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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 3 April

High Energy Astrophysical Phenomena

The hitchhiker's guide to the IXPE data analysis

Alessandro Di Marco

This chapter provides an almost comprehensive guide to the Imaging X-ray Polarimetry Explorer (IXPE) data analysis. The chapter briefly introduces the IXPE spacecraft and the instrument onboard; subsequently, the strategies adopted to extract polarimetric information and to optimize the response are given. Moreover, the data formats and processing steps to avoid potential systematic errors and to achieve the best results from the IXPE data are reported. Both the model-independent and the model-dependent analyses are summarized, as the instrument response functions and their different available flavors. The idea behind this chapter is to collect suggestions and answers to questions that are typically raised by users, aiming to enable researchers to maximize the scientific return from IXPE observations.
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Earth and Planetary Astrophysics

The PLATO field selection process III. Selection of the Prime Sample for the LOPS2 field

V. Nascimbeni, G. Piotto, V. Granata et al. (+30 more)

The PLanetary Transits and Oscillations of stars (PLATO) mission will begin its four-year nominal mission in early 2027 by monitoring its Long-duration Observation Phase field at South (LOPS2) for at least two years continuously. The primary aim of PLATO is a very ambitious and challenging one: the discovery of Earth-like planets in the habitable zone of nearby and bright solar analogues. To this purpose, the PLATO Mission Consortium, through its Ground-based Observing Program, will perform the follow-up needed to confirm part of the candidate planets photometrically detected by PLATO and measure their masses through radial velocity curves. For the LOPS2, the Ground-based Observing Program is committed (as part of the PLATO mission) to follow-up the candidate exoplanets discovered orbiting the 15,000 high-quality target subset of the PLATO Input Catalog (PIC) known as the Prime Sample. The Prime Sample will be made public nine months before launch in the context of the first Guest Observer call for proposals to be issued by the European Space Agency. Here, we present the quantitative metrics and thresholds defined to select and prioritize the Prime Sample. Our method is perfectly general and suitable to rank any list of stars surveyed for transiting planets. We also describe the astrophysical properties of the LOPS2 Prime Sample, both in a statistical sense and for some specific targets of interest.
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All authors V. Nascimbeni, G. Piotto, V. Granata, S. Marinoni, P. M. Marrese, M. Montalto, J. Cabrera, C. Aerts, G. Altavilla, K. Belkacem, S. Benatti, M. Bergemann, A. Börner, G. Covone, M. Deleuil, S. Desidera, L. Gizon, M. J. Goupil, M. Günther, A. M. Heras, L. Malavolta, J. M. Mas-Hesse, D. Nardiello, H. P. Osborn, I. Pagano, C. Paproth, D. Pollacco, L. Prisinzano, R. Ragazzoni, G. Ramsay, H. Rauer, S. Udry, T. Zingales

Earth and Planetary Astrophysics

POSEIDON II: The Anti-Aligned Orbit of the Warm Neptune TOI-1710 A b

Juan I. Espinoza-Retamal, Hareesh Bhaskar, Joshua N. Winn et al. (+7 more)

We present an observation of the Rossiter-McLaughlin effect for the TOI-1710 system with the NEID spectrograph on the WIYN 3.5 m telescope. The system hosts a warm Neptune ($P\sim24$ days), and our observations reveal that it orbits in the opposite direction to the stellar spin, with a sky-projected obliquity $\lambda=179\pm19^{\circ}$. Combined with information about the rotation period of the host star, we measure a true obliquity $\psi=158_{-13}^{+11}\,^{\circ}$. The host star has an M-dwarf companion at a separation of $\sim3600$ au, but this companion is too distant to be solely responsible for misaligning the warm Neptune. The host star also shows a long-term radial velocity trend, indicative of a companion at intermediate separations. We show that such a companion can dynamically couple the warm Neptune to the distant M dwarf, enabling the transfer of inclination from the wide binary orbit to the planetary orbit. Assuming this scenario is correct, we predict the intermediate companion is a $\sim5\,M_J$ planet on a $\sim15$ au orbit that is nearly aligned with the transiting planet's orbit.
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All authors Juan I. Espinoza-Retamal, Hareesh Bhaskar, Joshua N. Winn, Cristobal Petrovich, Rafael Brahm, Caleb Lammers, Gu{\dh}mundur Stefánsson, Elise Koo, Andrés Jordán, Felipe I. Rojas

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Friedmann cosmology with fluids and hyperfluids

Ilaria Andrei, Damianos Iosifidis, Laur Järv et al. (+1 more)

We discuss flat Friedmann-Lemaitre-Robertson-Walker (FLRW) metric-affine cosmology where the metric and connection as well as the matter energy-momentum and hypermomentum all obey the symmetry of spatial homogeneity and isotropy. In particular, we outline a scenario where a dark dust fluid carries spin hypermomentum which makes its effective equation of state dynamical and might relate to the DESI DR2 data.
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All authors Ilaria Andrei, Damianos Iosifidis, Laur Järv, Margus Saal

Astrophysics of Galaxies

Stars Born in the Wind II: Widespread Extra-planar Star Formation in M82's Halo

Vaishnav V. Rao, Eric F. Bell, Adam Smercina et al. (+6 more)

Galaxies evolve in tandem with their environments – mergers and gas inflows drive galaxy growth while galactic outflows launched by supernovae may seed the galactic environment with gas, metals, and energy, fueling star-formation far from the main bodies of galaxies. The formation histories of young stars in the stellar halos of nearby galaxies can help understand this interplay. We thus present the most detailed map to date of young stars in the stellar halo of M82, a starburst galaxy in the M81 Group that hosts a prototypical outflow, using Hubble Space Telescope (HST) and Subaru Hyper-Suprime Cam observations. We find widespread extraplanar populations of stars with ages $\lesssim630$ Myr, with clear detections of stars up to $\sim5$ kpc to the south in unique arc-like stellar features (Southern Arcs) and in a new stellar trail up to $\sim20$ kpc to the east (M82's Tail), originating from the Southern Arcs. We estimate a total halo star formation of $\sim4\times10^6\,M_\odot$ in the last $630$ Myr. Overall, the star formation history (SFH) of the M82 Tail is correlated with periods of heightened star cluster formation in the M82 disk, which suggests the influence of the starburst outflow. Further, the fraction of young stars decreases as we move away from M82 to the east. We forward a picture where the M82 Tail formed from ram pressure stripped gas arising from M82's westward motion, triggered by shocks from the outflow.
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All authors Vaishnav V. Rao, Eric F. Bell, Adam Smercina, Elliott Besirli, Andrew Dolphin, Antonela Monachesi, Benjamin Williams, Julianne J. Dalcanton, Roelof S. de Jong

Cosmology and Nongalactic Astrophysics

UNIONS-3500 Weak Lensing: II. B-mode validation for cosmic shear

C. Daley, A. Guinot, S. Guerrini et al. (+9 more)

At Stage-III sensitivities, cosmic shear $B$ modes unambiguously indicate systematic contamination and are often used to inform data selection and scale cuts for cosmological inference. We validate $B$ modes for the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS)-3500 (2894 deg$^2$, $n_\mathrm{eff} \approx 5.0$ arcmin$^{-2}$) using three $E$/$B$-separable statistics: pure-mode correlation functions $\xi_\pm^{\mathrm{B}}(\theta)$, Complete Orthogonal Sets of $E$/$B$-mode Integrals (COSEBI) $B$-mode amplitudes $B_n$, and harmonic-space power spectra $C_\ell^{BB}$. For each statistic, we compute probability-to-exceed (PTE) values over a two-dimensional grid of scale-cut boundaries; our adopted cuts lie in broad stable regions of acceptable PTE. $B$-mode detections and PTE failures on initial catalog versions led us to investigate galaxy size cuts and stellar halo masking. After cuts, all three statistics pass the null test (minimum PTE $= 0.18$). Before scale cuts, we measure an oscillatory COSEBI $B$-mode pattern consistent with repeating additive shear bias, a detector-level effect seen across multiple Stage-III surveys including CFHTLenS, which used the same MegaCam camera; scale cuts that exclude the charge-coupled device (CCD) angular scale suppress it. Although these statistics probe the same two-point shear field, scale cuts in one do not map exactly onto cuts in another, because their respective filter functions weight angular scales differently. The most conservative validation therefore requires scale and sample selections that pass null tests across all frameworks simultaneously, an approach that applies directly to Stage-IV surveys where systematic errors dominate.
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All authors C. Daley, A. Guinot, S. Guerrini, F. Hervas-Peters, L. W. K. Goh, C. Murray, M. Kilbinger, A. Wittje, M. J. Hudson, H. Hildebrandt, L. van Waerbeke, A. W. McConnachie

Solar and Stellar Astrophysics

Parametric SED Modelling of Protoplanetary Discs: Validation and Application to an Unstudied YSO

Volkan Bak{\i}ş and Ayşe Yadigar Habal{\i}

We present a physically motivated spectral energy distribution (SED) modelling framework for deriving stellar and circumstellar disc parameters from broadband photometry. The model combines a parametrized disc structure, dust opacity, and interstellar extinction within a Bayesian Markov Chain Monte Carlo (MCMC) inference scheme, allowing correlated parameters to be constrained self-consistently. Initial parameter estimates are obtained via non-linear least-squares fitting and subsequently refined through MCMC sampling. The method is first validated using the well-studied debris disc system 49 Cet, for which the model successfully reproduces key literature properties. It is then applied to the previously uncharacterised young stellar object (YSO) candidate 2MASS J02512618+6012576, using photometric measurements compiled from multiple surveys. The resulting fit indicates a late-type pre-main-sequence star surrounded by a substantial circumstellar disc consistent with a moderately embedded Class II object. We further assess the sensitivity of the inferred parameters to the adopted extinction law and find that the high reddening required by the model is robust against variations in $R_V$. This work demonstrates that physically meaningful constraints on disc structure can be obtained from broadband SED modelling when extinction and distance are treated within a statistically consistent framework.
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Earth and Planetary Astrophysics

CO and N2 Produced from H2O, CO2, and NH3 Cometary Ice Analogs

Alexandra McKinnon, Alexia Simon, Michelle R. Brann et al. (+3 more)

Hypervolatile species such as carbon monoxide (CO) and molecular nitrogen (N2) have been detected in comets, and could be used to constrain comet formation temperature conditions if their presence is due to freeze-out and/or entrapment. Here we instead explore another plausible origin of cometary hypervolatiles: photodissociation of less volatile species. We characterize CO and N2 formation following ultraviolet (UV) irradiation and electron bombardment of carbon dioxide (CO2), ammonia (NH3), H2O:CO2, H2O:NH3, and H2O:CO2:NH3 cometary ice analogs. We find that CO and N2 form in all photoprocessed ices at temperatures between 10 K and 100 K, resulting in 0.4-0.9 % CO and 0.03-0.7 % N2 relative to water, and CO/CO2 and N2/NH3 mixing ratios of 2.5-62 % and 0.7-9 %, respectively, across the experiments. Because our initial ices are reasonably well-matched to interstellar ices and we use UV exposure similar to a dark cloud, we can compare the resulting ratios directly to cometary abundances. Such a comparison shows that while only a few of CO observations in comets are readily explained by photodissociation, almost all observed cometary N2 can be accounted for by photodissociation of NH3 embedded in water ice. The latter result is also consistent with observed similarly elevated isotopic ratios of N2 and NH3 in 67P. Taken together, our results suggest that N2/H2O ratios less than 1 % should be used cautiously when inferring a comet's formation location, while the more substantial CO abundances seen in many comets do likely imply entrapment at low ice temperatures.
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All authors Alexandra McKinnon, Alexia Simon, Michelle R. Brann, Elettra L. Piacentino, Karin I. Oberg, Mahesh Rajappan

High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Revisiting the Rhoades-Ruffini bound

David Blaschke and Adrian Wojcik

We revisit the derivation of the Rhoades-Ruffini bound on the upper limit for the maximum mass of neutron stars and find that the assumption made there for the onset of an ultimately stiff phase of high-density matter is not stringent. Relaxing this assumption and allowing for an onset of stiff non-nucleonic matter under neutron star constraints at the saturation density or below boost the upper limit of the theoretically possible maximum mass to $4~M_\odot$ or higher, in the mass-gap region between neutron stars and stellar-mass black holes. We provide a fit formula for the dependence of this upper limit on the speed of sound and the onset density of the deconfinement transition.
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Astrophysics of Galaxies

DeepDISC-Euclid: Source Classification and Photometric Redshifts in Euclid Deep Field North With a Pixel-Level Deep Learning Approach

Yuanzhe Jiang, Yue Shen, Grant Merz et al. (+8 more)

The first Euclid Quick Data Release (Q1) provides extensive imaging and spectroscopic data for hundreds of millions of photometric objects across several deep fields. Accurate classifications and photometric redshifts (photo-z) for these sources are crucial to maximizing the value of these data. In this work, we perform source classification and photo-z estimation for the Euclid Deep Field North (EDF-N) around the North Ecliptic Pole, using a deep learning framework (DeepDISC) that learns and infers using 9-band images simultaneously. We train three dedicated models for (1) source detection and classification, (2) galaxy photo-z, and (3) quasar photo-z. The Euclid Q1 input source catalog, and classifications and spectroscopic redshifts (spec-z) from the Dark Energy Spectroscopic Instrument Data Release 1 are adopted as our training data. DeepDISC source detection achieves overall completeness of ~93% and purity of ~80% if using the Euclid source catalog as the ground truth. Using a JWST source catalog within EDF-N as the reference, we estimate a true purity of ~ 90% for DeepDISC sources. About 99.2%, 99.0%, and 84.8% of stars, galaxies, and quasars, respectively, are correctly recovered with their spectroscopic classifications. The DeepDISC photo-zs show good agreement with spectroscopic redshifts, for both galaxies and quasars. Comparisons with other Euclid Q1 products demonstrate that DeepDISC provides comparable or improved performance in source detection/deblending, classification and photo-z, especially for quasars. These results demonstrate the potential of pixel-level deep learning approaches for large-scale sky surveys such as Euclid and Roman, which will continue to improve with better training labels. We release the full DeepDISC source catalog (~13 million objects) for EDF-N with classifications and photo-zs, including photo-z probability distributions.
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All authors Yuanzhe Jiang, Yue Shen, Grant Merz, Shurui Lin, Xin Liu, Zhiwei Pan, Mingyang Zhuang, William Roster, Mara Salvato, Malgorzata Siudek, Grant Stevens

Cosmology and Nongalactic Astrophysics

Mapping the redshift drift at various redshifts through cosmography

Anna Chiara Alfano and Orlando Luongo

The redshift drift provides a kinematic test of the cosmic expansion history through the slow time variation of the redshift of comoving sources. Motivated by the expected Sandage-Loeb measurements from future facilities, we investigate the drift within a cosmographic framework, modeling the Hubble rate through both a second-order Taylor expansion and a $(2,1)$ Padé approximant. We constrain the cosmographic parameters $(H_0,q_0,j_0)$ by combining Pantheon+ and SH0ES type Ia supernovae with gamma-ray bursts and then examine the impact of adding baryon acoustic oscillation measurements from the second DESI data release. The resulting constraints are used to construct a mock Sandage-Loeb catalog, after which the analyses are repeated including the simulated drift data. In this way, we assess the internal consistency of the reconstructed background rather than perform an independent forecast. Accordingly, we find that, for the SNeIa+GRB analysis, the Taylor reconstruction is compatible at the $1\sigma$ level with the $\omega_0\omega_1$CDM scenario, whereas the Padé parameterization improves the agreement of $q_0$ with the $\Lambda$CDM paradigm. Once DESI BAO data are included, the agreement with the reference background models weakens to the $2\sigma$ level. The addition of the mock Sandage-Loeb sample mainly tightens the bounds on $q_0$ and $j_0$, with moderate shifts in the central values. We finally compare the reconstructed redshift drift with the corresponding behavior predicted by the $\Lambda$CDM and $\omega_0\omega_1$CDM scenarios.
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Cosmology and Nongalactic Astrophysics

Cosmological Constraints from Gravitational Wave-Fast Radio Burst Associations without Redshift Measurements for LIGO-Virgo and Cosmic Explorer

Jiaming Zhuge, Marios Kalomenopoulos, Carl-Johan Haster et al. (+1 more)

The potential association between gravitational waves (GWs) and fast radio bursts (FRBs) offers a unique multi-messenger probe for cosmology. In this paper, we develop a redshift-independent framework to constrain cosmological parameters using the luminosity distance - dispersion measure relation, accounting for realistic astrophysical uncertainties. We perform a comprehensive comparative analysis across different GWs detector sensitivities and modeling assumptions. Specifically, we investigate the performance of the current LIGO-Virgo (LV) network (at $z < 0.2$) versus the future Cosmic Explorer (CE). Our study further evaluates the impact of different dispersion measure (DM) distributions—specifically the corrected Macquart's PDF (Zhuge+2025) and the log-normal distribution—and explores the influence of including or excluding host galaxy DM contributions. Using realistic simulated observations, we find that while the current LV network lacks the precision to provide meaningful constraints, CE will enable high-precision cosmology. Even without spectroscopic redshifts, CE observations can effectively break parameter degeneracies and robustly constrain both cosmology and host galaxy parameters. These results highlight the necessity of next-generation detectors.
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All authors Jiaming Zhuge, Marios Kalomenopoulos, Carl-Johan Haster, Bing Zhang

Solar and Stellar Astrophysics

Isochrone-cloud fitting and asteroseismology of the Kepler open cluster NGC6866

Haotian Wang, Gang Li, Dario J. Fritzewski et al. (+2 more)

We investigate how isochrones computed with different input physics and initial conditions affect the age dating of the open cluster NGC 6866, and compare the results with asteroseismic ages derived from Kepler photometry. Using Gaia DR3 data, we identified 180 cluster members with a clustering algorithm. We then developed an isochrone-cloud fitting method that accounts for a range of free parameters in the input physics. Variable stars were subsequently identified among the cluster members. For 19 g-mode pulsators, we carried out modelling with a dedicated grid of rotating stellar models, constrained by spectroscopic and photometric parameters, the asymptotic gravity-mode period spacing, and the near-core rotation rate. We considered two cases: modelling each pulsator individually and modelling them under the assumption of a common cluster age. PARSEC and MIST isochrones yield discrepant ages of 690 and 467 Myr, respectively. The isochrone-cloud fit indicates an initial critical rotation distribution peaking at 0.6, about a factor of two higher than inferred from asteroseismology. The seismic modelling shows agreement between seismic and isochronal masses, but substantial differences in the derived ages due to differences in internal mixing. When the g-mode pulsators are modelled with a shared cluster age, we obtain 759 Myr, consistent with the PARSEC isochronal age. We conclude that age dating of open clusters is sensitive to the adopted input physics and initial conditions, highlighting the need for better calibrated stellar evolutionary models.
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All authors Haotian Wang, Gang Li, Dario J. Fritzewski, Timothy Van Reeth, Conny Aerts

Astrophysics of Galaxies

The tidal evolution of satellite galaxies in cosmological simulations: insights from COLIBRE

Feihong He, Jiaxin Han, Joop Schaye et al. (+12 more)

We investigate the co-evolution of the stellar and dark matter mass of satellite galaxies using the COLIBRE cosmological hydrodynamical simulations with subhaloes resolved by the history-based HBT-HERONS subhalo finder. We identify a universal tidal track connecting stellar mass loss to subhalo mass loss characterized by two distinct phases, which can be well described by the two-parameter model. The initial phase consists primarily of dark matter stripping, whereas stellar stripping becomes significant only after the subhalo bound mass fraction drops below a critical value ($\sim 0.057$). We find a bimodal mass loss rate distribution of subhaloes. In satellites with modest mass loss rates, the stellar mass is largely frozen. By contrast, the galaxy quickly becomes unresolved, along with the dark matter component for the extreme-mass-loss population, naturally explaining the lack of “orphan” galaxies in previous hydrodynamical simulations. Our model also predicts the formation condition for dark-matter-deficient galaxies (DMDGs), whose abundance peaks at $m_{*}\sim 10^{9.5}\,\rm{M}_{\odot}$. The abundance of DMDGs can be very sensitive to numerical effects, with COLIBRE resolving a much larger DMDG population than previous hydrodynamical simulations. We also estimate the influence of artificial disruption on the satellite stellar mass function, which can amount to 20 (50) per cent at $m_* \sim 10^{9} (10^{8}) \, \rm M_\odot$, given a baryonic mass resolution of $\sim 10^{6}\,\rm{M}_{\odot}$.
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All authors Feihong He, Jiaxin Han, Joop Schaye, Wenting Wang, Zhaozhou Li, Sylvia Ploeckinger, Evgenii Chaikin, Robert J. McGibbon, Filip Huško, Matthieu Schaller, Alejandro Benítez-Llambay, Alexander J. Richings, James W. Trayford, Carlos S. Frenk, Fangzhou Jiang

Cosmology and Nongalactic Astrophysics

Which filaments matter: the relative scalings of anisotropic infall

Junsup Shim, Dmitri Pogosyan, Myoungwon Jeon et al. (+1 more)

Dark-matter haloes do not form in isolation but within the surrounding cosmic web. By the time a halo begins to collapse, its larger-scale environment has typically collapsed along two axes, forming filaments that channel anisotropic infall toward the halo. In this work, we derive from first principles the characteristic Lagrangian scale ratio at which such an anisotropic tidal field most strongly influences halo formation. Specifically, we identify the inflection point of the conditional probability that the tidal field, smoothed on a scale Rsd, undergoes two-dimensional compression, given the presence of a density peak of rarity nu on a smaller scale Rpk. For a standard LambdaCDM cosmology, we find (Rsd/Rpk)infl = 2.2 + (nu-2.5) for Rpk corresponding to a tophat filter of 8Mpc/h. This result implies that the anisotropic tidal influence on a collapsing halo typically extends to 2-3 times the size of its Lagrangian patch. Recast as a function of formation redshift z, the characteristic filament scale around 2.5 sigma peaks can be approximated by Rsd(z) = 31 /(2+(1+z)**2)Mpc/h. We provide practical scaling laws for selecting dynamically relevant smoothing scales in large-scale surveys and for setting initial patch sizes in high-resolution zoom simulations.
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All authors Junsup Shim, Dmitri Pogosyan, Myoungwon Jeon, Christophe Pichon

Solar and Stellar Astrophysics

Quantitative spectroscopy of single and multiple OB-type stars. Non-LTE spectrum analysis with machine learning

P. Aschenbrenner and N. Przybilla

The plethora of spectra of OB-type stars in observatory archives and the much larger numbers to come from the WEAVE and 4MOST spectroscopic facilities require efficient, but also accurate and precise methods for (semi)automatic quantitative analyses. Neural networks were used to emulate the spectra of single- and multi-star systems, trained on hybrid non-local thermodynamic equilibrium (non-LTE) models that cover a wide range of atmospheric parameters and chemical compositions. To derive the full set of stellar atmospheric parameters and uncertainties, a Markov chain Monte Carlo algorithm was implemented to fit high-resolution spectra within 3000A-10500A. The neural networks and fitting algorithm were bundled into a programme called Spectral Analysis Tool Using Restricted Neural networks (SATURN). In its current implementation, SATURN facilitates the emulation of synthetic spectra for spectral types O7 to B9, which differ only negligibly from computed models. SATURN was tested on a number of benchmark stars that have been studied before, including single OB stars and a detached eclipsing binary (DEB) system. Excellent agreement of atmospheric parameters and elemental abundances for up to ten metal species is found with respect to the data in the literature, often with reduced uncertainties. For DEB components, the uncertainties are larger, in particular for the fainter secondaries when only a single-epoch spectrum is considered. Uncertainties of elemental abundances are typically <0.10dex. Some first applications of SATURN for analyses of new targets are shown to demonstrate its capabilities, such as fast rotators, including HD149757 (Zeta Ophiuchi). Consistent results are also found at reduced spectral resolutions relevant for observations with WEAVE and 4MOST.
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Earth and Planetary Astrophysics

A 1151-Year Quasi-Commensurability of the Solar System: Empirical Detection, Statistical Characterization, and the Anomalous Exclusion of Uranus

Carlos Baiget Orts

We report the empirical detection of a multi-planet quasi-commensurability in the Solar System and identify an anomalous exclusion that may bear on the dynamical history of Uranus. An exhaustive search identifies T* = 420,403 days (approx. 1,151 years) as the global minimum of a series-comparison similarity metric applied to daily heliocentric ecliptic longitudes of seven planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, and Neptune – computed from the DE441 ephemeris over +/-1,300 years. At this interval, the mean simultaneous angular displacement of all seven planets is 13.4 degrees, with a standard deviation of 0.65 degrees sustained over a century-long window and stable across 1,200 years of reference epochs. T* ranks first among all 2,600 candidates, with a gap of 1.09 degrees to the second best. No sub-multiple produces a comparable result. Seven of the eight planets participate in the synchronism. The sole exception is Uranus, whose sidereal residue at T* is -108.3 degrees – nearly one-third of a full orbit – while Neptune's residue is only -5.2 degrees, one of the smallest among all seven planets after Earth's. This sharp asymmetry between the two ice giants constitutes an independent empirical signature consistent with the hypothesis that Uranus's orbital period was substantially modified by a catastrophic early impact. The interval 1,151 years was identified by Babylonian astronomers as the Venus return period (de Jong 2019); the present work shows it is simultaneously optimal for six additional planets. Source code and data are publicly available.
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Solar and Stellar Astrophysics

A statistical study of the environmental age of core-collapse supernovae based on VLT/MUSE integral-field-unit spectroscopy

Qiang Xi, Ning-Chen Sun, Yihan Zhao et al. (+13 more)

We aim to understand the progenitor channels of CCSNe via a statistical study of the ages of their environments. We compiled a large and minimally biased sample of 128 CCSNe discovered by untargeted wide-field transient surveys and with archival VLT/MUSE integral-field-unit spectroscopy. We measured the local H{\alpha} luminosity within a 300-pc aperture centered on the SN explosion site as an empirical proxy for the environmental age. We find that the mean local H$\alpha$ luminosities are ordered as II(P) $\approx$ IIb $\lesssim$ Ib $<$ Ic. The differences among Types~II(P), IIb and Ib are very small, if any. Type~Ic SNe are located in clearly younger environments than the other types. Our result suggests that Type Ic SNe have much younger and more massive progenitors than the other CCSN types and they likely originate from a distinct progenitor channel. The distinction between Types II(P), IIb and Ib SNe is insensitive to progenitor mass and mainly due to the different binary separation; in contrast, Type Ic SNe predominantly require much higher-mass progenitors accompanied by close companions with large mass ratios and/or much stronger stellar wind that depends sensitively on progenitor mass.
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All authors Qiang Xi, Ning-Chen Sun, Yihan Zhao, Emmanouil Zapartas, Dimitris Souropanis, Chun Chen, Xiaohan Chen, César Rojas-Bravo, Justyn R. Maund, Zexi Niu, Adam J. Singleton, Anyu Wang, Zhiyi Wang, Ziyang Wang, Junjie Wu, Jifeng Liu

Solar and Stellar Astrophysics

Evidence of Enhanced Ionization in Protostellar Envelopes

Kamber R. Schwarz, S. Maret, M. R. A. Wells et al. (+4 more)

Ionization is a major driver of both physical and chemical evolution in protostellar systems. Recent observations reveal substantial chemical processing in protoplanetary disks by the time the surrounding envelope has cleared. Thus, physical conditions during the preceeding phase, when an infalling envelope of material is still present, are crucial for determining the extent of chemical processing at early stages. We used observations of H13CO+ and C18O from the Northern Extended Millimeter Array (NOEMA) and IRAM 30m telescope to constrain the ionization rate in the envelopes of three Class 0 protostars: NGC-1333 IRAS4A, L1448-C, and L1157. We find ionization rates in the range zeta = 1e-16 - 1e-13 s$^{-1}$ , several orders of magnitude above the ionization rate of zeta = 6e-17 s$^{-1}$ in the diffuse interstellar medium. This supports the idea that ionization driven chemistry is more efficient at earlier stages (< 1e5 years) of protostellar evolution.
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All authors Kamber R. Schwarz, S. Maret, M. R. A. Wells, C. Gieser, A. Belloche, P. Andre, C. Codella

Instrumentation and Methods for Astrophysics

Machine Learning Assisted NEO Discovery and Polarimetric Characterisation with Astronomical Surveys

G.A. Verdoes Kleijn, T. Grobler, S.J. Chong et al. (+12 more)

We are a group of over two dozen astronomers, computer scientists, data scientists and digital Big Data research platform experts at 11 universities and research institutes in South Africa and Europe. We study Near-Earth Objects (NEOs) for Planetary Defence and scientific purposes. We present our research and development programme for algorithms and digital data analysis platforms for machine learning-assisted NEO discovery and polarimetric characterisation in astronomical surveys. Typically, this is serendipitous because these surveys are designed for galactic and extragalactic science.
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All authors G.A. Verdoes Kleijn, T. Grobler, S.J. Chong, O.R. Williams, M. Micheli, D. Koschny, T. Saifollahi, L.V.E. Koopmans, D. Dirkx, T. Santana-Ros, Y.-Z. Ma, M. Pöntinen, S. Bagnulo, M. Granvik, B.Y. Irureta-Goyena

Astrophysics of Galaxies

Tracing the relic nature of compact galaxies through their globular cluster systems

Micheli T. Moura, Ana L. Chies-Santos, Cristina Furlanetto et al. (+6 more)

We investigate the synthetic model of globular cluster (GC) systems of 17 compact massive galaxies (CMGs) from the Illustris TNG100 simulation to explore their connection with massive relic galaxies, systems that have undergone little structural evolution across cosmic time. The co-evolution of the GC systems and their host galaxies is based on a GC formation and evolution model that assigns clusters to stellar particles according to age and local conditions, providing positional, kinematic, and chemical information for individual GCs. By combining stellar assembly histories, effective radius evolution, and GC properties such as in-situ vs. ex-situ origin, metallicity, and spatial distribution, we identify consistent signatures of early formation and late-time accretion. We find that the GC mass fraction traces the host assembly history more robustly than the GC number fraction, as massive clusters better preserve the imprint of the early accretion history. Three CMGs from TNG100 emerge as strong massive relic analogs, exhibiting high in-situ GC fractions, narrow metallicity distributions, and compact spatial distributions. A tight correlation between the host stripped fraction and the extent of the ex-situ GC population further reveals the possibility to consider GC spatial profiles as a signature to identify tidal stripping processes. These results indicate that the combined analysis of GC populations and host stellar assembly offers a robust diagnostic for identifying massive relic galaxies and constraining their evolutionary histories.
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All authors Micheli T. Moura, Ana L. Chies-Santos, Cristina Furlanetto, Yingtian Chen, Oleg Y. Gnedin, Michael A. Beasley, Anna Ferré-Mateu, Ling Zhu, Juan Pablo Caso

Solar and Stellar Astrophysics

PENELLOPE: IX. Lithium, iron and barium elemental abundances in eight nearby young clusters

R. Carini, K. Biazzo, A. Frasca et al. (+19 more)

We conducted a homogeneous chemical analysis of pre-main sequence stars with effective temperatures ranging from $\sim$ 3000 K to $\sim$ 5500 K in eight nearby star-forming regions (SFRs): Chamaeleon I, $\eta$ Chamaeleonis, Lupus, Orion OB1a, Orion OB1b, $\sigma$Orionis, Taurus, and Corona-Australis. Our study aims to: 1) derive the lithium abundance (A(Li)) and highlight the impact of veiling correction on both A(Li) and age determination; 2) perform the iron (Fe) and barium (Ba) abundance analysis in regions with scarce previous measurements; 3) investigate the possible Ba enhancement. The analyzed data were obtained as part of the PENELLOPE Large Program using the ESPRESSO, UVES, and X-Shooter instruments. We measured the equivalent width of the lithium line (EWLi) at $\lambda$ = 6707.8 Angstrom, from which A(Li) is derived using the curves of growth method. The Fe and Ba abundances have been measured through spectral synthesis analysis. Using the EAGLES code, we derived an upper limit on the age of the eight SFRs. Our findings underscore the necessity of veiling corrections on EWLi, which can shift A(Li) and age estimates by up to $\sim$ 0.7 dex and $\sim$ 20 Myr, respectively. Accounting for veiling, the A(Li) distributions peak in a range between 3.3 and 3.8 dex for most clusters, and the upper age limit is approximately 5 Myr for all SFRs. We successfully measured the mean iron and barium abundances in Lupus, Taurus, Cha I, and $\eta$ Cha, showing slightly sub-solar iron abundance, and a clear Ba overabundance, with [Ba/H] values reaching up to 0.75 dex.
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All authors R. Carini, K. Biazzo, A. Frasca, C.F. Manara, J.M. Alcalá, P. Ábráham, J. Campbell-White, R. Claes, M. Fang, M. Gangi, J.F. Gameiro, Á. Kóspál, K. Mauco, I. Mendigutía, B. Nisini, M. Robberto, C.E. Robinson, C. Schneider, M. Siwak, T. Sperling, L. Tychoniec, L. Venuti

High Energy Astrophysical Phenomena

Optical observations and atomic environment of supernova remnant G25.1-2.3

Ebru Aktekin, Hicran Bak{\i}ş, Volkan Bak{\i}ş et al. (+4 more)

The supernova remnant (SNR) G25.1-2.3 was identified in the radio band during the Sino-German $\lambda$6 cm survey of the Galactic plane. We present a detailed investigation of the optical, HI, and CO emission towards the G25.1-2.3 to better understand its characteristics and environment. In this study, optical spectroscopic data of the remnant and its environment have been analysed for the first time, providing new insights into their emission properties. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and 1.5-m Russian-Turkish Telescope (RTT150) data show variations across the observed regions, with [SII]/H$\alpha$ ranging from 0.16 to 0.83. We identified shock-heated gas in the northern and southern regions and several photoionized regions around the SNR based on their [SII]/H$\alpha$ ratios derived from spectra. The [SII]$\lambda$6716/$\lambda$6731 ratio observed in the northern region suggests electron densities ($n_{\rm e}$) ranging from 120 to 1030 cm$^{-3}$, whereas the southern regions show higher values, between 490 and 4500 cm$^{-3}$. The variations in the observed H$\alpha$/H$\beta$ ratios indicate significant differences in extinction across the regions. H$\alpha$ images obtained using the 1-m Turkish Telescope (T100) reveal optical emission in the northern and southern, characterized by filamentary and diffuse structures. We newly found a hole-like distribution of HI, whose spatial extent is roughly consistent with the diameter of the SNR. Based on radio data, we examine the evolutionary stage of G25.1-2.3 using the surface brightness-diameter ($\Sigma-D$) relation and the equipartition method.
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All authors Ebru Aktekin, Hicran Bak{\i}ş, Volkan Bak{\i}ş, Yuya Asano, Hidetoshi Sano, Yasuo Fukui, Aytap Sezer

Solar and Stellar Astrophysics

Tearing Driven Reconnection: Energy Conversion Involving Firehose Kinetic Instabilities (2D Hybrid Möbius Simulations)

Etienne Berriot, Petr Hellinger, Olga Alexandrova et al. (+2 more)

This study focuses on energy conversion related to tearing-driven magnetic reconnection in the context of weakly collisional astrophysical plasmas. We present results from a two-dimensional hybrid particle-in-cell simulation employing novel periodic conditions with a topology akin to the Möbius strip, which double the computation efficiency as compared to regular periodic conditions. Evaluation of the ion electric work rate ($\mathbf{j}_i \cdot \mathbf{E}$) and pressure strain interaction ($\mathbf{P}_i : \mathbf{\nabla u}_i)$ shows that most of the energy conversion occurs during the nonlinear phase of the instability, where magnetic energy is transferred towards ion kinetic energy (bulk outflows) and internal energy (heating). These energy conversion rates are of the same order but inhomogeneous. Heating predominantly occurs within the magnetic islands, while near the X-points, nearly the same amount of magnetic energy is transferred to bulk plasma flow and heating. The reconnected plasma moreover exhibits an ion temperature higher parallel than perpendicular to the local magnetic field $\mathbf{B}$. This temperature anisotropy is sustained by the islands' contraction, but eventually gets regulated by kinetic firehose instabilities (parallel and oblique), and/or firehose-like processes, whose main effect is to redistribute the internal energy from the parallel to the perpendicular direction.
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All authors Etienne Berriot, Petr Hellinger, Olga Alexandrova, Alexandra Alexandrova, Pascal Démoulin

Astrophysics of Galaxies

Holmberg IX: A Unique, Infant but Inactive Galaxy as Revealed via a Multiwavelength Approach

Ye-Wei Mao, Luis C. Ho, Alexei V. Moiseev et al. (+2 more)

In this Letter, we report a novel discovery of unique characteristics for the tidal dwarf galaxy (candidate) Holmberg IX via a multiwavelength investigation. New observations are taken for deeply mapping H{\alpha} emission and combined with archival/published data for comprehensively probing dust, gas, and stellar populations in this galaxy. We find in Holmberg IX a dearth of dust incompatible with its rich gas and metal; globally young stellar populations with prominent far-ultraviolet but deficient and marginal H{\alpha} emissions, distinct from other tidal dwarf galaxies ever known. By assuming a normal initial mass function (IMF), Holmberg IX is suggested to be born ~130 Myr ago from a bursty star formation event, which then rapidly ceased, with very few stars formed in the past ~80 Myr that demarcates a lower age limit for the galactic mainbody; current star formation occurs only in outskirts, bringing a conundrum about the reason for the recent quenching in such a gas-rich environment. Contradicting the general expectation for tidal dwarf galaxies hosting continuous star formation, the present quiescence implies Holmberg IX currently staying in a rarely-seen transient period. Without star formation continuing, Holmberg IX is likely transforming into a dwarf spheroidal galaxy, or oppositely into a(n) (ultra-)diffuse system which will probably dissolve in the end. Instead, if Holmberg IX possesses peculiar IMF and hosts low-mass, weak-H{\alpha} star formation, it is able to maintain long-term survival in its current status. On whichever evolutionary pathway in reality, Holmberg IX appears as a special case updating conventional understandings of tidal dwarf galaxies and hinting potential existence of similar analogs in the Universe.
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All authors Ye-Wei Mao, Luis C. Ho, Alexei V. Moiseev, Oleg V. Egorov, Andrej M. Sobolev

Cosmology and Nongalactic Astrophysics

Single field slow-roll inflation with step uplift to $n_s=1$

Hao-Shi Yuan, Ze-Yu Peng and Yun-Song Piao

The early dark energy resolution of Hubble tension seems to be suggesting a scale-invariant Harrison-Zeldovich spectrum of primordial scalar perturbation, i.e. $n_s=1$ ($|n_s-1|\sim {\cal O}(0.001)$) for $H_0\sim 73$km/s/Mpc. In this work, we propose a possibility to acquire $n_s=1$ in single field slow-roll models of inflation. In our consideration, the potential of inflaton during inflation still preserve the shape of well-known single field inflation models in deep slow-roll region, but inflation ends suddenly due to a large step of inflaton potential. In particular, we investigate the implication of our scheme for chaotic inflation and Starobinski inflation, and show how they can be compatible with the observation for $n_s=1$.
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Cosmology and Nongalactic Astrophysics

Inferring population III star properties from the 21-cm global signal

Sho Ukai, Hayato Shimabukuro, Kenji Hasegawa et al. (+1 more)

Investigating the properties of the first stars in the universe, known as Population III (Pop~III) stars, is essential, yet it remains an open question. One way to explore these stars is by examining their effects on the surrounding gas during the cosmic dawn. In this study, we investigate whether the 21-cm global signal can constrain the typical mass and star formation efficiency of first-generation stars. We perform semi-numerical simulations that include the escape fraction of ionizing photons, which depends on stellar and halo masses, as well as the heating structure surrounding a halo that hosts the first star, determined by radiation hydrodynamics (RHD) simulations. Using a Fisher analysis that includes thermal noise for an integration time of $1000\,\mathrm{h}$, we find that the global signal provides information for constraining these properties if the foreground spectrum can be perfectly removed. However, when the smooth foreground spectrum is modeled using a log-polynomial and inferred from the same data, its spectral variation becomes strongly degenerate with the changes produced by the Pop~III parameters, substantially weakening the constraints. These results demonstrate that accurate foreground modeling and removal are essential for extracting information about Pop~III properties from the global 21-cm signal.
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All authors Sho Ukai, Hayato Shimabukuro, Kenji Hasegawa, Kiyotomo Ichiki

High Energy Astrophysical Phenomena

Spin effects in superfluidity, neutron matter and neutron stars

Armen Sedrakian and Peter B. Rau

We review selected aspects of the interior physics of compact stars, focusing on the microscopic and macroscopic manifestations of spin, magnetic fields, and nucleonic superfluidity and superconductivity. Spin statistics of fermions allow quantum degeneracy pressure to determine the stability and global properties of neutron stars, whose structure depends sensitively on the strong interactions among baryons in dense matter. Using a generic metamodeling framework based on an expansion of the nuclear energy density around the isospin-symmetric and saturation-density limits, we highlight how various lesser-known terms in this expansion affect compact-star observables and review multimessenger constraints on mass, radius, and moment of inertia. The influence of magnetic fields on dense matter is examined, showing that substantial effects in their structure require extremely strong fields, whereas lower fields are sufficient to affect their superfluid phases. At the mesoscopic scale, the coexistence of superfluid and superconducting components features vortex and flux-tube lattices, with pinning and mutual friction processes playing central roles in neutron-star rotational dynamics. We discuss unresolved issues concerning vortex structure, flux-tube configurations, and the origin of pulsar glitches and postglitch relaxation. We also briefly address the possible emergence of deconfined quark phases in compact-star cores, including their color-superconducting properties, as well as the associated vortex structures and magnetic-field responses in such phases.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Gravitational edge mode powers galaxy flat rotation curves

Obinna Umeh

The point-particle approximation is foundational to modelling clustering of matter in the universe, but is fundamentally inconsistent within General Relativity due to associated spacetime singularities. This bottleneck has historically restricted the study of matter clustering to linear scales. We resolve this by utilising the recent observation that a matter horizon precedes the formation of caustics in expanding spacetimes. This allows for the isolation of singularities via spacetime surgery. By glueing distinct spacetime sheets related by a discrete transformation across the shared boundary, we derive a covariant backreaction term that contributes to the effective energy-momentum tensor. Crucially, we identify this backreaction contribution with gravitational edge modes; physical degrees of freedom residing on boundaries that arise from the breaking of the diffeomorphism group. These gravitational edge modes modify local particle trajectories, naturally producing flat galaxy rotation curves in the outskirts without invoking dark matter particles. Our framework thus demonstrates that gravitational edge modes can act as effective dark matter, offering a first-principles alternative to particle dark matter for explaining galactic dynamics.
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Astrophysics of Galaxies

PhDLspec: physical-prior embedded deep learning method for spectroscopic determination of stellar labels in high-dimensional parameter space

Tianmin Wu, Maosheng Xiang, Jianrong Shi et al. (+4 more)

Unlocking the full physical information encoded in low-resolution spectra poses a significant challenge for astronomical survey analysis. Such a task demands modeling spectra and optimizing astrophysical parameters in high-dimensional space, as a consequence of line blending. Here we present PhDLspec – a deep learning framework embedded with physical priors for stellar spectra modeling and analysis. By imposing differential spectra derived from ab initio stellar atmospheric model calculation on a transformer framework, PhDLspec can rigorously and precisely model stellar spectra by simultaneously taking into account more than 30 physical parameters, at a computational speed hundreds of times faster than ab initio model calculation. With such a flexible stellar modeling approach, PhDLspec can effectively derive ~30 stellar labels from a low-resolution spectrum using affordable optimization techniques. Application to LAMOST spectra (R~1800) yields stellar elemental abundances in good agreement with high-resolution spectroscopic surveys, following essential calibrations to correct systematic biases in elemental abundance estimates using wide binaries and reference high-resolution datasets. We provide a catalog of 25 elemental abundances for 116,611 subgiant stars with precise age estimates. The successful application of PhDLspec to LAMOST spectra for high-dimensional parameter determination sheds light on similar challenges faced by other surveys and disciplines.
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All authors Tianmin Wu, Maosheng Xiang, Jianrong Shi, Meng Zhang, Lanya Mou, Hong-Liang Yan, A-Li Luo