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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 15 September

Earth and Planetary Astrophysics

The asymmetric limbs of HD 209458 b observed with JWST NIRCam F322W2/F444W

Cathal Maguire, Eva-Maria Ahrer, Charlotte Fairman et al. (+6 more)

We present a reanalysis of JWST NIRCam F322W2/F444W transit observations of the hot Jupiter HD 209458 b to extract morning and evening transmission spectra. To determine whether asymmetries in the transit light curves arise from atmospheric structure, we refine the HD 209458 system parameters through a reanalysis of archival transit and radial velocity data. We then extract limb-resolved spectra using two independent light curve modelling frameworks, Harmonica and catwoman,which yield consistent results. We interpret the transmission spectra using both 1D and 1.5D (i.e.,retrievals in which each limb of the planet is modelled independently) atmospheric retrievals. From our 1.5D free-chemistry retrievals, we find a strong preference (Delta ln Z = 2.81 +/- 0.49) for a model in which the morning and evening limbs are retrieved independently over one in which they share atmospheric parameters, despite the additional free parameters this requires. This asymmetry is most pronounced in the retrieved cloud properties, consistent with 3D atmospheric circulation models that predict longitudinally varying cloud distributions, and to a lesser extent in the CH4 and CO abundances. In contrast, the H2O and CO2 abundances and the isothermal temperature structure remain largely consistent between limbs. Similarly, our 1.5D equilibrium chemistry retrieval reveals a uniform composition between the limbs, alongside a marginally hotter evening limb relative to the morning limb. While the retrieved temperatures, chemical abundances, metallicities and carbon-to-oxygen ratios (C/O) are uniform across both limbs, they exhibit significant differences from our 1D retrieval results, highlighting the importance of multidimensional modelling in mitigating 1D retrieval biases.
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All authors Cathal Maguire, Eva-Maria Ahrer, Charlotte Fairman, Hannah R. Wakeford, Duncan Christie, James Kirk, Elspeth K. Lee, Evert Nasedkin, Michael Radica

High Energy Astrophysical Phenomena

Testing a Pre-Supernova Contribution to $^{44}$Ti in Cassiopeia A

Toshiki Sato, Joshua Issa, Falk Herwig et al. (+4 more)

The radioactive isotope $^{44}$Ti in Cassiopeia A has been used as a tracer of the innermost ejecta and explosion asymmetries in core-collapse supernova explosions. However, recent stellar-evolution models suggest substantial $^{44}$Ti may also be synthesized prior to explosion during oxygen-carbon (O-C) shell mergers, a process proposed for the Cas A progenitor. We investigate this pre-supernova contribution by combining NuSTAR measurements of the spatial and kinematic distribution of $^{44}$Ti with X-ray and infrared ejecta diagnostics. The low- and intermediate-velocity $^{44}$Ti components are more closely associated with O-layer tracers than with shocked Fe-rich material. If the $^{44}$Ti associated with the O-layer tracers was synthesized prior to core collapse, it could contribute up to $\sim7\times10^{-5}~M_\odot$, about half of the total. We find that this amount of $^{44}$Ti can be produced in O-C shell-merger models with ingestion rates and convective velocities higher than those in standard one-dimensional stellar-evolution calculations. Stable Fe-group abundance ratios measured with XRISM provide an additional constraint on the explosive contribution, as three-dimensional models with larger $^{44}$Ti yields tend to predict Ti/Fe and Mn/Cr ratios above the observed values. These results suggest that both pre-supernova shell-merger nucleosynthesis and explosive burning contribute to the observed $^{44}$Ti.
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All authors Toshiki Sato, Joshua Issa, Falk Herwig, Yui Kuboike, J. Martin Laming, Kai Matsunaga, Ryo Sawada

Earth and Planetary Astrophysics

H$_2$O emission as tracer of pebble drift: insights from coupling transport and thermochemical models

Marissa Vlasblom, Andrew D. Sellek and Ewine F. van Dishoeck

(Abridged) The composition of the inner regions of protoplanetary disks is known to change with time due to the delivery of icy grains. Cold H$_2$O emission seen with JWST-MIRI is often hypothesized to be a tracer of this pebble drift. However, it is unclear to what extent processes such as photodissociation or the co-delivery of dust may impede such detections. We aim to obtain an improved, 2D view of transport in disks, to better understand how these processes can be traced by H$_2$O emission as seen with JWST-MIRI. We combine the 1D transport code DiscEvolution with the 2D thermochemical code DALI to create several grids of models in which the gas-phase abundances, dust properties, or both are varied according to the transport model. We consider scenarios with and without a traffic jam inside the H$_2$O snowline. The transport of both gas and dust leads to significant temperature changes within the disk, which strongly influence line fluxes and ratios. When a traffic jam is present, the delivery of H$_2$O can proceed unnoticed due to the co-delivery of dust. In addition, the relative strength of cold H$_2$O lines is not found to be sensitive to this delivery of gas-phase H$_2$O. Instead, the cold H$_2$O lines can be greatly enhanced by the delivery of only dust to the inner disk when a traffic jam is present, and one can create a spectrum with strong cold H$_2$O emission solely through the delivery of dust rather than H$_2$O. Recent work has used the 1500/6000 K H$_2$O line ratio as a proxy to determine the pebble mass flux crossing the H$_2$O snowline, but we find that this line ratio is rather sensitive to the temperature and dust distribution of the disk, and is often influenced not only by the cold H$_2$O mass, but also by the hot H$_2$O mass. This introduces complexities and trends as a function of time that do not match the true evolution of the pebble flux.
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Solar and Stellar Astrophysics

The study of AF And. I. Hydrogen abundance constraints and dynamically-consistent wind model of the hot state

E. O. Dedov, A. E. Kostenkov, A. S. Vinokurov et al. (+1 more)

This paper starts a series of works devoted to an in-depth study of luminous blue variable AF And in the M31 galaxy. Here we present the results of non-LTE modelling of the star in a hot state with CMFGEN code. In addition to the $\beta$-velocity law, widely used in the analysis of stellar atmospheres, we used a velocity distribution obtained from the balance of radial forces in the wind, including centrifugal forces for several models. Such a dynamically consistent approach reduces the parameter space during modelling and, in addition, allows us to estimate the current stellar mass whose inner hydrostatic layers are obscured by a dense wind that contaminates the absorption profiles. Based on our modelling we estimate the parameters of AF And as follows: luminosity $L \approx 6.5\times10^5~\text{L}_\odot$, mass loss rate $\dot{M}$ $\approx 3\times10^{-5}~\text{M}_\odot~\text{yr}^{-1}$, terminal velocity $v_\infty \approx 300~\text{km s}^{-1}$ and effective temperature $T_{\rm eff} \approx 17~\text{kK}$. modelling of the hot state of AF And is of particular interest due to the possibility to place constraints on the ratio of hydrogen and helium abundances for further use in constructing models of the cold state of this star. We conclude that the current hydrogen mass fraction in the wind lies in the range from $20$ to $30$ per cent. Self-consistent modelling gives the current mass $M_*$ estimation in the range $15.6 - 17.7~\text{M}_\odot$. By employing evolutionary tracks, we were able to estimate the initial stellar mass as $M_{*,~init} \approx 50~\text{M}_\odot$.
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All authors E. O. Dedov, A. E. Kostenkov, A. S. Vinokurov, A. N. Sarkisyan

High Energy Astrophysical Phenomena

Population synthesis of low-mass binaries with wind-accreting neutron stars

Marina Afonina and Sergei Popov

We perform population synthesis modeling of neutron star binary systems containing a low-mass main-sequence companion underfilling its Roche lobe. About $10^5$ such systems are expected to exist in the Milky Way. In the majority of such systems, NSs are expected to start accreting the stellar wind matter within a few Gyr, resulting in the appearance of a dim X-ray source. The exact value of this fraction mainly depends on the efficiency of the propeller spin-down, properties of the stellar wind, and common envelope efficiency. Mostly, NSs in such systems are formed in electron capture supernovae. Thus, they obtain a low natal kick. Due to this, the center-of-mass velocities of such binaries are low, too. Only in the case of high common envelope efficiency ($\alpha_\mathrm{CE}\gtrsim 3$), a few tens of long-lived high-velocity binaries can be produced in core-collapse supernovae.
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Astrophysics of Galaxies

Lower central dark matter densities in nearby galaxies than predicted by simulations

Yu Lei, Ling Zhu, Meng Yang et al. (+9 more)

Baryonic feedback in hydrodynamical simulations is typically invoked to alleviate the core–cusp problem in dwarf galaxies. Yet baryonic processes also induce adiabatic contraction of dark matter, producing overly steep density profiles and excessively high dark matter fractions in the inner regions of massive galaxies. The dark matter distribution of galaxies across a wide stellar-mass range is therefore a critical test for such simulations, but a comprehensive benchmark has remained absent. Here, we consistently measure the dark matter distribution from galaxy centres out to radii of 20–50 kpc for 136 nearby galaxies that together span the local mass–size relation over the stellar mass interval $10^9$–$10^{11.5}\,M_{\odot}$. We identify central regions with lower dark matter densities relative to $\Lambda$CDM simulation expectations—whose extent grows from about 10 kpc to $>50$ kpc as stellar mass increases from $10^{10} M_{\odot}$ to $10^{11.5} M_{\odot}$. Although their physical origin remains unclear, these low–dark matter regions are clearly indicated by the data. Our results provide an important observational benchmark for future hydrodynamical simulations that explore alternative dark matter models and feedback processes.
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All authors Yu Lei, Ling Zhu, Meng Yang, Giulia Despali, Zheng Zheng, Ran Li, Dandan Xu, Niankun Yu, Jesús Falcón-Barroso, Fangzhou Jiang, Glenn van de Ven, Jie Wang

Earth and Planetary Astrophysics

Discovery of radio emission from the exoplanet $\beta$ Pictoris b

Kevin N. Ortiz Ceballos, Edo Berger and Yvette Cendes

Planetary magnetic fields shape atmospheric escape, mediate interactions with stellar winds, and encode information about planetary interiors, yet they have not been directly measured for planets beyond the Solar System. A direct observable signature is auroral radio emission produced by the electron cyclotron maser instability, whose highest emitted frequency is set by the magnetic field strength at its source. Although auroral radio bursts are observed in Solar System planets and in some ultracool dwarfs, no radio detection has previously been unambiguously localized to an extrasolar planet rather than its host star. Here, we report the first direct detection of auroral radio emission from an exoplanet, the giant planet $\beta$ Pictoris b, with the MeerKAT array. We detect rapid, recurring, and highly circularly polarized bursts, as well as persistent emission, at frequencies of 0.85 to 3.5 GHz. We identify the emission as electron cyclotron maser radiation, which implies a magnetic field of $\gtrsim 1.25$ kG at the planet, the first such direct field strength measurement for an exoplanet.
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Cosmology and Nongalactic Astrophysics

Cosmological information from field-level analysis in redshift space

Julia Stadler

The field-level analysis of galaxy clustering with a forward model based on the Effective Field Theory of Large Scale structure provides cosmological measurements at optimal statistical precision which are simultaneously robust with respect to theoretical uncertainties regarding galaxy formation. Yet, the quantitative gains of field-level analysis in the perturbative regime over the current state-of-the-art, set by the combination of power- and bispectrum, are not obvious, and they depend on analysis choices, the cosmological model, and the observed galaxy population. We therefore quantify the precision improvement from field-level analysis over power- and bispectrum from redshift-space snapshots that closely resemble the DESI LRG sample. Our mock data are created with the LEFTfield forward model, which we also use for the subsequent field-level analysis and for a Fisher forecast of the power- and bispectrum precision. We find significant improvements from the field-level analysis over the power- and bispectrum for a $\Lambda$CDM cosmology; in particular the primordial fluctuation amplitude can be measured twice as precisely. Precision gains at the field-level are even more pronounced for extended cosmologies with a more flexible dependence between power spectrum shape and structure growth; they reach up to a factor of three in the primordial amplitude and a factor of two in parameters that capture deviations from $\Lambda$CDM. Our results highlight the potential of field-level analysis for future discoveries. Realizing this potential will require substantial developments on the modeling of observations and observational systematics as well as on the numerical inference techniques.
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Astrophysics of Galaxies

Probing the All-sky Distribution of Soft X-ray Emission Associated with the Milky Way

Kazuki Ampuku, Ikuyuki Mitsuishi, Philip Kaaret et al. (+5 more)

We present an all-sky analysis of soft X-ray emission associated with the Milky Way using HaloSat and ROSAT data, extending our previous study of five Galactic-plane regions to 330 fields across the sky. We performed uniform spectral fitting with a model including an unabsorbed Local Hot Bubble and two additional absorbed thermal components, representing emission from warm-hot and hot plasma, while accounting for solar wind charge exchange and the cosmic X-ray background. The warm hot component is often interpreted as emission from the circumgalactic medium, whereas the origin of the hot component remains uncertain. Individual-field fits generally favored the inclusion of the hot component, and the field-to-field temperature distributions had medians of kT = 0.19 and 0.74 keV, with 16th-84th percentile ranges of 0.17-0.21 and 0.61-0.90 keV, respectively. The corresponding 16th-84th percentile EM ranges were (1.0-8.2) x 10-2 and (0.5-4.1) x 10-3 cm-6 pc. Stacked spectra from fields within 60 deg. <= l <= 180 deg. supported the individual-field results. After excluding bright X-ray sources and large-scale Galactic structures, we modeled the EM distributions of 178 fields using a hybrid spatial framework comprising stellar emission and disk-like and halo-like diffuse-plasma components. The warm-hot emission was described mainly by the disk-like term, whereas the hot emission was described mainly by stellar emission with an additional halo-like term. These results support a widespread two temperature description and suggest a composite origin for the hot emission.
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All authors Kazuki Ampuku, Ikuyuki Mitsuishi, Philip Kaaret, Kyoko Matsushita, Kotaro Fukushima, Lorella Angelini, Dimitra Koutroumpa, K. D. Kuntz

High Energy Astrophysical Phenomena

Radiation Pressure Instability-Driven Variability of Line-Driven Disk Winds in AGNs: Connection to Periodic Luminosity Variations and UFO Appearance

Yutaro Kuroda, Ken Ohsuga, Mariko Nomura et al. (+1 more)

We investigated the temporal variability of line-driven disk winds induced by radiation pressure instability in accretion disks surrounding supermassive black holes. This is the first study to self-consistently couple one-dimensional hydrodynamic simulations of accretion disks with two-dimensional radiation hydrodynamic simulations of line-driven winds and to analyze their time-dependent evolution. Our results show that periodic luminosity oscillations caused by radiation pressure instability lead to corresponding changes in both the mass outflow rate and the covering factor of gas expected to be observed as ultra-fast outflows (UFOs), with a delay comparable to the viscous timescale around the wind base. The viewing angles from which UFOs are expected to be observed also change with time. Our results therefore imply that, depending on the viewing angle, UFOs may not be detected even during high-luminosity states, whereas they may be detected even at lower luminosities. These findings are consistent with observations showing that UFOs are not always detected at high luminosities and can sometimes be detected even at lower luminosities. For a black hole mass of $10^{7.4}M_\odot$, a mass accretion rate of $1.3L_{\rm Edd}/c^2$ at a radius of about 100 Schwarzschild radii, a viscosity parameter of $\alpha=0.1$, and a viscosity prescription parameter of $\mu=0.45$, the mass outflow rate shows a delay of approximately 2–5 yr relative to the luminosity variation, and the covering factor consequently reaches a maximum of $\sim 30\%$ from the high-luminosity phase through the declining phase. Our results suggest that the intermittent detection of UFOs in luminosity-variable AGNs can be explained by radiation pressure instability driven variability of the line-driven disk winds.
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All authors Yutaro Kuroda, Ken Ohsuga, Mariko Nomura, Kenya Watarai

High Energy Astrophysical Phenomena

Supernova nucleosynthesis: a review

Shuai Zha, Yudong Luo and Zhanwen Han

Supernovae are major drivers of cosmic chemical evolution. They synthesize heavy elements and disperse them into the interstellar medium via their explosion shocks. Light elements are converted into heavier ones during both presupernova evolution and the explosive event itself. Supernova explosions generate nucleosynthesis environments rich in neutrons, protons, and neutrinos under unique thermodynamic conditions, which can enable the production of heavy elements beyond iron. Modern numerical simulations are constructing increasingly realistic explosion models of various supernova channels, providing more accurate nucleosynthesis conditions and chemical yields. In tandem with advances in large-scale spectroscopic surveys delivering precise, high-resolution stellar abundance data, as well as isotopic ratios from presolar grains and meteorites, our understanding of the supernova role in cosmic nucleosynthesis is poised to advance significantly. We review recent progress in modeling various supernova channels, with particular emphasis on nucleosynthesis yields derived from state-of-the-art simulations. We examine the roles of Type Ia, core-collapse, electron-capture, and pair-instability supernovae in producing intermediate-mass, iron-peak, trans-iron, and very heavy elements, as well as their characteristic chemical imprints. We also outline major theoretical uncertainties that affect yield predictions. We intend this review to serve as a timely reference for theoretical model development and a practical guide for interpreting observational abundance data.
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Earth and Planetary Astrophysics

Multi-wavelength Constraints on Dust Dynamics and Size Evolution in Protoplanetary Disk Rings. II. Observational Implications

Linhan Yang, Ya-Ping Li, Ruobing Dong et al. (+6 more)

Spatially resolved dust rings in protoplanetary disks are widely used to infer disk and dust physics from multi-wavelength continuum observations. Their interpretation, however, often neglects grain growth and the evolution of the size distribution, limiting the connection between observed ring profiles and dust-evolution parameters. Building on a physical dust-ring model that includes coagulation and fragmentation, we develop a Bayesian inference framework that jointly incorporates radiative transfer and finite angular resolution. When applied to two rings in HD 163296 and two in LkCa 15, our framework yields gas-dependent estimates of the key dust-evolution parameters such as turbulence strength $\alpha$ and the fragmentation velocity $v_{\rm frag}$ in a self-consistent way. Most rings admit both a low-$\alpha$, low-$v_{\rm frag}$ branch with small grains, and a higher-$\alpha$, higher-$v_{\rm frag}$ branch with larger grains. Typical low-$\alpha$ branches have $\alpha\sim10^{-5}$–$10^{-4}$ and fragmentation velocities of order cm s$^{-1}$ level, whereas the higher-$\alpha$ branches reach $\alpha\sim10^{-3}$–$10^{-2}$ and fragmentation velocities of a few to $20$ m s$^{-1}$. The observed broad and wavelength-dependent profiles near the ring peaks can be reproduced by intrinsically narrow dust rings. This new framework offers a more direct route from multi-wavelength continuum data to the microphysics of dust growth and trapping—a connection that can be robustly tested with future high-resolution observations at longer wavelengths.
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All authors Linhan Yang, Ya-Ping Li, Ruobing Dong, Yinhao Wu, Hauyu Baobab Liu, Kiyoaki Doi, Anibal Sierra, Greta Guidi, Pinghui Huang

Cosmology and Nongalactic Astrophysics

Probing multi-state dark matter via optical absorption lines in DESI spectra

Anoma Ganguly and Shadab Alam

We search for dark matter through absorption lines imprinted on the spectra of background sources whose sightlines pass through foreground dark matter halos. Such a line is a generic feature of multi-state dark matter models that couple to photons through higher-order electromagnetic moments. We focus on the minimal case of a two-state system with a magnetic dipole transition, in which the ground state absorbs a photon and makes a transition to the excited state. For transition energy $\Delta E \sim O \,(\text{eV})$, the line falls in the optical band, within reach of spectroscopic surveys such as DESI. Stacking 145,087 spectra of DESI Early Data Release objects paired with foreground GAMA galaxy groups, we find a stacked optical depth consistent with zero and place $2\sigma$ upper limits on the magnetic dipole transition cross-section. The limits are strongest at $\Delta E \sim$ 3-5 eV for a few MeV dark matter mass in the parameter space that is inaccessible to both cosmological (BBN+CMB) and direct detection experiments. We forecast that the full DESI and the next-generation spectroscopic surveys will tighten these limits by more than an order of magnitude, establishing spectroscopic stacking as a competitive probe of electromagnetically interacting multi-state dark matter.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Bridging Between Statistical Mechanics and Black Hole Evolution: Theoretical Formalism

Suvodip Mukherjee

Black holes in the Universe span nearly ten orders of magnitude in mass over a large cosmic timescale, dating back to at least the Universe's early history, when it was only a few hundred million years old. The formation and evolution of these objects remain a mystery because no direct probe can trace each black hole across the full mass range and cosmic time. This work shows, for the first time, a statistical mechanical description of black hole evolution. I show that though each black hole and its evolution are governed by stochastic processes, one can make a macroscopic description of the distribution function of black holes in the Universe, and its evolution over the entire mass range and cosmic time can be expressed in terms of the Kramers-Moyal expansion. This bridging between statistical mechanics and black hole evolution in terms of the Kramers-Moyal expansion enables the discovery of the underlying physical processes that play a role in the evolution of black holes. In the future, the application of this technique to data accessible from different messengers, such as gravitational waves and electromagnetic waves, which probe black holes in the Universe, can lead to a data-driven understanding of the underlying physical processes by this statistical mechanics technique despite the ignorance of the underlying microscopic stochastic processes.
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Instrumentation and Methods for Astrophysics

Design of an atmospheric dispersion corrector and double scrambler for improved fiber coupling and illumination uniformity for the HET HRS

Devika K Divakar, Joseph Strubhar, Andrew Pinckney et al. (+1 more)

The Hobby–Eberly Telescope High Resolution Spectrograph (HET–HRS) is undergoing a major instrument upgrade to improve its performance over the 360–1000 nm wavelength range. As part of this effort, a new fiber-feed system has been developed to increase throughput and enhance illumination stability. This paper presents the optical and opto-mechanical designs of the upgraded HRS Input Head Module Package and lens-based Double Scramblers. The Input Head incorporates a static Atmospheric Dispersion Corrector (ADC) and relay optics optimized for the HET operational zenith-angle range, reducing the residual atmospheric dispersion to less than 0.42 arcsec while improving wavelength-dependent fiber coupling. Separate Double Scrambler designs were developed for the 260 \textmu m and 320 \textmu m science fibers to exchange the near-field and far-field illumination distributions. Geometrical image analyses demonstrate stable near-field and far-field illumination, reduced coupling losses, and acceptable angular acceptance across both fiber geometries. The opto-mechanical designs supporting the Input Head and Double Scrambler are also presented to provide the alignment accuracy and mechanical stability required for the upgraded fiber-feed system. These results establish the proposed architecture as a practical solution for improving the optical performance and illumination stability of HET–HRS.
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All authors Devika K Divakar, Joseph Strubhar, Andrew Pinckney, Phillip MacQueen

Astrophysics of Galaxies

The Study of Detailed Morphology of Milky Way Dwarf Galaxies: Draco and Boötes I

Kyosuke S. Sato, Masafumi Yagi and Sakurako Okamoto

We present a photometric study of the outer stellar structures of the Milky Way dwarf spheroidal galaxies (dSphs) Draco and Boötes I, using deep wide-field imaging data. The old main-sequence stars are used to trace their spatial distributions beyond their tidal radii. We derive global structural parameters and radial profiles of number density, ellipticity, and position angle from their stellar distributions. Draco and Boötes I show contrasting features. Draco shows no prominent extended stellar distribution, although weak elongations are detected toward the eastern and northwestern directions. Its stellar distribution remains relatively compact compared with its estimated Jacobi tidal radius ($r_J=57.2^{+13.5}_{-11.1}$ arcmin), suggesting that the stellar component is tightly bound by its gravitational potential. In contrast, the radial number-density profiles of Boötes I along several directions show excess from the best-fit exponential profile outside of around $r\sim20$ arcmin, near the estimated Jacobi radius ($r_J=21.6^{+9.3}_{-7.6}$ arcmin). In addition, the ellipticity of Draco decreases with radius, whereas that of Boötes I increases toward larger radii. Bo"otes I also exhibits a prominent S-shaped stellar structure extending approximately along its orbital direction. Together, the radial density excess, increasing ellipticity, and S-shaped morphology suggest that the outer stellar structure of Boötes I may trace tidal tails produced by interactions with the Milky Way. The contrasting morphologies of Draco and Boötes I further suggest that the response of dwarf galaxies to the Milky Way tidal field may depend not only on their orbital histories, but also on the internal structure of their dark-matter halos.
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Solar and Stellar Astrophysics

The Variation of Circumstellar Parameters through Early Stellar Evolution

Michael Connelley, Christian Flores and Bo Reipurth

We report on the evolution of extinction, mass accretion rate, and spectral index from analysis of SpeX observations and AllWISE spectral energy distributions, compared to stellar parameters (mass, age, and veiling) derived from analysis of previously reported and newly analyzed iSHELL observations of the same young stellar objects (YSOs). By using stellar gravity as an age indicator, we are able to infer age without any assumptions about the circumstellar environment. Our sample consists of 109 Class I, II, and III YSOs. The spectral index broadly decreases with time but with sufficient scatter that Class I-III YSOs can all be found at the same age. There is a wide range of extinction (A_V) from nearly 0 to greater than 30 mag for ages up to 5 Myr, showing no clear trend with age. The mass accretion rate declines from a median of 10^-8 solar masses per year at ~1 Myr to less than 10^-10 solar masses per year at ages greater than 10 Myr, with a scatter of the mass accretion rate of +/- 1 dex. Accretion seems to effectively end by ~ 5 Myr, by which time the median mass gained is 0.05 solar masses. We find a wide range of veiling (rK) from zero to three (limited by our need to detect photospheric lines) for Class I and II YSOs, with the median veiling declining after ~2 Myr. Class I YSOs appear to be physically very similar to Class II YSOs, with similar accretion rates and overlapping age and mass distributions. There are no objects with a high spectral index and low extinction, suggesting that once starved of circumstellar material, the spectral index rapidly declines.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Charging of rotating black holes: kinetic simulations of black hole magnetospheres

Martin Kološ, Farukh Abdulkhamidov, Arman Tursunov et al. (+2 more)

Whether a rotating black hole (BH) immersed in an external magnetic field charges up to the Wald value $Q_{\rm W}=2aMB$, where $M$ and $a$ are the BH mass and spin parameter, and $B$ is the strength of the external field, is a long-standing open question in BH electrodynamics, with consequences for charge separation, particle acceleration and the structure of BH magnetospheres. We address it with axisymmetric general-relativistic particle-in-cell simulations performed with GRZeltron, including self-consistent pair creation. For representative values of the BH spin, we evolve the same asymptotically uniform Wald field from two opposite initial horizon charges, $Q_{0}=0$ and $Q_{0}=Q_{\rm W}$, and track the accumulated charge through the BH horizon. We find that both branches relax within a few tens of gravitational times to the same saturated charge value. Thus, the equilibrium is a dynamical attractor of the kinetic magnetosphere rather than a memory of the initial data. The attractor lies well below $Q_{\rm W}$, at $\xi_{\rm eq}\equiv Q_{\rm eq}/Q_{\rm W}\approx 0.3$ for $a\lesssim0.7$, then falling almost to $\xi_{\rm eq}\approx0$ for large spins $a\approx1$. We derive an analytic expression for $\xi_{\rm eq}$ by requiring equal magnetic fluxes through the horizon associated with positive and negative charges, and find its spin dependence to be in agreement with the simulations. The charge state of an astrophysical BH is therefore driven by kinetic plasma processes, and the Wald charge is an upper bound, not a general equilibrium value. Since $\xi_{\rm eq}<1$, charging does not quench the horizon-infinity potential drop that powers energy-extraction processes such as the Blandford-Znajek mechanism.
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All authors Martin Kološ, Farukh Abdulkhamidov, Arman Tursunov, Jorge A. Rueda, Benoît Cerutti

Monday 14 September

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

Testing Higgs-Coupled Minimal Dark Matter with Solar Neutrinos after the LZ High-Recoil Event

Mattia Di Mauro

The LUX-ZEPLIN (LZ) Collaboration has reported a nuclear-recoil candidate at $248$ keV, motivating interpretations in terms of endothermic dark matter (DM). We investigate this signal in Higgs-coupled minimal dark matter (HC-MDM), where the same electroweak interaction responsible for the terrestrial recoil also induces DM capture in the Sun and a potentially observable high-energy neutrino signal. We independently determine the mass splittings required to reproduce the LZ event and perform an improved calculation of Solar capture and post-capture evolution. Our treatment includes natural isotope mixtures, exact inelastic kinematics, nuclear form factors, finite-temperature nuclear motion near kinematic closure, orbital cooling through loop-induced elastic scattering, and an explicit capture–annihilation equilibrium test. The resulting Solar predictions are numerically stable and robust against the astrophysical and nuclear variations considered. For the two thermal benchmarks within the released IceCube DM mass grid, $3_M2_D$ and $5_M4_D$, the predicted annihilation rates exceed the mass-matched $W^+W^-$ IceCube response by factors of approximately $2.2\times10^3$ and $91$, placing both standard-halo solutions under strong tension within the $W^+W^-$ response mapping used here. For the heavier representations, whose masses lie above the published $10$ TeV IceCube grid, we construct a response-based extrapolation to higher masses. The $22$ TeV $7_M6_D$ benchmark remains in strong tension with IceCube even under our conservative response-loss extrapolation, while the $48$ TeV $9_M8_D$ benchmark also remains above the extrapolated response, although much closer to the sensitivity boundary. The $82$ TeV $11_M10_D$ benchmark is response dependent, whereas the $130$ TeV $13_M12_D$ benchmark remains below the extrapolated IceCube sensitivity.
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Cosmology and Nongalactic Astrophysics

FOSSIL: A future mission for CMB spectral distortion measurements

N. Aghanim, B. Maffei, J. Aumont et al. (+96 more)

We present FOSSIL, a proposed space mission which is designed to deliver unprecedented absolute spectroscopic measurements of the sky intensity over a broad frequency range (50GHz to 2THz) to accurately measure chemical-potential mu-type, Compton y-type, and Compton relativistic y-type CMB spectral distortions. FOSSIL will reach monopole sensitivities representing a gain of roughly three orders of magnitude over COBE/FIRAS. These capabilities will allow us to constrain primordial density fluctuations on scales k~(10 to 10^4)Mpc^-1, test inflationary models, probe dark matter annihilation/decay/interactions, constrain primordial black hole seed scenarios, and pin down feedback models in galaxy evolution and structure formation by measuring the cosmic thermal energy content. Furthermore, its 130 spectral channels will enable legacy astrophysics, including precise characterisation of the Cosmic Infrared Background, line intensity mapping during cosmic noon, and detailed Galactic dust mapping.
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All authors N. Aghanim, B. Maffei, J. Aumont, A. Beelen, B. Borgo, E. Bozzo, J. Chluba, X. Coulon, S. Couturier, F. Cuttaia, B. Cyr, P. De Bernardis, C. De Jabrun, J.-J. Diaz-Garcia, D. Eckert, G. Fabbian, L. Ferrari, F. Finelli, T. Gascard, J. E. Gudmundsson, A. Kogut, G. Lagache, M. Loquet Le Gall, S. Martin, A. I. Silva Martins, A. Monfardini, C. O'Sullivan, L. Pagano, D. Paoletti, G. Pisano, M. Remazeilles, V. Reveret, J. A. Rubino-Martin, V. Sauvage, G. Savini, L. Spencer, A. Tartari, L. Terenzi, N. Trappe, D. Watts, B. Winter, E. Baker, E. S. Battistelli, R. Battye, J. L. Bernal, A. Besnard, F. R. Bouchet, M. Braglia, C. Burigana, M. Calvo, S. Caminade, M. Citran, D. Clements, W. Coulton, E. Courau, G. De Zotti, E. Di Valentino, H. Dole, G. Domenech, S. Evangelista, S. Farrens, M. Frailis, K. A. Glasscock, V. Hervier, E. Kovetz, H. Liu, T. Louis, F. Madec, A. S. Maniyar, C. J. A. P. Martins, S. Masi, L. Maurin, F. Moll, L. Morelli, S. K. Naess, A. Nicola, F. Pace, N. Ponthieu, V. Poulin, E. Prele, N. Sanchez, W. Qin, L. Rodriguez, D. Scott, F. Simon, J. Singal, T. Slatyer, E. M. Teixeira, L. Thiele, M. Tristram, T. Trombetti, L. Vacher, S. Vinzl, A. Zacchei, E. Allys, K. Aryan, J. M. Casas Gonzales, O. Lahav, C. Sidiropoulos

Solar and Stellar Astrophysics

Characterizing bright $\delta$ Scuti pulsators using TESS light curves:II. Pulsation amplitude and energy distributions

Prasad Mani, Timothy Bedding, Simon Murphy et al. (+2 more)

Pulsations in $\delta$ Scuti stars exhibit a wide range of excited frequencies and amplitudes, but the underlying principles governing their amplitude distribution remain unclear. We revisit this problem using a global, energy-based perspective. For a complete sample of 3200 bright $\delta$ Scuti stars observed by TESS, integrated power spectral density (PSD) of the Fourier spectrum allows us to measure the overall pulsation signal. From this, we derive a proxy for the total pulsation energy. We uncover a bimodality among higher-frequency delta Scuti stars in their integrated PSD, possibly suggesting the presence of two distinct pulsation regimes. In addition, we identify an apparent upper limit to the total pulsation energy, indicating a constrained energy budget for these pulsations. This feature is not evident when stars are characterized solely by their dominant mode amplitude.
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All authors Prasad Mani, Timothy Bedding, Simon Murphy, Daniel Hey, Tom Love

High Energy Astrophysical Phenomena

Right Energy, Wrong Profile: Why the 43 GeV Cluster Line Is Unlikely to Be Dark Matter

Stefano Profumo

A narrow gamma-ray line would be a distinctive signature of dark matter, but its interpretation depends as much on its spatial distribution as on its energy. We reanalyze the reported 43 GeV feature in Fermi-LAT observations of Virgo, Fornax, and Ophiuchus. The excess is reproduced in the same public data and survives event-type partitions, a test using data withheld from the original selection, and detector-coordinate permutation tests. Realistic hadronic and inverse-Compton emission is too broad to explain it. A spatial–spectral likelihood analysis restricted to Good Time Intervals and including diffuse backgrounds and catalogued sources finds a broad line-like component. Uniform surface brightness and substructure-enhanced annihilation are preferred, whereas smooth NFW annihilation and a central point source are unlikely explanations. An independent annular analysis agrees: the events associated with the excess extend through much of the virial region. Calibration over 20–70 GeV and five morphologies gives a conditional global significance of approximately $2.7\sigma$, peaking at 44.5 GeV for uniform brightness. This result is conditional on the preselected three-cluster sample. The broad morphology is the main obstacle to a dark-matter interpretation. Such an interpretation would require photons to be a leading annihilation channel, annihilation to remain efficient in cold subhalos, and subhalos to supply nearly all the cluster luminosity. Yet a boost consistent with $\Lambda$CDM drives the required two-photon cross section into the range most tightly constrained by Galactic-halo line limits. The most likely explanation is a chance fluctuation amplified by analysis and target-selection effects, possibly compounded by residual Galactic diffuse or unresolved-source mismodeling; if celestial, its morphology makes a simple dark-matter interpretation unlikely.
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Instrumentation and Methods for Astrophysics

RAMA: A new agile AO bench for the telescope FEELINGS

Matteo Pasinetti, Rodrigo Andres Munoz Gomez, Benjamin Andres Gonzalez Barraza et al. (+16 more)

The ground-based observation of extended objects such as satellites suffer from severe atmospheric propagation constraints. Specifically, high tracking velocities and low-elevation lines of sight generate non-stationary turbulence alongside strong scintillation. Developing robust wavefront control strategies is therefore critical to maintain stable observations. In this context, we present RAMA, an adaptive optics (AO) testbench deployed on ONERA's 60\,cm FEELINGS telescope. Designed as a pathfinder for future systems like the PROVIDENCE ground station, RAMA evaluates a visible, non-modulated Pyramid Wavefront Sensor (PWFS). The hardware baseline also includes two pupil-conjugated deformable mirrors (DM97 and DM192) driven by the DAO Real-Time Computer (RTC). Inheriting the modular and evolving philosophy of the PAPYRUS project, the bench provides a flexible environment to test new components on-sky and allows for direct comparisons between classical controllers and advanced, data-driven strategies. By implementing Convolutional Neural Networks (CNN) for phase reconstruction and Reinforcement Learning (RL) for loop control, RAMA aims to overcome the specific limitations associated with scintillation and extended-object observations. This paper details the opto-mechanical design, numerical simulations of the bench expected wavefont control performance, preliminary laboratory closed-loop results and the first on-sky optical coupling with the telescope.
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All authors Matteo Pasinetti, Rodrigo Andres Munoz Gomez, Benjamin Andres Gonzalez Barraza, Francisco Oyarzun, Sylvain Cetre, Jean-François Sauvage, Axel Vincent-Randonnier, Julien Charton, Marie Laslandes, Roméo Roudeix, Nicolas Védrenne, Cyril Petit, Pierre-Louis Mayeur, Esteban Vera Rojas, Andrew Reeves, Perrine Lognoné, Morgan Gray, Thierry Fusco, Benoit Neichel

Astrophysics of Galaxies

CNN-Based Inference of Gaseous Halo Properties from Synthetic X-ray and 21-cm HI Observations

Kalvyn N. Poncelet Adams, Benjamin D. Oppenheimer, Naomi Gluck et al. (+3 more)

Quantifying the information content in multi-wavelength observations is critical for setting exposure times for upcoming X-ray and 21-cm HI radio surveys. We train convolutional neural networks (CNNs) on mock observations of halos from the IllustrisTNG100 and TNG300 simulations, combining data from soft X-ray channels from a CCD or a microcalorimeter with HI intensity, velocity, and dispersion maps, to infer halo mass, gas fractions, metallicity, and [O/Fe] abundance. Multi-band (X-ray and HI) combinations consistently outperform single-band inference for gas fractions. X-ray outperforms HI observations for measuring halo mass, but both bands contribute similarly when measuring the cool (T<10^5 K) gas fraction in halos with significant cool gas content. Using matched exposure times, a micro-calorimeter improves metallicity inference over the CCD by a factor of 1.75, enabling precise measurements of [O/Fe] alpha-enhancement for the largest halos. The larger volume of TNG300 allows inference of group halo masses, finding an inference RMSE of 0.04 dex with a 100 ksec X-ray exposure time. These results demonstrate how deep learning can evaluate strategies for developing instruments and designing surveys for these expensive observations targeting gaseous halos.
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All authors Kalvyn N. Poncelet Adams, Benjamin D. Oppenheimer, Naomi Gluck, Caleb Ogle, Matthew Ho, Daisuke Nagai

Astrophysics of Galaxies

SAMI and TNG-Cluster: tracing galaxy spin and environmental transformation across cluster phase-space and cosmic time

Gustavo F. Gonçalves, Ilaria Marini, A. Fraser-McKelvie et al. (+4 more)

The dense environment of galaxy clusters suppresses star formation and alters the kinematic properties of infalling satellites through gas stripping, tidal interactions, gravitational harassment and starvation. Projected phase-space diagrams connect the present-day distribution of cluster galaxies to their accretion histories. We combine SAMI Galaxy Survey integral field spectroscopy with the TNG-Cluster simulation to investigate how the stellar spin parameter ($\lambda_R$), $(g-i)$ colour, and sSFR vary across projected phase-space infall regions. At $z = 0$, TNG-Cluster reproduces the direction and broad strength of the phase-space trends observed in SAMI, including the weak yet significant $\lambda_R$-clustercentric distance correlation. Leveraging this agreement, we extend the analysis across the last 8 Gyr, tracing the statistical evolution of galaxy properties within each infall region, and complement this with individual orbital histories of representative satellites. While colour and sSFR show clear monotonic gradients with both phase-space position and cosmic time, $\lambda_R$ behaves differently: it remains largely uniform across the outer infall regions, with only the virialised core exhibiting systematically lower values, and displays a slow monotonic decline toward the present day across all regions. We find that angular momentum suppression driven by the cluster environment is a slow, cumulative process requiring several Gyr of exposure to the cluster core, modulated by orbital history and stellar mass. This gradual nature explains why the $\lambda_R$-environment correlation appears weak across phase-space regions in statistical samples; the effect emerges when individual satellite histories are tracked, revealing a sustained dynamical response to prolonged cluster residence.
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All authors Gustavo F. Gonçalves, Ilaria Marini, A. Fraser-McKelvie, Natan de Isídio, Rubens E. G. Machado, Richards P. Albuquerque, Daudi T. Mazengo

Instrumentation and Methods for Astrophysics

Commissioning the AIP's ultrafast laser Inscription facility: defining the parameter space for type-I waveguide fabrication

Rima Islam, Aline N. Dinkelaker, Abani Shankar Nayak et al. (+2 more)

Astrophotonics offers a compact, stable alternative to bulk optics in traditional astronomical instrumentation, spanning high-precision spectroscopy to high-contrast interferometry. However, the strict requirements for throughput, accuracy, precision, and stability require tailored manufacturing processes that go beyond standard telecommunications technology. This work presents the iterative experimental and statistical methods used to determine the optimal laser-writing conditions for passive waveguides in silica glass using a femtosecond laser inscription setup. We systematically explored the parameter space by varying pulse energy, repetition rate, translation speed, and scan numbers to identify the optimal conditions for Type-1 waveguides, characterized by a positive refractive-index modification in their cores. We report on the refinement of these parameters to manufacture single-mode, high-throughput waveguides that operate in the astronomical J-band (1300-1400 nm). A key focus of this optimization is to match the mode field diameter (MFD) to the SMF28 fibre and minimize insertion losses. This development is critical for astrophotonics devices, such as photonic reformatters, beam combiners, and pupil remappers, as well as post-fabrication correction of phase errors in photonic components fabricated using traditional photolithographic methods. Some of these components will be used for future on-sky validation at the Calar Alto Observatory and the CHARA array.
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All authors Rima Islam, Aline N. Dinkelaker, Abani Shankar Nayak, Kalaga Madhav, Martin Roth

Instrumentation and Methods for Astrophysics

Optomechanical design of an ADC and image rotator for the HJST Coudé Spectrograph at McDonald Observatory

Devika K Divakar, Phillip MacQueen, Andrew Pinckney et al. (+1 more)

High-resolution spectroscopic observations require stable slit illumination and mitigation of atmospheric refraction effects that degrade throughput and spectral fidelity. We present the optical and mechanical design of a Rotational Atmospheric Dispersion Corrector (RADC) for the coudé Tull Spectrograph on the Harlan J. Smith 2.7 m Telescope. Atmospheric dispersion introduces wavelength-dependent image displacement that increases with zenith distance and reaches approximately 4 arcsec across the 350 - 1000 nm wavelength range at a zenith angle of 65{\deg}, leading to wavelength-dependent slit losses and non-uniform slit illumination. The RADC employs a pair of counter-rotating Amici prisms to provide continuous correction over the operational zenith-angle range while maintaining image quality and compatibility with the existing coudé pre-slit optics. The optical and mechanical design of the deployable ADC subsystem, its integration within the limited relay envelope, and its expected impact on throughput and slit illumination stability are presented. In addition, we discuss a K-mirror image rotator as a potential future upgrade for observations of extended and non-point-like targets, where maintaining a fixed slit position angle on the sky may be desirable during long integrations. Preliminary optical studies of the image-rotation concept and its integration considerations within the HJST coudé relay are briefly summarized. Together, these developments support enhanced observing capabilities for high-resolution spectroscopy on the HJST.
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All authors Devika K Divakar, Phillip MacQueen, Andrew Pinckney, Joseph Strubhar

High Energy Astrophysical Phenomena

Properties of the circumstellar matter around the pair-instability supernova candidate SN 2018ibb revealed by its light curve

Takashi J. Moriya, Steve Schulze, Alexander Heger et al. (+2 more)

SN 2018ibb is one of the best pair-instability supernova (PISN) candidates identified to date. It, however, showed unexpected blue flux excess in late-phase spectra, likely originating from the interaction between supernova (SN) ejecta and dense circumstellar matter (CSM). We develop synthetic light-curve models of PISNe interacting with dense CSM and estimate the CSM properties of SN 2018ibb by comparing the synthetic and observed light curves. We found that the bolometric luminosity evolution of SN 2018ibb from 150 d after the peak can be well reproduced by the interaction with the CSM formed by a mass-loss rate of 0.01(v_CSM/1,000 km/s) Msun/yr, where v_CSM is the CSM velocity. The observed luminosity break at around 300 d from the peak indicates that the CSM interaction ended at this time and the dense CSM radius was 8.5e16 cm. The CSM radius then implies that the mass loss of the progenitor was enhanced for 28/(v_CSM/1,000 km/s) yr before explosion. We conclude that PISN progenitors may experience short-term mass-loss enhancement within decades before explosion, similar to what is often observed in progenitors of core-collapse SNe.
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All authors Takashi J. Moriya, Steve Schulze, Alexander Heger, Sergei I. Blinnikov, Marat Sh. Potashov

Astrophysics of Galaxies

NOCTURNE. II. Extreme radio variability in the heart of early-stage active galactic nuclei

Emilia Järvelä, Patrizia Romano, Anne Lähteenmäki et al. (+1 more)

We report the discovery of extreme 37 GHz radio variability in early-stage active galactic nuclei (AGN). Most of these sources belong to the class of narrow-line Seyfert 1 (NLS1) galaxies, which harbour fast-growing, low-mass supermassive black holes that accrete at high Eddington ratios. At 37 GHz, these extraordinary AGN exhibit amplitude variability of three to four orders of magnitude over timescales of a few days. Notably, despite several attempts, we have not detected relativistic jets in these sources, suggesting that this phenomenon may occur very close to the black hole and may represent a new form of AGN variability. One of these sources, which flared at 37 GHz, was followed up with the Karl G. Jansky Very Large Array and Swift XRT/UVOT. Based on these observations, we estimated an e-folding timescale of mere hours, leading to variability brightness temperatures and variability Doppler factors that are extremely difficult to explain by an incoherent emitter. This suggests a possible detection of coherent emission from an AGN, although more observations will be needed to distinguish between alternative scenarios.
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All authors Emilia Järvelä, Patrizia Romano, Anne Lähteenmäki, Marco Berton

Solar and Stellar Astrophysics

Using Gravity as an Age Indicator for Young Stars

Michael Connelley, Christian Flores and Bo Reipurth

The age of a young star is difficult to measure and yet is a fundamental property that is essential for understanding stellar evolution. Accurate age indicators across the early phases of low-mass stars are scarce and often rely on properties of the circumstellar environment. We investigate stellar surface gravity as a practical age estimator from the class I to the class III phases of low-mass stars. Gravity increases monotonically as young stars descend their Hayashi tracks. Gravity is a physical property of the central star and is independent of the circumstellar environment or evolutionary models. Also, gravity can be measured for individual objects. We performed two tests for the reliability of gravity as an age indicator: (1) the relative ages of the components of young binary stars and (2) the relative ages of a young moving group. We show that young binary stars have consistent gravities, as expected, if they are coeval. Similarly, we find similar gravities among the TW Hya group and derive a median age of 12.8 +/- 1.2 Myr. In both cases, differences in gravities may reflect real differences in the ages. We show that there is no correlation between veiling emission and gravity, showing that circumstellar disk emission does not affect our ability to infer ages from measurements of photospheric stellar gravity.
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