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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 8 April

High Energy Astrophysical Phenomena

Particle-acceleration mechanisms in multispecies relativistic plasmas

Claudio Meringolo, Mario Imbrogno, Alejandro Cruz-Osorio et al. (+2 more)

While collisionless plasmas are ubiquitously present near astrophysical compact objects, the impact that their composition has on the high-energy emission is presently unknown. We present the first investigation of particle-acceleration mechanisms in kinetic, special-relativistic turbulence, modeling electrons, positrons, and protons with realistic mass ratios. Under global charge neutrality, we introduce a positron fraction and cover regimes ranging from an electron-proton plasma over to pair-dominated plasmas. Using a novel generalized Ohm's law for multispecies relativistic plasmas, we analyze particle acceleration due to electric fields in reconnection events that self-consistently emerge from turbulence. We demonstrate, for the first time, that energization occurs at reconnection current sheets driven by the divergence of the relativistic pressure tensor, which locally aligns with the particle velocity and leads to an efficient energy transfer. The imbalance between electrons and positrons systematically favors electron acceleration, highlighting the necessity of realistic multispecies modeling to capture the nonthermal contributions in accretion flows and relativistic jets from black holes.
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All authors Claudio Meringolo, Mario Imbrogno, Alejandro Cruz-Osorio, Sergio Servidio, Luciano Rezzolla

High Energy Astrophysical Phenomena

Complex Nuclear Structure in Seyfert 2 Galaxy NGC 4388 Revealed by XRISM Observation

Kanta Fujiwara, Yoshihiro Ueda, Shoji Ogawa et al. (+13 more)

We report results from the simultaneous XRISM (183 ks) and NuSTAR (62 ks) observations of the Seyfert-2 galaxy NGC 4388. This AGN has the brightest Fe K$\alpha$ line among Compton-thin, obscured sources. To model the reflection continuum and fluorescent lines, we employ an updated version of XCLUMPY and a broad line region model with a disk-like geometry. The profile of the neutral Fe-K fluorescent line is well described as the sum of three components convolved with Gaussians with FWHM values of $\sim 290\ \mathrm{km\ s^{-1}}$, $\sim 1470\ \mathrm{km\ s^{-1}}$, and $\sim 11100\ \mathrm{km\ s^{-1}}$. These line widths correspond to radii of 1.5 pc, 0.060 pc, and $1.0\times10^{-3}$ pc by assuming Keplerian motion, which we interpret as the dusty torus, its inner edge region, and the BLR, respectively. The data suggest that the Fe K$\alpha$ BLR component is larger than that of H$\alpha$ (FWHM of 4500 $\mathrm{km\ s^{-1}}$) in the polarized optical spectrum, implying that the velocity field of the BLR is dominated by that parallel to the equatorial plane. In addition, Fe XXVI Ly$\alpha$ and Fe XXV absorption lines are detected, characterized by $\log{\xi} \sim 3.50~\mathrm{erg\ cm\ s^{-1}}$, $\log{N_{\mathrm{H}}} \sim 22.1~\mathrm{cm^{-2}}$, $v_{\mathrm{out}} \sim 40\ \mathrm{km\ s^{-1}}$, and $\sigma_v \sim 160\ \mathrm{km\ s^{-1}}$. We infer that the absorber is gravitationally bound and is possibly associated with a failed wind, consistent with a radiation-driven fountain flow.
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All authors Kanta Fujiwara, Yoshihiro Ueda, Shoji Ogawa, Yuya Nakatani, Jon M. Miller, Takashi Okajima, Taiki Kawamuro, Peter G. Boorman, Luigi Gallo, Misaki Mizumoto, Richard Mushotzky, Hirofumi Noda, Yuichi Terashima, Francesco Tombesi, Bert Vander Meulen, Satoshi Yamada

Earth and Planetary Astrophysics

Variable Earth's Rotation Speed in the 14th to 16th Centuries: New {\Delta}T Constraints from Chinese Eclipse Records

Hisashi Hayakawa, Mitsuru Sôma and Naiqi Li

Total solar eclipses are not only astronomical spectacles but also great astrophysical laboratories. Their historical records are particularly helpful for assessing the past variability of the Earth's rotation speed. Chinese records played a key role for such analyses. However, Chinese eclipse records from the Míng period have not been used for {\Delta}T reconstructions, partially because most of the contemporaneous eclipse reports are found not in official histories but in local treatises. This study examines eclipse records in the (quasi-)contemporaneous local treatises, concentrating on what explicitly mentioned eclipse totality on the day of a total solar eclipse and what were compiled during the Míng Dynasty. On their basis, our study revised the {\Delta}T constraint in 1361 to -408 s =< {\Delta}T =< 601 s and set new {\Delta}T constraints of 277 s =< {\Delta}T =< 890 s in 1514, -328 s =< {\Delta}T =< 332 s in 1542, and -1762 s =< {\Delta}T =< 1091 s in 1575, respectively. We also revised most of the existing {\Delta}T constraints in the 14th to 16th centuries, using the ephemeris data of the NASA JPL DE 441. Overall, our {\Delta}T constraints generally tighten the {\Delta}T variations more than what M+21 fit for their {\Delta}T spline curve, requiring downward modification and upward modifications for the {\Delta}T reconstructions around 1361 and 1542, respectively. Our results suggest that the {\Delta}T decrease between 1514 and 1567 was slightly steeper than previously considered.
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High Energy Astrophysical Phenomena

An Intrinsic Degeneracy in a Simplified Semi-Analytic Two-Spot Model for Thermal X-Ray Pulse-Profiles

Tong Zhao, Mingyu Ge and Renxin Xu

We identify an intrinsic degeneracy in the simplified semi-analytic two-spot model for parameter inference in thermal X-ray pulse-profile modeling. Although the exact algebraic degeneracy exists in our simplified model without Doppler effects, we generate synthetic pulse-profiles and show that this degeneracy can still result in two peaks on the likelihood surface if Doppler effects, statistic errors, and the instrument response are considered. The analytic degeneracy we discovered may provide intuition for multi-modal posterior distributions discovered in previous works~\citep{Vinciguerra2023,Vinciguerra2024,Miller2019,Miller2021}. However, whether the effect of this degeneracy persists in real observational posteriors with background models and more complex spot geometries still requires further systematic study.
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Astrophysics of Galaxies

Euclid Quick Data Release (Q1). AgileLens: A scalable CNN-based pipeline for strong gravitational lens identification

Euclid Collaboration: X. Xu, R. Chen, T. Li et al. (+307 more)

We present an end-to-end, iterative pipeline for efficient identification of strong galaxy–galaxy lensing systems, applied to the Euclid Q1 imaging data. Starting from VIS catalogues, we reject point sources, apply a magnitude cut (I$_E$ $\leq$ 24) on deflectors, and run a pixel-level artefact/noise filter to build 96 $\times$ 96 pix cutouts; VIS+NISP colour composites are constructed with a VIS-anchored luminance scheme that preserves VIS morphology and NISP colour contrast. A VIS-only seed classifier supplies clear positives and typical impostors, from which we curate a morphology-balanced negative set and augment scarce positives. Among the six CNNs studied initially, a modified VGG16 (GlobalAveragePooling + 256/128 dense layers with the last nine layers trainable) performs best; the training set grows from 27 seed lenses (augmented to 1809) plus 2000 negatives to a colour dataset of 30,686 images. After three rounds of iterative fine-tuning, human grading of the top 4000 candidates ranked by the final model yields 441 Grade A/B candidate lensing systems, including 311 overlapping with the existing Q1 strong-lens catalogue, and 130 additional A/B candidates (9 As and 121 Bs) not previously reported. Independently, the model recovers 740 out of 905 (81.8%) candidate Q1 lenses within its top 20,000 predictions, considering off-centred samples. Candidates span I$_E$ $\simeq$ 17–24 AB mag (median 21.3 AB mag) and are redder in Y$_E$–H$_E$ than the parent population, consistent with massive early-type deflectors. Each training iteration required a week for a small team, and the approach easily scales to future Euclid releases; future work will calibrate the selection function via lens injection, extend recall through uncertainty-aware active learning, explore multi-scale or attention-based neural networks with fast post-hoc vetters that incorporate lens models into the classification.
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All authors Euclid Collaboration: X. Xu, R. Chen, T. Li, A. R. Cooray, S. Schuldt, J. A. Acevedo Barroso, D. Stern, D. Scott, M. Meneghetti, G. Despali, J. Chopra, Y. Cao, M. Cheng, J. Buda, J. Zhang, J. Furumizo, R. Valencia, Z. Jiang, C. Tortora, N. E. P. Lines, T. E. Collett, S. Fotopoulou, A. Galan, A. Manjón-García, R. Gavazzi, L. Iwamoto, S. Kruk, M. Millon, P. Nugent, C. Saulder, D. Sluse, J. Wilde, M. Walmsley, F. Courbin, R. B. Metcalf, B. Altieri, A. Amara, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, R. Bender, A. Biviano, E. Branchini, M. Brescia, S. Camera, V. Capobianco, C. Carbone, V. F. Cardone, J. Carretero, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, H. M. Courtois, M. Cropper, A. Da Silva, H. Degaudenzi, G. De Lucia, C. Dolding, H. Dole, F. Dubath, X. Dupac, S. Dusini, S. Escoffier, M. Farina, R. Farinelli, S. Farrens, S. Ferriol, F. Finelli, P. Fosalba, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, W. Gillard, B. Gillis, C. Giocoli, P. Gómez-Alvarez, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, E. Maiorano, O. Mansutti, S. Marcin, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, M. Melchior, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, R. Nakajima, C. Neissner, R. C. Nichol, S.-M. Niemi, J. W. Nightingale, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, G. Polenta, M. Poncet, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, D. Sapone, M. Schirmer, P. Schneider, T. Schrabback, A. Secroun, G. Seidel, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, L. Stanco, P. Tallada-Crespí, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, G. Verdoes Kleijn, A. Veropalumbo, Y. Wang, J. Weller, A. Zacchei, G. Zamorani, F. M. Zerbi, E. Zucca, M. Ballardini, M. Bolzonella, C. Burigana, R. Cabanac, M. Calabrese, A. Cappi, T. Castro, J. A. Escartin Vigo, L. Gabarra, S. Hemmati, J. Macias-Perez, R. Maoli, J. Martín-Fleitas, N. Mauri, P. Monaco, A. A. Nucita, A. Pezzotta, M. Pöntinen, I. Risso, V. Scottez, M. Sereno, M. Tenti, M. Tucci, M. Viel, M. Wiesmann, Y. Akrami, I. T. Andika, G. Angora, S. Anselmi, M. Archidiacono, F. Atrio-Barandela, L. Bazzanini, P. Bergamini, D. Bertacca, M. Bethermin, F. Beutler, L. Blot, S. Borgani, M. L. Brown, S. Bruton, A. Calabro, B. Camacho Quevedo, F. Caro, C. S. Carvalho, F. Cogato, S. Conseil, O. Cucciati, S. Davini, G. Desprez, A. Díaz-Sánchez, S. Di Domizio, J. M. Diego, P.-A. Duc, V. Duret, M. Y. Elkhashab, A. Enia, Y. Fang, A. Finoguenov, A. Franco, K. Ganga, T. Gasparetto, E. Gaztanaga, F. Giacomini, F. Gianotti, G. Gozaliasl, M. Guidi, C. M. Gutierrez, A. Hall, C. Hernández-Monteagudo, H. Hildebrandt, J. Hjorth, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, K. Kiiveri, J. Kim, C. C. Kirkpatrick, F. Lepori, G. Leroy, G. F. Lesci, J. Lesgourgues, T. I. Liaudat, S. J. Liu, M. Magliocchetti, E. A. Magnier, F. Mannucci, C. J. A. P. Martins, L. Maurin, M. Miluzio, C. Moretti, G. Morgante, K. Naidoo, A. Navarro-Alsina, S. Nesseris, D. Paoletti, F. Passalacqua, K. Paterson, L. Patrizii, A. Pisani, D. Potter, G. W. Pratt, S. Quai, M. Radovich, K. Rojas, W. Roster, S. Sacquegna, M. Sahlén, D. B. Sanders, E. Sarpa, C. Scarlata, A. Schneider, M. Schultheis, D. Sciotti, E. Sellentin, L. C. Smith, K. Tanidis, C. Tao, F. Tarsitano, G. Testera, R. Teyssier, S. Tosi, A. Troja, A. Venhola, D. Vergani, G. Vernardos, G. Verza, S. Vinciguerra, N. A. Walton, A. H. Wright, H. W. Yeung

Instrumentation and Methods for Astrophysics

UMI: GPU-Accelerated Asymmetric Robust Estimator for Photometric Detrending in Exoplanet Transit Searches

Omar Khan

We present UMI (Unified Median Iterative), a novel robust location estimator for detrending photometric time series in exoplanet transit surveys. UMI modifies the standard Tukey bisquare M-estimator with two innovations: (1) an asymmetric weight function that penalizes downward deviations (transit dips) more aggressively than upward ones, exploiting the physical constraint that transits are always below the stellar continuum, and (2) an upper-RMS scale estimator computed from above-median residuals only, ensuring that transit dips never contaminate the noise estimate. Implemented as a fused HIP/CUDA GPU kernel, UMI achieves 69x faster detrending (3.4 ms vs 234 ms per star) and 37x faster full pipeline throughput compared to the wotan biweight implementation. Injection-recovery tests across TESS, Kepler, and K2 show that UMI's advantage is concentrated at planet-scale transit depths above the photometric noise floor: at 0.1% transit depth, UMI reduces median depth recovery error from 20.5% to 15.8% on TESS (23% improvement) and from 14.6% to 4.2% on Kepler (71% improvement). At shallower depths approaching the noise floor, all sliding-window methods converge to comparable performance. Validated across 802 confirmed exoplanets from TESS and Kepler, UMI occupies a previously unfilled region of the speed-accuracy tradeoff for transit detrending. The tool is publicly available as pip install torchflat.
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Earth and Planetary Astrophysics

An Aligned Very-Low-Mass Star Orbiting an M dwarf and Obliquity Patterns Across Giant Planets, Brown Dwarfs, and Binary Stars

Tianjun Gan, Alexandrine L'Heureux, Étienne Artigau et al. (+4 more)

Stellar obliquity serves as a key diagnostic for tracing the dynamical evolution of bound systems-from giant planets and brown dwarfs to stellar binaries-revealing whether these diverse populations share analogous histories. Here, we report the first obliquity measurement for a double M dwarf system, determined via the Rossiter-McLaughlin effect. The spin axis of the primary star, TOI-5375 ($M_\ast=0.62\pm0.02\,M_\odot$), is well aligned with the orbit of its low-mass stellar companion ($M_c=84.8\pm1.5\, M_J$, $\rm P=1.72\,days$) with a projected obliquity of $\lambda=-13.5_{-13.8}^{+12.4}\,^{\circ}$ and a true 3D obliquity of $\psi=37.5_{-13.4}^{+10.6}\,^{\circ}$. The result indicates that the system either formed with a primordially aligned configuration or has undergone tidal realignment. We further investigate obliquity patterns across giant planets, brown dwarfs and binary stars. It turns out that a few obliquity trends observed in giant planets also tentatively exhibit in the latter two higher-mass populations: 1) well-aligned orbits are preferentially found around cooler host stars ($T_{\rm eff}\leq 6250\,K$); 2) wide-orbit ($a/R_\ast\geq 10$) companions are predominantly aligned; 3) no significant correlation shows up between obliquity and orbital eccentricity in any of the companion classes. By modeling $|\lambda|$ with a two-component Gaussian distribution, we find that the low-$|\lambda|$ components of binary stars and brown dwarfs are more concentrated near zero than giant planets while the high-$|\lambda|$ components of brown dwarfs and binaries remain unclear due to the small sample size.
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All authors Tianjun Gan, Alexandrine L'Heureux, Étienne Artigau, Charles Cadieux, René Doyon, Neil J. Cook, Shude Mao

High Energy Astrophysical Phenomena

Plasma Dynamics of Radiative Cooling Accretion Flow in AM Herculis with XRISM

Yukikatsu Terada, Kaya Mori, Takayuki Hayashi et al. (+14 more)

We present XRISM/Resolve high-resolution X-ray spectroscopy of the prototypical magnetic cataclysmic variable AM Herculis. All satellite lines of highly ionized Fe are fully resolved. Lighter element lines (Si, S, Ca) show 2 - 3 eV widths consistent with purely thermal broadening, while the broader 6 - 7 eV Fe lines require additional bulk Doppler broadening. Spin-phase-resolved modulations are clearly detected in the Fe XXV and Fe XXVI lines, with semi-amplitudes of $81.8\pm6$ km s$^{-1}$ and $132.5\pm9$ km s$^{-1}$, and mean velocities of $143.6\pm6$ km s$^{-1}$ and $225.6\pm8$ km s$^{-1}$, respectively. After removing these bulk Doppler shifts, we obtain intrinsic Doppler widths of $5.23_{-0.15}^{+0.16}$ eV for Fe XXV and $6.23_{-0.18}^{+0.19}$ eV for Fe XXVI, directly revealing gradients of bulk velocity and temperature in the cooling-flow plasma. We additionally examined the resonance anisotropy predicted by Terada et al. (1999, 2001): the equivalent widths of the Fe XXV and Fe XXVI resonance lines increase at the pole-on phase by factors of 1.30 - 1.35, in positive correlation with their oscillator strengths. Combining XRISM with simultaneous NuSTAR data and PSAC/MCVSPEC plasma models, we derive a self-consistent shock temperature of $24.0\pm0.1$ keV and shock velocity of $1,116\pm2$ km s$^{-1}$. Radiative transfer simulations of the resonance lines further constrain the shock density to about $(5 - 6)\times10^{15}$ cm$^{-3}$, providing a new density diagnostic for accretion columns. The resulting accretion column geometry has a height of 200 - 300 km and a radius of 200 - 400 km.
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All authors Yukikatsu Terada, Kaya Mori, Takayuki Hayashi, Gabriel L. Bridges, Manabu Ishida, Axel D. Schwope, Mariko Kimura, Masayoshi Nobukawa, David A. H. Buckley, Solen Balman, Taichi Ichikawa, Atsuto Matsumura, Mai Takeo, Charles J. Hailey, Gavin Ramsay, Antonio Rodriguez, Samantha Walker

High Energy Astrophysical Phenomena

The host galaxies and merger environments of short and long gamma-ray bursts producing kilonovae

Hannah Skobe, Brendan O'Connor, Antonella Palmese et al. (+3 more)

Gamma-ray bursts (GRBs) have traditionally been classified by their prompt emission duration and spectral hardness, with short GRBs (sGRB; $\lesssim2 \ \rm{s}$) originating from compact object mergers and long GRBs (LGRB; $\gtrsim2 \ \rm{s}$) from massive star core-collapse. Recent kilonova (KN) associations with long-duration GRBs have challenged this standard picture. We analyze the host galaxies of nine GRBs with associated kilonova candidates at $z<0.6$, including five sGRB-KNe and four LGRB-KNe. Using both parametric and non-parametric modeling of the host light distributions, we investigate the progenitor environments of these events and test whether their hosts show evidence for recent galaxy interactions that could favor dynamical formation channels or isolated pathways following merger-driven star formation episodes for neutron star binaries. We find that five of the nine hosts display tidal features that show they have likely undergone recent mergers, suggesting that merger-driven, dynamical formation pathways may contribute in some systems. We find no clear morphological distinction between sGRB-KN and LGRB-KN hosts as both populations span a wide range of morphologies, including ellipticals, spirals, and interacting systems with tidal features. Multi-Sérsic modeling of the host light profiles further shows that host-normalized offsets inferred from single-Sérsic fits can be overestimated when the transient is associated with a specific subcomponent of a complex host light profile. These results highlight the importance of decomposing host morphology into physically relevant components when interpreting GRB environments and galactocentric offsets.
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All authors Hannah Skobe, Brendan O'Connor, Antonella Palmese, Lewi Westcott, Christopher J. Conselice, Katelyn Breivik

Astrophysics of Galaxies

The Illusion of Morphology in Tidal Structures: Changes to Stellar Shells and Streams in Non-Spherical Haloes

Smrithi Gireesh Babu, Viraj Ekanayaka, William H. Oliver et al. (+1 more)

We identify shell-like tidal structures in flattened haloes that appear stream-like under different projections. This projection dependence demonstrates how changes in the host halo directly impact the formation and classification of tidal debris, highlighting the challenges of relying solely on visual inspection. To address this, we employ our clustering-based classification framework to systematically categorise tidally disrupted satellites into stream-like and shell-like structures. Our host consists of a static three-component MW model with flattening introduced along the z-axis NFW dark halo. We consider three halo shapes: spherical q = 1, extremely oblate q = 0.5, and prolate q = 1.5. We evolve three subhalo types: a highly radial massive subhalo favouring shell formation, an eccentric orbit leading to stream formation, and an intermediate orbit. We first classify the tidal structures visually using face-on and edge-on density projections of the 3D position distribution. This reveals shell-like and stream-like formations across face-on projections, while edge-on views lead to contrary classifications in some cases. To resolve these ambiguities, we apply the classification method developed in our earlier work, analysing structures in ordered density, radial, and energy-angle space. We further investigate the spatial dispersion of stream-like structures and the rate at which core density reduces as the flattening parameter varies. Our results demonstrate that halo shape variations affect tidal debris formation and classification, as well as the spatial dispersion and core density evolution of streams. These findings offer new insights into the role of dark matter halo geometry in shaping tidal structure formation and its contribution to hierarchical galaxy formation and evolution.
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All authors Smrithi Gireesh Babu, Viraj Ekanayaka, William H. Oliver, Geraint F. Lewis

Solar and Stellar Astrophysics

Harmonic phase diagnostics of long secondary periods. Testing predictions of oscillatory convective dipole modes in the OGLE sample

Benjamin Courtney-Barrer, Xavier Haubois, Michael Ireland et al. (+1 more)

Long secondary periods (LSPs) in luminous red giants remain the only major class of long-period stellar variability without a secure physical origin. Competing hypotheses include binaries with dusty companions and oscillatory convective dipole modes. We identify the physical and geometric conditions under which oscillatory convective dipole modes produce distinctive harmonic signatures that contrast with those expected from binary systems, and apply this diagnostic to a filtered subset of the OGLE-III LSP sample to identify examples consistent with oscillatory convective dipole modes. We model the geometric flux modulation from oscillatory convective dipole modes and map the range of inclinations, temperature amplitudes, and observing wavelengths for which harmonic features are observable. Using OGLE-III I-band light curves, we require statistically significant power at both sequence D and its harmonic, keeping a filtered sample of 249 stars (2.1% of the ridge-selected sample). We apply iterative Lomb-Scargle and weighted Fourier decomposition to isolate the fundamental and harmonic components. The relative phase ($\Delta\phi$) between these distinguishes secondary maxima predicted by an inclined dipole from secondary minima caused by eclipsing or ellipsoidal binary systems. The majority of high amplitude stars in the filtered subset show $\Delta\phi$ consistent with secondary minima produced by binary systems. However, a small but statistically non-negligible subset exhibits $\Delta\phi$ consistent with secondary maxima that are difficult to reconcile by eclipsing or ellipsoidal binaries, and instead match the geometric predictions for highly inclined, non-rotating oscillatory convective dipole modes with temperature amplitudes consistent with published models.
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All authors Benjamin Courtney-Barrer, Xavier Haubois, Michael Ireland, Peter Wood

Solar and Stellar Astrophysics

Solar Neutrino Flux Fluctuations Caused by Solar Gravity Modes

Yoshiki Hatta, Yuuki Nakano, Sho Sugama et al. (+3 more)

We have evaluated fluctuations in neutrino fluxes caused by solar gravity (g) modes based on the analysis of linear adiabatic oscillation of a spherically symmetric star. We find that the first-order fluctuation is zero due to geometrical cancellation. We still find that the second-order fluctuation is non-zero, which consists of time-varying and non-time-varying components. The amplitude of the time-varying component is small (${\sim} 10^{-9}$ in relative difference, in the case of $\mathrm{^{8}B}$ neutrino) and well below the detection limits of the current neutrino detectors, when we assume the g-mode amplitude parameter $A_{n \ell}$ to be $10^{-5}$, which corresponds to the assumed maximum relative temperature perturbation inside the Sun. Thus, it is at the moment fair to say that detecting individual solar g-modes via the solar neutrino flux measurement is almost impossible. However, the net increase in the mean neutrino flux that originates from the non-time-varying component could be non-negligible. In particular, since $A_{n \ell}$ may be related to convection amplitude, which could change in accordance with the solar magnetic activity, the total net increase in the neutrino flux, which is proportional to $A_{n \ell}^2$, should also change with the solar activity cycle. Such a long-period variation~(${\sim} 11$~years) in the neutrino flux could thus be interpreted as evidence for a bunch of solar g-modes. Comparison of the theoretical prediction with the solar neutrino measurements by, e.g., Super-Kamiokande, may have a potential to put constraints on the theory of the excitation mechanism of solar g-modes.
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All authors Yoshiki Hatta, Yuuki Nakano, Sho Sugama, Masanobu Kunitomo, Hiroshi Ito, Takashi Sekii

Tuesday 7 April

Astrophysics of Galaxies · Cross-listed from physics.class-ph

Potentials of axisymmetric razor-thin disks

J.An

We investigate the gravitational potentials generated by axisymmetric, razor-thin disks. Within certain limitations, the potential on one side of the disk is shown to be equivalent to the potential produced by a linear mass distribution along the axis perpendicular to the disk. We first establish the connection between two mass distributions that generate the same potential. We then consider all disk surface density profiles that produce the potential equivalent to those generated by linear mass distributions, specifically those defined by the elementary beta distribution and its relatives on the interval $[0,1]$, $[1,\infty)$ or $[0,\infty)$. These families of models are important because the potentials in all cases are given by, at most, a single real quadrature of elementary functions of the coordinates, and furthermore, many cases result in closed-form expressions. The potential of many realistic disks may be constructed from some combinations of these disk models.
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Instrumentation and Methods for Astrophysics

PowerSpectR: An R Package for Radial Power Spectrum Estimation

Rafael S. de Souza

I present here PowerSpectR, an R package for computing and visualizing median-based radial Fourier power spectra from imaging data. Power spectra provide a representation of spatial structure by decomposing contributions across spatial scales, and the resulting slopes can serve as compact, low-dimensional summaries of morphological complexity across images. PowerSpectR provides a workflow for estimating these slopes, combining edge-effect mitigation through Hann windowing, Fourier-domain analysis, and radial binning with azimuthal median statistics. The use of median aggregation helps to reduce sensitivity to bright compact sources, masking artifacts, and other localized features that can bias standard estimators. PowerSpectR is released under the MIT license at \href{https://github.com/RafaelSdeSouza/PowerSpectR}{this repository}.
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Astrophysics of Galaxies

The Galaxy Activity, Torus, and outflow Survey (GATOS) XIII: Coupling Driven H2 Excitation in Seyferts

Daniel E. Delaney, Erin K. S. Hicks, Lulu Zhang et al. (+31 more)

We utilize JWST/MIRI IFU observations from the Galaxy Activity, Torus and Outflow Survey (GATOS) to investigate the diverse range of ionized outflow rates of obscured AGN with similar bolometric luminosity and explore potential associations with AGN feedback. We explore spatial correlations between ionized emission potentially associated with fast shocks ([Fe II]5.34{\mu}m) and the excitation of H2. We further constrain our investigation to the inner 400 pc (the nuclear and circumnuclear regions r < 200 pc), and estimate the excitation temperature and column density of H2 assuming local thermodynamic equilibrium (LTE) and using the S(1) to S(8) rotational H2 emission lines visible to JWST/MIRI spectroscopy. We report the molecular gas temperature of the deprojected 400 pc nuclear region to correlate with the ionized mass outflow rate. We also observe the stronger degree of spatial correlation between [Fe II]5.34um emission and H2 gas temperature. We observe regions of enhanced [Fe II]5.34{\mu}m / [Ar II]6.99{\mu}m spatially coincident with the ionization cones of objects with higher ionized outflow rate and [Fe II]5.34{\mu}m / [Ar II]6.99{\mu}m in the deprojected 400 pc nuclear region to scale positively with both ionized outflow rate and estimated molecular gas temperature. We do not observe the estimated jet cavity power within the central 400 pc to strongly correlate with the ionized mass outflow rate or molecular gas temperature of the nuclear region. We take the preceding observations to suggest a higher degree of interaction between AGN outflows and the circumnuclear disk.
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All authors Daniel E. Delaney, Erin K. S. Hicks, Lulu Zhang, Ric Davies, Chris Pacham, Rogemar A. Riffel, Miguel Pereira Santaella, Enrica Bellocchi, Nancy A. Levenson, Steph Campbell, David J. Rosario, Houda Haidar, Cristina Ramos Almeida, Anelise Audibert, Claudio Ricci, Laura Hermosa Munoz, Francoise Combes, Almudena Alonso-Herrero, Santiago Garcia-Burillo, Federico Espositio, Ismael Garcia-Bernete, Taro Shimizu, Martin Ward, Omaira Gonzalez Martin, Alvaro Labiano, Oscar Veenema, Enrique Lopez-Rodriguez, Dimitra Rigopopoulou, Marko Stalevski, Sebastian F. Honig, Donaji Esparza-Arredondo, Tkuma Izumi, Lindsay Fuller, Daniel Rouan

Instrumentation and Methods for Astrophysics · Cross-listed from hep-ex

Improving Neutrino Point Source Sensitivity with Source-Informed Event Selection

Jeffrey Lazar, Carlos A. Argüelles and Pavel Zhelnin

Neutrino telescopes employ multi-level reconstruction chains, where computationally expensive high-quality reconstructions are applied only to events that survive initial quality cuts based on fast, coarse directional estimates. Currently, event selection between reconstruction levels is source-agnostic, giving no priority to events from directions of known neutrino source candidates. We propose a simple modification to inter-level event selection: preferentially retain events whose early-level reconstruction places them within an angular tolerance of pre-specified candidate source directions from established multi-messenger catalogs, while continuing to subsample remaining events at the baseline rate. Using a realistic two-level detector model with energy-dependent angular resolution, we show that this source-informed selection can improve median point source sensitivity by factors of $\sim 2$–$3$ compared to uniform subsampling, with the improvement depending on the baseline selection efficiency, angular tolerance, and correlation between reconstruction qualities at different levels. For catalogs of $\mathcal{O}(100)$ sources, the additional computational overhead is modest ($\sim 7$–$14\%$). This approach offers a path to substantially enhance the discovery potential of current and future neutrino telescopes without requiring new detector capabilities.
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Astrophysics of Galaxies

A Close Quasar Pair in a Massive Galaxy Merger at $z=5.7$

Minghao Yue, Xiaohui Fan, Anna-Christina Eilers et al. (+3 more)

Close quasar pairs are rare products of galaxy mergers in which both supermassive black holes (SMBHs) are actively accreting, offering strong constraints on merger-driven active galactic nuclei (AGN) evolution. Identifying close quasar pairs at $z\gtrsim4$ is challenging due to the declining quasar number density in the early Universe. Here we report the confirmation of a close quasar pair at $z=5.7$, J2037–4537, utilizing high-resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations. The quasar host galaxies exhibit tidal disturbed features in both the far-infrared continuum emission and the {\cii} line emission, ruling out the doubly-imaged lensed quasar scenario. The two quasar hosts are massive $(M_\text{dyn}\gtrsim10^{10}M_\odot)$ and star-forming (SFR $\gtrsim500 M_\odot~ \mathrm{yr^{-1}}$). The confirmation of J2037–4537 puts a lower limit on the quasar pair fraction at $5.5<z<6$, $F_\text{pair}>1.2\%$, which is much higher than the quasar pair fraction at $z\lesssim4$. J2037–4537 is expected to form a gravitationally-bound SMBH binary within $\lesssim2$ Gyr. The elevated quasar pair fraction at $z>5.5$, as indicated by J2037–4537, likely contributes to the high gravitational-wave background reported by recent Pulsar Timing Array experiments.
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All authors Minghao Yue, Xiaohui Fan, Anna-Christina Eilers, Feige Wang, Jinyi Yang, Robert A. Simcoe

High Energy Astrophysical Phenomena

Data-Driven Constraints on Magnetar Population: No Evidence for a Distinct White Dwarf Channel

R. V. Lobato

Magnetars are usually interpreted as highly magnetized neutron stars, yet a small subset of low spin-down sources has motivated alternative scenarios involving highly magnetized white dwarfs. We test whether the observed magnetar sample is consistent with a single neutron-star population or whether the data favor an additional compact-object channel. We combine exploratory machine-learning diagnostics with hierarchical Bayesian population modeling. First, we apply K-means clustering and principal component analysis in a five-dimensional feature space $(P,\dot{P},L_X,kT,|Z|)$, where $P$ is the spin period, $\dot{P}$ its time derivative, $L_X$ the X-ray luminosity, $kT$ the thermal spectral temperature, and $|Z|$ the absolute Galactic scale height. We then train a Random Forest classifier with leave-one-out cross-validation to identify the observables driving the empirical split. Subsequently, we construct a hierarchical Bayesian mixture model linking spin parameters to magnetic-field distributions through covariate-dependent mixing fractions. Posterior inference is performed with Hamiltonian Monte Carlo, and predictive performance is assessed using Pareto-smoothed importance sampling leave-one-out cross-validation. The exploratory analysis reveals a reproducible substructure: the Random Forest achieves $>95\%$ LOOCV accuracy, with $L_X$, $\dot{P}$, and $kT$ emerging as the dominant predictors. However, Bayesian model comparison shows no statistically significant preference for a two-population model. Instead, a few low spin-down sources receive intermediate posterior membership probabilities, suggesting transitional or outlying behavior rather than membership in a distinct class. Overall, current data do not require a separate white-dwarf magnetar population and are adequately described by a predominantly neutron-star population.
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Astrophysics of Galaxies

The Evolution of Star-Forming Gas in STARFORGE: From Clouds, to Cores, to Stars

Ananya Kaalva, Stella S. R. Offner, Nina Filippova et al. (+1 more)

Star formation occurs within dense regions of giant molecular clouds (GMCs), however, exactly how gas collects and evolves to form individual stars and what role dense cores play remains unclear. We use the Lagrangian cell information in the STARFORGE simulation suite to track star-forming gas in three GMCs with varying magnetic field strengths. We find that, once a protostar forms, the lifetime of the unaccreted gas correlates with the final stellar mass, where low-mass stars ($M_*$ < 0.5 M$_\odot$) accrete for 0.5-0.6 Myr from a relatively local reservoir of gas, and high-mass stars ($M_*$ > 2 M$_\odot$) accrete over 3.3-4.7 Myr from a much larger volume. Although the protostellar accretion time increases weakly with magnetic field strength, the accreting gas radii, velocity dispersions, virial parameters, and magnetic energy ratios are largely insensitive to the global cloud properties. At the time of protostar formation, the unaccreted gas exhibits linewidth-size and mass-size relations characteristic of turbulently regulated, isothermal dense cores, following $\sigma_v \propto R^{0.47-0.55}$ and $M \propto R^{1.0-1.1}$, respectively. Low- and intermediate-mass stars undergo relatively continuous accretion and their accretion histories are well-fit by either isothermal sphere, turbulent core, or competitive accretion models, where no one model fits all masses. However, many high-mass stars experience intermittent accretion and their accretion histories are not well-fit by any of these models. While the distribution of accreting gas is more extended than typically-defined dense cores, the physical properties and structure of the star-forming gas resemble those of observed cores and are largely regulated by turbulence and feedback.
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All authors Ananya Kaalva, Stella S. R. Offner, Nina Filippova, Michael Y. Grudic

Solar and Stellar Astrophysics

No Period Change in Two Long-Period AM CVn Binaries

Matthew J. Green, Thomas R. Marsh, Jan van Roestel et al. (+25 more)

Ultracompact binary systems, consisting of two compact objects in an orbit $\lesssim 0.5 R_\odot$, should exhibit measurable rates of orbital period change ($\dot{P} \neq 0$) due to the emission of gravitational waves (GWs). Measurements of \pdot\ have so far been limited to the shortest-period ultracompact binaries ($\lesssim 20$\,min). Among the AM\,CVn-type subclass, several works have proposed the presence of extra angular momentum loss beyond GW emission, with magnetic braking being a widely discussed mechanism. If present, this magnetic braking would dominate the angular momentum loss of AM\,CVn-type binaries with orbital periods $\gtrsim 30$\,min. In this work, we present a long-term eclipse timing study of two AM\,CVn-type binaries, YZ\,LMi and Gaia14aae, with respective orbital periods of 28.3\,min and 49.7\,min and continuous observations since 2006 and 2015. Both systems show $\dot{P}$ consistent with zero within $2\sigma$. Their $3\sigma$ upper limits are $1.1 \times 10^{-13}\,{\rm s \, s}^{-1}$ and $9.7 \times 10^{-14}\,{\rm s \, s}^{-1}$ respectively. These non-detections are most simply explained by a scenario in which secular angular momentum loss is not substantially stronger than GW emission at all orbital periods, but is combined with deviations from the secular $\dot{P}$ whose timescales span decades but whose amplitude is $\lesssim 10^{-13}\,{\rm s \, s}^{-1}$. %, orders of magnitude smaller than the eclipse timing variations seen in hydrogen-dominated cataclysmic variables. Our non-detections of $\dot{P}$ represent a limit on the strength of any enhanced angular momentum loss beyond pure GW emission.
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All authors Matthew J. Green, Thomas R. Marsh, Jan van Roestel, Tin Long Sunny Wong, Diogo Belloni, Mukremin Kilic, Elme Breedt, Alex Brown, Chris M. Copperwheat, Anurak Chakpor, V. S. Dhillon, Noel Castro Segura, Martin J. Dyer, James Garbutt, Dan Jarvis, Vasu Kengkriangkrai, Mark R. Kennedy, Paul Kerry, Thomas Kupfer, S. P. Littlefair, James McCormac, James Munday, Steven G. Parsons, Eleanor Pike, Ingrid Pelisoli, Pablo Rodriguez-Gil, David I. Sahman, Amalie Yates

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Gauge Theoretic Signal Processing I: The Commutative Formalism for Single-Detector Adaptive Whitening

James Kennington and Joshua Black

We present a geometric framework for adaptive whitening in gravitational-wave detectors, reformulating the problem from a sequence of spectral factorizations to parallel transport on a principal bundle. We identify the whitening filter as a section over the manifold of power spectra and derive the minimum-phase connection as the unique geometric structure that enforces signal causality while preserving signal-to-noise ratio. This construction yields a rigorous definition of geometric drift, a coordinate-independent scalar measuring the intrinsic instability of the detector noise floor. The central result is the flatness theorem, which proves that the curvature of the connection vanishes for scalar fields. This establishes a holonomic update law, guaranteeing that the optimal filter correction is path-independent and determined solely by the instantaneous noise state, free from geometric phase or hysteresis. This framework unifies the static theory of Wiener-Hopf factorization with the dynamic requirements of real-time control, providing a rigorous certification for the stability of zero-latency calibration routines and establishing a foundation for gauge-theoretic signal processing (GTSP) in next-generation detector networks. In the wider context of gravitational-wave astronomy, this result governs the latency and fidelity of low-latency searches and provides the single-detector foundation for the multi-detector network extensions of the framework. The update law is integrated into a production matched-filter pipeline and validated on detector data in a companion paper.
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High Energy Astrophysical Phenomena

Neutrino transport and flavor instabilities in a post-merger disk

Erick Urquilla, Swapnil Shankar, Debraj Kundu et al. (+6 more)

Neutron star mergers are multimessenger sources whose dynamics and signals depend critically on neutrinos and their flavor transformations. We investigate whether fast and collisional neutrino flavor instabilities (FFIs and CFIs) arise in a GW170817-like post-merger accretion disk, and how they develop and relax, by performing global and local classical and quantum-kinetic simulations that resolve anisotropies and inhomogeneities in the full six-dimensional phase space. In the accretion disk, the neutrino radiation field naturally develops electron-lepton-number crossings through the interplay between the more isotropic electron neutrino field and the more anisotropic electron antineutrino field. The neutrino field in the disk is also unstable to CFI, although on longer timescales than the FFI. Using local, multi-energy quantum-kinetic calculations at selected points, we find that the growth of unstable modes is well-predicted by a fully anisotropic linear stability analysis and the flavor transformation increases the heavy lepton neutrino fluxes. CFI likewise enhances heavy-flavor fluxes, shows significant impacts from the growth of multi-energy anisotropic modes, and breaks the symmetry of the heavy-flavor sector by raising the average energy of heavy-flavor antineutrinos above that of heavy-flavor neutrinos. However, the CFI remains subdominant to the FFI in most of the disk. In our global quantum-kinetic simulations with an attenuated Hamiltonian, flavor coherence develops primarily in the polar regions. Because the attenuation causes advection to outpace the growth of the instabilities, coherence and flavor conversion remain artificially suppressed within the disk. These results emphasize the resolution and scaling requirements for future global simulations that capture instability growth, saturation, and advection simultaneously.
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All authors Erick Urquilla, Swapnil Shankar, Debraj Kundu, Julien Froustey, Sherwood Richers, Jonah M. Miller, Gail C. McLaughlin, James P. Kneller, Francois Foucart

Instrumentation and Methods for Astrophysics

Reliability of uGMRT Band-4 Polarimetry: Results from a Quadrature Hybrid Polarizer Bypass Experiment

Arpan Pal, Sanjeet Rai and Ganesh Kumbhar

Polarimetric observations at sub-GHz frequencies offer unique access to the magnetized universe through Faraday rotation and depolarization studies, but achieving reliable polarization calibration at these frequencies remains challenging. We report the identification and resolution of a systematic polarization calibration instability in the upgraded Giant Metrewave Radio Telescope (uGMRT) Band 4 (550–750\,MHz). Through diagnostic observations of multiple calibrators, we discovered that the cross-hand phase response varies with the fractional polarization of the observed source, violating the fundamental assumption of calibration transferability in radio interferometry. Systematic engineering tests traced this behaviour to the Quadrature Hybrid (QH) polarizer in the frontend signal chain. We conducted a controlled experiment in which the QH was bypassed in seven antennas, converting them to linear polarization feeds. The bypassed system shows dramatically improved performance: instrumental leakage reduced from 10–15% to 2–5%, residual leakage after calibration reduced from $\sim$0.5% to less than $0.2\%$, and stable cross-hand phases independent of source polarization. For the polarized source DA\,240 (RM\,$=$\,3.3\,rad\,m$^{-2}$), the QH-bypassed system accurately recovers the expected $25^\circ$ polarization angle rotation across the band, which the with QH system fails to reproduce. These results establish that the QH polarizer is the dominant source of polarimetric instability in uGMRT Band\,4 and demonstrate that its removal enables reliable sub-GHz polarimetry. We recommend the linear feed configuration for science cases requiring accurate polarization angle and rotation measure measurements.
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Earth and Planetary Astrophysics

Determining the Host Stars of Planets in Binary Star Systems with Asterodensity Profiling: Investigating the Canonical Radius Gap

Nathanael Burns-Watson, Kendall Sullivan and Adam Kraus

Over the past 30 years, thousands of exoplanets have been discovered, revealing detailed demographics of planets outside the Solar System. One of the most dramatic features of the planet radius distribution is the radius gap, a lack of planets between $\sim$1.8-2 $R_\oplus$. The radius gap is thought to mark the distinction between rocky and gas planets. Recent research has found that the radius gap may not be present in binary star systems. In past studies of planets in binary star systems, the common assumption has been that all of the planets are hosted by the primary star. In many cases, the radius of the planet would be significantly larger if it were orbiting the companion star, which could potentially affect the true radius distribution. It is possible to identify the host stars of planets through stellar density estimates obtained from transit fitting. Using this method, we made probabilistic estimates for the host stars of a sample of 15 transiting exoplanets across 10 binary star systems hosting either 1 or 2 planets, at least one of which would reside in the canonical radius gap if it was circumprimary. We found that 5 of the planets are highly likely to be circumprimary, while the remainder have ambiguous host stars. The lack of unambiguously circumsecondary planets is caused by physical and observational biases that favor circumprimary planets. Nonetheless, the summed posterior probabilities suggest that the canonical radius gap appears less vacant for planets in binaries.
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Solar and Stellar Astrophysics

Binary Star Evolution Modules in REBOUNDx

Mohamad Ali-Dib

Close-binary evolution couples Roche-lobe overflow (RLOF), common-envelope (CE) drag, stellar winds, magnetic braking, and gravitational-wave losses, exchanging mass and angular momentum while reshaping orbits and spins. We present interoperable effects in the REBOUNDx extension to REBOUND that embed these processes within high-accuracy N-body dynamics. The suite includes: a momentum-conserving RLOF operator with conservative and systemic channels and configurable specific-j loss; a CE drag model based on Mach-dependent dynamical friction with kick limiting; isotropic Reimers winds, Parker-type thermal winds, and Eddington-limited outflows powered by a parametric stellar-evolution module supplying mass-dependent R and L; magnetic braking via the Verbunt-Zwaan/Kawaler torque with a saturation-aware closed-form spin update; and post-Newtonian corrections 2PN point-mass and spin-spin; 2.5PN radiation reaction. Linear momentum is conserved for conservative transfer, a minimal corrective torque enforces angular-momentum consistency, and adaptive sub-stepping stabilizes evolution near contact. Inter-module flags coordinate wind/RLOF/CE activity. The unit-agnostic framework enables self-consistent, time-resolved studies of close binaries in isolated or dynamically rich settings. Multiple examples and comparisons against other codes are provided in the Appendix. The code is available at https://github.com/malidib/ReboundS .
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Solar and Stellar Astrophysics

New insights from cross-correlation studies between solar activity indices and cosmic-ray flux during Forbush decrease events

Mihailo Savić, Nikola Veselinović, Aleksandar Dragić et al. (+4 more)

Observed galactic cosmic ray intensity can be subjected to a transient decrease. These so-called Forbush decreases are driven by coronal mass ejection induced shockwaves in the heliosphere. By combining in situ measurements by space borne instruments with ground-based cosmic ray observations, we investigate the relationship between solar energetic particle flux, various solar activity indices, and intensity measurements of cosmic rays during such an event. We present cross-correlation study done using proton flux data from the SOHO/ERNE instrument, as well as data collected during some of the strongest Forbush decreases over the last two completed solar cycles by the network of neutron monitor detectors and different solar observatories. We have demonstrated connection between the shape of solar energetic particles fluence spectra and selected coronal mass ejection and Forbush decrease parameters, indicating that power exponents used to model these fluence spectra could be valuable new parameters in similar analysis of mentioned phenomena. They appear to be better predictor variables of Forbush decrease magnitude in interplanetary magnetic field than coronal mass ejection velocities.
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All authors Mihailo Savić, Nikola Veselinović, Aleksandar Dragić, Dimitrije Maletić, Dejan Joković Vladimir Udovičić, Radomir Banjanac, David Knežević

Solar and Stellar Astrophysics

The Wonderful World of Binary Stars

Andrea Barone, Henri M. J. Boffin, Beatrice Caccherano et al. (+6 more)

During the 2026 ESO La Silla Observing school, about twenty students attended lectures and performed observations to learn various aspects of observational astronomy. The school, which took place during the first two weeks of February 2026, made use of EFOSC2/NTT and HARPS+NIRPS/3.6m. One of the groups was devoted to the study of binary stars. Several projects were considered and followed up by some of the six students in this group. The first subgroup used HARPS to study the Rossiter-McLaughlin effect in binary stars to infer the relative inclination of the rotation axis of the primary with respect to the orbital plane. A detailed study of the contact binary system HD 115264 led to the conclusion that the primary is well aligned, likely as a result of strong tidal forces within the binary. The second subgroup analysed blue straggler stars (BSS) in open clusters, using both HARPS and EFOSC2. With HARPS, they looked at some well-known long-period binary with the aim of determining their chemical abundances, thereby confirming their membership to the cluster, as well as looking for any chemical anomalies that might be explained by mass transfer. EFOSC2 was used to derive radial velocities of rapidly varying BSS. For one of them - the star Rediet - the students clearly detected and analysed the radial velocity variations due to the second overtone pulsation, thereby confirming its delta Scuti character. Finally, one student used EFOSC2 to study planetary nebulae (PN) - taking nice images of some of these intricate objects, as well as doing time-resolved photometry and spectra of some others. In one case, the binary nature of the central star of the PN was proven, confirming some previous estimates done with ZTF. Each subgroup was thus able to obtain useful research results, which we present hereafter.
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All authors Andrea Barone, Henri M. J. Boffin, Beatrice Caccherano, Simona Di Stefano, Akhila Divakaran, Alexandra S. Murphy, María José Rain, Elyar Sedaghati, Paul V. Steimle

Astrophysics of Galaxies

Constraints on a fifth force from the stellar orbits around the central supermassive black hole of the Milky Way

Predrag Jovanović, Duško Borka and Vesna Borka Jovanović

Here we investigate a possible presence of a fifth force at the Galactic Center (GC), and its potential influence on the stellar orbits around the central supermassive black hole of our Galaxy. For this purpose we simulated the stellar orbits in a Yukawa gravity model that predicts the emergence of a fifth force, and fitted them into the observed orbit of S2 star around Sgr A* at the GC. The fitting was performed using Markov chain Monte Carlo method which enabled us to constrain the parameters of Yukawa interaction describing the strength $\delta$ and the range $\lambda$ of a fifth force. We studied the following cases for a fifth force range $\lambda$, when it is: i) about a few hundred AU (i.e. deep inside the orbit of S2 star), ii) about a thousand AU (i.e. approximately the size of S2 star orbit), and iii) several thousand AU (i.e. much larger than the size of S2 star orbit). The obtained results showed that as the range $\lambda$ of a fifth force increases, its strength $\delta$ also increases and relative error $\Delta\delta/\delta$ decreases. The resulting fifth-force strengths in all three cases are respectively: $\delta\sim$ 0.005, 0.02 and 0.15. These results are consistent with the corresponding results of both our previous studies and those of other authors, regardless of the different Yukawa-like potentials used to model a fifth force. In addition, we also studied whether the possible small discrepancies from the prediction of General Relativity for the Schwarzschild precession of S2 star could be caused by a fifth force. For this purpose we used the $f_\mathrm{SP}$ parameter that was recently measured in the case of S2 star by GRAVITY Collaboration in 2020. We found that the obtained estimates in all three cases are compatible, within the error intervals, with the measured value of $f_\mathrm{SP} = 1.10\pm 0.19$.
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Cosmology and Nongalactic Astrophysics

Joint Curvature and Growth Rate measurements with Supernova Peculiar Velocities and the CMB

Camilo Crisman, Miguel Quartin and João Rebouças

Type Ia supernova (SN) magnitudes present correlations due to the fact that their peculiar velocities are sourced by the large-scale structure of the Universe. This effect can be used to constrain properties related to the distribution and growth of matter perturbations. We analyze both Pantheon+ and Dark Energy Survey (DES-Y5 and DES-Dovekie) SN catalogues in combination with CMB data from Planck PR4 to constrain $\sigma_8$ in $\Lambda$CDM, optionally including both curvature and a modified growth index $\gamma$. We show that SN and CMB datasets are highly complementary and capable of measuring $\sigma_8$, $\gamma$ and $\Omega_k$ simultaneously. Using only SN, we find $\sigma_8 = 0.73 \pm 0.22$ ($0.70_{-0.38}^{+0.31}$) [$1.02^{+0.38}_{-0.45}$] for Pantheon+ (DES-Y5) [DES-Dovekie] in the base flat $\Lambda$CDM model. Interestingly, allowing for free $\gamma$ and $\Omega_k$, we find hints of positive curvature: $\Omega_k = -0.011 \pm 0.006$ $(-0.013^{+0.005}_{-0.006})$ $[-0.008^{+0.004}_{-0.006}]$, which exclude flatness at 2.0$\sigma$ (2.6$\sigma$) [1.8$\sigma$], for the combination of CMB with Pantheon+ (DES-Y5) [DES-Dovekie]. Such hints do not degrade if we also include a modified amplitude of CMB lensing, parametrized by $A_L$. We find that $\gamma = 0.519^{+0.061}_{-0.099}$ ($0.500^{+0.054}_{-0.098}$) [$0.525^{+0.074}_{-0.073}$], which are consistent with the predictions of General Relativity. Finally, the strong degeneracy between all three $\Omega_k$, $\gamma$ and $H_0$ results in a broader CMB $H_0$ posterior. However, if we include SH0ES $H_0$ data, which is in known strong tension with the CMB in flat $\Lambda$CDM, we find that the $H_0$ tension is recast in terms of a significantly negative curvature and suppressed growth of structures.
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Astrophysics of Galaxies

Multi-scale Gas Structure and Dynamics in an Extragalactic Central Molecular Zone

Liam M. Wang, Jiayi Sun, Yu-Hsuan Teng et al. (+4 more)

The structures and dynamics of the interstellar medium are governed by a combination of self-gravity, external gravity, and various sources of ordered and random motions on different spatial scales. This paper uses ALMA CO (3-2) observations at 0.1" $\approx$ 5 pc resolution to examine the scale dependence of molecular gas structure and dynamics in the central molecular zone (CMZ) of a nearby galaxy, NGC 3351. We use the dendrogram technique to characterize hierarchical molecular gas structures spanning two decades in spatial scales and measure their size, gas mass, and velocity dispersion. Their size-linewidth relation shows a power-law slope of 0.58, comparable to measurements for CMZs in other galaxies and suggestive of significant contribution from ordered motion on large scales. We further decompose the observed velocity dispersion in each gas structure into ordered versus random motions. The former appears stronger in gas structures at $\gtrsim$ 30 pc while the latter becomes more dominant at $\lesssim$ 30 pc. Modulo uncertainties with the CO-to-H$_2$ conversion factor, the estimated gravitational free-fall time is comparable to the crossing time of ordered motions for structures on all spatial scales, and both becomes longer than the crossing time of random motions at small, $\lesssim$ 10 pc scales. Our results highlight the varying sources and drivers of gas motions on different spatial scales in the CMZ of a Milky Way-like galaxy.
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All authors Liam M. Wang, Jiayi Sun, Yu-Hsuan Teng, Eric W. Koch, Sanghyuk Moon, Elias Oakes, Erik Rosolowsky