Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae4d38
Ruihui Wang, 瑞慧 王, Jie Jiang, 杰 姜, Yukun Luo and 昱琨 罗
Solar polar fields are essential for the solar cycle and the heliospheric magnetic field. Cycle 25 is now entering its declining phase, the critical period during which most of the cycle’s polar fields are established. Therefore, reliable polar-field prediction is now especially important. Polar-field evolution is governed by the poleward transport of already-emerged active-region (AR) flux over a timescale of a few years. Thus, surface flux-transport models can reliably provide 1 yr predictions without requiring information about future AR emergence. Our prediction method is validated using simulations of the surface magnetic field from 2020 to 2025 and hindcasts of the 2023–2024 polar fields, employing a newly constrained profile of the meridional flow. Using the most recent Helioseismic and Magnetic Imager synoptic magnetogram as the initial condition, we predict the polar-field evolution from 2025 October to 2026 October. The southern polar field is predicted to strengthen gradually, while the northern field is expected to decline sharply until 2026 March due to some ARs with abnormal polarity. By that time, the northern polar field becomes exceptionally weak, and the southern field remains relatively weak, raising concerns about the polar-field strength at the cycle 25/26 minimum and the amplitude of cycle 26.
{"title":"Prediction of the Solar Polar Fields in 2026: An Unusually Weak Level across the Last Five Solar Cycles","authors":"Ruihui Wang, 瑞慧 王, Jie Jiang, 杰 姜, Yukun Luo and 昱琨 罗","doi":"10.3847/1538-4357/ae4d38","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4d38","url":null,"abstract":"Solar polar fields are essential for the solar cycle and the heliospheric magnetic field. Cycle 25 is now entering its declining phase, the critical period during which most of the cycle’s polar fields are established. Therefore, reliable polar-field prediction is now especially important. Polar-field evolution is governed by the poleward transport of already-emerged active-region (AR) flux over a timescale of a few years. Thus, surface flux-transport models can reliably provide 1 yr predictions without requiring information about future AR emergence. Our prediction method is validated using simulations of the surface magnetic field from 2020 to 2025 and hindcasts of the 2023–2024 polar fields, employing a newly constrained profile of the meridional flow. Using the most recent Helioseismic and Magnetic Imager synoptic magnetogram as the initial condition, we predict the polar-field evolution from 2025 October to 2026 October. The southern polar field is predicted to strengthen gradually, while the northern field is expected to decline sharply until 2026 March due to some ARs with abnormal polarity. By that time, the northern polar field becomes exceptionally weak, and the southern field remains relatively weak, raising concerns about the polar-field strength at the cycle 25/26 minimum and the amplitude of cycle 26.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506753","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae3aa2
Bradley E. Schaefer
Recurrent nova (RN) T Pyxidis (T Pyx) has a complex history of mass accreting onto and ejection from the white dwarf, with a classical nova eruption around 1866 kick-starting an RN-phase with six RN eruptions from 1890–2011. T Pyx is a primary progenitor candidate for Type Ia supernovae (SN Ia). This is chiefly a question of whether the mass accreted by the white dwarf (Maccreted) is more or less than the mass ejected by the nova eruptions (Mejecta) over the entire eruption cycle. Prior attempts to measure Mejecta from the traditional methods have a scatter of >130×, so only a new technique can provide a measure of adequate accuracy and reliability. This new technique is the timing experiment of measuring the orbital period from 1986–2025, where the period increased by +50.3 ± 7.9 ppm across the 2011 eruption. With simple and sure physics, the best estimate for the mass ejected by one RN event is >2400 × 10−7M⊙, with an extreme inviolate limit of ≫354 × 10−7M⊙. Over all eruptions in a cycle, Mejecta >17120 × 10−7M⊙, with an inviolate limit of Mejecta ≫2144 × 10−7M⊙. Over the full eruption cycle, the white dwarf accreted 220 × 10−7M⊙. So, Mejecta≫11.3 × Maccreted, and T Pyx can never become an SN Ia. This paper is the seventh in a series proving that each of various popular candidate SN Ia progenitors cannot possibly evolve to a supernova, including V445 Pup, U Sco, T CrB, all symbiotic stars, FQ Cir, V1405 Cas, and now T Pyx.
{"title":"Orbital Period Changes of Recurrent Nova T Pyxidis Demonstrate that M ejecta ≫ 11.3 × M accreted and that It Is Not a Type Ia Supernova Progenitor","authors":"Bradley E. Schaefer","doi":"10.3847/1538-4357/ae3aa2","DOIUrl":"https://doi.org/10.3847/1538-4357/ae3aa2","url":null,"abstract":"Recurrent nova (RN) T Pyxidis (T Pyx) has a complex history of mass accreting onto and ejection from the white dwarf, with a classical nova eruption around 1866 kick-starting an RN-phase with six RN eruptions from 1890–2011. T Pyx is a primary progenitor candidate for Type Ia supernovae (SN Ia). This is chiefly a question of whether the mass accreted by the white dwarf (Maccreted) is more or less than the mass ejected by the nova eruptions (Mejecta) over the entire eruption cycle. Prior attempts to measure Mejecta from the traditional methods have a scatter of >130×, so only a new technique can provide a measure of adequate accuracy and reliability. This new technique is the timing experiment of measuring the orbital period from 1986–2025, where the period increased by +50.3 ± 7.9 ppm across the 2011 eruption. With simple and sure physics, the best estimate for the mass ejected by one RN event is >2400 × 10−7M⊙, with an extreme inviolate limit of ≫354 × 10−7M⊙. Over all eruptions in a cycle, Mejecta >17120 × 10−7M⊙, with an inviolate limit of Mejecta ≫2144 × 10−7M⊙. Over the full eruption cycle, the white dwarf accreted 220 × 10−7M⊙. So, Mejecta≫11.3 × Maccreted, and T Pyx can never become an SN Ia. This paper is the seventh in a series proving that each of various popular candidate SN Ia progenitors cannot possibly evolve to a supernova, including V445 Pup, U Sco, T CrB, all symbiotic stars, FQ Cir, V1405 Cas, and now T Pyx.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"190 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506570","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae3f98
Saemi Bang, Atsuo T. Okazaki and Kimitake Hayasaki
We study the thermal and spectral properties of irradiated circumbinary disks (CBDs) around binary black holes (BBHs), using analytic, hydrogen-based opacity models that capture dependencies on temperature, density, and ionization. We solve the vertical hydrostatic equilibrium and energy balance, assuming gas pressure only, using Rosseland-mean opacities from free–free and bound–free absorption plus electron scattering, with ionization fractions given by the Saha equation. Four opacity models are considered, including a reference model with no physical opacity, constructed by Y. Lee et al., and three physically motivated alternatives. The midplane temperature profiles show significant variation across models, while the surface temperature remains largely unchanged in regions dominated by viscous heating. Opacity effects become pronounced in the outer disk, where irradiation reprocessing shapes the IR-optical continuum. Bound-free opacity introduces flattening and a mid-frequency peak in the spectral energy distribution. We compute spectra of a triple-disk system including the CBD and two accreting minidisks. The high-frequency peak arises from the hot minidisks, while the low-frequency excess originates from irradiated outer CBD layers. Comparing model spectra with the detection limits of Subaru, JWST, and Swift, we find that BBH systems within ∼10 Mpc can exhibit a detectable IR excess. Our results highlight the need for physically consistent opacity modeling to interpret electromagnetic (EM) signatures of BBHs approaching coalescence and support integration of metallicity-dependent opacity tables. Our opacity-informed framework for irradiated CBDs provides an EM template for identifying stellar- to intermediate-mass BBHs in a mass range sparsely sampled by LISA, thereby bridging the gravitational-wave–EM gap with testable IR/optical signatures.
{"title":"Spectral Properties of Irradiated Circumbinary Disks around Binary Black Holes Governed by Hydrogen Opacities Dependent on Temperature and Density","authors":"Saemi Bang, Atsuo T. Okazaki and Kimitake Hayasaki","doi":"10.3847/1538-4357/ae3f98","DOIUrl":"https://doi.org/10.3847/1538-4357/ae3f98","url":null,"abstract":"We study the thermal and spectral properties of irradiated circumbinary disks (CBDs) around binary black holes (BBHs), using analytic, hydrogen-based opacity models that capture dependencies on temperature, density, and ionization. We solve the vertical hydrostatic equilibrium and energy balance, assuming gas pressure only, using Rosseland-mean opacities from free–free and bound–free absorption plus electron scattering, with ionization fractions given by the Saha equation. Four opacity models are considered, including a reference model with no physical opacity, constructed by Y. Lee et al., and three physically motivated alternatives. The midplane temperature profiles show significant variation across models, while the surface temperature remains largely unchanged in regions dominated by viscous heating. Opacity effects become pronounced in the outer disk, where irradiation reprocessing shapes the IR-optical continuum. Bound-free opacity introduces flattening and a mid-frequency peak in the spectral energy distribution. We compute spectra of a triple-disk system including the CBD and two accreting minidisks. The high-frequency peak arises from the hot minidisks, while the low-frequency excess originates from irradiated outer CBD layers. Comparing model spectra with the detection limits of Subaru, JWST, and Swift, we find that BBH systems within ∼10 Mpc can exhibit a detectable IR excess. Our results highlight the need for physically consistent opacity modeling to interpret electromagnetic (EM) signatures of BBHs approaching coalescence and support integration of metallicity-dependent opacity tables. Our opacity-informed framework for irradiated CBDs provides an EM template for identifying stellar- to intermediate-mass BBHs in a mass range sparsely sampled by LISA, thereby bridging the gravitational-wave–EM gap with testable IR/optical signatures.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"405 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506571","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae4bd9
Fangfang Qiao, Hao Li, Jiasheng Wang, Yadan Duan, Zheng Sun and Leping Li
Bipolar light bridges (BLBs) are bright regions located between sunspot umbrae of opposite magnetic polarity. They are typically characterized by strong magnetic fields and intense flows, which are believed to be closely associated with major solar flares. Despite their importance, their fine structure, formation, and evolution remain poorly understood. In this work, we analyze the observations of a well-defined BLB obtained by the Goode Solar Telescope (GST) at the Big Bear Solar Observatory and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. The high-resolution GST observations reveal that the BLB is composed of fine, penumbral filament-like structures with widths of approximately 100–150 km. The corresponding Doppler velocity maps present a stable pattern of spatially adjacent red- and blueshifted patches within the BLB throughout the 5.5 hr GST observation. HMI observations show that the BLB arises from the converging and shearing motions of sunspots with opposite polarities. Penumbral regions originating from different polarities gradually evolve and interact, eventually forming the BLB. The observed Doppler velocity pattern, characterized by red- and blueshifted patches, can be interpreted as a projection effect of the Evershed flow within the penumbrae. Therefore, we argue that the BLB is formed through the compression and stretching of penumbral structures from oppositely polarized sunspots.
{"title":"Fine Structure and Formation Mechanism of a Sunspot Bipolar Light Bridge in NOAA AR 13663","authors":"Fangfang Qiao, Hao Li, Jiasheng Wang, Yadan Duan, Zheng Sun and Leping Li","doi":"10.3847/1538-4357/ae4bd9","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4bd9","url":null,"abstract":"Bipolar light bridges (BLBs) are bright regions located between sunspot umbrae of opposite magnetic polarity. They are typically characterized by strong magnetic fields and intense flows, which are believed to be closely associated with major solar flares. Despite their importance, their fine structure, formation, and evolution remain poorly understood. In this work, we analyze the observations of a well-defined BLB obtained by the Goode Solar Telescope (GST) at the Big Bear Solar Observatory and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. The high-resolution GST observations reveal that the BLB is composed of fine, penumbral filament-like structures with widths of approximately 100–150 km. The corresponding Doppler velocity maps present a stable pattern of spatially adjacent red- and blueshifted patches within the BLB throughout the 5.5 hr GST observation. HMI observations show that the BLB arises from the converging and shearing motions of sunspots with opposite polarities. Penumbral regions originating from different polarities gradually evolve and interact, eventually forming the BLB. The observed Doppler velocity pattern, characterized by red- and blueshifted patches, can be interpreted as a projection effect of the Evershed flow within the penumbrae. Therefore, we argue that the BLB is formed through the compression and stretching of penumbral structures from oppositely polarized sunspots.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"52 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506699","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae4c4f
Yi’an Zhou, Xiaoli Yan, Zhike Xue, Liheng Yang, Jincheng Wang and Zhe Xu
This work presents a detailed spectroscopic case study of four long-duration transition-region (TR) explosive events (EEs) observed in NOAA Active Region 13213 on 2023 February 10 using the Interface Region Imaging Spectrograph. The dynamic spectral evolution of each event is tracked through multicomponent Gaussian fitting of the Si iv 1403 Å line profiles. Three recurrent spectral morphologies are identified and characterized: bilateral wing enhancement, exclusive red-wing enhancement, and exclusive blue-wing enhancement, among which bilateral enhancement is the most common in the studied cases. Throughout their lifetimes of 20–25 minutes, these events display sustained and evolving bidirectional flows, with high-velocity components (∣v∣ > 100 km s−1) emerging in late phases. These spectral signatures are interpreted as evidence of ongoing or recurrent magnetic reconnection, where bilateral profiles correspond to bidirectional outflows, and exclusive wing enhancements represent geometric or evolutionary phases of the same process. In contrast, cotemporal flare ribbons and loop structures exhibit pronounced, unidirectional redshifts. This study underscores that significant non-Gaussian wing enhancement, rather than exclusively high speed, constitutes a defining spectroscopic signature of EEs, and provides detailed kinematic constraints on the dynamics of such TR EEs.
本文介绍了使用界面区成像光谱仪对2023年2月10日在NOAA活跃区13213观测到的四个长时间过渡区（TR）爆炸事件（EEs）进行详细的光谱案例研究。通过Si iv 1403 Å谱线的多分量高斯拟合跟踪每个事件的动态谱演变。识别并表征了三种反复出现的光谱形态：双侧翼增强、专属红翼增强和专属蓝翼增强，其中双侧翼增强在研究病例中最为常见。在它们20-25分钟的生命周期中，这些事件显示出持续和不断发展的双向流动，高速成分（∣v∣> 100 km s - 1）在后期出现。这些光谱特征被解释为正在进行或反复发生的磁重联的证据，其中双边剖面对应于双向流出，专属翼增强代表同一过程的几何或演化阶段。相比之下，同时间耀斑带和环结构表现出明显的单向红移。这项研究强调了显著的非高斯翼增强，而不仅仅是高速，构成了EEs的定义光谱特征，并提供了此类TR EEs动力学的详细运动学约束。
{"title":"Spectroscopic Case Studies of Four Long-duration Transition-region Explosive Events","authors":"Yi’an Zhou, Xiaoli Yan, Zhike Xue, Liheng Yang, Jincheng Wang and Zhe Xu","doi":"10.3847/1538-4357/ae4c4f","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4c4f","url":null,"abstract":"This work presents a detailed spectroscopic case study of four long-duration transition-region (TR) explosive events (EEs) observed in NOAA Active Region 13213 on 2023 February 10 using the Interface Region Imaging Spectrograph. The dynamic spectral evolution of each event is tracked through multicomponent Gaussian fitting of the Si iv 1403 Å line profiles. Three recurrent spectral morphologies are identified and characterized: bilateral wing enhancement, exclusive red-wing enhancement, and exclusive blue-wing enhancement, among which bilateral enhancement is the most common in the studied cases. Throughout their lifetimes of 20–25 minutes, these events display sustained and evolving bidirectional flows, with high-velocity components (∣v∣ > 100 km s−1) emerging in late phases. These spectral signatures are interpreted as evidence of ongoing or recurrent magnetic reconnection, where bilateral profiles correspond to bidirectional outflows, and exclusive wing enhancements represent geometric or evolutionary phases of the same process. In contrast, cotemporal flare ribbons and loop structures exhibit pronounced, unidirectional redshifts. This study underscores that significant non-Gaussian wing enhancement, rather than exclusively high speed, constitutes a defining spectroscopic signature of EEs, and provides detailed kinematic constraints on the dynamics of such TR EEs.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae4c55
D. J. Mullan and J. MacDonald
Precise empirical estimates of stellar radii have revealed that the radii of certain low-mass stars are inflated relative to stellar structure predictions: the largest inflations occur in magnetically active stars. Theoretically, the radii of magnetically active stars are in some cases found to be “hyperinflated” to roughly double the radius of a nonmagnetic star with equal mass. Here we ask, do data exist that could allow us to search for empirical evidence in support of hyperinflated stars? A photometric study of 44 eclipsing binaries in the Kepler field by Cruz et al. may help us in our search. The Cruz et al. study, although subject to large uncertainties, hints at the presence of hyperinflation in some of the 88 stars in their sample. Their data enable us to set theoretical limits on the maximum strength Bc of magnetic fields inside their sample stars. According to our magnetoconvective model, the average empirical inflations found from analysis of the Cruz et al. data can be replicated if Bc ≈ 10 kG inside stars with masses greater than ∼0.6 M⊙. On the other hand, in stars with masses less than ∼0.4 M⊙, our model predicts that the average empirical inflations of the stars may approach hyperinflated status. Such stars may require significantly stronger internal fields, i.e. Bc ≈ 100–300 kG. High-resolution spectroscopy of the Kepler binaries could help to confirm or refute our conclusions.
{"title":"Searching for Low-mass Stars with Magnetically Induced Hyperinflated Radii","authors":"D. J. Mullan and J. MacDonald","doi":"10.3847/1538-4357/ae4c55","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4c55","url":null,"abstract":"Precise empirical estimates of stellar radii have revealed that the radii of certain low-mass stars are inflated relative to stellar structure predictions: the largest inflations occur in magnetically active stars. Theoretically, the radii of magnetically active stars are in some cases found to be “hyperinflated” to roughly double the radius of a nonmagnetic star with equal mass. Here we ask, do data exist that could allow us to search for empirical evidence in support of hyperinflated stars? A photometric study of 44 eclipsing binaries in the Kepler field by Cruz et al. may help us in our search. The Cruz et al. study, although subject to large uncertainties, hints at the presence of hyperinflation in some of the 88 stars in their sample. Their data enable us to set theoretical limits on the maximum strength Bc of magnetic fields inside their sample stars. According to our magnetoconvective model, the average empirical inflations found from analysis of the Cruz et al. data can be replicated if Bc ≈ 10 kG inside stars with masses greater than ∼0.6 M⊙. On the other hand, in stars with masses less than ∼0.4 M⊙, our model predicts that the average empirical inflations of the stars may approach hyperinflated status. Such stars may require significantly stronger internal fields, i.e. Bc ≈ 100–300 kG. High-resolution spectroscopy of the Kepler binaries could help to confirm or refute our conclusions.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"59 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506751","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae4902
Cory M. Whitcomb, J.-D. T. Smith, Elizabeth Tarantino, Karin Sandstrom, Thomas S.-Y. Lai, 劭愉 賴, Lee Armus, Alberto Bolatto, Martha Boyer, Daniel A. Dale, Bruce T. Draine, Brandon S. Hensley, Desika Narayanan, Julia Roman-Duval and Evan D. Skillman
We explore the physical origins of the observed deficit of polycyclic aromatic hydrocarbons (PAHs) at subsolar metallicity using JWST/NIRCam imaging of the nearby galaxy M101, covering regions from solar metallicity (Z⊙) down to 0.4 Z⊙. These maps are used to trace the radial evolution of the shortest-wavelength PAH feature at 3.3 μm, which is emitted preferentially by the smallest PAHs (<100 carbon atoms). The fractional contribution of PAH 3.3 μm to the total PAH luminosity (ΣPAH) increases by 3× as metallicity declines, rising from ∼1% to ∼3% over the observed range, consistent with prior predictions from the inhibited grain growth model based on Spitzer spectroscopy. We explore model refinements including photon effects and alternative size evolution prescriptions and find that a modest amount of small grain photodestruction remains possible, provided the grain size cutoff does not exceed ∼55 carbon atoms. The best-fit models predict 3.3 μm/ΣPAH will rise to ∼5.6%–7.7% at 10% Z⊙. Surprisingly, even as ΣPAH drops significantly relative to the total infrared luminosity (TIR) as metallicity declines, 3.3 μm/TIR alone rises, potentially indicating the mass fraction of the smallest PAH grains increases as the total dust content in galaxies drops. The current model cannot fully reproduce this trend even if the unusually strong effects of changing radiation field hardness on 3.3 μm/TIR are included. This may be evidence that the smallest PAHs are uniquely robust against destruction and inhibited growth effects. These results highlight the pivotal role that short-wavelength PAH emission can play in studies of low-metallicity and high-redshift galaxies.
{"title":"The Metallicity Dependence of PAH Emission in Galaxies. II. Insights from JWST/NIRCam Imaging of the Smallest Dust Grains in M101","authors":"Cory M. Whitcomb, J.-D. T. Smith, Elizabeth Tarantino, Karin Sandstrom, Thomas S.-Y. Lai, 劭愉 賴, Lee Armus, Alberto Bolatto, Martha Boyer, Daniel A. Dale, Bruce T. Draine, Brandon S. Hensley, Desika Narayanan, Julia Roman-Duval and Evan D. Skillman","doi":"10.3847/1538-4357/ae4902","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4902","url":null,"abstract":"We explore the physical origins of the observed deficit of polycyclic aromatic hydrocarbons (PAHs) at subsolar metallicity using JWST/NIRCam imaging of the nearby galaxy M101, covering regions from solar metallicity (Z⊙) down to 0.4 Z⊙. These maps are used to trace the radial evolution of the shortest-wavelength PAH feature at 3.3 μm, which is emitted preferentially by the smallest PAHs (<100 carbon atoms). The fractional contribution of PAH 3.3 μm to the total PAH luminosity (ΣPAH) increases by 3× as metallicity declines, rising from ∼1% to ∼3% over the observed range, consistent with prior predictions from the inhibited grain growth model based on Spitzer spectroscopy. We explore model refinements including photon effects and alternative size evolution prescriptions and find that a modest amount of small grain photodestruction remains possible, provided the grain size cutoff does not exceed ∼55 carbon atoms. The best-fit models predict 3.3 μm/ΣPAH will rise to ∼5.6%–7.7% at 10% Z⊙. Surprisingly, even as ΣPAH drops significantly relative to the total infrared luminosity (TIR) as metallicity declines, 3.3 μm/TIR alone rises, potentially indicating the mass fraction of the smallest PAH grains increases as the total dust content in galaxies drops. The current model cannot fully reproduce this trend even if the unusually strong effects of changing radiation field hardness on 3.3 μm/TIR are included. This may be evidence that the smallest PAHs are uniquely robust against destruction and inhibited growth effects. These results highlight the pivotal role that short-wavelength PAH emission can play in studies of low-metallicity and high-redshift galaxies.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"219 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506694","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae4aa8
Henggeng Han, Song Wang, Huiqin Yang, Xue Li, Chuanjie Zheng, Xiangyu Li, Cunshi Wang and Jifeng Liu
Core–envelope coupling provides a reasonable explanation of the spin-down stalling of stars in open clusters, which was not predicted by classical gyrochronology. However, it remains an open question whether the coupling efficiency is constant or variable. M dwarfs, possessing thicker convective envelopes and thus longer coupling timescales than other late-type stars, are ideal objects for this investigation. In this work, based on the measurements from Large Sky Area Multi-Object Fiber Spectroscopic Telescope and Dark Energy Spectroscopic Instrument spectra, we construct new rotation–activity relations for M dwarfs. Unlike the traditional picture, we suggest that the new relation consists of three distinct regimes of fast, intermediate, and slow rotation, closely matching the three sequences of gyrochronology, namely the “Convective” sequence, “Gap,” and “Interface” sequence. Our study reveals, for the first time, a variable activity decay rate in the intermediate-rotation regime (i.e., the “Gap” region). This implies a varying core–envelope coupling efficiency, peaking toward the end of this region. It also coincides with the well-known stage of stalled stellar spin-down.
{"title":"Varying Core–Envelope Coupling Efficiency Identified from the Stellar Rotation–Activity Relation","authors":"Henggeng Han, Song Wang, Huiqin Yang, Xue Li, Chuanjie Zheng, Xiangyu Li, Cunshi Wang and Jifeng Liu","doi":"10.3847/1538-4357/ae4aa8","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4aa8","url":null,"abstract":"Core–envelope coupling provides a reasonable explanation of the spin-down stalling of stars in open clusters, which was not predicted by classical gyrochronology. However, it remains an open question whether the coupling efficiency is constant or variable. M dwarfs, possessing thicker convective envelopes and thus longer coupling timescales than other late-type stars, are ideal objects for this investigation. In this work, based on the measurements from Large Sky Area Multi-Object Fiber Spectroscopic Telescope and Dark Energy Spectroscopic Instrument spectra, we construct new rotation–activity relations for M dwarfs. Unlike the traditional picture, we suggest that the new relation consists of three distinct regimes of fast, intermediate, and slow rotation, closely matching the three sequences of gyrochronology, namely the “Convective” sequence, “Gap,” and “Interface” sequence. Our study reveals, for the first time, a variable activity decay rate in the intermediate-rotation regime (i.e., the “Gap” region). This implies a varying core–envelope coupling efficiency, peaking toward the end of this region. It also coincides with the well-known stage of stalled stellar spin-down.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae44f1
Rahul Sengar, David L. Kaplan, Emil Lenc, Akash Anumarlapudi, Natasha Hurley-Walker, Ziteng Wang, Laura Driessen, Dougal Dobie and Tara Murphy
We report the discovery and timing of two pulsars from a sample of four circularly polarized sources identified in radio continuum images taken as part of the Australian SKA Pathfinder Variables and Slow Transients survey. Observations with the Parkes (Murriyang) radio telescope confirmed both sources as normal pulsars with high dispersion measures (DMs). PSR J1646−4451 has a spin period of 217 ms and a DM of 928 cm−3 pc, while PSR J1837−0616 exhibits a spin period of 118 ms and a DM of 793 cm−3 pc. These pulsars show extreme pulse broadening due to scattering, with measured scattering timescales of 117 ms and 75 ms at observing frequencies of ∼1.8 GHz, respectively. These measurements imply extrapolated scattering timescales at 1 GHz of ∼1346 ms and 740 ms, placing them among the most heavily scattered known pulsars. Our findings underscore the potential of using circular polarization in radio continuum images as a tool for identifying highly scattered pulsars. Future wide-field radio continuum surveys are poised to uncover a broader population of extreme pulsars, particularly those that are heavily scattered at 1.4 GHz, intrinsically faint, or residing in binaries—offering valuable insights into both pulsar demographics and the complex structure of the ionized interstellar medium.
{"title":"Discovery of Two Highly Scattered Pulsars from Image-based Circular Polarization Searches with the Australian SKA Pathfinder","authors":"Rahul Sengar, David L. Kaplan, Emil Lenc, Akash Anumarlapudi, Natasha Hurley-Walker, Ziteng Wang, Laura Driessen, Dougal Dobie and Tara Murphy","doi":"10.3847/1538-4357/ae44f1","DOIUrl":"https://doi.org/10.3847/1538-4357/ae44f1","url":null,"abstract":"We report the discovery and timing of two pulsars from a sample of four circularly polarized sources identified in radio continuum images taken as part of the Australian SKA Pathfinder Variables and Slow Transients survey. Observations with the Parkes (Murriyang) radio telescope confirmed both sources as normal pulsars with high dispersion measures (DMs). PSR J1646−4451 has a spin period of 217 ms and a DM of 928 cm−3 pc, while PSR J1837−0616 exhibits a spin period of 118 ms and a DM of 793 cm−3 pc. These pulsars show extreme pulse broadening due to scattering, with measured scattering timescales of 117 ms and 75 ms at observing frequencies of ∼1.8 GHz, respectively. These measurements imply extrapolated scattering timescales at 1 GHz of ∼1346 ms and 740 ms, placing them among the most heavily scattered known pulsars. Our findings underscore the potential of using circular polarization in radio continuum images as a tool for identifying highly scattered pulsars. Future wide-field radio continuum surveys are poised to uncover a broader population of extreme pulsars, particularly those that are heavily scattered at 1.4 GHz, intrinsically faint, or residing in binaries—offering valuable insights into both pulsar demographics and the complex structure of the ionized interstellar medium.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506689","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae4c3a
T. Emil Rivera-Thorsen, Brian Welch, Taylor Hutchison, Matthew J. Hayes, Jane R. Rigby, Keunho Kim, Suhyeon Choe, Michael Florian, Matthew B. Bayliss, Gourav Khullar, Keren Sharon, Håkon Dahle, John Chisholm, Erik Solhaug, M. Riley Owens and Michael D. Gladders
At present, the best opportunity for detailed Lyman continuum (LyC) escape studies is in gravitationally lensed galaxies at z ≳ 2. Only one such galaxy currently exists in the literature with sufficient magnification and spatial resolution: the Sunburst Arc at redshift z = 2.37. Here, we present rest-frame optical JWST NIRSpec integral field observations of the Sunburst Arc that cover a large fraction of the source plane. From this dataset, we generate precise maps of interstellar medium (ISM) kinematics, dust geometry, ionization, and chemical enrichment. We extract a stacked spectrum of five gravitationally lensed images of the LyC leaking star cluster, as well as a μ−1 weighted, integrated spectrum of most of the galaxy, enabling a direct comparison to other LyC leakers in the literature. We find that the galaxy rotates but also shows strong, possibly dominant, signatures of turbulence, which are indicative of recent or ongoing major interaction. The cluster that leaks ionizing photons shows little difference from the rest of the galaxy in terms of kinematics or dust coverage, but dramatically elevated ionization, indicating that photoionization is the predominant mechanism that creates paths for LyC escape. We propose that tidal stripping of H i gas due to an interaction may have removed a large portion of the neutral ISM around the LyC emitting cluster, making it easier for the cluster to completely ionize the rest.
{"title":"The Sunburst Arc with JWST. IV. The Importance of Interaction, Turbulence, and Feedback for Lyman-continuum Escape","authors":"T. Emil Rivera-Thorsen, Brian Welch, Taylor Hutchison, Matthew J. Hayes, Jane R. Rigby, Keunho Kim, Suhyeon Choe, Michael Florian, Matthew B. Bayliss, Gourav Khullar, Keren Sharon, Håkon Dahle, John Chisholm, Erik Solhaug, M. Riley Owens and Michael D. Gladders","doi":"10.3847/1538-4357/ae4c3a","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4c3a","url":null,"abstract":"At present, the best opportunity for detailed Lyman continuum (LyC) escape studies is in gravitationally lensed galaxies at z ≳ 2. Only one such galaxy currently exists in the literature with sufficient magnification and spatial resolution: the Sunburst Arc at redshift z = 2.37. Here, we present rest-frame optical JWST NIRSpec integral field observations of the Sunburst Arc that cover a large fraction of the source plane. From this dataset, we generate precise maps of interstellar medium (ISM) kinematics, dust geometry, ionization, and chemical enrichment. We extract a stacked spectrum of five gravitationally lensed images of the LyC leaking star cluster, as well as a μ−1 weighted, integrated spectrum of most of the galaxy, enabling a direct comparison to other LyC leakers in the literature. We find that the galaxy rotates but also shows strong, possibly dominant, signatures of turbulence, which are indicative of recent or ongoing major interaction. The cluster that leaks ionizing photons shows little difference from the rest of the galaxy in terms of kinematics or dust coverage, but dramatically elevated ionization, indicating that photoionization is the predominant mechanism that creates paths for LyC escape. We propose that tidal stripping of H i gas due to an interaction may have removed a large portion of the neutral ISM around the LyC emitting cluster, making it easier for the cluster to completely ionize the rest.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"21 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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