High Energy Astrophysical Phenomena
UV and Optical Signatures of Late-time Disk Instabilities in Tidal Disruption Events
Daichi Tsuna, V. Ashley Villar, Anthony L. Piro et al. (+1 more)
Tidal disruption events (TDEs) are unique probes of evolving
accretion in supermassive black holes. Recent models of TDE disks show that they undergo brief thermal instabilities with temporal super-Eddington
accretion at late times, which has been suggested as a possibility to explain the ubiquitous late
radio emergence in TDEs. We model the ultraviolet (UV) and optical signatures of such disk instabilities, expected from the
accretion power being reprocessed by the optically-thick
outflow following super-Eddington
accretion. Our model predicts brief UV-bright transients lasting for days, with luminosities of $10^{42}$-$10^{43}$ erg s$^{-1}$ in near-UV and $10^{41}$-$10^{42}$ erg s$^{-1}$ in optical for a typical TDE by a $10^6~M_\odot$ black hole. These could be detectable by near-future surveys such as ULTRASAT, Vera C. Rubin Observatory and Argus Array, for TDEs of
redshifts out to $\approx 0.1$. We further conduct a search for these transients in existing nearby TDEs using data from the Zwicky Transient Facility, placing upper limits on the
flare rate for each TDE of $1$-$2$ yr$^{-1}$ dependent on the
outflow mass. In the era of future surveys, combined UV/optical and
radio monitoring would be an important test to the disk instability phenomena, as well as its explanation for the late-time
radio emission in TDEs.
Read the full abstract ▾
All authors Daichi Tsuna, V. Ashley Villar, Anthony L. Piro, Samantha C. Wu
Astrophysics of Galaxies
Intracluster globular clusters as tracers of the mass assembly of the Hydra I galaxy cluster
Felipe S. Lohmann, Magda Arnaboldi, Michael Hilker et al. (+7 more)
In
galaxy clusters, hierarchical assembly predicts the formation of
stellar substructures and intracluster light (ICL), a diffuse
stellar component tracing the global cluster potential. Because these features are extremely faint, alternative tracers such as globular clusters (GCs) provide a powerful tool to study cluster assembly. We use deep VLT/FORS $V$- and $I$-band imaging to investigate the GC population in the nearby Hydra I
galaxy cluster ($\sim 45.7$ Mpc). GC candidates were selected from the $VI$ colour-magnitude diagram and divided into blue and red subpopulations. We find a clear spatial dichotomy: red GCs are concentrated around the massive central
galaxies NGC 3311 and NGC 3309, while blue GCs are more extended and offset from the centre, coinciding with a secondary peak of X-ray-emitting gas. In the central regions, GC spatial distributions further depend on
stellar population properties: young metal-rich GCs are more extended and may be linked to ram-pressure stripping, whereas old metal-poor GCs are more centrally concentrated, possibly originating from disrupted
dwarf galaxies. Comparing the GC number density profiles to the surface brightness profile of NGC 3311, we find that the red GCs closely follow the
galaxy light, while the blue population significantly deviates from it and traces the global gravitational potential of the cluster. This is also reflected in the specific frequency of blue GCs, which is approximately $\sim 5\times$ higher in the ICL-dominated outskirts than in the inner regions dominated by red GCs. Finally, we present a novel method to constrain the
evolution of the
galaxy luminosity function of the cluster using GC specific frequencies and colour distributions, yielding a past faint-end slope of $\alpha=-1.81^{+0.16}_{-0.16}$ compared to $\alpha=-1.41^{+0.08}_{-0.05}$ today, consistent with high-
redshift observations and cosmological simulations.
Read the full abstract ▾
All authors Felipe S. Lohmann, Magda Arnaboldi, Michael Hilker, Andreas Burkert, Marilena Spavone, Ortwin Gerhard, Marina Rejkuba, Marco Mirabile, Michele Cantiello, Enrichetta Iodice
High Energy Astrophysical Phenomena
PSR J0024$-$7204ai: a massive, eccentric binary system in the globular cluster 47 Tucanae
D. Risbud, A. Ridolfi, P. C. C. Freire et al. (+9 more)
In this paper we present PSR J0024$-$7204ai, a 13.026-ms binary
pulsar recently discovered in the globular cluster 47 Tucanae by the MeerKAT
radio telescope. This is the slowest spinning
pulsar known in this globular cluster, and has a $\sim1.67$-day orbit with an eccentricity of $e\approx0.18$. Although it was not yet possible to derive an unambiguous phase-connected timing solution, by combining detections obtained from MeerKAT and archival Parkes data we were able to measure the rate of advance of periastron to high significance, $\dot{\omega}$ = 0.1601 $\pm 0.0046$ deg yr$^{-1}$. This value implies a total system mass of $2.41 \pm 0.11\, \mathrm{M}_\odot$ (68.3% C. L.), which, when combined with the binary mass function, gives a maximum
pulsar mass of $\sim 1.7 \, \mathrm{M}_\odot$ and a minimum companion mass of $\sim 0.7\, \mathrm{M}_\odot$. Apart from being the slowest
pulsar in 47~Tucanae, its orbit is by far the most eccentric and its companion is the most massive among all known binary
pulsars in this globular cluster. One possibility is that system is an old MSP - Carbon-Oxygen White
Dwarf binary, whose orbit was perturbed by
stellar dynamical interactions in the cluster core. Further follow-up observations of this system will be essential for a more detailed characterisation of this system and its
evolution.
Read the full abstract ▾
All authors D. Risbud, A. Ridolfi, P. C. C. Freire, M. Cadelano, W. Chen, L. Zhang, R. Nag, F. Camilo, P.V. Padmanabh, A. Corongiu, F. Abbate, A. Possenti
Instrumentation and Methods for Astrophysics · Cross-listed from physics.ao-ph
IT-DPC-SRI: A Cloud-Optimized Archive of Italian Radar Precipitation (2010-2025)
Gabriele Franch, Elena Tomasi, Uladzislau Azhel et al. (+11 more)
We present IT-DPC-SRI, the first publicly available long-term archive of Italian weather radar precipitation estimates, spanning 16 years (2010–2025). The
dataset contains Surface Rainfall Intensity (SRI) observations from the Italian Civil Protection Department's national radar mosaic, harmonized into a coherent Analysis-Ready Cloud-Optimized (ARCO) Zarr datacube. The archive comprises over one million timesteps at temporal resolutions from 15 to 5 minutes, covering a $1200\times1400$ kilometer domain at 1 kilometer spatial resolution, compressed from 7TB to 51GB on disk. We address the historical fragmentation of Italian radar data - previously scattered across heterogeneous formats (OPERA BUFR, HDF5, GeoTIFF) with varying spatial domains and projections - by reprocessing the entire record into a unified store. The
dataset is accessible as a static versioned snapshot on Zenodo, via cloud-native access on the ECMWF European Weather Cloud, and as a continuously updated live version on the ArcoDataHub platform. This release fills a significant gap in European radar data availability, as Italy does not participate in the EUMETNET OPERA pan-European radar composite. The
dataset is released under a CC BY-SA 4.0 license.
Read the full abstract ▾
All authors Gabriele Franch, Elena Tomasi, Uladzislau Azhel, Giacomo Tomezzoli, Alessandro Camilletti, Virginia Poli, Renata Pelosini, Gianfranco Vulpiani, Gabriella Scipione, Giuseppe Trotta, Matteo Angelinelli, Leif Denby, Irene Livia Kruse, Marco Cristoforetti
Instrumentation and Methods for Astrophysics
Well-being and career instability across genders in the Spanish Astronomical Society
Maritza A. Lara-Lopez, I. Rebollido, A. Vidal-Garcia et al. (+9 more)
We present the results of a comprehensive survey conducted among members of the Spanish Astronomical Society (Sociedad Espanola de Astronomia, SEA) to assess well-being, professional satisfaction, and family-work balance of researchers in astronomy. The survey addressed multiple aspects of professional life, including happiness, career stability, publication pressure, and access to childcare services during scientific meetings. Responses were examined across gender and career stages to identify trends and sources of dissatisfaction.
Read the full abstract ▾
All authors Maritza A. Lara-Lopez, I. Rebollido, A. Vidal-Garcia, A. Rouco Escorial, S. Berlanas, I. Garcia-Bernete, B. Agis-Gonzalez, M. Rodriguez-Baras, N. Barrado-Izagirre, I. Pintos Castro, N. Ospina, S. Bonoli
Earth and Planetary Astrophysics
Coupled Map Lattice for Astronomical Object Formation: A Scenario for Evolution from Star to Disk, Arms, and Companions
Erika Nozawa
We present a new dynamic formation model of a
star, a disk, arms, and companions using a coupled map
lattice (CML), a complex systems approach. This CML simulates the viscoelastic and chaotic dynamics and
evolution of gas clumps containing a little
dust with a minimal set of one Eulerian procedure for the flow formation of gas clumps due to gravitational interaction, and one Lagrangian procedure for the collision and mixture of gas clumps due to viscoelastic advection. Despite its simplicity, this CML successfully obtains four typical astronomical objects consistent with protoplanetary disk observations: a central
star, Keplerian disk, spiral arms, and even
stellar, substellar, and planetary companions. All these formation processes are truly dynamic, with the central
star "starring" in them, and they are not based on the conventional disk gravitational instability but on the central
star gravitational instability with high-dimensional chaotic gas ejection, namely the chaotic itinerancy. Of particular note is the process in which diverse companions are formed due to the rapid density increase caused by the intersection of spiral arms. This suggests a novel companion formation scenario that should be called "arm-crossing companion formation" with a view to
planet formation, which may overcome the radial drift barrier and angular momentum problem.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics
Prospects of Indirect Detection of Dark Matter via Primordial Black Hole Induced Gravitational Waves
Debarun Paul, Md Riajul Haque and Supratik Pal
Primordial black holes (PBHs), produced in the early Universe, can source a
stochastic background of induced gravitational waves (GWs) and provide a non-thermal origin for dark matter (DM). We investigate DM production in a PBH-dominated cosmological framework, including contributions from PBH evaporation, gravitational production, and thermal freeze-in and freeze-out mechanisms, and determine the regions consistent with the observed DM relic abundance. We find that thermal freeze-in can compensate for the underabundance of PBH-sourced DM, while indirect detection remains largely insensitive due to the feeble interaction strength, making future GW observatories such as LISA and the Einstein
Telescope (ET) unique probes of this scenario. For freeze-out DM, indirect detection experiments constrain regions with relatively large annihilation cross-sections, whereas GW observations probe complementary regions with heavier DM masses and smaller interaction strengths. Consequently, the same DM parameter space cannot be simultaneously probed by both indirect detection searches and GW missions. These results establish GW observations as a powerful and independent probe of DM production in PBH-dominated cosmologies, opening a new observational window into DM properties and the thermal history of the pre-BBN Universe.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Modeling isolated magnetar spin-down evolution and implications for long-period radio transients
Jon Kwong and Kaya Mori
Long-period
radio transients (LPTs) are a new class of
radio sources characterized by long
spin periods ($P_{\text{spin}}>10^3$ s) and highly variable
radio emission. While known magnetars are relatively young ($\tau<10^5$ yrs) with
spin periods clustered between $1-10$ sec, it has been proposed that LPTs may be linked to a missing population of older magnetars. In this paper, we present an extensive parametric analysis of isolated magnetar
spin evolution using various propeller
spin-down models. In general, at higher initial magnetar B-fields ($B_0>\sim10^{15}$ G) and larger ambient densities ($n_0>\sim10^2$ cm$^{-3}$), magnetars will transition to the propeller phase earlier, and they start accreting gas from the ISM or molecular clouds after $\tau\sim10^8$ yrs. We found that a transition from the
pulsar to the propeller phase is required to reach the observed LPT period range of $P>10^3$ s. More specifically, our population synthesis study based on Monte-Carlo simulations shows that two propeller models can account for most of the observed LPT periods ($P\sim1-400$ [min]) and their period derivative constraints ($\dot{P}<10^{-9}$ s s$^{-1}$). Our
spin-down models predict that (1) nearby
radio-quiet
neutron stars with the estimated dipole $B$-field range of $B\sim(1-5)\times10^{13}$ G will transition to the propeller phase eventually after $\tau>\sim10^7$ yrs; (2) thermal X-ray emission from
accretion-phase magnetars becomes too faint for detection after traveling ($d>\sim10$ kpc) from their birth places; (3) sporadic
radio outbursts observed from LPTs may not be explained by regular
radio pulsar and magnetar emission mechanisms that operate during the propeller phase.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics
Gravitational Wave Echoes of the First Order Phase Transition in a Kination-Induced Big Bang
Richard Casey, Katherine Freese and Evangelos I. Sfakianakis
Gravitational waves (GWs) produced during first-order phase transitions (FOPTs) in the early universe provide a powerful probe of nonstandard cosmological histories. We study GW production from a FOPT ending a kination-dominated epoch in the Kination-Induced Big Bang scenario, in which a period of kination domination terminates through a phase transition that reheats the universe into radiation domination. A rolling scalar field drives the kination epoch. In the specific model we consider, its derivative coupling to a second scalar (tunneling field) dynamically traps the latter in a false
vacuum, with the phase transition triggered as the kination field slows due to Hubble friction. We compute the resulting
stochastic GW background from bubble nucleation and collisions, presenting analytic estimates and numerical results for the peak amplitude and frequency. In all cases we find an upper bound $\Omega_{\rm GW} h^2\lesssim 2\times10^{-7}$ from the bubble percolation condition. In the case where the false
vacuum energy dominates at the transition (yet the kination field drives the FOPT), we find $\Omega_{\rm GW}h^2\gtrsim 10^{-12}$. We further find that the Hubble scale during the phase transition across a broad set of model parameters is bounded by $\mathscr{O}(10^{-13})M^2/M_{\rm Pl}\lesssim H_* \lesssim \mathscr{O}(0.1)M^2/M_{\rm Pl}$, where $M$ is the mass-scale controlling the strength of the interaction between the kination and tunneling fields. The predicted signal spans frequencies from nHz to MHz, allowing the model to explain the signal reported by
Pulsar Timing Array experiments and to be constrained or probed by interferometers such as LISA, Advanced LIGO,
Cosmic Explorer, and BBO. Interestingly, a FOPT can occur even if the bare tunneling potential has a single minimum, as metastability is generated dynamically by the coupling between the tunneling and the kination field.
Read the full abstract ▾
Solar and Stellar Astrophysics
Generalization from Low- to Moderate-Resolution Spectra with Neural Networks for Stellar Parameter Estimation: A Case Study with DESI
Xiaosheng Zhao, Yuan-Sen Ting, Rosemary F.G. Wyse et al. (+5 more)
Cross-survey generalization is a critical challenge in
stellar spectral analysis, particularly in cases such as transferring from low- to moderate-resolution surveys. We investigate this problem using pre-trained models, focusing on simple neural networks such as multilayer perceptrons (MLPs), with a case study transferring from LAMOST low-resolution spectra (LRS) to DESI medium-resolution spectra (MRS). Specifically, we pre-train MLPs on either LRS or their
embeddings and fine-tune them for application to DESI
stellar spectra. We compare MLPs trained directly on spectra with those trained on
embeddings derived from
transformer-based models (self-supervised foundation models pre-trained for multiple downstream tasks). We also evaluate different fine-tuning strategies, including residual-head fine-tuning, LoRA, and full fine-tuning. We find that MLPs pre-trained on LAMOST LRS achieve strong performance, even without fine-tuning, and that modest fine-tuning with DESI spectra further improves the results. For iron abundance,
embeddings from a
transformer-based model yield advantages in the metal-rich ([Fe/H] > -1.0) regime, but underperform in the metal-poor regime compared to MLPs trained directly on LRS. We also show that the optimal fine-tuning strategy depends on the specific
stellar parameter under consideration. These results highlight that simple pre-trained MLPs can provide competitive cross-survey generalization, while the role of spectral foundation models for cross-survey
stellar parameter estimation requires further exploration.
Read the full abstract ▾
All authors Xiaosheng Zhao, Yuan-Sen Ting, Rosemary F.G. Wyse, Alexander S. Szalay, Yang Huang, László Dobos, Tamás Budavári, Viska Wei
Earth and Planetary Astrophysics
Geodetically Anchored 0.30m Digital Elevation Model of the Chandrayaan-3 Vikram Landing Site from Chandrayaan-2 Orbital High Resolution Camera (OHRC) Stereo Imagery
Chandra Tungathurthi
ISRO's terrain characterization and hazard mapping from Chandrayaan-2 Orbiter High Resolution Camera (OHRC) stereo imagery were central to the safe landing of Chandrayaan-3 - the first successful landing in the lunar south polar region. However, these elevation products were generated with a proprietary pipeline and have not been publicly released. We present a 0.30 m/pixel digital elevation model (DEM) of the Chandrayaan-3 Vikram landing site using a fully open workflow based on ISIS, the Ames Stereo Pipeline, and ALE, achieving sub-meter resolution comparable to mission-reported products. The reconstruction covers 2.18 x 2.24 km with 91.2% valid pixel coverage, 8.1 cm median triangulation error, and 40-50 cm relative vertical precision. The Vikram lander and Pragyan rover are individually resolved. Geodetic
alignment to an LROC NAC stereo DEM achieves approximately 30 m horizontal accuracy; pixel-wise validation at 3 m resolution confirms negligible vertical bias (median dz = +0.28 m) and robust dispersion (NMAD = 2.88 m). Stable OHRC stereo convergence requires Community Sensor Model (CSM) camera models; the legacy ISIS camera model failed across two independent sites. At 0.30 m, these DEMs complement LROC NAC DTMs (approximately 1 m), resolving sub-meter hazards below the NAC detection threshold. Applied to the extensive OHRC south polar archive, this methodology provides independent capability for hazard mapping and landing site analysis for upcoming missions including Chandrayaan-4, LUPEX, and Artemis.
Read the full abstract ▾
Solar and Stellar Astrophysics
The radial velocity curve for HeII emission cannot be used for component mass determination in SS433
A.V. Dodin, K.A. Postnov and A.M. Cherepashchuk
More than 150 measurements of the HeII 4686A emission line in spectra of SS433 were obtained during 388 nights in 2020-2025 with the Transient Double-beam Spectrograph on the 2.5 m
telescope of Caucasian Mountain Observatory of Sternberg Astronomical Institute. We found that the HeII emission line formation region is not eclipsed and is significantly larger than both the donor
star and the photosphere of the supercritical
accretion disk. The HeII radial velocity curve was found to be independent of the precessional phase and inconsistent with the photometric curve. These findings suggest that the HeII line does not reflect the orbital motion of the compact object. Therefore, spectroscopic estimates of the masses of the components in SS433 based on the HeII emission line can be unrealistic.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics
Improved frequency hierarchy treatment for anisotropic spectral distortions
Jens Chluba, Sara Evangelista, Tom Daman et al. (+1 more)
Spectral distortion anisotropies of the
cosmic microwave background (CMB) provide a new probe of the early Universe that can be accessed using traditional CMB imaging techniques. It is possible to compute the creation and
evolution of anisotropic signals for various scenarios using the frequency hierarchy method recently developed for CosmoTherm. However, the current treatment is not perfect and some approximations had to be made. Here, we carefully construct a modified form for the
evolution equations that has the full
equilibrium solutions built into the formulation. We improve the formalism to account for i) additional stimulated scattering effects, ii) kinematic corrections to the thermalization terms, iii) corrections to the standard perturbation variables and iv) direct
photon sources. These effect could not be captured with the original formulation of the frequency hierarchy method but are indeed important for cleanly separating real distortions from temperature signals. However, we show that previous results are not altered significantly when compared to the improved formulation presented here. As a new worked example, which could indeed not be treated before, we also illustrate how possible changes in the temperature-
redshift relation would create spectral distortion anisotropies in the pre-recombination era. The theoretical methods presented here are also an important step towards being able to consistently predict the CMB spectral distortion anisotropies in
photon-dark
photon and
photon-
axion conversion scenarios.
Read the full abstract ▾
All authors Jens Chluba, Sara Evangelista, Tom Daman, Geoff Vasil
Astrophysics of Galaxies
Multi-frequency mapping of the S255IR region at a wavelength of 1~mm
E. A. Mikheeva, S. V. Kalenskii, S.-Y. Liu et al. (+2 more)
The results of interferometric observations of the
star-forming region S255IR in the frequency range 210–250 GHz are presented. The observations were carried out with the
antenna array SMA (Hawaii, USA). Fifty-three molecules were detected, including complex organic molecules (COMs) such as CH$_3$CHO, CH$_3$CN, CH$_3$CH$_2$CN, and many others. Typical rotational temperatures in the hot core SMA1 fall in the range 100–200 K. Optical depths in the lines of methanol and some other molecules in the cores SMA1 and SMA2 were estimated. In SMA1, the optical depth of one of the strongest methanol lines, $5_{-1}-4_{-1}E$, proved to be $23.8 \pm 1.5$. Based on this value, one can assume that the lines of other oxygen-containing COMs, such as CH$_3$OCHO, CH$_3$OCH$_3$, CH$_3$CH$_2$OH, which are typically much less abundant in hot cores than methanol, are optically thin in SMA1. Most of the detected molecules can be roughly divided into two groups. The molecules of the first group emit exclusively toward the hot core SMA1, while some or all lines of the molecules of the second group, in addition to SMA1, can be seen toward a ring-like structure to the west of SMA1. This structure is most likely associated with the walls of a cavity formed by high-velocity
outflows driven by young
stellar objects (YSOs) in molecular cores SMA1, SMA2, and possibly SMA3. The gas temperature and density in the cavity walls were estimated using methanol lines. The temperature was found to be about 50–60 K, and the density about $10^7-10^8$ cm$^{-3}$. The column density of methanol near the brightness peaks in the lines of this molecule is about $5\times 10^{15}$~cm$^{-2}$. The column densities of other COMs in the ring-like structure will be determined in future studies with increased sensitivity achieved by spectral line stacking.
Read the full abstract ▾
All authors E. A. Mikheeva, S. V. Kalenskii, S.-Y. Liu, A. M. Sobolev, S. Kurtz
Solar and Stellar Astrophysics
[C/N] Ages and Extra-Mixing for [Fe/H] <- 0.5: Insights from the LMC and SMC
Yuxi Lu, John D. Roberts, Joshua T. Povick et al. (+4 more)
The [C/N]-age relation has become a powerful tool for reconstructing the formation history of the Milky Way (MW), providing the largest age sample for field
giant stars. However, at
metallicities below [Fe/H] $< -0.5$,
stellar surfaces are altered by a poorly understood process known as extra mixing, which modifies [C/N] in a mass- and
metallicity-dependent manner. This effect complicates the application of the traditional [C/N]-age relation in metal-poor regimes. Within the MW, constraining the mass dependence of extra mixing is particularly challenging because
stars at [Fe/H] $< -0.5$ are predominantly old and therefore low-mass, leading to strong degeneracies between mass and
metallicity. In this work, we explore the potential of the Magellanic Clouds (MCs) to disentangle these effects and constrain extra mixing as a function of age and
metallicity. By comparing empirical corrections calibrated in the MW with predictions from thermohaline mixing models, we isolate the mass dependence of extra mixing in the MCs down to [Fe/H] $\sim-0.7$. We find that the empirical calibration performs well for lower-mass
stars ($< 1.25$ $M_{\odot}$), while theoretical models successfully reproduce the observed mass dependence down to $\sim$ 1.25 $M_{\odot}$. We further present the first observational evidence that extra mixing becomes ineffective above $\sim$ 1.8 $M_{\odot}$ at [Fe/H] $\sim -0.7$. Our results demonstrate the feasibility of deriving [C/N]-based ages for individual
stars in external
galaxies. Future observations targeting higher-$\log g$ or fainter
stars in the MCs will provide stronger constraints on extra-mixing processes and enable the calibration of [C/N]-age relation that can be applied to low-
metallicity individual
stars in the MW or external
galaxies.
Read the full abstract ▾
All authors Yuxi Lu, John D. Roberts, Joshua T. Povick, Marc H. Pinsonneault, Madeline Howell, David L. Nidever, Jennifer A. Johnson
Earth and Planetary Astrophysics
Microphysical Model of Jupiter's Great Red Spot Upper Chromophore Haze
Asier Anguiano-Arteaga, Santiago Perez-Hoyos, Agustin Sanchez-Lavega et al. (+1 more)
The origin of the red colouration in Jupiter's Great Red Spot (GRS) is a long-standing question in planetary science. While several candidate chromophores have been proposed, no clear conclusions have been reached regarding its nature,
evolution, or relationship to atmospheric dynamics. In this work, we perform microphysical simulations of the reddish haze over the GRS and quantify the production rates and timescales required to sustain it. Matching the previously reported chromophore column mass and effective radius in the GRS requires column-integrated injection fluxes in the range $1\times10^{-12}$-$7\times10^{-12}$ kg m$^{-2}$ s$^{-1}$, under low upwelling velocities in the upper troposphere ($v_{\mathrm{trop}}\lesssim 1.5\times10^{-4}$ m s$^{-1}$) and particle charges of at least 20 electrons per $\mu$m. Such rates exceed the mass flux that standard photochemical models of Jupiter currently supply via NH$_3$-C$_2$H$_2$ photochemistry at 0.1-0.2 bar, the most popular chromophore pathway in recent literature. We find a lower limit of 7 years on the haze formation time. We also assess commonly used size and vertical distribution parameterisations for the chromophore haze, finding that eddy
diffusion prevents the long-term confinement of a thin layer and that the extinction is dominated by particles that can be represented by a single log-normal size distribution.
Read the full abstract ▾
All authors Asier Anguiano-Arteaga, Santiago Perez-Hoyos, Agustin Sanchez-Lavega, Patrick G. J. Irwin
Solar and Stellar Astrophysics
First detection of the TiO i1Pi-a1Delta system in stellar spectra and its laboratory characterization
M. R. Schmidt
TiO plays an important role in determining the atmospheric structure of M-type
stars and in shaping the visual part of their spectra. We compute synthetic spectra for late-type M
giants and identify systematic discrepancies in the wavelength range 5810-5850 A. To investigate the origin of these discrepancies, we analyse experimental TiO absorption cross-sections. We report the detection of a molecular band of the singlet system $^{1}\Pi$-a$^{1}\Delta$ of the TiO, with an R-head located at 5814.8 A, overlapping the 1-3 band of the C$^3\Delta$-X$^3\Delta$ system. The lower state of the band is identified as the a$^1\Delta$ v"=0 state, while the upper state is most likely the $^1\Pi$ in its ground vibrational state. The empirical band intensity is derived by comparing the relative strengths of neighbouring bands from the C$^3\Delta$-X$^3\Delta$ and B$^3\Pi$-X$^3\Delta$ systems in the experimental cross-section. The band intensity is further validated by synthetic spectrum calculations for the late-type
giant 30 Her (M6 III) and comparison with its observed spectrum from the MELCHIORS library. The newly identified band is sufficiently strong to affect the flux distribution in the spectra of cool
stars.
Read the full abstract ▾
Instrumentation and Methods for Astrophysics
Recalibrating the Sensitivities of the STIS First-Order, Medium-Resolution Modes
Alex Fullerton
The sensitivities of STIS first-order, medium resolution modes were redetermined from on-orbit observations and CALSPEC models (version 11) of the primary white-
dwarf spectrophotometric standard
stars G191-B2B, GD 71, and GD 153. The sensitivity of an additional configuration was updated by comparing observations of the secondary standard BD +75 325 with the STIS low-resolution spectrum that has been calibrated consistently with the version 11 models. The procedures used to derive the sensitivities and verify the PHOTTAB reference files prior to their activation in CRDS (on May 1, 2025) are described. Results are presented in graphical form in an extensive appendix. Issues and uncertainties are discussed briefly, along with recommendations for future work.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics
Multiwavelength Characterization of a Dynamically Relaxed Cool Core Galaxy Cluster at $z=1.5$
Anthony M. Flores, Adam B. Mantz, Steven W. Allen et al. (+5 more)
We present imaging and spectroscopic analyses of Chandra and XMM-Newton observations of ACT-CL J0123.5$-$0428, one of the most massive, highest
redshift galaxy clusters detected within the survey fields of the Atacama Cosmology
Telescope. The Chandra data are sufficient to characterize the morphology of this cluster and constrain the geometrically deprojected temperature in 2 spatial bins out to $r_{2500}$, revealing a dynamically relaxed system whose temperature drops to $kT = 1.8\pm0.6$ keV in the inner $\sim40$kpc. Within this same inner radius, the surface brightness and density of the ICM is sharply peaked, and the cooling time falls to $t_\mathrm{cool}=280^{+150}_{-120}$ Myr. A novel forward-modeling analysis of the XMM data extends imaging and spectroscopic measurements of this system out to $r_{500}$, constraining the
redshift to $z=1.50\pm0.03$, with a mean temperature of $kT = 7.3\pm1.1$ keV and an emission-weighted mean
metallicity of $Z/Z_\odot = 0.43^{+0.46}_{-0.25}$. We also utilize the limited optical/IR photometric coverage of the cluster to characterize the properties of the brightest cluster
galaxy (BCG), which is coincident with the X-ray peak. Despite the high
redshift and strong cool core, the BCG exhibits no signs of recent or ongoing
star formation, suggesting AGN feedback has been acting persistently to stem
star formation since $z\sim 2.5$. These measurements identify ACT-CL J0123.5$-$0428 as the highest
redshift, dynamically relaxed, cool core
galaxy cluster discovered to date, making it a premier target for future astrophysical and cosmological studies.
Read the full abstract ▾
All authors Anthony M. Flores, Adam B. Mantz, Steven W. Allen, R. Glenn Morris, Abigail Y. Pan, Taweewat Somboonpanyakul, Haley R. Stueber, Michael McDonald
High Energy Astrophysical Phenomena
Exploring the magnetic field of the ultraluminous X-ray pulsar NGC 4631 X-8
Amar Deo Chandra
NGC 4631 X-8 is an ultraluminous X-ray
pulsar (ULXP) having a
spin period of about 9.7 s, discovered using XMM-Newton observations in 2025. The
pulsar is known to show one of the largest
spin-up rates ($\sim -9.6 \times 10^{-8}$ s s$^{-1}$) among the ULXP population. We explore the surface
magnetic field of the
neutron star in this source using different models, and find that the inferred
magnetic field lies in the range of about $0.3-7 \times 10^{14}$G. We study the long-term
magnetic field and
spin period
evolution of the
pulsar assuming steady
accretion using prevalent theoretical mechanisms and find that the
pulsar will likely evolve to become a millisecond
pulsar having decayed
magnetic field of about $\sim 10^{9}$G in about a million years. The scenario of the formation of a millisecond
pulsar is also probed using an estimate of the super-Eddington duty cycle of about 14% from the literature, which suggests that the
neutron star would accrete sufficient matter to likely become a recycled millisecond
pulsar. Exploring the
magnetic field as well as the
spin period
evolution properties of ULXPs may enable us to understand the poorly understood evolutionary features of ULXPs, shed light on one of the pathways of millisecond
pulsar formation and also help us to understand the possibility of transient super-Eddington
accretion phases in newborn magnetars, which are believed to power energetic events such as long gamma-ray bursts and Type I superluminous
supernovae.
Read the full abstract ▾
Astrophysics of Galaxies
Reduction of bar fraction in paired galaxies in the SDSS
Linlin Li, Shuai Feng, Shiyin Shen et al. (+3 more)
We investigate the bar fraction in
galaxy pairs from the SDSS to assess how
galaxy interactions affect bar structures. Compared to isolated
galaxies, close pairs exhibit a significantly reduced bar fraction at projected separations within 25 kpc. This reduction is driven almost entirely by systems showing clear merger or disturbance signatures, indicating that
tidal interactions suppress bars. The decline is dominated by a decrease in weak bars, while the fraction of strong bars remains largely unchanged. Bar suppression is primarily associated with major mergers and is strongest in massive host
galaxies. A weaker but statistically significant suppression is detected in minor mergers only for massive
galaxies with small bulges. In contrast, no significant dependence of bar suppression on the relative orientation between pair members is found. These findings provide observational evidence that
tidal perturbations in major mergers play a key role in regulating bar
evolution.
Read the full abstract ▾
All authors Linlin Li, Shuai Feng, Shiyin Shen, Qi'an Deng, Ying Zu, Wenyuan Cui
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Gauge-independent gravitational waves from a minimal dark $U(1)$ sector with viable dark matter candidates
Wan-Zhe Feng and Zi-Hui Zhang
Searches for
stochastic gravitational wave backgrounds generated by first-order phase transitions offer a powerful probe of hidden sectors, but quantitative predictions in gauge theories are obstructed by the gauge dependence of the finite-temperature effective potential and the associated tunneling action. We study a minimal gauged $U(1)$ dark sector containing a dark
Higgs and a dark
photon, optionally supplemented by a vectorlike dark
fermion, coupled to the Standard Model through the
Higgs portal or kinetic mixing. Using the Nielsen identity together with a controlled derivative expansion and power counting, we construct a gauge-independent effective action in the high- and low-temperature limits, enabling model-intrinsic nucleation dynamics and robust gravitational wave predictions. We perform dedicated Monte Carlo scans in both limits and map viable microscopic parameters to detector-facing peak frequencies and amplitudes, spanning bands relevant to
pulsar timing arrays and planned space-based interferometers. In our scans, supercooled phase transitions typically produce much stronger signals and are more likely to fall within the sensitivity range of current and future gravitational wave detectors, whereas parametrically high-temperature phase transitions generally yield weaker signals. We further connect the phase transition phenomenology to viable dark matter candidates within the same minimal field content, providing
benchmark targets for dark
photon dark matter and dark
fermion dark matter, and highlighting their complementarity with gravitational wave observables. Overall, our results provide an end-to-end, gauge-independent pipeline from a minimal hidden sector Lagrangian to gravitational wave spectra and cosmologically viable dark matter
benchmarks, yielding the most reliable and concrete predictions to date for a minimal gauged $U(1)$ dark sector.
Read the full abstract ▾
Earth and Planetary Astrophysics
Statistical Validation and Photometric Characterization of the Hot Jupiter Candidate TOI 7475.01
Biel Escolà-Rodrigo
We present the statistical validation and full photometric characterization of the
exoplanet candidate TOI 7475.01 (TIC 376866659), detected by the TESS mission. Using a custom pipeline combining natural flux preservation with robust BLS detection, we identified a transit signal with a period of $3.2538$ days and a depth of $\sim 4600$ ppm. To rule out false positives, we performed centroid analysis, spatial contamination checks using
Gaia DR3, and a statistical validation using TRICERATOPS. Our results show a Signal-to-Noise Ratio (SNR) of 294.13 and a False Positive Probability (FPP) of $\approx 0$. Based on the clean spatial environment, stable centroids, and high statistical probability, we validate TOI 7475.01 as a planetary companion. We subsequently performed a
Bayesian transit fit using juliet with Dynesty nested sampling, and derived physical parameters via Monte Carlo error propagation. We find a planetary radius of $R_p = 1.18^{+0.39}_{-0.40}\ R_\mathrm{Jup}$ and an
equilibrium temperature of $T_\mathrm{eq} = 1455^{+77}_{-56}$ K, consistent with a hot Jupiter classification. The
planet mass is estimated at $M_p \approx 2.2\ M_\mathrm{Jup}$ (MAP) via the Chen&Kipping mass-radius relation; radial velocity follow-up is required for a precise measurement. The impact parameter remains unconstrained ($b = 0.46 \pm 0.34$), a limitation of single-band TESS photometry that future CHEOPS observations could resolve.
Read the full abstract ▾
High Energy Astrophysical Phenomena
A universal critical accretion rate for black hole jet formation
Adelle J. Goodwin and Andrew Mummery
It has long been suspected that black hole
accretion-
outflow coupling is invariant from the
stellar to supermassive scales.
Stellar mass black hole
accretion flows are known to launch jets and
outflows as they transition through critical
accretion rate thresholds, with values well constrained observationally owing to their short evolutionary timescales. In contrast,
accretion flows in typical supermassive black hole (SMBH) systems (those in active
galactic nuclei) evolve over thousands of years, making the critical transitions at which jets are launched impossible to constrain in individual systems.
Tidal disruption events (TDEs) provide the unique opportunity to witness the birth and
evolution of an
accretion flow onto a SMBH which evolves on timescales of years. Here we show that TDEs launch
outflows during a super-Eddington
accretion phase and a second, physically distinct
outflow, at a critical
accretion rate of $L_{\rm crit} \approx0.02$ $L_{\rm Edd}$, the same as the critical
accretion rate for state transitions observed in accreting
stellar mass black holes. This work naturally explains the mechanism, observed properties, and detection rate for
prompt and delayed
outflows observed in TDEs, which until now have been open problems. More broadly, we demonstrate that SMBHs exhibit the same
accretion-
outflow coupling as
stellar mass black holes and that the critical low
accretion rate threshold for jet formation in black holes is scale invariant.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics
The impact of the formation channel on gravitational-wave-galaxy cross-correlations
Kabir Chakravarti and Federico R. Urban
The angular, harmonic cross-correlation between gravitational wave (GW) events and
galaxy catalogues contains rich information on the large-scale structure and the origin of compact binary mergers. In this work, we study how uncertainties in the binary formation channel affect the predicted cross-correlation signal for both current-generation and next-generation networks of detectors. We generate five mock GW catalogues for which we vary the progenitor-to-remnant mass-transfer function and the time-delay probability distribution between progenitor and remnant. We then cross-correlate these catalogues with
galaxy samples modelled on the 2MASS Photometric
Redshift catalogue (2MPZ) and the
Gaia-unWISE
quasar catalogue (Quaia). We find that the mass-transfer function has negligible effect on the cross-correlation signal, with differences remaining within
redshift uncertainties. In contrast, the time-delay distribution dramatically affects the
redshift distribution of the GW events and, with it, the cross-correlation signal, particularly for shallow
galaxy catalogues. In particular, current-generation facilities can achieve significant detections only for the longest time delays when cross-correlated with 2MPZ, whilst all cross-correlations with the deeper Quaia catalogue are marginally detectable or consistent with zero. Our exploratory results thus demonstrate that forecasts on cosmological or astrophysical parameters derived from GW-
galaxy cross-correlations are, as expected, strongly sensitive to the assumed binary formation history.
Read the full abstract ▾
Instrumentation and Methods for Astrophysics
The Habitable Worlds Observatory in Historical Context
Marc Postman and Karl Stapelfeldt
We summarize the past four decades of astrophysics and
exoplanet direct imaging mission concept studies, technology developments, and scientific progress that have led to the initiation of the Habitable Worlds Observatory project by NASA.
Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
Excavation of a 69-m diameter and 94-m high cavern for the Hyper-Kamiokande detector
Y. Asaoka, H. Tanaka, S. Nakayama et al. (+14 more)
The excavation of the Hyper-Kamiokande cavern, 600 m underground, is complete. Measuring 69 m in diameter and 94 m in height, it is among the world's largest rock caverns. A vertically oriented, dome-capped cylindrical design was chosen to optimize cost and performance. The geometry, combined with substantial overburden, posed major engineering challenges. This paper outlines the underground works, main cavern design, excavation plan, and the
evolution of support design and construction methods during excavation, namely the information-based (observational) design and construction approach.
Read the full abstract ▾
All authors Y. Asaoka, H. Tanaka, S. Nakayama, K. Abe, K. Ishita, S. Moriyama, M. Shiozawa, K. Horinokuchi, C. Miura, Y. Suzuki, H. Morioka, D. Inagaki, H. Kurose, T. Suido, T. Kobuchi, M. Tobita, M. Utsuno
Astrophysics of Galaxies
Carbon chain diversity in L1544 and IRAS 16293-2422: an astrochemical pathfinder study for the SKAO
Lisa Giani, Eleonora Bianchi, Anthony Remijan et al. (+12 more)
Astrochemical observations have revealed a surprisingly high level of chemical complexity, including long carbon chains, in the earliest stages of Sun-like
star formation. The origin of these species and whether they undergo further growth, possibly contributing to the molecular complexity of planetary systems, remain open questions. We present recent observations performed using the 100-m Green Bank
Telescope of the prestellar core L1544 and the protostellar system IRAS 16293-2422. In L1544, we detected several complex carbon-bearing species, including $\mathrm{C_2S}$, $\mathrm{C_3S}$, $\mathrm{C_3N}$, $\mathrm{c\text{-}C_3H}$, $\mathrm{C_4H}$, and $\mathrm{C_6H}$, complementing previously reported emission of cyanopolyynes. In IRAS 16293-2422, we detected $\mathrm{c\text{-}C_3H}$ and, for the first time, $\mathrm{HC_7N}$. Thanks to the high spectral resolution, we refine the rest frequencies of several $\mathrm{c\text{-}C_3H}$ and $\mathrm{C_6H}$ transitions. We perform radiative transfer analysis, highlighting a chemical difference between the two sources: IRAS 16293-2422 shows column densities 10-100 times lower than L1544. We perform astrochemical modeling, employing an up-to-date chemical network with revised reaction rates. The models reproduce the general trends, with cyanopolyyne and polyynyl radical abundances decreasing as molecular size increases, but they underestimate the abundances of cyanopolyynes longer than $\mathrm{HC_5N}$ by up to two orders of magnitude. Current models, which include the dominant neutral-neutral formation routes, cannot account for this discrepancy, suggesting that the chemical network is incomplete. We propose that additional ion-molecule reactions are crucial for the formation of these species. Developing a more comprehensive chemical network for long carbon chains is essential for accurately interpreting present and future observations.
Read the full abstract ▾
All authors Lisa Giani, Eleonora Bianchi, Anthony Remijan, Claudio Codella, Giovanni Sabatini, Linda Podio, Cecilia Ceccarelli, Marta De Simone, Nadia Balucani, Paola Caselli, Eric Herbst, Francois Lique, Silvia Spezzano, Charlotte Vastel, Brett McGuire
Solar and Stellar Astrophysics
Evidence for the merger hypothesis in V4332 Sgr: a low $^{12}$C/$^{13}$C ratio and multiple outbursts
D. P. K. Banerjee, A. Evans, Watson P. Varricatt et al. (+1 more)
Following the detections of the first extragalactic “Luminous Red Nova” (LRN) M31 RV in 1989, and its first
Galactic counterpart V4332~Sgr in 1994, there have been many discoveries of similar, or closely related, objects. They are important because they bridge the luminosity gap between the brightest novae and
supernovae, a largely unexplored parameter space. The cause of eruptions in LRNe is still unclear, a
stellar merger being the most favored mechanism. However, barring V1309~Sco, there has been no direct evidence for a merger in the other objects. Here we present strong evidence that V4332~Sgr was a merger event. High resolution infrared observations of the CO fundamental band show an unusually small $^{12}$C/$^{13}$C ratio of $3.5\pm1$. This indicates that a violent event had occurred, whose effects penetrated deep enough to allow CNO cycle processed $^{13}$C in the inner H burning shell to be brought to the surface. We rule out planetary ingestion, and propose that the eruption was due to a merger between V4332~Sgr and a companion
star. It is shown that V4332~Sgr was likely surrounded by an edge-on disk before its eruption. If this disk was a flattened common envelope containing V4332~Sgr and a companion
star, then a merger scenario would not be inconsistent. Furthermore, V4332~Sgr had multiple outbursts, previously unreported but an important piece of information, since multiple outbursts are a trait shared by many LRNe.
Read the full abstract ▾
All authors D. P. K. Banerjee, A. Evans, Watson P. Varricatt, N. M. Ashok
Solar and Stellar Astrophysics
Infrared period-luminosity relations of Galactic Miras based on multi-epoch photometry and the Gaia parallax uncertainty
S. Uttenthaler, T. Lebzelter and S. Meingast
Miras and other long-period variable (LPV)
stars on the AGB follow period-luminosity (PL) relations. These relations have been difficult to study for
Galactic LPVs because their distances were poorly known in the past. We aim to establish the PL relations of
solar-neighbourhood Miras for several near-IR photometric bands. To this end, we used multi-epoch photometry from the DIRBE and unTimely/WISE catalogues,
Gaia parallax distances, and contemporary pulsation periods obtained from optical observations of a well-selected sample of
solar-neighbourhood Miras. We show that clearly defined PL relations in the nine investigated near-IR bands emerge from our data, and we report the slopes and zero-point magnitudes. We find that
Galactic Miras are fainter in the K band than their Large Magellanic Cloud siblings. We derive average period-temperature, period-bolometric-luminosity, and period-radius relations from fits to synthetic SEDs constructed from the PL relations. By applying AGB evolutionary models, the scatter of
stars around the PL sequences can also be used to test whether the parallax uncertainties quoted in the
Gaia catalogue are realistic. Furthermore, we performed such tests based on a comparison with parallaxes obtained with the VLBI and with a sample of LPVs in the globular cluster 47 Tuc. We conclude that, for
Galactic Miras with a fractional parallax uncertainty of <0.1 in the
Gaia catalogue, the parallax uncertainty is underestimated by factors between 1.0 and 1.8. For more uncertain parallaxes, we find evidence that the distances (parallaxes) are generally overestimated (underestimated). Nevertheless, we find strong evidence that the large error-inflation factors reported for AGB
stars in the literature are unrealistic. Our results lend confidence to the parallax measurements of these highly extended, variable
stars.
Read the full abstract ▾