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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 28 September

Earth and Planetary Astrophysics

Planets Around Solar Twins/Analogs (PASTA) III: Chemical Clock Relations in Planet-Hosting Solar Analogs

Qinghui Sun, Serat M. Saad, Yuan-Sen Ting et al. (+10 more)

Context. Abundance ratios between elements synthesized on different nucleosynthetic timescales provide empirical chemical clocks for estimating stellar ages, but robust calibrations require homogeneous samples with precise stellar parameters and elemental abundances. Aims. We aim to investigate whether the presence of planets modifies empirical chemical clock relations. Methods. We present high-precision stellar parameters and elemental abundances for 52 new planet-hosting targets observed with Keck/HIRES, LBT/PEPSI, and Subaru/HDS. Combined with PASTA I and II, the full sample comprises 94 stars, of which 81 are identified as planet-hosting solar twins and analogs, and is used to characterize Galactic chemical evolution and derive empirical chemical clock relations. Results. We recover the expected Galactic chemical evolution trends, with $\alpha$-elements such as Mg and S increasing with stellar age, while s-process elements such as Y, Ba, and Sr show negative age correlations. In contrast, Fe-peak elements and the r-process element Eu show little or no significant age dependence. These trends give rise to tight chemical clock relations based on [Y/Mg], [Y/Al], [Ba/Mg], [Ba/Al], and [Sr/Mg], with [Y/Mg] and [Y/Al] providing the strongest correlations. [Ba/Al] shows the steepest age dependence, and the Ba-based ratios are generally more sensitive to age than their Y-based counterparts. Conclusions. Planet-hosting solar analogs follow chemical-clock relations consistent with those of nearby solar twins, with no evidence for a significant planet-related effect. The derived relations are primarily applicable to local solar twins and analogs in the Galactic thin disk.
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All authors Qinghui Sun, Serat M. Saad, Yuan-Sen Ting, Jiayue Zhang, Chenyang Ji, Fei Dai, Sharon Xuesong Wang, Bryant Randolph, Yunzhe Gu, Ilya Ilyin, Yaguang Li, Jie Yu, Fan Liu

High Energy Astrophysical Phenomena

Gravitational Waves from Core-Collapse Supernovae: Dependence on the Progenitor Star, Rotation Rate and Nuclear Equation of State

Jade Powell, Bailey Sykes and Bernhard Müller

We simulate 137 axisymmetric core-collapse supernova explosions to systematically investigate the impact of different progenitor properties, rotation rates, and equations of state on the supernova gravitational-wave emission. We use 15 different progenitor stars, with masses ranging from $9.71\,\mathrm{M}_{\odot}$ to $36.61\,\mathrm{M}_{\odot}$, three equations of state, and three rotation rates, with durations extending up to 5.5\,s after bounce. We find substantial differences in the gravitational-wave emission between equations of state, with the CMF equation of state producing lower gravitational-wave amplitudes and a longer low frequency mode due to the standing accretion shock instability that remains visible even at $\sim5$\,s post bounce. Rapid rotation also significantly alters the gravitational-wave signal, with more visible modes in the gravitational-wave emission, and lower energies due to later shock revival times. We include the gravitational-wave emission due to neutrino memory, and show it can significantly improve the detectability of core-collapse supernovae for observatories with improved low frequency sensitivity. We propose a recalibration of universal relations for the high frequency mode, using fits to our waveforms, that reduces the fit error at late times in the gravitational-wave signal. Finally, we investigate, for the first time, the impact of random seed perturbations on the gravitational-wave emission. We find that stochastic perturbations can produce dramatic variations in gravitational-wave amplitude, and can alter the signal-to-noise ratio of a detection by as much as 62% for models close to the boundary between failed and successful shock revival.
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Solar and Stellar Astrophysics

Numerical analysis of electron density and response time delay during solar flares in mid-latitudinal lower ionosphere

Sayak Chakraborty and Tamal Basak

Impacts of solar flare vary at different parts of the lower ionosphere depending on its proximity to the direct exposure of incoming solar radiation. The quantitative analysis of this phenomenon can be attributed to the solar zenith angle (chi(t)) profile over the ionosphere. We numerically solve the electron continuity equation to obtain the lower ionospheric electron density profile (Ne(t)). The electron production rate (q(t)) is governed by the (i) X-ray profile (phi(t)) of the flare, (ii) chi(t)-values during the flare occurrence, etc. For analyzing the X-ray profile during flares, we use the GOES-15 satellite observations. Since we are working on an electron continuity equation based simplified ionospheric model, we confined our analysis to the comparatively stable mid-latitude ionosphere only. We choose three flares each from C, M, and X-classes for Ne(t)-profile computation. We observe that temporal Ne(t)-profiles differ when computed for the lower ionosphere over different discrete latitudes. Further, we compute the spatial Ne(t)-profile across the mid-latitude region at the time when phi(t) = phi_max. Now we assume that these flares repeat themselves every day of a year (DoY) at the same time of a day and we compute Ne(t)-profiles for each day. We found a seasonal effect on the Ne(t)-profile due to solar flare. Further, we investigate the response time delay (Delta t) of the lower ionosphere, which is the time difference between incidence of X-ray and the respective change in Ne(t)-profiles during solar flares. Strong seasonal effects on Ne(t)-profile and Delta t are the unique results of this work.
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Astrophysics of Galaxies

R Coronae Borealis fadings: a dusty gas cloud eclipse model

Mark A. Walker, Artem V. Tuntsov and Arthur G. Suvorov

R Coronae Borealis stars (RCBs) are hydrogen-deficient supergiants that undergo deep fading events due to transient extinction by dust. First observed over two centuries ago, that behaviour remains poorly understood. Our aim is to investigate the possibility that the fading events are eclipses by orbiting, dusty gas clouds. We construct a simple physical model of the dust wind that is driven from the cloud surface by the stellar radiation field, and we calculate the extinction and scattered light from wind and cloud. We consider a broad range of dust compositions. For the model that best matches the data, we sketch out implications for the RCB phenomenon more broadly. Our calculations show that conventional dust materials like graphite and silicate produce eclipses whose ingress is too slow and whose morphology too symmetric to account for RCB fadings. But dust made of solid H2 yields a good match: the eclipses are deep and strongly asymmetric, with rapid onset and slow recovery, and event timescales are about right if the clouds' periastra are within a few tens of AU. Such close approaches imply tidal stripping/disruption of each cloud, with hydrogen-deficient debris accreting onto the star via a disk. Starlight incident on the disk creates a metal-ion plasma that emits a powerful bremsstrahlung continuum, peaking in the mid-IR. We conclude that eclipses by orbiting, dusty clouds could be the cause of RCB fading events, but only if the dust is made of solid H2, in which case both the unusual, hydrogen-deficient nature of the stars and their mid-IR excess follow naturally. It is, however, challenging to account for the high eclipse rates that are observed; we propose a scenario in which the progenitor star is a wide binary inside a massive halo of clouds, suggesting a connection to the Galactic "missing mass" problem.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Medium effects on neutron star modified and direct Urca cooling rates

B. X. Zhou, Jin-Biao Wei, Z. H. Li et al. (+2 more)

We study the effects of in-medium modification of the elementary cooling processes on observable properties of isolated neutron stars. We then deduce the neutron star mass distributions compatible with the cooling analysis and compare with current theoretical models. We conclude that current cooling data require fast direct Urca (DU) cooling, moderated by proton superfluidity, to be active in most neutron stars, and that the DU onset threshold must lie below canonical masses. In that case medium modifications of modified Urca (MU) rates are practically insignificant, but the $nn$ Bremsstrahlung rate plays a dominant role.
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All authors B. X. Zhou, Jin-Biao Wei, Z. H. Li, G. F. Burgio, H.-J. Schulze

Astrophysics of Galaxies

Toward Resolution Convergence for Star Formation and Galactic Winds in Galaxy Simulations

Xue-Fu Li, Weishan Zhu, Tian-Rui Wang et al. (+2 more)

The predictive power of hydrodynamic simulations of galaxies is often hampered by the resolution dependence of sub-grid models for star formation (SF) and stellar feedback. We present three-dimensional hydrodynamic simulations of an M82-like low-mass starburst galaxy at resolutions of 4, 8, 16, 32 pc and develop optimized sub-grid prescriptions to mitigate these numerical inconsistencies. For star formation, we adopt a $\sim20$ pc physical-scale control volume, corresponding to the typical size of giant molecular clouds (GMCs), for gas accretion onto sink particles, reducing its dependence on numerical resolution. We further incorporate an empirical, resolution- and density-dependent star formation scheme that accounts for variations in gas surface density across spatial scales, as suggested by observations. Furthermore, we refine the supernova feedback coupling by anchoring the injection volume to the physical cooling radius of the supernova remnant ($R_{\rm cool}$) and utilizing a resolution-dependent thermal-to-kinetic energy partition. These improvements substantially enhance convergence across 4 to 32 pc: variations in the total stellar mass formed and kinetic energy are reduced to $\sim20\%$, while relative errors in the cool-phase mass outflow rate and integrated X-ray luminosity decrease to below $\sim40\%$. The warm and hot outflow phases remain less well converged, with variations of $\sim50\%$ and $\sim75\%$, respectively. The upgraded model also improves the convergence of normalized wind properties, with relative errors below $\sim50\%$, $\sim80\%$, and $\sim20\%$ for the time-averaged mass loading factor, energy loading factor, and X-ray emission efficiency, respectively. Our results provide a practical framework for achieving more robust simulations of starburst galaxies.
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All authors Xue-Fu Li, Weishan Zhu, Tian-Rui Wang, Huan Chen, Long-Long Feng

Astrophysics of Galaxies

A Study on the Evolution of NGC6822. I. Investigating the Star Formation History through Evolved Stellar Populations

Fatemeh Khatamsaz, Mahdi Abdollahi, Atefeh Javadi et al. (+4 more)

NGC6822 is an isolated dwarf irregular galaxy in the Local Group at a distance of $\sim$ 490 kpc . In this paper, we derived the star formation history (SFH) of NGC6822 employing a method based on evolved asymptotic giant branch (AGB) stars, known as long-period variable (LPV) stars. We utilized a dataset of 329 LPVs in JHK$_s$ bands to estimate the star formation rate (SFR) over time and reconstructed the SFH of the galaxy. In addition to obtaining the SFH assuming constant metallicity values within the range of 0.0001 $<$ Z $<$ 0.012, we also adopted three distinct age-metallicity relations (AMRs) to account for variations in the chemical content of the galaxy throughout its lifetime. The SFH has been investigated in two regions. The bar region encloses a central area of 189 arcmin$^{2}$, and the outer region encircles a field beyond the bar region, extending to the radial distance of 3 kpc. In the bar region, we identified three episodes of star formation peaking at $t \sim$ 4.7 Gyr (log $t = 9.67$), $t \sim$ 1.6 Gyr (log $t = 9.21$), and $t \sim$ 48 Myr (log $t = 7.63$), where $t$ is the look-back time. In the outer region, we found one episode of star formation occurring at $t \sim$ 4.6 Gyr. The significant peak observed $\sim$ 4-5 Gyr ago further supports the hypothesis suggested by the previous research, indicating that NGC6822 passed through the virial radius of the Milky Way in the past.
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All authors Fatemeh Khatamsaz, Mahdi Abdollahi, Atefeh Javadi, Hamidreza Mahani, Jacco Th. van Loon, Hedieh Abdollahi, Sepideh Ghaziasgar

Astrophysics of Galaxies

Improving Lens Modelling from Ground-Based Imaging with Deconvolution

Eric Paic, Kenneth C. Wong, Anupreeta More et al. (+1 more)

Accurate and precise mass modelling of strong lensing systems is essential for extracting insights into cosmology, galaxy environments, and the nature of dark matter. The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP), which has mapped $\sim$1000 square degrees of the sky, discovered over 1000 definite or probable galaxy-scale gravitational lens candidates. As the resolution of ground-based imaging poses challenges for accurate lens modelling, high-resolution imaging is traditionally sought after for detailed analyses of these systems. In this work, we instead propose applying the STARRED algorithm, which leverages starlet wavelet regularisation, as a preprocessing step before lens modelling to maximise the scientific output of the large HSC-SSP sample. We test this approach on seven HSC-like mock lensing systems with different lensing configurations. Our results show that the resolution boost from $\sim$0.6" to $\sim$0.15" enables improved accuracy and sub-3% precision measurements of key lensing parameters such as the Einstein radius and the mass axis ratio for ground-based images. These results pave the way for accurate measurements of key strong lensing quantities from a large sample of ground-based observations.
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All authors Eric Paic, Kenneth C. Wong, Anupreeta More, Anton T. Jaelani

Cosmology and Nongalactic Astrophysics

Reconstructing the evolution of deceleration parameter with the Lagrange interpolation method

Kaituo Zhang, Bing Xu, Hongwei Yu et al. (+1 more)

In this paper, we reconstruct the evolution of the deceleration parameter using cubic and quartic Lagrange interpolation methods, based on the latest observational data. This data includes baryon acoustic oscillation (BAO) measurements from DESI, cosmic microwave background (CMB) distance priors from Planck 2018, and three datasets of type Ia supernovae (SNe Ia): DES-Dovekie, Pantheon+, and Union3. To mitigate the impact of the nonuniform distribution of data in redshift, we carry out the reconstruction not only in the standard redshift $z$ but also in the $y$-redshift $y\equiv z/(1+z)$ and the log-redshift $\zeta\equiv\ln(1+z)$. The cubic and quartic reconstructions of $q(z)$ from the DESI BAO+CMB+SNe Ia datasets indicate a clear deviation from the $\Lambda$CDM model at low redshift ($z<0.3$), supporting a weaker present-day cosmic acceleration than the predictions of the $\Lambda$CDM model. The reconstructed $q(z)$ exhibits an overall oscillatory pattern around the $\Lambda$CDM model throughout its evolution. Only the cubic-$y$ and cubic-$\zeta$ reconstructions with the DESI BAO+CMB+Union3 data provide evidence that the cosmic acceleration appears to have already reached its maximum value and is beginning to slow down. However, when incorporating the measurement of the Hubble constant $H_0$ from the Supernovae and $H_0$ for the Equation of State (SH0ES) Collaboration, the evolution of $q(z)$ from cubic reconstructions shifts toward the $\Lambda$CDM prediction. Regardless of the presence or absence of the $H_0$ prior, all reconstructions imply that the deceleration-acceleration transition occurred earlier than predicted by the $\Lambda$CDM model. Nevertheless, the Bayesian evidence still favors $\Lambda$CDM, while the frequentist analysis indicates a $>2\sigma$ preference for the Lagrange-interpolation reconstructions, hinting at the existence of dynamical dark energy.
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All authors Kaituo Zhang, Bing Xu, Hongwei Yu, Puxun Wu

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Freeze-in of anapole and charge-radius inelastic dark matter: X-ray probes of a decoupled vector portal

Krzysztof Jodłowski and Chih-Ting Lu

We study freeze-in production and experimental probes of inelastic dark matter (iDM) coupled to the Standard Model through dimension-6 transition anapole and charge-radius operators. These interactions arise upon integrating out the heavy dark photon of a broken $U(1)_D$ vector portal. We focus on mass splittings below the dielectron threshold, where the excited-state decay is cosmologically long-lived and decays predominantly through $\chi_1\to\chi_0+3\gamma$, producing a distinctive keV–MeV photon spectrum. We calculate the decay rate and photon spectrum analytically in the Euler–Heisenberg limit and evaluate finite-electron-mass corrections using the full one-loop amplitude. We then combine X-ray limits with freeze-in relic density targets and complementary direct detection (DD) and accelerator constraints. The surviving $\chi_1$ population also leads to exothermic downscattering signatures at DD experiments, including the possibility of explaining the LZ signal, while the three-photon decay is constrained by X-ray data. At $\Delta=900\,\mathrm{keV}$, INTEGRAL/SPI probes the Boltzmann-suppressed high-mass branches of the freeze-in targets, whereas the NuSTAR limits at $\Delta=100\,\mathrm{keV}$ are substantially weaker because of the steep splitting dependence of the decay width. Our results demonstrate the potential of X-ray observations as a probe of freeze-in through a decoupled vector portal and of the reheating temperature governing the iDM production.
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Astrophysics of Galaxies

Trigonometric Parallaxes of Maser Sources toward the Far Side of the Milky Way

Z. H. Lin, Y. Xu, M. Reid et al. (+2 more)

We present trigonometric parallaxes and proper motions for eight maser sources associated with high-mass star-forming regions. Four 22 GHz H$_2$O masers and four 6.7 GHz CH$_3$OH masers were observed over eight epochs between 2024 and 2025. Combining parallax, proper-motion, and radial-velocity information, we determine distances and spiral-arm assignments for these sources. The newly measured far-side masers extend the known distributions of the Sagittarius and Perseus arms toward Galactic longitudes as small as $\ell\sim10^\circ$. Their locations and kinematics agree well with recently updated spiral-arm models based on maser astrometry. In particular, the new measurements show that the far-side Sagittarius and Perseus arms tend to converge toward a common spiral feature in the inner Galaxy. This configuration is consistent with the bifurcation scenario proposed for the Milky Way spiral structure, although an unresolved inter-arm structure provides an alternative interpretation that cannot yet be excluded.
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All authors Z. H. Lin, Y. Xu, M. Reid, J. J. Li, S. B. Bian

Astrophysics of Galaxies

Large-Scale Spiral Structure of the Milky Way Traced by Young Classical Cepheids

Z. H. Lin, C. J. Hao, D. J. Liu et al. (+5 more)

Using 985 classical Cepheids younger than 100 Myr, we investigate the large-scale spiral structure of the Milky Way by comparing their spatial and kinematic distributions with the R19 (four-arm) and X23 (multiple-arm) spiral-arm models. Both models provide reasonably good descriptions of the current sample: R19 yields slightly smaller point-to-arm distances, whereas X23 has a higher supported-arm fraction, but the descriptive statistics do not provide a decisive preference between them. Model-dependent arm assignment and refitting suggest that the distribution of the youngest Classical Cepheids (20–60 Myr) is consistent with an X23-like multiple-arm in which the Perseus and Norma arms form two dominant inner arms extending toward the ends of the Galactic bar, the Sagittarius and Centaurus segments are possible branches of these inner arms, and Local, Outer, and other features constitute additional arm segments. The updated model improves the constraints on the southern spiral structure, yielding smaller point-to-arm distances and a higher supported-arm fraction. Some of these structures extend to heliocentric distances of approximately 15~kpc.
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All authors Z. H. Lin, C. J. Hao, D. J. Liu, Y. J. Li, J. J. Li, Y. W. Dong, Y. X. He, Jarken Esimbek

Astrophysics of Galaxies

Morphological Statistic of Milky Way-like Galaxies

Zehao Lin, Junye Wei, Ye Xu et al. (+5 more)

We analyze the spiral morphology of 1,738 nearby galaxies with similar Hubble type of the Milky Way ($i<60^\circ$, $z<0.048$) using multi-band optical images from the Sloan Digital Sky Survey and Digitized Sky Survey. Multiple-arm systems dominate, comprising $\sim$50-60% of the sample and $\sim$75% of large galaxies ($d_{\rm max} \geqslant 18~\mathrm{kpc}$). In $90\pm3$% of multiple-arm galaxies, two inner arms extend into multiple outer arms; three-arm inner structures occur in $9\pm2$%, and four or more are rare ($<1$%). Morphology and inner-arm counts are consistent across bands at $\sim$80%. Bifurcation points, marking the transition from two inner arms to multiple outer arms, occur in up to $\sim$40% of galaxies, are more prominent in bluer bands tracing younger stellar populations, and cluster within 4-7~kpc of galaxy centers. These statistics suggest that the Milky Way's inner two-arm and outer multiple-arm morphology, including bifurcations at similar radii, is broadly consistent with that of a typical multiple-arm spiral galaxy.
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All authors Zehao Lin, Junye Wei, Ye Xu, Yingjie Li, Chaojie Hao, Dejian Liu, Yiwei Dong, Zhen-yu Wu

High Energy Astrophysical Phenomena

Comment on "Fermi-LAT Galactic Center Excess Morphology of Dark Matter in Simulations of the Milky Way Galaxy"

Kevork N. Abazajian, Jason Kumar and Oscar Macias

Muru et al. [Phys. Rev. Lett. 135, 161005 (2025)] conclude from the HESTIA constrained simulations that the $\gamma$-ray morphologies of the Galactic Center Excess predicted by dark matter annihilation and by an old stellar population are essentially indistinguishable. Their "quadratic dark matter" maps, however, show the square of the mass projected along the line of sight, $\bigl[\int\rho\,s^{2}\,ds\bigr]^{2}$, rather than the annihilation integral $\int\rho^{2}\,ds$. Squaring a nonnegative map preserves its isophote shapes at corresponding intensity levels, as confirmed by the reported contour axis ratios. The corrected calculation on the same simulations does not support their conclusion.
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Astrophysics of Galaxies

PEGASUS (Pfs Emission-line GAlaxy SUrvey with Subaru): II. Metal Poor AGNs in High Equivalent-Width Narrow-Band Emitters

Hisakazu Uchiyama, Tohru Nagao, Mariko Kubo et al. (+19 more)

We present Subaru 'Ōnohi'ula Prime Focus Spectrograph (PFS) optical–NIR spectroscopic follow-up of high-equivalent-width (EW) narrow-band (NB) emission-line galaxies selected from Hyper Suprime-Cam Subaru Strategic Program, to assess whether high-EW sources preferentially host low-metallicity AGNs. PFS spectroscopy yielded secure identifications for 583 targets, including 581 sources with reliable PFS redshift solutions and two manually identified $z\sim4$ interlopers. We construct BPT diagnostics for the 70 objects with significant detections in all four BPT lines. Among them, $\sim34\%$ are located in the AGN region of the BPT diagram, suggesting that AGNs constitute a significant fraction of the sample. A non-negligible fraction does not populate the classical AGN branch; instead, it lies in the intermediate “valley” between the star-forming and AGN sequences. Comparison to Cloudy models suggests that the valley population is consistent with sub-solar metallicities. Three He II/[Ne V]-detected sources are also found in the star-forming region of the BPT diagram and extend to lower-metallicity solutions, consistent with $Z/Z_{\odot}\approx0.25-0.5$ ($12+\log({\rm O/H})\approx8.1-8.4$). One object shows a clear broad H$\alpha$ component; a multi-component fit yields $M_{\rm BH}\approx8.8\times10^{6} M_{\odot}$ and $\lambda_{\rm Edd}\approx0.035$, consistent with near-solar narrow-line region metallicity. The fraction of point-like sources in the parent target sample ($22\%\pm2\%$) is intermediate between those of star-forming galaxies ($12\%\pm5\%$) and AGN ($33\%\pm10\%$), consistent with a contribution from compact components. Stacked [O III] line profiles show no clear evidence for strong outflows. Our findings suggest that high-EW NB selection efficiently identifies candidates for metal-poor AGNs.
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All authors Hisakazu Uchiyama, Tohru Nagao, Mariko Kubo, Tadayuki Kodama, Rhythm Shimakawa, Akio Inoue, Masayuki Tanaka, Jialai Wang, Ronaldo Laishram, Yuma Sugahara, Masato Onodera, Kazuki Daikuhara, Ko Ishida, Ryo Albert Sutanto, Haruka Kusakabe, Yoshiki Matsuoka, Alberto Rodriguez-Ardila, Yuta Suzuki, Yoshiki Toba, Xinfeng Xu, Yongquan Xue, Yongming Liang

Earth and Planetary Astrophysics

A JWST Study of Stardust. II. Polycyclic Aromatic Hydrocarbons in Comet 81P/Wild 2 and Implications for Primitive Solar System Carbon

Nathan X. Roth, Stefanie N. Milam, Diane H. Wooden et al. (+11 more)

We report observations of comet 81P/Wild 2, target of the Stardust sample return mission, on UT 2023 March 20 and 24 at a heliocentric distance ($r_H$) of 1.85 au using the NIRSpec and MIRI integral field unit spectrographs on board the James Webb Space Telescope (JWST). This study is the first compositional comparison between JWST remote-sensing spectroscopy of a solar system object against terrestrial analysis of its returned samples. Recent work determined contributions of molecular emission from coma volatiles and thermal emission from the nucleus and coma dust grains to these spectra. Subtracting the molecular and thermal emission models produces a residual spectrum with a clear resonance near 3.37 $\mu$m and multiple others spanning the $6 - 12$ $\mu$m region. Analysis of these residuals provides strong evidence for the presence of polycyclic aromatic hydrocarbons (PAHs) in the coma of 81P/Wild 2. The resulting PAH populations reflect material incorporated into the nucleus of 81P/Wild 2 that was inherited from the diffuse interstellar medium, the interstellar medium, and the protoplanetary disk. The PAHs sensed by JWST are compared to those detected in laboratory analyses of the Stardust mission returned samples.
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All authors Nathan X. Roth, Stefanie N. Milam, Diane H. Wooden, Els Peeters, Charles E. Woodward, Dominique Bockelee-Morvan, Michael S. P. Kelley, Steven B. Charnley, Simon J. Clemett, Martin A. Cordiner, Perry A. Gerakines, David E. Harker, Ella Sciamma-O'Brien, Geronimo L. Villanueva

Earth and Planetary Astrophysics

Dynamical Impacts of Accretion Streamers on Protoplanetary Disks

Han-Gyeol Yun, Jeong-Eun Lee, Jaehan Bae et al. (+1 more)

Recent observations suggest that accretion streamers are common in protoplanetary disks, yet their dynamical impact on disk evolution remains poorly understood. Using three-dimensional hydrodynamic simulations with mass infall rates of $10^{-8}$–$10^{-6} \ M_{\odot}\ \mathrm{yr}^{-1}$, we investigate how streamer accretion influences the structure and evolution of protoplanetary disks. We find that a prograde streamer can excite disk eccentricity globally to values as high as $\sim0.4$. The resulting eccentric disk develops prominent spiral arms and crescent-shaped overdensities whose spatial structures agree remarkably well with analytic eccentric-disk theory. It also undergoes significant warping, and exhibits enhanced and variable stellar accretion. In contrast, retrograde streamer accretion efficiently removes disk angular momentum, producing a compact disk and, in extreme cases, triggering disk breaking. Using synthetic ALMA molecular-line observations, we show that streamer-driven perturbations generate observable kinematic signatures, including Doppler flips in moment maps and wiggles in position–velocity diagrams. Remarkably, these signatures can persist for up to $100\ \mathrm{kyr}$ after infall has ceased, suggesting that some kinematic disturbances observed in disks without currently detected streamers may be relics of past infall events. Finally, we discuss the implications of streamer-driven disk evolution for planet formation and planet–disk interactions.
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All authors Han-Gyeol Yun, Jeong-Eun Lee, Jaehan Bae, Woong-Tae Kim

High Energy Astrophysical Phenomena

Discovery of a 62-min long-period transient with near-orthogonal rotator geometry

Scott D. Hyman, Natasha Hurley-Walker, Dale A. Frail et al. (+2 more)

We report the serendipitous discovery of J155543.7$-$563102 (hereafter LPT J1555$-$5631) with a period of 62.2 min in MeerKAT and ASKAP survey data. The source emitted bright (10-30 mJy), steep-spectrum ($\alpha\sim-1.5$), highly polarized radio pulses during a 15-hr active window in May 2022, with no other quiescent or pulsed emission detected before or after over $\sim5$ years. The mean light curve exhibits two alternating pulses per cycle. A main pulse (MP) and an interpulse (IP) separated by $\Delta\phi=165.4^\circ$ with similar amplitudes, but different polarization properties: the wider MP (3.9%) is partially linearly and circularly polarized and shows a constant polarization position angle, while the narrow IP (1.1%) is $\sim$100% circularly polarized. We classify LPT J1555$-$5631 as a near-orthogonal rotator, for which emission from both magnetic poles is visible during one rotation and the magnetic and rotation axes are almost perpendicular. The 14.6$^\circ$ deviation from an antipodal separation and the nearly constant polarization position angle suggest that the emission does not arise from the standard dipolar polar-cap geometry of ordinary pulsars, but instead originates within a broader, more complex magnetosphere. The observed properties of LPT J1555$-$5631 can be accommodated by extended emission regions, and favor coherent emission mechanisms such as the electron cyclotron maser instability, although they do not uniquely determine the progenitor or emission physics. If these inferences apply more broadly to the LPT population, they could account for why their beam widths are decoupled from rotation periods, the prevalence of flat polarization position angles, and may favor an elevated incidence of orthogonal rotators.
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All authors Scott D. Hyman, Natasha Hurley-Walker, Dale A. Frail, Emil Polisensky, W. D. Cotton

Sunday 27 September

Earth and Planetary Astrophysics · Cross-listed from physics.space-ph

An autonomous approach to model daytime behavior of sub-ionospheric VLF signals over short and medium propagation paths in India

Sayak Chakraborty, Tamal Basak, Sourav Palit et al. (+1 more)

We present an autonomous model to simulate the daytime variation of sub-ionospheric Very Low Frequency (VLF) signal amplitude, beginning with the computation of the D-region electron density by numerically solving the electron continuity equation (ECE). From the resulting altitude-dependent electron density profile (Ne), we extract Wait's ionospheric parameters (h' and beta) using a log-linear fitting method. The study focuses on two VLF propagation paths (one short and one medium in length) in India, originating from the VTX (18.2 kHz) transmitter. The model employs the Long Wave Propagation Capability (LWPC) framework to reproduce the daytime VLF signal amplitude profile. It accurately captures the daytime variations observed at the Bengaluru (BAN) station, where the ground-wave component is dominant, as well as at Khukurdaha, WB (KHK). A quantitative comparison between the simulated (Asim) and observed (Aobs) amplitudes shows good agreement, supporting the physical consistency and potential predictive capability of the proposed approach.
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All authors Sayak Chakraborty, Tamal Basak, Sourav Palit, Sandip K. Chakrabarti

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Sub-MeV gamma-ray lines from an endothermic interpretation of the LZ recoil candidate

Maíra Dutra, Jacinto P. Neto and Clarissa Siqueira

Endothermic upscattering of heavy dark matter offers a compelling interpretation of the high-energy nuclear-recoil candidate recently reported by LUX-ZEPLIN (LZ), with a characteristic recoil energy $E_R \propto \delta$, where $\delta$ is the mass splitting between the dark matter states. Cosmological and experimental constraints motivate the depletion of the primordial heavier state, which can be regenerated in the Galactic halo. We show that, if the heavier state decays radiatively, the same mass splitting sets the energy of a gamma-ray line, $E_\gamma \simeq \delta$. For our benchmark, this leads to a sub-MeV line within the projected reach of the Compton Spectrometer and Imager (COSI), scheduled for launch in 2027. The confirmation of the LZ candidate event as a dark matter signal would therefore motivate dedicated searches for sub-MeV gamma-ray lines, with COSI providing a timely opportunity to test this interpretation.
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Solar and Stellar Astrophysics

Carrington's Last Sunspot Drawing in 1870

Hisashi Hayakawa and E. Thomas H. Teague

Richard Christopher Carrington carried out extensive sunspot observations from 1853 to 1861 and left numerous scientific legacies. However, despite his fame, consulting his original manuscripts, we have found Carrington's last sunspot drawing, which he never published. We date this drawing 23 Dec 1870, when Carrington was based at his Churt Observatory. The drawing allows us to count 3 sunspot groups and 10 individual sunspots and measure the group positions at N14{\deg} W37{\deg}, N11{\deg} W46{\deg}, and S08{\deg} W08{\deg}, where our longitude values represent longitudinal distance from the central meridian. In comparison with the existing datasets, his raw group counts look slightly lower than the contemporaneous observers. His position data look consistent. These additions contribute to the ongoing efforts for the sunspot number recalibration and butterfly diagram constructions, as long as we follow the standard assumption for the homogeneity of the "Schmidt backbone". Otherwise, this case instead questions the validity of the common assumption of "Schmidt backbone" keeping the data homogeneity. This sunspot drawing is unlikely to represent the tip of a huge, lost iceberg, but rather an isolated drawing that he left from his Churt era. Carrington may have temporarily revived his interest upon the solar eclipse of 22 Dec 1870. Otherwise, Carrington's references to his sunspot research in his Churt era are confined to priority claims in response to Chevalier's RAS obituary and a local newspaper report. The former confirms that Carrington was probably the first person, who counted and published sunspot data from Thomas Harriot's original sunspot drawings.
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Astrophysics of Galaxies

Constraining the Light Curves of Magnified Stellar Events at z ~ 0.725

Carter Meyerhoff, Hayley Williams, Rafael Ortiz III et al. (+5 more)

Extreme magnification by lensing galaxy clusters allows the detection of high-luminosity stars during cluster caustic transient events at cosmological distances. The Dragon Arc at z=0.725 is a frontier target for identifying transient events due to its high frequency of microlensing events, and so far >100 of these events have been detected. The high frequency of events and high cadence of observations allow for the measurement of minimal flux variation between epochs, and therefore the magnification evolution as a source approaches or recedes from a microcaustic can be measured from light curves. In this work, we model the light curves of 10 transient events in the Dragon Arc across eight epochs from two JWST/NIRCam medium-band filters taken over four days. Injected synthetic observations demonstrate that with additional observations, individual transient light curves allow the of apparent degeneracies between stellar characteristics and properties of motion.
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All authors Carter Meyerhoff, Hayley Williams, Rafael Ortiz III, Gibson B. Bowling, Rogier A. Windhorst, Zach Borowiak, Hunter Sparks, Charles L. Steinhardt

Instrumentation and Methods for Astrophysics

Lidar-monitoring of atmospheric fluctuations for millimeter-wave astronomical observations

Jacques Delabrouille, Patrick Chazette, Étienne Burtin et al. (+15 more)

Ground-based millimeter-wave astronomical observations suffer from strong contamination by the emission of inhomogeneous water vapor in the Earth's atmosphere. This emission reduces the observing efficiency and data quality even from a high-altitude, dry location such as the Atacama plateau in Chile. We propose to continuously monitor atmospheric water vapor with a co-pointing dedicated Raman lidar system. We show, with numerical simulations and proof-of-concept observations, how a synergistic use of atmospheric lidar data has the potential to substantially improve the quality of astronomical data sets.
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All authors Jacques Delabrouille, Patrick Chazette, Étienne Burtin, Christophe Chailan, Josquin Errard, Shamik Ghosh, Manuel Gonzalez, John Groh, Reijo Keskitalo, Valérian Le Lorec, Sotiris Loucatos, Christophe Magneville, Jean-Baptiste Melin, Michel Piat, Damien Prêle, Julien Tang, Timothée Tollet, Julien Totems

Instrumentation and Methods for Astrophysics

A Probabilistic Method for Estimating VLBI Jet-Component Ejection Epochs. Application to MOJAVE 15 GHz VLBA Kinematics

Vladislav A. Makeev, Yuri Y. Kovalev, Cecilia Degli Agosti et al. (+1 more)

Ejection epochs of parsec-scale jet components in active galactic nuclei (AGN), tracked with Very Long Baseline Interferometry (VLBI), are commonly estimated by extrapolating fitted trajectories back to the VLBI core. However, trajectory uncertainties, non-radial motion, acceleration, and the finite size and position variability of the core can make such estimates uncertain and restrict usable samples. We develop a probabilistic framework for estimating VLBI-component ejection epochs, including accelerated features, and for quantifying how consistently each backward-extrapolated trajectory is associated with an effective VLBI core region. We apply the framework to 1923 jet-component trajectories from the 15 GHz MOJAVE kinematic sample. Ejection epochs are defined as the times of closest approach of the extrapolated trajectories to the core, with trajectory uncertainties propagated through Monte Carlo sampling. The effective core radius is treated as a random variable, whose population-level scale is calibrated from the distribution of closest-approach positions. Each component is then assigned a model-dependent probability that its closest approach lies within this effective core region. The method yields 1589 ejection epochs. The fitted effective core-region scale is $\sigma_{\rm c}=0.16\pm0.02$ mas, corresponding to an average core radius of $0.20\pm0.03$ mas, and gives a population-level upper limit of $\lesssim0.16$ mas on the characteristic 15 GHz core wander perpendicular to the jet. Using the same probability weighting, the full probabilistic sample has $N_{\rm eff}=624$, 2.8 times the legacy MOJAVE value of 222, while the overlapping ejection epochs remain consistent with previous estimates. The framework provides a flexible basis for population studies and cross-correlation analyses of jet structural evolution and AGN variability.
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All authors Vladislav A. Makeev, Yuri Y. Kovalev, Cecilia Degli Agosti, Daniel C. Homan

Solar and Stellar Astrophysics · Cross-listed from hep-ph

Constraining Ultra-Light Vector Bosons via Solar Neutrino Oscillations: The Gauged $L_\mu - L_\tau$ Model and Prospects for JUNO and XLZD

Ilídio Lopes

We present an extension of the Standard Model based upon the gauged $U(1)_{L_\mu - L_\tau}$ symmetry, featuring an ultra-light vector boson that couples to the difference of muon and tau lepton numbers. This anomaly-free construction, historically motivated by the muon's anomalous magnetic moment, is employed here as an independent phenomenological framework for solar neutrino physics. Through kinetic mixing with the photon, the $Z^\prime$ boson generates an effective matter potential within the solar interior, thereby modifying neutrino flavour oscillations via the Mikheyev–Smirnov–Wolfenstein mechanism. Utilising recent solar neutrino measurements from Borexino, SNO, and Super-Kamiokande, together with an up-to-date standard solar model, we constrain the boson mass to be below $5.7\times 10^{-17}\,{\rm eV}$, a potential ultra-light dark matter candidate. The optimal model, with coupling parameter $\eta_o \approx -2$, yields $\chi_\nu^2 = 2.7$, compared with $\chi_\nu^2 = 3.1$ for the standard three-flavour scenario. This best fit corresponds to an effective four-fermion coupling $g_{Z^\prime}^2 \varepsilon / m_{Z^\prime}^2 \approx 6.6 \times 10^{-23}\,{\rm eV}^{-2}$, approximately $5.7$ times the Fermi constant, equivalent for $\varepsilon \approx 1$ and a reference mediator mass of $1\,{\rm eV}$ to a gauge coupling $g_{Z^\prime} \approx 8\times 10^{-12}$. We also present projections for forthcoming experiments: the Jiangmen Underground Neutrino Observatory (JUNO), operating since August 2025 with world-leading precision on oscillation parameters, together with the XLZD consortium, should substantially refine these constraints. Such ultra-light particles may address long-standing discrepancies in galaxy simulations within the cold dark matter paradigm, whilst terrestrial long-baseline neutrino experiments provide complementary probes of this parameter space.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Heavy Higgsino Dark Matter With Low Reheating in View of the LZ High-Recoil Event

C. Pallis

We show that a heavy higgsino $\tilde h$ with mass $m_{\tilde h}\sim0.1~{\rm PeV}$, which can be made consistent with the recent LUX-ZEPLIN event avoiding constraints from direct and indirect detection, can account for the present cold dark matter abundance of the universe, if the reheating temperature is bounded as $T_{\rm rh}\lesssim 595~{\rm GeV}$. These values can be achieved by a possible out-of-equilibrium decay of a modulus $\phi$ with mass $m_{\phi}\gg m_{\tilde h}$ and a non-vanishing branching ratio into $\tilde h$'s which plays a decisive role in reducing $T_{\rm rh}$ below its upper limit via the non-thermal $\tilde h$ production. The modulus $\phi$ can be identified with the scalar component of the goldstino superfield which is involved in the generation of the $\mu$ parameter of MSSM (with $\mu\simeq m_{\tilde h}$) via the Giudice-Masiero mechanism.
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Astrophysics of Galaxies

Constraining the galaxy-halo connection at $z>10$ using the neighbors of UV-bright galaxies

Ivan Nikolić and Charlotte A. Mason

JWST has discovered an overabundance of UV-luminous galaxies compared to extrapolations from pre-JWST galaxy formation models. Distinguishing between proposed theoretical explanations requires constraining the halo masses of these systems, which can be probed through clustering. However, at $z>10$, low galaxy number densities render traditional clustering measurements challenging. We introduce a novel formalism that uses information about the local environments ($\lesssim$2 arcmin) of individual UV-bright galaxies at $z>10$ to test the galaxy-halo connection implied by theoretical models for the UVLF excess. We create mock JWST observations using (500 cMpc)$^3$ 21cmFAST simulations to forward-model the spatial distribution of fainter photometric candidates around UV-bright galaxies. We find that the distance to the nearest neighbor is sensitive to the stochasticity of the UV luminosity-halo mass relation, and can distinguish between models where UV luminosity is boosted uniformly in galaxies versus models with high stochasticity in UV luminosity at fixed halo mass. As a proof-of-concept, we apply our framework to observations around the two brightest confirmed galaxies at $z>10$, GN-z11 and JADES-GS-z14-0, and find that the lack of neighbors within $<0.5$ arcmin of these sources disfavors models where UV luminosity is boosted uniformly, suggesting that stochasticity is important for explaining their high UV luminosities. We forecast that distinguishing between these models at high significance requires deep imaging surveying $<1.1$ arcmin around $7$-$15$ bright galaxies ($M_{\rm UV}\lesssim-21$) at $z =10$-$12$, dropping to $\lesssim5$ at $z\sim14$, capable of detecting their neighbors down to $M_{\rm UV,lim}\approx-18$. These observations are within reach of JWST, Roman and Euclid surveys, providing a path to constraining the galaxy-halo connection at our redshift frontier.
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High Energy Astrophysical Phenomena

Observations of Repeating Tidal Disruption Events

Iair Arcavi and Thomas Wevers

The disruption of stars by supermassive black holes (SMBHs) as tidal disruption events (TDEs) can produce transient flares across the electromagnetic spectrum. Such flares can be used to probe SMBH properties, accretion physics and stellar dynamics in galactic nuclei. However, it can be difficult to distinguish TDE flares and those arising from other accretion phenomena around SMBHs, such as active galactic nuclei disk instabilities. Repeated flares from the same location can be produced by either such instabilities or by repeated partial disruptions of the same star, with the former expected to be at random intervals and the latter roughly periodic. Repeating nuclear transients can thus be used to distinguish between full and partial TDEs, as well as between TDEs and other accretion phenomena. Here we review observations of such repeating nuclear flares at various wavelengths. As time domain surveys become wider, deeper and faster, and as they accumulate longer baselines of data, more repeating phenomena at various time scales are being revealed. While these events show the potential for constraining several open questions regarding SMBH accretion phenomena, the small number of cases so far, the limited observational coverage for many of them, and the overall diversity of emission and repetition properties observed make it difficult to robustly associate most cases with physical scenarios at this stage. However, in the near future, as more data accumulate, the nature of various classes of repeating nuclear transients should become more clear, and with it the nature of many of the one-time flares as well.
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Cosmology and Nongalactic Astrophysics

Dark energy and negative compressibility of the Universe: A study based on cosmic equations of state

Felipe A. Asenjo, Ósmar Rodríguez, Ariel Órdenes Morales et al. (+1 more)

All cosmological models are defined through energy and matter, which describe the evolution of the targeted Universe. Whether the content is simple or complex, it can be defined through an effective equation of state (EoS). We study different cosmological models by analyzing the properties of the complete EoS of their fluid contents. We obtained general expressions for the ratio between pressure $p$ and energy density $\rho$, and for their derivative $dp/d\rho$ in terms of deceleration and jerk parameters. We show that, in general, a cosmology whose energy density is constructed from multiple ideal gases cannot be described by the EoS of a single, ideal gas. This is directly related to a variation in the deceleration parameter during the evolution of the Universe. Furthermore, we studied the effective compressibility properties of the EoS, demonstrating that dark energy features of the fluid should be related to the negative compressibility of the contents. These features depend on the dynamics of the jerk parameter for each cosmological system, implying that the knowledge of dark energy evolution is encoded in the third-order derivatives of the scale factor. This approach to understanding the properties of cosmological models indicates that the accelerating evolution of some models, such as the lambda-cold dark matter model ($\Lambda$CDM) or the Chaplygin gas model, is due to the EoS of their nonideal content fluids rather than an associated anomalous (dark energy) nature. On the contrary, models such as $w$-cold dark matter ($w$CDM), $w_0$$w_a$-cold dark matter ($w_0$$w_a$CDM), or Dvali-Gabadadze-Porrati models, include by construction fluids with anomalous content, implying a negative compressibility and an effective dark energy behavior. Our work highlights the importance of treating all contents of the Universe as a nonideal fluid system, with a unique EoS.
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All authors Felipe A. Asenjo, Ósmar Rodríguez, Ariel Órdenes Morales, Alejandro Clocchiatti

Solar and Stellar Astrophysics

Synthesis of organo-phosphorous species in space: the reaction of P$^+$ with C$_2$H$_2$

Matteo Michielan, Jorge Alonso de la Fuente, Roland Thissen et al. (+8 more)

Despite its low cosmic abundance, phosphorus is a bioessential element whose prebiotic availability and incorporation into biomolecules remain open questions. Only a few phosphorous containing molecules with P to C bonds have been detected in astronomical environments (CP, CCP, HCP). More complex species have been proposed, but their formation and destruction pathways remain poorly constrained. Gas-phase ion molecule chemistry involving P cations may contribute to organophosphorus formation, particularly in protostellar shocks and outflows, while reactions of ground state P cations with closed-shell neutrals provide benchmarks for spin-forbidden mechanisms. We investigate the reaction of P+ with C$_2$H$_2$ through a joint experimental and theoretical study aimed at revising astrochemical database rate coefficients. Absolute cross sections and branching ratios were measured as a function of collision energy and complemented by high-level electronic structure calculations and a refined capture model accounting for higher-order long-range interactions and intermediate complex formation. Channel-specific rate coefficients were derived in the range from 10 to 5000 K. The reaction produces predominantly HCCP$^+$ + H (branching ratio 99%), while CCP$^+$ + H$_2$ is a minor channel (branching ratio 1%) arising from intersystem crossing from the triplet to the singlet potential energy surfaces. The total rate coefficient at 300 K agrees well with the SIFT value, but it increases with decreasing temperature, deviating from a pure Langevin trend. The reaction should be included in astrochemical models where phosphorus is released as P+, such as during energetic processing of icy grains in shocks. It provides a pathway to linear HCCP$^+$, a potentially relevant precursor to the observed CP and CCP species through dissociative recombination
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All authors Matteo Michielan, Jorge Alonso de la Fuente, Roland Thissen, Christian Alcaraz, Nicolas Solem, Cristina Sanz Sanz, Susana Gómez Carrasco, Miroslav Polášek, Alexandre Zanchet, Marcelino Agúndez, Daniela Ascenzi