Pub Date : 2026-02-04DOI: 10.1051/0004-6361/202557499
Suyeon Son, Minjin Kim, Luis C. Ho
Temporal asymmetry in the flux variability of active galactic nuclei (AGNs) offers key insights into the physical mechanisms driving AGN variability. In this study, we investigated the variability of the torus by analyzing temporal asymmetry in the mid-infrared (MIR) continuum. We compared ensemble structure functions between the brightening and dimming phases for AGNs at 0.15 < z < 0.4, using monitoring data in the optical from the Zwicky Transient Facility and in the MIR from the Near-Earth Object Wide-field Infrared Survey Explorer. We found that AGNs with bluer optical-to-MIR colors exhibit positive temporal asymmetry in the MIR, indicating that their variability amplitude is larger when brightening. Conversely, those with redder colors show negative asymmetry, exhibiting larger variability amplitude when decaying. However, there is no significant temporal asymmetry in the g band variability driven by the accretion disk, suggesting that the temporal asymmetry in the MIR continuum primarily originates from intrinsic processes in the torus instead of the reflection of the ultraviolet-optical variability from the accretion disk. Analysis of the composite light curves revealed that AGNs with bluer optical-to-MIR colors tend to brighten gradually in the MIR, leading to the observed temporal asymmetry. This finding suggests that hot-dust-rich AGNs evolve with a gradual decline in hot dust emission, while hot-dust-poor AGNs are associated with a steady increase.
活动星系核（AGN）通量变异性的时间不对称性为了解驱动AGN变异性的物理机制提供了关键的见解。在这项研究中，我们通过分析中红外（MIR）连续体的时间不对称性来研究环面变异性。我们比较了在吸积盘驱动下，agn在0.15 z g波段变亮和变暗阶段的系综结构函数，表明MIR连续体的时间不对称性主要来自环面的固有过程，而不是来自吸积盘的紫外光学变率的反射。复合光曲线分析表明，具有较蓝光色的agn在MIR中逐渐变亮，导致观测到的时间不对称。这一发现表明，富含热尘的agn随着热尘排放的逐渐减少而演变，而缺乏热尘的agn则与热尘排放的稳定增加有关。
{"title":"Asymmetric torus variability in active galactic nuclei driven by global brightening and dimming","authors":"Suyeon Son, Minjin Kim, Luis C. Ho","doi":"10.1051/0004-6361/202557499","DOIUrl":"https://doi.org/10.1051/0004-6361/202557499","url":null,"abstract":"Temporal asymmetry in the flux variability of active galactic nuclei (AGNs) offers key insights into the physical mechanisms driving AGN variability. In this study, we investigated the variability of the torus by analyzing temporal asymmetry in the mid-infrared (MIR) continuum. We compared ensemble structure functions between the brightening and dimming phases for AGNs at 0.15 < <i>z<i/> < 0.4, using monitoring data in the optical from the Zwicky Transient Facility and in the MIR from the Near-Earth Object Wide-field Infrared Survey Explorer. We found that AGNs with bluer optical-to-MIR colors exhibit positive temporal asymmetry in the MIR, indicating that their variability amplitude is larger when brightening. Conversely, those with redder colors show negative asymmetry, exhibiting larger variability amplitude when decaying. However, there is no significant temporal asymmetry in the <i>g<i/> band variability driven by the accretion disk, suggesting that the temporal asymmetry in the MIR continuum primarily originates from intrinsic processes in the torus instead of the reflection of the ultraviolet-optical variability from the accretion disk. Analysis of the composite light curves revealed that AGNs with bluer optical-to-MIR colors tend to brighten gradually in the MIR, leading to the observed temporal asymmetry. This finding suggests that hot-dust-rich AGNs evolve with a gradual decline in hot dust emission, while hot-dust-poor AGNs are associated with a steady increase.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"1 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146115837","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 : 2026-02-04DOI: 10.1051/0004-6361/202557526
Z. Vashalomidze, C. Quintero Noda, T. V. Zaqarashvili, M. Benko, D. Kuridze, P. Gömöry, J. Rybák, S. Lomineishvili, M. Collados, C. Denker, M. Verma, C. Kuckein, A. Asensio Ramos
We performed high-spatial-resolution spectropolarimetric observations of the active region NOAA 13363 during a C-class flare with the Gregor Infrared Spectrograph (GRIS) on 16 July 2023. We examined the coupling between the photosphere and the chromosphere, studying the polarimetric signals during a period that encompasses the decaying phase of a C-class flare and the appearance of a new C-class flare at the same location. We focused on the analysis of various spectral lines. In particular, we studied the Si I 10827 Å, Ca I 10833.4 Å, Na I 10834.9 Å, and Ca I 10838.9 Å photospheric lines, as well as the He I 10830 Å triplet. GRIS data revealed the presence of flare-related red- and blueshifted spectral line components, reaching Doppler velocities of up to ∼90 km s −1, and complex Si I profiles in which the He I spectral line contribution is blueshifted. In contrast, the photospheric Ca I and Na I transitions remain unchanged, indicating that the flare did not modify the physical conditions of the lower photosphere. We combined that information with simultaneous imaging in the Ca II H line and TiO band with the improved High-resolution Fast Imager (HiFI+), finding that the flare emission did not affect the inverse granulation or nearby plage, in agreement with the results from GRIS. We also complemented the previous studies with a forward modelling computation, concluding that the He I spectral line emission reflects a complex response of the flaring chromosphere. Radiative excitation from coronal EUV irradiation, energy deposition by flare-accelerated electrons, and dynamic field-aligned plasma flows likely act together to produce the observed supersonic downflows and upflows. We plan to expand these findings through inversions of the He I 10830 Å triplet signals in the future.
2023年7月16日，利用格雷戈尔红外光谱仪（GRIS）对c级耀斑活动区域NOAA 13363进行了高空间分辨率的光谱偏振观测。我们研究了光球层和色球层之间的耦合，研究了c级耀斑的衰减阶段和在同一位置出现新的c级耀斑期间的偏振信号。我们着重分析了各种光谱线。特别是,我们研究了Si 我10827,Ca 我10833.4,Na 我10834.9,我Ca photospheric 10838.9线,以及他 我10830三联体。GRIS数据揭示了与闪焰相关的红移和蓝移谱线成分的存在，其多普勒速度高达~ 90 km s−1，以及He I谱线贡献为蓝移的复杂Si I剖面。相比之下，光球Ca I和Na I的跃迁保持不变，表明耀斑没有改变下层光球的物理条件。我们将这些信息与Ca II H线和TiO波段的同时成像与改进的高分辨率快速成像仪（HiFI+）相结合，发现耀斑发射不影响逆颗粒或附近斑块，与GRIS的结果一致。我们还用正演模拟计算补充了先前的研究，得出He I光谱线发射反映了耀斑色球的复杂响应。日冕极紫外光照射的辐射激发、耀斑加速电子的能量沉积和动态场对准等离子体流可能共同作用，产生了观测到的超音速下行和上行。我们计划在未来通过He I 10830 Å三重态信号的反转来扩展这些发现。
{"title":"Infrared spectropolarimetry of a C-class solar flare footpoint plasma","authors":"Z. Vashalomidze, C. Quintero Noda, T. V. Zaqarashvili, M. Benko, D. Kuridze, P. Gömöry, J. Rybák, S. Lomineishvili, M. Collados, C. Denker, M. Verma, C. Kuckein, A. Asensio Ramos","doi":"10.1051/0004-6361/202557526","DOIUrl":"https://doi.org/10.1051/0004-6361/202557526","url":null,"abstract":"We performed high-spatial-resolution spectropolarimetric observations of the active region NOAA 13363 during a C-class flare with the Gregor Infrared Spectrograph (GRIS) on 16 July 2023. We examined the coupling between the photosphere and the chromosphere, studying the polarimetric signals during a period that encompasses the decaying phase of a C-class flare and the appearance of a new C-class flare at the same location. We focused on the analysis of various spectral lines. In particular, we studied the Si I 10827 Å, Ca I 10833.4 Å, Na I 10834.9 Å, and Ca I 10838.9 Å photospheric lines, as well as the He I 10830 Å triplet. GRIS data revealed the presence of flare-related red- and blueshifted spectral line components, reaching Doppler velocities of up to ∼90 km s <sup>−1<sup/>, and complex Si I profiles in which the He I spectral line contribution is blueshifted. In contrast, the photospheric Ca I and Na I transitions remain unchanged, indicating that the flare did not modify the physical conditions of the lower photosphere. We combined that information with simultaneous imaging in the Ca II H line and TiO band with the improved High-resolution Fast Imager (HiFI+), finding that the flare emission did not affect the inverse granulation or nearby plage, in agreement with the results from GRIS. We also complemented the previous studies with a forward modelling computation, concluding that the He I spectral line emission reflects a complex response of the flaring chromosphere. Radiative excitation from coronal EUV irradiation, energy deposition by flare-accelerated electrons, and dynamic field-aligned plasma flows likely act together to produce the observed supersonic downflows and upflows. We plan to expand these findings through inversions of the He I 10830 Å triplet signals in the future.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"108 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146115749","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 : 2026-02-04DOI: 10.1051/0004-6361/202452890
Arianna Nigioni, Diego Turrini, Camilla Danielski, Danae Polychroni, John E. Chambers
<i>Context<i/>. Planetary formation might occur at different stages of the stellar evolution. In particular, theoretical studies have been focusing on addressing whether formation can occur around compact binaries that evolved beyond the main sequence. Formation of second-generation planets has been tested in circumbinary disks formed by the ejection of stellar material from binaries composed of either a main-sequence star and a white dwarf or a double white dwarf (DWD). In the latter case, formation appears to be common and to create sub-Neptunian, Neptunian, and giant planets that can migrate within 1 au of the central binary. Nevertheless, the orbital stability of these systems has yet to be studied.<i>Aims<i/>. We investigate whether planetary systems that formed around compact DWDs in nonresonant and resonant configurations can be dynamically stable over a timescale of a few million years.<i>Methods<i/>. We performed <i><b>N<b/><i/>-body simulations of circumbinary multiplanetary systems that initially hosted two, three, four or five planets by employing a hybrid symplectic integrator made specifically for circumbinary systems. We recorded the catastrophic events that planetary systems experience and employed a variety of metrics, such as orbital spacing, variation in the center of mass, and normalized angular momentum deficit, to explore the outcomes of their long-term evolution. Furthermore, we evaluated the potential for detecting these systems in their final configurations with the Laser Interferometer Space Antenna mission by measuring the overall amplitude shift in the gravitational-wave frequency induced by their planets.<i>Results<i/>. Our results show that planets orbiting DWDs can be stable over the studied timescales. While planetary systems starting with two planets are more likely to survive unaltered, planetary systems with three, four, or five planets experience catastrophic events that cause them to lose some of their original planets. At the end of their phases of dynamical instability, the five-planet population is completely disrupted, and most of the systems host only two surviving planets. This increases the number of two-planet systems by 122% with respect to their initial abundance and creates a single-planet population of 7% of all systems. Additionally, the four-planet population decreases by 56.1% and the three-planet population by 22.5%. Finally, 7.7% of the systems are disrupted; they initially hosted more than two planets. Most of the systems that in the end only host a single planet are potential candidates for the Laser Interferometer Space Antenna mission. A handful of multiplanet systems might be detected. Finally, we provide a formula for estimating the amplitude shift in the gravitational-wave frequency for multiplanet systems orbiting DWDs.<i>Conclusions<i/>. Throughout our analysis, we highlight the importance of characterizing the system orbits and estimating their normalized angular momentum deficit in
{"title":"The quest for Magrathea planets","authors":"Arianna Nigioni, Diego Turrini, Camilla Danielski, Danae Polychroni, John E. Chambers","doi":"10.1051/0004-6361/202452890","DOIUrl":"https://doi.org/10.1051/0004-6361/202452890","url":null,"abstract":"<i>Context<i/>. Planetary formation might occur at different stages of the stellar evolution. In particular, theoretical studies have been focusing on addressing whether formation can occur around compact binaries that evolved beyond the main sequence. Formation of second-generation planets has been tested in circumbinary disks formed by the ejection of stellar material from binaries composed of either a main-sequence star and a white dwarf or a double white dwarf (DWD). In the latter case, formation appears to be common and to create sub-Neptunian, Neptunian, and giant planets that can migrate within 1 au of the central binary. Nevertheless, the orbital stability of these systems has yet to be studied.<i>Aims<i/>. We investigate whether planetary systems that formed around compact DWDs in nonresonant and resonant configurations can be dynamically stable over a timescale of a few million years.<i>Methods<i/>. We performed <i><b>N<b/><i/>-body simulations of circumbinary multiplanetary systems that initially hosted two, three, four or five planets by employing a hybrid symplectic integrator made specifically for circumbinary systems. We recorded the catastrophic events that planetary systems experience and employed a variety of metrics, such as orbital spacing, variation in the center of mass, and normalized angular momentum deficit, to explore the outcomes of their long-term evolution. Furthermore, we evaluated the potential for detecting these systems in their final configurations with the Laser Interferometer Space Antenna mission by measuring the overall amplitude shift in the gravitational-wave frequency induced by their planets.<i>Results<i/>. Our results show that planets orbiting DWDs can be stable over the studied timescales. While planetary systems starting with two planets are more likely to survive unaltered, planetary systems with three, four, or five planets experience catastrophic events that cause them to lose some of their original planets. At the end of their phases of dynamical instability, the five-planet population is completely disrupted, and most of the systems host only two surviving planets. This increases the number of two-planet systems by 122% with respect to their initial abundance and creates a single-planet population of 7% of all systems. Additionally, the four-planet population decreases by 56.1% and the three-planet population by 22.5%. Finally, 7.7% of the systems are disrupted; they initially hosted more than two planets. Most of the systems that in the end only host a single planet are potential candidates for the Laser Interferometer Space Antenna mission. A handful of multiplanet systems might be detected. Finally, we provide a formula for estimating the amplitude shift in the gravitational-wave frequency for multiplanet systems orbiting DWDs.<i>Conclusions<i/>. Throughout our analysis, we highlight the importance of characterizing the system orbits and estimating their normalized angular momentum deficit in ","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"280 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146115799","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 : 2026-02-04DOI: 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}
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