Pub Date : 2025-12-24DOI: 10.1051/0004-6361/202557322
J.-F. Donati, P. I. Cristofari, C. Moutou, A. Lavail, J. Bouvier, S. H. P. Alencar, P. Petit, A. Carmona, X. Delfosse
We outline in this paper observations of the young pre-main-sequence low-mass star TWA 7 hosting a debris disk and a distant planet. Using data collected with the near-infrared SPIRou spectropolarimeter and precision velocimeter at the Canada-France-Hawaii Telescope from early 2019 to mid 2021, we detected the magnetic field of TWA 7 from the circularly polarized Zeeman signatures and Zeeman broadening of atomic spectral lines and the rotational modulation of its longitudinal component at the known stellar rotation period (of 5.012 ± 0.007 d). We then modeled the large-scale and small-scale magnetic properties of TWA 7 using Zeeman-Doppler imaging. We find that TWA 7 hosted a mainly poloidal field that significantly evolved from 2019 to 2021 and that the dipole component became stronger (increasing from 0.5 kG in 2019 to 0.7 kG in 2021) and less inclined to the stellar rotation axis (from 22° in 2019 to 15° in 2021). We also analyzed the radial velocities of TWA 7 derived from the SPIRou data and found a tentative planet signature at a period of 15.2 d (with aliases at 20.8 and 30.4 d), which is very close to the detection limit of our data and would correspond to a 0.17 M♃ planet at a distance of 0.09 au if confirmed. Finally, we report that the 1083 nm He I and 1282 nm Paβ lines of TWA 7 are modulated with a period of 6.6 d, different from the rotation period. This potentially hints at the presence of a close-in planet triggering star-planet interactions.
{"title":"Searching for close-in planets around TWA 7 with SPIRou","authors":"J.-F. Donati, P. I. Cristofari, C. Moutou, A. Lavail, J. Bouvier, S. H. P. Alencar, P. Petit, A. Carmona, X. Delfosse","doi":"10.1051/0004-6361/202557322","DOIUrl":"https://doi.org/10.1051/0004-6361/202557322","url":null,"abstract":"We outline in this paper observations of the young pre-main-sequence low-mass star TWA 7 hosting a debris disk and a distant planet. Using data collected with the near-infrared SPIRou spectropolarimeter and precision velocimeter at the Canada-France-Hawaii Telescope from early 2019 to mid 2021, we detected the magnetic field of TWA 7 from the circularly polarized Zeeman signatures and Zeeman broadening of atomic spectral lines and the rotational modulation of its longitudinal component at the known stellar rotation period (of 5.012 ± 0.007 d). We then modeled the large-scale and small-scale magnetic properties of TWA 7 using Zeeman-Doppler imaging. We find that TWA 7 hosted a mainly poloidal field that significantly evolved from 2019 to 2021 and that the dipole component became stronger (increasing from 0.5 kG in 2019 to 0.7 kG in 2021) and less inclined to the stellar rotation axis (from 22<sup>°<sup/> in 2019 to 15<sup>°<sup/> in 2021). We also analyzed the radial velocities of TWA 7 derived from the SPIRou data and found a tentative planet signature at a period of 15.2 d (with aliases at 20.8 and 30.4 d), which is very close to the detection limit of our data and would correspond to a 0.17 M<sub>♃<sub/> planet at a distance of 0.09 au if confirmed. Finally, we report that the 1083 nm He I and 1282 nm Pa<i>β<i/> lines of TWA 7 are modulated with a period of 6.6 d, different from the rotation period. This potentially hints at the presence of a close-in planet triggering star-planet interactions.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"41 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823905","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 : 2025-12-23DOI: 10.1051/0004-6361/202554934
K. Youakim, K. Lind
Context. The Milky Way halo has been built-up over cosmic time through the accretion and dissolution of star clusters and dwarf galaxies as well as through their complex interactions with the Galactic disc. Traces of these accreted structures persist to the present day in the chemical and kinematic properties of stars and their orbits and allow for the disentangling of the accretion history of the Galaxy through observations of Milky Way stars.Aims. We utilised 6D phase-space information in combination with [Fe/H] measurements to facilitate a clustering analysis of stars using their kinematics and chemistry simultaneously, a technique known as chemo-kinematic tagging. We aim to associate large halo substructure groups with Milky Way halo globular clusters, stellar streams, and satellite galaxies in order to investigate the common origins of these groups of structures.Methods. We implemented t-distributed stochastic neighbour embedding (t-SNE) to perform dimensionality reduction and identify stars from clusters and streams that are co-localised in the kinematic and chemical parameter space. We used the orbital parameters E, Jr, Jz, Lz, rapo, rperi, and eccentricity as well as [Fe/H] as input into the algorithm, and we performed a clustering analysis for a sample of 5347 stars from 229 individual Milky Way substructures.Results. Most notably, we recovered several large-scale structures that have been reported in the literature, including GSE, Thamnos, Sequoia, I’itoi, LMS-1/Wukong, Sagittarius, Kraken/Koala, the splashed disc, and a candidate structure recently found in the literature. We assigned globular cluster populations to each of these accreted structures and find that 44% of Milky Way globular clusters are consistent with having an accreted origin. In addition, we find that the chemo-dynamic properties of Omega Cen are consistent with a common accretion with the Thamnos structure. Finally, we identified many small-scale structures, including several stream-progenitor associations, and a connection between the Orphan-Chenab stream and the Grus II ultra-faint dwarf galaxy, which supports previous findings that these two objects were brought into the Galaxy in the same accretion event.
{"title":"Identifying substructure associations in the Milky Way halo using chemo-kinematic tagging","authors":"K. Youakim, K. Lind","doi":"10.1051/0004-6361/202554934","DOIUrl":"https://doi.org/10.1051/0004-6361/202554934","url":null,"abstract":"<i>Context<i/>. The Milky Way halo has been built-up over cosmic time through the accretion and dissolution of star clusters and dwarf galaxies as well as through their complex interactions with the Galactic disc. Traces of these accreted structures persist to the present day in the chemical and kinematic properties of stars and their orbits and allow for the disentangling of the accretion history of the Galaxy through observations of Milky Way stars.<i>Aims<i/>. We utilised 6D phase-space information in combination with [Fe/H] measurements to facilitate a clustering analysis of stars using their kinematics and chemistry simultaneously, a technique known as chemo-kinematic tagging. We aim to associate large halo substructure groups with Milky Way halo globular clusters, stellar streams, and satellite galaxies in order to investigate the common origins of these groups of structures.<i>Methods<i/>. We implemented t-distributed stochastic neighbour embedding (t-SNE) to perform dimensionality reduction and identify stars from clusters and streams that are co-localised in the kinematic and chemical parameter space. We used the orbital parameters E, J<sub><i>r<i/><sub/>, J<sub><i>z<i/><sub/>, L<sub><i>z<i/><sub/>, r<sub><i>apo<i/><sub/>, r<sub><i>peri<i/><sub/>, and eccentricity as well as [Fe/H] as input into the algorithm, and we performed a clustering analysis for a sample of 5347 stars from 229 individual Milky Way substructures.<i>Results<i/>. Most notably, we recovered several large-scale structures that have been reported in the literature, including GSE, Thamnos, Sequoia, I’itoi, LMS-1/Wukong, Sagittarius, Kraken/Koala, the splashed disc, and a candidate structure recently found in the literature. We assigned globular cluster populations to each of these accreted structures and find that 44% of Milky Way globular clusters are consistent with having an accreted origin. In addition, we find that the chemo-dynamic properties of Omega Cen are consistent with a common accretion with the Thamnos structure. Finally, we identified many small-scale structures, including several stream-progenitor associations, and a connection between the Orphan-Chenab stream and the Grus II ultra-faint dwarf galaxy, which supports previous findings that these two objects were brought into the Galaxy in the same accretion event.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"27 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145813716","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 : 2025-12-23DOI: 10.1051/0004-6361/202557330
Dexin Lai, Tao Li, Sébastien Lebonnois, Maxence Lefèvre
Context. Stationary waves play a crucial role in vertically transporting momentum and energy in Venus’s atmosphere. Their global contributions (approximately −0.1 m s−1 day−1 at the upper cloud) are smaller than those of planetary-scale waves and meridional circulation (approximately ±1.0 m s−1 day−1), but stationary waves exert strong regional control, shaping the longitudinal structure of the super-rotating flow above highlands. Observations have linked wave signatures near the cloud top (~70 km) to underlying highland regions. However, their vertical propagation characteristics and contributions to the morphology of super-rotation remain poorly understood.Aims. This study aims to characterize the structure, variability, and propagation of stationary waves in Venus’s atmosphere and to evaluate their role in modulating the longitudinal structure of cloud-top super-rotation.Methods. We analyzed eight years of thermal emission data from Akatsuki/LIR to isolate stationary wave components. Simulations were performed using the high-resolution Venus planetary climate model, which incorporates a realistic topography and a hybrid vertical coordinate system.Results. Stationary wave signatures in the brightness temperature and horizontal winds are consistently observed and simulated above highland regions, with a notable local time dependence and long-term variability. The vertical transport of angular momentum and heat dominates the wave-induced momentum and energy budget, leading to zonal wind deceleration and adiabatic heating in the upper cloud layer. Despite filtering by two weak static stability layers in the deep atmosphere, stationary waves can propagate upward and impact cloud-top dynamics.Conclusions. Stationary waves exert a measurable influence on Venus’s upper-cloud super-rotation by vertically redistributing momentum and heat in longitude. Their effects are modulated by both vertical static stability and diurnal variations. These results highlight the crucial role of stationary waves in maintaining the observed longitudinal structure of the super-rotating atmosphere.
上下文。静止波在金星大气中垂直传递动量和能量方面起着至关重要的作用。它们的全球贡献（上层云约为±0.1 m s−1 day−1）小于行星尺度波和经向环流的贡献（约为±1.0 m s−1 day−1），但平稳波具有很强的区域控制作用，塑造了高原上空超旋转气流的纵向结构。观测将云顶附近（~70公里）的波特征与下面的高地地区联系起来。然而，它们的垂直传播特性和对超旋转形态的贡献仍然知之甚少。本研究旨在描述金星大气中驻波的结构、变异和传播特征，并评估它们在调节云顶超旋转的纵向结构中的作用。我们分析了8年来赤月/LIR的热发射数据，以分离出驻波分量。利用高分辨率金星行星气候模型进行了模拟，该模型结合了真实地形和混合垂直坐标系。高原地区的亮度、温度和水平风的驻波特征是一致的，具有明显的局地依赖性和长期变率。角动量和热量的垂直输送主导了波致动量和能量收支，导致纬向风减速和上层云层绝热加热。尽管有深层大气中两个弱静态稳定层的过滤，静止波仍能向上传播并影响云顶动力学。静止波通过在经度上垂直重新分配动量和热量，对金星上层云的超旋转施加可测量的影响。它们的作用受到垂直静态稳定性和日变化的调节。这些结果强调了驻波在维持观测到的超旋转大气纵向结构方面的关键作用。
{"title":"Stationary wave dynamics in Venus's upper clouds","authors":"Dexin Lai, Tao Li, Sébastien Lebonnois, Maxence Lefèvre","doi":"10.1051/0004-6361/202557330","DOIUrl":"https://doi.org/10.1051/0004-6361/202557330","url":null,"abstract":"<i>Context<i/>. Stationary waves play a crucial role in vertically transporting momentum and energy in Venus’s atmosphere. Their global contributions (approximately −0.1 m s<sup>−1<sup/> day<sup>−1<sup/> at the upper cloud) are smaller than those of planetary-scale waves and meridional circulation (approximately ±1.0 m s<sup>−1<sup/> day<sup>−1<sup/>), but stationary waves exert strong regional control, shaping the longitudinal structure of the super-rotating flow above highlands. Observations have linked wave signatures near the cloud top (~70 km) to underlying highland regions. However, their vertical propagation characteristics and contributions to the morphology of super-rotation remain poorly understood.<i>Aims<i/>. This study aims to characterize the structure, variability, and propagation of stationary waves in Venus’s atmosphere and to evaluate their role in modulating the longitudinal structure of cloud-top super-rotation.<i>Methods<i/>. We analyzed eight years of thermal emission data from Akatsuki/LIR to isolate stationary wave components. Simulations were performed using the high-resolution Venus planetary climate model, which incorporates a realistic topography and a hybrid vertical coordinate system.<i>Results<i/>. Stationary wave signatures in the brightness temperature and horizontal winds are consistently observed and simulated above highland regions, with a notable local time dependence and long-term variability. The vertical transport of angular momentum and heat dominates the wave-induced momentum and energy budget, leading to zonal wind deceleration and adiabatic heating in the upper cloud layer. Despite filtering by two weak static stability layers in the deep atmosphere, stationary waves can propagate upward and impact cloud-top dynamics.<i>Conclusions<i/>. Stationary waves exert a measurable influence on Venus’s upper-cloud super-rotation by vertically redistributing momentum and heat in longitude. Their effects are modulated by both vertical static stability and diurnal variations. These results highlight the crucial role of stationary waves in maintaining the observed longitudinal structure of the super-rotating atmosphere.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"22 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145813719","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 : 2025-12-22DOI: 10.1051/0004-6361/202557011
P. F. Lazorenko, J. Sahlmann, M. Mayor, E. L. Martin, M.-R. Zapatero Osorio, J. Girard
We present a method of resolving the geometric structure in unresolved CCD images of the two-component stellar objects with relative separations below the full width at half maximum (FWHM). The practical applicability of this method has been demonstrated on example tests of the newly discovered binary, DENIS-P J1756296-451822, with a relative separation of about 0.15″ (or 0.25 × FWHM). For this purpose, we used unresolved binary images obtained with the VLT/FORS2 camera, which provided precise astrometric positions of the system photocenter. Using the same images, we applied a new, tested method capable of resolving the geometry of the binary by taking into account the difference of the image shape of the binary and of single stars, adopting an effective elliptical point spread function (PSF). In this way, we derived independent additional information on the geometry of the binary system, which allowed us to estimate the mass ratio and improved the overall orbit fit. Also, we used a single series of adaptive optics observations with NACO. Combining these data, we derived a relative flux of the secondary in the I band of 0.66 ± 0.04 and a mass ratio of q ≃ 0.886 ± 0.049, along with dynamical masses of M1 = 63.9−2.1+2.5MJup for the primary and M2 = 56.6−1.9+2.7MJup for the secondary. We note that these values are below the substellar limit. Using theoretical cooling curves for brown dwarfs, we were able to estimate the age of this binary system at between 200 and 350 Myr.
{"title":"Resolving the unresolved: Discovery and dynamical masses of the brown dwarf binary DE1756−45★","authors":"P. F. Lazorenko, J. Sahlmann, M. Mayor, E. L. Martin, M.-R. Zapatero Osorio, J. Girard","doi":"10.1051/0004-6361/202557011","DOIUrl":"https://doi.org/10.1051/0004-6361/202557011","url":null,"abstract":"We present a method of resolving the geometric structure in unresolved CCD images of the two-component stellar objects with relative separations below the full width at half maximum (FWHM). The practical applicability of this method has been demonstrated on example tests of the newly discovered binary, DENIS-P J1756296-451822, with a relative separation of about 0.15″ (or 0.25 × FWHM). For this purpose, we used unresolved binary images obtained with the VLT/FORS2 camera, which provided precise astrometric positions of the system photocenter. Using the same images, we applied a new, tested method capable of resolving the geometry of the binary by taking into account the difference of the image shape of the binary and of single stars, adopting an effective elliptical point spread function (PSF). In this way, we derived independent additional information on the geometry of the binary system, which allowed us to estimate the mass ratio and improved the overall orbit fit. Also, we used a single series of adaptive optics observations with NACO. Combining these data, we derived a relative flux of the secondary in the <i>I<i/> band of 0.66 ± 0.04 and a mass ratio of <i>q<i/> ≃ 0.886 ± 0.049, along with dynamical masses of <i>M<i/><sub>1<sub/> = 63.9<sub>−2.1<sub/><sup>+2.5<sup/><i>M<i/><sub>Jup<sub/> for the primary and <i>M<i/><sub>2<sub/> = 56.6<sub>−1.9<sub/><sup>+2.7<sup/><i>M<i/><sub>Jup<sub/> for the secondary. We note that these values are below the substellar limit. Using theoretical cooling curves for brown dwarfs, we were able to estimate the age of this binary system at between 200 and 350 Myr.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"66 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145801445","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 : 2025-12-22DOI: 10.1051/0004-6361/202556734
D. Kleiner, P. Serra, A. Loni, S. H. A. Rajohnson, F. M. Maccagni, W. J. G. de Blok, P. Kamphuis, R. C. Kraan-Korteweg, M. A. W. Verheijen
We present the deepest H I mass function (H IMF) ever measured, outside the Local Group. The observations are part of the MeerKAT Fornax Survey and cover a 4 × 4 deg2 field, corresponding to the approximate Rvir. The 3σ detection limit is log(MHI/M⊙) = 5.7 for a 50 km s−1-wide point source. We detect H I in 35 galaxies and 44 clouds with no optical counterparts. Using deep optical images from the Fornax Deep Survey, we measure the 5σ optical flux limit of the H I clouds and show that they are a distinct population, separated by a four magnitude gap from the faintest H I-detected galaxies. Three quarters (33 out of 44) of the clouds are associated with the two galaxies with the most H I in the cluster – NGC 1365 and NGC 1427A, although the clouds contribute a negligible amount to the total MHI budget. By performing a signal-to-noise analysis and computing the Rauzy statistic on the H I detections, we demonstrate that our catalogue is complete down to log(MHI/M⊙) = 6, and we are therefore readily able to probe the H IMF down to this level. We find an abrupt drop in the number density of H I-detected galaxies at log(MHI/M⊙) = 7, signifying a clear absence of galaxies between 6 < log(MHI/M⊙) ≤ 7. We use the modified maximum likelihood method to fit a Schechter function down to log(MHI/M⊙) ≥ 7, the range where the H IMF follows a power law. The measured low-mass slope is α = −1.31 ± 0.13, with a characteristic knee mass of log(M*/M⊙) = 10.52 ± 1.89. The low-mass slope matches the slope in the field, while the knee is defined by a single galaxy and is unconstrained. Below log(MHI/M⊙) = 7, there is a sharp departure from a Schechter function, and we report the first robust measurement of the collapse of a H IMF. For the H IMF below log(MHI/M⊙) = 7 to follow a power law, tens of galaxies are needed – a factor of ∼6 higher than what is observed. The collapse of the Fornax H IMF is likely due to the rapid removal of H I from low-mass galaxies.
{"title":"The MeerKAT Fornax Survey","authors":"D. Kleiner, P. Serra, A. Loni, S. H. A. Rajohnson, F. M. Maccagni, W. J. G. de Blok, P. Kamphuis, R. C. Kraan-Korteweg, M. A. W. Verheijen","doi":"10.1051/0004-6361/202556734","DOIUrl":"https://doi.org/10.1051/0004-6361/202556734","url":null,"abstract":"We present the deepest H I mass function (H IMF) ever measured, outside the Local Group. The observations are part of the MeerKAT Fornax Survey and cover a 4 × 4 deg<sup>2<sup/> field, corresponding to the approximate <i>R<i/><sub>vir<sub/>. The 3<i>σ<i/> detection limit is log(<i>M<i/><sub>HI<sub/>/<i>M<i/><sub>⊙<sub/>) = 5.7 for a 50 km s<sup>−1<sup/>-wide point source. We detect H I in 35 galaxies and 44 clouds with no optical counterparts. Using deep optical images from the Fornax Deep Survey, we measure the 5<i>σ<i/> optical flux limit of the H I clouds and show that they are a distinct population, separated by a four magnitude gap from the faintest H I-detected galaxies. Three quarters (33 out of 44) of the clouds are associated with the two galaxies with the most H I in the cluster – NGC 1365 and NGC 1427A, although the clouds contribute a negligible amount to the total <i>M<i/><sub>HI<sub/> budget. By performing a signal-to-noise analysis and computing the Rauzy statistic on the H I detections, we demonstrate that our catalogue is complete down to log(<i>M<i/><sub>HI<sub/>/<i>M<i/><sub>⊙<sub/>) = 6, and we are therefore readily able to probe the H IMF down to this level. We find an abrupt drop in the number density of H I-detected galaxies at log(<i>M<i/><sub>HI<sub/>/<i>M<i/><sub>⊙<sub/>) = 7, signifying a clear absence of galaxies between 6 < log(<i>M<i/><sub>HI<sub/>/<i>M<i/><sub>⊙<sub/>) ≤ 7. We use the modified maximum likelihood method to fit a Schechter function down to log(<i>M<i/><sub>HI<sub/>/<i>M<i/><sub>⊙<sub/>) ≥ 7, the range where the H IMF follows a power law. The measured low-mass slope is <i>α<i/> = −1.31 ± 0.13, with a characteristic knee mass of log(<i>M<i/><sub>*<sub/>/<i>M<i/><sub>⊙<sub/>) = 10.52 ± 1.89. The low-mass slope matches the slope in the field, while the knee is defined by a single galaxy and is unconstrained. Below log(<i>M<i/><sub>HI<sub/>/<i>M<i/><sub>⊙<sub/>) = 7, there is a sharp departure from a Schechter function, and we report the first robust measurement of the collapse of a H IMF. For the H IMF below log(<i>M<i/><sub>HI<sub/>/<i>M<i/><sub>⊙<sub/>) = 7 to follow a power law, tens of galaxies are needed – a factor of ∼6 higher than what is observed. The collapse of the Fornax H IMF is likely due to the rapid removal of H I from low-mass galaxies.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"5 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145801424","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}
Context. Solar hard X-ray (HXR) observations provide diagnostics of the hottest plasmas and of nonthermal electron populations present during solar flares and coronal mass ejections. HXR images of specific energy ranges often contain overlapping contributions of these components, complicating their interpretation. This is even more challenging as HXR imagers generally use an indirect imaging system.Aims. Our work aims to separately image individual spectral components, such as thermal loops, superhot sources, and nonthermal footpoint sources, rather than obtaining images of specific energy ranges that show a combination of all components.Methods. We introduced a new method called “spectral component imaging” and applied it to observations provided by the Spectrometer/Telescope for Imaging X-rays (STIX) aboard Solar Orbiter. First, the flare integrated HXR spectrum was fit with individual spectral components to get the relative contributions (“weights”) of each component in each native STIX energy channel. In a second step, a set of linear equations was created based on these weights and the observed, energy-dependent STIX visibilities. The visibilities of the individual spectral components were derived by means of a linear least-squares approach and were subsequently utilized for image reconstructions.Results. We demonstrate the effectiveness of spectral component imaging on four different flares observed by STIX. This method provides powerful diagnostics, particularly for flares with hot and superhot components, allowing us to spatially separate these two thermal components. We applied our methodology to the nonthermal peak of the X7.1 flare SOL2024-10-01, and we find that the superhot component is located 4.8 Mm away from the hot thermal loops. The thermal energy of the superhot component is approximately 20% of the energy content of the hot component, highlighting the significance of superhot components in the total flare energy budget.Conclusions. Spectral component imaging provides a powerful tool to image individual spectral components (i.e., thermal and nonthermal X-ray sources), rather than creating images over fixed energy ranges. Because there is no need to select an energy range, spectral component imaging has the potential to automate the image reconstruction process and to establish a robust STIX image database once the spectral components have been defined.
{"title":"Spectral component imaging of solar X-ray flares","authors":"Muriel Zoë Stiefel, Paolo Massa, Alessia Guidetti, Marina Battaglia, Säm Krucker","doi":"10.1051/0004-6361/202557373","DOIUrl":"https://doi.org/10.1051/0004-6361/202557373","url":null,"abstract":"<i>Context.<i/> Solar hard X-ray (HXR) observations provide diagnostics of the hottest plasmas and of nonthermal electron populations present during solar flares and coronal mass ejections. HXR images of specific energy ranges often contain overlapping contributions of these components, complicating their interpretation. This is even more challenging as HXR imagers generally use an indirect imaging system.<i>Aims.<i/> Our work aims to separately image individual spectral components, such as thermal loops, superhot sources, and nonthermal footpoint sources, rather than obtaining images of specific energy ranges that show a combination of all components.<i>Methods.<i/> We introduced a new method called “spectral component imaging” and applied it to observations provided by the Spectrometer/Telescope for Imaging X-rays (STIX) aboard Solar Orbiter. First, the flare integrated HXR spectrum was fit with individual spectral components to get the relative contributions (“weights”) of each component in each native STIX energy channel. In a second step, a set of linear equations was created based on these weights and the observed, energy-dependent STIX visibilities. The visibilities of the individual spectral components were derived by means of a linear least-squares approach and were subsequently utilized for image reconstructions.<i>Results.<i/> We demonstrate the effectiveness of spectral component imaging on four different flares observed by STIX. This method provides powerful diagnostics, particularly for flares with hot and superhot components, allowing us to spatially separate these two thermal components. We applied our methodology to the nonthermal peak of the X7.1 flare SOL2024-10-01, and we find that the superhot component is located 4.8 Mm away from the hot thermal loops. The thermal energy of the superhot component is approximately 20% of the energy content of the hot component, highlighting the significance of superhot components in the total flare energy budget.<i>Conclusions.<i/> Spectral component imaging provides a powerful tool to image individual spectral components (i.e., thermal and nonthermal X-ray sources), rather than creating images over fixed energy ranges. Because there is no need to select an energy range, spectral component imaging has the potential to automate the image reconstruction process and to establish a robust STIX image database once the spectral components have been defined.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"28 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145801477","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 : 2025-12-19DOI: 10.1051/0004-6361/202557089
M. S. Murga, I. V. Loginov, D. S. Wiebe, D. R. Fedotova, V. S. Krasnoukhov, I. O. Antonov
Aims. This work investigates the catalytic role of dust grains in forming aromatic hydrocarbons via acetylene cyclotrimerization on their surfaces within the circumstellar envelopes of carbon-rich asymptotic giant branch (AGB) stars.Methods. We present a comprehensive computational astrochemical model coupling the gas-phase, gas-surface, and surface (cyclotrimerization) reactions, and the physical evolution of the dust grains (coagulation). The model expands upon the basic chemical network from previous models, enhancing them with updated reactions involving hydrocarbons up to pyrene. We applied this model to simulate the chemical evolution of the envelope of the prototypical AGB star IRC+10216, utilizing physical conditions derived from a hydrodynamical model available in literature. To quantify the impact of surface chemistry, we compared scenarios with and without the cyclotrimerization reaction, further testing the sensitivity of our results by varying the key parameter of hydrocarbon desorption energy.Results. We find that surface-catalyzed cyclotrimerization is a viable pathway for aromatic formation in circumstellar environments, capable of enhancing the total abundance of aromatic species by up to an order of magnitude. Crucially, we show that gas-phase chemistry and dust surface processes are intrinsically linked; their synergistic evolution should be modeled self-consistently to accurately predict chemical abundances. This work underscores that constraining uncertain parameters, particularly desorption energies of hydrocarbons, is essential for future realistic modeling of astrochemical processes in evolved stellar systems.
{"title":"The impact of surface acetylene cyclotrimerization on the abundance of aromatic hydrocarbons in carbon-rich asymptotic giant branch stars","authors":"M. S. Murga, I. V. Loginov, D. S. Wiebe, D. R. Fedotova, V. S. Krasnoukhov, I. O. Antonov","doi":"10.1051/0004-6361/202557089","DOIUrl":"https://doi.org/10.1051/0004-6361/202557089","url":null,"abstract":"<i>Aims<i/>. This work investigates the catalytic role of dust grains in forming aromatic hydrocarbons via acetylene cyclotrimerization on their surfaces within the circumstellar envelopes of carbon-rich asymptotic giant branch (AGB) stars.<i>Methods<i/>. We present a comprehensive computational astrochemical model coupling the gas-phase, gas-surface, and surface (cyclotrimerization) reactions, and the physical evolution of the dust grains (coagulation). The model expands upon the basic chemical network from previous models, enhancing them with updated reactions involving hydrocarbons up to pyrene. We applied this model to simulate the chemical evolution of the envelope of the prototypical AGB star IRC+10216, utilizing physical conditions derived from a hydrodynamical model available in literature. To quantify the impact of surface chemistry, we compared scenarios with and without the cyclotrimerization reaction, further testing the sensitivity of our results by varying the key parameter of hydrocarbon desorption energy.<i>Results<i/>. We find that surface-catalyzed cyclotrimerization is a viable pathway for aromatic formation in circumstellar environments, capable of enhancing the total abundance of aromatic species by up to an order of magnitude. Crucially, we show that gas-phase chemistry and dust surface processes are intrinsically linked; their synergistic evolution should be modeled self-consistently to accurately predict chemical abundances. This work underscores that constraining uncertain parameters, particularly desorption energies of hydrocarbons, is essential for future realistic modeling of astrochemical processes in evolved stellar systems.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"30 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145801449","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 : 2025-12-19DOI: 10.1051/0004-6361/202557610
L. Lange, T. Bertrand, V. Belissa, S. Carpy, L. A. Young, A. Falco
Context. The equatorial region of Cthulhu as revealed by New Horizons appears to be generally dark and largely devoid of volatiles because its surface albedo is low. Localized bright patches, however, which are interpreted as CH4 frost, are observed on crater rims and slopes.Aims. Previous studies suggested that these frosts might result from the peculiar insolation driven by the geometry of these slopes, but this has never been tested quantitatively. We investigated the origin, stability, and potential role of these localized frost deposits in the volatile cycle of Pluto.Methods. We implemented a new subgrid-scale slope parameterization in the volatile transport model for Pluto, which accounts for the specific solar irradiation and the resulting surface and subsurface temperatures on sloped terrains. This parameterization also allows the condensation and sublimation of volatiles (either N2 or CH4) on slopes, including the effect of large-scale transport of these species. This is key to determining the amount of frost that forms or disappears.Results. Our simulations reproduce the observed CH4 frost on north-facing slopes as seasonal deposits that currently sublimate, predict perennial CH4 frost on south-facing slopes, and show that the slope microclimates are not expected to alter global volatile cycles.Conclusions. Seasonal and perennial N2 and CH4 frosts can form on the Pluto slopes, even in its darkest and warmest regions, because the locally sunlight received on inclined terrain is reduced. Despite the abundance of sloped surfaces on Pluto, the slope microclimates still only appear to have a minor effect on the global volatile cycles of the planet.
{"title":"Modeling the formation of N2 and CH4 frost on the Pluto slopes","authors":"L. Lange, T. Bertrand, V. Belissa, S. Carpy, L. A. Young, A. Falco","doi":"10.1051/0004-6361/202557610","DOIUrl":"https://doi.org/10.1051/0004-6361/202557610","url":null,"abstract":"<i>Context<i/>. The equatorial region of Cthulhu as revealed by New Horizons appears to be generally dark and largely devoid of volatiles because its surface albedo is low. Localized bright patches, however, which are interpreted as CH<sub>4<sub/> frost, are observed on crater rims and slopes.<i>Aims<i/>. Previous studies suggested that these frosts might result from the peculiar insolation driven by the geometry of these slopes, but this has never been tested quantitatively. We investigated the origin, stability, and potential role of these localized frost deposits in the volatile cycle of Pluto.<i>Methods<i/>. We implemented a new subgrid-scale slope parameterization in the volatile transport model for Pluto, which accounts for the specific solar irradiation and the resulting surface and subsurface temperatures on sloped terrains. This parameterization also allows the condensation and sublimation of volatiles (either N<sub>2<sub/> or CH<sub>4<sub/>) on slopes, including the effect of large-scale transport of these species. This is key to determining the amount of frost that forms or disappears.<i>Results<i/>. Our simulations reproduce the observed CH<sub>4<sub/> frost on north-facing slopes as seasonal deposits that currently sublimate, predict perennial CH<sub>4<sub/> frost on south-facing slopes, and show that the slope microclimates are not expected to alter global volatile cycles.<i>Conclusions<i/>. Seasonal and perennial N<sub>2<sub/> and CH<sub>4<sub/> frosts can form on the Pluto slopes, even in its darkest and warmest regions, because the locally sunlight received on inclined terrain is reduced. Despite the abundance of sloped surfaces on Pluto, the slope microclimates still only appear to have a minor effect on the global volatile cycles of the planet.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"123 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145801473","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 : 2025-12-18DOI: 10.1051/0004-6361/202558117
A. García Muñoz, D. De Fazio, D. J. Wilson, K. France
Context. Neptune-sized exoplanets (i.e., exo-Neptunes) are fundamental to the study of exoplanet diversity. Their evolution is sculpted by atmospheric escape, often traced by absorption in the H I Lyman-α line at 1216 Å and the He I triplet line at 1.08 μm. On the warm exo-Neptunes HAT-P-11 b, GJ 3470 b and GJ 436 b, H I Lyman-α absorption causes extreme in-transit obscuration of their host stars. This suggests that the He I triplet line absorption would be strong as well, yet it has only been identified on two of these planets.Aims. We explore processes that had previously been omitted, which might act to attenuate the He I triplet line on warm exo-Neptunes. In particular, we assess the role of vibrationally excited H2 to remove the He+ ion that acts as precursor of the absorbing He(23S).Methods. We determined thermal rate coefficients for this chemical process, leveraging the available theoretical and experimental data. The process becomes notably fast at the temperatures expected in the atmospheric layers probed by the He I triplet line.Results. Our simulations show that this removal process severely mutes the line on GJ 3470 b and leads to the nondetection on GJ 436 b. The overall efficiency of this mechanism is connected to the location in the atmosphere of the H2-to-H transition and, ultimately, to the amount of high-energy radiation received by the planet. The process will be more significant on small exoplanets than on hotter or more massive ones since, in the latter case, the H2-to-H transition generally occurs deeper in the atmosphere.Conclusions. Weak He I triplet line absorption does not necessarily imply the lack of a primordial, H2-He-dominated atmosphere, an idea to bear in mind when interpreting observations of other small exoplanets.
{"title":"Vibrationally excited H2 muting the He I triplet line at 1.08 μm on warm exo-Neptunes","authors":"A. García Muñoz, D. De Fazio, D. J. Wilson, K. France","doi":"10.1051/0004-6361/202558117","DOIUrl":"https://doi.org/10.1051/0004-6361/202558117","url":null,"abstract":"<i>Context.<i/> Neptune-sized exoplanets (i.e., exo-Neptunes) are fundamental to the study of exoplanet diversity. Their evolution is sculpted by atmospheric escape, often traced by absorption in the H I Lyman-<i>α<i/> line at 1216 Å and the He I triplet line at 1.08 μm. On the warm exo-Neptunes HAT-P-11 b, GJ 3470 b and GJ 436 b, H I Lyman-<i>α<i/> absorption causes extreme in-transit obscuration of their host stars. This suggests that the He I triplet line absorption would be strong as well, yet it has only been identified on two of these planets.<i>Aims.<i/> We explore processes that had previously been omitted, which might act to attenuate the He I triplet line on warm exo-Neptunes. In particular, we assess the role of vibrationally excited H<sub>2<sub/> to remove the He<sup>+<sup/> ion that acts as precursor of the absorbing He(2<sup>3<sup/><i>S<i/>).<i>Methods.<i/> We determined thermal rate coefficients for this chemical process, leveraging the available theoretical and experimental data. The process becomes notably fast at the temperatures expected in the atmospheric layers probed by the He I triplet line.<i>Results.<i/> Our simulations show that this removal process severely mutes the line on GJ 3470 b and leads to the nondetection on GJ 436 b. The overall efficiency of this mechanism is connected to the location in the atmosphere of the H<sub>2<sub/>-to-H transition and, ultimately, to the amount of high-energy radiation received by the planet. The process will be more significant on small exoplanets than on hotter or more massive ones since, in the latter case, the H<sub>2<sub/>-to-H transition generally occurs deeper in the atmosphere.<i>Conclusions.<i/> Weak He I triplet line absorption does not necessarily imply the lack of a primordial, H<sub>2<sub/>-He-dominated atmosphere, an idea to bear in mind when interpreting observations of other small exoplanets.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"2 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145784703","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 : 2025-12-18DOI: 10.1051/0004-6361/202555791
Adrienn Pataki, Péter Raffai, István Csabai, Gábor Rácz, István Szapudi
We constrain AvERA cosmologies in comparison with the flat Λ-cold dark matter (ΛCDM) model using cosmic chronometer (CC) data and the Pantheon+ sample of type Ia supernovae (SNe Ia). The analysis includes fits to both CC and SN datasets using the dynesty dynamic nested sampling algorithm. For the model comparison, we used the Bayesian model evidence and Anderson-Darling tests applied to the normalized residuals to assess consistency with a standard normal distribution. Best-fit parameters were derived within the redshift ranges z ≤ 2 for CCs and z ≤ 2.3 for SNe. For the baseline AvERA cosmology, we obtained best-fit values of the Hubble constant of from the CC analysis and from the SN analysis, each consistent within 1σ with the corresponding AvERA simulation value of H(z = 0). While both the CC and SN datasets yield higher Bayesian evidence for the flat ΛCDM model, they favor the AvERA cosmologies according to the Anderson-Darling test. We have identified signs of overfitting in each model, which suggests the possibility of overestimating the uncertainties in the Pantheon+ covariance matrix.
{"title":"Constraints on AvERA cosmologies from cosmic chronometers and type Ia supernovae","authors":"Adrienn Pataki, Péter Raffai, István Csabai, Gábor Rácz, István Szapudi","doi":"10.1051/0004-6361/202555791","DOIUrl":"https://doi.org/10.1051/0004-6361/202555791","url":null,"abstract":"We constrain AvERA cosmologies in comparison with the flat Λ-cold dark matter (ΛCDM) model using cosmic chronometer (CC) data and the Pantheon+ sample of type Ia supernovae (SNe Ia). The analysis includes fits to both CC and SN datasets using the dynesty dynamic nested sampling algorithm. For the model comparison, we used the Bayesian model evidence and Anderson-Darling tests applied to the normalized residuals to assess consistency with a standard normal distribution. Best-fit parameters were derived within the redshift ranges <i>z<i/> ≤ 2 for CCs and <i>z<i/> ≤ 2.3 for SNe. For the baseline AvERA cosmology, we obtained best-fit values of the Hubble constant of from the CC analysis and from the SN analysis, each consistent within 1<i>σ<i/> with the corresponding AvERA simulation value of <i>H<i/>(<i>z<i/> = 0). While both the CC and SN datasets yield higher Bayesian evidence for the flat ΛCDM model, they favor the AvERA cosmologies according to the Anderson-Darling test. We have identified signs of overfitting in each model, which suggests the possibility of overestimating the uncertainties in the Pantheon+ covariance matrix.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"83 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145786034","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：