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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 15 July

Astrophysics of Galaxies

Probing the Orientation Distribution of Nearby Double White Dwarfs through Gravitational Waves with LISA

N. Seto and G.C. Liu

We present a framework to study the orientation distribution of nearby double white dwarf binaries with LISA, explicitly accounting for the fourfold degeneracy in the polarization angle. Exploiting the belt-like sky distribution of the nearby sample along the Galactic plane, we show that the low-multipole extraction can be recast as an effectively one-dimensional Fourier analysis along Galactic longitude, within a spherical-harmonic expansion based on the Wigner-\(D\) formalism. The symmetry with respect to the Galactic plane governs the sensitivity: modes even under reflection across the plane remain accessible, while odd modes are strongly suppressed. For a fiducial sample of about 500 binaries within \(\lesssim 4\) kpc, corresponding to roughly 5% of the resolved Galactic population, the method yields an uncertainty of order 0.02 for the even coefficients with \(\ell \leq 3\), and is readily applicable to the forthcoming LISA catalog.
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Cosmology and Nongalactic Astrophysics

Radial velocity statistics of cosmic voids as a probe of interacting dark energy

Kin Ho Luo, Ming-chung Chu, Kwan Chuen Chan et al. (+1 more)

Due to their vast sizes and extremely low densities, the dynamics of cosmic voids are largely decoupled from complex, small-scale baryonic physics and are highly sensitive to the background expansion of the Universe. This makes them clean and sensitive probes of dark energy's properties. Using N-body simulations, we show that the void radial velocity and velocity dispersion profiles are sensitive to the Type 3 interacting dark energy model parameters, the momentum coupling $\beta$ ($<0$) and the scalar field parameter $\lambda$. Within the $1\sigma$ range of the best-fit values of $\beta$ and $\lambda$ constrained by Planck CMB, DESI BAO, and DES-Y5 supernova data, we find up to $\sim 30\%$ deviations in the void radial-velocity and velocity-dispersion profile spans relative to the uncoupled scenario, which can be well-approximated by a 4-parameter quadratic regression model. This demonstrates that the void radial velocity statistics provide an independent and observationally accessible probe of the dark-sector interaction in the Type 3 model.
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All authors Kin Ho Luo, Ming-chung Chu, Kwan Chuen Chan, Wangzheng Zhang

Instrumentation and Methods for Astrophysics

Linear motion (R-FLEX) for minature 6.2 mm pitch optical fiber position robots with polar (R-theta) kinematics

Nicholas R. Wenner, Joseph H. Silber, Michael S. Schubnell et al. (+4 more)

R-FLEX is a compact, low-part-count flexure-based radial positioning mechanism designed for the next generation of massively parallel fiber-fed spectroscopic telescope instruments. Current instruments such as the Dark Energy Spectroscopic Instrument (DESI) employ 5,000 robotic fiber positioners at 10.4 mm pitch, whereas future surveys require 2.5-3x higher packing density, necessitating new positioning technologies. The R-FLEX mechanism converts small rotations at the flexure base into large, nearly tilt-free radial motion at the fiber tip, achieving naturally low-backlash linear motion within a compact 5.8 mm diameter package. Coupled with a rotating theta-stage, this enables overlapping circular patrol areas at 6.2 mm pitch, as envisioned for projects like Spec-S5. Development proceeded through parametric modeling and optimization, finite element analysis, fabrication, and prototype testing. Prototype units characterized by optical centroiding achieved a corrected radial accuracy consistently better than 4 um RMS over a 3.9 mm travel range, with maximum fiber tilt 0.092 deg, defocus 42 um over the required range, and durability over more than 400,000 targets per robot across operating and survival temperature extremes. Preliminary Spec-S5 accuracy, defocus, and fiber tilt requirements are specified for the complete R-theta robot, and these radial-stage results exceed those requirements, leaving margin for the companion theta-stage. A parametric optimization pipeline makes R-FLEX a versatile, mass-producible platform that can be re-optimized for precision-positioning applications beyond Spec-S5. This offers the precision, compactness, and reliability needed to collect hundreds of millions of spectra for new studies of the large-scale structure of the universe.
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All authors Nicholas R. Wenner, Joseph H. Silber, Michael S. Schubnell, David J. Schlegel, Robert W. Besuner, William V. Shourt, Andrew P. Hope

Tuesday 14 July

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

Reconstructions of Horndeski Subclasses by Gaussian Processes

Marco C. Mendoza Marcos and Ana A. Avilez Lopez

In this work we reconstruct two subclasses of theories from the Horndeski class, the most general scalar-tensor theories of gravity with second-order equations, according to a variety of late-universe cosmological data: model independent measurements of Hubble rate from Cosmic Chronometers, as well as Hubble rate and distance measurements from Baryonic Acoustic Oscillations. In the modified gravity family considered, the scalar field is non-minimally coupled to gravity leading to time variations in the gravitational constant at cosmological scales. The theories considered are also consistent with constraints on the propagation speed of gravitational waves. The reconstruction is carried out by using the Gaussian Processes bayesian technique either for the Brans-Dicke and the Cubic Galileon subclasses of Horndeski theory. We find that the most likely Gaussian Process reconstruction for the data favors a cosmology from the Brans-Dicke subclass over $\Lambda$CDM in the range $z \in (0.4, 1.7)$, and for the Cubic Galileon subclass we find that the most likely reconstruction indeed favors modifications of the scalar field to gravity with evolving dark energy density in the whole range of redshift observations.
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Earth and Planetary Astrophysics

Revisiting TOI-4438 and TOI-442 planetary systems with new observations from SPIRou and TESS

J. Serrano Bell, G. Hébrard, E. Martioli et al. (+26 more)

We present a comprehensive re-analysis of two star-planet systems: TOI-4438, an M3.5V star hosting a mini-Neptune in a 7.4-day orbit, and TOI-442, an M1V star with a 4-day period planet located within the hot Neptune desert. Both systems were originally identified as transiting planet candidates by TESS and subsequently validated through the radial velocity (RV) method. Our work incorporates new TESS transit data and high-resolution spectroscopy from the SPIRou near-infrared spectropolarimeter. We detect a persistent and relatively strong Zeeman signature in TOI-442, while TOI-4438 exhibits weaker and intermittent magnetic activity, and we infer the stellar rotation periods of both stars from the variability of the longitudinal magnetic field. We jointly fit photometry and RV models for each system. For TOI-4438\,b we combine archival CARMENES data with 81 SPIRou observations and five TESS sectors. This yields a refined planetary mass of $M_{\rm p} = 4.11^{+0.40}_{-0.38}\,M_{\oplus}$ and a radius of $R_{\rm p} = 2.40^{+0.09}_{-0.10}\,R_{\oplus}$, consistent with the previous estimate within 1.1$\sigma$ while improving by 53% the precision on the mass and 22% on the radius. For TOI-442\,b, we add 29 SPIRou RV measurements to an extensive archival dataset, significantly extending the temporal baseline. With a new TESS sector, we tighten the mass to $M_{\rm p} = 28.38^{+0.77}_{-0.73}\,M_{\oplus}$ and radius to $R_{\rm p} = 4.25^{+0.10}_{-0.08}\,R_{\oplus}$, which agrees to the previous values within 1.5$\sigma$ and improves the precisions by 46% and 67% respectively. We find no clear signs of additional planets in the available RV data, although we detect a single-transit event in the TOI-4438 light curve. We compare various RV models and find that those accounting for stellar variability-induced signals yield improved constraints on the planetary parameters.
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All authors J. Serrano Bell, G. Hébrard, E. Martioli, R. F. Díaz, L. de Almeida, D. Lorenzo-Oliveira, A. Salmi, C. Dorn, M. Valatsou, A. Carmona, M. Ould-Elhkim, L. Arnold, É. Artigau, I. Boisse, X. Bonfils, C. Cadieux, Z. Chakir, N. J. Cook, X. Delfosse, J.-F. Donati, R. Doyon, N. Heidari, J. M. Jenkins, F. Kiefer, S. Lafrance, A. L'Heureux, C. Moutou, J. Morneau, X. Vandelac

Cosmology and Nongalactic Astrophysics

The $H_0$ world cup. II. A comprehensive competition between proposed Hubble tension solutions

Nils Schöneberg, Vivian Poulin, Angelo G. Ferrari et al. (+6 more)

Cosmology stands at a crossroads. The Hubble tension has reached a nominal significance above $7\sigma$, while analyses combining DESI BAO and Type Ia supernova data show emerging hints of departures from $\Lambda$CDM. Meanwhile, high-precision CMB measurements from ACT and SPT enable a timely and more stringent reassessment of proposed solutions to the tension. In this paper, we revisit the $H_0$ Olympics, a systematic contest comparing proposed alternatives to $\Lambda$CDM using common datasets, likelihoods, and statistical criteria. In this updated edition, the $H_0$ World Cup, we subject fourteen representative solutions to a common analysis of current CMB, BAO, and SN data. The contenders span four broad mechanisms: late-time modifications of the expansion history, modified recombination, additional pre-recombination radiation, and early non-radiative energy injection. Relative to the original analysis, the present competition includes models and mechanisms proposed in the intervening years and evaluates all contenders using both Bayesian and Frequentist tests of tension and model performance, letting the neutrino mass sum vary. We further test if late-time extensions through curvature or the Chevallier-Polarski-Linder (CPL) dark energy parametrization can aid the success of the models. Finally, we subject the leading contenders to dedicated robustness tests involving alternative CMB likelihoods and multipole cuts, supernova samples, large-scale-structure information, and big-bang nucleosynthesis constraints. This framework assesses both the ability of each mechanism to ease the Hubble tension and the robustness of our conclusions to datasets and analysis choices.
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All authors Nils Schöneberg, Vivian Poulin, Angelo G. Ferrari, Fabio Finelli, Julien Lesgourgues, Luca Morelli, Markus R. Mosbech, Ravi Kumar Sharma, Théo Simon

Cosmology and Nongalactic Astrophysics

The $H_0$ World Cup. I. Summary of the baseline group stage results

Nils Schöneberg, Vivian Poulin, Angelo G. Ferrari et al. (+6 more)

The Hubble tension has reached a nominal significance above $7\sigma$, while new high-precision measurements of the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO) sharpen the test of proposed solutions. Using a common framework, we compare fourteen representative alternatives to the standard $\Lambda$ Cold Dark Matter ($\Lambda$CDM) model in light of up-to-date CMB, BAO and supernovae data to gauge their ability to resolve the tension. The models span late-time modifications, modified recombination, and exotic pre-recombination expansion histories driven by additional radiation or a localized dark energy injection. We evaluate each proposal with complementary frequentist and Bayesian measures of the residual calibration tension and of the improvement in the joint fit. Both approaches identify the same broad hierarchy. Early dark energy and early modified gravity models perform best, shifting the $H_0$ inference without local measurement priors toward $70\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$ and reducing the residual discrepancy with SH0ES to approximately $2.5-3.6\sigma$, depending on the model and statistic, while receiving strong support over $\Lambda$CDM in the combined fit. Varying the electron mass at recombination yields an intermediate improvement, whereas the enhanced-radiation and late-time scenarios do not improve over $\Lambda$CDM. This Letter summarizes the group stage of the competition; in a companion paper (Paper II) we present the results of an exhaustive set of analyses and assess their robustness to variations in modeling assumptions and datasets.
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All authors Nils Schöneberg, Vivian Poulin, Angelo G. Ferrari, Fabio Finelli, Julien Lesgourgues, Luca Morelli, Markus R. Mosbech, Ravi Kumar Sharma, Théo Simon

Astrophysics of Galaxies

COSMOS2025: A Machine Learning Census of Massive Quiescent Galaxies at $2.5 < \text{z} < 5$

Vahid Asadi, Hosein Haghi and Akram Hasani Zonoozi

The existence of massive quiescent galaxies at high redshifts ($ \text{z} \gtrsim 2$) strongly constrains the rapid quenching mechanisms in galaxy evolution models. We present a machine learning framework to identify massive ($\log(\text{M}_*/\text{M}_\odot) > 9.5$) quiescent galaxies at $2.5 < \text{z} < 5$ in the COSMOS2025 catalog. We train a CatBoostClassifier on mock photometry from the Santa Cruz semi-analytic models (SAMs), incorporating key JWST NIRCam bands and realistic noise to transfer the SAM-derived quiescent label (based on specific star-formation rate) to the observational space. When validated against the SAM ground truth, our classifier achieves a significantly higher recall (completeness) of 78% (compared to 53% for spectral energy distribution (SED)-fitting), while maintaining a high purity of 82%. Applied to the COSMOS2025 sample, and assuming the SAM definition of quiescence transfers to the real Universe, the model identifies 1111 quiescent candidates, a population 2.6 times larger than the 427 candidates identified via the catalog's simple SED-fitting configuration. Under the SAM definition of quiescence, this consistent pattern of high purity but poor completeness suggests that the SED-fitting methods, constrained by simplified parametric star-formation histories, may miss a significant fraction of the quiescent population, likely galaxies in crucial transitional evolutionary stages. The trained classifier and classified COSMOS2025 sample are publicly available.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Neural-Accelerated Bayesian Calibration of Chiral Mean-Field Models to Nuclear Saturation and Vacuum Properties

Isaac Legred, Mateus Reinke Pelicer, Veronica Dexheimer et al. (+2 more)

Chiral models of nuclear interactions provide approximate, phenomenological descriptions of dense matter that respect the symmetries of quantum chromodynamics. Their Lagrangian parameters, however, are difficult to calibrate because these models are not controlled effective theories. Furthermore, repeated model evaluations are computationally expensive, and most parameter choices fail to reproduce acceptable saturation properties or hadron masses in vacuum. To address this, we develop a Bayesian inference framework to identify parameter regions consistent with nuclear saturation properties and vacuum experimental constraints. We implement this framework through a neural-network surrogate approximation that accelerates the repeated mapping from model parameters to nuclear and particle observables. Our fully-modular, neural-accelerated Bayesian framework interfaces the open-source MUSES Calculation Engine, the Bilby inference library, and the PyTorch machine-learning toolkit. We then apply the framework to the chiral mean-field model with a new generalized quartic vector self-interaction sector. We find that viable solutions are rare but broadly distributed within certain regions of parameter space, with the data constraining combinations of couplings more strongly than individual Lagrangian parameters. The resulting degeneracies imply that distinct saturation-compatible models can lead to qualitatively different descriptions of dense nuclear matter and, thus, of neutron stars, highlighting the need to combine terrestrial and astrophysical information.
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All authors Isaac Legred, Mateus Reinke Pelicer, Veronica Dexheimer, Jacquelyn Noronha-Hostler, Nicolás Yunes

Instrumentation and Methods for Astrophysics

MORFEO: Advancing Towards Final Design

Lorenzo Busoni, Guido Agapito, Marco Bonaglia et al. (+106 more)

The Multiconjugate adaptive Optics Relay For ELT Observations (MORFEO) is a first-generation adaptive optics module for the Extremely Large Telescope (ELT), designed to deliver a diffraction-limited, highly uniform 53x53 arcsec field of view to the MICADO near-infrared camera. As the project advances toward its Final Design Review (FDR), significant consolidations have been achieved across all subsystems. This paper presents an updated overview of the MORFEO system, highlighting its dual operational modes (MCAO and SCAO) and recent developments in its opto-mechanical architecture. We dedicate specific focus to the core adaptive hardware, detailing the fifth-generation post-focal deformable mirrors, the highly complex Laser Guide Star (LGS) objective zoom system required to track sodium layer variations, and the Natural Guide Star (NGS) low-order and reference sensing strategies. Furthermore, we detail the advanced pseudo-open-loop control strategy managed by a split Hard and Soft Real-Time Computer architecture. Finally, we report the latest end-to-end performance estimations obtained via the SPECULA simulation framework, demonstrating compliance with the stringent Strehl Ratio and sky coverage requirements under median atmospheric conditions.
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All authors Lorenzo Busoni, Guido Agapito, Marco Bonaglia, Alfio Puglisi, Marco Xompero, Matteo Aliverti, Francesca Annibali, Carmelo Arcidiacono, Natalia Auricchio, Nicolò Azzaroli, Andrea Balestra, Alessandro Ballone, Louis Barbier, Andrea Baruffolo, Federico Battaini, Maria Bergomi, Andrea Bianco, Michele Cantiello, Giulio Capasso, Giulia Carlà, Enrico Cascone, Ed Chapin, Manal Chebbo, Simonetta Chinellato, Vincenzo Cianniello, Paolo Ciliegi, Mirko Colapietro, Jean-Jacques Correia, Giuseppe Cosentino, Elia Costa, Matteo D'ambrogio, Vincenzo De Caprio, Giuseppe De Luca, Nicholas Devaney, Ivan Di Antonio, Amico Di Cianno, Simone Di Filippo, Benedetta Di Francesco, Ugo Di Giammatteo, Chiara Di Prospero, Gianluca Di Rico, Andrea Di Rocco, Daphne Diretto, Christian Eredia, Simone Esposito, Jacopo Farinato, Italo Foppiani, Takashi Funakawa, Fulvio Gianotti, Laurence Gluck, Davide Greggio, Sylvain Guieu, Marco Gullieuszik, Yuuichi Harikane, Masahiro Ikoma, Laurent Jocou, Dan Kerley, Mikio Kurita, Salvatore Lampitelli, Tommaso Lapucci, Fulvio Laudisio, Yves Magnard, Demetrio Magrin, Hossein Mahmoodzadeh, Dheeraj Malik, Luca Marafatto, Laurence Michaud, Christophe Michel, Satoshi Miyazaki, Kentaro Motohara, David Mouillet, Thibaut Moulin, Matteo Munari, Kentaro Nagamine, Sylvain Oberti, Fabrice Pancher, Giorgio Pariani, Sophie Penger, Amedeo Petrella, Laurent Pinard, Cédric Plantet, Elisa Portaluri, Kalyan Radhakrishnan, Roberto Ragazzoni, Edoardo Redaelli, Edgar Renault, Colin Richardson, Marco Riva, Sylvain Rochat, Gabriele Rodeghiero, Luca Rosignoli, Bernardo Salasnich, Benoit Sassolas, Salvatore Savarese, Marcello Scalera, Pietro Schipani, Danilo Selvestrel, Mahshid Shiri, Mina Sibalic, Malcolm Smith, Sebastian Soler, Rosanna Sordo, Alessandro Tacchini, Alessio Taranto, Ludovico Teodori, Gabriele Umbriaco, Yoshinori Uzawa, Angelo Valentini, Jean-Pierre Véran

Earth and Planetary Astrophysics

Piercing through the Haze: Characterizing Titan-like terrestrial exoplanets with JWST

L. C. Mayorga, Jacob Lustig-Yaeger, Andrew P. Lincowski et al. (+5 more)

As we enter a new era of using JWST to characterize exoplanet atmospheres, a top priority is defining observational needs and parameters in the search for life on an exoplanet. Although some studies have begun to consider Titan-like exoplanet atmospheres, more work is needed to prepare for the potential discovery and characterization of Titan analogues with JWST and future missions. We explore the effectiveness of exoplanet atmospheric retrieval methodologies on the Cassini/VIMS-IR spectrum of Titan assuming agnostic haze properties and tholin hazes, as well as a self-consistent photochemical model. We compare our retrieved chemical abundances and haze profiles against fiducial values and Cassini/ISS-NAC UV observations and the forward modeled truths. We generalize these findings to a Titan-like exoplanet in the TRAPPIST-1 system and find that JWST-like observations have limited potential to identify features beyond methane in a Titan-like atmosphere, but may be able to identify the presence of the haze to a few hundred kilometers. The diagnostic features which would differentiate between different haze model (scattering) properties are shortward of 1\,\micron{} and further demonstrate the important role of nUV – optical observatories in constraining the properties of exoplanet atmospheres. We also find that agnostic priors for the bulk atmosphere can lead to a degeneracy in which a spectrally active gas ($\rm CH_4$) is erroneously favored as the dominant atmospheric constituent over a spectrally inactive molecule (N_2).
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All authors L. C. Mayorga, Jacob Lustig-Yaeger, Andrew P. Lincowski, Kathleen E. Mandt, Ryan C. Felton, Adrienn Luspay-Kuti, Kristin S. Sotzen, Cameron A. Gutsgell

High Energy Astrophysical Phenomena

Time-resolved leptonic modeling of the prompt emission of GRB 211211A

Maria Petropoulou, Maria Gkoni, Konstantinos Xyloportas et al. (+3 more)

GRB 211211A is a long duration gamma-ray burst with a compact object merger origin. In this work, we model the time-resolved prompt-emission spectra of GRB 211211A within a leptonic radiation framework. Our goal is to infer the physical properties of the emitting region, study the temporal evolution of the radiating particle distribution, and make predictions for prompt emission at TeV energies. We perform Markov Chain Monte Carlo fitting of the time-resolved numerical spectral energy distribution (SED) models computed with the time-dependent non-thermal radiation code LeHaMoC. Our calculations include synchrotron emission and self-absorption, inverse Compton scattering including cooling in the Klein-Nishina regime, and photon-photon pair production. We find that the prompt emission of GRB 211211A between 10 keV and 10 MeV can be successfully reproduced by synchrotron radiation from a population of relativistic electrons. The spectral evolution during the first minute of the burst reflects different physical conditions in the emitting region. Our best-fit models favor fast-cooling solutions for the first 8 s, followed by a transition to slow-cooling solutions at later times. The accompanying synchrotron self-Compton emission extends to TeV energies, with predicted fluxes that would be detectable by CTAO for a burst similar to GRB 211211A, provided a sufficiently rapid response to a Fermi-GBM trigger or if the burst occurs within the CTAO field of view. The observed short variability of this burst requires very high Doppler factors ($\sim1000-2500$) throughout the burst evolution. Such extreme Doppler factors are difficult to reconcile with the jet Lorentz factor inferred from afterglow modeling unless the prompt-emitting regions are themselves moving relativistically with respect to the jet plasma.
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All authors Maria Petropoulou, Maria Gkoni, Konstantinos Xyloportas, Stamatios I. Stathopoulos, Georgios Vasilopoulos, Apostolos Mastichiadis

Instrumentation and Methods for Astrophysics

Rigidity spectra and onset geometry of the two largest Forbush decreases of solar cycle 25 from visibility-graph curvature

D. Sierra-Porta

We apply a geometric network diagnostic – the nodal Forman-Ricci (FR) curvature of natural visibility graphs (NVG) – to the two largest Forbush decreases (FDs) of solar cycle 25: the Gannon storm of 2024 May 10-11 and the 2025 June 1 event. Using 30-min NMDB records from six NM64 stations spanning cutoff rigidities $R_c \simeq 0$-$7\,$GV, we show that nodal FR curvature exhibits a sharp, coherent minimum at FD onset in both events, with onset-to-quiet median curvature ratios of 2.5-5.2 (Gannon) and 3.3-8.2 (June 2025). A placement (block-permutation) test that preserves the full autocorrelation structure confirms the onset signature at $p \lesssim 2 \times 10^{-3}$ (the floor of the test) for all 24 station-phase combinations, with $|z| = 4.7$-$23.7$. The signature is robust to edge weighting of the Forman curvature and to sliding-window (6-24 h) graph construction, and an amplitude-blind (horizontal-visibility) control confirms that it is specific to the amplitude geometry of the decrease. Nodal FR curvature nearly doubles the effect size obtained from the NVG degree sequence alone (mean Cliff's $\delta$ of 0.89 vs 0.54), because it encodes two-hop (neighbor-degree) structure. Folding the station amplitudes through the Dorman coupling function yields FD spectral indices $\gamma = 0.80$ (Gannon) and $0.50$ (June 2025) with $A_{10} = 11.2\%$ and $18.8\%$: the deeper event is also spectrally harder. Across the 12 station-event pairs the curvature extreme scales with FD amplitude as $|\mathcal{F}_{\min}| \propto A^{0.57}$ (Spearman $\rho = 0.75$). These results establish local graph curvature as a compact, rigidity-resolved descriptor of FD morphology.
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Astrophysics of Galaxies

When X-ray Features Fail to Identify Intrinsic Emitters: Label Noise and Luminosity Overlap in Machine Learning Classification of AGN and Star-forming Galaxies

Jaymin Ding

Previously, we found that adding an X-ray flux feature to a Random Forest classifier of active galactic nuclei (AGN) and star-forming galaxies (SFGs) coincided with a decrease in classification accuracy from 97.51% to 89.26%, a counterintuitive result given the prevailing theory that X-rays are a reliable AGN diagnostic. We investigate this discrepancy through both astrophysical and machine learning lenses. On the astrophysical side, we show that the X-ray luminosities of AGN and SFGs in the sample substantially overlap across the canonical $10^{42}$ erg/s threshold, reflecting the moderate luminosity characteristic of an optically-selected sample and the contribution of high-mass X-ray binaries (HMXBs) to SFG emission. On the machine learning side, we argue that BPT-derived training labels carry instance-dependent label noise concentrated near the BPT demarcation line, where X-ray data would be most useful as a discriminator. We show that objects misclassified in 5-fold cross-validation cluster near the Kewley demarcation curve, with a median distance of 0.123 dex versus 0.743 dex for correctly classified objects (Kolmogorov-Smirnov $D = 0.745,\; p = 1.67\times 10^{-9}$). A controlled cross-validation decomposition shows that the previously reported decrease reflects predominantly sample selection: on a fixed sample, adding the X-ray feature leaves class-resolved metrics unchanged, and its permutation importance is consistent with zero across resampled splits. The classifier therefore makes negligible use of a physically informative feature, consistent with training labels coupled to the optical features. We conclude that future classifiers operating on optically-selected samples should employ independent label sources or noise-robust training methods.
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Earth and Planetary Astrophysics

Growing Planets Produce Extreme Dust Signatures

Philip J. Carter and Zoë M. Leinhardt

Collisions between planetary bodies are essential to the assembly of rocky planets like the Earth, but they are extremely difficult to observe. We therefore rely on indirect signatures of planetary impacts such as extreme debris disks - bright infrared excesses around other stars. Extreme debris disks are thought to be the result of energetic collisions that ejected large amounts of vaporized rock which rapidly condensed into mm- or cm-sized dust. However, previously there has been no clear way to relate the observed mass of dust to the collision that produced it. Here, we show that the colliding bodies required are orders of magnitude more massive than the mass of dust observed. We find that more massive extreme debris disks require proportionally larger colliding bodies. As a consequence, the most massive observed extreme debris disks require collisions of Mars- to Earth-mass bodies. Extreme debris disks thus reveal the ongoing formation of rocky planets comparable in size to the rocky planets of our own solar system.
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Solar and Stellar Astrophysics

Near-Infrared Observations of BD+44 493 with IGRINS-2

Vinicius M. Placco and William D. Vacca

We present high-resolution (R~45,000), high signal-to-noise (S/N>200) H and K-band spectra of BD+44 493, obtained with the newly commissioned IGRINS-2 instrument on the Gemini North Telescope. BD+44 493 is a well-known carbon-enhanced (CEMP; [C/Fe]=+1.40) ultra metal-poor (UMP; [Fe/H]~-4.0) star that has been extensively studied with high-resolution spectroscopy from the ultraviolet to the infrared. From the IGRINS-2 data, we derive new estimates of the abundances of C, Mg, Si, and Ca by measuring the equivalent widths of several atomic absorption features and comparing the values and line profiles with synthetic models. We measure, for the first time, a weak atomic carbon absorption feature (C I) in a UMP star in the H-band. Our estimated abundance agrees well with other values derived from CH molecules in the optical. The abundance values for the other elements are also in good agreement with previous estimates derived from ultraviolet, optical, and near-infrared observations, confirming the speculations that BD+44 493 is a bona fide second-generation star. With these data, we demonstrate that IGRINS-2 is a powerful new resource for studying and characterizing low-metallicity stars in the Milky Way and beyond.
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Earth and Planetary Astrophysics

Probing Planet Formation with JWST Spectroscopy of IC348: Sustained Diversity but Limited Chemical Evolution and Pebble Drift

John S. Carr and Joan R. Najita

Inner disk chemistry offers a valuable window onto disk evolution and planet formation. Key planet formation processes, including pebble drift, planetesimal and planet formation, dust traps, and snow lines, determine the delivery rates of oxygen and carbon to the inner disk. As a result, measurements of molecules sensitive to the gas-phase C/O ratio, in disks over a range of ages, can constrain the relative importance and time evolution of these processes. Here we report JWST/MIRI observations of T Tauri disks in the young cluster IC 348, extending to older ages previous studies of disks. Like younger disks, IC 348 sources show a broad range of molecular ratios, indicating diverse planet formation histories. However, the similar HCN/H$_2$O and C$_2$H$_2$/H$_2$O flux ratio distributions of IC 348 (2–5 Myr old) and Taurus (1–2 Myr old) sources imply little to no evolution in the inner disk C/O ratio over this time interval, even as disk masses decline by a factor of 5 on average. This result contradicts the general prediction of increasing C/O ratio with time in models of disk chemical evolution, indicating the need to better understand the interplay between (and efficiencies of) planet formation and disk evolution processes. We also find that the cold-to-warm water flux ratios show no evolution and do not correlate with the hydrocarbon-to-water ratios. These results suggest that most inner T Tauri disks are not dominated by rapid icy pebble drift and avoid the ”meter-size barrier problem” once thought to be an obstacle to planet formation.
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Astrophysics of Galaxies

Dynamics in Nuclear Stellar Clusters: The Impact of Collisions and Disrupted Binaries

Barak Rom and Re'em Sari

The nuclear stellar clusters surrounding supermassive black holes (SMBHs) host millions of stars and stellar remnants. We study how stellar collisions and binary disruptions, alongside two-body scattering and gravitational-wave (GW) emission, shape the stellar distribution and regulate the abundance of stars on tightly bound orbits. We show the following. (a) Stars in the inner region of the cluster follow a steady-state density profile scaling as $n(r)\propto r^{-5/4}$, set by the balance between collisional depletion and binary replenishment. This profile is largely independent of whether two-body scattering or GW emission drives the orbital evolution prior to the collisions. (b) For SMBHs with $M\lesssim2 \times 10^7 M_\odot$, roughly half of the stars injected by the Hills mechanism eventually collide. The rest are tidally disrupted while on orbits with periods of order months to years. (c) For more massive SMBHs, these short-orbital-period tidal disruption events are suppressed, and most injected stars are ultimately destroyed by collisions. (d) Stellar extreme-mass-ratio inspirals (sEMRIs) can form around SMBHs with $M\gtrsim2\times10^6 M_\odot$, but are typically terminated by collisions before circularizing. Our model highlights the dynamical challenge stellar collisions pose for the formation of sEMRIs and, consequently, for stellar models of quasiperiodic eruptions. Applied to the Galactic Center, the collision-regulated density profile is consistent with the observed stellar distribution slope. Based on this profile, we estimate the stellar mass within the orbit of S2, finding it consistent with the observational upper limit, account for the recently discovered star S301, predict that most stars near Sgr$~{\rm A}^*$ follow eccentric orbits, and determine their typical eccentricities.
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Astrophysics of Galaxies

Evaluating the flexibility of the MillenniumTNG galaxy formation model with multi-zoom re-simulations

Francisco Maion, Raul E. Angulo, Volker Springel et al. (+2 more)

In this study we introduce a new simulation campaign designed to understand how parameters that control star-formation and AGN feedback processes in cosmological hydrodynamical simulations impact observables such as the galaxy stellar-mass function (GSMF) and the gas fractions in large dark matter halos. These simulations are zoom-ins to halos selected from the MillenniumTNG (MTNG) simulation, and are run employing a novel multi-zoom approach which simultaneously re-simulates several sub-regions of a given large volume at a higher resolution than the background, thus reducing computational cost and imbalances in parallelization. We measure the GSMF and gas-fractions in halos for each of the re-simulations, and train Gaussian-process emulators on these quantities. The resulting emulators predict the GSMF and gas-fractions in halos with $\sim0.1\,\mathrm{dex}$ and $\sim 10\%$ precision respectively. Using the emulators we can simultaneously fit recent measurements of both quantities, in particular the lower gas fractions now observed even for comparatively massive clusters. Interestingly, we find a combination of parameters of the MTNG galaxy formation model that provides a qualitatively good fit to both the measured GSMF and gas fractions. This combination of parameters differs from the fiducial one mainly by requiring that stellar-feedback is significantly less energetic, and that kinetic AGN feedback events are significantly more energetic and rare. This finding implies that the MTNG model can be consistent with scenarios of strong feedback that remove large amounts of gas from groups and clusters, albeit we caution that we have not extensively examined the effect of these new parameters on many quantities for which MTNG made successful predictions.
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All authors Francisco Maion, Raul E. Angulo, Volker Springel, Shy Genel, Greg L. Bryan

High Energy Astrophysical Phenomena

Semi-supervised morphological classification of fast radio bursts from the second CHIME/FRB catalogue

Bo Lin Fan, Renée Hložek and Antonio Herrera Martin

Understanding the morphology of fast radio bursts (FRB), and whether all sources repeat, are key challenges that are becoming more tractable given the increase in data from surveys such as the Canadian Hydrogen Intensity Mapping Experiment FRB project (CHIME/FRB). We present a Convolutional Autoencoder unsupervised classifier for separating the CHIME/FRB data into morphological classes. This data-driven approach is more reproducible than visual inspection, since groupings are learned from the data itself and not subject to differences between expert annotations. While most bursts occupy a similar area of morphological parameter space, we identify three classes of bursts separate from the general FRB population. While one class contains bursts with short bandwidth, and downward-drifting sub-burst structure, the characteristic bursts of other classes have very short temporal width, and occupy the entire CHIME observing band. We identify two distinct subgroups of temporally short, simple broadband bursts; one with minimal scattering and the other with higher scattering. As an additional output of our classifier, we provide a binary FRB repeatability classification, and train the classifications on simulations that mimic the first FRB catalogue from CHIME/FRB. We are able to correctly identify 86$\%$ of repeater bursts. We find that our approach is able to independently recover the downward linear drifting burst morphologies previously defined through visually inspection. Overall, we find that although there exists FRB subgroups with higher or lower proportion of repeaters, there is substantial overlap between the morphological properties of repeaters and one-off bursts consistent with previous studies.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

The soft volume of ultra-high energy neutrinos experiments

Stefano Palmisano, Diego Redigolo, Michele Tammaro et al. (+1 more)

We develop a semi-analytical framework to map ultra-high-energy neutrino fluxes onto event rates at neutrino telescopes. The formulation is based on the Boltzmann equation for the distribution of secondary muons produced by neutrino interactions in matter, and naturally accounts for the effective target volume relevant for through-going tracks. This "soft volume" is controlled by muon propagation and stochastic energy losses, and can be significantly larger than the instrumented detector volume. Exploiting the dominance of soft energy losses, we derive a controlled second-order expansion of the collision operator, reducing the transport problem to a drift-diffusion equation in energy space, with rare hard scatterings treated perturbatively. The resulting master formula provides a fast alternative to full Monte Carlo simulations while retaining a direct connection to the microscopic muon energy-loss processes. We apply the formalism to IceCube through-going muon data, marginalizing over theoretical uncertainties in the transport coefficients, and obtain a diffuse-flux fit compatible with the experimental result. We also revisit the interpretation of the ultra-high-energy track event reported by KM3NeT, assessing its consistency with IceCube non-observation in the same energy range. Our results provide a first-principles bridge between neutrino-flux models and track-event observables, with direct applications to precision neutrino astronomy and searches for physics beyond the Standard Model.
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All authors Stefano Palmisano, Diego Redigolo, Michele Tammaro, Andrea Tesi

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

S-matrix bootstrap bounds on self-interacting dark matter

Qing Chen, Zhuo-Hui Wang and Shuang-Yong Zhou

Self-interacting dark matter turns the structure of galactic halos into a direct requirement on a low-energy scattering amplitude. We show that, for weakly coupled scalar dark matter, this requirement implies a much stronger mass bound on the dark matter particle than partial-wave unitarity alone. Using analyticity, crossing symmetry, locality and partial-wave unitarity, we compute the maximal allowed threshold amplitude with a dispersive primal S-matrix bootstrap, assuming only a weakly coupled EFT below a scale $\Lambda$ and allowing arbitrary UV particle content above $\Lambda$. For the benchmark self-interaction cross section $\sigma_{\rm self}=10^{-24}(M/\mathrm{GeV})\mathrm{cm}^2$, the mass of a generic weakly coupled scalar satisfies $M\lesssim 0.3\,\mathrm{GeV}$ in the controlled EFT regime. If dark matter is a derivative-dominated pseudo-Nambu-Goldstone boson, the mass bound is lowered to the MeV scale or below, depending on the hierarchy $M/\Lambda$.
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High Energy Astrophysical Phenomena

Fe K$\alpha$ line from the Broad Line Region of PDS456 with XRISM/Resolve

Alfredo Luminari, Fabrizio Nicastro, Stefano Bianchi et al. (+1 more)

The high-luminosity, high-mass and likely super-Eddington quasar PDS 456 is known for its extremely dynamic environment. A wealth of observational features from the millimetric up to the X-ray band shows energetic outflows at all scales, from accretion disc up to galaxy scales. Broad Emission Lines in the optical and UV show significant widths and line-of-sight velocities. Moreover, NIR interferometry revealed a partially outflowing Broad Line Region. Thanks to the unprecedented energy resolution of the X-ray microcalorimeter Resolve onboard XRISM, we detect a neutral Fe K$\alpha$ line, the main tracer of cold matter around AGNs. The line blueshift ($v_{\rm out}=2700$ km s$^{-1}$) and width ($\sigma \leq 700$ km s$^{-1}$) are on the lower bound of the range of values of the optical-UV emission lines, possibly suggesting a stratified medium. The derived column density, $N_{\rm H} \approx 10^{22}$ cm$^{-2}$, is significantly lower than what expected for Broad Line Regions, again in agreement with a composite emission. The very small Equivalent Width (9 eV) marks one of the smallest measurements in the literature and probes the high-luminosity end of the so-called Iwasawa-Taniguchi (or X-ray Baldwin) effect.
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All authors Alfredo Luminari, Fabrizio Nicastro, Stefano Bianchi, Elias Kammoun

Earth and Planetary Astrophysics

Photometric Variability and Rotation of Beta Pictoris b from JWST NIRCam Coronagraphic Imaging

Yifan Zhou, Beth A. Biller, Aarynn L. Carter et al. (+28 more)

We report the detection of photometric variability in the directly imaged super-Jupiter $\beta$ Pictoris b. Using JWST NIRCam dual-band coronagraphic imaging, we conducted a 16-hour continuous photometric monitoring campaign in the F210M and F410M filters. We developed and validated a time-series photometry framework that combines PSF subtraction, principal component analysis for systematic noise removal, and injection-and-recovery tests to confirm signal fidelity. Both light curves show consistent sinusoidal variability at $\sim$5$\sigma$ and $\gg 5\sigma$ significance in the F210M and F410M bands, respectively. A joint sinusoidal fit yields a rotation period of $P_{\rm rot} = 9.00 \pm 0.13$ hr and variability amplitudes of $0.85 \pm 0.07\%$ and $0.89 \pm 0.04\%$ in F210M and F410M, respectively. The near-identical amplitudes and periods in both bands confirm a common astrophysical origin in a heterogeneous atmosphere. Combining $P_{\rm rot}$ with the previously measured projected rotational velocity, we constrain the line-of-sight spin axis inclination of $\beta$ Pic b. The result favors an equator-on viewing geometry, consistent with line-of-sight spin-orbit alignment: the planetary spin axis, orbital plane, debris disk, and stellar equator are all mutually aligned. This stands in sharp contrast to the large obliquities of wide-separation companions that are likely formed via gravitational fragmentation. Together with the system's young age, this observation provides independent dynamical evidence that $\beta$ Pic b formed via core accretion. This result constitutes the first detection of rotational modulation in a close-in, high-contrast exoplanet that likely formed via core accretion, demonstrating that time-series coronagraphic imaging with JWST opens a powerful new window onto the rotation, atmospheric dynamics, and spin-orbit architecture of this population.
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All authors Yifan Zhou, Beth A. Biller, Aarynn L. Carter, Marshall D. Perrin, Michael Poon, Genaro Suárez, Ben J. Sutlieff, Johanna M. Vos, Jason J. Wang, William O. Balmer, Marta L. Bryan, Anthony Boccaletti, Julien H. Girard, Eileen C. Gonzales, Jens Kammerer, Jarron M. Leisenring, Paulina Palma-Bifani, Kevin R. Wagner, Dániel Apai, Mickäel Bonnefoy, Brendan P. Bowler, Kyle Franson, Pengyu Liu, Marcio Meléndez, Stanimir A. Metchev, Simon Petrus, Laurent Pueyo, Isabel Rebollido, Andrew J. Skemer, Xianyu Tan, Niall Whiteford

Cosmology and Nongalactic Astrophysics

Here, There and Everywhere: How AGN jets affect galaxy cluster environments

Isaac Rosenberg, Martine Lokken, Renée Hložek et al. (+3 more)

Active galactic nuclei (AGN) feedback via black hole-driven jets and winds plays a key role in redistributing matter across megaparsec scales. However, the implementation of jet feedback in cosmological simulations remains highly prescriptive, leading to uncertainties in the predicted state of the Warm-Hot Intergalactic Medium and other extragalactic observables. We investigate how variations in AGN jet velocity, orientation, and delayed hydrodynamic coupling impact the thermodynamic state of gas surrounding galaxy clusters. We aim to identify observational signatures in the thermal Sunyaev-Zel'dovich (tSZ) effect and galaxy properties that can constrain these models. We employ zoom-in hydrodynamic simulations centered on three galaxy clusters from The Three Hundred, utilizing the SIMBA-C model and various feedback parameters. We use filament-finding algorithms and oriented stacking to probe the effect on large-scale structure and compare our results to observational data for brightest cluster galaxies from eRASS1, black hole-halo mass relations and baryonic mass fractions. Jet velocity is the dominant tested parameter in heating low-density environments at $z > 1$. At lower-$z$, higher velocity jets quench star formation, expel baryonic matter, and prevent black hole growth. While the tSZ signal within the central cluster and surrounding filaments is only affected by $\sim10\%$, the signal in under-dense regions outside filaments is enhanced by $\sim100\%$. In this case study, high velocity AGN jets provide the best match to galaxy properties from eRASS1 and other X-ray surveys. We find that hot gas in low-density regimes is a sensitive probe of AGN feedback. Future high-resolution tSZ surveys like the Simons Observatory and spectral-distortion experiments like FOSSIL have the potential to probe the thermal state of the gas outside clusters to distinguish between these feedback models.
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All authors Isaac Rosenberg, Martine Lokken, Renée Hložek, Weiguang Cui, Sara Santoni, Romeel Davé

High Energy Astrophysical Phenomena

Synchrotron Emission from Cooled Particle Distributions

Ross Ferguson and Ben Margalit

Synchrotron emitting electrons can lose energy (`cool') through various processes including radiative losses (e.g., synchrotron or inverse-Compton cooling) and adiabatic expansion. Such cooling will shift electrons in energy-space and therefore change the electron distribution function. This in turn alters the nature of synchrotron emission and absorption from these electrons. In past literature these effects have typically been considered using either simplified one-zone frameworks, or using numerical methods as part of more accurate local modeling. In this work we extend the latter `local' treatment by deriving analytic expressions that are both accurate and more computationally efficient than previous numerical approaches. Considering two concrete cases of injected power-law and thermal electron distribution functions, we derive analytic fitting functions for the resulting emission and absorption coefficients including the effects of cooling. These fitting functions can be applied to synchrotron afterglow modeling from a variety of astrophysical sources, such as gamma-ray bursts (GRBs), luminous fast blue optical transients (LFBOTs), and jetted tidal disruption events (TDEs).
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Dark Energy and Neutrino Flavor from the Weak Axion

Pedro Bittar and Carlos E. M. Wagner

Dynamical dark energy offers an alternative to a cosmological constant with distinct observational signatures. However, the small energy density scale, Hubble-sized mass, and Planckian excursions make simple models fine-tuned and unnatural. In this work, we show that a weak version of the axion, identified with the phase field of the anomalous $U(1)_{B+L}$ of the Standard Model, can generate the scale hierarchies expected for dark energy. The axion potential is controlled by sources of explicit baryon and lepton number violation and is radiatively stable. We show that the leading contribution comes from two inequivalent Weinberg operators, one $B+L$-conserving and one $B+L$-violating, which generate the axion potential. We propose a flavor selection rule in the lepton sector that simultaneously removes the quadratic divergence and dominant temperature-dependent contributions to the effective potential. The resulting potential first appears at quartic order in the axion-dependent neutrino masses and, depending on the flavor model and PMNS parameters, its amplitude is parametrically close to the dark-energy density. Since the scale of dark energy is sensitive to changes in the neutrino parameters, improved measurements of $m_{\beta\beta}$, the sum of neutrino masses, $\delta_{\rm CP}$ and $\theta_{23}$ can favor certain models. Cosmologically, the field behaves as thawing quintessence, stays frozen by Hubble friction until late times and never enters the adiabatic regime.
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Earth and Planetary Astrophysics

On the Detectability of Volcanic Exo-Ios That May Fuel Auroras on Super-Jupiters

Brooke Kotten, Mary Anne Limbach, Johanna M. Vos et al. (+12 more)

Studies suggest Jupiter's aurorae are supplied with plasma from volcanic outflows on the planet's innermost moon, Io. Repeating bursts of radio emission thought to trace massively scaled-up analogs of Jupiter's aurorae have been detected around nearly a dozen isolated substellar worlds, yet the source of the electrons fueling the aurorae remains unknown. Volcanism from tidally heated exosatellites may provide the plasma that fuel the aurora on these worlds. We assess whether transit observations provide a viable means of detecting exosatellites around aurorally active substellar worlds, thereby enabling future tests of this hypothesis. Specifically, we analyze JWST near- and mid-infrared light curves of SIMP 0136+0933, a $12.7 M_J$ "super-Jupiter", known to exhibit auroral emission. We demonstrate the capability to detect exosatellites in the SIMP 0136+0933 system with satellite-to-host mass ratios comparable to those of Jupiter's Galilean moons, achieving detection success rates of 66% for Io-to-Jupiter mass ratio satellites and 93% for Ganymede-to-Jupiter mass ratio satellites. Although the existing light curve is sufficient to demonstrate that this technique is capable of detecting transiting exosatellites, the available archival data are too short in duration to place meaningful constraints on the presence of a transiting satellite in this system. We conclude that JWST light curves spanning $\sim$1.5 days for 4-12 known aurorally active super-Jupiters would be sufficient to yield evidence for or against this hypothesis. A small target sample may suffice, as short satellite periods boost transit probabilities and aurorally active worlds may be preferentially observed near edge-on inclinations.
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All authors Brooke Kotten, Mary Anne Limbach, Johanna M. Vos, Merle Schrader, Allison McCarthy, Melodie M. Kao, Mikayla J. Wilson, Andrew Householder, Andrew Skemer, Kevin B. Stevenson, Genaro Suarez, Beth Biller, Jacqueline Faherty, Eileen C. Gonzales, Philip Muirhead

Solar and Stellar Astrophysics

Simulating the convection in red super-giant stars: wobbling jets in common envelope evolution

Shlomi Hillel, Ron Schreier and Noam Soker

We use our newly constructed three-dimensional red supergiant (RSG) stellar model, which also mimics nuclear energy production and photospheric emission, to calculate the stochastic component of the angular momentum of the mass that a companion spiraling within the RSG's envelope accretes during common envelope evolution (CEE). The accreted mass has a fixed-direction angular-momentum component arising from the density gradient in the RSG envelope and orbital motion. The angular momentum component with a stochastically varying direction results from vigorous envelope convection. We do not include the companion's influence on the RSG envelope during the CEE and consider an undisturbed, non-rotating RSG stellar model. We find that the fluctuating angular momentum amplitude can be several times the fixed-axis angular momentum. The total specific angular momentum of the accreted mass easily forms intermittent accretion disks around neutron stars and black holes, but it is only marginally sufficient, or not at all, to form accretion disks around main-sequence stellar companions. The intermittent accretion disks we expect to form will launch wobbling jets with varying axes. We discuss aspects of wobbling jets in the CEE and the grazing envelope evolution (GEE), which might precede the CEE or replace it altogether. Studies have claimed that jets are a crucial ingredient in many cases of CEE, and the standard CEE should include jets that the companion launches, before (like the GEE), during, and/or at the exit from the CEE. Our study supports this claim and emphasizes the importance of wobbling jets.
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Solar and Stellar Astrophysics

The Carbon-Dependent Binary Frequency of CEMP-no Stars

John D. Dixon, Terese T. Hansen, Jennifer Marshall et al. (+15 more)

Studies of the oldest and most metal-poor stars in the Milky Way confirm a common chemical signature of high carbon abundances and subsolar neutron-capture enrichment. The so-called CEMP-no stars are speculated to be bona fide population II stars, potentially tracing the nucleosynthesis of the first stars in the universe. However, constraining the binary nature of CEMP-no stars is crucial for understanding their origins. The binary fraction of CEMP-no stars has tentatively been found to vary with carbon enhancement, independent of metallicity. Here we present the results of radial-velocity monitoring of 30 CEMP-no stars over five years, increasing the total number of CEMP-no stars with a constrained binary status by ${\sim}30\%$ in order to better investigate the CEMP-no binary fraction as a function of carbon. Combining our results with literature data, we find an overall binary frequency of $50^{+13}_{-13}\%$ among high-carbon ($A(\rm{C})\ge7.3$) CEMP-no stars, compared to $18^{+5}_{-4}\%$ for low-carbon ($A(\rm{C}) < 7.3$) stars, establishing a statistically significant increase in the CEMP-no binary frequency as a function of carbon for the first time. Our results indicate no correlation between metallicity and binary frequency. Additionally, we derive orbital parameters for three new CEMP-no stars in binary systems and estimate secondary masses for these stars as well as seven binaries from the literature. We discuss these mass estimates in the context of investigating the nature of the unseen companions and the plausibility of a mass-transfer formation channel for high-carbon CEMP-no stars.
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All authors John D. Dixon, Terese T. Hansen, Jennifer Marshall, Vinicius M. Placco, Timothy C. Beers, Anke Ardern-Arentsen, Birgitta Nordström, Lauren N. Aldoroty, Jared Cathey, Peter S. Ferguson, Katherine Kristofek, Karin Lind, Hudson Malone, Ferner Moreno, Jessica Myron, Alexander H. Riley, Else Starkenburg, Kaitlin B. Webber