Astrophysics of Galaxies
RIGEL: Feedback-regulated cloud-scale star formation efficiency in a simulated dwarf galaxy merger
Yunwei Deng, Hui Li, Federico Marinacci et al. (+5 more)
Major mergers of
galaxies are likely to trigger bursty
star formation activities. The accumulation of dense gas and the boost of
star formation efficiency (SFE) are considered to be the two main drivers of starbursts. However, it remains unclear how each process operates on the scale of individual
star-forming clouds. Here, we present a high-resolution (2 Msun) RHD simulation of a gas-rich
dwarf galaxy merger using the RIGEL model to investigate how mergers affect the properties of the structure of dense
star-forming gas and the cloud-scale SFE. We tracked the
evolution of sub-virial dense clouds in the simulation by mapping them across successive snapshots taken at intervals of 0.2 Myr. We find that the merger triggers a 130 fold increase in the SFR and shortens the
galaxy-wide gas-depletion time by two orders of magnitude compared to those in two isolated
galaxies. However, the depletion time of individual clouds and their lifetime distribution remained unchanged over the simulation period. The cloud life cycles and cloud-scale SFE are determined by the local
stellar feedback rather than such environmental factors as
tidal fields regardless of the merger process, and the integrated SFE ($\epsilon_{\rm int}$) of clouds in complex environments remains well-described by an $\epsilon_{\rm int}-\Sigma_{\rm tot}$ relation found in idealized isolated-cloud experiments. During the peak of the starburst, the media SFE was lower by only 0.17-0.33 dex compared to the value when the
galaxies were not interacting. The merger boosts the SFR through the accumulation and compression of dense gas fueling
star formation. Strong
tidal torques assemble $>10^5$ Msun clouds, which seed massive
star clusters. The average separation between
star-forming clouds decreases during the merger, which in turn decreases the cloud–cluster spatial de-correlation from >1 kpc to 0.1 kpc depicted in tuning fork diagrams.
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All authors Yunwei Deng, Hui Li, Federico Marinacci, Yang Ni, Boyuan Liu, Aaron Smith, Rahul Kannan, Greg L. Bryan
Earth and Planetary Astrophysics
Magma ocean interactions can explain JWST observations of the sub-Neptune TOI-270 d
Matthew C. Nixon, R. Sander Somers, Arjun B. Savel et al. (+9 more)
Sub-Neptunes with substantial atmospheres may possess magma oceans in contact with the overlying gas, with chemical interactions between the atmosphere and magma playing an important role in shaping atmospheric composition. Early JWST observations have found high abundances of carbon- and oxygen-bearing molecules in a number of sub-Neptune atmospheres, which may result from processes including
accretion of icy material at formation or magma-atmosphere interactions. Previous work examining the effects of magma-atmosphere interactions on sub-Neptunes has mostly been limited to studying conditions at the atmosphere-mantle boundary, without considering implications for the upper atmosphere which is probed by spectroscopic observations. In this work, we present a modeling architecture to determine observable signatures of magma-atmosphere interactions. We combine an
equilibrium chemistry code which models reactions between the core, mantle and atmosphere with a radiative-convective model that determines the composition and structure of the observable upper atmosphere. We examine how different conditions at the atmosphere-mantle boundary and different core and mantle compositions impact the upper atmospheric composition. We compare our models to JWST NIRISS+NIRSpec observations of the sub-Neptune TOI-270~d, finding that our models can provide a good fit to the observed transmission spectrum with little fine-tuning. This suggests that magma-atmosphere interactions may be sufficient to explain high abundances of molecules such as H$_2$O, CH$_4$ and CO$_2$ in sub-Neptune atmospheres, without additional
accretion of icy material from the protoplanetary disk. Although other processes could lead to similar compositions, our work highlights the need to consider magma-atmosphere interactions when interpreting the observed atmospheric composition of a sub-Neptune.
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All authors Matthew C. Nixon, R. Sander Somers, Arjun B. Savel, Jegug Ih, Eliza M.-R. Kempton, Edward D. Young, Hilke E. Schlichting, Tim Lichtenberg, Luis Welbanks, William Misener, Anjali A. A. Piette, Nicholas F. Wogan
Astrophysics of Galaxies
A JWST MIRI LRS Survey of 37 Massive Star-Forming Galaxies and AGN at Cosmic Noon – Overview and First Results
Jed McKinney, Miriam Eleazer, Alexandra Pope et al. (+17 more)
We present a large spectroscopic survey with JWST's Mid-Infrared Instrument (MIRI) Low Resolution Spectrometer (LRS) targeting $37$ infrared-bright
galaxies between $z=0.65-2.46$ with infrared luminosities $\log L_{\rm IR}/L_\odot>11.5$ and $\log M_*/M_\odot=10-11.5$. Targets were taken from a Spitzer $24\,\mu$m-selected sample with archival spectroscopy from the Infrared Spectrograph (IRS) and include a mix of
star-forming
galaxies and
dust-obscured AGN. By combining IRS with the increased sensitivity of LRS, we expand the range of spectral features observed between $5-30\,\mu$m for every
galaxy in our sample. In this paper, we outline the sample selection, JWST data reduction, 1D spectral extraction, and polycyclic aromatic hydrocarbon (PAH) feature measurements from $\lambda_{rest}=3.3-11.2\,\mu$m. In the JWST spectra, we detect PAH emission features at $3.3-5.3\,\mu$m, as well as Paschen and Brackett lines. The $3.3\,\mu$m feature can be as bright as $1\%$ of the $8-1000\,\mu$m infrared luminosity and exhibits a tight correlation with the
dust-obscured
star-formation rate. We detect absorption features from CO gas, CO$_2$ ice, H$_2$O ice, and aliphatic
dust. From the joint JWST and Spitzer analysis we find that the $11.3/3.3\,\mu$m PAH ratios are on-average three times higher than that of local luminous, infrared
galaxies. This is interpreted as evidence that the PAH grains are larger at $z\sim1-2$. The size distribution may be affected by coagulation of grains due to high gas densities and low temperatures. These conditions are supported by the observation of strong water ice absorption at $3.05\,\mu$m, and can lower
stellar radiative feedback as large PAHs transmit less energy per
photon into the interstellar medium.
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All authors Jed McKinney, Miriam Eleazer, Alexandra Pope, Anna Sajina, Stacey Alberts, Meredith Stone, Leonid Sajkov, Virginia Vanicek, Allison Kirkpatrick, Thomas Lai, Caitlin M. Casey, Lee Armus, Tanio Diaz-Santos, Andrew Korkus, Olivia Cooper, Lindsay R. House, Hollis Akins, Erini Lambrides, Arianna Long, Lin Yan
High Energy Astrophysical Phenomena
Diffuse continuum emission and large extended sources at MeV energies
Markus Ackermann, Denys Malyshev and Dmitry V. Malyshev
Future gamma-ray survey instruments, such as newASTROGAM and AMEGO-X, will significantly improve previous and current all-sky surveys at MeV energies. In this paper we discuss the continuum emission from the Milky Way, two prominent large extended sources, the
Fermi bubbles and Loop I, and the extragalactic gamma-ray background. We highlight the importance of measurements in the MeV to GeV energy range for understanding CR production and propagation in the
Galaxy, for the determination of the nature of the
Fermi bubbles and Loop I, and for exploring the origin of the extragalactic gamma-ray background.
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High Energy Astrophysical Phenomena
Probing evolution of Long GRB properties through their cosmic formation history aided by Machine Learning predicted redshifts
Dhruv S. Bal, Aditya Narendra, Maria Giovanna Dainotti et al. (+3 more)
Gamma-ray Bursts (GRBs) are valuable probes of
cosmic star formation reaching back into the epoch of reionization, and a large
dataset with known
redshifts ($z$) is an important ingredient for these studies. Usually, $z$ is measured using spectroscopy or photometry, but $\sim80\%$ of GRBs lack such data.
Prompt and afterglow correlations can provide estimates in these cases, though they suffer from systematic uncertainties due to assumed cosmologies and due to detector threshold limits. We use a sample with $z$ estimated via machine learning models, based on
prompt and afterglow parameters, without relying on cosmological assumptions. We then use an augmented sample of GRBs with measured and predicted
redshifts, forming a larger
dataset. We find that the predicted
redshifts are a crucial step forward in understanding the
evolution of GRB properties. We test three cases: no
evolution, an
evolution of the beaming factor, and an
evolution of all terms captured by an
evolution factor $(1+z)^\delta$. We find that these cases can explain the density rate in the
redshift range between 1-2, but neither of the cases can explain the derived rate densities at smaller and higher
redshifts, which may point towards an
evolution term different than a simple power law. Another possibility is that this mismatch is due to the non-homogeneity of the sample, e.g., a non-collapsar origin of some long GRB within the sample.
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All authors Dhruv S. Bal, Aditya Narendra, Maria Giovanna Dainotti, Nikita S. Khatiya, Aleksander L. Lenart, Dieter H. Hartmann
Astrophysics of Galaxies
Confirming Near- to Mid-IR Photometrically-Identified Obscured AGNs in the JWST era
George H. Rieke, Yang Sun, Jianwei Lyu et al. (+6 more)
We evaluate the underlying assumptions for the identification of Active
Galactic Nuclei (AGNs) through near- and mid-infrared photometry and spectral energy distribution (SED) fitting out to z ~ 3. For massive
galaxies, log(M) > 9.5, our high resolution spectra of the rest optical range generally confirm the results of SED fitting, which relies primarily on excesses above the
stellar emission between 1 and 6 microns to identify AGN. However, the method is undermined if the
redshift used for the SED fitting is incorrect. Low mass
galaxies, log(M) < 9:5, can contain relatively warm
dust that emits in the 4 - 6 micron range. We show that the potential contamination of AGN samples by purely
star forming low-mass
galaxies can be avoided by the use of the infrared properties of Haro 11 as a limiting
star-forming SED template. However, relatively few
star forming
galaxies emit as strongly in the 3 - 6 micron range as this template, so this could result in missing some obscured AGNs to avoid a minor contamination. Including the behavior of the
galaxies at rest lamda ~ 13.5 microns can mitigate this problem and yield more complete samples of bona fide AGN. JWST/MIRI supports this approach out to z ~ 0.6.
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All authors George H. Rieke, Yang Sun, Jianwei Lyu, Christopher N. A. Willmer, Yongda Zhu, Pierluigi Rinaldi, Meredith A. Stone, Kevin N. Hainline, Pablo G. Perez-Gonzalez
Earth and Planetary Astrophysics
A Comoving Framework for Planet Migration
Ximena S. Ramos and Pablo Benitez-Llambay
The migration of
planets within their nascent protoplanetary disks is a fundamental process that shapes the final architecture of planetary systems. However, studying this phenomenon through direct hydrodynamical simulations is computationally demanding, with traditional methods on fixed grids being ill-suited for tracking
planet migration over long timescales due to their high cost and limited domain. In this work, we present a self-consistent comoving framework designed to overcome these challenges. Our method employs a coordinate transformation that scales with the
planet's evolving semi-major axis, keeping the
planet stationary with respect to its local computational grid. This transforms the standard hydrodynamic equations by introducing a source term that accounts for the inertial forces of the non-inertial reference frame. We implement this framework in the FARGO3D code and validate it through a
benchmark test, demonstrating excellent agreement with conventional fixed-grid simulations until the latter are compromised by boundary effects. Our analysis shows that, for long-range migration scenarios, the comoving method can be over an order of magnitude more computationally efficient, dramatically reducing the cost of simulating migrating
planets and making secular timescale simulations computationally feasible. This framework serves as both a powerful numerical and theoretical tool, simplifying the time-dependent flow around a migrating
planet that offers clearer physical insight. It enables long-term, self-consistent studies of
planet-disk interaction, representing a crucial step towards performing
planet-population synthesis based on full hydrodynamical simulations.
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Cosmology and Nongalactic Astrophysics
The cosmic web's Lyman-$\alpha$ glow at $z \approx 2.5$; hydrodynamic models, dust, and wide-field, narrow-band detection
Oleksii Sokoliuk, John K. Webb, Kenneth M. Lanzetta et al. (+12 more)
The diffuse Lyman-$\alpha$ glow of the
cosmic web has long been predicted but has so far eluded direct detection over cosmologically significant volumes. We construct synthetic Lyman-$\alpha$ surface-brightness maps using five state-of-the-art hydrodynamic simulations (IllustrisTNG, EAGLE, CROCODILE, SIMBA, and Sherwood), modeling recombination, collisional excitation,
star formation, and localized
dust attenuation. Our study focuses on the
redshift range $2.0<z<2.7$, motivated by the numerous detailed studies of the COSMOS region. Significant variations are seen in the results obtained from these independent simulations. Using the Anderson-Darling statistic to probe these statistical differences, we demonstrate that a $5\sigma$ statistical detection of the total intergalactic and circumgalactic Lyman-$\alpha$ emission is achievable with current facilities at flux thresholds brighter than $\sim 8 \times 10^{-17} \text{ erg s}^{-1}\text{ cm}^{-2}\text{ arcsec}^{-2}$. Conversely, isolating the underlying low-density component of the
cosmic web requires ultra-deep sensitivity, with the most optimistic simulation (IllustrisTNG) reaching a 5$\sigma$ detection only for background noise levels below $\sigma \sim 2 \times 10^{-19} \text{ erg s}^{-1}\text{ cm}^{-2}\text{ arcsec}^{-2}$. These quantitative limits validate the feasibility of ongoing wide-field narrow-band campaigns, opening a new era of empirical intergalactic cartography.
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All authors Oleksii Sokoliuk, John K. Webb, Kenneth M. Lanzetta, Michael M. Shara, Stefan Gromoll, James S. Bolton, Robert F. Carswell, Gaspar Galaz, Cédric Ledoux, Gaspare Lo Curto, Alain Smette, David Valls-Gabaud, Anja von der Linden, Frederick M. Walter, Joris Witstok
Astrophysics of Galaxies
Beyond diagnostic-diagrams: A critical exploration on the classification of ionization processes
S. F. Sánchez, C. Muñoz-Tuñón, J. Sánchez Almeida et al. (+2 more)
Optical emission-line diagnostic diagrams, such as the classical BPT, are widely used to identify ionisation mechanisms in
galaxies but often suffer from degeneracies, especially when multiple sources coexist. We critically evaluate the effectiveness of these diagnostics in distinguishing
star-forming
galaxies, retired
galaxies (RGs), and active
galactic nuclei (AGNs), and propose refined methods to reduce misclassifications. Using a large sample of nearby
galaxies from the NASA-Sloan Atlas cross-matched with SDSS spectroscopy, we define representative subsamples of late-type/
star-forming
galaxies, early-type/RGs, and multiwavelength-selected AGNs. Their distributions are analysed across traditional and modern diagnostics, including WHaN, WHaD, and the newly introduced WHaO diagram, which combine H{\alpha} equivalent width with [N II]/H{\alpha}, {\sigma}(H{\alpha}), and [O III]/[O II], respectively. Quantitative comparisons reveal that classical BPT diagrams overestimate
star-forming
galaxies by ~10% and misclassify up to 45% of AGNs and nearly all RGs. Diagnostics incorporating EW(H{\alpha}) achieve improved accuracy, reducing misclassifications to {\sim} 20\ % for AGNs and {\sim} 15% for RGs. A revised classification scheme based on EW(H{\alpha}) thresholds and consistent WHaD/WHaO results yields the highest purity (8-25% misclassifications) and better reflects underlying physical conditions. Our analysis demonstrates that BPT-based methods fail to reliably separate ionisation mechanisms, particularly in
galaxies hosting weak AGNs or evolved
stellar populations. Updated EW(H{\alpha})-based diagnostics offer a more accurate framework for studying
galaxy ionisation and should replace traditional schemes in future population studies.
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All authors S. F. Sánchez, C. Muñoz-Tuñón, J. Sánchez Almeida, O. González-Martín, E. Pérez
Earth and Planetary Astrophysics
JWST-TST High Contrast: Medium-resolution spectroscopy reveals a carbon-rich circumplanetary disk around the young accreting exoplanet Delorme 1 AB b
Mathilde Mâlin, Kimberly Ward-Duong, Sierra L. Grant et al. (+21 more)
Young accreting planetary-mass objects are thought to draw material from a circumplanetary disk (CPD) composed of gas and
dust. While the gas within the disk is expected to disperse within the first million years, strong
accretion has nonetheless been detected in older systems, including the 30–45 Myr-old planetary-mass companion Delorme 1 AB b. We conducted spectroscopic observations with JWST/MIRI to investigate the presence of circumplanetary material around this young, accreting
planet, and to characterize the
planet's atmospheric properties and composition. We perform forward modeling using atmospheric models to characterize the
planet's atmosphere. Beyond 10 microns, the SED becomes dominated by this CPD rather than the
planet itself. We detect strong emission from HCN and C$_2$H$_2$, while no O-bearing species are observed in the CPD spectrum, suggesting the gas in the CPD has an elevated C/O. We also identify spatially extended H$_2$ emission around the
planet, tracing warm gas, with indications that it may be at a higher temperature than the non-extended component. The mid-infrared spectrum of the planetary-mass companion Delorme 1 AB b reveals the first detection of bright C-bearing species in a CPD, together with an
outflow traced by H$_2$ extended emission, that could be interpreted as a disk wind. The hot
dust continuum emission suggests an inner cavity in the CPD. The presence of warm gas in the CPD provides constraints on the disk's chemical composition and physical conditions, opening up new avenues for disk studies. The study of these long-lived "Peter Pan" disks will enhance our understanding of how
accretion persists in evolved low-mass systems, shedding light on their formation, longevity, and evolutionary pathways in planetary systems.
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All authors Mathilde Mâlin, Kimberly Ward-Duong, Sierra L. Grant, Nicole Arulanantham, Benoit Tabone, Laurent Pueyo, Marshall Perrin, William O. Balmer, Sarah Betti, Christine H. Chen, John H. Debes, Julien H. Girard, Kielan K. W. Hoch, Jens Kammerer, Cicero Lu, Isabel Rebollido, Emily Rickman, Connor Robinson, Kadin Worthen, Roeland P. van der Marel, Nikole K. Lewis, Sara Seager, Jeff A. Valenti, Remi Soummer
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Gauge dependence of scalar-induced gravitational waves from isocurvature perturbations: Analytical results
Arshad Ali, Yang Lei and Mudassar Sabir
We analytically study the gauge dependence of scalar-induced gravitational waves (SIGWs) sourced by
primordial isocurvature perturbations during radiation domination (RD), working across nine gauges. Through analytical integrations of the kernels supported by graphical comparison we identify a clear dichotomy. We find that in some gauges viz. the uniform-density (UD), total-matter (TM), uniform-
curvature (UC), comoving-orthogonal (CO) and transverse-traceless (TT) gauges the energy density grows polynomially in conformal time $\eta^n$, where $n$ varies from $2$ to $8$. While in rest of the gauges viz. the longitudinal (Long.), uniform-expansion (UE), Newtonian-motion (Nm), and N-body (Nb) gauges the late-time energy spectrum converges, and SIGWs behave as radiation. For subhorizon modes ($ k\eta \gg 1 $), the divergence becomes severe, showing that SIGWs are gauge-dependent observables in this regime. We resolve it through a kernel projection that isolates the luminal, freely propagating gravitational wave components (oscillating as $\sin(k\eta)$ and $\cos(k\eta)$), eliminating spurious contributions. The resulting kernel decays as $ (k\eta)^{-1} $ and yields a finite, gauge-independent late-time spectrum, confirming that only luminal modes represent physical SIGWs.
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High Energy Astrophysical Phenomena
Testing new-physics scenarios with the combined LHAASO and Carpet-3 fluence spectrum of GRB 221009A: axion-like particles and Lorentz-invariance violation
P.S. Satunin and S.V. Troitsky
From gamma-ray burst (GRB) 221009A, very high-energy
photons were detected: >10 TeV with LHAASO and >100 TeV with Carpet-3. Such energetic
photons are expected to be absorbed via electron-positron pair production on their way to the Earth. Their observation might be explained by new physics, including Lorentz invariance violation (LIV) or
photon mixing with
axion-like particles (ALPs). Here, we construct a joint fluence spectrum by combining flux measurements from both experiments, and fit it under these hypotheses. While LIV can account for the Carpet-3 observation, it provides only a modest improvement over standard physics in the overall fit and requires parameters excluded by other constraints. ALP mixing improves the description of both LHAASO and Carpet-3 data, yielding a substantial enhancement in fit quality for a specific region of the ALP parameter space.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
GW231123: extreme spins or microglitches?
Anarya Ray, Sharan Banagiri, Eric Thrane et al. (+1 more)
The recently reported binary black hole merger, GW231123, has unusual properties that make it hard to explain astrophysically. Parameter estimation studies are consistent with maximally spinning black holes and the dimensionless
spin of the more massive component is constrained to be $\chi_1\gtrsim 0.8$. Analysis of data also revealed potential systematics that could not be fully replicated with simulated studies. We explore the possibility that these measurements are biased due to unmodeled non-Gaussian noise in the detectors, and that the actual black hole
spins are more modest. We present evidence for a population of microglitches in LIGO gravitational-wave strain data that can lead to biases in the parameter estimation of short-duration signals such as GW231123. Using simulated data of a massive event like GW231123, we demonstrate how microglitches can bias our measurements of black hole
spins toward $\chi\approx1$ with negligible posterior support for the true value of $\chi\approx0.7$. We develop a noise model to account for microglitches and show that this model successfully reduces biases in the recovery of signal parameters. We characterize the microglitch population in real interferometer data surrounding GW231123 and find a single detector glitch duty cycle of $0.57_{-0.19}^{+0.21}$, which implies nearly a $100\%$ probability that at least one event through the fourth gravitational wave transient catalog coincides with microglitches in two detectors. We argue that further investigations are required before we can have a confident picture of the astrophysical properties of GW231123.
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All authors Anarya Ray, Sharan Banagiri, Eric Thrane, Paul D. Lasky
High Energy Astrophysical Phenomena
High-energy variability of the gravitationally lensed blazar PKS 1830-211
Sarah M. Wagner, Jeffrey D. Scargle, Greg Madejski et al. (+4 more)
The production site and process responsible for the highly variable high-energy emission observed from blazar jets are still debated. Gravitational lenses can be used as microscopes to investigate the nature of such sources. We study the broad-band spectral properties and the high-energy variability of the gravitationally-lensed blazar PKS 1830-211, for which
radio observations have revealed two images, to put constraints on the jet physics and the existence of a gravitationally-induced time delay and magnification ratio between the images. We utilize Swift/XRT, Nustar, and
Fermi-LAT observations from 2016 and 2019 to compare periods of low activity and high activity in PKS 1830-211. Short-timescale variability is elucidated with an unbinned power spectrum analysis of time-tagged NuSTAR
photon data. To study the gravitationally-induced time delay in the gamma-ray light curve observed with
Fermi-LAT, we improve existing autocorrelation function based methods. Our modified auto-correlation method yields a delay of t_0=21.1 +/- 0.1 d and magnification factor a=0.13 +/- 0.01. These parameters remain time-invariant. In data from 2016 and 2019, the X-ray spectra remain remarkably stable, contrasting with extreme changes in gamma-rays. Both states can be fitted with a single component from Comptonisation of infrared emission from the dusty
torus, with different gamma-ray states arising solely from a shift in the break of the electron energy distribution. The detection of a consistent lag throughout the whole light curve suggests that they originate from a persistent location in the jet.
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All authors Sarah M. Wagner, Jeffrey D. Scargle, Greg Madejski, Andrea Gokus, Krzysztof Nalewajko, Patrick Günther, Karl Mannheim
Instrumentation and Methods for Astrophysics
AppleCiDEr. II. SpectraNet: A Spectroscopic Neural Network Classifier for Transients Demonstrated on ZTF Follow-up Data
Maojie Xu, Argyro Sasli, Alexandra Junell et al. (+21 more)
Time-domain surveys such as the Zwicky Transient Facility have opened a new frontier in the discovery and characterization of transients. While photometric light curves provide broad temporal coverage, spectroscopic observations remain crucial for physical interpretation and source classification. However, existing spectral analysis methods, often reliant on template fitting or parametric models, are limited in their ability to capture the complex and evolving spectra characteristic of such sources, which are sometimes only available at low resolution. In this work, we introduce SpectraNet, a deep convolutional neural network designed to learn robust representations of optical spectra from transients. Our model combines multi-scale convolution kernels and pooling operations to extract features from preprocessed spectra in a hierarchical and interpretable manner. We train and validate SpectraNet on low-resolution time-series spectra obtained from the Spectral Energy Distribution Machine and other instruments, demonstrating better performance in classification compared to other known pipelines.
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All authors Maojie Xu, Argyro Sasli, Alexandra Junell, Felipe Fontinele Nunes, Yu-Jing Qin, Christoffer Fremling, Sam Rose, Theophile Jegou Du Laz, Benny Border, Antoine Le Calloch, Sushant Sharma Chaudhary, Hailey Markoff, Avyukt Raghuvanshi, Nabeel Rehemtulla, Jesper Sollerman, Yashvi Sharma, Niharika Sravan, Judy Adler, Tracy X. Chen, Richard Dekany, Reed Riddle, Mansi M. Kasliwal, Matthew J. Graham, Michael W. Coughlin
Instrumentation and Methods for Astrophysics
Probing the cosmological 21~cm global signal from the Antarctic ice sheet
Shijie Sun, Jiaqin Xu, Minquan Zhou et al. (+7 more)
The redshifted 21 cm line, arising from neutral hydrogen, offers a unique probe into the intergalactic medium and the first
stars and
galaxies formed in the early universe. However, detecting this signal is a challenging task because of artificial
radio-frequency interference (RFI) and systematic errors such as ground effects. The interior of the Antarctic continent provides an excellent location to make such observations, with minimal RFI and relatively stable foreground signals. Moreover, a flat plateau in central Antarctica, with an ice cap over 2000 m deep, will show less ground reflection of
radio waves, reducing the signal complexity in the area around the probing
antenna. It may be advantageous to perform cosmological 21 cm experiments in Antarctica, and a 21 cm Antarctic global spectrum experiment can potentially be deployed on the Antarctic ice cap. We have performed preliminary instrumental design, system calibration, and implementation of such an instrument optimized for extreme cold and capable of long-term autonomous operation. This system shows the ability to effectively detect the 21~cm signal, confirming Antarctica as an excellent observational site for
radio cosmology.
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All authors Shijie Sun, Jiaqin Xu, Minquan Zhou, Shenzhe Xu, Fengquan Wu, Haoran Zhang, Juyong Zhang, Bin Ma, Zhaohui Shang, Xuelei Chen
Earth and Planetary Astrophysics
Fomalhaut's debris disc is not dominated by primordial Plutos
Tim D. Pearce, Torsten Löhne and Alexander V. Krivov
A key challenge in debris-disc science is that we do not know the masses of debris discs, nor the sizes of the largest debris bodies. This is because modern observations can only detect objects up to centimetre sizes, whilst larger planetesimals, which dominate disc mass, remain hidden. We must therefore use other arguments, such as dynamics, to indirectly infer disc masses and body sizes. This paper presents a new method, applicable to narrow debris discs like Fomalhaut. We argue that such discs cannot be too massive, nor the largest bodies too large, otherwise they would self-scatter and the disc would be much broader than observed. Using n-body dynamics and collisional theory, we demonstrate that the mass of Fomalhaut's disc cannot be dominated by
primordial Plutos. Instead, if the mass is dominated by
primordial bodies, then they should have radii below $300^{+80}_{-70}$ km ($0.3 \pm 0.1$ RPluto) and above $5^{+20}_{-4}$ km. Such bodies would each have less than 1 per cent the mass of Pluto. Our conclusions are robust to additional physics, including shepherding
planets and collisional damping. Our results provide independent, dynamical support for the idea that the masses of bright debris discs are dominated by objects smaller than Pluto.
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High Energy Astrophysical Phenomena
Archival Inference for Eccentric Stellar-Mass Binary Black Holes in Space-Based Gravitational Wave Observations
Han Wang, Michael J. Williams, Ian Harry et al. (+1 more)
Space-based gravitational-wave observatories will detect the early inspiral of
stellar-mass binary black holes and can track their eccentricity
evolution. However, untargeted searches in the space band are computationally demanding and require relatively high detection thresholds (signal-to-noise ratio $\sim 15$). Information from ground-based detections can significantly shrink the parameter space for space-band analyses and thereby substantially reduce the detection threshold. We present a
Bayesian inference pipeline for ground-triggered archival space-band analyses that includes eccentricity. Using ground-informed priors, we demonstrate that with one year of LISA or TianQin data a GW190521-like source with signal-to-noise ratio $\sim 7$ can be distinguished and tightly constrained. In this setup, space observations sharpened the redshifted chirp mass from $\mathcal{O}(10^{-3})M_\odot$ to $\mathcal{O}(10^{-5})M_\odot$, and constrain the eccentricity to $\mathcal{O}(10^{-5})$ around the injected value $e_{0.01\mathrm{Hz}}=0.1$. These results demonstrate that inference of eccentric
stellar-mass binary black holes in noisy space-band data is practically feasible, supports an expanded yield of multiband detections, and strengthens prospects for future astrophysical and gravitational tests.
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All authors Han Wang, Michael J. Williams, Ian Harry, Yi-Ming Hu
Solar and Stellar Astrophysics
Disk fraction among free-floating planetary-mass objects in Upper Scorpius
Tommy Rodrigues, Hervé Bouy, Sean N. Raymond et al. (+9 more)
Free-floating planetary-mass objects (FFPs) have been detected through direct imaging in several young, nearby
star-forming regions. The properties of circumstellar disks around these objects may provide a valuable probe into their origin but are currently limited by the small sample sizes explored. We aim to perform a statistical study of the occurrence of circumstellar disks down to the planetary-mass regime. We performed a systematic survey of disks among the population identified in the 5-10 Myr-old Upper Scorpius association (USC), restricted to members outside the younger, embedded Ophiuchus region and with estimated masses below 105 M_Jup. We took advantage of unWISE photometry to search for mid-infrared excesses in the WISE (W1-W2) color. We implemented a
Bayesian outlier detection method, which models the photospheric sequence and computes excess probabilities for each object, enabling a statistically sound estimation of disk fractions. We explored disk fractions across an unprecedentedly fine mass grid, reaching down to objects as low as ~6 M_Jup assuming 5 Myr or ~8 M_Jup assuming 10 Myr, thus extending the previous lower boundary of disk fraction studies. Depending on the age, our sample includes between 17 and 40 FFPs. We confirm that the disk fraction steadily rises with decreasing mass and exceeds 30% near the substellar-to-planetary mass boundary at ~13 M_Jup. We find hints of a possible flattening in this trend around 25-45 M_Jup, potentially signaling a transition in the dominant formation processes. This shift in trend should be considered with caution and needs to be confirmed with more sensitive observations. Our results are consistent with the gradual dispersal of disks over time, as disk fractions in Upper Scorpius appear systematically lower than those in younger regions.
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All authors Tommy Rodrigues, Hervé Bouy, Sean N. Raymond, Eduardo L. Martín, Emmanuel Bertin, Javier Olivares, David Barrado, Núria Huélamo, Motohide Tamura, Núria Miret Roig, Phillip A. B. Galli, Jean-Charles Cuillandre
Cosmology and Nongalactic Astrophysics
CURLING – II. Improvement on the $H_{0}$ Inference from Pixelized Cluster Strong Lens Modeling
Yushan Xie, Huanyuan Shan, Yiping Shu et al. (+9 more)
Strongly lensed
supernovae (glSNe) provide a powerful, independent method to measure the Hubble constant, $H_{0}$, through time delays between their multiple images. The accuracy of this measurement depends critically on both the precision of time delay estimation and the robustness of lens modeling. In many current cluster-scale modeling
algorithms, all multiple images used for modeling are simplified as point sources to reduce computational costs. In the first paper of the CURLING program, we demonstrated that such a point-like approximation can introduce significant uncertainties and biases in both magnification reconstruction and cosmological inference. In this study, we explore how such simplifications affect $H_0$ measurements from glSNe. We simulate a lensed
supernova at $z=1.95$, lensed by a
galaxy cluster at $z=0.336$, assuming time delays are measured from LSST-like light curves. The lens model is constructed using JWST-like imaging data, utilizing both Lenstool and a pixelated method developed in CURLING. Under a fiducial cosmology with $H_0=70\rm \ km \ s^{-1}\ Mpc^{-1}$, the Lenstool model yields $H_0=69.91^{+6.27}_{-5.50}\rm \ km\ s^{-1}\ Mpc^{-1}$, whereas the pixelated framework improves the precision by over an order of magnitude, $H_0=70.39^{+0.82}_{-0.60}\rm \ km \ s^{-1}\ Mpc^{-1}$. Our results indicate that in the next-generation observations (e.g., JWST), uncertainties from lens modeling dominate the error budget for $H_0$ inference, emphasizing the importance of incorporating the extended surface brightness of multiple images to fully leverage the potential of glSNe for cosmology.
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All authors Yushan Xie, Huanyuan Shan, Yiping Shu, Nan Li, Ji Yao, Ran Li, Xiaoyue Cao, Zizhao He, Yin Li, Eric Jullo, Jean-Paul Kneib, Guoliang Li
Earth and Planetary Astrophysics
Polka-dotted Stars II: Starspots and obliquities of Kepler-17 and Kepler-63
Sabina Sagynbayeva and Will M. Farr
Starspots trace
stellar magnetic activity and influence both
stellar evolution and
exoplanet characterization. While occultation-based spot analyses have been applied to individual systems, comparative studies remain limited. We apply the StarryStarryProcess
Bayesian surface-mapping framework to archival Kepler light curves of two
planet hosts, Kepler-63 and Kepler-17, extending the validation established on TOI-3884 (Paper I). Across both systems, we infer characteristic spot radii smaller than 10 degrees. The latitudinal spot distributions of these G
dwarfs show active latitudes: Kepler-63 near 30 degrees and Kepler-17 near 15 degrees. Our analysis yields
stellar obliquity measurements in excellent agreement with previous studies, validating our methodology and demonstrating that transit-based surface mapping can simultaneously recover planetary parameters,
stellar orientations, and
magnetic morphologies. Together, these results reveal a range of
stellar geometries from nearly aligned (Kepler-17) to highly misaligned (Kepler-63).
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Unified Dark Matter and Dark Energy in a model of Non-Canonical Scalar-Tensor Theory
Nihal Jalal Pullisseri and Sanil Unnikrishnan
We consider a model of non-canonical scalar-tensor theory in which the kinetic term in the Brans-Dicke action is replaced by a non-canonical scalar field Lagrangian $\mathcal{L}(X, \phi)= \lambda X^\alpha \phi^\beta - V(\phi)$ where $X = (1/2) \partial_{\mu} \phi \partial^{\mu} \phi$ and $\alpha$, $\beta$ and $\lambda$ are parameters of the model. This can be considered as a simple non-canonical generalization of the Brans-Dicke theory with a potential term which corresponds to a special case of this model with the values of the parameter $\alpha = 1$, $\beta = -1$ and $\lambda = 2w_{_{BD}}$ where $w_{_{BD}}$ is the Brans-Dicke parameter. Considering a spatially flat Friedmann-Robertson-Walker Universe with scale factor $a(t)$, it is shown that, in the matter free Universe, the kinetic term $\lambda X^\alpha \phi^\beta$ can lead to a power law solution $a(t)\propto t^{n}$ but the maximum possible value of $n$ turns out to be $(1+\sqrt{3})/4 \approx 0.683$. When $\alpha \geq 18$, this model can lead to a solution $a(t)\propto t^{2/3}$, thereby mimicking the
evolution of scale factor in a cold dark matter dominated epoch with Einstein's General Relativity (GR). With the addition of a linear potential term $V(\phi) = V_{0}\phi$, it is shown that this model mimics the standard $\Lambda$CDM model type
evolution of the Universe. The larger the value of $\alpha$, the closer the
evolution of $a(t)$ in this model to that in the $\Lambda$CDM model based on Einstein's GR. The purpose of this paper is to demonstrate that this model with a linear potential can mimic the GR based $\Lambda$CDM model. However, with an appropriate choice of the potential $V(\phi)$, this model can provide a unified description of both dark matter and dynamical dark energy, as if it were based on Einstein's GR.
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Earth and Planetary Astrophysics
Machine Learning for Radial Velocity Analysis I: Vision Transformers as a Robust Alternative for Detecting Planetary Candidates
Anoop Gavankar, Tanish Mittal, Joe Ninan et al. (+1 more)
Extreme precision radial velocity (EPRV) surveys usually require extensive observational baselines to confirm planetary candidates, making them resource-intensive. Traditionally, periodograms are used to identify promising candidate signals before further observational investment, but their effectiveness is often limited for low-amplitude signals due to
stellar jitter. In this work, we develop a machine learning (ML) framework based on a
Transformer architecture that aims to detect the presence and likely period of planetary signals in time-series spectra, even in the presence of
stellar activity. The model is trained to classify whether a planetary signal exists and assign it to one of several discrete period and amplitude bins. Injection-recovery tests on randomly selected 100 epoch observation subsets from NEID
solar data (2020-2022 period) show that for low-amplitude systems ($<$1 ms$^{-1}$), our model improves planetary candidate identification by a factor of two compared to the traditional Lomb-Scargle periodogram. Our ML model is built on a
Vision Transformer (ViT) architecture that processes reduced representations of
solar spectrum observations to predict the period and semi-amplitude of planetary signal candidates. By analyzing multi-epoch spectra, the model reliably detects planetary signals with semi-amplitudes as low as 65 cms$^{-1}$. Even under real
solar noise and irregular sampling, it identifies signals down to 35 cms$^{-1}$. Comparisons with the Lomb-Scargle periodogram demonstrate a significant improvement in detecting low-amplitude planetary candidates, particularly for longer orbital periods. These results underscore the potential of machine learning to identify planetary candidates early in EPRV surveys, even from limited observational counts.
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All authors Anoop Gavankar, Tanish Mittal, Joe Ninan, Shravan Hanasoge
High Energy Astrophysical Phenomena
Imprints of a galactic environment on TDEs: Suppressed peaks, shallower decays and late-time rebrightening episodes
Cedric Oña, Sean Fortuna and Ian Vega
Classic models of
tidal disruption events (TDEs), employing a purely Keplerian description of
stellar debris dynamics, have proven remarkably successful in describing the observed early-time emission of these transients. By construction, however, this picture treats the disruption as an isolated
star-black hole encounter, leaving the gravitational influence of the surrounding
galaxy absent from the dynamics. We relax this assumption by
embedding the debris within the gravitational field of a spherically symmetric mass distribution representing either the host
galaxy or a dark matter
halo, while deliberately retaining a minimal Newtonian framework so that the environmental contribution remains transparent and straightforward to interpret. Within this extended model, we find that the host potential can imprint clear signatures on the light curve that lie outside the predictive scope of traditional models, such as a suppressed initial
accretion peak, phases of shallow decay and rebrightening episodes. For TDEs in ordinary
galaxies, however, the latter signatures turns on far too late to be captured by current observations, explaining why simple Keplerian models have proven so effective despite neglecting the
galactic environment. Only at much longer times does the broader
galactic structure begin to reshape the fallback dynamics, gradually steering the system away from the canonical $t^{-5/3}$ decay. This provides an exciting opportunity for next-generation time-domain surveys to capture the long-term
evolution of TDEs, enabling searches for delayed signals that encode information about the surrounding
galactic mass.
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Astrophysics of Galaxies
The formation of Gaia BH3
Daniel Marín Pina, Mark Gieles, Sara Rastello et al. (+1 more)
The
Gaia collaboration announced the discovery of a massive black hole (BH) with a low-mass
giant star companion,
Gaia BH3, located in the ED-2
stellar stream. The properties of
Gaia BH3 bridge the gap between known Milky Way BHs and extragalactic BHs found with gravitational waves (GWs). We aim to determine the most likely formation scenario for
Gaia BH3 in the progenitor cluster of the ED-2 stream. We perform $N$-body simulations of that progenitor cluster and find that, most likely,
Gaia BH3 formed from a
stellar binary that formed during cluster formation, which then underwent multiple dynamical interactions that significantly altered its properties, including exchanging the companion
star. We highlight the importance of cluster dynamics and discard a formation scenario where it evolved in quasi-isolation.
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All authors Daniel Marín Pina, Mark Gieles, Sara Rastello, Giuliano Iorio
Astrophysics of Galaxies
Machine Learning Techniques to Distinguish Giant Stars from Dwarf Stars Using Only Photometry – Pushing Redwards
Keyi Ding, Carrie Filion, Rosemary F.G. Wyse et al. (+6 more)
We present our photometric method, which combines Subaru/HSC $NB515$, g, and i band filters to distinguish
giant stars in Local Group
galaxies from Milky Way
dwarf contamination. The $NB515$ filter is a narrow-band filter that covers the MgI+MgH features at $5150$ Å, and is sensitive to
stellar surface
gravity. Using synthetic photometry derived from large empirical
stellar spectral libraries, we model the $NB515$ filter's sensitivity to
stellar atmospheric parameters and chemical abundances. Our results demonstrate that the $NB515$ filter effectively separates
dwarfs from
giants, even for the reddest and coolest M-type
stars. To further enhance this separation, we develop machine learning models that improve the classification on the two-color ($g-i$, $NB515-g$) diagram. We apply these models to photometric data from the Fornax
dwarf spheroidal
galaxy and two fields of M31, successfully identifying red
giant branch
stars in these
galaxies.
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All authors Keyi Ding, Carrie Filion, Rosemary F.G. Wyse, Evan N. Kirby, Itsuki Ogami, Masashi Chiba, Yutaka Komiyama, László Dobos, Alexander S. Szalay
Earth and Planetary Astrophysics
Modeling the formation of N2 and CH4 frost on Pluto's slopes
L.Lange, T.Bertrand, V.Belissa et al. (+3 more)
Context. The equatorial region of Cthulhu as revealed by New Horizons appears to be generally dark and largely devoid of volatiles because its surface albedo is low. Localized bright patches, however, which are interpreted as CH4 frost, are observed on crater rims and slopes. Aims. Previous studies suggested that these frosts might result from the peculiar insolation driven by the geometry of these slopes, but this has never been tested quantitatively. We investigated the origin, stability, and potential role of these localized frost deposits in the volatile cycle of Pluto. Methods. We implemented a new subgrid-scale slope parameterization in the volatile transport model for Pluto, which accounts for the specific
solar irradiation and the resulting surface and subsurface temperatures on sloped terrains. This parameterization also allows the condensation and sublimation of volatiles (either N2 or CH4) on slopes, including the effect of large-scale transport of these species. This is key to determining the amount of frost that forms or disappears. Results. Our simulations reproduce the observed CH4 frost on north-facing slopes as seasonal deposits that currently sublimate, predict perennial CH4 frost on south-facing slopes, and show that the slope microclimates are not expected to alter global volatile cycles. Conclusions. Seasonal and perennial N2 and CH4 frosts can form on the Pluto slopes, even in its darkest and warmest regions, because the locally sunlight received on inclined terrain is reduced. Despite the abundance of sloped surfaces on Pluto, the slope microclimates still only appear to have a minor effect on the global volatile cycles of the
planet.
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All authors L.Lange, T.Bertrand, V.Belissa, S.Capry, L.A. Young, A.Falco
High Energy Astrophysical Phenomena
Revealing the Temporally Stable Bimodal Energy Distribution of FRB 20121102A with a Tripled Burst Set from AI Detections
Yidan Wang, Jing Han, Pei Wang et al. (+34 more)
Active repeating Fast
Radio Bursts (FRBs), with their large number of bursts, burst energy distribution, and their potential energy
evolution, offer critical insights into the FRBs emission mechanisms. Traditional pipelines search for bursts through conducting dedispersion trials and looking for signals above certain fluence thresholds, both of which could result in missing weak and narrow-band bursts. In order to improve the completeness of the burst set, we develop an End-to-end DedispersE-agnostic Nonparametric AI model (EDEN), which directly detect bursts from dynamic spectrum and is the first detection pipeline that operates without attempting dedispersion. We apply EDEN to archival FAST L-band observations during the extreme active phase of the repeating source FRB 20121102A, resulting in the largest burst set for any FRB to date, which contains 5,927 individual bursts, tripling the original burst set. The much enhanced completeness enables a refined analysis of the temporal behavior of energy distribution, revealing that the bimodal energy distribution remains stable over time. It is rather an intrinsic feature of the emission mechanisms than a consequence of co-evolving with burst rate.
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All authors Yidan Wang, Jing Han, Pei Wang, Di Li, Hanting Chen, Yuchuan Tian, Erbil Gugercinoglu, Jianing Tang, Zihan Zhang, Kaichao Wu, Xiaoli Zhang, Yuhao Zhu, Jinhuang Cao, Mingtai Chen, Jiapei Feng, Zhaoyu Huai, Zitao Lin, Jieming Luan, Hongbin Wang, Junjie Zhao, Chaowei Tsai, Weiwei Zhu, Yongkun Zhang, Yi Feng, Aiyuan Yang, Dengke Zhou, Jianhua Fang, Jiaying Xu, Chenhui Niu, Jiarui Niu, Jumei Yao, Chunfeng Zhang, Rushuang Zhao, Lei Zhang, Junshuo Zhang, Wanjin Lu, Qingyue Qu
Earth and Planetary Astrophysics
Protoplanetary disc population synthesis I. Linking mass-dependent viscosity, star formation history and environment to observations
Jose L. Gomez, Octavio M. Guilera, Marcelo M. Miller Bertolami et al. (+2 more)
Context. Recent studies highlight the importance of
stellar mass sampling when determining disc lifetimes through observed disc fractions. Low-mass
stars host discs with average lifetimes exceeding 5~Myr, and
accretion rates show a strong correlation with
stellar mass ($\dot{M} \propto M_\star^2$). Aims. We aim to identify the optimal parameters of a protoplanetary disc
evolution model capable of reproducing both observed disc fractions and mass
accretion rates in young
stellar populations. Methods. We conducted a population synthesis study modelling disc
evolution via viscous
accretion and internal/external photoevaporation. Initial disc masses and radii were drawn from observational distributions. We explored the viscosity parameter $\alpha$ as a function of
stellar mass, and incorporated a
stellar mass distribution and a
star formation rate (SFR). Results. Matching observed disc fractions and
accretion trends requires that $\alpha$ increases with
stellar mass. External photoevaporation and a systematic underestimation of gas disc masses (due to
dust evolution and hidden solids) are needed to reproduce the $\dot{M}-M_{\rm d}$ plane. Accounting for a time-dependent SFR enhances
accretion in young clusters and extends disc lifetimes in older ones. Introducing a
stellar mass cut-off reproduces distance-dependent biases in cluster disc fractions. Conclusions.
Stellar and environmental dependencies are both essential to explain observed disc properties. A
stellar-mass-dependent viscosity recovers the $\dot{M}-M_\star$ relation, while external photoevaporation and extended
star formation histories shape
accretion rate distributions across environments, emphasizing the value of multi-faceted population synthesis models.
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All authors Jose L. Gomez, Octavio M. Guilera, Marcelo M. Miller Bertolami, Elisa Castro-Martínez, María Paula Ronco
Solar and Stellar Astrophysics
Understanding an origin of palladium in metal-poor stars based on the non-LTE analysis of Pd~I lines
L. Mashonkina and A. Smogorzhevskii
Palladium is one of poorly observed
neutron-capture elements. Abundance determinations for
stellar samples covering a broad
metallicity range are needed for better understanding the mechanisms of Pd synthesis during the
Galaxy evolution. We aim to obtain accurate abundances of Pd for the Sun and the sample of metal-poor
stars based on the non-local thermodynamic
equilibrium (non-LTE) line formation for Pd~I. We present a new, comprehensive model atom of Pd~I. Abundances of Pd, Sr, Ba, and Eu were derived for 48
stars from the non-LTE analyses of high resolution and high signal-to-noise ratio spectra provided by the ESO archives. Non-LTE leads to weakened Pd~I lines and positive non-LTE abundance corrections growing from 0.2~dex for the
solar lines up to 0.8~dex for the lines in the most luminous
star of the sample. Depending on a treatment of inelastic collisions with hydrogen atoms, the
solar non-LTE abundance amounts to log eps = 1.61+-0.02 to 1.70+-0.02 and agrees within the error bars with the meteoritic abundance log eps_met = 1.65. Non-LTE largely removes the discrepancies in the LTE abundances between the
giant and
dwarf stars of similar
metallicities. Palladium tightly correlates with Eu in the -1.71 < [Fe/H] < -0.56 range indicating the r- and s-process contributions to Pd synthesis of approximately 70% and 30%, respectively. Palladium is of pure r-process origin in our two r-II
stars, and a dominant contribution of the r-process to the Pd abundances is found for another two very metal-poor (VMP, [Fe/H] < -2)
stars. The two VMP
stars, which are strongly enhanced with Sr relative to Ba and Eu, reveal also enhancements with Pd. We propose that the source of extra Sr and Pd in these
stars are VMP, fast rotating massive
stars. Non-LTE is essential for obtaining the observational constraints to future models of the
Galactic Pd
evolution.
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