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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 17 October

Earth and Planetary Astrophysics

Multiwavelength analysis of polarized light in HD 100453

J. Ma, R. Tazaki, H. M. Schmid et al. (+4 more)

HD 100453 disk is a prototypical companion-disk interaction system hosting a pair of spirals and a substellar companion. We present new noncoronagraphic high-contrast imaging observations of HD 100453 with $V$ filter on SPHERE/ZIMPOL. We combined high-contrast imaging data of the reflected light from 0.55 to 2.2 $\mu m$ using the $V$, $I'$, $J$, and $Ks$ band data of ZIMPOL and IRDIS at VLT/SPHERE. For each observational epoch, we corrected for the smearing effect to derive the intrinsic disk-integrated polarized flux. We derived a steady increase with wavelengths from $\hat{Q}_{\varphi}/I_{\star}(V)=0.3\%$ to $\hat{Q}_{\varphi}/I_{\star}(K)=1.2\%$. We applied reference differential imaging to extract the disk intensity for the $V$ and $Ks$ bands using star hopping observations. We obtained the first $V$-band total intensity for HD 100453 with ZIMPOL star hopping. The integrated total flux $I_{\rm disk}/I_{\star}(V)=1.5\%$ increases to $I_{\rm disk}/I_{\star}(K)=4.8\%$. Both the total intensity and the polarization fraction show red colors, and the intrinsic maximum degree of polarization increases moderately from $40\%$ to $55\%$. We then used RADMC-3D radiative transfer modeling with a parametrized Henyey-Greenstein phase function to constrain the dust properties. From the $V$ to $Ks$ band, the dominating dust in the outer disk has an increasing scattering albedo and degree of polarization, while the asymmetry parameter slightly decreases. The outer disk of HD 100453 contains sub-micron-sized low porosity grains/aggregates. The cavity in scattered light is not empty and is replenished with optically thin dust with a maximum size of $\leq 0.1\mu m$. The linear polarization is higher in the spiral region than in the other regions, suggesting different dust properties in those regions.
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All authors J. Ma, R. Tazaki, H. M. Schmid, G. Duchêne, C. Dominik, C. Ginski, F. Ménard

Astrophysics of Galaxies

Very Massive Stars and High N/O: A Tale of the Nitrogen-enriched Super Star Cluster in the Sunburst Arc

Yanlong Shi, Liang Dai, Norman Murray et al. (+3 more)

The lensed Sunburst Arc ($z = 2.369$) hosts a young ($\sim2$–$4\,\rm Myr$), massive ($M_\star \sim 10^7\,M_\odot$), compact ($R_{\rm eff} \sim 8\,\rm pc$) Lyman-continuum (LyC) leaking super star cluster, which powers a compact ($< 10\,\rm pc$), high-pressure nebula at sub-solar metallicity $\sim0.2\,Z_\odot$ and with an anomalously elevated nitrogen-to-oxygen ratio $\log({\rm N/O}) \sim -0.2$. We present semi-analytic models and 3D magnetohydrodynamic simulations with radiative feedback in an attempt to reproduce this system. The results indicate that the progenitor giant molecular cloud (GMC) may have $M_{\rm cloud} \gtrsim 3 \times 10^7\,M_\odot$ and $R_{\rm cloud} \sim 70\,\rm pc$, corresponding to a surface density $\sim10^3$–$10^4\,M_\odot\,{\rm pc}^{-2}$. Incorporating feedback from individual Very Massive Stars (VMSs; $\ge 100\,M_\odot$) sampled from the Kroupa initial mass function, we find that their winds rapidly enrich $\sim 10^4\,M_\odot$ of nearby gas with nitrogen ($\sim 1\,$dex) and helium ($\sim 0.1$–$0.2\,$dex). In the first $1$–$3\,$Myr, some cold gas falls to the system center where a central cluster builds up from sub-cluster mergers. There, the gas is photoionized, pressurized, and chemically enriched by the newly formed VMSs, before being radiatively expelled in the next $\sim1\,\rm Myr$. We find that both VMS feedback and a high-surface-density progenitor GMC are necessary to reproduce the observed nebular properties, such as high N/O, high pressure, and stellar proximity. Low metallicity ($Z \le 0.004$) may be essential to avoid overproduction of carbon from WC stars. Such enrichment processes localized to compact starburst events may have caused strong nitrogen emission from dense ionized gas as observed in high-redshift galaxies such as GN-z11 and GS_3073.
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All authors Yanlong Shi, Liang Dai, Norman Murray, Claire S. Ye, Christopher D. Matzner, Massimo Pascale

Cosmology and Nongalactic Astrophysics

The kinetic Sunyaev Zeldovich effect as a benchmark for AGN feedback models in hydrodynamical simulations: insights from DESI + ACT

Leah Bigwood, Masaya Yamamoto, Jared Siegel et al. (+7 more)

Baryonic feedback remains one of the largest uncertainties in cosmological hydrodynamical simulations, with different prescriptions producing divergent predictions for the fraction of gas expelled from halos, the radial extent of the gas expulsion and the impact on large scale matter clustering. We present the first systematic study of the kinetic Sunyaev-Zel'dovich (kSZ) effect across a wide range of simulations (FLAMINGO, ANTILLES, BAHAMAS, SIMBA, FABLE and their variants), and compare them directly to DESI Year 1 + ACT kSZ measurements. We ensure a like-for-like comparison with observations by developing a robust methodology that accounts for the halo mass selection using galaxy-galaxy lensing, cosmic variance, miscentering and satellites, establishing the kSZ effect as a new benchmark for the simulations. We find that fiducial feedback models are disfavoured by >3 sigma, while simulations with more powerful AGN feedback within the FLAMINGO and BAHAMAS suites, as well as SIMBA, reproduce the observed kSZ signal within <2 sigma. We use the ANTILLES simulation suite to demonstrate that the amplitude of the kSZ effect is a strong predictor of matter power spectrum suppression, competitive with baryon fraction metrics. These results establish the kSZ as a critical probe for evaluating feedback physics and for advancing the fidelity of cosmological simulations.
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All authors Leah Bigwood, Masaya Yamamoto, Jared Siegel, Alexandra Amon, Ian G. McCarthy, Romeel Dave, Jaime Salcido, Matthieu Schaller, Joop Schaye, Tianyi Yang

Cosmology and Nongalactic Astrophysics

Impact of neutrino decays on the Cosmic Neutrino Background anisotropies

Nicola Terzaghi, Guillermo Franco Abellán, Fabian Zimmer et al. (+1 more)

The anisotropies of the Cosmic Neutrino Background (C$\nu$B) offer an ideal tool to test non-standard neutrino interactions, since they directly trace the perturbations in the neutrino distribution function. Here, we study how invisible neutrino decays impact the C$\nu$B anisotropies, in a framework where neutrinos decay non-relativistically to dark radiation and lighter neutrinos in a manner consistent with the measured mass splittings. For this purpose, we perform the first implementation of such a late-time neutrino decay scenario within a linear Einstein-Boltzmann solver, and compute the C$\nu$B angular power spectra from the Boltzmann hierarchy solutions for a range of lifetimes and decay channels. We find that neutrino decays leave very strong signatures on the C$\nu$B angular spectra, about two orders of magnitude larger than on the CMB angular spectra, particularly for lifetimes comparable to the age of the Universe. We show that a future polarized tritium target run of the PTOLEMY experiment, with sufficient counting statistics to measure just the first $\sim 15$ multipoles of the neutrino sky map, could test neutrino decay models that remain undetectable with CMB data.
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All authors Nicola Terzaghi, Guillermo Franco Abellán, Fabian Zimmer, Shin'ichiro Ando

Instrumentation and Methods for Astrophysics

BREAKFAST: A Framework for general joint BA duty and follow-up guidance of multiple $\gamma$-ray monitors

Chen-Wei Wang, Peng Zhang, Shao-Lin Xiong et al. (+30 more)

With the growing number of gamma-ray monitors in operation, several research teams have adopted a strategy of joint operation and scientific duty to improve efficiency. A successful example is the GECAM-HXMT-SVOM (GHS) constellation collaboration, which sets a precedent for other gamma-ray monitor constellations. However, joint duty also presents challenges to Burst Advocates (BAs), including the increased number of triggers and, more importantly, the frequent switching between various systems due to incompatibilities among different missions, which complicates the situation. To address the current requirements of multi-wavelength and multi-messenger astronomy, we developed a customized framework for unified trigger processing within the GHS joint duty, named "BA's Rapid Evaluation and Analysis Kit for Formulating Alerts and Summary Tools" (BREAKFAST). This framework incorporates a series of automated, semi-automated, and manual pipelines designed to rapidly process triggers of prompt emissions in the gamma-ray band from different instruments, while maintaining flexible compatibility for future missions. The pursuit of BREAKFAST goes beyond merely providing trigger processing for BAs. BREAKFAST also aims to filtering high-value targets and guiding follow-up telescopes through rapid analysis and reporting, thus serving as an important bridge between prompt emission observations and afterglow observations. To this end, a suite of comprehensive analysis modules is included in BREAKFAST, particularly the specially designed module that predicts X-ray afterglow brightness based on prompt emission properties. The framework's effectiveness has already been demonstrated in recent observational campaigns, and it is expected to play a significant role in the discovery and observation of peculiar transients in the future.
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All authors Chen-Wei Wang, Peng Zhang, Shao-Lin Xiong, Yue Huang, Wen-Jun Tan, Zheng-Hang Yu, Yue Wang, Wang-Chen Xue, Chao Zheng, Hao-Xuan Guo, Ce Cai, Yong-Wei Dong, Jiang He, Cheng-Kui Li, Xiao-Bo Li, Jia-Cong Liu, Xing-Hao Luo, Xiang Ma, Rahim Moradi, Yang-Zhao Ren, Li-Ming Song, Ping Wang, Jin Wang, Bo-Bing Wu, Shuo Xiao, Sheng-Lun Xie, Shu-Xu Yi, Xue-Yuan Zao, Xiao-Yun Zhao, Li Zhang, Shuang-Nan Zhang, Yan-Qiu Zhang, Shi-Jie Zheng

Astrophysics of Galaxies

Velocity dispersion profiles of dwarf spheroidal galaxies with self-interacting ultralight dark matter

K. Korshynska, E. V. Gorbar, Y. M. Bidasyuk et al. (+2 more)

Dark-matter-dominated dwarf galaxies provide an excellent laboratory for testing dark matter models at small scale and, in particular, the ultralight dark matter (ULDM) class of models. Within the framework of self-interacting bosonic dark matter, we use the observed velocity-dispersion profiles of seven dwarf spheroidal galaxies to constrain the parameters of ULDM. In our modeling, we account for the impact of the baryonic component on the velocity dispersion and ULDM halo structure. We find that the repulsive self-interaction of ULDM, which fits the observations, is almost negligible, consistent with non-interacting ULDM with a boson mass of approximately $1.6 \times 10^{-22}\,\mathrm{eV}$. In contrast, for attractively interacting ULDM, the best fit corresponds to a smaller boson mass of about $1.3 \times 10^{-22}\,\mathrm{eV}$, with self-interaction playing a significant role in shaping the dark-matter halo and thereby influencing the interpretation of observations.
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All authors K. Korshynska, E. V. Gorbar, Y. M. Bidasyuk, A. I. Yakimenko, Y. Revaz

Cosmology and Nongalactic Astrophysics

A rising tide: Intrinsic alignments since the turn of the millennium

Nora Elisa Chisari

The alignments of galaxies across the large-scale structure of the Universe are known to be a source of contamination for gravitational lensing, but they can also probe cosmology and the physics of galaxy evolution in many ways. In this review, I cover developments in our understanding of intrinsic alignments over the past 25 years on: (1) different approaches to model intrinsic alignments across a range of scales, (2) existing observational constraints, (3) predictions from cosmological numerical $N$-body and hydrodynamical simulations, (4) mitigation strategies to account for their contamination to lensing observables and (5) cosmological and astrophysical applications. While the review focuses mostly on two-point statistics of intrinsic alignments, I also give a summary of other statistics beyond two-point. Finally, I point out some of the open problems hindering the understanding or application of intrinsic alignments and how they might be overcome in the future.
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Solar and Stellar Astrophysics

Rare Find: Discovery and chemo-dynamical properties of two s-process enhanced RR Lyrae stars

Valentina D'Orazi, Giuliano Iorio, Borbála Cseh et al. (+15 more)

We report the serendipitous discovery of two RR Lyrae stars exhibiting significant s-process element enrichment, a rare class previously represented solely by TY Gruis. Our goal is to characterise these objects chemically and dynamically, exploring their origins and evolutionary histories. Using high-resolution spectroscopy from HERMES@AAT and UVES@VLT, we derived detailed chemical abundances of key s-process elements, carbon along with $\alpha$-elements. We also employed Gaia DR3 astrometric data to analyse their kinematics, orbital properties, and classify their Galactic population membership. We compared observational results with theoretical asymptotic giant branch nucleosynthesis models to interpret their enrichment patterns. Both stars exhibit clear signatures of s-process enrichment, with significant overabundances in second-peak elements such as Ba and La compared to first-peak Y and Zr. Comparison with AGB nucleosynthesis models suggests their progenitors experienced pollution of s-process-rich material, consistent with early binary interactions. However, notable discrepancies in dilution factors highlight the need for more refined low-metallicity asymptotic giant branch (AGB) models. We also explore and discuss alternative scenarios, including sub-luminous post-AGB-like evolution or double episodes of mass transfer. Our findings confirm the existence of s-process-enhanced RR Lyrae stars and demonstrate the importance of combining chemical and dynamical diagnostics to unveil their complex evolutionary pathways. Future detailed binary evolution modelling and long-term orbital monitoring are essential to resolve their formation scenarios and assess the role of binarity in the evolution of pulsating variables.
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All authors Valentina D'Orazi, Giuliano Iorio, Borbála Cseh, Chris Sneden, Hedieh Abdollahi, László Molnár, Alexey Bobrick, Giuseppe Bono, Vittorio F. Braga, Amanda Karakas, Maria Lugaro, Simon W. Campbell, Michele Fabrizio, Giuliana Fiorentino, Ian U. Roederer, Nicholas Storm, Maria Tantalo, Juliana Crestani

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Relativistic tidal divergences in circular orbits and the dynamics of light rings

Victor F. C. Vieira, Rafael P. Bernar and Caio F. B. Macedo

Tidal forces acting on orbiting bodies arise from inhomogeneities in the gravitational field, generating stresses that can deform or even disrupt these objects. In this work, we analyze relativistic tidal forces associated with ultracompact objects described by static and spherically symmetric spacetimes, focusing on observers in circular geodesic motion. We show that, in contrast to the case of radial geodesics, tidal forces diverge as the orbit approaches null circular geodesics. As illustrative examples, we study two uniform-density stellar models: one isotropic and another supported purely by tangential stresses. We conjecture that the divergence of tidal forces near light rings may play a role in the nonlinear stability of ultracompact, horizonless objects.
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High Energy Astrophysical Phenomena

Born to be recycled: a comprehensive population synthesis of the Galactic millisecond pulsars

Mattéo Sautron, Jérôme Pétri, Dipanjan Mitra et al. (+2 more)

Millisecond pulsars (MSPs) are the oldest but fastest pulsars known to date. In the 1980s, to explain how these pulsars could be formed, a new hypothesis was formulated: the recycling of pulsars, i.e the fact that a pulsar could accrete matter from a companion and been spun up. In this paper, we developed a population synthesis algorithm for pulsars which belong to a binary, in order to check whether most of the observed recycled pulsars were formed via an accretion mechanism and derive statistics about their properties, that are difficult to obtain through observations. We also make predictions for future surveys. Toward the presented objectives, we use the code Stellar EVolution for N-body (SEVN) to take into account all the binary processes and our own code to evolve each pulsar self-consistently by taking into account the secular evolution of a force-free magnetosphere, the magnetic field decay, gravitational braking and spatial evolution. Each pulsar is born in binary with a main sequence companion, and evolve to present time. The radio and $\gamma$-ray emission locations were modeled by the polar cap geometry and striped wind model, respectively. Our simulations seem to reproduce well the population of radio and $\gamma$-ray pulsars observed in the selected surveys. We also found that there should be less than $220$ unidentified pulsars in the Fourth Fermi-LAT catalogue of $\gamma$-ray sources (4FGL). High values of the viewing angle $\zeta$ seem to be needed to be able to observe the recycled pulsars, and it also seems difficult to observe recycled pulsars with an aligned rotation axis and magnetic axis (i.e., $\chi \leq 10${\deg}). We find that only a small fraction, approximately $\sim 7.6\times10^{-3}$ %, of oxygen-neon white dwarfs (ONeWDs) in binary systems appear to contribute to the population of mildly recycled pulsars through accretion-induced collapse.
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All authors Mattéo Sautron, Jérôme Pétri, Dipanjan Mitra, Adélie Dupuy–Junet, Marie-Eloïse Pietrin

Solar and Stellar Astrophysics

Glycolaldehyde and ethanol toward the L1157 outflow: resolved images and constraints on glycolaldehyde formation

Juliette Robuschi, Ana López-Sepulcre, Cecilia Ceccarelli et al. (+3 more)

Two main formation routes have been proposed for interstellar complex organic molecules (iCOMs): on dust grain surfaces and in the gas phase. Observing such molecules in protostellar outflow shock regions - provided that their ages are well-constrained - can help distinguish between these pathways by probing chemical evolution over time. This study focuses on the potential daughter-mother relationship of glycolaldehyde (CH$_2$OHCHO) and ethanol (C$_2$H$_5$OH), previously proposed in the literature. We test whether gas-phase reactions converting ethanol into glycolaldehyde derived in these works can explain the observed abundance of the latter in star-forming regions. We target the southern outflow of L1157, which hosts three shock regions, B0, B1 and B2, of increasing ages: about 900, 1500 and 2300 yr. We obtained high-resolution IRAM NOEMA maps of three lines of glycolaldehyde and one line of ethanol. We derived their abundances in the three shocks and used a pseudo time-dependent astrochemical model to simulate gas-phase and grain-surface formation scenarios for glycolaldehyde. Ethanol is assumed to form on grains and be released in the gas by shocks, where it is gradually converted into glycolaldehyde via the ethanol-tree reaction network. We present the first spatially resolved maps of glycolaldehyde and ethanol in the L1157 southern outflow, and more generally toward solar-like star forming regions. The abundance ratio [CH$_2$OHCHO]/[C$_2$H$_5$OH] increases from B1 to B2, consistent with model predictions. However, the model cannot reproduce all three shocked regions simultaneously, suggesting that one of the assumptions of our model, such as the same excitation temperature and grain composition in B0, B1 and B2, or gas temperature evolution, is wrong. Nonetheless, our modeling rules out the possibility that all the observed gaseous glycolaldehyde is a grain-surface product.
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All authors Juliette Robuschi, Ana López-Sepulcre, Cecilia Ceccarelli, Layal Chahine, Claudio Codella, Linda Podio

Astrophysics of Galaxies

Spectroscopic Follow-up of Young High-$\alpha$ Dwarf Star Candidates: Still Likely Genuinely Young

Yuxi Lu, Catherine Manea, Maryum Sayeed et al. (+9 more)

The question of whether genuinely young high-$\alpha$ stars exist has been discussed for over a decade since their discovery from asteroseismology of giant stars as it is challenging to break the degeneracy between the binary interaction and the genuinely young scenarios. Young high-$\alpha$ stars are hard to explain with traditional chemical evolution model as the high-$\alpha$ disk is typically associated with the early epoch of star formation in the Milky Way. Combined with recent advances of gyrochronology, and that $^7$Li can serve as an unambiguous indicator for identifying merger products in dwarfs thanks to its low burning temperature, we identified young high-$\alpha$ dwarf candidate stars through their fast rotation in a previous study. In this paper, we performed high-resolution spectroscopic follow-up of these candidates using Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI), and confirm 3 additional stars that are most likely genuinely young. Together with the star from the earlier paper, we find three out of four of them center around [Fe/H]=-0.5 dex, are ~5 Gyr old, and have a similar amount of elevated Li (~0.5 dex) and Al (~0.1 dex) compared to stars with matching $\log g$, $T_{\rm eff}$, Mg, and Fe within observational uncertainties, hinting at their common formation pathway.
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All authors Yuxi Lu, Catherine Manea, Maryum Sayeed, Stephanie T. Douglas, Madeleine McKenzie, Dominick Rowan, Ilya Ilyin, Adam Wheeler, Sven Buder, Louis Amard, Marc H. Pinsonneault, Jennifer A. Johnson

Cosmology and Nongalactic Astrophysics

High-redshift transverse BAO measurements with the SDSS quasar catalog

Felipe Avila, Armando Bernui, Miguel A. Sabogal et al. (+1 more)

Transverse Baryon Acoustic Oscillation (BAO) measurements offer a robust geometric probe of the Universe expansion, presenting minimal dependence on fiducial cosmological models. In this work, we analyze the SDSS-DR16 quasar catalog to search for the 2D BAO signal in the unexplored redshift interval $1.5 \leq z \leq 2.0$. Performing a fine tomographic analysis in 50 thin disjoint redshift shells ($\Delta z = 0.01$), to suppress line-of-sight projection smearing, and incorporating a full analytical covariance matrix, we detect the acoustic peak in two uncorrelated redshift shells: $\theta_{\rm BAO} = 1.911^{\circ} \pm 0.062^{\circ}$ and $\theta_{\rm BAO} = 1.727^{\circ} \pm 0.081^{\circ}$ centered at $z_{\rm eff} = 1.725$ and $z_{\rm eff} = 1.775$, with statistical significances of $3.4\,\sigma$ and $3.0\,\sigma$, respectively. By introducing a dimensionless shift parameter $\alpha$ in our empirical parameterization procedure, we then obtain two scaled angular diameter distances: $D_A/r_d = 11.00 \pm 0.36$ at $z_{\rm eff}=1.725$ and $D_A/r_d = 11.96 \pm 0.56$ at $z_{\rm eff}=1.775$. Incorporating these two novel data points into a literature compilation of 16 transverse BAO measurements, we perform a flat-$\Lambda$CDM parameter estimation, obtaining $\Omega_{m,0} = 0.41 \pm 0.06$ and $h r_d = 99.3 \pm 2.0$ Mpc. Our measurements successfully bridge a significant observational gap at high redshift, which remain highly consistent with the constraints reported by the Planck and DESI collaborations, demonstrating the potential of quasar tomographic surveys for dynamical dark energy studies.
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All authors Felipe Avila, Armando Bernui, Miguel A. Sabogal, Rafael C. Nunes

High Energy Astrophysical Phenomena

Simulating the LOcal Web (SLOW) – VI: Gamma-ray Emission in the Local Universe

Ludwig M. Böss, Ildar Khabibullin, Daniel Karner et al. (+4 more)

Context: Diffuse $\gamma$-ray emission from cosmic-ray (CR) protons scattering off the gas in the intracluster and intergalactic medium remains out of reach for current observations. Detecting this emission would provide constraints on the nonthermal pressure support by CR protons in these environments. Aims: We provide estimates for diffuse $\gamma$-ray emission in the Fermi-LAT band from galaxy clusters and the cosmic web in the local Universe. Methods: In this work, we show results from the first cosmological magnetohydrodynamic simulation with an on-the-fly spectral CR model. We modeled CR injection at shocks, accounted for adiabatic energy changes and advection of CR protons, and obtained their $\gamma$-ray emissivity directly from the simulated CR energy density and spectra. To do this, we used constrained initial conditions that evolved in a field closely resembling that of the local Universe, allowing a direct comparison to Fermi-LAT data on massive clusters. Results: We find CR proton acceleration at all structure formation and accretion shocks in galaxy clusters and cosmic web filaments. These protons provide the basis for diffuse $\gamma$-ray emission in these regimes. The absolute value of the diffuse $\gamma$-ray emission in our simulation lies a few orders of magnitude below the current upper limits found by Fermi-LAT. Under the assumption of our model, a sensitivity of $F_\gamma < 10^{-11} \: \gamma~ \text{s}^{-1}~\text{cm}^{-2}$ would be required for a detection of diffuse emission in Coma. This provides a lower limit for diffuse emission from CR protons accelerated at structure formation shocks.
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All authors Ludwig M. Böss, Ildar Khabibullin, Daniel Karner, Klaus Dolag, Ulrich P. Steinwandel, Elena Hernandez-Martinez, Jenny G. Sorce

Earth and Planetary Astrophysics

Molecular line emission from 1000 au scales outflows to <30 au compact structures in NGC1333 IRAS4A2

Osmar M. Guerra-Alvarado, N. van der Marel, P. Nazari et al. (+6 more)

Aims. Studying protostellar objects in their earliest stages, particularly during the Class 0 phase, provides key insight into the beginnings of planet formation and dust evolution. Disentangling the various components, however, is particularly challenging. High spatial and spectral resolution observations of molecular line emission with the Atacama Large Millimeter/submillimeter Array (ALMA) are therefore crucial for probing their complex environments. Methods. In this work, we present high-resolution ($\sim$30 au) ALMA observations at 1.3 millimeters of the Class 0 protostellar system IRAS4A2. Results. We detected large, well-traced outflows in HCN (3-2), H$_{2}$CO$(2_{1~2}-1_{1~1})$, and HCO$^{+}$ (3-2), along with numerous complex organic molecules (COMs) tracing central, more compact regions. Using moment maps, we analyzed the kinematics and spatial distributions of the molecular emission, revealing a wide range of spatial scales, from compact structures within the IRAS4A2 core at $\sim$8 au in radius, to extended $\sim$5000 au outflow emission. Specifically, we find that CH$_{3}$CDO and CH$_{3}$OCHO could be both good tracers of the disk, possibly tracing its rotation. Lines of OCS (22-21), SO$_{2}~(13_{3~11}-13_{2~12})$, HCN, H$_{2}$CO, and HCO$^{+}$, show more extended structures around IRAS4A2, likely tracing the envelope, disk, accretion shocks, the base of an outflow, and the outflow itself. Conclusions. Most COMs appear to trace distinct inner regions near the central protostar, while other molecules trace more extended structures, such as the envelope or outflows. The kinematics, emission patterns, and position-velocity diagrams suggest that individual molecules trace multiple components simultaneously, making it challenging to disentangle their true origins. Altogether, these findings highlight the complex spatial distribution within the IRAS4A2 system. Abridged.
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All authors Osmar M. Guerra-Alvarado, N. van der Marel, P. Nazari, J. Di Francesco, Ł. Tychoniec, L. W. Looney, E. G. Cox, D. J. Wilner, M. R. Hogerheijde

Solar and Stellar Astrophysics

Magnetic fields in planetary nebulae detected through non-thermal radio continuum emission

Marcin Hajduk, Timothy Shimwell, Glenn White et al. (+3 more)

Context. Planetary nebulae are shells ejected by low- and intermediate-mass stars. The slow wind ejected by the asymptotic giant branch star is compressed by a fast stellar wind to produce an expanding gaseous shell surrounding a hot bubble. The shell is a source of thermal radio emission which shows a spectral index between -0.1 and 2. Only two planetary nebulae are known to show non-thermal radio emission indicating magnetic fields and non-thermal electrons. Aims. The aim of this paper is verification of presence of magnetic fields of planetary nebulae. Magnetic fields can have a significant influence on shaping planetary nebulae. Methods. We observed a sample of northern planetary nebulae in radio continuum at 144 MHz with the Low Frequency Array. We combined our observations with archival observations at higher frequencies. Results. The spectral indices in 30 planetary nebulae were below -0.1, indicating non-thermal radio emission. The majority of this sample consists of bipolar planetary nebulae, which are known to originate from binary central stars. Most of the nebulae have sizes larger than 20 arcsec. Magnetic fields and nonthermal emission may be common in smaller planetary nebulae, but can be suppressed by thermal emission. Our results suggest that different mechanisms can be responsible for the origin of magnetic fields and non-thermal emission in planetary nebulae.
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All authors Marcin Hajduk, Timothy Shimwell, Glenn White, Marijke Haverkorn, Jesús A. Toalá, Ralf-Jürgen Dettmar

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Anisotropic Dark Matter Bosonic Stars in regularized 4D Einstein$-$Gauss$-$Bonnet gravity

Mohamamd Mazhari

In this work, we have constructed anisotropic bosonic dark-matter star (DMS) solutions in the context of a regularized four-dimensional Einstein$-$Gauss$-$Bonnet (4D EGB) gravity theory. Using dimensional regularization, we solve modified Tolman$-$Oppenheimer$-$Volkoff equations for a self-interacting complex scalar field in the dilute polytropic regime, $p_r = K \rho^2$, with anisotropy parameterized as $\sigma = \beta\, p_r \left( 1 - e^{-2\lambda} \right)$. We perform a comprehensive numerical analysis across the \((\alpha,\beta)\) parameter domain, where \(\alpha \in [0,8]~\mathrm{km}^2\) and \(\beta \in [-2,0]\), to examine mass$-$radius relations and evaluate multiple stability indicators including static equilibrium \(dM/dp_c\), sound-speed causality, the radial adiabatic index \(\Gamma_r\), and energy conditions. Positive Gauss$-$Bonnet coupling enhances both the maximum mass and compactness (e.g., \(M_{\rm max} \approx 1.62\, M_\odot\) at \(\alpha=0\) rising to \(\approx 2.09\, M_\odot\) at \(\alpha = 8~\mathrm{km}^2\)), while negative anisotropy reduces them (e.g., from \(\approx 2.21\, M_\odot\) at \(\beta=0\) to \(\approx 1.73\, M_\odot\) at \(\beta = -2\)). The resulting configurations remain statically stable up to the mass peak and satisfy physical criteria. This work extends previous isotropic boson-star analyses by systematically incorporating anisotropy within a regularized 4D EGB framework. These findings provide observationally relevant predictions for compact dark-matter objects under modified gravity.
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Solar and Stellar Astrophysics

The lack of fast rotators in Cyg OB2. I. Insights from spectral reclassification of its B0 population

D. Galán-Diéguez, S.R. Berlanas, A. Herrero et al. (+4 more)

Context. Cygnus OB2, in the Cygnus X complex – one of the most active star-forming regions of the Galaxy – hosts hundreds of O- and B-type stars at different evolutionary stages. This association provides a unique laboratory to study massive star evolution and dynamics. However, despite extensive studies, the absence of a fast-rotating group ($v\sin{i}>200\,\mathrm{km\,s^{-1}}$) among the O-type population of Cygnus OB2 challenges current models of massive star evolution. Aims. Stellar rotation strongly impacts spectral line shapes of O-type stars, and high rotation can potentially lead to misclassifications. We investigate whether some stars in Cygnus OB2, classified at low spectral resolution as B0, are actually rapidly rotating late-O types. Such cases could explain the observed lack of fast rotators in Cygnus OB2. Methods. Accounting for rotation, we reclassified the known B0 population in Cygnus OB2, using the MGB tool and both the new and pre-existing optical spectroscopy. Finally, we computed the projected rotational velocities using iacob-broad. Results. About $19\,\%$ of the initial B0 population in Cygnus OB2 are, in fact, late-O types. Only six stars in the entire dataset show $v\sin{i}>200\,\mathrm{km\,s^{-1}}$, with just one new O-type star exceeding this threshold. Conclusions. In our study of Cygnus OB2, we continue to find a notable lack of fast rotators among its O-type population. We propose a combination of three factors as the most likely explanation: (i) the young age of Cygnus OB2 may imply that fast rotators have not been produced yet due to binary interactions; (ii) fast rotators may have been dynamically ejected from the core as runaway stars; and (iii) local star formation conditions may hinder binary formation (reducing spin-up interactions) or result in slower rotational velocities at birth.
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All authors D. Galán-Diéguez, S.R. Berlanas, A. Herrero, M. Abdul-Masih, D.J. Lennon, C. Martínez-Sebastián, F.M. Pérez-Toledo

High Energy Astrophysical Phenomena

J-GEM near-infrared follow-up observations of the gravitational wave event S240422ed

Ichiro Takahashi, Tomoki Morokuma, Masaomi Tanaka et al. (+9 more)

We report our near-infrared (NIR) follow-up observations of the gravitational wave (GW) event S240422ed using the Subaru Telescope/MOIRCS. S240422ed was initially classified as a black hole-neutron star merger with $>$ 99% probability of electromagnetic wave emission. We started follow-up observations 7.8 hours after the event. Over two nights, we observed 206 nearby galaxies in $Y$ and $K_{\rm s}$ bands down to about 21.4 and 21.1 AB mag (3$\sigma$), respectively. The total completeness of our survey based on galaxy $B$-band luminosity is 22%. As a result of our observations, five candidate counterparts were identified. We show that properties of these five objects are not consistent with kilonova such as AT2017gfo. Four objects are consistent with known classes of transients such as supernovae or dwarf nova outbursts. On the other hand, the nature of the remaining one object, which shows a red color and rapid decline, remains unclear. Although later analyses of GW signal reclassified S240422ed as likely terrestrial noise, our NIR observations provide valuable lessons for future NIR surveys for GW sources. We demonstrate that deep NIR follow-up observations as presented in this work would effectively constrain the presence of red kilonova even at 200 Mpc distance. We also discuss the importance of deep and wide NIR reference images and of understanding the properties and frequency of Galactic transients.
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All authors Ichiro Takahashi, Tomoki Morokuma, Masaomi Tanaka, Mahito Sasada, Hiroshi Akitaya, Ichi Tanaka, Nozomu Tominaga, Michitoshi Yoshida, Yousuke Utsumi, Ryosuke Itoh, Kyohei Kawaguchi, the J-GEM collaboration

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

Antikaon condensation in magnetized neutron star matter within the framework of the $\sigma$-cut scheme

Fei Wu and Chen Wu

This study investigates the effects of strong magnetic fields on antikaon condensation in neutron star matter using the extended FSUGold model model. It is found that the presence of strong magnetic fields alters the threshold density of antikaon condensation significantly, which means the threshold density of antikaon condensation is shifted to higher density compared with the magnetic field-free case. In the presence of strong magnetic fields, the equation of state (EoS) becomes stiffer than that of the zero field case. The effects of the $\sigma$-cut scheme on the EoS are also researched when the appearance of antikaon condensation is occurred. Through careful choice of the parameter of the $\sigma$-cut scheme, we are able to produce a maximum mass neutron star heavier than 2$M_{sun}$.
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Earth and Planetary Astrophysics

Eruption column modelling of explosive volcanism on Venus

Maxence Lefèvre, Matteo Cerminara and Antonio Costa

Volcanism on Venus has never been directly observed, but several measurements indicate present-day activity. Volcanism could potentially play a role in climatic processes on Venus, especially in the sulfur cycle like on Earth. Observation of volcanic activity is the primary objective of future Venus spacecraft. However, there are many unknowns regarding its Venusian characteristics, like the condition at the vent, the volatile content and composition. Past modelling efforts have only studied explosive volcanic plume propagation over a limited range of flow parameters at the vent and in an idealised Venus atmospheric configuration. We propose to use the 1D FPLUME volcanic plume model in a realistic Venusian environment. In similar Venusian conditions, the height of the plume is consistent with past modelling. The present study shows that explosive volcanism would preferably reach 15 km of altitude. Under certain conditions, plumes are able to reach the VenSpec-H tropospheric altitude range of observations and even the 45 km cloud floor. For the first time, the impact of wind was quantified, and the super-rotating winds have a substantial impact by plume-bending of reducing the height of plumes. Contrary to the Earth, the atmospheric heat capacity depends greatly on temperature, and will disadvantage lower plumes and allow larger plumes to propagate at higher altitudes. The high latitude atmospheric environment, due to the thermal profile and weaker winds, is favorable to plumes reaching higher altitudes.
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Earth and Planetary Astrophysics

Definition and Realization of the International Lunar Reference Frame

Krzysztof Sośnica, Agnès Fienga, Dmitry Pavlov et al. (+2 more)

All future lunar missions require a definition of the lunar reference system and a realization in the form of the lunar reference frame to ensure consistent products for positioning, navigation, cartography, and timing. This paper defines the origin, orientation, and scale of the Lunar Reference System (LRS), as well as provides numerical solutions for the first realization of the International Lunar Reference Frame (ILRF). ILRF is defined as the Principal Axis (PA) system, attached to the surface and co-rotating with the Moon, with its origin in the lunar center of mass (lunocenter). The ILRF realization is based on variance component estimation of the three lunar ephemeris solutions: INPOP21a, DE430, and EPM2021 for the series of the position of the lunar center of mass and rotation Euler angles – precession, nutation, and proper rotation. The solution is valid starting with the period covered by Lunar Laser Ranging (LLR) data in 1970 and ending with extrapolated ILRF realizations in 2052 for future lunar missions. Results. The combined ILRF is characterized by the mean error of 17.6 cm for 2010-2030, where 15.3 cm comes from the origin and 8.6 cm from the orientation realization. The error in the realization of the origin is mainly caused by a poor geometry of the retroreflector network, resulting in a high correlation between the scale and the X component of the lunocenter in PA. The LLR post-fit residuals in ILRF are at the level of 2-3 cm in terms of the standard deviations of one-way ranges for best-performing LLR stations. The mean errors of the transformation between ILRF and other reference frame realizations in PA are at the level of 3 cm, whereas the mean transformation error to the DE421 Mean Earth frame equals 5 cm.
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All authors Krzysztof Sośnica, Agnès Fienga, Dmitry Pavlov, Nicolas Rambaux, Radosław Zajdel

Earth and Planetary Astrophysics

The effect of near-surface winds on surface temperature and dust transport on Venus

Maxence Lefèvre, Sébastien Lebonnois, Aymeric Spiga et al. (+1 more)

The knowledge of the Venus near-surface atmosphere is sparse. Few spacecrafts landed on the surface and measured winds with amplitudes below 1 m/s. The diurnal cycle of the wind amplitude and orientation is not known. Recent numerical simulations showed that slope winds along topographic structures could strongly impact the direction of winds. This study presents the first mesoscale modelling of such winds on Venus. A change of direction is occurring during the day in the main slopes, with upslope winds at noon due to solar heating and downslope winds at night. This is due to efficient IR cooling of the surface during the night, being colder than its surroundings slope atmospheric environment and leading to displacement of air. The temperature is impacted by the adiabatic cooling/warming induced by those winds. A strong heating effect is occurring for the downslope winds, leading to an anti-correlation between the surface temperature diurnal amplitude and the topography. This diurnal amplitude reaches 4 K in the plains and below 1 K in the mountains. The saltation of sediment by those winds was also quantified, with a higher probability at night along the slopes on the western flanks.
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All authors Maxence Lefèvre, Sébastien Lebonnois, Aymeric Spiga, François Forget

High Energy Astrophysical Phenomena

Disentangling two spectral components in the X-ray emission of the blazar 1ES 0229+200

Alicja Wierzcholska and Hubert Siejkowski

X-ray observations are essential to achieve a deeper understanding of the broadband emission mechanism in blazars. Here, we present a long-term spectral and temporal analysis of X-ray and optical observations of 1E 0229+200 collected with the Neil Gehrels Swift Observatory from 2008 to 2024, complemented by hard X-ray observations from the Nuclear Spectroscopic Telescope Array NuSTAR. The blazar 1ES 0229+200 is a high-frequency, peaked BL Lac object, known for its exceptionally hard very high-energy (VHE) $\gamma$-ray spectrum extending up to 10 TeV. In August 2021, NuSTAR observed the source in a low X-ray state, revealing a concave spectral shape with a distinct upturn around 25 keV. This feature contrasts with previous observations performed with NuSTAR and Swift-BAT, which showed no such spectral upturn. Previous observations of 1ES 0229+200 and broadband SED (spectral energy distribution) modelling suggest that its X-ray emission extends beyond 100 keV without a significant cutoff. The newly detected spectral upturn may indicate a transition between the synchrotron and inverse Compton components or could be linked to photohadronic processes involving high-energy neutrinos. We discuss the implications of this finding in the context of blazar spectral energy distributions, particularly the potential existence of a third SED bump in the kiloelectronvolt to megaelectronvolt range. The observed spectral features support the hypothesis that 1ES 0229+200 could be a source of high-energy neutrino emission.
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High Energy Astrophysical Phenomena

Strong gravitational-wave lensing posterior odds

Otto A. Hannuksela, K. Haris, Justin Janquart et al. (+4 more)

Like light, gravitational waves are gravitationally lensed by intervening massive astrophysical objects, such as galaxies, clusters, black holes, and stars, resulting in a variety of potentially observable gravitational-wave lensing signatures. Searches for gravitational-wave lensing by the LIGO-Virgo-KAGRA (LVK) collaboration have begun. One common method focuses on strong gravitational-wave lensing, which produces multiple "images": repeated copies of the same gravitational wave that differ only in amplitude, arrival time, and overall "Morse phase." The literature identifies two separate approaches to identifying such repeated gravitational-wave events based on frequentist and Bayesian approaches. Several works have discussed selection effects and identified challenges similar to the well-known "birthday problem", namely, the rapidly increasing likelihood of false alarms in an ever-growing catalogue of event pairs. Here, we discuss these problems, unify the different approaches in Bayesian language, and derive the posterior odds for strong lensing. In particular, the Bayes factor and prior odds are sensitive to the number of gravitational-wave events in the data, but the posterior odds are insensitive to it once strong lensing time delays are accounted for. We confirm the Lo et al. (2023) finding that selection effects enter the Bayes factor as an overall normalisation constant. However, this factor cancels out in the posterior odds and does not affect frequentist approaches to strong lensing detection.
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All authors Otto A. Hannuksela, K. Haris, Justin Janquart, Harsh Narola, Hemantakumar Phurailatpam, Jolien D. E. Creighton, Chris Van Den Broeck

Cosmology and Nongalactic Astrophysics

Exploring Ultra-Slow-Roll Inflation in Composite Pseudo-Nambu-Goldstone Boson Models: Implications for Primordial Black Holes and Gravitational Waves

Marco Merchand

We study inflation driven by a scalar potential arising from composite-sector dynamics, inspired by generalized composite Higgs models. The introduction of a non-minimal coupling, possessing the same functional form as the potential, induces a flattening at large field values that enables successful inflation. We analyze the conditions for ultra-slow-roll inflation, which leads to enhanced curvature perturbations, by combining analytical criteria near the inflection point with comprehensive numerical scans of the parameter space. The region consistent with Cosmic Microwave Background constraints and yielding approximately $N_e \approx 55\text{--}60$ e-folds also predicts primordial black holes with masses in the range $10^3\text{--}10^5\,\mathrm{g}$. Although such ultra-light primordial black holes are typically expected to have evaporated, recent proposals invoking evaporation suppression via memory-burden effects could allow their survival as viable dark matter candidates. Under this assumption, the predicted gravitational wave signal lies in a frequency range currently inaccessible to any existing or proposed detectors. Although no experimental proposals presently reach this frequency band, our results provide strong motivation to push the frontiers of gravitational wave detection towards these unexplored high-frequency regimes.
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High Energy Astrophysical Phenomena

Event types in H.E.S.S.: a combined analysis for different telescope types and energy ranges

Rodrigo Guedes Lang, Tim Unbehaun, Lars Mohrmann et al. (+3 more)

Imaging atmospheric Cherenkov telescopes (IACTs) are the main technique for detecting gamma rays with energies between tens of GeV and hundreds of TeV. Amongst them, the High Energy Stereoscopic System (H.E.S.S.) has pioneered the use of different telescope types to achieve an energy range as broad as possible. A large, 28 m diameter telescope is used in monoscopic mode to access the lowest energies ($E \gtrsim 30$ GeV), while the four smaller, 12 m diameter telescopes are used in stereoscopic mode to study energies between 150 GeV and 100 TeV. Nevertheless, a combination of both telescope types and trigger strategies has proven to be challenging. In this work, we propose for the first time an analysis based on event types capable of exploiting both telescope types, trigger strategies, and the whole energy range of the experiment. Due to the large differences between monoscopic and stereoscopic reconstructions, the types are defined based on Hillas parameters of individual events, resulting in three types (Type M, Type B, and Type A), each dominating over a different energy range. The performances of the new analysis configurations are compared to the standard configurations in the H.E.S.S. Analysis Package (HAP), Mono and Stereo. The proposed analysis provides optimal sensitivity over the whole energy range, in contrast to Mono and Stereo, which focus on smaller energy ranges. On top of that, improvements in sensitivity of 25-45% are found for most of the energy range. The analysis is validated using real data from the Crab Nebula, showing the application to data of an IACT analysis capable of combining significantly different telescope types with significantly different energy ranges. Larger energy coverage, lower energy threshold, smaller statistical uncertainty, and more robustness are observed. The need for a run-by-run correction for the observation conditions is also highlighted.
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All authors Rodrigo Guedes Lang, Tim Unbehaun, Lars Mohrmann, Simon Steinmassl, Jim Hinton, Stefan Funk

Solar and Stellar Astrophysics

Extending TESS flare frequency distributions with CHEOPS: Power-law versus lognormal

Julien Poyatos, Octavi Fors and José Maria Gómez Cama

Stellar flares are intense bursts of radiation caused by magnetic reconnection on active stars. They are especially frequent on M dwarfs, where they can significantly influence the habitability of orbiting planets. Flare frequency distributions (FFDs) are typically modelled as power laws. However, recent studies challenge this assumption and propose alternatives such as lognormal laws that imply different flare generation mechanisms and planetary impacts. This study investigates which statistical distribution best describes flare occurrences on M dwarfs, considering both equivalent duration (ED), directly measured from light-curve photometry, and bolometric energy, relevant for physical interpretation and habitability. We analysed 110 M dwarfs observed with TESS and CHEOPS, detecting 5620 flares. We decomposed complex events, corrected for detection biases in recovery rate and energy estimation, and scaled the FFDs to construct a combined distribution spanning six orders of magnitude in bolometric energy. We find that ED-based FFDs follow a power law, reflecting intrinsic photometric flare occurrence. However, bolometric-energy-based FFDs deviate from a pure power law. They are better described by a lognormal distribution, although the best fit is a truncated power law with a break at $1.8 \times 10^{35}$ erg. Using right-tail-stabilised Kolmogorov-Smirnov and exceedance tests, we attribute this deviation to limited sampling of the most energetic events. Our results show that the low-energy flattening, previously interpreted as lognormal behaviour, arises from observational biases and can be corrected through flare injection-recovery and combining observations with different sensitivities. Current instruments cannot reliably sample flares above $10^{35}$ erg, the most relevant for exoplanetary atmospheres. The upcoming PLATO mission will be able to investigate both regimes.
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High Energy Astrophysical Phenomena

Sensitivity of Nuclear Reaction Rates in X-ray Burst Models

I. Sultana, A. Estrade, B. S. Meyer et al. (+1 more)

Type I X-ray bursts (XRBs) are thermonuclear runaways on the surface of accreting neutron stars, powered by rapid proton-capture and alpha-capture processes on neutron-deficient nuclei. Uncertainties in the corresponding reaction rates remain a major limitation in modeling burst light curves and ashes. We present a systematic study of the sensitivity of XRB models to uncertainties in charged-particle-induced reaction rates across a broad parameter space of accretion rates and fuel compositions in low-mass X-ray binaries. The study proceeds in two stages: ignition conditions are first determined with a semi-analytic framework coupled to a full reaction network, followed by a sensitivity analysis using the ONEZONE model with individual rate variations. We identify 41 reactions that alter the burst light curve and 187 that significantly impact final abundances. Reactions on bottleneck isotopes in the alpha-p- and rp-process paths strongly affect both observables, while most (p, gamma) reactions on medium-mass (A > 32) and heavy-mass (A > 55) nuclei influence only the final composition. Medium-mass cases dominate in He-rich bursts, where the reaction flow terminates earlier, while heavy-mass cases appear in mixed H and He bursts with extended rp-process paths reaching A ~ 110. We identify a subset of reactions whose rate uncertainties exert influence on the final 12C yield in helium-rich bursts, which could have important consequences for the mechanism of ignition of carbon superbursts. Our results identify key targets for nuclear reaction experiments to reduce nuclear physics uncertainties in XRB models.
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All authors I. Sultana, A. Estrade, B. S. Meyer, H. Schatz

Solar and Stellar Astrophysics

A family of binaries with an extreme mass ratio

Yael Naze, Gregor Rauw, Piotr A. Kolaczek-Szymanski et al. (+2 more)

Multiplicity is ubiquitous among massive stars. While the stellar components usually display similar masses, some binaries with extremely low mass ratios were also observed. Some of them are primordial, while others arise from binary interactions. The identification of systems with extreme mass ratios brings valuable information, notably on the origin of fast rotation in massive stars. We identify new short-period systems with extreme mass ratios through the detection of eclipses and reflection effects. The physical properties of a dozen newly identified cases were precisely evaluated through high-quality photometry and spectroscopy. In addition to characterizing these binaries, we found a clear signature of apsidal motion in one system, and three other systems display long-term shifts in eclipse times. All systems we reported here are composed of a massive star and a cool low-mass companion. They are therefore primordial cases. This doubles the known number of these systems in the Galaxy. In this context, it is important to note that most massive stars in these systems, as well as in previous systems reported in the literature, rotate fast (supersynchronous compared to the orbital motion). The high incidence of fast rotation in these nascent binaries provides strong constraints for star formation models.
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All authors Yael Naze, Gregor Rauw, Piotr A. Kolaczek-Szymanski, Nikolay Britavskiy, Jonathan Labadie-Bartz