Solar and Stellar Astrophysics
A search for late-type brown dwarfs in the Euclid Quick Data Release 1
Frank Kiwy, J. Davy Kirkpatrick, Adam C. Schneider et al. (+7 more)
We present the identification and characterization of 15 mid-to-late T
dwarf candidates in the Euclid Quick Release 1 (Q1)
dataset, based on a combined photometric and spectroscopic analysis. Candidates were initially selected via color-based cuts in the Euclid $Y_E - J_E$ and $J_E - H_E$ color-color space, targeting the region occupied by ultracool
dwarfs in synthetic photometry from the Sanghi et al. (2024) sample. From an initial pool of 38,845 sources, we extracted low-resolution near-infrared spectra from the Euclid NISP instrument and applied a two-stage validation procedure that included spectral template fitting followed by visual inspection. Eight of the 15 validated candidates are newly identified objects with no prior literature association. We examined their morphological and photometric properties and compared them with established spectral standards. Photometric distances were derived using band-averaged distance modulus estimates. We discuss the limitations and promise of the Euclid survey for ultracool
dwarf studies, and demonstrate the potential for discovering substellar populations beyond the reach of current wide-field surveys.
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All authors Frank Kiwy, J. Davy Kirkpatrick, Adam C. Schneider, Aaron M. Meisner, Jacqueline K. Faherty, Marc J. Kuchner, Daniella Bardalez Gagliuffi, Sarah L. Casewell, Thomas P. Bickle, The Backyard Worlds: Planet 9 Collaboration
Astrophysics of Galaxies
The Competing Influence of Ram Pressure and Tidal Interaction in NGC 2276
Luka Matijević, Neven Tomičić, Antonino Marasco et al. (+9 more)
The
evolution of
galaxies in groups is profoundly influenced by a variety of physical processes, with ram pressure and
tidal interactions playing pivotal roles in shaping their structural and evolutionary pathways. The relative influence of these two processes is still debated in groups compared to clusters, as ram pressure is less understood there. We study NGC 2276, a nearby
galaxy (z$\sim$0.0079) where the dominant process is still an open question. We examine the distribution of
stellar populations in NGC 2276 using multiwavelength data to assess potential evidence of
tidal interactions and ram-pressure stripping. We present the first HST WFC3/UVIS images of NGC 2276, and use them to investigate the distribution of
stellar populations across the disk of NGC 2276, where we assume that the bluer broadband filters mainly trace younger
stellar populations, while the redder filters trace mainly older
stellar populations. Furthermore, by comparing HST images with maps of H$\alpha$ emission from Calar Alto's PMAS/PPAK integral field unit (IFU) and near-IR maps from Spitzer's IRAC, we identify arm-like overdensity features that trace the spiral structure of this
galaxy and tracked the variation of their pitch angle with radius. Our results indicate that the distribution of the
stellar populations is asymmetrical. The youngest
stellar populations (up to $\sim$100 Myr) show higher concentration on the leading side of the
galaxy and are more diffuse on the trailing side, consistent with gas compression due to ram-pressure. This asymmetry is visible in the red filters as well. We also show that the average pitch angles of the overdensity features increase with galactocentric distance. Our findings are consistent with the fact that ram pressure is the leading mechanism for the peculiar morphology of NGC 2276, but do not exclude the possibility that
tidal interactions could have played a role.
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All authors Luka Matijević, Neven Tomičić, Antonino Marasco, Alessandro Ignesti, Augusto E. Lassen, Rory Smith, Paul Sell, Ian D. Roberts, Andreas Zezas, Konstantina Anastasopoulou, Panagiotis Kotoulas, Roko Bašić
Solar and Stellar Astrophysics
Using a neural network approach and starspots dependent models to predict effective temperatures and ages of young stars
Marco Tarantino, Loredana Prisinzano, Nicoletta D Angelo et al. (+2 more)
This study presents a statistical approach to accurately predict the effective temperatures of pre-main sequence
stars, which are necessary for determining
stellar ages using the isochrone methodology and cutting-age starspots-dependent models. By training a Neural Network model on high-quality spectroscopic temperatures from the
Gaia-ESO Survey as the response variable, and using photometric data from
Gaia DR3 and 2MASS catalogs as explanatory variables, we implemented a methodology to accurately derive the effective temperatures of much larger populations of
stars for which only photometric data are available. The model demonstrated robust performance for low-mass
stars with temperatures below 7000 K, including young
stars, the primary focus of this work. Predicted temperatures were employed to construct Hertzsprung-Russell diagrams and to predict
stellar ages of different young clusters and
star forming regions through isochrone interpolation, achieving excellent agreement with spectroscopic-based ages and literature values derived from model-independent methods like lithium equivalent widths. The inclusion of starspot evolutionary models improved the age predictions, providing a more accurate description of
stellar properties. Additionally, the results regarding the effective temperature and age predictions of the young clusters provide evidence for intrinsic age spreads in the youngest clusters, suggesting multiple formation events over time.
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All authors Marco Tarantino, Loredana Prisinzano, Nicoletta D Angelo, Francesco Damiani, Giada Adelfio
Instrumentation and Methods for Astrophysics
Super-resolution wavefront reconstruction in adaptive-optics with pyramid sensors
Carlos M. Correia, Charlotte Z. Bond, João Aveiro et al. (+3 more)
Super-resolution (SR) refers to a combination of optical design and signal processing techniques jointly employed to obtain reconstructed wave-fronts at a higher-resolution from multiple low-resolution samples, overcoming the intrinsic limitations of the latter. After compelling examples have been provided on multi-Shack-Hartman (SH) wave-front sensor (WFS) adaptive optics systems performing atmospheric
tomography with
laser guide
star probes, we broaden the SR concept to pyramid sensors (PyWFS) with a single sensor and a natural guide
star. We revisit the analytic PyWFS diffraction model to claim two aspects: i) that we can reconstruct spatial frequencies beyond the natural Shannon-Nyquist frequency imposed by the detector pixel size and/or ii) that the PyWFS can be used to measure amplitude aberrations (at the origin of scintillation). SR offers the possibility to control a higher actuator density deformable mirror from seemingly fewer samples, the quantification of which is one of the goals of this paper. A super-resolved PyWFS is more resilient to mis-registration, lifts
alignment requirements and improves performance (against aliasing and other spurious modes AO systems are poorly sensitive to) with only a factor up to 2 increased real-time computational burden.
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All authors Carlos M. Correia, Charlotte Z. Bond, João Aveiro, François Leroux, Cédric Taïssir Heritier, Christophe Vérinaud
High Energy Astrophysical Phenomena
On Signatures of a Possible New Physics Resonance in Atmospheric Air Showers Using a Parameterized Model
Jiri Kvita
We present a parameterized model of atmospheric particle showers initiated by
cosmic rays. Few physics shower parameters are tuned in a comparison to the Conex generator. Resulting shower properties are studied, with a comment on the cases where multiple shower maxima develop. Finally, we implement simple models of new physics resonance of masses of 100 GeV and 1 TeV and examine their effects on the shower profile, depth and maximum variation in dependence of the decay channel of the hypothetical resonance. It is shown that a new resonance effects can appear at the energy threshold and can persist for about a decade in $\log_{10} E/\mathrm{eV}$. Various assumed decay modes of the hypothetical resonance have different effects on the direction and shape of the modified average shower depth as function of the energy, with possible implications for current or future measurements. It is shown that, within the presented model, the visibility of the resonance in modified shower depth strongly depends on the resonance width. A significant modification at 10% width gradually diminishes towards the percent-level width. We propose that looking at the 2D distributions of the two first individual shower moments can also reveal signatures of new physics.
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Instrumentation and Methods for Astrophysics
Super-resolution-enabled atmospheric tomography for astronomical multi-wavefront-sensor adaptive-optics systems
Carlos M. Correia, Pierre Jouve, Jesse Cranney et al. (+1 more)
Recent work by Oberti et al, (Astron. Astrophys., 667, 48, 2022) argued and made a compelling case that classical astronomical adaptive optics (AO)
tomography performance can be further enhanced by carefully designing and optically configuring the system to leverage inherent super-resolution (SR) capabilities. Our goal here is to further materialise the concept by providing the means to compute SR-enabling tomographic reconstructors for AO and showcase its broad uptake on soon every 10 m-class VIS/NIR
telescopes and
Giant Segmented Mirror
Telescopes of up to 40 m in diameter. To that end we indicate the necessary
tomography generalisations where we: (i) clarify how model-and-deploy is a generic methodological umbrella for linear minimum-mean-squared-error (LMMSE) tomographic reconstructors arising naturally from the solution of the tomographic inverse problem, thus unifying various solutions presented as distinct in the literature within a single framework, (ii) recall how such solutions are found as limiting cases of a model-based optimal control problem, thus elucidating how pseudo-open-loop control is a feature of the latter that allows LMMSE reconstructors to be adapted to closed-loop systems, (iii) review the two forms of the LMMSE tomographic reconstructors, highlighting the necessary adaptations to accommodate super-resolution, (iv) review the implementation in either dense-format vector-
matrix-multiplication or sparse iterative forms and (v) discuss the implications for runtime and off-line real-time implementations, anticipating widespread adoption. We illustrate our examples with physical-optics numerical simulations for 10 m and 40 m-scale systems showing the performance benefits of super-resolution in the order of several tens of nm rms and the computational burden associated.
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All authors Carlos M. Correia, Pierre Jouve, Jesse Cranney, Guido Agapito Cédric Taïssir Heritier
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Kinetic-Theory Bounds on the Equation of State of Dense QCD Matter
Michał Marczenko
We derive bounds on the equation of state of cold, dense matter by extending the causal, model-agnostic interpolation between
chiral effective field theory and perturbative calculations with a microscopic constraint from relativistic kinetic theory. The additional condition restricts the stiffest admissible behavior of the equation of state and systematically reduces the range of allowed equations of state, with the strongest effect at high densities. The resulting bounds remain consistent with known low- and high-density limits, while the strength of the constraint depends on the density above which the kinetic-theory condition is applied. These bounds can be readily incorporated into future studies of cold, dense matter and used to assess the impact of microscopic stability conditions on equation-of-state inference.
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Instrumentation and Methods for Astrophysics
ESO Expanding Horizons: Underluminous Thermonuclear Supernovae
Paul J. Groot, Simone Scaringi and Nancy Elias-Rosa
Underluminous Thermonuclear
Supernovae (uTSNe) are an emerging class of transient events that resemble classic
Supernovae Type Ia, but peak at much lower luminosities. Suspected to be the deflagrations of white
dwarfs, they directly link the final stages of low-mass binary
star evolution to extragalactic studies that are critical for cosmology. The ability to detect and study uTSNe is limited by the lack of high spatial resolution (<0.1"), wide-field (>10'x10') imaging capabilities in the optical, as well as large-scale segmented-
telescope spectroscopic abilities that allow highly dynamic time-critical spectroscopy of short-duration transient events. Neither capability is currently foreseen for the European Southern Observatory and is therefore an excellent candidate for the Expanding Horizons program.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
In situ substrate birefringence characterization in gravitational wave detectors using a heterodyne polarimetry method
Satoshi Tanioka, Terri Pearce, Yuta Michimura et al. (+6 more)
High-quality test mass substrates play essential roles in
laser interferometric gravitational wave detectors. Inhomogeneous birefringence distribution in test mass substrates, however, can degrade the sensitivity of the detector by introducing the optical loss and disturbing the interferometer controls. In this paper, we present a heterodyne polarimetry method that enables in situ birefringence characterizations, hence diagnosing the gravitational wave interferometer. We experimentally demonstrate the proposed method with a tabletop setup. We also discuss its applicability to current and future gravitational wave detectors and the detectable limit.
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All authors Satoshi Tanioka, Terri Pearce, Yuta Michimura, Kazuhiro Agatsuma, Martin Van Beuzekom, Alberto Vecchio, Stephen Webster, Matteo Leonardi, Keiko Kokeyama
Astrophysics of Galaxies
ODIN: A New Lyman Alpha Blob Selection Method, Sample, and Statistical Analysis at $z\sim3.1$
Byeongha Moon, Yujin Yang, Kyoung-Soo Lee et al. (+26 more)
Ly$\alpha$ blobs (LABs) are large, spatially extended Ly$\alpha$-emitting objects whose nature remains unclear. Their statistical properties such as number densities and luminosity functions are still uncertain because of small sample sizes and large
cosmic variance. The One-hundred-deg$^2$ DECam Imaging in Narrowbands (ODIN) survey, with its large volume, offers an opportunity to overcome these limitations. We describe our LAB selection method and present 112 new LABs in the 9 deg$^2$ E-COSMOS field. We begin with the conventional LAB selection approach, cross-matching LAEs with extended Ly$\alpha$ sources, yielding 89 LAB candidates. To obtain a more complete LAB sample, we introduce a new selection pipeline that models all
galaxies detected in deep broadband imaging, subtracts them from the narrowband image, and then directly detects extended Ly$\alpha$ emission. This method successfully identifies 23 additional low-surface-brightness LABs which could otherwise be missed by the conventional method. The number density of ODIN LABs near an ODIN protocluster ($n=7.5\times10^{-5}$ cMpc$^{-3}$) is comparable to that found in the SSA22 proto-cluster and is four times higher than the average across the field. The cumulative Ly$\alpha$ luminosity function within the protocluster regions is similar to that measured for the LABs in the SSA22 proto-cluster, suggesting a large excess of luminous LABs relative to the average field. These findings suggest the Ly$\alpha$ luminosities and number densities of LABs are environment-dependent. ODIN will provide an expansive LAB and protocluster samples across six additional fields and two more
redshifts, allowing us to investigate the nature of LABs in relation to their environments.
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All authors Byeongha Moon, Yujin Yang, Kyoung-Soo Lee, Eric Gawiser, Arjun Dey, Francisco Valdes, Dustin Lang, Robin Ciardullo, Caryl Gronwall, Ann Zabludoff, Vandana Ramakrishnan, Nicole M. Firestone, Ethan Pinarski, Seok-jun Chang, Lucia Guaita, Sungryong Hong, Ho Seong Hwang, Sang Hyeok Im, Woong-Seob Jeong, Eunsoo Jun, Seongjae Kim, Jaehyun Lee, Seong-Kook Lee, Gautam Nagaraj, Julie B. Nantais, Nelson Padilla, Changbom Park, Hyunmi Song, Paulina Troncoso
Solar and Stellar Astrophysics
Quantifying sunspot group nesting with density-based unsupervised clustering
Nurdan Karapinar, Emre Isik, Natalie A. Krivova et al. (+1 more)
Sunspot groups often emerge in spatial-temporal clusters, known as nests or complexes of activity. Quantifying how frequently such nesting occurs is important for understanding the organisation and recurrence of
solar magnetic fields. We introduce an automated approach based on kernel density estimation and DBSCAN clustering to identify nests in the longitude-time domain and to measure the fraction of sunspot groups that belong to them. The method combines a smooth representation of emergence patterns with a density-based clustering procedure, validated using synthetic
solar-like cycles and corrected for variations in data density. We apply this method to 151 years of sunspot-group observations from the Royal Greenwich Observatory Photoheliographic Results (RGO, 1874-1976) and Kislovodsk Mountain Astronomical Station (KMAS, 1955-2025) catalogues. Across all cycles and latitude bands, the mean nesting degree is $\langle D\rangle = 0.61 \pm 0.12$, implying that about 60 percent all sunspot groups emerge within nests. Nesting is strongest at mid-latitudes (10$^\circ$-20$^\circ$), and results from the two independent
datasets agree in the period of overlap. The nesting degree significantly correlates with the
solar activity level, with the correlation strengthening when small groups are excluded. The characteristic inter-nest spacing contracts from $\sim$200-500~Mm at low activity to $\sim$60-100~Mm at
solar maximum, approaching typical sunspot-group dimensions. The identified nests range from compact clusters to long-lived, drifting structures, offering new quantitative constraints on the persistence and organisation of
solar magnetic activity.
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All authors Nurdan Karapinar, Emre Isik, Natalie A. Krivova, Hakan V. Senavci
Solar and Stellar Astrophysics
Prediction of the Solar Polar Fields in 2026: An Unusually Weak Level Across the Last Five Solar Cycles
Ruihui Wang, Jie Jiang and Yukun Luo
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 one-year predictions without requiring information about future AR emergence. Our prediction method is validated using simulations of the surface
magnetic field from 2020-2025 and hindcasts of the 2023-2024 polar fields, employing a newly constrained profile of the meridional flow. Using the most recent HMI synoptic magnetogram as the initial condition, we predict the polar-field
evolution from October 2025 to October 2026. The southern polar field is predicted to strengthen gradually, while the northern field is expected to decline sharply until March 2026 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.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Origin of Quasi-Periodic Oscillations and Accretion Process in X-Ray Binaries around Quantum Lee-Wick Black Hole
Orhan Donmez, G. Mustafa, M. Yousaf et al. (+3 more)
In this study, we investigate the
accretion dynamics and test particle motion around a non-rotating, spherically symmetric Lee-Wick black hole (BH) to reveal how the model parameters affect orbital stability and the quasi-periodic oscillations (QPOs) observed in X-ray binary systems. The spacetime geometry, characterized by the BH mass and the coupling parameters $S_1$ and $S_2$, includes exponential and oscillatory corrections arising from the Lee-Wick terms. Using the effective potential approach, we derive specific energy, angular momentum, epicyclic frequencies, and the locations of the innermost stable circular orbits (ISCOs) of test particles. In addition to the analytical analysis, we explore the effects of the Lee-Wick spacetime parameters on the shock-cone morphology produced by Bondi-Hoyle-Lyttleton (BHL)
accretion. To this end, we perform general relativistic hydrodynamic simulations in two characteristic regimes: Block-1 (weak Lee-Wick regime) and Block-2 (strong Lee-Wick regime). The results show that Block-1 solutions closely resemble the Schwarzschild case, while Block-2 models develop denser and asymmetric shock cones accompanied by stronger QPOs activity, shifting from low-frequency to high-frequency QPOs. These variations yield distinct observational signatures that may be detectable in high-resolution X-ray timing data. Our analytical and numerical findings demonstrate that the Lee-Wick parameters $S_1$ and $S_2$ cause measurable changes in the morphology of the
accretion flow and in the frequency ratios near the BH. This suggests that future multi-wavelength observations could provide an important avenue to test higher-derivative
gravity theories.
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All authors Orhan Donmez, G. Mustafa, M. Yousaf, Faisal Javed, Ikhtiyor Saidov, Farruh Atamurotov
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Ghost-free 2-form fields in cosmology: implications for gravitational parity violation
Yuki Horii, Tomoaki Murata and Tsutomu Kobayashi
We explore the possibility of parity-violating, nonminimally coupled 2-form field theories that retain the same dynamical degrees of freedom as a massive 2-form and thus are ghost-free. Starting from the most general kinetic terms and dimension four couplings between the 2-form field and the
curvature tensors, we find a two-parameter family of such theories. However, we also find that parity-violating terms involving the dual 2-form field can be absorbed into a field redefinition, leaving a theory with essentially the same structure as that obtained by Heisenberg and Trenkler (i.e., the parity-preserving coupling to the double dual Riemann tensor). After the field redefinition, the only place where parity-violating terms can appear is in the potential. We then consider a homogeneous and isotropic cosmological model with an isotropic configuration of a triplet of 2-form fields, and study tensor perturbations in this setup. There are three types of tensor perturbations, two of which are dynamical. We show that
chiral gravitational waves can be generated in the presence of parity-violating terms in the potential.
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High Energy Astrophysical Phenomena
Uncovering the population of compact binary mergers and their formation pathways with gravitational waves through the Einstein Telescope
M. Arca-Sedda, I. Dvorkin, G. Franciolini et al. (+19 more)
Ground-based gravitational-wave (GW) observatories have transformed our view of compact-object mergers, yet their reach still limits a comprehensive reconstruction of the processes that generate these systems. Only next-generation observatories, with order-of-magnitude improvements in sensitivity and access to lower frequencies, will be capable of radically extending this detection horizon. GW observations will make it possible to detect the complete population of binary black hole (BBH) mergers out to
redshifts of $z \simeq 100$. This capability will deliver an unprecedented map of merger events across
cosmic time and enable precise reconstruction of their mass and
spin distributions, while for several thousand events the signal-to-noise ratio will surpass 100, enabling precision physics of BHs and
neutron stars (NSs). The access to lower frequencies will also open the intermediate-mass window, detecting systems of order $\sim 10^3 M_\odot$, potentially in coordination with multi-band observations from LISA. At higher
redshifts, where Population III
stars have so far remained beyond reach - even for the James Webb Space
Telescope - GW observations by next-generation detectors will routinely provide observations of BH mergers thought to originate from these
primordial stellar populations. Such measurements are expected to play a central role in clarifying the early assembly of supermassive black holes. A single detection of a binary BH system at $z \gtrsim 30$, or of a compact object with sub-
solar mass and no
tidal deformability, would constitute strong evidence for the existence of
primordial black holes. Such a discovery would have profound consequences for our understanding of dark matter and the early Universe. Ultimately, the GW observations will become revolutionary for identifying the physical channels responsible for compact binary formation.
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All authors M. Arca-Sedda, I. Dvorkin, G. Franciolini, M. C. Artale, M. Branchesi, E. Bortolas, M. Colpi, V. De Luca, A. Ghosh, M. Maggiore, M. Mapelli, B. Mestichelli, M. Mezcua, S. Nissanke, L. Paiella, A. Riotto, F. Santoliquido, N. Tamanini, R. Schneider, C. Ugolini, M. P. Vaccaro, K. Yakut
Instrumentation and Methods for Astrophysics
Semantic Model for the SKA Regional Centre Network
Edgar Ribeiro João, Manuel Parra-Royón and Julián Garrido
The unprecedented volume of data from the Square Kilometre Array (SKA)
telescopes will require the implementation of robust and solid strategies for efficient data processing and management. In this context, the SKA Regional Centre Network (SRCNet) – a collaborative global infrastructure comprising multiple regional centres distributed across various geographical regions around the globe – is poised to play a critical role. This network will be instrumental in facilitating the effective handling and analysis of extensive data streams generated by the
telescopes, thereby enabling significant advancements in astronomical research and exploration. This paper introduces a semantic model implemented with JSON-LD designed specifically for the SRCNet, detailing its architecture, data distribution, and computing service. By explicitly defining nodes, resources, relationships, and workflows, this model lays a foundation for interoperability and efficient resource management within the distributed network. The model presented in this text supports two possible configurations: centralized and decentralized – depending where data reside – enabling a future service broker to efficiently plan workflows by querying nodes for real-time system availability. Consistency tests conducted using SPARQL queries were made on the model in order to validate and test its integrity. Therefore, this research contributes to the advancement of semantic modeling in astronomy by addressing the semantic model for the SRCNet, a topic that has not been previously explored. This semantic model serves as a precursor to the development of a precise mathematical representation of the network and establishes a foundational framework for a future service broker.
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High Energy Astrophysical Phenomena
Pulsed radio emission from a Central Compact Object
Lei Zhang, Alessandro Ridolfi, Di Li et al. (+7 more)
Located at the centres of
supernova remnants, central compact objects (CCOs) are among the most puzzling
neutron stars. CCOs are bright in thermal X-rays, yet have evaded detection by major
radio telescopes for decades, giving rise to the view that they are intrinsically
radio-quiet and possess exceptionally weak
magnetic fields. Here we show that the prototypical young CCO 1E 1207.4-5209 is in fact a faint
radio pulsar rotating at the 0.4s X-ray period. Analysis of its polarization indicates that the
radio beam intersects our line of sight near the
magnetic pole, affirming its
radio faintness' being intrinsic. Once its
supernova remnant dissipates, this source would be misidentified as an apparently gigayear-old
pulsar. The CCO's low
radio flux density may explain why many
supernova remnants lack detectable
radio pulsars and suggests a hidden population of young, slowly rotating
neutron stars.
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All authors Lei Zhang, Alessandro Ridolfi, Di Li, Erbil Gugercinoglu, Fernando Camilo, Wynn C. G. Ho, Matthew Bailes, Ping Zhou, Craig O. Heinke, Marcus E. Lower
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
A Search for Binary Black Hole Mergers in LIGO O1-O3 Data with Convolutional Neural Networks
Ethan Silver, Plamen Krastev and Edo Berger
Since the first detection of gravitational waves in 2015 by LIGO from the binary black hole merger GW150914, gravitational-wave astronomy has developed significantly, with over 200 compact binary merger events cataloged. The use of neural networks has the potential to significantly speed up the detection, classification, and especially parameter estimation for gravitational wave events, compared to current techniques, quite important for electromagnetic follow-up of events. In this work, we present a machine learning pipeline using neural networks to detect gravitational wave events. We generate training data using real LIGO data to train and refine neural networks that can detect binary black hole (BBH) mergers, and apply these models to search through LIGO's first three observing runs. We detect 57 out of the 75 total cataloged BBH events with two detectors of data in O1, O2, and O3, with 57 false positives that can mostly be ruled out with parameter inference and human inspection. Finally, we extensively test this pipeline on time-shifted data to characterize its False Alarm Rate (FAR). These results are an important step in developing machine learning-based GW searches, enabling low-latency detection and multi-messenger astronomy.
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High Energy Astrophysical Phenomena
Constraining the Nanohertz Gravitational Wave Background with an X-ray Pulsar Timing Array from NICER observations
Tian-Yong Cao, Shi-jie Zheng, Shu-Xu Yi et al. (+5 more)
We present constraints on the nanohertz gravitational wave background (GWB) using X-ray
pulsar timing data from the
Neutron Star Interior Composition Explorer(NICER). By analyzing six millisecond
pulsars over a six-year observational baseline, we employed a
Bayesian framework to model noise components and search for a common red signal consistent with a GWB from supermassive black hole binaries (assuming a spectral index $\gamma_{\rm gwb}=13/3$). Our results show no significant evidence for a GWB, yielding a 95% upper limit of $\log_{10}(A_{\rm gwb})<-13.4$. Weak evidence for Hellings-Downs spatial correlations was found (S=2.5), though the signal remains statistically inconclusive. Compared to
radio and $\gamma$-ray
pulsar timing arrays, the NICER constraint is currently less stringent but demonstrates the feasibility of X-ray timing with NICER for GWB studies and highlights the potential for improved sensitivity with future X-ray missions.
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All authors Tian-Yong Cao, Shi-jie Zheng, Shu-Xu Yi, Ming-Yu Ge, Yi-Tao Yin, Yao-Ming Duan, Xiang Yang, Wen
Earth and Planetary Astrophysics
A Near-Earth Object Model Calibrated to Earth Impactors
Sophie E. Deam, Hadrien A. R. Devillepoix, David Nesvorný et al. (+16 more)
The population of Earth-impacting meteoroids and its size-dependent orbital elements are key to understanding the origin of meteorites and informing on planetary defence efforts. Outstanding questions include the role of collisions in depleting meteoroids on highly evolved orbits and the relative importance of delivery resonances. Those depend on size, with current dynamical models considering only asteroids larger than 10m in diameter. Based on 1,202 sporadic meteoroids observed by the Global Fireball Observatory, we created a debiased model of the near-Earth meteoroid population in the 10g - 150kg in size (approximately 1cm - 0.5m) as they dynamically evolved from the main asteroid belt onto Earth-crossing orbits. The observed impact population is best matched with a collisional half-life decreasing from 3Myr for meteoroids of 0.6kg (7cm) or higher, to 1Myr below this size, extending to the model lower bound of 10g. Placing our results in context with near-Earth object models for larger sizes, we find that the inner main belt continues to dominate feeding the small 1m to 10m diameter population primarily via the $\nu_6$ secular resonance and the 3:1J mean motion resonance. We also evaluated the potential significance of physical processes other than collisions on Earth-impacting meteoroids, such as low-perihelion disruptions from thermal stresses.
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All authors Sophie E. Deam, Hadrien A. R. Devillepoix, David Nesvorný, Patrick M. Shober, Eleanor K. Sansom, Jim Albers, Eric Anderson, Zouhair Benkhaldoun, Peter G. Brown, Luke Daly, George DiBattista, Hasnaa Chennaoui Aoudjehane, Christopher D. K. Herd, Tom Herring, Jonathan Horner, Peter Jenniskens, Derek C. Poulton, Martin D. Suttle, Anna Zappatini
High Energy Astrophysical Phenomena
A VERITAS view of HESS J1857+026 within a multi-wavelength analysis
Y. Chen
HESS J1857+026 remains a mysterious gamma-ray emitter since its discovery in 2008. Despite the disclosure of a nearby
pulsar and multiple studies in the high-energy (HE, E > 100 MeV) and very-high-energy (VHE, E > 100 GeV) regimes, there have been no confirmed counterparts (e.g., an SNR shell or other extended structure) in X-ray or other wavelengths. We present the result of our study of the VHE emission of HESS~J1857+026 with VERITAS as part of a multi-wavelength investigation to uncover its emission mechanisms. Our result confirms the extended nature of the source and we characterize its spectral and morphological features in the VHE band. Using the morphology of the source revealed in our analysis, we also explore the underlying transport process of a possible electron population in a leptonic PWN scenario for the gamma-ray emission.
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Astrophysics of Galaxies
A robust morphological classification method for galaxies using dual-encoding contrastive learning and multi-clustering voting on JWST/NIRCam images
Xiaolei Yin, Guanwen Fang, Shiying Lu et al. (+3 more)
The two-step
galaxy morphology classification framework USmorph successfully combines unsupervised machine learning (UML) with supervised machine learning (SML) methods. To enhance the UML step, we employed a dual-encoder architecture (ConvNeXt and ViT) to effectively encode images, contrastive learning to accurately extract features, and principal component analysis to efficiently reduce dimensionality. Based on this improved framework, a sample of 46,176
galaxies at $0<z<4.2$, selected in the COSMOS-Web field, is classified into five types using the JWST near-infrared images: 33% spherical (SPH), 25% early-type disk (ETD), 25% late-type disk (LTD), 7% irregular (IRR), and 10% unclassified (UNC)
galaxies. We also performed parametric (Sérsic index, $n$,and effective radius, $r_{\rm e}$) and nonparametric measurements (Gini coefficient, $G$, the second-order moment of light, $M_{\rm 20}$, concentration, $C$, multiplicity, $\Psi$, and three other parameters from the MID statistics) for massive
galaxies ($M_*>10^9 M_\odot$) to verify the validity of our
galaxy morphological classification system. The analysis of morphological parameters is consistent with our classification system: SPH and ETD
galaxies with higher $n$, $G$, and $C$ tend to be more bulge-dominated and more compact compared with other types of
galaxies. This demonstrates the reliability of this classification system, which will be useful for a forthcoming large-sky survey from the Chinese Space Station
Telescope.
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All authors Xiaolei Yin, Guanwen Fang, Shiying Lu, Zesen Lin, Yao Dai, Chichun Zhou
Earth and Planetary Astrophysics
Surveying Ultra-hot Jupiters using Phase Curves with $\textit{Twinkle}$
Kaz Gary, Ji Wang, Anusha Pai Asnodkar et al. (+1 more)
Due to their high
equilibrium temperatures ($T_{eq}$ $>$ 2000 K), ultra-hot Jupiters (UHJs) are the best characterized
exoplanets to date. However, many questions about their formation,
evolution, and atmospheres remain unanswered. Phase curve observations can reveal answers to these questions by constraining multiple atmospheric properties including circulation, albedo, and chemistry. To this end, we simulate and forecast a survey of UHJ atmospheres via phase curve observations with the upcoming $\textit{Twinkle}$ mission. $\textit{Twinkle}$ is a spectroscopic satellite covering 0.5–4.5 micron with a spectral resolving power of R $\sim$ 50–70. Using a physically motivated model, we simulate white-light photometric phase curve observations for 14 UHJs in $\textit{Twinkle's}$ field of regard. We project that $\textit{Twinkle}$ will be able to detect all phase curve signals in our survey. Additionally, we simulate spectroscopic phase curves for the UHJ, WASP-189b. From our simulated spectroscopic phase curves, we generate mock phase-resolved emission spectra. Previously detected UHJ molecules (e.g. H$_2$O, CO and CO$_2$) produce notable features in the resulting spectra, allowing for detailed atmospheric characterization to study the 3D structure of UHJ atmospheric chemistry and dynamics. For
planets with hotspot phase offsets, $\textit{Twinkle}$ will be capable of detecting them both in the optical and infrared wavelength ranges. This future survey would represent the first UHJ phase curve survey with simultaneous coverage in optical and infrared wavelengths and will provide new constraints and reveal intriguing trends in these extreme environments.
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All authors Kaz Gary, Ji Wang, Anusha Pai Asnodkar, Ian Wong