Cosmology and Nongalactic Astrophysics
Gravitational Lensing Effects by Galaxy Clusters on Ionised Bubble Size Distribution during the Epoch of Reionisation
Di Wu, Nan Li, Huanyuan Shan et al. (+1 more)
The statistical properties of ionisation structures during the Epoch of Reionisation (EoR) provide valuable insights into the formation of the first
stars and
galaxies. However, size distributions of ionisation structures can be affected by gravitational
lensing from foreground massive structures such as
galaxy clusters. To quantify the impact of cluster
lensing on the ionised Bubble Size Distribution (BSD), we performed a series of multiple-lens-plane simulations combining light cones of clusters with source light cones based on different ionisation models. The deflector population is generated with a Monte Carlo method guided by the
halo mass function and empirical scaling relations, and the deflectors are modelled with truncated Navarro-Frenk-White (TNFW) profiles. Source light cones are produced semi-numerically or taken directly from the
Evolution of 21 cm Structure (EOS) project. Using the Mean Free Path method, we measure both unlensed and lensed BSDs. We find that gravitational
lensing increases the apparent abundance of large bubbles while leaving small bubbles nearly unchanged across all source models considered. In particular, for the EOS faint-
galaxies model, the apparent number of bubbles with R > 15 cMpc increases by 219% at z = 14; for the EOS bright-
galaxies model, it increases by 832% under the same conditions. Moreover, a directional projection test shows only minor
lensing-induced changes in line-of-sight direction, suggesting a possible route to recovering unlensed bubble statistics. Above all,
lensing introduces unavoidable systematics into BSD measurements that should be carefully taken into account for relevant studies in the SKA era.
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All authors Di Wu, Nan Li, Huanyuan Shan, Zhenghao Zhu
High Energy Astrophysical Phenomena
Imploding Remnants: detection bias against AGNs in massive clusters
Ross J. Turner and Georgia S. C. Stewart
We propose that an observed scarcity of remnant lobed AGNs in dense clusters results from a peculiarity in their dynamics upon the cessation of jet activity: a rapid `implosion' of lobes that, in their active phase, were primarily supported by the momentum flux of the jet. We investigate this behaviour by analysing the asymptotic behaviour of the RAiSE dynamical model and comparing our predictions both to the full model and hydrodynamic simulations. We find that remnant lobes powered by weak jets in massive clusters are unstable to implosion on the order of at most a few Myr. Consequently, remnant AGNs in massive clusters ($M_\text{halo} \sim 10^{14.5}$~M$_\odot$) will be under-counted by a factor of at least five compared to those in poorer groups ($M_\text{halo} \sim 10^{12}$~M$_\odot$). The lack of such remnants in observed populations may lead to a significant underestimate of the AGN feedback provided by low-powered jets, especially given their prevalence towards cluster cores where feedback is most effective. We discuss the influence of a stabilising
magnetic field sheath on the nature of the implosion: does the lobe cleanly implode in on itself, or do fluid instabilities turbulently mix the lobe and ambient medium?
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Solar and Stellar Astrophysics
An Orbit for a Massive Wolf-Rayet Binary in the LMC: An Example of Binary Evolution
Breelyn Cocke, Philip Massey, Nidia I. Morrell et al. (+6 more)
Wolf-Rayet (WR)
stars are helium-burning, evolved massive
stars which have had most of their hydrogen-rich outer layers removed either through
stellar winds and/or binary stripping. Here we report on LMC173-1, a WN3+O binary located in the Large Magellanic Cloud (LMC). Using spectra obtained from the Magellan and Gemini-S
telescopes, we have derived system parameters for this intriguing binary. The WR
star's mass is only 43% that of its companion, and we argue that this requires binary
evolution rather than mass loss by
stellar winds alone, given the
metallicity of the LMC. The
stars are close enough to each other with their 3.52 day period that the O
star is actually orbiting within the wind of the WR
star, as is the case for other well-known WR+O systems, such as V444 Cyg. As a result, high precision OGLE photometry reveals a WR atmospheric eclipse, as well as a 7-8 millimag ellipsoidal modulation due primarily to the
tidal distortion of the O
star. Modeling the light curve allows us to estimate the orbital inclination. Derivation of
stellar parameters suggests neither component is filling its Roche-lobe surface today. The O
star is spinning much faster than synchronous rotation. Using BPASS v2.2 binary models, we discuss the probable evolutionary history of the system. The WR progenitor likely underwent Case A Roche-lobe overflow (RLOF) before leaving the main-sequence. As it lost its H-rich envelope, it became a WN-type WR. The resulting system is a binary with similar luminosities but very different radii, representing a post-RLOF phase.
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All authors Breelyn Cocke, Philip Massey, Nidia I. Morrell, Laura R. Penny, Kathryn F. Neugent, Jan J. Eldridge, Michal K. Szymanski, Andrzej Udalski, Laurella C. Marin
Astrophysics of Galaxies
Sarah A. Bird, Chris Flynn, Rudra Sekhri et al. (+5 more)
We measure the luminosity function (LF) of the Milky Way's
stellar halo, using a magnitude complete, distance limited sample of
stars from $Gaia$ DR3.
Stars with high transverse velocities are selected, to isolate a high purity sample of the local
halo. We adopt a cutoff transverse velocity of 250$\,$km$\,$s$^{-1}$, yielding 24,471
stars, and compute the
halo LF, taking into account the effects of sample selection criteria. The LF displays similar features as are found in the well-probed LF of nearby, metal-rich disk
stars, showing a strong peak at an absolute magnitude of around $M_G=10$, and a flattening near $M_G\sim7$ (Wielen dip). The $Gaia$ sample yields the first measurement of the LF continuously from the dimmest main sequence
halo stars (subdwarfs) at an absolute $M_G$ magnitude near 13 mag to bright
giants at $M_G\sim-3$. We obtain a local
stellar halo number density of $1.7\times10^{-4}$
stars$\,$pc$^{-3}$ and disk-to-
halo ratio by
stellar number density of 480:1. We convert the $Gaia$ $G$ band measurements for our sample
stars to Johnson-Kron-Cousins $V$ band, compute the $V$-band
halo LF, and compare it to previous studies published over many decades that cover a wide range of techniques used. We discuss applications of the LF to the measurement of the luminosity and
stellar mass of the Milky Way
halo.
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All authors Sarah A. Bird, Chris Flynn, Rudra Sekhri, Hai-Jun Tian, Juntai Shen, Xiang-Xiang Xue, Chao Liu, Gang Zhao
Astrophysics of Galaxies
Balmer Decrements and Nebular-Stellar Reddening in JADES Galaxies at $2.7<z<7$
Shreya Karthikeyan, Leonardo Clarke, Alice E. Shapley et al. (+5 more)
We aim to characterize nebular and
stellar reddening in
star-forming
galaxies as a function of global
galaxy properties (
stellar mass, SFR,
metallicity) at $2.7 < z< 7.0$. We also provide a prescription to convert SED-based $E(B-V)_{\mathrm{star}}$ to $E(B-V)_{\mathrm{gas}}$ when direct measurements of nebular reddening are unavailable. Our results are based on JWST/NIRSpec measurements of both individual spectra, with a sample of 283
galaxies, and composite spectra, including a larger sample of 327
galaxies. We estimate nebular reddening using the Balmer decrement (H$\alpha$/H$\beta$) above $10^{8.5}$ $M_{\odot}$, where the sample is representative.
Stellar reddening and SFRs are derived through Prospector SED fitting, while gas-phase
metallicities are estimated from strong emission-line ratios. At fixed
stellar mass, Balmer decrements remain consistent within uncertainties across our
redshift range, indicating that
stellar mass primarily determines the overall
dust column even by $z \sim 7$. We find that differential reddening ($\Delta E(B-V) \equiv E(B-V)_{\mathrm{gas}} - E(B-V)_{\mathrm{star}}$) scales linearly with mass and SFR at $z \sim 2.7 - 4.0$, but shows no mass or SFR dependence above $z \sim 4.0$. We find evidence for smaller $\Delta E(B-V)$ above $z \sim 5.0$, suggesting that nebular emission and
stellar continuum probe increasingly similar
dust columns towards higher
redshift. Finally, we find that nebular reddening correlates strongly with
metallicity out to $z \sim 5$, whereas the correlation between
stellar reddening and
metallicity is weaker or absent. Together, these results suggest that both
dust mass and geometry play a significant role in shaping the observed reddening of high-
redshift galaxies.
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All authors Shreya Karthikeyan, Leonardo Clarke, Alice E. Shapley, Natalie Lam, Ryan L. Sanders, Naveen A. Reddy, Michael W. Topping, Gabriel B. Brammer
Instrumentation and Methods for Astrophysics
Proto-NUX: A prototype telescope for ground-based near-ultraviolet observations
Rasjied Sloot, Rudy Wijnands, Steven Bloemen et al. (+3 more)
The Near-UV-eXplorer (NUX) is a proposed ground-based, wide-field
telescope array with a field of view of $\sim$70 square degrees, designed to operate over the 300-350 nm wavelength range and to achieve a target sensitivity of 20 mag in 150 seconds (5 sigma). Its main scientific objective is the detection and characterization of hot, rapidly evolving transients in the near-UV (NUV). Proto-NUX is a pathfinder instrument for NUX, based on an off-the-shelf 36 cm Celestron RASA wide-field astrograph that has been modified to enhance throughput and image quality in the targeted NUV band. The main objectives of Proto-NUX are: (1) to quantify the NUV sensitivity of the prototype and assess the feasibility of the full NUX facility; and (2) to characterize atmospheric extinction in the NUV, including its temporal variability and its dependence on zenith angle. Using three filter configurations, we aim to measure the wavelength dependence of the atmospheric extinction and to disentangle the contributions from Rayleigh scattering (dominating at wavelengths >325 nm) and molecular ozone-dominated absorption (dominating <315 nm). On-site testing is scheduled for 2026 at the Pic du Midi Observatory (France, 2877 m altitude) in order to evaluate on-sky performance under high-altitude observing conditions.
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All authors Rasjied Sloot, Rudy Wijnands, Steven Bloemen, Rik ter Horst, Hans Ellermeijer, Alexander Hoogerbrug
Solar and Stellar Astrophysics
Strong Prevalence of Hammerhead Velocity Distributions Close to the Heliospheric Current Sheet
Srijan Bharati Das, Jaye L. Verniero, Samuel T. Badman et al. (+13 more)
The
solar wind undergoes non-adiabatic heating as it travels away from the Sun. The velocity phase space distribution of non-
equilibrium ions in the
solar wind indicate a source of free energy that could contribute significantly to this heating. Parker
Solar Probe (PSP) has observed velocity distributions containing highly anisotropic, perpendicularly diffused
proton beams with a distinctly constricted gap between the core and beam populations. These distributions resemble a “hammerhead" shape and were first reported in the fourth PSP encounter. Numerical simulations have reproduced the qualitative nature of hammerheads under certain initial conditions, but have not convincingly captured the prevalence or extreme attributes of the observed beam. This necessitates a broad study of the occurrence conditions and the associated
plasma processes to better guide simulations. We statistically investigate the occurrence of these structures from 20 recent PSP encounters, and find that hammerheads dominantly occur around the Heliospheric Current Sheet (HCS). As the inclination of the HCS at PSP crossing points increases over the rising phase of the
solar cycle, the occurrence of hammerheads is increasingly concentrated in narrow time periods around the HCS crossings. For comparison with previous work, we present statistical trends in the anisotropy of the
proton beam and its connection to the density of
proton beams as well as the drift speed of the beam to the core. Our study establishes a consistent occurrence pattern of hammerhead distributions around the HCS indicating hammerheads are diagnostics of energization processes associated with the HCS and its escaping wind.
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All authors Srijan Bharati Das, Jaye L. Verniero, Samuel T. Badman, Robert Alexander, Michael Terres, Federico Fraschetti, Kristoff W. Paulson, Fernando Carcaboso, Tatiana Niembro, Roberto Livi, Davin Larson, Ali Rahmati, Yeimy J. Rivera, Niranjana, Kristopher G. Klein, Michael L. Stevens
Solar and Stellar Astrophysics
New Observations of the Strongly Magnetic O-star NGC 1624-2 Reveal Its Magnetic South Pole
S. Seadrow, V. Petit, D. Bohlender et al. (+6 more)
NCG 1624-2 has the strongest detected
magnetic field of all known main-sequence O-type
stars. It was originally found that its magnetospheric emission lines followed a $\sim$5 month periodicity, and the existing line-of-sight
magnetic measurements were predominantly of strong positive (north) polarity. As such, the field's
geometric interpretation has been a mildly tilted (with respect to the rotational axis) dipole, such that only the
magnetic north pole is visible during a rotation cycle. However, S. Seadrow et al. (2026) recently reported that new magnetospheric observations no longer phased with the established ephemeris and that the period had to be decreased by a few days. S. Seadrow et al. (2026) also found that existing
magnetic measurements did not rule out a period twice as long (306.56 d). This period suggests a different
magnetic configuration with a larger dipolar tilt, making both
magnetic poles visible over a single rotation. Because previous spectropolarimetric observations did not have sufficient phase coverage to distinguish between the geometries, both were equally viable. In this paper, we present new spectropolarimetric observations obtained specifically to resolve this ambiguity. Our new
magnetic measurements have a strong negative (south) polarity, confirming that the rotational period of NGC 1624-2 is indeed nearly twice as long as previously thought. Our measurements show that both poles come within a similar angle to our line of sight and likely have roughly the same local
magnetic field strength (with a dipolar strength of 15-20 kG or more depending on the inclination angle).
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All authors S. Seadrow, V. Petit, D. Bohlender, A. David-Uraz, J. MacDonald, J. Maíz Apellániz, M. Oksala, M. Shultz, G. A. Wade
High Energy Astrophysical Phenomena
PACHA: Probing AGN Coronae with High-redshift AGN
Xiurui Zhao, Elias Kammoun, Marco Ajello et al. (+18 more)
The X-ray emission of active
galactic nuclei (AGN) is generally attributed to inverse Compton scattering of
accretion-disk
photons by hot electrons in a compact corona. In local AGN, directly constraining coronal properties is challenging because the high-energy cutoff often lies beyond the NuSTAR bandpass. High-
redshift, luminous
quasars enable systematic constraints on the high-energy cutoff, as cosmological
redshift shifts the spectal cutoff into the observable hard X-ray band. We present first results from the “Probing the AGN Coronae with High-
redshift AGN” (PACHA) project, based on quasi-simultaneous NuSTAR and XMM-Newton observations of 13
radio-quiet AGN at $z>1$. We constrain the high-energy cutoff and coronal temperature at 90% confidence level for 10 and 9 sources, respectively. The sample exhibits a mean cutoff energy of $E_{\rm cut}=80.8\pm8.1$ keV and a mean coronal temperature of $kT_{\rm e}=18.4\pm1.6$ keV, both significantly lower than those measured in local Swift-BAT AGN, while the mean optical depth ($\tau=4.8\pm0.3$) is significantly higher. The uncertainties are at 1~$\sigma$. Combining our high-
redshift sample with local AGN, we find a potential anti-correlation between cutoff energy and both X-ray luminosity and black hole mass, with no significant dependence on Eddington ratio. Within a hybrid coronal framework, the inferred temperatures lie well below the pair-production limits for purely thermal coronae, indicating a substantial efficient Compton cooling and/or non-thermal electron component. The detection of low coronal temperatures in high-luminosity AGN is broadly consistent with predictions from recent radiation MHD simulations that consider purely thermal electron populations, implying that non-thermal electrons may not be the primary drivers of the observed coronal properties in these systems.
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All authors Xiurui Zhao, Elias Kammoun, Marco Ajello, Yanfei Jiang, Giorgio Lanzuisi, Anne Lohfink, Stefano Marchesi, Elena Bertola, Peter G. Boorman, Francesca Civano, Luca Comisso, Paolo Coppi, Isaiah S. Cox, Martin Elvis, Roberto Gilli, Fiona A. Harrison, Ross Silver, Daniel Stern, Nuria Torres-Alba, Qian Yang, Lizhong Zhang
Solar and Stellar Astrophysics
Post-processing Probabilistic Forecasts of the Solar Wind by Data Mining Similar Scenarios
Daniel E. da Silva, Yash Parlikar, Shaela I. Jones et al. (+1 more)
The
solar wind speed at Earth is one of the most important parameters regarding the effects of space weather on society. Thus far, most approaches for predicting the
solar wind speed produce a single-value time series without uncertainty, or utilize ensemble methods which require custom calibration development. In this study, a method is developed that produces calibrated probabilistic forecasts of the
solar wind speed using skew normal distributions and a novel extension of analog ensembles. In our extension, the single-value predictions from a baseline model of the next $\Delta t$ days are used along with $\Delta window$ hours of recent observations and single-value predictions to create a
forecasting scenario vector that is compared against a historical database for outcomes. The baseline model used is the combined Air Force Data Assimilative Photospheric Flux Transport-Wang Sheeley Arge (ADAPT-WSA) model and the WSA point parcel simulation, but the method is directly applicable to other deterministic models including components such as Enlil or the Heliospheric Upwind Extrapolation with time dependence model (HUXt). The approach works notably well on the
benchmark of whether observations fall within the $p^{th}$ percentile $p\%$ of the time (for $p$ between 0 and 100). Falling back on the mean or median of the predicted distribution as a non-probabilistic prediction yields a direct improvement in root-mean-square error (RMSE) over the original WSA point parcel simulation, and is shown to beat $\approx$ 1
solar rotation recurrence for 1-5 day ahead forecasts.
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All authors Daniel E. da Silva, Yash Parlikar, Shaela I. Jones, Charles N. Arge
Instrumentation and Methods for Astrophysics
Two Point Correlation Function Estimation with Contaminated Data
Arya Farahi
The two-point correlation function (2PCF) is a cornerstone of precision cosmology, yet its estimation from imaging surveys is vulnerable to contamination and incompleteness arising from imperfect target selection and pipeline-level inclusion decisions. In practice, the scientific target is a physically defined population, while the working catalog is constructed from noisy measurements and selection cuts, leading to mismatches between true and observed inclusion. These errors are often spatially structured, correlating with survey depth, observing conditions, and foregrounds, and can imprint spurious large-scale power or suppress the true clustering signal. High-resolution spectroscopic samples provide gold-standard inclusion in the target population but are typically available for only a small subset of objects. We introduce a prediction-powered Landy–Szalay (PP–LS)
estimator that combines noisy inclusion labels across the full catalog with exact labels on a small spectroscopic subset while preserving the standard random-catalog normalization for survey geometry and selection. PP–LS debiases pair counts using residual-based, design-weighted corrections computed only on the labeled subset, requiring no probability calibration, known misclassification rates, or explicit modeling of contamination. Under simple random sampling of the labeled subset, we establish recovery of the oracle (true-label) Landy–Szalay pair counts and thus consistency for the target 2PCF. In simulations with clustered and spatially structured contaminants, PP–LS removes the bias of naive catalog-level
estimators while achieving substantially lower variance than spectroscopic-only clustering. The resulting
estimator is statistically principled, computationally lightweight, and integrates directly with standard pair-counting pipelines, enabling robust clustering inference in next-generation surveys.
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High Energy Astrophysical Phenomena
Neutrino Spectral Pinching in 3D Core-Collapse Supernovae: Late-Time Convergence, Failed-Explosion Signatures, and Viewing-Angle Dispersion
Nicolás Viaux M
We present a systematic survey of the
neutrino spectral pinching parameter alpha_p(t, M, n-hat) across the Princeton Fornax ensemble of 3D core-collapse
supernova simulations. We analyze 25 simulations spanning progenitor masses 8.1-100 M_sun with durations up to 8.47 s post-bounce, computed with the Fornax code and the SFHo equation of state. The pinching parameter alpha_p = (2^2 - E_rms^2)/(E_rms^2 - ^2) is derived from 12-bin spectral moments on a 128x256 sky grid for three
neutrino species, enabling time- and angle-resolved spectral characterization. Four results emerge. (1) The nu-bar_e pinching floor is alpha_p = 1.92 +/- 0.10 (N=13 long-running models), lying 0.2-0.4 below 1D predictions due to 3D PNS convection. (2) Both BH-forming models (12.25, 14 M_sun) show anti-pinching (alpha_p < 0.9) before collapse, with deficit Delta alpha_p ~ 0.65 visible from t = 0.5 s. (3) Two of six long-running models exhibit a hierarchy reversal ( > ) after t = 5 s; leptonic
flavors carry (40 +/- 3)% of radiated energy. (4) The LESA dipole is suppressed by >3x in BH-forming models; viewing-angle spread Delta alpha_p(68%) ~ 0.8-1.5 dominates spectral-inversion uncertainty. Mollweide sky maps reveal coherent angular structures with alpha_p anticorrelated with luminosity and correlated with mean energy. Detection rates at Hyper-Kamiokande, DUNE, JUNO, and IceCube yield 8-12% NMO/IMO discrimination during Kelvin-Helmholtz cooling. The late-time nu-bar_e pinching floor represents the first 3D characterization of spectral convergence during Kelvin-Helmholtz cooling.
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Astrophysics of Galaxies
Very long-term relaxation of harmonic 1D self-gravitating systems
Kerwann Tep, Jean-Baptiste Fouvry and Christophe Pichon
One-dimensional self-gravitating systems admit genuine thermodynamical
equilibria. For systems with strictly monotonic orbital frequency profile, the Landau and Balescu-Lenard theories predict a relaxation time scaling linearly with the number of particles, $N$, in agreement with simulations. Yet, these theories become ill-posed for degenerate frequency profiles, as is the case in the harmonic potential, where all particles share the exact same mean orbital frequency. Using an exact collision-driven 1D integrator, we investigate numerically the self-consistent relaxation of 1D harmonic self-gravitating systems. We show that harmonic systems relax on a timescale that grows quadratically with $N$. We show that systems that are only partially degenerate display the same quadratic scaling for low $N$, but transition to the linear, non-degenerate behaviour for larger $N$. The larger the fraction of degenerate orbits, the larger the value of $N$ at which this transition of dynamical regime occurs. Finally, we explore the dynamics of fully non-degenerate systems, albeit with finite radial support: we confirm that their relaxation time scales linearly with $N$, though with a substantially larger prefactor than in non-compact systems. Astrophysically, this investigation should offer some new clues on the dynamics of density cores, as in the center of
dwarf galaxies.
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Solar and Stellar Astrophysics
Unveiling Massive Main-Sequence Stars in Sextans A through Panchromatic Photometry
Maude Gull, Daniel R. Weisz, Yumi Choi et al. (+9 more)
We present a study of the metal-poor (~6% Z_sun) massive (>8 M_sun) main-sequence
star population in the
star-forming
dwarf galaxy Sextans A. By modeling near-UV to near-IR photometry of individual
stars using the
Bayesian Extinction and
Stellar Tool (BEAST) we infer
stellar parameters such as effective temperature, luminosity, and initial mass. We identify 867 massive main-sequence
star candidates (present-day mass >8 M_sun and surface
gravity >3.7 dex [cgs]) with a plausible spectral energy distribution (SED) fit, 500 of which show a probable SED fit. Comparisons to spectral types of existing observed spectra are consistent with the BEAST-derived
stellar parameters, with most discrepancies explained. We identify 292 OBe
star candidates through IR photometric signatures and find lower-limit OBe fractions of 15% for M > 8 M_sun, 23% for M > 15 M_sun, and 17% for M > 20 M_sun. We find 57 OB associations and that 24-28% of massive
stars are isolated (distance to nearest massive
star >28 pc). We discuss six likely runaway candidates (suggested velocities of ~ 50-340 km/s) not clearly associated with any major
star-forming complexes. Lastly, we predict Lyman continuum (LyC) escape fractions of f_esc=0.27-0.76 across the
star-forming regions and a global value of 0.35-0.71 by assuming low overall extinction and a range of porous geometries, indicating efficient leakage of ionizing
photons. Future spectroscopic follow-up and resolved ISM studies will refine these constraints and solidify Sextans A as a
benchmark for studying massive-
star evolution and feedback at extremely low
metallicity.
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All authors Maude Gull, Daniel R. Weisz, Yumi Choi, Benjamin F. Williams, Karoline M. Gilbert, Julianne J. Dalcanton, Kareem El-Badry, Puragra Guhathakurta, Steven R. Goldman, Kristen B. W. McQuinn, Alessandro Savino, Evan D. Skillman
Earth and Planetary Astrophysics
Cold giant discoveries from a joint radial-velocity and astrometry framework
Pablo A. Peña, James S. Jenkins, Fabo Feng et al. (+11 more)
The population of long-period
giant planets shapes planetary system architectures and formation pathways, but these cold Jupiters remain relatively unexplored. Radial velocity (RV) surveys lose sensitivity at multi-AU separations, while transit surveys have poor detection probability at long periods. Absolute astrometry from the Hipparcos and
Gaia missions offer an additional source for
stellar motion that can break the orbital inclination degeneracy and strengthen detection confidence. This is especially timely ahead
Gaia DR4/DR5, expected to enable routine astrometric vetting and true-mass measurements for long-period RV
planets. Extending the Chile-Hertfordshire
ExoPlanet Survey (CHEPS) by combining RVs spanning up to 16 years with absolute astrometry, we search for and characterise cold
giants around metal-rich FGK
stars. We upgrade the EMPEROR framework, incorporating astrometric differencing to jointly fit RVs and astrometry for five CHEPS targets, performing
Bayesian model comparison and quantify the astrometric contribution. Our analysis characterises orbital parameters for two known
planets in HIP 21850 and detects five new: a warm Jupiter–HIP 10090c, orbital period $P=321.8 \pm 0.5$ d and mass $M=0.85 \pm 0.08$ $M_J$, and four Jupiter analogues–HIP 8923b, with $P=14.1 \pm 0.06$ yr and $M=9.98\pm 0.47 M_J$, HIP 10090b with $P=8.1\pm 0.3$ yr and $M=3.87\pm 0.63$ $M_J$, HIP 39330b with $P=12.7\pm 0.7$ yr and $M=1.68\pm 0.15$ $M_J$, and HIP 98599b with $P=7.3\pm 0.1$ yr and $M=6.85\pm 0.16$ $M_J$. Adding astrometry reduces period and mass uncertainties by factors between 3 and 10 and increases the Bayes factor by up to 60. The synergy of long-baseline RVs and absolute astrometry provides a robust pathway to discover and characterise cold
giant planets. Our results demonstrate that astrometry meaningfully improves detection confidence and converts minimum masses into true masses.
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All authors Pablo A. Peña, James S. Jenkins, Fabo Feng, Douglas R. Alves, Florence de Almeida, Frédéric Dux, Guang-Yao Xiao, Joanne M. Rojas M., Jose I. Vines, Rafael I. Rubenstein, R. Ramírez Reyes, Suman Saha, Connor J. Cheverall, Matías R. Díaz
Solar and Stellar Astrophysics
Upgrading Alpha Crucis to a seven star system. Discovery of Bb and orbital misalignment
Idel Waisberg and Boaz Katz
Alpha Crucis is the closest very high multiplicity massive
star to the Sun. At its heart is the $4" \leftrightarrow 430 \text{ au}$ binary $\alpha^1$ (A) + $\alpha^2$ (B) Cru, which combined make up the 13th visually brightest
star in the night sky. Here we make use of archival VLTI data of $\alpha$ Cru A+B in order to study its multiplicity and orbital architecture. The data spatially resolved the close (6 mas) companion in $\alpha$ Cru A (a known spectroscopic binary) and revealed that $\alpha$ Cru B is also a close (17 mas) binary, which upgrades $\alpha$ Cru to a seven
star system. By combining the interferometric data with radial velocities, we solve for the full orbit of Aa+Ab and find dynamical masses $M_{Aa}=17.2\pm1.2 M_{\odot}$ and $M_{Ab}=6.8\pm0.3 M_{\odot}$. While the data on Alpha Cru B are not yet sufficient to tightly constrain all orbital parameters, we find that the orbital period is most likely 405 days (with 203 days also a possibility). The orientation of the orbital planes are sufficiently constrained to yield a mutual inclination between Aa+Ab and Ba+Bb of either $50 \pm 5^{\circ}$ or $137\pm5^{\circ}$, pointing to a dynamical formation scenario for the system. The photometric masses $M_{Ba}=12.4 M_{\odot}$ and $M_{Bb}=9.8 M_{\odot}$ together with the less massive wide component $\alpha$ Cru Ca+Cb+D yield a total mass $M\simeq52 M_{\odot}$. At larger distances, the seven-
star nature of Alpha Crucis would be arguably very challenging to unveil, suggesting that the companion frequency in massive
star surveys may be underestimated.
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Solar and Stellar Astrophysics
Thermal Evolution of the Central Star in Pa 30
Anthony L. Piro, Yossef Zenati and Tin Long Sunny Wong
Pa 30 has been identified as the nebular remnant of the historical SN 1181. It is host to a hot ($\approx200,000\,{\rm K}$) central
star (WD J005311) with a fast wind ($\approx16,000\,{\rm km\,s^{-1}}$) radiating at roughly the Eddington luminosity for a
solar mass ($\approx1.5\times10^{38}\,{\rm erg\,s^{-1}}$). We explore the thermal
evolution of this
star to understand how it progressed toward the state it is observed as today as well as to constrain its underlying physical properties. We develop a semi-analytic two-component model, which approximates the central
star as a hot radiating envelope contracting and cooling above a relatively cool core. Comparing this model with the observed luminosity and radius requires a core mass $M_c\approx1.15-1.4\,M_\odot$ with a core radius $R_c\approx(6-8)\times10^8\,M_\odot$, and a hot envelope mass $\Delta M\approx0.02-0.04\,M_\odot$. The small envelope mass is the best constrained of these parameters due to the need to reach the observed radius of $\approx0.15\,R_\odot$ in a timescale of $\approx845\,{\rm yrs}$. These results favor a picture where SN 1181 involved the merger of O/Ne and C/O white
dwarfs, and where the majority of the latter was ejected in the explosion. We also explore which models ignite carbon burning at the base of the hot envelope, demonstrating that this is possible but not necessarily required to explain the current thermal state of the central
star.
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High Energy Astrophysical Phenomena
Not Where You Left Them: Displaced $\gamma$-Rays and X-Rays Reveal the Cosmic Ray Scattering Rate
Manami Roy, Mark R. Krumholz, Roland M. Crocker et al. (+1 more)
Modern X-ray and $\gamma$-ray instruments are revealing a growing class of
Galactic non-thermal sources whose emission centroids are measurably offset from the nearest plausible sites of
cosmic ray (CR) acceleration. Such "displaced" sources are seen in keV X-rays and TeV-PeV $\gamma$-rays but not in GeV $\gamma$-rays, have hard spectra, and are not associated with gas clumps, suggesting a leptonic origin. We develop a general framework for understanding displacement, whereby relativistic CR electrons (CRe) injected into the interstellar medium (ISM) with a strongly anisotropic pitch-angle distribution propagate a finite distance from their acceleration site before scattering processes isotropise their directions sufficiently for the emission to become visible. We use CR transport simulations to investigate under what circumstances displacement is likely, finding that it requires an initial pitch angle distribution $\lesssim 45^\circ$ wide, a line of sight broadly edge-on to the
magnetic field, and that the source be measured in a waveband where emission is dominated by CRe for which the radiative-loss and pitch-angle scattering timescales are comparable. For typical
Galactic conditions the latter condition is satisfied only for CRe energies $\gtrsim$ 10 TeV, explaining why displaced sources appear at X-ray and TeV but not GeV energies. We further show that, when displacement is detected, it allows a direct inference of the CRe pitch-angle scattering rate.
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All authors Manami Roy, Mark R. Krumholz, Roland M. Crocker, Todd A. Thompson
Cosmology and Nongalactic Astrophysics
Imprints of Reheating Dynamics on Gravitational Waves from Phase Transitions
Basabendu Barman, Maciej Kierkla, Marek Lewicki et al. (+1 more)
We investigate how perturbative reheating after inflation modifies the
primordial gravitational wave (GW) spectrum generated by cosmological phase transitions. Within a specific inflationary setup, we show that the thermodynamic quantities that control the phase transition depend on the effective equation of state of the cosmological background, which is itself set by the form of the inflaton potential during reheating. Assuming reheating proceeds via perturbative dissipation of the inflaton condensate into
boson or
fermion pairs, we find that phase transitions taking place in this epoch generally produce GW signals that are systematically suppressed compared with the standard radiation-dominated scenario. We also identify characteristic spectral features that may arise in this case, which could serve as distinctive signatures of the modified expansion history during reheating.
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All authors Basabendu Barman, Maciej Kierkla, Marek Lewicki, Marco Merchand
Astrophysics of Galaxies
AGN obscuration in optical and X-rays: Host properties and the interplay of nuclear and galactic gas and dust in a combined SDSS-XMM sample
G. Mountrichas, F.J. Carrera, E. Quintin et al. (+3 more)
We investigate the link between optical obscuration and X-ray absorption in active
galactic nuclei (AGN) by combining X-ray spectroscopy from 4XMM-DR11 with SDSS DR16Q spectroscopy.
Bayesian X-ray spectral fits were obtained within the XMM2Athena project, and host-
galaxy properties were derived via CIGALE SED fitting. Our final sample comprises 241 X-ray AGN at $z<1.9$. For 172 sources ($\sim70\%$), the optical broad-line (BL) or narrow-line (NL) classification agrees with their X-ray obscuration based on $N_{\rm H}$, but two mismatched populations emerge. Eleven BL AGN show signs of X-ray absorption (BLAbs) and elevated gas-to-
dust ratios compared to BL AGN, consistent with
dust-free or host-scale absorbers. Conversely, 58 NL AGN appear unobscured in X-rays (NLUnabs) and low gas-to-
dust ratios. Nearly half are assigned type~1 properties by SED fitting, suggesting diluted or intrinsically weak broad-line regions, host contamination, or variability. Optical line diagnostics support this picture: NL AGN show higher Balmer decrements than NLUnabs, indicating stronger extinction and different ionization conditions. Host diagnostics further reinforce the contrasts: at $\rm z<0.8$, NLUnabs show
star-formation rates and
accretion efficiencies that are comparable to BL AGN, whereas NL AGN reside in more quiescent hosts with lower
star formation and less efficient black-hole growth. BLAbs match BL AGN in host and
accretion properties, with their peculiarity lying in excess X-ray absorption. These findings demonstrate that obscuration arises not only from orientation but also from multi-scale distributions of gas and
dust. Identifying such mismatched populations will be crucial for interpreting AGN demographics in ongoing and upcoming surveys such as Euclid and VRO/LSST.
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All authors G. Mountrichas, F.J. Carrera, E. Quintin, A. Viitanen, A. Corral, N. Webb
Astrophysics of Galaxies
A systematic study of AGN feedback in a disk galaxy I: global overview
Yuxuan Zou, Feng Yuan, Suoqing Ji et al. (+5 more)
This is the first paper in a series using our MACER framework to investigate the
evolution of a disk
galaxy, which emphasizes the role of active
galactic nucleus (AGN) feedback and incorporates cosmological inflows. This paper presents the model setup and the overall results. The predicted AGN duty cycle of approximately 0.49% is consistent with observations. Analysis of the AGN luminosity and
star formation rate (SFR) light curves reveals a positive correlation between the two. We find that cold filaments condense in the circumgalactic medium (CGM) region due to radiative cooling and subsequently fall onto the
galaxy, significantly enhancing both the SFR and AGN activity. The
galaxy is then quenched over a timescale of approximately 1 Gyr by the strong feedback from the enhanced AGN activity. This indicates that a positive correlation between SFR and AGN luminosity does not preclude AGN feedback from acting as the quenching mechanism for the
galaxy. Notably, models without AGN feedback exhibit significantly lower peak SFRs than those with it. We attribute this difference to cumulative AGN feedback, which drives gas from the
galaxy into the CGM, facilitating the formation of more massive cold filaments and ultimately promoting more intense starburst episodes.
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All authors Yuxuan Zou, Feng Yuan, Suoqing Ji, Luis C. Ho, Yingjie Peng, Jing Wang, Bocheng Zhu, Tao Wang
Cosmology and Nongalactic Astrophysics
Spontaneous Baryogenesis and Primordial Black Hole Dark Matter from Ultra-Slow-Roll Inflation
Shyam Balaji
We propose a unified framework where the totality of dark matter (DM), the
baryon asymmetry of the universe, and a detectable
stochastic gravitational wave (GW) background originate from ultra-slow-roll (USR) inflation. The drastic suppression of the inflaton velocity during the USR phase, required for
primordial black hole (PBH) DM production, can also set the initial conditions for spontaneous baryogenesis via a derivative coupling. This mechanism establishes a predictive correlation between the PBH abundance and the
baryon yield, effectively fixing the reheating temperature $T_\textrm{reh}$ as a function of the post-peak spectral slope of the
primordial power spectrum and the tensor-to-scalar ratio on CMB scales $r_\textrm{CMB}$. We perform a simple scan of the parameter space, demonstrating that while “flat” spectral tails allow for high-scale inflation ($r_{\rm CMB} \lesssim 10^{-3}$, $T_{\rm reh} \lesssim 10^{14} \text{ GeV}$) with a small wedge of tensor-to-scalar ratios potentially accessible to future CMB B-mode experiments, steep spectral tails enforce drastically lower scale inflation with an unobservably small $r_{\rm CMB}$ to avoid
baryon overproduction. This degeneracy can be broken by GW astronomy: while LISA and DECIGO are capable of detecting the induced GW background associated with asteroid-mass PBH DM, the Einstein
Telescope (ET) can act as a spectral discriminator, sensitive only to the broadband signals of high-scale scenarios.
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