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}
Pub Date : 2026-01-29DOI: 10.1051/0004-6361/202558046
I. A. Zinchenko, J. M. Vílchez, C. Kehrig, P. Papaderos, J. E. Méndez-Delgado
We present new precise measurements of the electron temperatures and oxygen abundances in the southeast knot of I Zw 18, one of the most metal poor blue compact dwarf galaxies known. We used spectroscopic data from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1). For the first time in I Zw 18, we directly measured the electron temperature in the low-ionization zone using the rarely detected [O II]λλ7320,7330 doublet. We also detected the [O III]λ4363 and [S III]λ6312 auroral lines, which are associated with high- and intermediate-ionization zones, respectively. We derived Te([O III]) = 21 200 ± 860 K, Te([O II]) = 16 170 ± 950 K, and Te([S III]) = 17 290±1750, which highlights a significant temperature difference between the ionization zones. Using these direct temperature measurements, we determined a total oxygen abundance of 12+log(O/H) = 7.066 ± 0.046, log(N/O) = –1.509 ± 0.097, and log(S/O) = –1.558 ± 0.041. Our results extend the calibration of t2 − t3 relations to the highest temperatures and provide important anchor points for the temperature structure of extremely metal-poor H II regions, including high-redshift galaxies, for which direct temperature measurements are especially challenging.
{"title":"First direct electron temperature measurement in [O II] zone in I Zw 18","authors":"I. A. Zinchenko, J. M. Vílchez, C. Kehrig, P. Papaderos, J. E. Méndez-Delgado","doi":"10.1051/0004-6361/202558046","DOIUrl":"https://doi.org/10.1051/0004-6361/202558046","url":null,"abstract":"We present new precise measurements of the electron temperatures and oxygen abundances in the southeast knot of I Zw 18, one of the most metal poor blue compact dwarf galaxies known. We used spectroscopic data from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1). For the first time in I Zw 18, we directly measured the electron temperature in the low-ionization zone using the rarely detected [O II]<i>λλ<i/>7320,7330 doublet. We also detected the [O III]<i>λ<i/>4363 and [S III]<i>λ<i/>6312 auroral lines, which are associated with high- and intermediate-ionization zones, respectively. We derived T<sub><i>e<i/><sub/>([O III]) = 21 200 ± 860 K, T<sub><i>e<i/><sub/>([O II]) = 16 170 ± 950 K, and T<sub><i>e<i/><sub/>([S III]) = 17 290±1750, which highlights a significant temperature difference between the ionization zones. Using these direct temperature measurements, we determined a total oxygen abundance of 12+log(O/H) = 7.066 ± 0.046, log(N/O) = –1.509 ± 0.097, and log(S/O) = –1.558 ± 0.041. Our results extend the calibration of <i>t<i/><sub>2<sub/> − <i>t<i/><sub>3<sub/> relations to the highest temperatures and provide important anchor points for the temperature structure of extremely metal-poor H II regions, including high-redshift galaxies, for which direct temperature measurements are especially challenging.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"43 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146073388","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: 10.1051/0004-6361/202555798
M. Archipley, A. Hryciuk, L. E. Bleem, K. Kornoelje, M. Klein, A. J. Anderson, B. Ansarinejad, M. Aravena, L. Balkenhol, P. S. Barry, K. Benabed, A. N. Bender, B. A. Benson, F. Bianchini, S. Bocquet, F. R. Bouchet, E. Camphuis, M. G. Campitiello, J. E. Carlstrom, J. Cathey, C. L. Chang, S. C. Chapman, P. Chaubal, P. M. Chichura, A. Chokshi, T.-L. Chou, A. Coerver, T. M. Crawford, C. Daley, T. de Haan, R. P. Deane, K. R. Dibert, M. A. Dobbs, M. Doohan, A. Doussot, D. Dutcher, W. Everett, C. Feng, K. R. Ferguson, K. Fichman, B. Floyd, A. Foster, S. Galli, A. E. Gambrel, R. W. Gardner, F. Ge, N. Goeckner-Wald, A. Gonzalez, S. Grandis, T. R. Greve, R. Gualtieri, F. Guidi, S. Guns, N. W. Halverson, R. Hill, E. Hivon, G. P. Holder, W. L. Holzapfel, J. C. Hood, N. Huang, F. Kéruzoré, A. R. Khalife, L. Knox, M. Korman, C.-L. Kuo, K. Levy, A. E. Lowitz, C. Lu, G. P. Lynch, A. Maniyar, E. S. Martsen, F. Menanteau, M. Millea, J. Montgomery, Y. Nakato, T. Natoli, G. I. Noble, Y. Omori, A. Ouellette, Z. Pan, K. A. Phadke, A. W. Pollak, K. Prabhu, W. Quan, S. Raghunathan, M. Rahimi, A. Rahlin, C. L. Reichardt, C. Reuter, M. Rouble, J. E. Ruhl, E. Schiappucci, A. Simpson, J. A. Sobrin, B. Stalder, A. A. Stark, N. Sulzenauer, C. Tandoi, B. Thorne, C. Trendafilova, C. Umilta, J. D. Vieira, A. Vitrier, D. Vizgan, Y. Wan, A. Weiß, N. Whitehorn, W. L. K. Wu, M. R. Young, J. A. Zebrowski, D. Zhou
Context. The South Pole Telescope third-generation camera (SPT-3G) has observed over 10 000 square degrees of sky at 95, 150, and 220 GHz (3.3, 2.0, 1.4 mm, respectively) and will significantly overlap the ongoing 14 000 square-degree Euclid Wide Survey. The Euclid collaboration recently released Euclid Deep Field South (EDF-S) observations of 23 square degrees at wide field depths in the first quick data release (Q1).Aims. With the goal of releasing complementary millimeter-wave data and encouraging legacy science, we performed dedicated observations of a 57-square-degree field overlapping the EDF-S.Methods. The observing time totaled 20 days, and we reached noise depths of 4.3, 3.8, and 13.2 μK-arcmin at 95, 150, and 220 GHz, respectively.Results. In this work we present the temperature maps and two catalogs constructed from these data. The emissive source catalog contains 601 objects (334 inside EDF-S) with 54% synchrotron-dominated sources and 46% thermal dust emission-dominated sources. The 5σ detection thresholds are 1.7, 2.0, and 6.5 mJy in the three bands. The cluster catalog contains 217 cluster candidates (121 inside EDF-S) with median mass M500c = 2.12 × 1014M⊙/h70 and median redshift z = 0.70, corresponding to an order-of-magnitude improvement in cluster density over previous tSZ-selected catalogs in this region (3.81 clusters per square degree).Conclusions. The overlap between SPT and Euclid data will enable a range of multiwavelength studies of the aforementioned source populations. This work serves as the first step toward joint projects between SPT and Euclid and provides a rich dataset containing information on galaxies, clusters, and their environments.
{"title":"Millimeter-wave observations of Euclid Deep Field South using the South Pole Telescope","authors":"M. Archipley, A. Hryciuk, L. E. Bleem, K. Kornoelje, M. Klein, A. J. Anderson, B. Ansarinejad, M. Aravena, L. Balkenhol, P. S. Barry, K. Benabed, A. N. Bender, B. A. Benson, F. Bianchini, S. Bocquet, F. R. Bouchet, E. Camphuis, M. G. Campitiello, J. E. Carlstrom, J. Cathey, C. L. Chang, S. C. Chapman, P. Chaubal, P. M. Chichura, A. Chokshi, T.-L. Chou, A. Coerver, T. M. Crawford, C. Daley, T. de Haan, R. P. Deane, K. R. Dibert, M. A. Dobbs, M. Doohan, A. Doussot, D. Dutcher, W. Everett, C. Feng, K. R. Ferguson, K. Fichman, B. Floyd, A. Foster, S. Galli, A. E. Gambrel, R. W. Gardner, F. Ge, N. Goeckner-Wald, A. Gonzalez, S. Grandis, T. R. Greve, R. Gualtieri, F. Guidi, S. Guns, N. W. Halverson, R. Hill, E. Hivon, G. P. Holder, W. L. Holzapfel, J. C. Hood, N. Huang, F. Kéruzoré, A. R. Khalife, L. Knox, M. Korman, C.-L. Kuo, K. Levy, A. E. Lowitz, C. Lu, G. P. Lynch, A. Maniyar, E. S. Martsen, F. Menanteau, M. Millea, J. Montgomery, Y. Nakato, T. Natoli, G. I. Noble, Y. Omori, A. Ouellette, Z. Pan, K. A. Phadke, A. W. Pollak, K. Prabhu, W. Quan, S. Raghunathan, M. Rahimi, A. Rahlin, C. L. Reichardt, C. Reuter, M. Rouble, J. E. Ruhl, E. Schiappucci, A. Simpson, J. A. Sobrin, B. Stalder, A. A. Stark, N. Sulzenauer, C. Tandoi, B. Thorne, C. Trendafilova, C. Umilta, J. D. Vieira, A. Vitrier, D. Vizgan, Y. Wan, A. Weiß, N. Whitehorn, W. L. K. Wu, M. R. Young, J. A. Zebrowski, D. Zhou","doi":"10.1051/0004-6361/202555798","DOIUrl":"https://doi.org/10.1051/0004-6361/202555798","url":null,"abstract":"<i>Context<i/>. The South Pole Telescope third-generation camera (SPT-3G) has observed over 10 000 square degrees of sky at 95, 150, and 220 GHz (3.3, 2.0, 1.4 mm, respectively) and will significantly overlap the ongoing 14 000 square-degree <i>Euclid<i/> Wide Survey. The <i>Euclid<i/> collaboration recently released <i>Euclid<i/> Deep Field South (EDF-S) observations of 23 square degrees at wide field depths in the first quick data release (Q1).<i>Aims<i/>. With the goal of releasing complementary millimeter-wave data and encouraging legacy science, we performed dedicated observations of a 57-square-degree field overlapping the EDF-S.<i>Methods<i/>. The observing time totaled 20 days, and we reached noise depths of 4.3, 3.8, and 13.2 μK-arcmin at 95, 150, and 220 GHz, respectively.<i>Results<i/>. In this work we present the temperature maps and two catalogs constructed from these data. The emissive source catalog contains 601 objects (334 inside EDF-S) with 54% synchrotron-dominated sources and 46% thermal dust emission-dominated sources. The 5σ detection thresholds are 1.7, 2.0, and 6.5 mJy in the three bands. The cluster catalog contains 217 cluster candidates (121 inside EDF-S) with median mass <i>M<i/><sub>500c<sub/> = 2.12 × 10<sup>14<sup/> <i>M<i/><sub>⊙<sub/><i>/h<i/><sub>70<sub/> and median redshift <i>z<i/> = 0.70, corresponding to an order-of-magnitude improvement in cluster density over previous tSZ-selected catalogs in this region (3.81 clusters per square degree).<i>Conclusions<i/>. The overlap between SPT and <i>Euclid<i/> data will enable a range of multiwavelength studies of the aforementioned source populations. This work serves as the first step toward joint projects between SPT and <i>Euclid<i/> and provides a rich dataset containing information on galaxies, clusters, and their environments.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"281 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146073389","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: 10.1051/0004-6361/202558345
B. Mosser, M. Takata, C. Pinçon, M. S. Cunha, M. Vrard, K. Belkacem, S. Deheuvels, M. Matteuzzi
Context. Dipole mixed modes observed in the oscillation pattern of red giant stars probe the radiative regions in the stellar core.Aims. Oscillation spectra of helium-core-burning stars sometimes show extra peaks that remain unexplained by the dipole mixed-mode pattern expected from the coupling of a radiative cavity in the stellar core and a pressure cavity in the stellar envelope.Methods. We use the asymptotic expansion developed for a multi-cavity star in order to characterize these extra peaks.Results. The analytical resonance condition of the multi-cavity gravito-acoustic modes, with two inner gravity cavities and an outer pressure cavity, helps us explain that the apparent extra peaks are dipole mixed modes that follow the three-cavity oscillation pattern. The derivation of the two asymptotic period spacings associated with the two distinct regions in the radiative core provides an estimate of the full radiative cavity.Conclusions. Our results provide new constraints for analyzing the overshoot or mixing in the core of helium-core-burning stars. An important structure discontinuity inside the radiative core may explain the larger than expected observed period spacings.
{"title":"Extra modes in helium-core-burning stars probing an infra core cavity","authors":"B. Mosser, M. Takata, C. Pinçon, M. S. Cunha, M. Vrard, K. Belkacem, S. Deheuvels, M. Matteuzzi","doi":"10.1051/0004-6361/202558345","DOIUrl":"https://doi.org/10.1051/0004-6361/202558345","url":null,"abstract":"<i>Context.<i/> Dipole mixed modes observed in the oscillation pattern of red giant stars probe the radiative regions in the stellar core.<i>Aims.<i/> Oscillation spectra of helium-core-burning stars sometimes show extra peaks that remain unexplained by the dipole mixed-mode pattern expected from the coupling of a radiative cavity in the stellar core and a pressure cavity in the stellar envelope.<i>Methods.<i/> We use the asymptotic expansion developed for a multi-cavity star in order to characterize these extra peaks.<i>Results.<i/> The analytical resonance condition of the multi-cavity gravito-acoustic modes, with two inner gravity cavities and an outer pressure cavity, helps us explain that the apparent extra peaks are dipole mixed modes that follow the three-cavity oscillation pattern. The derivation of the two asymptotic period spacings associated with the two distinct regions in the radiative core provides an estimate of the full radiative cavity.<i>Conclusions.<i/> Our results provide new constraints for analyzing the overshoot or mixing in the core of helium-core-burning stars. An important structure discontinuity inside the radiative core may explain the larger than expected observed period spacings.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"8 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146073391","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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