Instrumentation and Methods for Astrophysics
Molecular absorption of Cherenkov light at CTAO
G. Voutsinas, M. Dalchenko, M. Gaug et al. (+3 more)
The Cherenkov
Telescope Array Observatory (CTAO) is the next-generation observatory for high energy \gamma-ray astronomy with unprecedented sensitivity and accuracy. Accurate estimation and mitigation of systematic uncertainties are crucial for its scientific performance. Atmospheric properties significantly influence both the generation and extinction of Cherenkov light generated by gamma and
cosmic rays interacting in the atmosphere. This study provides a detailed analysis of molecular extinction processes, including Rayleigh scattering and molecular absorption, and their impact on the transmission of Cherenkov light. We examine typical summer and winter behaviour of Rayleigh scattering and seasonal and event-driven variations of the main absorbing molecules, such as ozone and nitrogen
oxides, at the two CTAO array sites. Using simulations, we assess the effects of these variations on image intensity and trigger effective area, particularly during dynamic atmospheric events like stratosphere-to-troposphere transport. Based on our findings, we propose an atmospheric monitoring and calibration strategy to ensure that the CTAO meets its systematic uncertainty requirements, particularly for low-energy gamma-ray observations.
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All authors G. Voutsinas, M. Dalchenko, M. Gaug, O. Gueta, T. Montaruli, R. Zanin
Cosmology and Nongalactic Astrophysics
Diffusive dark fluids with Planck-2018 and DESI BAO DR2 Measurements
Shambel Sahlu and Amare Abebe
In this paper, we constrain the diffusive dark fluid cosmological model, wherein energy is transferred between the two dark components through a
diffusion process. We extended the work in Ref. \cite{sahlu2026observational} by employing
Cosmic Microwave Background (CMB) data from the Planck 2018 measurements in combination with
Baryon Acoustic Oscillation (BAO) data from the Dark Energy Spectroscopic Instrument (DESI) DR2 (2024). From the results, we found that the discrepancies in \(H_0\) measurements are \(1.90\sigma\) and \(1.72\sigma\) between the Planck 2018 value \((H_0 = 67.4\pm0.5\ \mathrm{km,s^{-1},Mpc^{-1}})\) and our diffusive model values, \(H_0 = 67.27^{+0.54}_{-0.55}\;,\) and \(68.35^{+0.31}_{-0.29} \), respectively. We also observe that the effects of the interaction on
cosmic evolution and structure formation; we emphasize this by computing the scale-dependent density contrast and the matter power spectrum, compared with the $\Lambda$CDM model.
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Instrumentation and Methods for Astrophysics
Single-star optical turbulence profiling techniques for the SHIMM and other Shack-Hartmann instruments
Ryan Griffiths, Timothy Butterley, Richard Wilson et al. (+1 more)
Atmospheric optical
turbulence (OT) monitoring is crucial for site characterisation at astronomical observatories and optical communications ground stations. The Shack-Hartmann Image Motion Monitor (SHIMM) instrument implements a fast, infrared Shack-Hartmann sensor to measure a low-resolution OT profile continuously throughout the day and night. This work presents advances made in Shack-Hartman optical
turbulence profiling techniques implemented on the SHIMM, including the derivation and validation of Z-tilt weighting functions, implementation of methods for correcting for non-zero exposure times, and for estimating the coherence time of optical
turbulence using the profile coupled with the Fast Defocus method. These techniques were tested via end-to-end Monte Carlo simulations of the SHIMM instrument. All measurements of integrated OT parameters were found to be in strong agreement with the simulation inputs evidenced by correlation coefficients close to one, small RMS error and bias. The accuracy of a four-layer model was also investigated, which showed high correlation with simulation inputs for all layers even in daytime OT conditions. This study suggests a Cn^2 sensitivity limit in the region of 2x10^-15 m^(1/3) and displays evidence of a cross-talk effect between the strong ground layer and first atmospheric layer.
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All authors Ryan Griffiths, Timothy Butterley, Richard Wilson, James Osborn
Astrophysics of Galaxies
Overmassive and Undermassive Massive Black Holes: The Role of Environment and Gravitational-Wave Recoils
David Izquierdo-Villalba
Understanding the connection between
galaxy properties and their central massive black holes (MBHs) is key to unveiling their co-
evolution. We use the ${\tt L{-}Galaxies{-} \it BH}$ semi-analytical model and the ${\tt Millennium}$ suite of simulations to investigate the physical origin of
galaxies hosting overmassive and undermassive MBHs with respect to the $M_{\rm BH}-M_*$ relation, across
stellar mass and
cosmic time. We find that distinct evolutionary pathways drive different offsets from the scaling relation. Overmassive MBHs are primarily associated with
galaxies that experienced enhanced merger history and secular activity. At $z\,{>}\,4$, this activity often leads to early, rapid MBH growth, frequently involving super-Eddington
accretion episodes. At low
redshift, a minority of overmassive systems ($20\%$) instead arise from environmental effects that reduce the
stellar mass of the host, shifting
galaxies above the relation without requiring additional MBH growth. Undermassive MBHs originate from two main channels. In massive
galaxies, gravitational
recoil following MBH mergers can eject the central MBH, temporarily leaving the
galaxy without a
nucleus. During this phase, MBHs coming from previous
galaxy mergers can become the new central MBHs, but their masses remain below the expected ones from the scaling relation, as they never co-evolved with their new host
galaxy. In low-mass
galaxies ($M_*<10^9 M_\odot$), undermassive MBHs are more commonly linked to a quiescent evolutionary history, with limited mergers and weak secular processes that suppress an efficient MBH growth. We therefore conclude that outliers of the $M_{\rm BH}-M_*$ do not arise from a single mechanism, but from the interplay between environmental effects, gravitational
recoils, and diverse MBH fueling histories, whose relative importance varies with
galaxy mass and
redshift.
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High Energy Astrophysical Phenomena
Discovery of energy-dependent phase variations in the polarization angle of Cen X-3
Qing-Chang Zhao, Lian Tao, Sergey S. Tsygankov et al. (+7 more)
We present a detailed polarimetric analysis of Cen X-3 using \ixpe observations during its high state, revealing complex energy-dependent polarization behavior. While phase-averaged polarization shows marginal energy dependence, phase-resolved analysis reveals that the energy dependence of the polarization angle (PA) is strongly phase-dependent, with dramatic variations visible in a few specific phase intervals. We model this behavior using a two-component polarization framework consisting of a pulsed component governed by the Rotating Vector Model (RVM) and an additional phase-dependent component. By allowing the additional component's polarized flux to vary with pulse phase while fixing its PA, the observed complex behavior can be reconciled with a single set of RVM parameters across all energies. Spectroscopic analysis using \ixpe, \nicer and \nustar during the high state reveals phase-modulated intrinsic hydrogen column density and covering fraction, suggesting that the wind properties are modulated with pulse phase. Our findings indicate that phase-dependent scattering in the disk wind may significantly alter the observed polarization properties of X-ray
pulsars.
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All authors Qing-Chang Zhao, Lian Tao, Sergey S. Tsygankov, Juri Poutanen, Hua Feng, Shuang-Nan Zhang, Hancheng Li, Mingyu Ge, Liang Zhang, Alexander A. Mushtukov
Earth and Planetary Astrophysics
Ionic Liquid Biospheres
Sara Seager, William Bains, Iaroslav Iakubivskyi et al. (+4 more)
Liquid is a fundamental requirement for life as we understand it, but whether that
liquid has to be water is not known. We propose the hypothesis that ionic
liquids (ILs) and deep eutectic solvents (DES) constitute a class of non-aqueous planetary
liquids capable of persisting on a wide range of bodies where stable
liquid water cannot exist. This hypothesis is motivated by key physical properties of ILs and DES. Many exhibit vapor pressures orders of magnitude lower than that of water and remain
liquid across exceptionally wide temperature ranges, from cryogenic to well above terrestrial temperatures. These properties permit stable
liquids to exist where
liquid water would rapidly evaporate or freeze and outside of bulk phases as persistent microscale reservoirs-such as thin films and pore-filling droplets. In other words, ILs and DES can persist in environments without requiring oceans, thick atmospheres, or narrowly regulated
climate conditions. We further hypothesize that ILs and DES could act as solvents for non-Earth-like life. Our hypothesis ex-tends to the idea that ILs and DES could enable prebiotic chemistry by providing long-lived, protective
liquid environments for complex organic molecules on bodies such as comets and asteroids, where
liquid water is absent. Based on the occurrence of DES-like mixtures as protective intracellular
liquids in desiccation-tolerant plants, we propose that ILs and DES might be solvents that life elsewhere purposefully evolves. We review
protein and other biomolecule studies in ILs and DES and outline planetary environments in which ILs and DES might occur by discussing available anions and cations. We present strategies to advance the IL/DES solvent hypothesis using laboratory studies, computational chemistry, planetary missions, analysis of existing spectroscopic
datasets, and modeling of
liquid microniches and chemical survival on small bodies.
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All authors Sara Seager, William Bains, Iaroslav Iakubivskyi, Rachana Agrawal, John Jenkins, Pranav Shinde, Janusz J. Petkowski
Astrophysics of Galaxies
Compact Absorbers surrounding the M87 AGN Revealed by ALMA Band 3 Observations1
Mahitosh Ray and Chorng-Yuan Hwang
We report detection of two compact absorption features surrounding the M87
nucleus and some extended absorption features perpendicular to the M87 jet using the Atacama Large millimeter-submillimeter-Array (ALMA) Band 3 data. One compact absorption feature appears at the position of the M87 AGN and the other $0.5\arcsec$ away from the AGN. These two compact features appear as well-defined negative structures in the integrated intensity map from the velocity range of $-500$ to $+2000~{\rm km~s^{-1}}$. These two features are separated by a distance of $\sim$40~pc assuming the distance of M87. The origin of these features could be dense molecular fragments associated with super massive black holes (SMBHs), possibly associated with a rotating
torus filament, or in-falling molecular fragments/objects feeding the
nucleus. The extended absorption features perpendicular to the jet appear in all velocity ranges and can be caused by shock compressed regions associated with the jet
knots A and C.
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Instrumentation and Methods for Astrophysics
Simulation and Data Processing of Beamforming Experiments with Four 21CMA Stations
Feiyu Zhao, Quan Guo, Junhua Gu et al. (+3 more)
We present an end-to-end simulation and data-processing framework for digital beamforming experiments conducted with four stations of the 21 Centimeter Array (21CMA). Motivated by the need to characterize instrumental systematics, such as those arising from station-level digital beam synthesis and two-stage channelization, and to validate the data-processing pipeline framework for a future upgraded 21CMA with beamforming capability across all stations, we simulate interferometric visibilities using realistic four-station layouts with
radio interferometer simulation software OSKAR. Two representative pointings are considered: a bright, complex Cassiopeia A field and a near-north celestial pole (NCP) calibration field. The sky model combines cataloged point sources with a diffuse
Galactic component from the Global Sky Model (GSM), and frequency-dependent thermal noise is injected. We further quantify the imprint of two-stage channelization by comparing an ideal beamformer with a coarse-channel phase approximation, demonstrating that off-axis sources exhibit a characteristic piecewise-linear spectral modulation across coarse-channel boundaries. A data-processing pipeline, including
Radio Frequency Interference (RFI) mitigation, calibration, imaging, and mosaicking steps consistent with current low-frequency
radio astronomy practice, is constructed. The resulting synthetic images and background root-mean-square (RMS) noise measurements demonstrate the feasibility of adapting established 21CMA calibration and imaging strategies to digital beamforming modes, and provide a framework that can be further developed for beam-aware processing in future full-scale 21CMA beamforming observations.
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All authors Feiyu Zhao, Quan Guo, Junhua Gu, Qian Zheng, Yan Huang, Yun Yu
Astrophysics of Galaxies
FEASTS and MHONGOOSE: HI Column Density Distribution at $z=0$ for $N_\mathrm{HI}>10^{17.8}\, \mathrm{cm}^{-2}$
Jing Wang, Xuchen Lin, Ze-Zhong Liang et al. (+24 more)
We present the first $z=0$ HI column density distribution function, $f(N_\mathrm{HI})$, extending down to $\log (N_\mathrm{HI}/\mathrm{cm}^{-2})=17.8$. This was derived from high-sensitivity 21-cm emission-line imaging at $\sim$1 kpc resolution. At high-column-densities (19.8$< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <$21.3), our results align with earlier $z=0$ studies but benefit from 100 times greater sensitivity. Comparisons with $z\sim3$
quasar absorption-line studies reveal that $f(N_\mathrm{HI})$ at $z=0$ is systematically lower by 0.1-0.4 dex for $19.2< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <21$. However, the distributions become comparable at $17.8< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <19.2$, suggesting weak
evolution in this regime. Extrapolating the length incidence ($\mathrm{d}N/\mathrm{d}X$) for $\log (N_\mathrm{HI}/\mathrm{cm}^{-2}) >17.5$ implies a covering fraction ($f_\mathrm{cov}$) of $\sim0.7$ within 1-kpc-scale HI-detected pixels at $z=0$. Notably, for $17.8< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <20$, impact parameters at a given $N_\mathrm{HI}$ are significantly lower than previous $z\sim0$ absorption-line results and TNG50 simulation predictions. This discrepancy indicates challenges in identifying
galaxy counterparts for absorbers and in recovering low-column-density HI within cosmological simulations. Finally, we derive a covering fraction of 0.006 for $\log (N_\mathrm{HI}/\mathrm{cm}^{-2}) >17.8$ gas within the virial radius around Milky-Way-like
galaxies. These findings provide new constraints on the baryonic flows and gaseous dynamics governing
galaxy evolution.
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All authors Jing Wang, Xuchen Lin, Ze-Zhong Liang, W.J.G. De Blok, Hong Guo, Zhijie Qu, Céline Péroux, Kentaro Nagamine, Luis C. Ho, Dong Yang, Simon Weng, Claudia Del P. Lagos, Xinkai Chen, George Heald, J. Healy, Qifeng Huang, Peter Kamphuis, D. Kleiner, Di Li, Siqi Liu, F. M. Maccagni, Lister Staveley-Smith, Zherong Su, Freeke Van De Voort, Fabian Walter, Fangxiong Zhong, Siwei Zou
High Energy Astrophysical Phenomena
Transverse Oscillations and Wave Propagation in the Magnetically Dominated M87 Jet
Hyunwook Ro, Motoki Kino, Kazuhiro Hada et al. (+6 more)
We present an in-depth analysis of transverse oscillations in the M87 jet, as identified in our previous study (Ro et al. 2023a), which reported oscillatory patterns with a characteristic period of $\sim$1 year in the edge-brightened jet structure extending up to 12\,mas from the core. This work is based on high-cadence KaVA 22\,GHz observations conducted from December 2013 to June 2016. By analyzing the transverse velocity profiles and the spatial
evolution of the oscillations, we find that the oscillations propagate downstream along the jet, with a wavelength of $\sim9-10$\,mas. A single-mode sinusoidal wave model applied to the ridge lines successfully reproduces the observed transverse oscillations and yields superluminal wave speeds of $\sim2.7-2.9\,c$, consistent with the bulk jet velocity in this region. These findings suggest that the transverse oscillations may be interpreted either as transverse MHD waves – possibly excited by jet precession, nutation, or quasi-periodic
magnetic flux eruptions near the central engine – or as manifestations of jet instabilities, such as current-driven instabilities (CDIs). Further investigation is required to distinguish between these scenarios and to clarify the dominant physical mechanism.
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All authors Hyunwook Ro, Motoki Kino, Kazuhiro Hada, Yosuke Mizuno, Yuzhu Cui, Kunwoo Yi, Tomohisa Kawashima, Jongho Park, Bong Won Sohn
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Weinberg Angle, Neutron Abundance in BBN, and Lifetime
Cheng Tao Yang and Johann Rafelski
We present state of the art kinetic theory determination of the
neutron abundance available for the Big-Bang nucleosynthesis (BBN). Our work is motivated by the study of the
neutron lifespan measured in the laboratory and the unknown strength of weak interactions coupling constant $G_\mathrm{F}$ at finite temperature in the
primordial Universe. We draw
attention to the relevant dependence of $G_\mathrm{F}$ on the
symmetry breaking Weinberg angle $s^2_\mathrm{W}$, a free parameter in the standard model of particle physics. We establish how the value of $s^2_\mathrm{W}$ by way of $G_\mathrm{F}$ modification influences
neutron abundance available for BBN and
neutron lifetime.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Sommerfeld enhancement from unstable final-state particles in dark matter annihilation
Tomohiro Abe, Ryosuke Sato and Takumu Yamanaka
We study the Sommerfeld enhancement of the annihilation cross section of dark matter into heavier unstable particles. In this process, the annihilation products become non-relativistic near the kinematical threshold. If they experience long-range interactions with each other, their wave function is distorted from a plane wave, and the annihilation cross section can be significantly enhanced. When evaluating the Sommerfeld enhancement from the long-range interactions between the annihilation products, the decay of the products needs to be taken into account. We treat this issue by including the decay width in the Schrödinger equations of the two-body wave function of the annihilation products. We find that bound states of the annihilation products with a narrow decay width enhance the annihilation cross section through a resonant effect. At the same time, this formulation automatically includes the annihilation process with off-shell final state particles, which is relevant for a wide decay width. We show that the resonant effect significantly affects the prediction of the dark matter relic abundance.
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Astrophysics of Galaxies
The MUSE-Faint survey V. The binary fraction of Leo T
Daniel Vaz, Jarle Brinchmann, Sebastian Kamann et al. (+3 more)
The Leo T
dwarf galaxy, the faintest and least massive
galaxy known to have recent
star formation ($\leq 1~Gyr$), exhibits a high dynamical mass-to-light ratio based on its
stellar velocity dispersion ($7.07^{+1.29}_{-1.12}~\mathrm{km\ s^{-1}}$), indicating extreme dark matter dominance. We present the first measurement of the binary fraction of Leo T using MUSE-Faint multi-epoch spectroscopy. We also determine the binary fraction for both young and old
stellar populations separately and gain insights into binary properties in more metal-poor environments than the Milky Way or Magellanic Clouds. Finally, we investigate the potential impact of binaries on the inferred
stellar velocity dispersion. We employed a forward model methodology combining empirical scaling relations to predict
stellar velocity variations and a constrained binary distribution from the literature. To estimate the close binary fraction, we limited the maximum semi-major axis ($a < 10~\mathrm{au}$) and repeated the analysis with a semi-amplitude threshold ($\geq~10~ \mathrm{km\ s^{-1}}$) to check the impact on the inferred
stellar velocity dispersion.} The overall binary fraction of Leo T is estimated to be $55^{+40}_{-9} \%$, consistent with similar systems. The close binary fraction ($a < 10~\mathrm{au}$) is $30^{+34}_{-9} \%$, which is aligned with low-
metallicity environments. We found a lower binary fraction for the older
stellar population ($15^{+43}_{-15} \%$) when compared to the younger population ($35^{+40}_{-6} \%$). Finally, we found no significant inflation of the velocity dispersion estimate due to binary motions when compared to the dispersion inferred from the co-added spectra. This suggests that the co-added spectra effectively provide period-averaged velocities of the
stars, thus mitigating the impact of binaries on the overall velocity dispersion measurement.
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All authors Daniel Vaz, Jarle Brinchmann, Sebastian Kamann, Sara Saracino, P. A. C. Cunha, Mariana P. Júlio
Solar and Stellar Astrophysics
Polarity-Resolved Far-Side Magnetograms Based on Helioseismic Measurements
Amr Hamada, Kiran Jain, Hanna Strecker et al. (+2 more)
Understanding and monitoring
solar active regions is essential for operational space-weather
forecasting and improved
solar dynamo modeling. This requires comprehensive 360-degree observations of the Sun. While space-weather
forecasting has long relied successfully on high-quality observations of the Earth-facing hemisphere, a critical gap remains due to the lack of direct, continuous
magnetic field measurements of far-side active regions, particularly
magnetic field strength, polarity configurations, and related parameters. We present a methodology for inferring
magnetic field distributions of active regions in helioseismic maps of the far hemisphere. The analysis focuses on identifying the
magnetic polarities of opposing components of a helioseismic signature and applying stable, continuous polarity assignment to large-scale
magnetic structures derived from such maps. These helioseismic signatures reliably resolve strong active regions, especially those that later appear as major rotation regions when they rotate into Earth view. Polarity boundaries are identified by analyzing the bimodal longitudinal variance profile of the seismic signal within each region, after which Hales law is applied to establish east-west ordering consistent with the
solar cycle. The method produces polarity-resolved far-side magnetograms suitable for integration with near-side observations, enabling construction of full-Sun
magnetic boundary conditions for coronal and
solar wind modeling and providing a critical step toward improved heliospheric simulations and operational
forecasting.
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All authors Amr Hamada, Kiran Jain, Hanna Strecker, Charles Lindsey, David Orozco Suarez
Earth and Planetary Astrophysics
Dynamics of planetary rings under thermal forces
Wen-Han Zhou, Eiichiro Kokubo, Harrison Agrusa et al. (+5 more)
Planetary rings provide natural laboratories for studying the fundamental processes that govern the
evolution of planetary systems. However, several key features, such as the sharp inner edges of Saturn's rings remain unresolved. In this work, we introduce and quantify the Eclipse-Yarkovsky (EY) effect, a thermal torque arising from asymmetric thermal emission of particles during planetary eclipses, which is effective for particles larger than millimeters in size. We formulate this effect within a continuum framework appropriate for collisionally coupled planetary rings and derive the continuum
evolution equation that includes the EY torque and viscous
diffusion (Eq.26), constraining its magnitude using ring particle
spin distributions obtained from N-body simulations. We find that the EY effect systematically produces a positive angular momentum flux that could overcome the viscous torque, driving ring material outward and leading to long-term decretion. The total EY torque principally depends on the optical depth, in which we identify three dynamical regimes: dense, transitional, and tenuous regimes, each exhibiting distinct evolutionary pathways. In the dense or transition regimes, the EY torque can produce a sharp inner edge such as that of Saturn's A ring. In the tenuous regime, it can drive an entire ring outward while preserving shape. This outward transport may also facilitate satellite formation beyond the Roche limit. We also quantitatively show that planetary thermal radiation on rings exerts an opposing torque, namely planetary-Yarkovsky effect, whose importance depends on planetary emissivity and ring-particle albedo, and may lead to inward transport in Saturn's close-in rings.
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All authors Wen-Han Zhou, Eiichiro Kokubo, Harrison Agrusa, Gregorio Ricerchi, Aurelien Crida, David Vokrouhlicky, Yun Zhang, Ronald-Louis Ballouz
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Nonlinear physics of axion inflation
Oleksandr Sobol, Richard von Eckardstein, Elias Koch et al. (+3 more)
An
axion-like field coupled to an Abelian gauge field provides one of the simplest inflationary models that is free from the eta problem and possesses an efficient reheating mechanism. For sufficiently large coupling, this system enters a regime of strong gauge-field backreaction, exhibiting rich and intricate dynamics. In this work, we employ a semi-analytical method, the gradient-expansion formalism, to perform a comprehensive parameter scan and determine the precise conditions under which backreaction sets in. Previous studies have shown that the Anber-Sorbo solution, in which the potential-gradient force acting on the
axion is balanced by Hubble friction and gauge-field backreaction, is unstable. Here, we broaden the parameter space and identify a new region in which the Anber-Sorbo solution remains stable despite strong backreaction. Although our analysis is restricted to a homogeneous
axion field and to perturbations that depend only on time, we expect that this stability property can be extrapolated to generic time- and space-dependent perturbations. This newly identified region therefore represents a distinct type of backreaction - stable backreaction - which may not be accompanied by the rapid growth of perturbations. We further investigate the nonlinear behavior of solutions in the backreaction regime in a toy model (de Sitter, constant potential slope, no
axion gradients), identifying a supercritical
Hopf bifurcation at the onset of instability, a nontrivial limit cycle in the unstable regime, and burst-like oscillatory dynamics. Finally, we present a more stringent criterion for the onset of (unstable) backreaction, based on crossing the instability threshold, and apply this criterion to two
benchmark inflationary models.
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All authors Oleksandr Sobol, Richard von Eckardstein, Elias Koch, Svetlana Gurevich, Uwe Thiele, Kai Schmitz
Astrophysics of Galaxies
A Tale of Two Origins: In-Situ versus Accreted Nitrogen-Rich Field Stars in the MW
Yi Qiao, Baitian Tang, José G. Fernández-Trincado et al. (+14 more)
Spectroscopic surveys have identified significant numbers of metal-poor nitrogen-rich (N-rich) field
stars. These
stars are strong candidates for escapees from globular clusters (GCs), as their distinctive nitrogen enhancement mirrors the chemical patterns observed in some of the members of GCs. As part of the effort to characterize their chemodynamical properties, we derived abundances for up to 25 elements in a sample of 33 N-rich field
giant stars (18 of them are studied for the first time) using high-resolution optical spectroscopy. We confirm their elevated abundances of N, Na, and Al, strongly supporting a GC origin. Given that
Galactic GCs themselves formed within diverse progenitor
galaxies, we sought to identify the ancestral systems of these N-rich field
stars. By analyzing their dynamical parameters, we separated the sample into high-energy (HE) and low-energy (LE) groups. The HE group exhibits lower [{\alpha}/Fe] and enhanced r-process abundances compared to the LE group. This indicates that the HE
stars likely escaped from GCs accreted from massive
dwarf galaxies (e.g.,
Gaia-Sausage-Enceladus), while the LE
stars probably originated from in-situ GCs. We also find that the chemical pattern of these N-rich
stars with [Fe/H] {\lessapprox} -1.0 are similar to the high-
redshift ”N-emitters”. Furthermore, orbital integrations revealed a close encounter between one N-rich field
star and the globular cluster NGC 6235. Our work demonstrates the potential of using chemodynamical analyses to trace
Galactic assembly through chemical peculiar
stars, while highlighting that larger samples and more precise data in the future are crucial to establish definitive origins.
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All authors Yi Qiao, Baitian Tang, José G. Fernández-Trincado, Mingjie Jian, Carlos Allende Prieto, Hongliang Yan, Zhen Yuan, Yang Huang, Thomas Masseron, Beatriz Barbuy, Jianrong Shi, Chengyuan Li, Ruoyun Huang, Jiajun Zhang, Jing Li, Chao Liu, Weishan Zhu
Earth and Planetary Astrophysics
An Adolescent and Near-Resonant Planetary System Near the End of Photoevaporation
Mu-Tian Wang, Fei Dai, Hui-Gen Liu et al. (+28 more)
Young
exoplanets provide vital insights into the early dynamical and atmospheric
evolution of planetary systems. Many multi-
planet systems younger than 100 Myr exhibit mean-motion resonances, likely established through convergent disk migration. Over time, however, these resonant chains are often disrupted, mirroring the Nice model proposed for the
Solar System. We present a detailed characterization of the ~200-Myr-old TOI-2076 system, which contains four sub-Neptune
planets between 1.4 and 3.5 Earth radii. We demonstrate that its
planets are near but not locked in mean-motion resonances, making the system dynamically fragile. The four
planets have comparable core masses but display a monotonic increase in hydrogen and helium (H/He) envelope mass fractions (stripped-1%-5%-5%) with decreasing
stellar insolation. This trend is consistent with atmospheric mass-loss due to photoevaporation, which predicts that the envelopes of irradiated
planets either erode completely or stabilize at a residual level of ~1% by mass within the first few hundred million years, with more distant, less-irradiated
planets retaining most of
primordial envelopes. Additionally, previous detections of metastable helium
outflows rule out a pure water-world scenario for TOI-2076
planets. Our finding provides direct observational evidence that the dynamical and atmospheric reshaping of compact planetary systems begin early, offering an empirical anchor for models of their long-term
evolution.
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All authors Mu-Tian Wang, Fei Dai, Hui-Gen Liu, Howard Chen, Zhecheng Hu, Erik Petigura, Steven Giacalone, Eve Lee, Max Goldberg, Adrien Leleu, Andrew W. Mann, Madyson G. Barber, Joshua N. Winn, Karen A. Collins, Cristilyn N. Watkins, Richard P. Schwarz, Howard M. Relles, Francis P. Wilkin, Enric Palle, Felipe Murgas, Avi Shporer, Ramotholo Sefako, Keith Horne, Hugh P. Osborn, Yann Alibert, Luca Fossati, Andrea Fortier, Sérgio Sousa, Alexis Brandeker, Pierre Maxted, Alexia Goldenberg
Instrumentation and Methods for Astrophysics
Mechanism for reduction of the afterpulsing rate of PMTs
Kai Morita, Mitsunari Takahashi, Habib Ahammad Mondal et al. (+7 more)
Photomultiplier tubes (PMTs) are used in Imaging Atmospheric Cherenkov
Telescopes (IACTs) to detect Cherenkov light produced by air showers induced by gamma rays in the atmosphere. The afterpulsing rate of the PMTs for the Large-Sized
Telescopes (LSTs) of the Cherenkov
Telescope Array Observatory (CTAO) was found to increase if they were kept unused in storage. In contrast, PMTs that had been operated in the first LST showed a slight decrease in the rate. This decrease could be explained by a reduction of residual gas caused by ion feedback, although the detailed mechanism remained unclear. In this study, to investigate factors responsible for the
evolution in the afterpulsing rate, we operated several PMTs under different high voltage and light illumination conditions. We monitored their rate daily for three weeks to compare their
evolution under different conditions. We found that the reduction of afterpulses require both illumination and high-voltage operation. Notably, the reduction strongly depends on the applied high voltage and is closely correlated with the integrated anode current. Therefore, we conclude that the reduction of residual gas is mainly caused by ionization occurring at later dynodes of the PMTs, and the ions are trapped by the dynodes. We also discuss a possible explanation of the reduction of afterpulsing rate by later dynodes.
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All authors Kai Morita, Mitsunari Takahashi, Habib Ahammad Mondal, Hidetoshi Kubo, Hideyuki Ohoka, Seiya Nozaki, Shunsuke Sakurai, Takayuki Saito, Tokonatsu Yamamoto, Yusuke Inome
Solar and Stellar Astrophysics
The solar-like latitudinal distribution of flaring activities revealed by TESS, APOGEE and GALAH
Huiqin Yang, Shuai Liu, Yang Huang et al. (+2 more)
Flare flux reflect contribution from active regions rather than the whole hemisphere of a
star. Unlike the amplitude of light-curves caused by starspots, the
flare detection is independent of inclination. The two valuable properties of
flares can be used to reveal the latitudinal distribution of active regions (LaDAR) given that LaDAR is coupled with inclination and location information in spatially unresolved
stars. We detected $\sim 27000$
flares of 1510 flaring
stars in the TESS mission with the corresponding inclinations obtained. The detection rate of flaring
stars shows that
flares are hard to detect on
stars with low inclination, indicating that
flares occur mainly at low latitudes. Further investigation of the relationship between the apparent flaring activity and inclination along with the rotation period finds that as the rotation period increases from a
solar-like rotation to an ultra-fast rotation, the mean latitude of active regions increases from $\theta \approx 15^{\circ}$ to $\theta \approx 27^{\circ}$, whose trend is in line with the rotation–activity relationship. The LaDAR indicates that
flares are attributed to small-scale fields that are formed at low latitudes, while polar spots that are associated with large-scale fields are inactive and are difficult to trigger
flares.
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All authors Huiqin Yang, Shuai Liu, Yang Huang, Bowen Zhang, Jifeng Liu
High Energy Astrophysical Phenomena
Observational Properties of Near-Maximally Spinning Supermassive Black Holes
Tegan A. Thomas, Angelo Ricarte, Cora Prather et al. (+1 more)
Black holes described by the Kerr metric can have a theoretical maximum dimensionless
spin parameter of $a_\bullet = 1$, but several effects may limit the maximum
spin parameter in astrophysical systems. We perform general relativistic magnetohydrodynamics simulations of
accretion flows around black holes with $a_\bullet = 0.9375$ and $a_\bullet = 0.998$, each corresponding to a proposed astrophysical limit in the literature. We then perform full polarized general relativistic ray-tracing to produce astrophysical movies of these simulations, as can be spatially resolved by the Event Horizon
Telescope (EHT) and its extensions. Although many properties of black holes and
accretion flows evolve rapidly as $a_\bullet \to 1$, we find that our $a_\bullet=0.9375$ and $a_\bullet=0.998$ simulations are remarkably similar, both in terms of their GRMHD fluid properties and their full-Stokes, time-variable images. This suggests that previous work using simulations with $a_\bullet \approx 0.9375$ may be representative of models with $a_\bullet \gtrsim 0.9375$ in most practical cases. Our calculations suggest that shape and size constraints on the
photon ring, enabled by extensions of the EHT into space by missions such as the Black Hole Explorer (BHEX) may be the only practical way to distinguish between models with different
spin parameters as $a\to 1$.
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All authors Tegan A. Thomas, Angelo Ricarte, Cora Prather, Hyerin Cho
High Energy Astrophysical Phenomena
Evidence for a Delayed UV Counterpart to X-ray Quasi-periodic Eruptions in Ansky
Hengxiao Guo, Zhen Yan, Ya-Ping Li et al. (+15 more)
X-ray quasi-periodic eruptions (QPEs) represent a novel population of extreme, repeating
nuclear transients whose physical origins remain debated. A defining characteristic of QPEs has been their exclusive detection in the X-ray band, with a notable absence of correlated multi-wavelength counterparts. Here we report the first detection of a recurrent UV response temporally coupled to the X-ray QPE signal in the source Ansky/ZTF19acnskyy. The UV emission displays coherent periodic modulations over five consecutive cycles, systematically lagging the X-ray eruptions by $0.96^{+0.38}_{-0.39}$ days, with a cross-correlation coefficient of $r_{\rm max} \sim 0.6$. We suggest that the detectability of this corresponding signal may be enabled by Ansky's unusually long recurrence timescale, which could reduce the temporal smearing of the UV response seen in more rapid QPEs. The observed delay may correspond to a
diffusion timescale associated with heated blobs. However, we cannot exclude the possibility that the lag corresponds to the light-crossing time associated with X-ray irradiation that originates near the central black hole and propagates to the outer UV-emitting region. While numerous QPE models have been proposed, any viable model for Ansky must be able to simultaneously explain the presence of a UV counterpart, its measured time lag, and the previously observed steadily increasing recurrence period.
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All authors Hengxiao Guo, Zhen Yan, Ya-Ping Li, Joheen Chakraborty, Paula Sánchez-Sáez, Lorena Hernández-García, Wenda Zhang, Jingbo Sun, Shuang-liang Li, Hongping Deng, Wenwen Zuo, Hiromichi Tagawa, Xin Pan, Minghao Zhang, Patricia Arévalo, Paulina Lira, Chichuan Jin, Minfeng Gu
Astrophysics of Galaxies
Effects of resolution and local stability on galactic disks: Halo resolution and softening on bar formation
SungWon Kwak, Ivan Minchev, Matthias Steinmetz et al. (+1 more)
Using N-body simulations, we examine the impact of dark matter (DM)
halo resolution and gravitational softening on bar formation. We generate isolated disk-
halo systems with fixed
stellar disk parameters, varying the number of
halo particles, softening lengths, and
halo concentration to modulate disk stability via the central DM fraction. The effects of DM resolution ($\mratio=1$, 10, and 100) on bar formation are less pronounced in more unstable disks, in which the overall evolutionary path is similar except that the lowest DM resolution model suffers gradual bar weakening. Irrespective of the
halo resolution, large softening, $\epsdm$, flattens the central
halo density profile within the softening scale, impeding angular momentum transfer to the nascent bar and preventing bar formation in more stable models. In unstable models with $\epsdm=0.96 \, \kpc$, a small bar still emerges due to enhanced initial instability and a larger seed perturbation, yet its strength remains capped at $F_2 \approx 0.3$ owing to unresolved central dynamical friction. Despite the destabilizing effect of reduced central DM fractions, our results indicate that deficient central angular momentum exchange can still suppress bar growth. Furthermore,
halo softening influences buckling instability, as larger values ($\epsdm=0.30$ and $0.60 \, \kpc$) inhibit central vertical heating, exacerbating radial-vertical velocity dispersion anisotropies and triggering stronger buckling. We recommend adopting $ \mratio \le 10 $, $ \mstar \leq 10^4 \, \Msun $, and $ \epsdm < 0.30\,\mathrm{kpc}$ when investigating the formation and
evolution of non-axisymmetric structures in Milky Way-mass
galaxies.
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All authors SungWon Kwak, Ivan Minchev, Matthias Steinmetz, Sukyoung K. Yi
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Probing Planck-Scale Physics with High-Frequency Gravitational Waves
Stefano Profumo
We develop a framework for testing
quantum gravity through the
stochastic gravitational-wave background produced by evaporating near-Planck-mass
primordial black holes. Because gravitons free-stream from the emission region without rescattering, they preserve a direct spectral record of the black-hole temperature–mass relation $T(M)$, a relation that is erased for all other Hawking-radiated species by rapid thermalization. We translate six representative phenomenological beyond-semiclassical frameworks (the generalized uncertainty principle, loop
quantum gravity, noncommutative geometry, asymptotic safety, string/Hagedorn physics, and tunneling backreaction) into distinct $T(M)$ parametrizations and compute the resulting gravitational wave spectra numerically. Modifications that suppress $T(M)$ shift the spectral peak by up to ten decades in frequency, in some cases into the sensitivity bands of next-generation interferometers or resonant-cavity detectors, while models imposing a hard evaporation cutoff produce distinctive peak morphologies that discriminate between
quantum-
gravity scenarios. We further discuss the impact of different choices for post-inflationary conditions in the very early universe. We find that the relative spectral displacement between the standard Hawking prediction and any modified model is cosmology-independent, hence spectral shape rather than absolute peak frequency provides the cleanest probe of Planck-scale physics.
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