bonnefoy, H. Bonnet, M. S. Bordoni, G. Bourdarot, W. Brandner, F. Cantalloube, P. Caselli, G. Chauvin, A. Chavez, A. Chomez, E. Choquet, V. Christiaens, Y. Clénet, V. Coudé du Foresto, A. Cridland, R. Davies, R. Dembet, J. Dexter, A. Drescher, G. Duvert, A. Eckart, F. Eisenhauer, N. M. Förster Schreiber, P. Garcia, R. Garcia Lopez, T. Gardner, E. Gendron, R. Genzel, S. Gillessen, J. H. Girard, S. Grant, X. Haubois, Th. Henning, S. Hinkley, S. Hippler, M. Houllé, Z. Hubert, L. Jocou, M. Keppler, P. Kervella, L. Kreidberg, N. T. Kurtovic, A.-M. Lagrange, V. Lapeyrère, J.-B. Le Bouquin, D. Lutz, A.-L. Maire, F. Mang, G.-D. Marleau, A. Mérand, P. Mollière, J. D. Monnier, C. Mordasini, D. Mouillet, E. Nasedkin, M. Nowak, T. Ott, G. P. P. L. Otten, C. Paladini, T. Paumard, K. Perraut, G. Perrin, O. Pfuhl, N. Pourré, L. Pueyo, D. C. Ribeiro, E. Rickman, Z. Rustamkulov, J. Shangguan, T. Shimizu, D. Sing, J. Stadler, T. Stolker, O. Straub, C. Straubmeier, E. Sturm, L. J. Tacconi, A. Vigan, F. Vincent, S. D. von Fellenberg, F. Widmann, J. Woillez, S. Yazici, K. Abd El Dayem, N. Aimar, A. Berdeu, C. Correia, D. Defrère, M. Fabricius, H. Feuchtgruber, A. Foschi, S. F. Hönig, S. Joharle, R. Laugier, O. Lai, J. Leftley, B. Lopez, F. Millour, M. Montargès, N. Morujão, H. Nowacki, J. Osorno, R. Petrov, P. O. Petrucci, S. Rabien, S. Robbe-Dubois, M. Sadun Bordoni, J. Sánchez Bermúdez, D. Santos, J. Sauter, J. Scigliuto, F. Soulez, M. Subroweit, C. Sykes
Context. This study presents the first application of high-precision astrometry to search for exomoons around substellar companions, as this field remains largely unexplored.Aims. We investigate whether the orbital motion of the companion HD 206893 B exhibits astrometric residuals consistent with the gravitational influence of an exomoon or binary planet.Methods. Using the VLTI/GRAVITY instrument, we monitored the astrometric positions of HD 206893 B and c on short (days to months) and long (yearly) timescales. This enabled us to isolate potential residual wobbles in the motion of component B attributable to an orbiting moon.Results. Our analysis reveals tentative astrometric residuals in the HD 206893 B orbit. If interpreted as an exomoon signature, these residuals correspond to a candidate (HD 206893 B I) with an orbital period of approximately 0.76 years and a mass of ~0.4 Jupiter masses. However, the origin of these residuals remains ambiguous and could be due to systematics. Complementing the astrometry, our analysis of GRAVITY R = 4000 spectroscopy for HD 206893 B confirms a clear detection of water, but no CO was found using cross-correlation. We also found that AF Lep b, and β Pic b are the best short-term candidates to look for moons with GRAVITY+.Conclusions. Our observations demonstrate the transformative potential of high-precision astrometry in the search for exomoons and proves the feasibility of the technique to detect moons with masses lower than Jupiter and potentially down to less than Neptune in optimistic cases. Crucially, further high-precision astrometric observations with VLTI/GRAVITY are essential to verify the reality and nature of this signal and apply this technique to a range of planetary systems.
{"title":"Exomoon search with VLTI/GRAVITY around the substellar companion HD 206893 B","authors":"Q. Kral, J. Wang, J. Kammerer, S. Lacour, M. Malin, T. Winterhalder, B. Charnay, C. Perrot, P. Huet, R. Abuter, A. Amorim, W. O. Balmer, M. Benisty, J.-P. Berger, H. Beust, S. Blunt, A. Boccaletti, M. Bonnefoy, H. Bonnet, M. S. Bordoni, G. Bourdarot, W. Brandner, F. Cantalloube, P. Caselli, G. Chauvin, A. Chavez, A. Chomez, E. Choquet, V. Christiaens, Y. Clénet, V. Coudé du Foresto, A. Cridland, R. Davies, R. Dembet, J. Dexter, A. Drescher, G. Duvert, A. Eckart, F. Eisenhauer, N. M. Förster Schreiber, P. Garcia, R. Garcia Lopez, T. Gardner, E. Gendron, R. Genzel, S. Gillessen, J. H. Girard, S. Grant, X. Haubois, Th. Henning, S. Hinkley, S. Hippler, M. Houllé, Z. Hubert, L. Jocou, M. Keppler, P. Kervella, L. Kreidberg, N. T. Kurtovic, A.-M. Lagrange, V. Lapeyrère, J.-B. Le Bouquin, D. Lutz, A.-L. Maire, F. Mang, G.-D. Marleau, A. Mérand, P. Mollière, J. D. Monnier, C. Mordasini, D. Mouillet, E. Nasedkin, M. Nowak, T. Ott, G. P. P. L. Otten, C. Paladini, T. Paumard, K. Perraut, G. Perrin, O. Pfuhl, N. Pourré, L. Pueyo, D. C. Ribeiro, E. Rickman, Z. Rustamkulov, J. Shangguan, T. Shimizu, D. Sing, J. Stadler, T. Stolker, O. Straub, C. Straubmeier, E. Sturm, L. J. Tacconi, A. Vigan, F. Vincent, S. D. von Fellenberg, F. Widmann, J. Woillez, S. Yazici, K. Abd El Dayem, N. Aimar, A. Berdeu, C. Correia, D. Defrère, M. Fabricius, H. Feuchtgruber, A. Foschi, S. F. Hönig, S. Joharle, R. Laugier, O. Lai, J. Leftley, B. Lopez, F. Millour, M. Montargès, N. Morujão, H. Nowacki, J. Osorno, R. Petrov, P. O. Petrucci, S. Rabien, S. Robbe-Dubois, M. Sadun Bordoni, J. Sánchez Bermúdez, D. Santos, J. Sauter, J. Scigliuto, F. Soulez, M. Subroweit, C. Sykes","doi":"10.1051/0004-6361/202557127","DOIUrl":"https://doi.org/10.1051/0004-6361/202557127","url":null,"abstract":"<i>Context<i/>. This study presents the first application of high-precision astrometry to search for exomoons around substellar companions, as this field remains largely unexplored.<i>Aims<i/>. We investigate whether the orbital motion of the companion HD 206893 B exhibits astrometric residuals consistent with the gravitational influence of an exomoon or binary planet.<i>Methods<i/>. Using the VLTI/GRAVITY instrument, we monitored the astrometric positions of HD 206893 B and c on short (days to months) and long (yearly) timescales. This enabled us to isolate potential residual wobbles in the motion of component B attributable to an orbiting moon.<i>Results<i/>. Our analysis reveals tentative astrometric residuals in the HD 206893 B orbit. If interpreted as an exomoon signature, these residuals correspond to a candidate (HD 206893 B I) with an orbital period of approximately 0.76 years and a mass of ~0.4 Jupiter masses. However, the origin of these residuals remains ambiguous and could be due to systematics. Complementing the astrometry, our analysis of GRAVITY <i>R<i/> = 4000 spectroscopy for HD 206893 B confirms a clear detection of water, but no CO was found using cross-correlation. We also found that AF Lep b, and <i>β<i/> Pic b are the best short-term candidates to look for moons with GRAVITY+.<i>Conclusions<i/>. Our observations demonstrate the transformative potential of high-precision astrometry in the search for exomoons and proves the feasibility of the technique to detect moons with masses lower than Jupiter and potentially down to less than Neptune in optimistic cases. Crucially, further high-precision astrometric observations with VLTI/GRAVITY are essential to verify the reality and nature of this signal and apply this technique to a range of planetary systems.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"2 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146073390","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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