Instrumentation and Methods for Astrophysics
Solver-in-the-Loop Applications in Astrophysical (Magneto)hydrodynamics
Leonard Storcks and Tobias Buck
We present two promising applications of training machine learning models inside a differentiable astrophysical (magneto)hydrodynamics simulator. First, we address the problem of slow convergence in hydrodynamical simulations of wind-blown bubbles with radiative cooling. We demonstrate that a learned cooling function can recover high-resolution dynamics in low-resolution simulations. Secondly, we train a convolutional neural network to correct 2D magnetohydrodynamics simulations of a specific blast wave problem. These case studies pave the way for the principled application of more general machine learning models inside astrophysical simulators. The code is available open source under https://github.com/leo1200/eurips25corr.
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Solar and Stellar Astrophysics
The SPHINX M dwarf Spectral Grid. II. New Model Atmospheres and Spectra to Derive Fundamental Properties of mid-to-late type M-dwarfs
Aishwarya R. Iyer, Michael R. Line, Philip S. Muirhead et al. (+2 more)
M-
dwarfs are the most dominant
stars in the
Galaxy. Their interiors and atmospheres exhibit complex processes including
dust condensation, convective feedback, and
magnetic activity-driven heterogeneity. Standard
stellar characterization methods often struggle to capture these coupled effects. Part I of this series introduced SPHINX I, a validated grid of self-consistent radiative-convective model atmospheres and spectra for M-
dwarfs with up-to-date molecular opacities suitable for early-to-mid M-
dwarfs. Here, we present SPHINX II, which extends the model grid to cover mid-to-late type M-
dwarfs, including both gray and physically motivated condensate cloud treatments and shorter convective mixing lengths. We validate SPHINX II using 39
benchmark FGK+M binary systems observed with SpeX IRTF (Mann et al. 2014) and apply it to 32 mid-to-late-type M-
dwarfs from the SpeX Prism Library. SPHINX II yields improved fits that are statistically consistent with empirical
benchmarks, achieving precisions of 0.078 dex in
metallicity and 0.13 dex in C/O. Across the model grid, condensate cloud mass peaks between 2100-2400 K, decreasing sharply toward both cooler and hotter temperatures. We find the onset of the cloud-free regime around 2900 K, and below 2100 K, we see formation of deep/buried clouds. As a case study, we also model Trappist-1 and show that even mass-limited silicate grains subtly modify its emergent spectrum, suppressing near-infrared flux and reddening the mid-infrared slope via shallow cloud formation near 1e-2 bar. In sum, SPHINX II provides an improved framework for constraining the fundamental properties of mid-to-late M-
dwarfs.
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All authors Aishwarya R. Iyer, Michael R. Line, Philip S. Muirhead, Jonathan J. Fortney, Jacqueline K. Faherty
Instrumentation and Methods for Astrophysics
Evaluating the Prospects of Cyclic Deconvolution across 312 Pulsars
Jacob E. Turner
We use the cyclic figure of merit to determine the likelihood of achieving cyclic deconvolution for 312
pulsars with sub-40 ms
spin periods across 15 different
telescope-observing frequency combinations. We find that the optimal frequency range for achieving cyclic deconvolution for most
pulsars is between $\sim$80$-$300 MHz, making low frequency observatories such as uGMRT, LOFAR, and MWA the best-suited instruments for the technique. Moreover, we find that, as quantified by the total number sources with sufficient cyclic merits that are observed within the full deconvolution regime, uGMRT is likely the best current instrument for cyclic spectroscopy among the ten
telescopes we considered, with LOFAR being the second best, although our simulations predict that the DSA may become the top instrument once a greater fraction of
galactic millisecond
pulsars are discovered. The relatively high cyclic merit of the Crab
Pulsar in the frequency ranges considered for GBT, MWA, LOFAR, and uGMRT suggests that some faster-spinning canonical
pulsars may be able to achieve cyclic deconvolution, and we discuss potential follow-up analyses on other non-recycled
pulsars. We conclude by advocating for near real-time cyclic spectroscopy backends to be considered for current and upcoming low frequency
telescopes to increase the accessibility of this technique.
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Solar and Stellar Astrophysics
Evolution of the Accretion Rate of Young Intermediate Mass Stars: Implications for Disk Evolution and Planet Formation
Sean D. Brittain, Joshua W. Kern, Gwendolyn Meeus et al. (+1 more)
This work presents a study of the
evolution of the
stellar accretion rates of pre-main-sequence intermediate-mass
stars. We compare the
accretion rate of the younger intermediate-mass T Tauri
stars (IMTTSs) with the older Herbig
stars into which they evolve. We find that the median
accretion rate of IMTTSs (1.2$\times$10$^{-8}$ M$_{\odot}$ yr$^{-1}$) is significantly lower than that of Herbig
stars (1.9$\times$10$^{-7}$ M$_{\odot}$ yr$^{-1}$). This increase stands in stark contrast with canonical models of disk
evolution that predict that the
stellar accretion rate declines with age. We put forward a physically plausible scenario that accounts for the systematic increase of
stellar accretion based on the increase of the effective temperature of the
stars as they evolve towards the zero-age main sequence. For example, the temperature of a 2M$_{\odot}$
star will increase from 4900~K in the IMTTS phase to 9100~K during the Herbig phase. Thus, the luminosity of the far ultraviolet (FUV) radiation will increase by orders of magnitude. We propose that this increase drives a higher
stellar accretion rate. The scenario we propose to account for the increase in the
stellar accretion rate solves the lifetime problem for Herbig disks because the increasing
stellar accretion rates require lower initial disk masses to account for present-day disk masses. This work highlights the importance of the role FUV radiation has in driving the
accretion rate, predicts a large population of pre-main-sequence non-accreting A
stars, and has implications for interpreting disk morphologies that may serve as signposts of embedded gas
giant planets in Herbig disks.
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All authors Sean D. Brittain, Joshua W. Kern, Gwendolyn Meeus, Rene D. Oudmaijer
Solar and Stellar Astrophysics
Convective Heat Transport Asymptotic Law in an $\alpha^2$ dynamo model
Giuseppina Nigro
Stellar activity and planetary magnetospheres are powered by an underlying dynamo mechanism generated by magnetoconvection coupled with rotation. In astrophysical contexts, magnetoconvection typically occurs in parameter regimes that are currently inaccessible to direct numerical simulations (DNS). We investigate convective heat transfer in a magneto-convection and dynamo model under extreme parameter conditions, specifically high Rayleigh and Prandtl numbers, in a
plasma flow with maximum kinetic helicity compatible with fast-rotating objects. Our approach to studying magneto-convection and dynamo mechanisms employs a simplified thermally driven shell model.
Magnetic polarity reversals are obtained by including a pitchfork bifurcation term in the large-scale
magnetic field equation, while nonlinear dynamics are described by a shell model formulation. The low computational cost of the model allows us to explore the asymptotic behavior of convective heat transfer in regimes beyond those reached by current DNS. Our results reveal that the Nusselt number $Nu$ – a dimensionless measure of convective heat transport – generally increases with
turbulence, following a power-law scaling and showing a strong correlation with Ra and Pr. This relationship appears to be more pronounced than that observed in non-magnetized fluids, suggesting that
magnetic fields may significantly enhance convective heat transfer. Despite the assumption to neglect spatial information such as density stratification – an assumption that is necessary in the shell model approach – our model captures the gross dynamical features of turbulent magnetoconvection in asymptotic regimes. It allows for a broad exploration of parameter space, indicating that
magnetic fields may play a central role in modulating heat transport in
stellar and planetary interiors.
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Astrophysics of Galaxies
$S^5$: Tidal Disruption in Crater 2 and Formation of Diffuse Dwarf Galaxies in the Local Group
Guilherme Limberg, Alexander P. Ji, Ting S. Li et al. (+19 more)
We present results of a spectroscopic campaign around the diffuse
dwarf galaxy Crater 2 (Cra2) and its
tidal tails as part of the Southern
Stellar Stream Spectroscopic Survey ($S^5$). Cra2 is a Milky Way
dwarf spheroidal satellite with extremely cold kinematics, but a huge size similar to the Small Magellanic Cloud, which may be difficult to explain within collisionless cold dark matter. We identify 143 Cra2 members, of which 114 belong to the
galaxy's main body and 29 are deemed part of its
stellar stream. We confirm that Cra2 is dynamically cold (central velocity dispersion $2.51^{+0.33}_{-0.30}\,{\rm km \ s^{-1}}$) and also discover a $\approx$7$\sigma$ velocity gradient consistent with its
tidal debris track. We separately estimate the stream's internal velocity dispersion to be $5.74^{+0.98}_{-0.83}\,{\rm km \ s^{-1}}$. We develop a suite of $N$-body simulations with both cuspy and cored density profiles on a realistic Cra2 orbit to compare with $S^5$ observations. We find that the velocity dispersion ratio between Cra2 stream and
galaxy ($2.30^{+0.41}_{-0.35}$) is difficult to reconcile with a cuspy
halo with fiducial concentration and an initial mass predicted by standard
stellar mass–
halo mass relationships. Instead, either a cored
halo with relatively small core radius or a low-concentration cuspy model can reproduce this ratio. Despite
tidal mass loss, Cra2 is metal-poor ($\langle \rm[Fe/H]\rangle=-2.16\pm0.04$) compared to the
stellar mass–
metallicity relation for its luminosity. Other diffuse
dwarf galaxies similar to Cra2 in the Local Group (Antlia 2 and Andromeda 19) also challenge
galaxy formation models. Finally, we discuss possible formation scenarios for Cra2, including ram-pressure stripping of a gas-rich progenitor combined with tides.
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All authors Guilherme Limberg, Alexander P. Ji, Ting S. Li, Denis Erkal, Sergey E. Koposov, Andrew B. Pace, Andrew P. Li, Petra Awad, Alexandra Senkevich, Joss Bland-Hawthorn, Lara Cullinane, Gary Da Costa, Alex Drlica-Wagner, Raphaël Errani, Peter S. Ferguson, Kyler Kuehn, Geraint F. Lewis, Sarah L. Martell, Jorge Peñarrubia, Nora Shipp, Yong Yang, Daniel B. Zucker
Solar and Stellar Astrophysics
Dynamics of Streamers and Pseudostreamers and Implications for the Solar Wind
Sahel Dey, David I. Pontin and Spiro K. Antiochos
The origin of the Sun's slow wind and its inherent variability remain unknown, but there is increasing evidence that interactions between closed and open
magnetic flux in the corona play a major role. This paper studies the dynamic
evolution of streamers and pseudostreamers with a particular focus on the release of
plasma from the closed to the open field region. We employ a global 2.5D magnetohydrodynamic model that extends from the
solar chromosphere to 30
solar radii, and that extends previous interchange
magnetic reconnection modelling by including self-consistent thermodynamics. We find that at both the helmet streamer and pseudostreamer there is a continual dynamic interaction between closed and open flux even in the absence of explicit driving. At the helmet streamer, the dynamics take the form of a ”breathing” cycle in which the closed flux contracts and expands, and plasmoids are released along the heliospheric current sheet. The pseudostreamer exhibits a back-and-forth motion, driving interchange reconnection alternately on its opposite flanks. The resulting release of hot, dense
plasma leads to density fluctuations in the open field that are significantly larger above the helmet streamer due to the persistence of the plasmoids there. Our model demonstrates that
plasma is continually being released into the heliosphere from both streamers and pseudostreamers. We discuss the implications of our simulation results for observations of the corona and inner heliosphere.
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High Energy Astrophysical Phenomena
High-Energy Extractions from Horizonless Compact Objects
Parth Bambhaniya and Elisabete M. de Gouveia Dal Pino
High-energy astrophysical sources such as active
galactic nuclei,
quasars, X-ray binaries, and gamma-ray bursts are powered by mechanisms that convert gravitational or rotational energy into radiation, jets, and relativistic
outflows. Understanding the physics of these processes remains a major challenge. Black holes have traditionally served as the central engines behind such phenomena, with well established energy extraction mechanisms including the Penrose process, the Blandford-Znajek process, and the Banados-Silk-West mechanism. However, studies in general relativity indicate that, under certain conditions, gravitational collapse may lead to the formation of naked singularities or other horizonless compact objects, which could in principle allow more efficient energy extraction than classical black holes. This brief review summarizes recent progress on energy extraction mechanisms in naked singularity spacetimes. We examine the roles of rotation, electromagnetic fields, and particle interactions in shaping extraction efficiency and dynamics. Particular
attention is given to negative energy orbits and ergoregion physics, which enable Penrose type and
magnetic Penrose mechanisms without an event horizon. We also discuss collisional Penrose processes and particle acceleration near the singularity, emphasizing their potential astrophysical implications. By comparing extraction efficiencies and physical conditions in black holes and naked singularities, we highlight how the absence of a horizon fundamentally alters the dynamics of energy release. These results suggest that naked singularities may serve as natural laboratories for strong field
gravity and as alternative engines for high-energy astrophysical phenomena in the era of multi-messenger observations.
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High Energy Astrophysical Phenomena
Impact of Nuclear Reaction Rate Uncertainties on Type I X-ray Burst Nucleosynthesis: A Monte Carlo Study
Qing Wang, Ertao Li, Zhihong Li et al. (+10 more)
Type I X-ray bursts are thermonuclear flashes on the surface of accreting
neutron stars, involving hundreds of
nuclei and thousands of reactions with larger uncertainties in reaction rate. To investigate the impact of
nuclear reaction rate uncertainties on type I X-ray burst nucleosynthesis, comprehensive Monte Carlo simulations were performed with temperature-independent and -dependent variations in reaction rates using the REACLIB and STARLIB libraries, respectively. A total of 1,711 $(p, \gamma)$, $(p, \alpha)$, $(\alpha, p)$, and $(\alpha, \gamma)$ reaction rates are varied simultaneously along with their inverse reactions via detailed balance. For the first time, it has been found that Monte Carlo sampling with larger perturbations to these reaction rates may lead to multi-peak abundance distributions for certain isotopes, such as $^{64}$Zn and $^{55}$Co. These multi-peak structures arise not only from coupled reactions but also from single reactions in some cases. Our studies also confirm previously identified key reactions and provide more robust lists that deserve priority consideration in future studies.
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All authors Qing Wang, Ertao Li, Zhihong Li, Youbao Wang, Bing Guo, Yunju Li, Jun Su, Shipeng Hu, Yinwen Guan, Dong Xiang, Yu Liu, Lei Yang, Weiping Liu
Earth and Planetary Astrophysics
SCExAO/CHARIS and Gaia Direct Imaging and Astrometric Discovery of a Superjovian Planet 3–4 lambda/D from the Accelerating Star HIP 54515
Thayne Currie, Yiting Li, Mona El Morsy et al. (+28 more)
We present the discovery of a superjovian
planet around the young A5
star HIP 54515, detected using precision astrometry from the Hipparcos
Gaia Catalogue of Accelerations and high-contrast imaging with SCExAO/CHARIS from the recently-commenced OASIS program. SCExAO/CHARIS detects HIP 54515 b in five epochs 0\farcs{}145–0\farcs{}192 from the
star ($\sim$3–4 $\lambda$/D at 1.65 $\mu m$), exhibiting clockwise orbital motion. HIP 54515 b lies near the M/L transition with a luminosity of log(L/L$_{\rm \odot}$) $\sim$ -3.52 $\pm$ 0.03. Dynamical modeling constrains its mass and mass ratio to be ${17.7}_{-4.9}^{+7.6}$ $M_{\rm Jup}$ and ${0.0090}_{-0.0024}^{+0.0036}$ and favors a $\sim$25 au semimajor axis. HIP 54515 b adds to a growing list of superjovian
planets with moderate eccentricities (e $\approx$ 0.4). Now the third
planet discovered from surveys combining high-contrast extreme adaptive optics imaging with precision astrometry, HIP 54515 b should help improve empirical constraints on the luminosity
evolution and eccentricity distribution of the most massive
planets. It may also provide a key technical test of the Roman Space
Telescope Coronagraph Instrument's performance in the low
stellar flux, small angular separation limit and a demonstration of its ability to yield constrainable
planet spectral properties.
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All authors Thayne Currie, Yiting Li, Mona El Morsy, Brianna Lacy, Maria Vincent, Taylor L. Tobin, Masayuki Kuzuhara, Jeffrey Chilcote, Olivier Guyon, Ziying Gu, Danielle Bovie, Dillon Peng, Qier An, Timothy D. Brandt, Robert J. De Rosa, Vincent Deo, Tyler D. Groff, Markus Janson, N. Jeremy Kasdin, Julien Lozi, Christian Marois, Bertrand Mennesson, Naoshi Murakami, Eric Nielsen, Sabina Sagynbayeva, Nour Skaf, William Thompson, Motohide Tamura, Taichi Uyama, Sébastien Vievard, Alice Zurlo
High Energy Astrophysical Phenomena
Inefficient Circularization, Delayed Stream-Disk Interaction and Reprocessing: A Five-Stage Model for the Intermediate-Mass Black Hole Tidal Disruption Event EP240222a
Wenkai Li, Ning Jiang, Tinggui Wang et al. (+7 more)
EP240222a is the first intermediate-mass black hole (IMBH)
tidal disruption event (TDE) captured in real-time with multi-wavelength observations and spectroscopic confirmation. However, its light curves deviate substantially from previous theoretical expectations. Motivated by these unique features, we have developed a novel model that successfully reproduces its peculiar
evolution. Our model delineates five stages: (1) Initial Stage of inefficient circularization; (2) Slow-Rising Stage with a faint X-ray precursor disk fed by successive self-crossings; (3) Fast-Rising Stage, where delayed stream-disk interaction at momentum flux matching drives a sharp luminosity rise; (4) Plateau Stage with super-Eddington
accretion,
outflow, reprocessing, and a clear polar line-of-sight; and (5) Decline Stage of sub-Eddington
accretion and ongoing reprocessing. Our fit indicates the disruption of a $M_* \approx 0.4~M_\odot$ main-sequence (MS)
star with a penetration factor $\beta \approx 1.0$. Our model, which incorporates key TDE processes, establishes EP240222a-like light curves as typical IMBH-TDE signatures. The distinctive identifier is a slow rise in X-rays and a corresponding slow rise/quasi-plateau in the UV/optical, followed by a brighter, super-Eddington plateau in both bands, though other forms exist, such as the rapid rise from white
dwarf (WD) disruptions over minutes to days.
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All authors Wenkai Li, Ning Jiang, Tinggui Wang, Rongfeng Shen, Erlin Qiao, Lixin Dai, Di Luo, Dongyue Li, Chichuan Jin, Jiazheng Zhu
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Linearly Polarized Gravitational Waves from Bubble Collisions
Katarina Trailović
Physics beyond the Standard Model may give rise to first-order phase transitions proceeding via the nucleation of
vacuum bubbles, whose subsequent collisions generate gravitational waves (GWs). Their detection would open the possibility of investigating the universe in its first instants. If the transition is slow enough, such that it completes with the nucleation and collision of only two bubbles, the resulting GW signal is linearly polarized. This would give a unique signature for the origin of such a GW signal. We show that even though such phase transitions would be slow, they still could lie within the detectability range of GW interferometers such as LISA and the Einstein
Telescope and the underlying two-bubble origin would be encoded in higher-order polarization statistics.
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High Energy Astrophysical Phenomena
AT2022zod: An Unusual Tidal Disruption Event in an Elliptical Galaxy at Redshift 0.11
Kristen C. Dage, Phelipe Darc, Thallis Pessi et al. (+16 more)
Tidal Disruption Events (TDEs) have long been hypothesized as valuable indicators of black holes, offering insight into their demographics and behaviour out to high
redshift. TDEs have also enabled the discovery of a few Massive Black Holes (MBHs) with inferred masses of $10^4$–$10^6\,M_\odot$, often associated with the
nuclei of
dwarf galaxies or ultra-compact
dwarf galaxies (UCDs). Here we present AT2022zod, an extreme and short-lived optical
flare in an elliptical
galaxy at z=0.11, residing within 3kpc of the
galaxy's centre. Its luminosity and ~30-day duration make it unlikely to have originated from the host
galaxy's central supermassive black hole (SMBH), which estimate to have a mass around $10^8\,M_\odot$. Assuming that the emission mechanism is consistent with known observed TDEs, we find that such a rapidly evolving transient could either be produced by a MBH in the intermediate-mass range or, alternatively, result from the
tidal disruption of a
star on a non-
parabolic orbit around the central SMBH. We suggest that the most plausible origin for AT2022zod is the
tidal disruption of a
star by a MBH embedded in a UCD. As the Vera C. Rubin Observatory's Legacy Survey of Space and Time comes online, we propose that AT2022zod serves as an important event for refining search strategies and characterization techniques for intermediate-mass black holes.
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All authors Kristen C. Dage, Phelipe Darc, Thallis Pessi, Rupesh Durgesh, Shravya Shenoy, Lilianne Nakazono, Celine Boehm, Ana L. Chies-Santos, Rafael S. de Souza, Zsofia V. Kovacs-Stermeczky, Arash Bahramian, Bahar Bidaran, Emille E. O. Ishida, Alberto Krone-Martins, Aarya A. Patil, Reinaldo R. Rosa, Andressa Wille, Richard M. Plotkin, Behzad Tahmasebzadeh
Earth and Planetary Astrophysics
Constraining the Occurrence of ZLK-Induced White Dwarf Pollution with Dissipative Precession
Isabella Trierweiler, Konstantin Gerbig and Malena Rice
Von Zeipel-Lidov-Kozai (ZLK) oscillations, induced by bound, perturbative companions to white
dwarfs, have been suggested as a dynamical mechanism that may contribute to white
dwarf pollution. To trigger ZLK oscillations, however, a 3-body system must reach a sufficiently large mutual inclination between orbits. The occurrence of these high-mutual-inclination configurations can be curtailed by dissipative precession at the protoplanetary disk stage, which pushes
exoplanet-hosting close binary systems toward preferential orbit-orbit
alignment. In this work, we constrain the fraction of white
dwarfs with binary companions that can undergo ZLK-driven pollution given the effects of dissipative precession. To accrete pollution via ZLK oscillations, a white
dwarf binary system must be sufficiently inclined and the characteristic timescale of the oscillations must be sufficiently short to perturb material within the white
dwarf's cooling age. Considering a sample of 4400 known white
dwarf/main sequence binaries, we find that $50-70\%$ have favorable parameters for ZLK pollution, depending on the orbital separation of the polluting body. While the conditions for oscillations are favorable, the tendency for ZLK to result in massive but more infrequent polluters likely restricts the rates of ZLK-induced pollution among the observed population. In general, dissipative precession is a limiting factor in pollution rates for more closely separated binaries (initial separations $<500-800$~au), while ZLK timescale constraints are most limiting for wider binaries.
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High Energy Astrophysical Phenomena
Dynamo and Jet interconnections in GRMHD simulations of black hole accretion disks
P. S. Santhiya, Pallavi Bhat, Prayush Kumar et al. (+2 more)
We present global 3D GRMHD simulations of black hole (BH)
accretion disks designed to investigate how MRI-driven dynamo action regulates jet formation and
evolution. Unlike standard SANE/MAD setups that impose a coherent large-scale poloidal loop, our "sub-SANE" initial conditions use multiple same-polarity small-scale
magnetic loops. Rapid reconnection erases
magnetic memory and enables large-scale dynamo to emerge early from MRI
turbulence. We perform two such sub-SANE simulations at different BH
spins ($a = 0.5, 0.9375$) and compare them with conventional SANE runs. The sub-SANE disks show regular large-scale dynamo cycles with periods of about ten orbits. Decomposition of the induction equation shows that the turbulent dynamo term is stronger in 3D compared to 2.5D and balances advection in the saturated state, confirming sustained large-scale field generation. These dynamo-generated fields are advected inward with minimal time lag, producing correlated peaks in both poloidal and toroidal field strengths from $r_{\rm max}$ to the horizon. Early in the
evolution, these peaks imprint directly onto the jet's electromagnetic energy flux, indicating that the jet mirrors the dynamo wave. Though jets form at early times, the sub-SANE runs eventually undergo jet shutdown. We show that this occurs when the
magnetic field at the horizon loses coherence, as quantified by a decline in the signed-to-unsigned flux ratio $\mathcal{C}_{\rm BH}$ below $\approx 0.6$. In contrast, the SANE reference case with similar
accretion rate and horizon
magnetic flux maintains high
magnetic coherence because its initial large-scale field persists, allowing its jet to survive. Our results show that both dynamo-driven field
evolution and horizon
magnetic-field coherence critically regulate jet longevity, establishing a direct dynamo-jet connection in GRMHD disks.
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All authors P. S. Santhiya, Pallavi Bhat, Prayush Kumar, Tushar Mondal, Indu K. Dihingia
Astrophysics of Galaxies
Ripples in the baryon to dark matter ratio in $\Lambda$CDM: implications for galaxy formation
Owen Jessop, Adrian Jenkins, Andrew Pontzen et al. (+3 more)
We use the FLAMINGO
galaxy formation model to quantify the impact of
baryon-CDM isocurvature perturbations on
galaxy formation in $\Lambda$CDM. In linear theory, these perturbations represent local, compensated variations in the ratio between the
baryon and CDM densities; they freeze in amplitude at late times, with an RMS amplitude of $1.5\%$ on the Lagrangian scale of a $10^{11}\,\rm M_\odot$
halo ($0.85\, \rm{Mpc}$). Although such perturbations arise naturally within $\Lambda$CDM, most cosmological simulations and semi-analytic models to date omit them. These perturbations are strongly anti-correlated with the matter overdensity field such that
halos form with
baryon fractions below the
cosmic mean, with earlier-collapsing
halos exhibiting stronger baryonic suppression. To isolate the
galaxy response, we analyse three hydrodynamical simulations with identical initial matter overdensity fields that: i) include isocurvature modes, ii) omit them, or iii) invert their amplitude. At $z=8$, isocurvature perturbations reduce the mean
baryon fraction and
star formation rates of resolved
halos by $ 5\%$ and $ 12\%$, respectively, relative to the null-isocurvature case. These effects are almost independent of
halo mass and diminish steadily with time, reaching $ 0.1\%$ and $ 1\%$ by $z=0$. We develop a model based on spherical collapse that accurately reproduces the mean
baryon fraction suppression. As high-
redshift observations become increasingly routine, incorporating isocurvature perturbations into simulations and semi-analytic models will be important for robust predictions of early
galaxy and black hole formation in the JWST era.
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All authors Owen Jessop, Adrian Jenkins, Andrew Pontzen, Joop Schaye, Matthieu Schaller, John C. Helly
Solar and Stellar Astrophysics
OASIS Survey Direct Imaging and Astrometric Discovery of HIP 71618 B: A Substellar Companion Suitable for the Roman Coronagraph Technology Demonstration
Mona El Morsy, Thayne Currie, Brianna Lacy et al. (+27 more)
We present the OASIS survey program discovery of a substellar companion orbiting the young A1V
star HIP 71618, detected using precision astrometry from
Gaia and Hipparcos and high-contrast imaging with SCExAO/CHARIS and Keck/NIRC2. Atmospheric modeling favors a spectral type of M5–M8 and a temperature of $\sim$2700 $\pm$ 100 $K$. Dynamical modeling constrains HIP 71618 B's mass to be ${60}_{-21}^{+27}$ $M_{\rm Jup}$ or ${65}_{-29}^{+54}$ $M_{\rm Jup}$, depending on the adopted companion mass prior. It has a nearly edge-on, 11 au-orbit with a high eccentricity. HIP 71618 B will be located within Roman Coronagraph's dark hole region during the instrument's technological demonstration phase. A high signal-to-noise ratio detection of HIP 71618 B at 575 nm would demonstrate a 5-$\sigma$ contrast of 10$^{-7}$ or better. The system is also located within or very close to Roman's Continuous Viewing Zone – near multiple candidate reference
stars for dark-hole digging – and its primary is bright ($V$ $\approx$ 5). The suitability of HIP 71618 as one potential Roman Coronagraph target for demonstrating the instrument's core requirement (TTR5) should motivate the timely, deep vetting of candidate reference
stars.
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All authors Mona El Morsy, Thayne Currie, Brianna Lacy, Taylor L. Tobin, Qier An, Yiting Li, Ziying Gu, Masayuki Kuzuhara, Danielle Bovie, Dillon Peng, Jeffrey Chilcote, Olivier Guyon, Timothy D. Brandt, Robert J. De Rosa, Vincent Deo, Tyler D. Groff, Markus Janson, N. Jeremy Kasdin, Julien Lozi, Christian Marois, Bertrand Mennesson, Naoshi Murakami, Eric Nielsen, Sabina Sagynbayeva, Nour Skaf, William Thompson, Motohide Tamura, Taichi Uyama, Sébastien Vievard, Alice Zurlo
Astrophysics of Galaxies
A value-added catalogue of neural network-based europium abundances for GALAH DR4
Sarah G. Kane, Zofia Kaczmarek, Andrew Garner et al. (+3 more)
The rapid
neutron-capture ($r$-process) element europium (Eu) is a valuable tracer of
neutron star mergers and other rare nucleosynthetic events. The
stellar spectroscopic survey GALAH's unique wavelength range and setup include the Eu absorption feature at $\sim6645$ Å for almost a million
stars in the most recent Data Release 4 (DR4). However, DR4 also saw a decreased precision in reported Eu measurements compared to previous data releases. In this work, we use a convolutional neural network (CNN) to perform label transfer, wherein we use the GALAH DR4 spectra and
stellar parameters to infer DR3 [Eu/H] abundances. This CNN is then applied to DR4 spectra without corresponding DR3 Eu abundances to develop a new, publicly available catalogue of [Eu/H] values for high signal-to-noise targets. We include [Eu/H] predictions for $118\,946$
stars, out of which $54\,068$
giants constitute our "golden sample" of high-confidence predictions, which pass stricter quality cuts and have a reported precision $\lesssim0.1$. To overcome the scarcity of training data in the low
metallicity regime, we provide an additional catalogue of [Eu/H] abundances for metal poor ($\mathrm{[Fe/H]}<-1$)
stars derived from synthesis of the Eu feature. Our "golden sample" can be combined with [Eu/H] values from GALAH DR3 to create a catalogue of over $100\,000$ vetted, high-quality abundances on a homogeneous scale. Moreover, we are able to reproduce known science results, including the elevated Eu abundances of accreted
stars and previously observed
Galactic chemical
evolution trends. This catalogue represents one of the largest available samples of [Eu/H] abundances for high signal-to-noise targets.
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All authors Sarah G. Kane, Zofia Kaczmarek, Andrew Garner, Sven Buder, Stephanie Monty, Elana Kane
Astrophysics of Galaxies
Kinematics of young stellar objects in NGC 2024 based on infrared proper motions
Alena Rottensteiner, Monika G. Petr-Gotzens, Stefan Meingast et al. (+6 more)
The most recently formed young
stellar objects (YSOs) in active
star forming regions are excellent tracers of their parent cloud motion. Their positions and dynamics provide insight into cluster formation and constrain kinematic decoupling timescales between
stars and gas. However, because of their strong extinction and young age, embedded YSOs are mainly visible at infrared wavelengths and thus absent from astrometric surveys such as
Gaia. We measured the proper motions of 6,769 sources toward the NGC 2024 cluster in the Flame Nebula using multi-epoch near-infrared observations from three ESO public surveys:
VISIONS, VHS, and the VISTA/VIRCAM science verification program. Cross-validation of our results with
Gaia using optically visible
stars shows excellent agreement, with uncertainties on the same order of magnitude. For 362 YSO candidates identified from the literature, we derived proper motions on the order of <5 mas/yr with mean measurement uncertainties of ~0.22 mas/yr. This is the first homogeneous proper motion measurement of this quality for more than half of these
stars. For Class I and flat-spectrum sources, our results provide a >13-fold increase in available proper motion measurements. We analyzed the positional and kinematic differences between YSO classes and confirmed a previously reported inside-out age segregation from younger to older
stars, likely driven by an outward movement of older
stars. No evidence of prolonged hierarchical assembly was found. Instead, the results support a rapid (<1 Myr) cluster collapse. This scenario also accounts for the observed slightly higher 1D velocity dispersion of Class I sources relative to Class flat objects. YSO radial velocities generally align with the gas velocities measured from 12CO(3-2), HNC(1-0), HCN(1-0), and show a weaker correlation with N_2H+(1-0). Some Class II and III objects appear to be already decoupling.
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All authors Alena Rottensteiner, Monika G. Petr-Gotzens, Stefan Meingast, João Alves, Emmanuel Bertin, Hervé Bouy, Martin Piecka, Sebastian Ratzenböck, Andrea Socci
Solar and Stellar Astrophysics
Untangling the Sources of Abundance Dispersion in Low-metallicity Stars II: Neutron Capture Elements
Emily J. Griffith, Marissa Blum, David H. Weinberg et al. (+4 more)
We present the abundances of 23 elements, including 11 heavy elements (Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, Eu) for up to 86 metal-poor (-2 < [Fe/H] < -1) subgiants. We use KORG, a state of the art spectral synthesis package, to derive 1D-LTE abundances from high-SNR and high-resolution spectra taken by the Large Binocular
Telescope with the Potsdam Echelle Polarimetric and Spectroscopic Instrument. These precise spectra and abundance measurements minimize the impact of
photon-noise (<0.06 dex), allowing us to robustly measure the intrinsic abundance scatter in [X/Fe]. After removing two
stars with exceptional s-process enhancement, we find that the intrinsic scatter among the s- and r-process elements tends to be larger than for the lighter elements, with heavy element scatter ranging from 0.11 (Zn) to 0.27 (Eu) dex. Intrinsic abundance scatter could have multiple origins, including
star-to-
star variations in the ratios of nucleosynthetic sources as well as
stochastic sampling of the progenitor
supernovae properties, such as mass, rotation, and
magnetic field strength. We explore the expected abundance scatter signature caused by
stochastic sampling, finding that a fraction of both rapidly rotating CCSN and magnetorotationally driven SN are needed to reach the observed abundances and intrinsic scatter. This analysis is limited by the restrictive parameter spaces spanned by existing yield sets. A diverse, finely sampled grid of
supernovae yields is needed to robustly model
stochastic abundance scatter.
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All authors Emily J. Griffith, Marissa Blum, David H. Weinberg, Jennifer A. Johnson, Tawny Sit, Ilya Ilyin, Klaus G. Strassmeier
Astrophysics of Galaxies
SEAMLESS Survey: Four Faint Dwarf Galaxies Tracing Low-Mass Galaxy Evolution Across Environments
Catherine E. Fielder, Michael G. Jones, David J. Sand et al. (+11 more)
We report on four Local Volume
dwarf galaxies identified through our ongoing SEmi-Automated Machine LEarning Search for Semi-resolved
galaxies (SEAMLESS): Hydrus A, LEDA 486718, Cetus B, and Sculptor 26, with the discovery of Hydrus A reported here for the first time. These four
galaxies span a wide range of environments and evolutionary states. Hydrus A (MV = -9.39+/-0.20, D = 3.38-0.30+0.32 Mpc) and LEDA 486718 (MV = -11.62+/-0.08, D = 4.80+/-0.17 Mpc) are among the most isolated
dwarfs known within 5 Mpc, while Cetus B (MV = -8.26+/-0.17, D = 3.32-0.23+0.25 Mpc) and Sculptor 26 (MV = -11.25+/-0.10, D =3.21+/-0.13 Mpc) lie < 2 Rvir of NGC 253. Hydrus A shows properties consistent with quenching driven by
cosmic reionization,
cosmic-web interactions, or internal feedback. LEDA 486718 is an isolated
star forming
dwarf. Cetus B appears quenched and morphologically disturbed, making it a low-mass satellite or backsplash candidate, while Sculptor 26 is red and seemingly gas-poor but displays signs of recent activity, consistent with a transitional evolutionary state. Together, these systems demonstrate the power of SEAMLESS for building a census of faint
galaxies beyond the Local Group.
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All authors Catherine E. Fielder, Michael G. Jones, David J. Sand, Denija Crnojevic, Burcin Mutlu-Pakdil, Paul Bennet, Amandine Doliva-Dolinsky, Richard Donnerstein, Laura Congreve Hunter, Ananthan Karunakaran, Donghyeon J. Khim, Deepthi S. Prabhu, Kristine Spekkens, Dennis Zaritsky
Astrophysics of Galaxies
VENUS: When Red meets Blue – A multiply imaged Little Red Dot with an apparent blue companion behind the galaxy cluster Abell 383
Miriam Golubchik, Lukas J. Furtak, Joseph F. V. Allingham et al. (+50 more)
We report the discovery of a doubly-imaged Little Red Dot (LRD) candidate behind the
galaxy cluster Abell 383, which we dub A383-LRD1. Initially classified as a dropout
galaxy in HST imaging with several ground-based emission line detections placing it at $z_{\mathrm{spec}}=6.027$, new JWST/NIRCam observations taken as part of the cycle 4 VENUS survey now reveal that the source consists of two underlying components: A red point-source with a V-shaped SED consistent with LRD selection criteria, and a nearby ($\sim 380$ pc) compact blue companion which was the main contributor to the previous rest-frame UV detections. Based on
lensing symmetry and its SED, the LRD appears to lie at a similar
redshift as well. The magnification of the two images of A383-LRD1 is $\mu_{\mathrm{A}}=16.2\pm1.2$ and $\mu_\mathrm{B}=9.0\pm0.6$, respectively, and the predicted time delay between them is $\Delta t_{\mathrm{grav}}=5.20\pm0.14$ yr ($\sim0.7$ yr in the rest-frame). After correcting for the
lensing magnification, we derive an absolute magnitude of $M_{\mathrm{UV,LRD}}=-16.8\pm 0.3$ for the LRD, and $M_{\mathrm{UV,BC}}=-18.2\pm 0.2$ for the blue companion. We perform SED fits to both components, revealing the LRD to be best fitted with a black hole
star (BH*) model and a substantial host
galaxy, and the blue companion with an extremely young, emission-line dominated
star-forming nebula. A383-LRD1 represents the second known multiply-imaged LRD detected to date, following A2744-QSO1, and to our knowledge, the first LRD system with a confirmed detection of [C $_{II}$]$\lambda158 \ \mu$m emission from ALMA observations. Thanks to
lensing magnification, this system opens a unique door to study the relation between a LRD, its host
galaxy, and its environment, and represents a
prime candidate for deep JWST spectroscopy and high-resolution ALMA follow-up observations.
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All authors Miriam Golubchik, Lukas J. Furtak, Joseph F. V. Allingham, Adi Zitrin, Hollis B. Akins, Vasily Kokorev, Seiji Fujimoto, Abdurro'uf, Ricardo O. Amorín, Franz E. Bauer, Rachel Bezanson, Marusa Bradač, Larry D. Bradley, Gabriel B. Brammer, John Chisholm, Dan Coe, Christopher J. Conselice, Pratika Dayal, Miroslava Dessauges-Zavadsky, Jose M. Diego, Andreas L. Faisst, Qinyue Fei, Henry C. Ferguson, Steven L. Finkelstein, Brenda L. Frye, Mauro González-Otero, Jenny E. Greene, Yuichi Harikane, Tiger Yu-Yang Hsiao, Kohei Inayoshi, Yolanda Jiménez-Teja, Kirsten Knudsen, Anton M. Koekemoer, Ivo Labbé, Ray A. Lucas, Georgios E. Magdis, Jorryt Matthee, Matteo Messa, Rohan P. Naidu, Minami Nakane, Gaël Noirot, Richard Pan, Casey Papovich, Johan Richard, Massimo Ricotti, Luke Robbins, Daniel P. Stark, Fengwu Sun, Tommaso Treu, Roberta Tripodi, Eros Vanzella, Chris Willott, Rogier A. Windhorst
Solar and Stellar Astrophysics
Hidden in Plain Sight II: Characterizing the luminous companion to Kappa Velorum with VLTI/GRAVITY
D. M. Rowan, S. Kraus and Todd A. Thompson
Kappa Velorum (Markeb, HD 81188) is one of the brightest
stars in the Southern sky and has long been known to be a single-lined spectroscopic binary. The binary mass function is large, $f(M)=1.15\ M_\odot$, suggesting that the bright (V=2.5) B2IV
star may host a dark, compact object companion. We use VLTI
GRAVITY observations to definitively test this possibility by directly resolving the binary. We detect a main sequence B
star companion and rule out the compact object scenario. By combining the relative astrometric orbit and archival radial velocities, we report an updated precise characterization of the orbit (period $P=116.795\pm0.002$ d, eccentricity $e=0.1764\pm0.0004$, inclination $i=74.04\pm0.01^{\circ}$) and estimate the masses of the B
stars. Using the original Hipparcos parallax measurement $\varpi = 6.05\pm0.48$ mas, we find $M_1 = 10^{+4}_{-2}\ M_\odot$ and $M_2 = 6.9\pm1.0\ M_\odot$. The uncertainties on the masses are primarily driven by the uncertain parallax, which we find is likely biased by the orbital motion. We use an archival UVES spectrum and MIST evolutionary tracks to refine our mass estimates. Finally, we discuss how interferometry and high-contrast imaging may be used to characterize other candidate
star+compact object binaries, including those that will be discovered with
Gaia DR4, as part of a larger effort to uncover the hidden population of black holes in the Milky Way.
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Astrophysics of Galaxies
Determining the Milky Way gravitational potential without selection functions
Taavet Kalda and Gregory Green
Selection effects, such as interstellar extinction and varying survey depth, complicate efforts to determine the gravitational potential - and thus the distribution of baryonic and dark matter - throughout the Milky Way
galaxy using
stellar kinematics. We present a new variant of the "Deep Potential" method of determining the gravitational potential from a snapshot of
stellar positions and velocities that does not require any modeling of spatial selection functions. Instead of modeling the full six-dimensional phase-space distribution function $f\left(\vec{x},\vec{v}\right)$ of observed kinematic tracers, we model the conditional velocity distribution $p\left(\vec{v}\mid\vec{x}\right)$, which is unaffected by a purely spatial selection function. We simultaneously learn the gravitational potential $\Phi\left(\vec{x}\right)$ and the underlying spatial density of the entire tracer population $n\left(\vec{x}\right)$ - including unobserved
stars - using the collisionless Boltzmann equation under the stationarity assumption. The advantage of this method is that unlike the spatial selection function, all of the quantities we model, $p\left(\vec{v}\mid\vec{x}\right)$, $\Phi\left(\vec{x}\right)$, and $n\left(\vec{x}\right)$, typically vary smoothly in both position and velocity. We demonstrate that this "conditional" Deep Potential method is able to accurately recover the gravitational potential in a mock
dataset with a complex three-dimensional
dust distribution that imprints fine angular structure on the selection function. Because we do not need to model the spatial selection function, our new method can effectively scale to large, complex
datasets while using relatively few parameters, and is thus well suited to
Gaia data.
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Astrophysics of Galaxies
Image simulations of highly magnified clumpy galaxies
Irene Mini, Massimo Meneghetti, Matteo Messa et al. (+5 more)
We present ClumPyLen, a Python-based simulator designed to produce realistic mock observations of strongly lensed, high-
redshift, clumpy
star-forming
galaxies. The tool models
galaxy components such as disks, bulges, and spiral arms using Sérsic profiles, and it populates them with
stellar clumps whose properties are sampled from physically motivated distributions. ClumPyLen includes the effects of gravitational
lensing through user-provided deflection angle maps and simulates realistic observational conditions by accounting for instrumental effects, Point-Spread-Function convolution, sky background, and
photon noise. The simulator can support a wide range of filters and instruments; here we focus on HST/ACS, HST/WFC3-IR, and JWST/NIRCam. We demonstrate the capabilities of the code through two examples, including a detailed simulation of the z = 6.145 source
Cosmic Archipelago lensed by MACS J0416.1-2403. The simulated images closely match the morphology and limiting magnitudes of real observations. ClumPyLen is designed to explore the detectability of
stellar clumps in terms of mass and size, especially in the low-mass regime, and it allows the study of clump blending effects. Thanks to its modular design, the code is highly adaptable to a wide range of scientific goals, including
lensing studies,
galaxy evolution, and the generation of synthetic
datasets for machine learning or forward modeling applications.
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All authors Irene Mini, Massimo Meneghetti, Matteo Messa, Lauro Moscardini, Eros Vanzella, Pietro Bergamini, Piero Rosati, Anita Zanella