Cosmology and Nongalactic Astrophysics
Observational constraints on scalar-vector-tensor dark energy with phantom-divide crossing
Nandan Roy, Shinji Tsujikawa, Ying-li Zhang et al. (+1 more)
We constrain a scalar-vector-tensor (SVT) dark-energy model in which the vector sector drives the dark-energy equation of state below $-1$ at earlier times, while a canonical scalar field subsequently drives it across $-1$ toward a present-day value above $-1$. We confront the model with DES Year 5
supernovae, DESI DR2 baryon acoustic oscillations, and compressed
cosmic microwave background information, and then include Gold-2017
redshift-space-distortion (RSD) measurements to probe structure growth. The background posterior assigns substantial weight to crossing histories and gives a better best fit than the flat $\Lambda$-cold-dark-matter ($\Lambda$CDM) model. The RSD analysis preserves this qualitative background
evolution, constrains the clustering amplitude, and increases the posterior support for the directional crossing criterion. Since the growth analysis also imposes additional perturbative support conditions, this increase cannot be attributed to the RSD likelihood alone. Matched PolyChord calculations give Bayes factors larger than unity for SVT relative to $\Lambda$CDM under both prior-volume conventions considered here. The quantitative Bayes factor depends on the prior normalization assigned to the regular radiation-era branch and is larger in the RSD analysis under either convention. Overall, current expansion and structure-growth data are consistent with a stable dynamical crossing of the phantom divide in the SVT model.
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All authors Nandan Roy, Shinji Tsujikawa, Ying-li Zhang, Zejun Zhang
Solar and Stellar Astrophysics
The NEMESIS general YSO catalogue - I. Supervised classification with deep learning methods
G. Marton, M. Madarász, J. Roquette et al. (+4 more)
In modern large-scale surveys, young stellar objects (YSOs) are mostly identified by the infrared excess in their spectral energy distributions (SEDs). To this end, YSO identification and classification were mostly based on certain colours, resulting in wavelength-specific methods. Using all available data allows us to construct a uniformly classified YSO catalogue by applying the same identification method to heterogeneous samples, reducing systematic differences and enabling more consistent studies of YSO populations and
star formation. Our goal is to develop a method that takes advantage of the heterogeneous data available in the VizieR database and to provide a tool that can be used to identify YSOs with high accuracy. We also aim to create the largest homogeneous catalogue of YSOs. We use the CDS VizieR and NASA/IPAC IRSA to collect data for a large number of objects of various types. The data collected included SEDs, light curves, and direct imaging and were used to build different image representations. These were used to teach deep learning
algorithms to differentiate between YSOs and all other types of sources. Architectures from the PyTorch library and custom-built convolutional neural networks were applied to create an ensemble of binary classifiers specialised at identifying YSOs. The resulting method is able to automatically identify YSO candidates with an accuracy higher than 90% while contamination is identified with an accuracy higher than 99%. We applied our classifier to numerous YSO catalogues to confirm the youth of the
stars and to create the largest catalogue of homogeneously identified potential YSOs ever – the NEMESIS General YSO catalogue contains 274\,408 unique, high reliability YSOs. Their positions on the colour-magnitude diagrams, and their distribution relative to the local Galactic structures, were also used to test their young nature.
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All authors G. Marton, M. Madarász, J. Roquette, M. Audard, I. Gezer, D. Hernandez, O. Dionatos
Cosmology and Nongalactic Astrophysics
Probing the cosmic web with fast radio bursts: II. Scintillation
Sharon Lapiner, Nir Mandelker, Paz Beniamini et al. (+1 more)
We consider the formation of multiphase gas in
cosmic web objects (CWOs) through cooling and fragmentation within the shock-heated medium of
cosmic sheets and filaments, and the circumgalactic medium (CGM) of
haloes. This leads to dense, cool ($\sim10^{4}\,\mathrm{K}$), small-scale cloudlets in pressure
equilibrium with their surroundings. Such ionized overdensities can affect the propagation of
radio waves emitted by fast
radio bursts (FRBs), allowing us to probe the small-scale structure in CWOs by examining their impact on the scintillation pattern of the observed FRB flux. While we find that the probability of encountering a high-temperature filament or sheet with cold cloudlets is rather small and usually confined to high
redshifts, the expected high rates of FRBs may still permit detection through scintillation along rare sightlines. We suggest scintillation from the Milky Way (MW) interstellar medium as a promising probe: CWO
plasma screens can suppress it, placing constraints on their cold-gas properties. Filaments and sheets can suppress MW scintillation from sources at $z_\mathrm{S}\gtrsim2$ and $3$, respectively, while cold and turbulent cloudlets in the CGM can be probed by sources at
redshifts as low as $z_\mathrm{S}\sim0.5$, constraining remarkably low volume-filling fractions, $f_\mathrm{v}$ (e.g. $f_\mathrm{v}\gtrsim10^{-5}$ for $z_\mathrm{S}\gtrsim2$). To provide testable predictions, we estimate the fraction of FRBs expected to encounter CWOs that may suppress MW scintillation below a given frequency, and express this as a function of the average extragalactic dispersion measure. Future FRB samples could map these constraints onto bounds on the existence and properties of cloudlets in CWOs, such as their density, size, $f_\mathrm{v}$, and
turbulence.
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All authors Sharon Lapiner, Nir Mandelker, Paz Beniamini, S. Peng Oh
Astrophysics of Galaxies
Simulating tidal disruption events in nuclear star clusters
Philip Cho, Kai Wu, Francesco Flammini Dotti et al. (+5 more)
Context. Nuclear
star clusters (NSCs) and supermassive black holes (SMBHs) often coexist at the centers of
galaxies, engaging in complex dynamical interactions that influence SMBH growth.
Stars that approach the SMBH too closely are tidally disrupted, and a fraction of their debris is accreted onto the black hole. Such events may contribute to SMBH growth in gas-deficient
galaxies. Aims. Our work aims to improve the theoretical framework for understanding the mass
accretion of stellar debris following tidal disruption events (TDEs) through numerical simulations. We perform direct N-body simulations of an NSC with a central SMBH embedded in a fully self-consistent dynamical model to test a new TDE
accretion prescription in a set of pilot simulations. Methods. The previous TDE prescription used a fixed
accretion radius and assumed that the entire stellar mass was accreted after disruption. In the new partial-mass
accretion model, the mass added to the SMBH depends on the orbital eccentricity and penetration factor of the disrupted
star. Results. We find that most TDEs involving main-sequence
stars are marginally eccentric or marginally
hyperbolic and contribute approximately half of the stellar mass to SMBH growth, consistent with recent hydrodynamical simulations. In all simulated models, the TDE-driven mass
accretion rate exhibits an early peak followed by a rapid decline. Models with higher initial SMBH masses exhibit a faster decline in the
accretion rate, consistent with more rapid loss-cone depletion and inefficient replenishment
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All authors Philip Cho, Kai Wu, Francesco Flammini Dotti, Taras Panamarev, Shuo Li, Shiyan Zhong, Klaus Reuter, Rainer Spurzem
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Set Transformer inference of the neutron star equation of state from stellar observations
Márcio Ferreira, Valéria Carvalho, Michał Bejger et al. (+1 more)
We develop a permutation-invariant Set
Transformer to reconstruct the equation of state (EoS) of dense matter from variable-size, unordered sets of
neutron star (NS) observations. The model takes stellar masses together with radii, tidal deformabilities, or both, and predicts either the pressure $P(n)$ or the sound speed $c_s^2(n)$ on a fixed density grid, along with density-dependent uncertainties. Nothing in the architecture prescribes which
star informs which density: self-
attention couples all observations nonlinearly, and each density point reads the full set through its own learnable query, so the
star-to-density mapping is learned from the data. Trained on independent piecewise-polytropic and Gaussian-process EoS ensembles, the model provides well-calibrated predictions whose uncertainty increases in density regions that stable
stars cannot probe. Reconstruction errors decrease with the number of observations, while tidal deformability generally improves accuracy at a fixed observation count, even when it carries its own measurement noise. Sensitivity analysis reveals a density-local mapping: in the pressure models, predictions at density $n$ depend most strongly on
stars whose central densities are near $n$. We also show that the sensitivity of the model to the inferred stellar compactness provides information on the minimum central density. These results demonstrate that set-based neural inference, in which the
star-to-density mapping is learned rather than assumed, can extract physically interpretable EoS information with calibrated uncertainties.
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All authors Márcio Ferreira, Valéria Carvalho, Michał Bejger, Constança Providência
Astrophysics of Galaxies
AKARI near-infrared spectroscopy of circumstellar hydrocarbon dust associated with young stellar objects
Yuki Kuroda, Hidehiro Kaneda, Natsuko Izumi et al. (+2 more)
We investigate the processing of the circumstellar polycyclic aromatic hydrocarbons (PAHs) associated with young stellar objects (YSOs) through their stellar activities. We analyze the AKARI near-infrared (2.6$-$4.4 $\mu$m) long-slit spectral data of 10 YSOs, focusing on the aromatic feature at a wavelength of 3.3 $\mu$m and the aliphatic features at 3.4$-$3.6 $\mu$m. The spectral fitting results show large variations from target to target in the flux ratio of the aliphatic to aromatic features, the shape of the aliphatic feature profile, and the central wavelength of the aromatic feature. In particular, HD 97048 and Elias 1 show strong aliphatic features at wavelengths longer than 3.5 $\mu$m, which is consistent with the hydrogenated nanodiamond features reported in previous studies. We find that the properties of the hydrocarbon dust vary under the influence of the YSO activity, where the degree of dust processing is likely to be related to the age of the YSO and the amount of the circumstellar dust. In addition, correlation is observed between the variations of the H$_2$O and CO$_2$ ice features and the aliphatic feature profiles, suggesting connection between the formation of CO$_2$ ice and the processing of aliphatic hydrocarbons. Finally, we find a significant correlation between the variations in the central wavelength of the aromatic feature and the shape of the aliphatic feature profile. These findings may be consistent with a tentative scenario in which circumstellar PAHs are converted to nanodiamonds through irradiation by high-energy particles produced by YSO activity.
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All authors Yuki Kuroda, Hidehiro Kaneda, Natsuko Izumi, Takuma Kokusho, Shinki Oyabu
High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph
Bayesian inference of non-Maxwellian distribution functions from collective Thomson scattering spectra
Kentaro Sakai, ByungJun Kang, Akito Nakano et al. (+1 more)
We investigate
Bayesian inference of non-Maxwellian electron distribution functions from collective Thomson scattering (CTS) spectra. We represent distribution functions using multiple candidate models of different complexity and perform inference on synthetic spectra generated from known non-Maxwellian distribution functions. Our analysis demonstrates that a sufficiently flexible model can approximate the overall shape of the ground-truth distribution function. The most plausible model is identified based on model evidence, a statistical measure representing the probability to obtain the observed data given the model. When the candidates include the ground-truth model, the model evidence favors the ground-truth model. Without the ground-truth model as a candidate, the model evidence favors the candidate model with the fewest parameters that adequately approximates the data. The posterior probability density function of the most plausible model reveals the characteristic features and associated uncertainties of the underlying distribution function. The origin of the additional spectral peaks is attributed to a combination of modifications to the dispersion relation and reduced Landau damping. This enables the objective and data-driven identification of distribution functions directly from observed CTS spectra.
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All authors Kentaro Sakai, ByungJun Kang, Akito Nakano, Takeo Hoshi
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Sub-Horizon and Quasi-Static Approximations in Interacting Dark Sector Models Involving Scalar Field Dark Energy
Priyanka Saha, Sharvari Nadkarni-Ghosh and Kaushik bhattacharya
We investigate the validity of the sub-horizon approximation (SHA) and quasi-static approximation (QSA) for linear matter perturbations in interacting scalar-field dark-energy models. We consider both quintessence and phantom scalar fields and derive their full relativistic perturbation
evolution to compare with the corresponding SHA and QSA solutions. We find that, while the SHA reproduces the full
evolution with percent-level accuracy for non-interacting and weakly interacting models on sufficiently sub-horizon scales, its accuracy progressively deteriorates with increasing interaction strength and towards larger scales. Moreover, unlike in $\Lambda$CDM and non-interacting scalar-field models, applying the SHA to interacting models does not fully recover the standard Newtonian fluid equations. The QSA generally provides a closer description of the full relativistic
evolution than the SHA over the scales considered. By comparing the scalar-field model with $\Lambda$CDM using the full relativistic equations and, separately, using the SHA system, we evaluated whether the SHA is capable of capturing the full extent of the physical differences introduced by the alternative model. We find that the difference between these two comparisons becomes increasingly important for stronger interactions and smaller wavenumbers. Finally, we demonstrate that the resulting differences can reach several percent on scales accessible to large-volume hydrodynamical simulations, implying that the validity of the SHA cannot be assumed solely from the sub-horizon condition. Our results highlight the need to
benchmark the approximation over the relevant interaction parameter and wavenumber ranges before employing interacting-dark-energy models in large-volume structure-formation simulations and precision comparisons with large-scale-structure observations.
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High Energy Astrophysical Phenomena
Convolutional non-parametric Gamma-Ray Signal and Background Separation
Scarlet Betterman, Emmanuel Moulin and Martin White
In very-high-energy gamma-ray astronomy, signals must be separated from the residual background which arises from misidentified
cosmic-ray
protons. Building on previous work, we introduce an ensemble of variational autoencoders that aims to perform automatic signal-background separation with minimal assumptions that include separability of the spatial and energy distributions in both the signal and background, with no prior specification of the number of components or the point-like/diffuse nature of the signal itself. In addition, we do not assume knowledge of which region of the coordinate space is background-dominated or where the signal is supposed to be located in the field of view. We test the model on an analytic point-source mixture scenario, a realistic simulation of dark matter annihilation in the Galactic centre, and real observations of the Crab nebula and MSH 15-52 from the public H.E.S.S data release. The model proves capable of completely reconstructing the signal and background at a pixel by pixel level in all scenarios, whilst also denoising the inputs. Stable performance and reasonable error estimates are obtained even for low signal-to-background ratios.
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Earth and Planetary Astrophysics
TS23/McDonald and FIES/NOT strike again. Two new warm Jupiter systems and outer companions in a third
E. Knudstrup, D. Gandolfi, W. D. Cochran et al. (+29 more)
Warm Jupiters (gas giant
planets with orbital periods of P$\sim$8-200 d) are thought to be largely unaffected by the tidal interactions that can erase information about the dynamical histories of hot Jupiters. Their orbital eccentricities ($e$) and stellar obliquities are therefore expected to be preserved, making them valuable probes of giant-
planet formation and migration. Our aim is to identify and characterise transiting warm Jupiters in order to expand the sample of well-characterised systems and enable further studies of giant-
planet formation and migration. We analyse TESS transit photometry together with ground-based radial velocity measurements and perform a joint fit of the photometric and spectroscopic data from the TS23 and FIES spectrographs to determine the planetary and orbital parameters. We report on the discovery and characterisation of two new, transiting warm Jupiters; TOI-5120 b ($M_p = 1.23\pm0.05$ M$_{\rm Jup}$, $R_p = 0.969\pm0.017$ R$_{\rm Jup}$, $P = 24.91645\pm0.00002$ d, $e = 0.10\pm0.02$) and TOI-5699 b ($M_p = 0.25\pm0.03$ M$_{\rm Jup}$, $R_p = 0.996\pm0.015$ R$_{\rm Jup}$, $P = 22.01850\pm0.00004$ d, $e = 0.30^{+0.09}_{-0.08}$). We also refine the parameters of the known warm Jupiter TOI-2158 b ($M_p = 0.87\pm0.04$ M$_{\rm Jup}$, $R_p = 0.899\pm0.015$ R$_{\rm Jup}$, $P = 8.60079^{+0.00002}_{-0.00001}$ d, $e = 0.028^{+0.013}_{-0.014}$). In addition, we detect an outer planetary companion, TOI-2158 c ($M_p \sin i = 1.62\pm0.13$ M$_{\rm Jup}$, $P = 414.5^{+1.5}_{-1.6}$ d, $e = 0.54\pm0.04$), and identify a long-term radial velocity trend that may indicate another planetary companion on a wide orbit. The diverse architectures of these systems, in particular the presence and absence of outer companions, highlight the range of dynamical pathways leading to warm Jupiters.
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All authors E. Knudstrup, D. Gandolfi, W. D. Cochran, M. Endl, P. MacQueen, T. Pugh, M. S. Lundkvist, C. M. Persson, A. Stokholm, M. L. Winther, J. R. Larsen, J. L. Rørsted, S. H. Albrecht, K. A. Collins, C. Watkins, B. Edwards, D. R. Ciardi, C. A. Clark, A. S. Polanski, C. Ziegler, C. Briceño, A. W. Mann, M. Everett, S. Howell, B. Safonov, T. Gan, K. Barkaoui, P. Benni, R. P. Schwarz, K. Horne, R. Sefako, D. Muthukrishna
Earth and Planetary Astrophysics · Cross-listed from cond-mat.soft
A Bonded-Particle Discrete-Element Model with Self-Gravity for the Collision and Reaccumulation of Rubble-Pile Asteroids: Formulation and Numerical Protocol
Yohann Trivino
I present a discrete-element approach developed to study the collisional and gravitational
evolution of small self-gravitating granular aggregates. Each body is represented as a composite of cohesively bonded spherical grains, so that fragmentation and reaccumulation emerge from the microscopic competition between short-range dissipative contact forces, an irreversible bond-breaking criterion, and pairwise Newtonian self-
gravity summed over every particle pair, including those internal to a single body. A numerical experiment is described: a random-sequential packing procedure that generates two bonded spherical aggregates, a controlled two-body encounter with tunable approach speed and impact parameter, and a systematic parameter sweep designed to map the conditions under which two bodies launched from rest under their mutual
gravity alone either merge into a single remnant or fail to settle after a low-speed encounter. Of the 125 simulated collisions, 56.8% result in the formation of a single residue. The cohesive network remains intact for $\Pi_\sigma\lesssim0.036$, is partially damaged with dispersion determined by the contact damping ratio, and breaks completely for $\Pi_\sigma\approx3.59$
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Solar and Stellar Astrophysics
Beating and coupling in pulsating stars: A unified Fourier description and observational diagnostics
József M. Benkő and Emese Plachy
Long-term amplitude and phase variations in pulsating
stars produce side peaks or multiplets in the
Fourier spectrum of the light curves around the pulsation frequency and its harmonics. Such structures are often attributed to modulation, although linear beating and the non-linear coupling of close oscillations can also produce similar patterns. We develop a unified analytical
Fourier description of these alternatives and identify observational relations that retain discriminatory power when their frequency patterns overlap. We represent the signal as a dominant, non-sinusoidal oscillation plus one or more secondary oscillations close to it, and analytically derive the frequencies, complex amplitudes, and phases resulting from linear superposition, quadratic and general non-linear coupling. We also illustrate the calculated phenomena using artificial light curves. We implement the resulting tests in a diagnostic tool "freqdiag", which compares modulation with primary–secondary quadratic coupling models anchored to either the higher- or lower-frequency side peak, using the same normalized complex amplitudes, and supplements the fit with hierarchical tests of side-peak amplitude progression. A sinusoidal secondary signal produces only one additional peak in the linear-beating case, whereas a non-sinusoidal secondary signal produces a harmonic sequence, whose separation from the primary harmonics increases with order. Quadratic coupling produces terms $nf_0+lf_B$, but their amplitudes and phases follow shifted-harmonic and combination relations. At general non-linear order, coupling and modulation occupy the same frequency grid. The formalism provides a practical framework for interpreting Blazhko-like RRc
stars, HADS variables, and other pulsating
stars in which modulation and coupling are difficult to separate observationally.
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Solar and Stellar Astrophysics
Near-infrared spectra of chemically peculiar stars and applications to kilonova spectra
Nanae Domoto, Masaomi Tanaka, Wako Aoki et al. (+11 more)
Kilonova spectra provide information on rapid
neutron-capture nucleosynthesis in
neutron star mergers. However, it remains challenging to identify individual elements in kilonova spectra, primarily due to incomplete atomic data for heavy elements at near-infrared wavelengths. Recent work demonstrated that spectra of chemically peculiar
stars offer excellent laboratory for studying kilonova spectra. In this paper, to expand our understanding of strong transitions of heavy elements at near-infrared wavelengths, we present high-resolution near-infrared spectra of 14 chemically peculiar
stars covering a range of effective temperatures, surface gravities, and abundance patterns, obtained with Subaru/IRD. The Sr II, Ce III, and Gd III lines, previously suggested to be among the strongest transitions, are detected in the spectra of most of our targets, confirming their intrinsic importance. In addition, Eu II and Nd III lines are detected in several
stars. By comparing observed equivalent widths and abundance ratios, we show that under a highly heavy-element-enriched abundance pattern, Eu II and Nd III lines may contribute to kilonova spectral features comparably to Sr II. Importantly, we find no unidentified lines systematically stronger than these transitions despite the larger stellar sample. These results further support the primary importance of the Sr II and Ce III transitions and provide new insights into the potential contribution of Eu II and Nd III.
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All authors Nanae Domoto, Masaomi Tanaka, Wako Aoki, Salma Rahmouni, Tomoyuki Kudo, Hiroki Harakawa, Teruyuki Hirano, Takayuki Kotani, Takashi Kurokawa, Masayuki Kuzuhara, Jun Nishikawa, Takuma Serizawa, Motohide Tamura, Akitoshi Ueda
Astrophysics of Galaxies
KBSS-InCLOSE II: First Detailed Insights on the Inner CGM of Low-Mass $z\sim2.3$ Galaxies
Evan Haze Nunez-Cravin, Charles C. Steidel, Gwen C. Rudie et al. (+7 more)
We present results from an extension to the Keck Baryonic Structure Survey (KBSS) that focuses on the Inner Circumgalactic Medium (CGM) of QSO Line Of Sight Emitting
galaxies at z$\sim$2.3 (InCLOSE). We analyze two low-mass
galaxies $\log{(\rm{M_*} / \rm{M_\odot})} \leq 9$ that are within small a projected distance of a QSO $D_{\rm tran} \leq 50~{\rm kpc}$ ($D_{\rm tran} /R_{\rm vir} \leq 0.75$). One
galaxy is detected as a bright Lyman- Emitter with Keck/KCWI (confirmed with follow-up Keck/MOSFIRE spectra), and the other as a serendipitous line emitter with Keck/MOSFIRE. Both
galaxies have nebular and morphological properties consistent with those of typical low-mass z$\sim$2.3
star-forming
galaxies. Analysis of their CGM absorption as seen with Keck/HIRES spectra of the background QSOs shows no detections of low-ionization metal absorption (low-ions; e.g., Si II), ubiquitous detections of intermediate- (e.g., C IV) and high-ions (O VI), kinematically complex absorption ($\geq$7 components per
galaxy halo) spread over $|\Delta v|\pm 150~{\rm km~s^{-1}}$, and no unambiguously unbound gas is detected in either
galaxy halo. We analyze the thermal properties of a subset of CGM components, finding that the majority (6/10) have temperatures consistent with heating from the metagalactic UV background ($\log{(T/\rm{K})_{\mathrm{med}}}=4.0$) while the remainder possess short-lived, intermediate temperature gas that would require additional heating or rapid replenishment ($4.6 \leq \log{(T/\rm{K})} \leq 5.1$), the internal energy of these absorbers are dominated by thermal broadening, their internal (turbulent) velocities are all subsonic, while their motions through the
halo are likely supersonic. These results hint that the z2.3 CGM changes with stellar mass in terms of kinematic complexity and unbound gas fraction, while thermal properties remain similar.
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All authors Evan Haze Nunez-Cravin, Charles C. Steidel, Gwen C. Rudie, Evan N. Kirby, Charis M. Hall, Nikolaus Z. Prusinski, Zhuyun Zhuang, Yuanze Ding, Alice E. Shapley, Ryan F. Trainor
Earth and Planetary Astrophysics
On the Compositions of Interstellar Objects
Matthew J. Hopkins, Michele T. Bannister, Bertram Bitsch et al. (+2 more)
As physical samples of distant planetary systems, the compositions of interstellar objects (ISOs) should correlate with the properties of their diverse parent
stars. We combine a chemical partition model with a sample of stellar elemental abundances from APOGEE DR17 to predict the abundances of commonly-observed cometary volatiles in ISOs. We find that the compositions of ISOs vary significantly between different
stars. In particular, we predict a strong correlation between an ISO's ammonia abundance and its parent
star's
metallicity: high-
metallicity stars will create ISOs rich in ammonia. This suggests the production rates of NH$_3$'s photolytic daughter products are an ideal observational tracer for the origins of ISOs. We infer that 2I/Borisov formed around a
star of near-solar
metallicity ($-0.4\lesssim[\mathrm{Fe}/\mathrm{H}]\lesssim0.3$), and corroborate the velocity- and isotope-based inferences that 3I/ATLAS formed around a lower-
metallicity star ($-0.8\lesssim[\mathrm{Fe}/\mathrm{H}]\lesssim0.0$). The production rates of 2I and 3I imply both only contain hypervolatiles such as CO and N$_2$ that are trapped in other less-volatile ices, similar to typical Solar System comets. Despite this, we argue that true hypervolatile-ice-rich ISOs may exist; they would exhibit high CO and N$_2$ production rate ratios, possibly similar to those of C/2016 R2 (PanSTARRS). Our predictions provide context for future ISO discoveries, opening a path to link the properties of their origin systems to observable production rates.
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All authors Matthew J. Hopkins, Michele T. Bannister, Bertram Bitsch, Chris Lintott, John C. Forbes
High Energy Astrophysical Phenomena
Long-term X-ray variability of the NLS1 Ark 564
Neha P R, Nikita S Arun, Savithri H. Ezhikode et al. (+4 more)
We present a systematic spectral study of the X-ray emission from the Narrow- Line Seyfert 1 (NLS1)
galaxy Ark 564 using Swift/XRT observations spanning sixteen years. The source exhibits significant variability in both the soft and hard X-ray bands, along with a strong positive correlation between them, indicating a closely coupled emission mechanism within the
accretion flow-corona system. A simple absorbed power-law model is statistically insufficient to describe the spectra, confirming the presence of an additional soft component. To investigate the origin of the soft excess, we performed multi-model spectral fitting. Incor- porating a warm Comptonization component yields a statistically improved fit, supporting the scenario in which the soft excess arises from Comptonization in a warm, optically thick corona. We also applied a relativistic reflection model to representative observations; however, given the moderate spectral resolution and limited high-energy coverage of Swift/XRT, the current data do not allow us to robustly determine whether reflection provides a superior or physically preferred description. Our results indicate that warm Comptonization offers a consistent explanation for the observed soft excess in Ark 564 within the limitations of the available data, while deeper broadband observations are required to defini- tively distinguish between competing models and comprehensively characterise the long-term X-ray spectral variability of the source
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All authors Neha P R, Nikita S Arun, Savithri H. Ezhikode, Ranjeev Misra, Bari Maqbool, Jeena K, Joe Jacob
Solar and Stellar Astrophysics
BS Cassiopeiae: A Contact Binary with Starspot-Driven Variability and Evidence for Additional Components
Min-Ji Jeong, Chun-Hwey Kim, Kyeongsoo Hong et al. (+5 more)
We present a comprehensive photometric and spectroscopic analysis of the contact eclipsing binary BS Cas, based on 22-yr multi-site light curves and 2-yr high-resolution spectra. The long-term photometry shows pronounced year-to-year changes in the light-curve shape, including eclipse-depth reversals between the primary and secondary minima and variations in the O'Connell effect. The first double-lined radial-velocity (RV) curves of BS Cas are derived from the spectra using broadening-function (BF) profiles. Sharp peaks absent from the 2018 BFs appear in the 2020 BFs, suggesting an additional component along the same line of sight as BS Cas. Simultaneous modeling of the BVR light curves and the RVs shows that BS Cas is a contact binary in which the more massive component is cooler than its less massive companion, with a mass ratio of 2.515 and a fill-out factor of 32.3%. Multi-epoch modeling suggests that the long-term photometric variations arise from evolving starspots and changes in the third-light contribution. The eclipse-timing variation diagram confirms a secular orbital period decrease at a rate of $-2.305 \times 10^{-7}~\mathrm{days\,yr^{-1}}$ consistent with angular momentum loss and mass transfer, along with an 18.376-yr modulation interpreted as a light-travel-time effect from a third body. The TESS timings reveal anti-correlated variations between the primary and secondary minima that appear to result from differential rotation of high-latitude starspots. These results suggest that BS Cas is a physically complex contact binary in which long-term photometric and eclipse-timing variations reflect multiple processes, including
magnetic activity and the influence of a third body.
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All authors Min-Ji Jeong, Chun-Hwey Kim, Kyeongsoo Hong, Mi-Hwa Song, Hye-Young Kim, Jang-Ho Park, Cheongho Han, Joh-Na Yoon
Earth and Planetary Astrophysics
Pulsed Accretion onto Eccentric Binaries in Highly Misaligned Circumbinary Disks
Ruiqi Yang, Jeremy L. Smallwood, Shang-Fei Liu et al. (+1 more)
We present three-dimensional smoothed particle hydrodynamics simulations of highly misaligned circumbinary disks (CBDs) around moderately eccentric equal-mass binaries ($e_\mathrm{b}=0.5$). We show that the binary
accretion is modulated on the binary orbital period and exhibits two pulses near periastron. The dominant pulse peaks before periastron for an initial binary-disk misalignment of $60^\circ$, shifts to after periastron at $90^\circ$, and occurs at an even later post-periastron phase at $120^\circ$. We further show that the two pulses are accompanied by a time-dependent response of the circumstellar disks (CSDs) and by different distributions of accreting material within the cavity and around the CSDs. The qualitative pre- versus post-periastron distinction is also present in individual binary orbits despite variations in pulse amplitude. Our results motivate future tests of whether pulse timing is related to binary-disk orientation.
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All authors Ruiqi Yang, Jeremy L. Smallwood, Shang-Fei Liu, Alessia Franchini
Solar and Stellar Astrophysics
A Sample of Long-Period Binaries with Dormant Compact-Object Candidates from LAMOST DR13 MRS and Gaia DR3
Junxing Zhou and Wei-Min Gu
Identifying dormant compact objects in non-interacting binaries is crucial for constraining the hidden population of stellar remnants. We present a systematic search for long-period compact-object candidates by combining Gaia DR3 astrometry with multi-epoch LAMOST DR13 medium-resolution spectroscopy. Starting from sources with elevated RUWE values, we required at least five LAMOST spectroscopic epochs and peak-to-peak RV variations exceeding 20 km/s. After RV extraction, orbital fitting, and subsequent screening, we obtained
Bayesian Keplerian orbital solutions for 19 long-period single-lined binary candidates, with periods spanning approximately 30-1500 days. Multi-wavelength spectral energy distribution fitting was used to constrain the visible
stars and evaluate the expected luminosities of unseen companions under a main-sequence assumption. Two systems are identified as the highest-priority compact-object candidates in our sample, each with a minimum companion mass exceeding 1 solar mass. Their spectra and optical-to-infrared photometry show no detectable secondary-light contribution, although such a contribution would be expected if the unseen companions were normal main-sequence
stars. These systems therefore represent the strongest compact-object candidates in our sample, although further observations are required to distinguish massive white dwarfs or
neutron stars from faint stellar companions or unresolved hierarchical systems. We also identify five intermediate-priority and 12 lower-priority systems for follow-up spectroscopy, ultraviolet imaging, and future astrometric constraints.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
Propagation delays and regional intensity changes in lensed hotspot images
Yong Li and Xiao-Gang Lan
Propagation delays cause an image recorded at a single observer time to combine radiation emitted at different stages of the source
evolution. Comparable changes in total intensity can accompany distinct and even opposite changes in apparent image size. Using regional intensities, centroids, and covariances, we apply the law of total covariance to separate changes in regional intensity weights from changes in internal widths and centroid separation. Ray tracing simulations of a finite Gaussian hotspot moving along a prescribed strong field trajectory show two events with comparable attenuation in screen integrated intensity but opposite changes in second moment size. In the contracting event, the regional weights move away from balance; in the expanding event, they move toward balance even as the centroids approach each other. Differential propagation delays therefore drive these opposite size responses by redistributing intensity between spatially separated image regions.
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Solar and Stellar Astrophysics
A Comprehensive Study of the Long-Period Cataclysmic Variable V630 Cassiopeiae
Ivan Mora Zamora, Gagik Tovmassian, Juan Echevarria et al. (+1 more)
We present a comprehensive review of V630 Cassiopeiae, which is a very long-period cataclysmic variable. Based on new observations combining spectroscopy and high-resolution photometry provided by TESS and precise distance data from GAIA, we confirm and extend previously described characteristics. The light curves show differential behaviors between different epochs, attributed to changes in the disk's brightness distribution, likely due to non-axial structures such as precessing eccentric disks. The spectroscopy reveals complex Ha line profiles, with dual components and an emission distribution that suggests a large, asymmetric, and possibly precessing disk, rather than a classic shock structure in the matter-flow impact region. Doppler
tomography indicates that the emission originates at the periphery of the disk, distributed in an asymmetric pattern rather than a compact point, complicating the interpretation of radial velocities and limiting their use for accurately determining masses. Through photometric and spectroscopic analysis, we established a donor mass estimate with an approximate value of 0.38 Ms at the adopted distance of 2409 pc, with significant uncertainty related to distance and other systematic factors. Finally, using the parameters of V630 Cas, binary
evolution simulations were conducted with MESA incorporating CARB
magnetic braking prescription to identify an evolutionary sequence that explains its properties.
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All authors Ivan Mora Zamora, Gagik Tovmassian, Juan Echevarria, Diogo Belloni
Astrophysics of Galaxies
A Cyanopolyyne-rich but COM-poor Massive Protostar: The First Hot Carbon Chain Chemistry Source G28.28-0.36
Kotomi Taniguchi, Masao Saito, Prasanta Gorai et al. (+6 more)
We present molecular emission line data from the massive young stellar object (MYSO) G28.28-0.36 (G28.28) obtained with the Atacama Large Millimeter/submillimeter Array Band 3. Cyanopolyynes (HC$_3$N and HC$_5$N) and three complex organic molecules (COMs; CH$_3$OH, CH$_3$CN, and CH$_3$CHO) are detected from the MYSO G28.28. In addition, strong emission regions of cyanopolyynes are identified between G28.28 and a nearby ultracompact H II region. The HC$_5$N emission is coincident with the dust continuum peak, where an excitation temperature of 100 K is derived from CH$_3$CN. These results suggest that the Hot Carbon Chain Chemistry (HCCC) mechanism produces cyanopolyynes in the hot region around G28.28. We find that G28.28 exhibits a unique chemical feature: cyanopolyynes are abundant, but COMs are deficient, unlike the other MYSOs studied previously. These results imply that G28.28 is a counterpart of the Warm Carbon Chain Chemistry (WCCC) low-mass source L1527. G28.28 is the first HCCC source identified so far.
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All authors Kotomi Taniguchi, Masao Saito, Prasanta Gorai, Olli Sipilä, Kazuhito Dobashi, Paola Caselli, Tirupati Kumara Sridharan, Tomomi Shimoikura, Jonathan C. Tan
Astrophysics of Galaxies
A VLA Study of the Disturbed Massive Cluster PLCK G165.7 + 67.0 and Its Two Narrow Angle Tail Galaxies
Aurora Wilde, Eric F. Jimenez-Andrade, Brenda L. Frye et al. (+11 more)
Since spectroscopic measurements provide only the line-of-sight velocity, transverse motions are difficult to constrain. As a result, transverse velocities have so far been measured only for local
galaxies.
Radio galaxies whose jets are bent back by ram pressure into nearly parallel Narrow-Angle Tails (NATs) offer a way to extend such measurements to higher
redshifts. Here, we present proprietary 15 GHz (Ku-band) and archival 6 GHz (C-band) continuum observations from the Very Large Array (VLA) of seven
radio galaxies in the
galaxy cluster field PLCK G165.7+67.0 (G165). VLA imaging resolves two of the cluster
galaxies into NATs whose tails both extend toward the Southwest, away from the cluster center of mass. Spectral index maps made at matched angular resolution resolve a steepening gradient consistent with radiative aging along the length of the tails. Physical properties of the NATs are measured and used to constrain two independent models: a Mach cone model and a nonrelativistic hydrodynamic flow model based on Euler's equation. The models returned space velocities of $\sim 2000 ~\rm km~ \rm s^{-1}$ for both
galaxies. One NAT is the brightest cluster
galaxy (BCG) and has a measured radial velocity of $-3300 ~\rm km ~\rm s^{-1}$, resulting in an even higher space velocity. The high inferred 3D velocity of the BCG may be explained if it is intercepted close to core passage.
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All authors Aurora Wilde, Eric F. Jimenez-Andrade, Brenda L. Frye, Patrick S. Kamieneski, Kevin C. Harrington, Megan Donahue, Min S. Yun, Anton M. Koekemoer, Marcel Neeleman, Massimo Pascale, Nicholas Foo, Reagen Leimbach, Seth Cohen, Rogier A. Windhorst
High Energy Astrophysical Phenomena
Deciphering the VHE gamma-rays spectra of Extreme High-Frequency peaked BL Lac Objects through a Photohadronic Model
Sarira Sahu, D. I. Páez-Sánchez, A. U. Puga Oliveros et al. (+7 more)
Extreme high-frequency peaked BL Lac objects (EHBLs) have their synchrotron peak above $\sim 1$ keV and their inverse Compton peak extends up to several TeVs. Due to low luminosity of EHBLs, these objects are often undetected, and only a small number of them are thus known. As a result, they are poorly understood. Using a photohadronic model and including extragalactic background light correction we analyzed 22 very high-energy (VHE) gamma-ray spectra of 15 EHBL sources observed in different periods. We find that the photohadronic model used can adequately describe the observed VHE spectral energy distribution and furthermore, we classify them according to the value of the
photon spectral index, $\delta$. The
redshift of the EHBL HESS J1943+213 is also tightly constrained using the same photohadronic model. Within the sample, a plurality of flaring epochs fall in the high-emission state which is followed by the low-emission state and the very-high-emission state respectively. These fractions of flaring epochs characterize only the present sample, not the EHBL population at large. Due to the anomalous behavior of the VHE gamma-ray spectra of the EHBL H 2356-309, we suggest it to be a new subclass of EHBL having hard and very soft intrinsic spectra during different flaring epochs.
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All authors Sarira Sahu, D. I. Páez-Sánchez, A. U. Puga Oliveros, M. E. Iglesias Martínez, Jose Guerra Carmenate, R.de J. Pacheco-Aké, G. Sánchez-Colón, Subhash Rajpoot, P. Fernández de Córdoba, Gaetano Lambiase