High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Can machine learning improve the detectability and disentanglement of the gravitational-wave background?
Hugo Einsle, Marie Anne Bizouard, Tania Regimbau et al. (+2 more)
Gravitational waves from compact binary coalescences and from early Universe processes are expected to form a gravitational-wave background. We employ a custom deep learning multi-scale multi-headed autoencoder architecture to isolate gravitational-wave background from detector noise, followed by a Markov chain Monte Carlo inference stage to separate the astrophysical and cosmological components. Analyzing $108$-day mock
datasets representative of the first period of the fourth LIGO-Virgo-KAGRA observing run, we show that we can detect with high confidence — $\log_{10}$ noise Bayes factor larger than 3 — a compact binary coalescence gravitational-wave background with an amplitude of $4.3^{+0.5}_{-0.4}\times10^{-9}$ at $f_{\rm ref}=25\,\mathrm{Hz}$, which is a factor $\sim5$ higher than the amplitude expected from compact binary sources. We also show that we can isolate a cosmological – assumed flat spectrum – gravitational-wave background as weak as $ 9.7^{+2.5}_{-2.4} \times 10^{-10}$ from the expected compact binary coalescence gravitational-wave background within simulated Gaussian noise mimicking the LIGO detectors sensitivity achieved in the fourth observing run. In blind-test comparisons with the standard pygwb pipeline, we show that our method achieves more accurate amplitude and spectral-index recovery and enables the separation of astrophysical and cosmological background components.
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All authors Hugo Einsle, Marie Anne Bizouard, Tania Regimbau, Mairi Sakellariadou, Jishnu Suresh
Astrophysics of Galaxies
On an empirical method to build near-equilibrium axisymmetric and triaxial galaxy models
Pierfrancesco Di Cintio, Alessandro Alberto Trani and Valentina Cesare
We introduce a numerical technique to implement $N-$body realizations of axisymmetric and triaxial self-gravitating system starting from a spherical self-consistent models for which a phase-space distribution is known. The method is an improvement of the so-called adiabatic squeezing technique and allows one to have a better control of the effective ellipticities of the particle distribution and produces virialized systems that can be used as non-spherical initial conditions for $N-$body simulations. Some numerical stability tests are presented and discussed.
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Instrumentation and Methods for Astrophysics
A Comparative Systems-Engineering Framework for RFI Coexistence in Radio Astronomy and Aviation Safety Systems
Simthembile Dlamini
Radio astronomy and aviation safety systems occupy opposite ends of the signal-power spectrum, yet both depend on the same finite resource and are increasingly squeezed by commercial broadband wireless services. The two fields protect their receivers using separately derived, apparently incommensurable criteria: the ITU-R RA.769 detrimental-interference threshold for
radio telescopes, and the radar-altimeter interference thresholds established by RTCA Special Committee 239 for the 5G C-band coexistence problem. We introduce a single coexistence-margin framework, M(f,d) = Pth(f) - Prx(f,d), and show both criteria to be special cases of it. We apply this framework to two case studies, the Karoo
Radio Quiet Zone surrounding MeerKAT and SKA-Mid, and the global 5G C-band/altimeter dispute, showing that, despite unrelated regulatory histories, both converged on the same three-lever solution: guard-band separation, bounded exclusion zones, and receiver-side filtering, governed by mandatory coordination rather than static exclusion. We then show that interference-excision, beamforming, and statistical-calibration pipelines developed for
radio interferometry are closely analogous to, and in several cases directly reusable for, operations required by ADS-B validation, phased-array radar clutter rejection, and predictive-maintenance anomaly detection. The unifying framework, and the finding that two independently-arising regulatory histories converge on the same design pattern, is this papers central contribution: M(f,d) has not, to our knowledge, been proposed before as a common formalism spanning these two protection regimes, and the toolkit mapping distinguishes genuine reuse from looser analogy. The result is a reusable design pattern and shared skills/infrastructure pipeline, applicable wherever a narrowband receiver must coexist with a growing broadband commercial neighbour.
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Instrumentation and Methods for Astrophysics
A Focal-plane X-ray Polarimeter with Spectral and Timing Capabilities for Future Missions
Hemanth Manikantan, Carlo Lefevre, Lorenzo Petrucci et al. (+16 more)
The NASA-ASI mission Imaging X-ray Polarimeter Explorer (IXPE) firmly established X-ray polarimetry as a core observation pillar of high-energy astrophysics, alongside imaging, timing, and spectroscopy. While IXPE made groundbreaking discoveries in the 2$-$8 keV range on both point and extended X-ray sources, the Gas Pixel Detectors onboard IXPE demand substantial improvements to be ready for the next generation of imaging X-ray polarimeters. Here, we present the development of a detector prototype that can deliver the next generation of sensitive imaging X-ray polarimetry across the energy band of 2–30 keV. We use Ar/DME based gas volume to absorb X-rays by the photoelectric effect and a pixelated CMOS readout ASIC, Timepix3, with excellent timing capabilities to image the resulting photoelectron track in three dimensions. The Timepix3 is integrated with a multiplication stage called InGrid that enables single-primary-electron detection from the gas volume. The photoelectron track reconstructed in three dimensions increases the polarimetric sensitivity towards the lowest operable energies, and the deadtime-free operation of the ASIC facilitates the usage as a focal plane instrument on high-throughput X-ray mirrors. With this prototype, we demonstrate a low-medium-energy X-ray polarimeter with excellent timing and moderate spectral capabilities.
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All authors Hemanth Manikantan, Carlo Lefevre, Lorenzo Petrucci, Paolo Soffitta, Fabio Muleri, Enrico Costa, Alda Rubini, Vladislavs Plesanovs, Markus Gruber, Jochen Kaminski, Klaus Desch, Alessandro Di Marco, Sergio Fabiani, Riccardo Ferrazzoli, Saba Imtiaz, Dawoon E. Kim, Alessandro Lacerenza, John Rankin, Ajay Ratheesh
Solar and Stellar Astrophysics
An extreme case of X-ray reflection in the symbiotic V648 Car
Jherssica Freitas, Raimundo Lopes de Oliveira and Koji Mukai
V648 Car is a $\delta$-type symbiotic
star known for its strong hard thermal X-ray emission, heavy local photoelectric absorption, and
stochastic variability. We analyze NuSTAR observations, complemented by nearly contemporaneous Swift/XRT observations, to check for the expected presence and physical implications of Compton reflection in its X-ray spectrum. The spectra were fitted with X-ray models that accounted for thermal
plasma components, different prescriptions to quantify the intrinsic absorption, the presence of the fluorescent iron line at 6.4 keV, and a reflection component. Our results reveal a strong Compton reflection contribution, accounting for approximately 37% of the total unabsorbed flux in the 3-50 keV band. The inclusion of reflection significantly improves the spectral fits and reduces the value for the maximum
plasma temperature by a factor of 2 (from about 49 keV to 25 keV). If the maximum temperature is attributed to strong shock of a Keplerian flow, the inferred white
dwarf mass decreases from about 20% (from $1.2$ to $0.95\,M_{\odot}$), demonstrating that neglecting reflection can lead to significant overestimates of this parameter. Reflection models yield high reflection scaling factors ($R \sim 2$), inconsistent with a simple picture of a primary X-ray source above a reflecting disk. The timing analysis reveals
stochastic flickering variability with no evidence for coherent periodic modulations, thus the accreting object is likely a non-
magnetic white
dwarf. We propose a multiple-reflection model to explain the extraordinary strength of reflection features in V648 Car.
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Astrophysics of Galaxies
Vortex State of Ultralight Dark Matter and the Fornax Timing Problem
V. Gorkavenko, O. Barabash, T. Gorkavenko et al. (+4 more)
We investigate the impact of the
vortex state of the ultralight dark matter (ULDM) on the dynamical friction acting on moving globular clusters. Comparing this force with that for the solitonic ground state, it is shown that the internal structure and rotation of the ULDM core strongly affect the orbital decay of globular clusters. In particular, co-directional rotation in a
vortex state can lead to significant suppression of dynamic friction at certain distances where globular clusters and ULDM velocities match. Applying these findings to the Fornax
dwarf galaxy, it is found that the Fornax timing problem is naturally alleviated.
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All authors V. Gorkavenko, O. Barabash, T. Gorkavenko, K. Korshynska, O. Teslyk, A. Zaporozhchenko, E. Gorbar
Solar and Stellar Astrophysics · Cross-listed from physics.space-ph
An Adaptive Approach for Modeling Collisionless Plasma Shocks and Ion Heating in the Shock Frame
Yuri A. Omelchenko, Igor V. Sokolov, Lulu Zhao et al. (+2 more)
We present a novel computational method for hybrid (kinetic ions, quasi-neutral fluid electrons) simulations of non-relativistic magnetized collisionless
plasma shocks, observed near the Sun, in the
solar system, and beyond. This Adaptive Frame-Of-Reference Approach (AFORA) enables simulations of shocks in their co-moving frames of reference, where shock
evolution remains quasi-steady for quasi-stationary upstream conditions, in contrast to moving shocks. We demonstrate our method in two spatial dimensions for a range of angles between the background
magnetic field and the shock normal (obliquities). Shock-frame simulations, conducted with a time-adaptive hybrid code, HYPERS, are shown to self-consistently capture upstream and downstream
magnetic fluctuations commonly observed by spacecraft at interplanetary shocks and Earth's bow shock. These fluctuations, which may be crucial for estimating the efficiency of ion acceleration at heliospheric and astrophysical shocks, are notably missing from many hybrid simulations of shocks, unless upstream external
turbulence is imposed. The quasi-stationary behavior of numerical shocks in the shock frame is confirmed in a series of animations and by demonstrating converged ion energy spectra in the downstream region. Our approach underscores computationally efficient and physically more accurate modeling of shock-driven
turbulence, downstream
plasma relaxation, and concomitant ion heating in the shock frame. The new method can be used for exploring ion relaxation at interplanetary (IP) shocks, more efficient studies of
cosmic rays (CRs) and
plasma turbulence, and more accurate predictions of seed populations of
Solar Energetic Particles (SEPs) at heliospheric shocks driven by coronal mass ejections (CMEs).
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All authors Yuri A. Omelchenko, Igor V. Sokolov, Lulu Zhao, Keheng Zhu, Michal Golan
Instrumentation and Methods for Astrophysics
Directional Anisotropic Sensitivity Curves for Pulsar Timing Arrays
Daniel J. Oliver, Jeffrey S. Hazboun, Martine Maggi et al. (+2 more)
After two decades of observations,
pulsar timing array collaborations have reported strong evidence for a
stochastic gravitational wave background, most likely sourced by an inspiraling population of supermassive black hole binaries. Because that population is finite, anisotropy in the background is inevitable, producing hotspots on the sky that track the loudest binaries. Building on the Fisher formalism for anisotropic backgrounds, we recast the directional Fisher information as effective sensitivity curves on the sky, distinguishing the radiometer and full-Fisher
estimators, along with a sky-weighted curve that reduces the anisotropic sky to a single spectrum and recovers the standard isotropic curve in the isotropic limit. We implement five sky-decomposition bases: pixel, spherical harmonic, square-root spherical harmonic, radiometer, and principal-map. We demonstrate the framework on an IPTA-like
pulsar timing array: characterizing the angular response, analyzing the Fisher structure, recovering injected anisotropic hotspots, and
forecasting future-array sensitivity. The framework is released as an extension to the sensitivity software package hasasia.
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All authors Daniel J. Oliver, Jeffrey S. Hazboun, Martine Maggi, Jeremy G. Baier, Kyle E. Gourlie
Astrophysics of Galaxies
Stellar mergers and chemical element mixing: implications for the metamorphic stellar evolution in AGN disks
Yanlong Shi, Xiaoshan Huang, Douglas N. C. Lin et al. (+1 more)
Chemical mixing during
stellar mergers can significantly influence the subsequent
evolution of the merger remnant. We perform a suite of three-dimensional hydrodynamical simulations of
stellar mergers, each evolved for $\sim100$
stellar dynamical times until the remnant reaches a quasi-hydrostatic
equilibrium. The simulations incorporate subgrid-scale
diffusion models to capture the turbulent mixing of chemical elements. Starting with an idealized polytropic equation of state (EOS), we first identify the dominant mixing mechanisms and investigate how the merger outcome depends on the mass ratio, relative velocity, impact parameter, and
stellar structure. We then extend our simulations to the context of
stars embedded in active
galactic nucleus (AGN) disks, using a realistic, composition-dependent EOS and AGN
stellar models generated with the
stellar evolution code MESA. We find that mergers with both younger metamorphic
stars and H-rich accreting AGN
stars can substantially rejuvenate old metamorphic
stars through efficient core mixing after thermal relaxation. The merger remnants are nitrogen-enriched, with ${\rm N/O}\sim1$–3 and ${\rm N/C}\gtrsim5$, comparable to the abundances observed in the nebula surrounding SN 1987A. During subsequent
stellar evolution, the remnants may converge onto the main sequence of isolated metamorphic AGN
stars once they reach
accretion–wind
equilibrium. They may also deposit a significant amount of chemically enriched material into the AGN disk. This work provides a physical framework for connecting hydrodynamical
stellar mergers with the long-term
evolution of AGN
stars and their observational and chemical signatures.
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All authors Yanlong Shi, Xiaoshan Huang, Douglas N. C. Lin, Norman Murray
Instrumentation and Methods for Astrophysics
Calibration of MEMS DM actuator gains using a Zernike wavefront sensor on the HiCAT testbed and implications for Habitable Worlds Observatory operations
Sarah Steiger, Raphaël Pourcelot, Rémi Soummer et al. (+4 more)
Deformable mirrors (DMs) are a key component of coronagraph instruments performing adaptive optics on the ground, and for future space observatories such as HWO and Roman CGI. Here, they will be used as part of the wavefront sensing and control system to "dig a dark zone” - remove residual
stellar light to create a high-contrast region in the focal plane where faint companions can be detected. To reach the deep contrasts needed to directly image cool or reflected light
planets (<1e-8) accurate calibration of the DM actuator gain is essential as picometer differences between the expected and realized DM surface can significantly degrade dark zone (DZ) digging efficiency. This increases the overheads needed to achieve a DZ and critically places more stringent requirements on observatory stability. Furthermore, DM gain varies with actuator stroke, necessitating rapid, in situ gain map recalculations to maintain DZ digging efficiency over time. Zernike wavefront sensors (ZWFS) are well-suited for this task as they efficiently provide picometer-level sensitivity and will likely already be included on board as part of a low order wavefront sensor for HWO. Here we present results from the HiCAT testbed at STScI where we calibrated gain maps for our Boston Micromachines 952-actuator micro electromechanical (MEMS) DMs using both a Fizeau interferometer and a ZWFS to compare performance. With the ZWFS we compute a gain map using both local linear fits around a given DM solution, and present a formalism for deriving more complex quadratic solutions which are more computationally intensive, but accurate over most of the dynamic range of each actuator. We then use these techniques to calibrate the DMs on the HiCAT testbed and show increased DZ digging efficiency with the new gain map and better contrast performance moving from 14 to 16 bit control electronics as enabled by these calibrations.
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All authors Sarah Steiger, Raphaël Pourcelot, Rémi Soummer, Emiel H. Por, Laurent Pueyo, Iva Laginja, Nathan Scott
Instrumentation and Methods for Astrophysics
WST instrument Exposure Time Calculator: full simulation of multi-mode spectrograph performance from source to detector
Matteo Ferro, Matteo Genoni, Henri M. J. Boffin et al. (+13 more)
We present a comprehensive Exposure Time Calculator (ETC) developed for the Wide-field Spectroscopic
Telescope (WST) concept. The WST, currently in its conceptual phase, is designed as a next-generation large spectroscopic survey facility featuring three complementary observing modes: an Integral Field Spectrograph (IFS) covering 370-930 nm at R of about 4800; a high-resolution Multi-Object Spectrograph (MOS-HR) with four bands at R of about 40000; and a low-resolution Multi-Object Spectrograph (MOS-LR) with four channels at R of about 3800-4900. The ETC simulates the complete
photon-propagation path from astronomical source to detector, incorporating wavelength-dependent system throughput (
telescope transmission, instrumental optics, detector
quantum efficiency), accurate sky background via ESO SkyCalc integration, and a comprehensive noise treatment (
photon noise, sky background, read-out noise, dark current). The computational core is implemented as the "pyetc_wst" Python library built on the MPDAF framework, supporting multiple target spectral energy distributions (
stellar templates, blackbody, power-law, emission lines, and user-uploaded spectra with arbitrary
redshift) and spatial morphologies (point sources and Sersic extended profiles). Four operational modes enable flexible exposure-time optimization. Full spectral outputs include wavelength-dependent signal-to-noise ratio (SNR), source and sky
photon counts, noise decomposition by component, and simulated extracted spectra. An interactive web interface, together with a REST API and a command-line tool, complete the user experience and enable batch survey-design workflows.
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All authors Matteo Ferro, Matteo Genoni, Henri M. J. Boffin, Jose Schiappacasse-Ulloa, Sofia Randich, Roland Bacon, Vincenzo Mainieri, Alessio Mucciarelli, Carmela Lardo, Michele Moresco, Cristian Vignali, Margherita Talia, Andrea Scaudo, Marco Landoni, Roelof S. de Jong, Olga Bellido-Tirado
Instrumentation and Methods for Astrophysics
An upgraded frequency-selectable laser source (FLS) calibrator for CMB bandpass characterization
Lauren J. Saunders, Sara M. Simon, Shreya Sutariya et al. (+4 more)
One of the biggest challenges for
Cosmic Microwave Background (CMB) experiments comes from the uncertainty in instrument bandpass calibration. Uncertainties in bandpass can limit foreground removal and spectral fitting, which are critical for inflationary and
galaxy cluster measurements. CMB experiments currently use
Fourier Transform Spectrometers (FTSes) to measure instrument bandpasses. However, FTS systems are currently systematics-limited, so significant improvements in bandpass measurements require novel calibrators. To this end, we developed a Frequency-selectable
Laser Source (FLS) calibrator, which uses a
laser with adjustable frequency coupled to a system that allows for
laser power attenuation. Following initial testing with the first FLS prototype, we developed an upgraded version of the calibrator with improved performance. We present the upgrades to the FLS calibrator, the characterization of the upgraded calibrator and new
laser source, and plans for testing with microwave instruments in the field.
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All authors Lauren J. Saunders, Sara M. Simon, Shreya Sutariya, Elisa Russier, Sanah Bhimani, Erin Healy, Jeffrey McMahon
Solar and Stellar Astrophysics
On Bimodality in the Eccentricity Distribution of Galactic Double Neutron Stars
Aldana Grichener, Paul Disberg, Ryosuke Hirai et al. (+1 more)
The detection of
Galactic double
neutron stars (DNSs) through
pulsar timing offers a unique opportunity to probe massive
stellar and binary
evolution. The observed DNS population exhibits an apparently bimodal eccentricity distribution, with an absence of systems at measured intermediate eccentricities, $0.4 \lesssim e_{\rm m} \lesssim 0.58$, whose origin remains unclear. We propose that this possible gap can arise naturally if the relationship between the progenitor masses and
neutron star (NS) masses is non-monotonic, provided that the second-born NS receives a sufficiently small natal kick. We illustrate this scenario using the population synthesis code COMPAS, and find that our DNS population model can reproduce the observed orbital period-eccentricity distribution relatively well, including the apparent bimodality. Although a larger observed sample is required to draw more robust conclusions, our results suggest that this model provides a natural pathway for explaining current observations of
Galactic DNSs through isolated binary
evolution.
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All authors Aldana Grichener, Paul Disberg, Ryosuke Hirai, Ilya Mandel
Earth and Planetary Astrophysics
The Dynamics of Planetary Ejection
Malena Rice, William DeRocco and Sean N. Raymond
The ubiquity of free-floating
planets inferred from microlensing and direct imaging surveys suggests that planetary ejection—a process in which
planets initially born encircling a
stellar host become gravitationally unbound—is common. Four overarching mechanisms have been proposed to induce planetary ejection: close approaches of neighboring
planets, instabilities in binary or multi-
star systems,
stellar and planetary flybys, and post-main-sequence
stellar evolution. Here we review the mechanisms underlying planetary ejection, as well as predictions derived from each. Current and upcoming microlensing surveys offer the potential to test existing models and distinguish between planetary ejection mechanisms, offering further insight into the demographic-level architectures of
exoplanets across
stellar environments.
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Cosmology and Nongalactic Astrophysics
Evidence for a thermal pressure deficit in galaxy groups from the tSZ effect and weak lensing
Jared Siegel, Alexandra Amon, Jenny E. Greene et al. (+3 more)
Measurements of the thermal Sunyaev-Zel'dovich (tSZ) effect have yet to form a consistent picture of the thermodynamic state of the gas in the intracluster medium: their interpretation is complicated by foreground contamination and uncertain
halo masses. We present new measurements of the tSZ effect around the Dark Energy Spectroscopic Instrument (DESI) Luminous Red
Galaxy (LRG) sample, together with
galaxy-
galaxy lensing (GGL) measurements that enable a like-with-like comparison to state-of-the-art hydrodynamical simulations. We robustly isolate the tSZ signal by directly modeling the
dust and
radio emission of the target
galaxies using the Atacama Cosmology
Telescope (ACT) single-channel temperature maps, substantially reducing uncertainties from astrophysical foregrounds. Across
halo masses $M_{500}=10^{13}-10^{14}~M_\odot$ and
redshifts $0.4<z<1$, we find that the fiducial 1 Gpc$^3$ FLAMINGO simulation significantly overpredicts the observed tSZ signal at $\lesssim3'$ (i.e., $\lesssim 4\,R_{500}$ at $z=0.7$). Even the simulation with the strongest gas expulsion—which successfully reproduces the gas density inferred from kinetic SZ measurements of the same
galaxy sample—overpredicts the thermal pressure. Because the strongest feedback model already reproduces the observed gas density, the remaining discrepancy is difficult to explain with additional gas depletion alone. Instead, current hydrodynamical simulations appear to overpredict the thermal pressure of
galaxy groups by a factor of two, pointing toward missing non-thermal pressure support or significant departures from hydrostatic
equilibrium.
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All authors Jared Siegel, Alexandra Amon, Jenny E. Greene, Ian G. McCarthy, Eliot Quataert, William Coulton
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Ubiquitous Corotation of Dark Matter Halos: Implications for Direct Detection
Dylan Folsom, Carlos Blanco, Mariangela Lisanti et al. (+1 more)
Cosmological simulations have recently begun to quantify the
halo-to-
halo variance in the phase-space distribution of dark matter around the Sun. We use a sample of nearly one hundred Milky Way-like
galaxies from the TNG50 simulation to determine what aspects of this variance control the predictions for dark matter direct detection. Contrary to the isotropy assumed in the standard
halo model, we find the dark matter median azimuthal velocity is nonzero and preferentially corotating, i.e., in the direction of the baryonic disk's rotation, ranging from 6-70 km/s (16th-84th percentile). This corotation suppresses predicted scattering rates in laboratory experiments searching for dark matter lighter than 50 GeV and significantly affects the expected daily modulation amplitude for directional detectors. In particular, this induces a 21% uncertainty on the upper limit of the dark matter-nucleon interaction cross section at peak sensitivity for a typical isotropic ton-scale experiment. This uncertainty is not irreducible, however: it is strongly correlated with the rotational velocity. If studies of the Milky Way's formation history determine the rotation speed, this astrophysical uncertainty is reduced to 7%.
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All authors Dylan Folsom, Carlos Blanco, Mariangela Lisanti, Mark Vogelsberger
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Extra-dimensional Origins of Chemical Potentials at the Cosmological Collider
Raman Sundrum and Zhaohui Xu
We study the realization of the chemical potential mechanism in cosmological
collider physics in a robust class of inflationary models arising from multiple higher-dimensional gauge fields. The rolling inflaton background corresponds to an electric field in the extra dimension in which charged particles are produced analogously to the Schwinger mechanism, while neutral particles can be produced through non-minimal interactions. We show that particles heavier than the inflationary Hubble scale can be created without Boltzmann suppression in both cases. In particular, charged Kaluza-Klein excitations can be created through minimal gauge interactions. We construct realistic models along these lines consistent with both theoretical and experimental constraints.
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Instrumentation and Methods for Astrophysics
The critical role of HST UV spectroscopy in constraining red supergiant binary systems
Daniel Jadlovský, Andreas Sander, Lee Patrick et al. (+3 more)
The Hubble Space
Telescope (HST) has advanced our knowledge of
stellar evolution thanks to its unique high-spectral resolution and high-sensitivity capabilities in the UV region, especially for hot massive
stars. Within the field of red supergiants (RSGs), it has led to several major insights as well, such as, for example, characterizing the embedded hot companion in the VV Cephei system, the detection of surface mass ejection from Betelgeuse, and unveiling the rich population of RSG+B binaries in the Magellanic Clouds. We demonstrate that nowadays (and in the decade to come) we need HST more than ever, as for the first time, thanks to the significant advances of high-angular-resolution interferometric and astrometric techniques, we can resolve the orbital motion of
stellar components in RSG systems. However, the long wavelengths are dominated by the cool RSGs. Thus, observing such companions in the UV with HST is the only way to constrain the properties and velocity of the hot companions, adding the required missing piece of information for constraining the orbital solution and evolutionary status of RSG systems. Such observations are critical for understanding the interaction and mass transfer in massive binary systems and their connection to the observed population of
supernovae.
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All authors Daniel Jadlovský, Andreas Sander, Lee Patrick, Jiří Krtička, Gemma González-Torà, Matheus Bernini-Peron
Cosmology and Nongalactic Astrophysics
Emulating the nonlinear effects of modified gravity on the matter power spectrum for reconstruction
Lanyang Yi, Kazuya Koyama, Qi Xiong et al. (+1 more)
Including nonlinear information from modified
gravity (MG) brings more constraining power to the model-independent reconstruction of MG functions. However, the calculation of the nonlinear matter power spectrum with MGCAMB+ReACT is expensive in repeated likelihood evaluations, which limits the exploration of the high-dimensional parameter space. In this work, we construct a neural-network emulator for the nonlinear correction $R_{\mathrm{MG}}(k,z)=P_{\mathrm{MG}}^{\mathrm{NL}}(k,z)/P_{\mathrm{MG}}^{\mathrm{L}}(k,z)$, which is trained with CosmoPower on approximately $9\times10^5$ samples and validated with representative spectra, an independent validation set, and MCMC tests with synthetic data. For $\Lambda$CDM and moderate MG nonlinear corrections, the emulated power spectra agree with the reference predictions to within $1.5\%$ over the full scale range considered. For the extreme nonlinear case, the same accuracy is retained for $k<0.8\,\mathrm{Mpc}^{-1}$. Over the independent validation set, the mean residual is close to zero, with the $2\sigma$ scatter below $1\%$ for $k<0.5\,\mathrm{Mpc}^{-1}$ and about $2\%$ on smaller scales. The synthetic data MCMC analyses recover the input $\Lambda$CDM cosmology and the GR limits of the reconstructed MG functions within the posterior uncertainties, showing the accuracy and reliability of the emulator for Stage-IV-like surveys. We also demonstrate three applications: using $R_{\mathrm{MG}}$ to distinguish models with nearly degenerate linear power spectra, using the emulator for theory predictions for current photometric-survey $3\times2$pt likelihoods, and
forecasting DESI+CSST constraints with principal component analysis.
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All authors Lanyang Yi, Kazuya Koyama, Qi Xiong, Gong-Bo Zhao
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Dark Photons from Perturbative Decay of a Misaligned Higgs Field
James M. Cline, Gonzalo Herrera and Jean-Samuel Roux
We reconsider the production of dark
photons $A'$ as dark matter, from the perturbative decay of a dark
Higgs field $h$, that is stochastically misaligned from the minimum of its potential during inflation. This is a simple and predictive framework for generating the $A'$ relic abundance. It is constrained by structure formation, since the $A'$ are initially boosted, and inflationary isocurvature fluctuations, which require small quartic couplings $\lambda h^4$. We identify $A'$ masses between 100 eV and 1 GeV and gauge couplings $g\sim 10^{-15}-10^{-10}$ that are consistent in this scenario, and which become more tightly constrained if a generic level of kinetic mixing is present. The favored parameter region could be tested through future CMB or Lyman-$\alpha$ observations, and, in the presence of kinetic mixing, by direct detection experiments or diffuse soft gamma-ray searches.
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Cosmology and Nongalactic Astrophysics
An optimal quadratic estimator for window-free cosmic shear power spectra
Taisei Terawaki and Masahiro Takada
The pseudo-$C_\ell$
estimator recovers the true
cosmic shear power spectrum by correcting for the survey window convolution while employing inverse-variance weighting based on intrinsic shape noise of source
galaxies. However, this weighting scheme is optimal only on small angular scales where shape noise dominates. In this paper, we derive a quadratic
estimator for the unwindowed
cosmic shear power spectrum by maximizing the Gaussian likelihood of the pixelized
galaxy-shape field using the full covariance
matrix, which accounts for both sample variance and shape noise. By combining FFTs in the flat-sky approximation, the conjugate-gradient method, and Monte Carlo realizations of Gaussian ancillary fields, we substantially reduce the computational cost of estimating the Fisher
matrix, a key ingredient of the
estimator that requires repeated inverse-covariance
matrix operations. Using Gaussian simulations of shape fields, we validate the method and demonstrate that it can recover the input $E$-mode power spectrum with statistically optimal precision across all angular scales. We then apply the method to shape fields generated from ray-tracing simulations for a $\Lambda$CDM cosmology and show that, compared with the pseudo-$C_\ell$ method, it reduces the statistical uncertainties in the $E$-mode power spectrum by 5–15% at multipoles of $\ell \lesssim 500$. We further demonstrate that the method significantly suppresses $E$- to $B$-mode leakage across the full multipole range. Our
estimator therefore provides a statistically optimal approach for measuring
cosmic shear power spectra from wide-area
galaxy survey data.
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Solar and Stellar Astrophysics
The IACOB project XIX. Revisiting massive-star evolution with empirical TAMS constraints: updated models, overshoot calibration, and the population of blue supergiants
Luca Sciarini, Abel de Burgos, Sophie Rosu et al. (+3 more)
Massive
stars play a fundamental role in the
evolution of the Universe. Yet, several physical processes governing their
evolution remain poorly constrained. Notably, the main-sequence width is sensitive to the convective boundary mixing efficiency; it becomes necessary to account for binary interactions to explain some observed properties of massive-
star populations. We constrain single-
star models using recent observations of massive
Galactic stars from the IACOB database. We use the latest proposed empirical location of the TAMS to calibrate the convective boundary mixing efficiency, and use this calibration to test single-
star evolution by comparing various model predictions to the observed populations of the IACOB sample. We compute several GENEC grids with various overshoot calibrations, angular momentum transport (AMT) treatments, initial masses and velocities. Finally, we generate synthetic populations from the tracks with SYCLIST and perform a direct comparison with the observed population. The calibrated models at slow rotation reproduce the empirical TAMS location. We find that a mass-dependent overshoot efficiency is required to fit the observational constraints. The overall rotational properties of the observed populations are well reproduced with single-
star models, independently of the AMT assumptions. Models accounting only for hydrodynamical instabilities are successful at reproducing the rotational properties, unlike previous genec grids, which we attribute to the choice of winds prescription. Although the empirical TAMS of slow rotators is well reproduced, we find that models are unsuccessful at explaining the velocity dependence of the TAMS location observed in the IACOB sample. Finally, we find that single-
star models fail at explaining the population of blue supergiants to the right of the TAMS location.
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All authors Luca Sciarini, Abel de Burgos, Sophie Rosu, Sylvia Ekström, Sergio Simón-Díaz, Cyril Georgy
Earth and Planetary Astrophysics
Critical Sizes of Satellite Constellations
Hugh G. Lewis
The precipitous growth of commercial space activity, largely from the development of satellite constellations, threatens to produce a runaway orbital debris population. National regulators are attempting to limit these risks through orbital debris mitigation requirements, but these fail to address the large scale and long lifetimes of satellite constellations. Instead, evaluations are based on the risks from single satellites, and the aggregate risks across constellations are neglected. This situation arises in part because of a lack of suitable approaches to evaluate constellation plans. Here a simple analytical approach reveals that several planned, partially deployed, or fully deployed constellations exceed their critical size producing an unstable or a runaway orbital debris population. Worryingly, this occurs both for small and large constellations, despite debris mitigation measures that go beyond internationally recognised good practices, and even when the constellations are deployed into a pristine, debris-free orbital environment. The results demonstrate the need for more stringent approaches to regulation and suggest careful consideration of some recent constellation plans.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Inflation and Reheating by Dynamical Torsion
Xiaolin Ma, Kamil Mudrunka and Kazunori Nakayama
In
gravity theories with torsion, inflation can be driven by the dynamical torsion. Since it naturally has a derivative coupling to the axial current consisting of Standard Model particles, the reheating dynamics should be much different from conventional inflation models like Starobinsky inflation. We calculate the inflaton decay rate in detail and find that, although the 2 body decay into the
fermion pair is vanishing in the massless
fermion limit, the anomaly-induced 2 body decay into the gauge
bosons and 3 body decay involving the
Higgs boson are non-vanishing and they give sizable contributions to the total decay width of the inflaton. This gives a natural lower bound on the reheating temperature in the inflation model with dynamical torsion.
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Solar and Stellar Astrophysics
On the use of field RR Lyrae as Galactic probes:. IX. Radial velocities
K. Baeza-Villagra, V. F. Braga, M. Fabrizio et al. (+25 more)
We present the largest and most homogeneous catalog of radial velocity (RV) measurements for field RR Lyrae (RRL) variables, based on both proprietary and publicly available spectroscopic data. The sample includes 17,563 RRLs pulsating in the fundamental mode (12,353 RRab), in the first overtone (5,011 RRc), and in double-mode (199 RRd). The RV curve (RVC) templates for metallic and Balmer lines were used to derive RV amplitudes and $V_{\gamma}$ velocities, defined as the RV of the
stellar barycenter with respect to the Sun. The typical accuracy across the catalog is on average 3.8 km s$^{-1}$ for well-sampled RVCs, 6.5 km s$^{-1}$ for RVCs with 3-7 phase points and 11.3 km s$^{-1}$ for RVCs with fewer than three phase points. The use of different spectroscopic diagnostics and RVC templates provides, within the errors, very similar $V_{\gamma}$ velocities. We found that the
metallicity dependence of RV amplitudes is vanishing for metallic lines, but becomes increasingly significant for H$\gamma$ and H$\delta$. Moreover, the scaling relations between photometric (V, $G_{BP}$, G, $G_{RP}$) and RV amplitudes are linear for RRc and nonlinear for RRab variables, independently of the adopted diagnostic. This circumstantial evidence indicates that convection affects more luminosity than RV amplitudes when moving from the blue (hot) to the red (cool) edge of the instability strip. The spectroscopic Bailey diagram (RV amplitude versus period) shows a smooth transition and a reduced spread at a fixed period, when moving from metal-poor to metal-rich RRLs. Finally, we also found evidence that the
metallicity distribution function of Blazhko RRLs is skewed toward the metal-intermediate and metal-rich regimes.
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All authors K. Baeza-Villagra, V. F. Braga, M. Fabrizio, G. Bono, V. D'Orazi, Z. Prudil, F. Berrilli, G. Böcek Topcu, G. Ceci, B. Chaboyer, M. Dall'Ora, D. Del Moro, M. Di Criscienzo, G. Fiorentino, M. Gholami, R.-P. Kudritzki, M. Marengo, N. Matsunaga, M. Monelli, J. P. Mullen, A. Nunnari, G. W. Preston, C. Sneden, M. Tantalo, F. Thévénin, I. B. Thompson, E. Valenti, M. Zoccali
Astrophysics of Galaxies
A Massive Galaxy at the Edge of Feedback-Free Efficiency
K. Aditya and Kartick C. Sarkar
The efficiency with which
galaxies convert their available baryonic reservoir into
stars sets a fundamental ceiling on
stellar mass assembly in the early Universe and encodes the cumulative effect of
stellar feedback. in this paper, we report the measurement of
star-formation efficiency (SFE) of a photometrically and spectroscopically vetted reference sample at $z=9-10$, out of which 31 are spectroscopically confirmed. Among them, we highlight a spectroscopically confirmed
galaxy, UNCOVER 3686 at $z = 9.31$, which has a
stellar mass $M_\star = 10^{9.55}$ M$_\odot$ and physical properties comparable to the predictions of the feedback-free starburst (FFB) scenario. We use this
galaxy as an anchor for the first direct observational test of whether
galaxy at
cosmic dawn with physical properties predicted in the FFB theory reach the maximum
baryon conversion efficiencies predicted by the feedback-free starburst scenario. We find the SFE for this
galaxy to lie between $\approx 20\%$ and $60\%$, a factor of 2 to 6 above empirical model predictions. The compact morphology ($R_e = 0.45$ kpc), young
stellar age ($\sim 160$ Myr), low
metallicity $(Z_\star/Z_\odot \approx 0.2)$, and inferred gas density $(n_{\rm gas} \sim 3\times 10^{3}$ cm$^{-3}$) of this
galaxy are consistent with feedback-free (FFB)
galaxy formation conditions. We conclude that UNCOVER 3686 is an excellent candidate for an FFB
galaxy in which the global
star formation efficiency approaches the theoretical limits due to weak
stellar feedback.
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Solar and Stellar Astrophysics
Asteroseismic models of the magnetic binary HD 156424
C.C. Lovekin, S. Davis and V. Khalack
HD 156424 is a hot
magnetic star in the Sco OB4 association and has previously been identified as part of a binary system. Spectropolarimetric results show that the companion
star is also strongly
magnetic, and thus this is a rare example of a doubly
magnetic hot binary. In this work, we aim to present a more detailed analysis of Transiting
Exoplanet Survey Satellite data including phase variation. We find short-term phase variation consistent with an oblique
magnetic rotator, as well as long-term phase variation consistent with the third element proposed previously. We performed asteroseismic modelling of the
star and determined that the pulsations are most likely associated with the primary of the system. Our best-fit models are universally young, and we find that the
star is well fitted by a model with $M$=7.5 M$_{\odot}$.
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Instrumentation and Methods for Astrophysics
The Tartu Observatory Fiber-fed Echelle Spectrograph (TOFES) Data Reduction Pipeline
Sandipan P. D. Borthakur, Tõnis Eenmäe, Nikolai Piskunov et al. (+9 more)
We introduce the data reduction pipeline for the Tartu Observatory Fiber-fed Echelle Spectrograph (TOFES). TOFES is installed in the Coudé room and will be connected to the 1.5 m Tartu Observatory AZT-12
telescope through a four-channel instrument adapter to be mounted at the Cassegrain focus of the
telescope. The spectrograph has an average spectral resolution of 30,000 and covers the 390 to 900 nm wavelength band in a single exposure. The data reduction pipeline, based on the PyReduce package, was tested on spectra of the Sun. We also present the Spectroscopy-Toolbox package, which was developed to provide additional tools for diagnostics and spectral line identification for radial velocity measurements. The spectrograph will address a range of scientific questions, including the
stellar characterisation of Herbig AeBe
stars to measure
accretion contamination from their protoplanetary disks, the
stellar characterisation of
exoplanet host-
stars including the Ariel space mission targets, and radial velocity monitoring of large-scale atmospheric variability in massive
stars.
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All authors Sandipan P. D. Borthakur, Tõnis Eenmäe, Nikolai Piskunov, Luca Fossati, Mihkel Kama, Thomas Marquart, Anni Kasikov, Heleri Ramler, Anna Aret, Christiane Helling, Laurits Leedjärv, Linn Boldt-Christmas
Cosmology and Nongalactic Astrophysics
Late Time Dynamical Dark Energy and the CMB-Distance Ladder Tension
George Efstathiou
The traditional distance ladder measures the standardized peak absolute magnitude M^B of Type Ia
supernovae (SNIa). According to the SH0ES collaboration, the distance ladder value of M^B is highly discrepant with the value inferred from the
cosmic microwave background (CMB) assuming the LCDM cosmology. This CMB-distance ladder tension is insensitive to the actual late time expansion history of the Universe. To derive a value of the Hubble constant H_0, from M^B requires a cosmological model. However, the magnitude-
redshift relation of SNIa provides tight constrains the expansion history. As a consequence, uncertainties in the conversion of M^B into H_0 have no significant impact on the CMB-distance ladder tension. The tentative claim by the Dark Energy Spectroscopic Instrument collaboration for late time
evolution of the dark energy equation of state does not alter this conclusion.
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Earth and Planetary Astrophysics
Warm Sub-Saturns Orbiting Single Stars Are Spin-Orbit Aligned
Xian-Yu Wang and Songhu Wang
In this work, we show that warm sub-Saturns orbiting single
stars are predominantly aligned, in contrast to hot sub-Saturns, which are frequently misaligned, with the two populations differing at the 3.2$\sigma$ level. Because both populations are observed around cool
stars, they are free from the ambiguity introduced by the $T_{\rm eff}$-$\lambda$ dependence. Together with the established
alignment of warm Jupiters, this demonstrates, among single-
star systems, that
spin-orbit misalignment arises specifically in the close-in “hot-Jupiter-analog” regime, where
tidal circularization is efficient ($\tau_e<\tau_{\rm age}$) and high-eccentricity migration is expected to operate. We further find that the transition between aligned and misaligned sub-Saturns occurs at wider orbital separations ($a_{\rm final}/R_p = 338\pm27$) than for Jupiters ($a_{\rm final}/R_p = 117\pm9$), consistent with the expectation that the lower masses (smaller $M_p/M_*$) and stronger
tidal dissipation (lower $Q_p$) of sub-Saturns allow them to be circularized into wider final orbits within their lifetimes. Taken together, these results provide the clearest direct evidence to date that, in single-
star systems,
spin-orbit misalignments are produced by high-eccentricity migration. If this framework is correct,
spin-orbit misalignments may also emerge among hot-Jupiter analogs in other mass regimes, including hot brown
dwarfs around hot
stars at $a_{\rm final}/R_p\lesssim100$ and isolated hot super-Earths at $a_{\rm final}/R_p\lesssim1000$, with the corresponding transition locations shifted by the dependence of the orbital-circularization timescale on $M_p/M_*$ and $Q_p$.
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