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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 10 February

Cosmology and Nongalactic Astrophysics

Constraining long-lived dark sector particles with CMB and Lyman-$\alpha$

Laura Lopez-Honorez and Sonali Verma

We use measurements of the intergalactic medium (IGM) temperature from the Lyman-$\alpha$ forest to place new limits on models in which long-lived dark sector (DS) particles, with lifetimes longer than $10^{16}$ s, deposit energy into the IGM through their decays. Such DS decays into Standard Model (SM) states can modify the late-time thermal history of the IGM, making Lyman-$\alpha$ data a sensitive probe of hidden sectors with cosmologically long lifetimes. Our analysis demonstrates that constraints from late-time IGM heating offer a complementary window to those from the Cosmic Microwave Background (CMB), in constraining dark sector parameter space. We further revisit limits on such decaying DS models from Planck's measurements of the optical depth to reionization and provide updates relevant for DS lifetimes longer than $10^{14}$ s. The model-independent constraints on the DS parameter space we derive in this work can be reinterpreted for a wide range of decaying hidden-sector scenarios, including evaporating primordial black holes and SM-coupled dark photons.
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Astrophysics of Galaxies

SDSS-V Local Volume Mapper (LVM): Helix Nebula public data, Data Analysis Pipeline data products

S. F. Sánchez, J.E. Méndez-Delgado, A. Mejía-Narváez et al. (+21 more)

We present a spatially resolved spectroscopic analysis of the Helix Nebula (NGC 7293) using data from the SDSS-V Local Volume Mapper (LVM), by applying the recently developed LVM Data Analysis Pipeline (LVM-DAP). Covering the full optical range (3600-9800 Å) over a contiguous ~ 0.5 degree field, the LVM data provide the first hexagonally sampled, wide-field emission-line maps of all major ionic species in this archetypal planetary nebula. The resulting flux, kinematic, and line-ratio maps reveal the well-known ionization stratification of the nebula, from the compact He++ core to the bright [O III] ring and the extended low-ionization envelope, enabling a detailed comparison with classical aperture spectroscopy. Owing to the sensitivity and uniform spatial sampling of the LVM, numerous faint auroral and diagnostic lines are detected across the nebula, including [O III] 4363, [N II] 5755, and He I lines, allowing precise measurements of weak-line morphology. The derived radial trends confirm the remarkably low dust content and the overall homogeneity of electron temperature and density across the main ring. Ionized-gas kinematics traced by H{\alpha} further support the scenario of a slowly expanding, limb-brightened shell consistent with previous studies. This work demonstrates the diagnostic power of LVM spectroscopy for extended nebulae and highlights its capability to recover both global and spatially resolved physical conditions across complex ionized structures.
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All authors S. F. Sánchez, J.E. Méndez-Delgado, A. Mejía-Narváez, C. Román-Zuñiga, O. V. Egorov, C. Morisset, N. Drory, G. A. Blanc, K. Kreckel, E. J. Johnston, Ivan Yu. Katkov, A. Roman Lopes, M. A. Villa-Durango, H. Ibarra-Medel, H.-W. Rix, R. de J. Zermeño, J. G. Fernández Trincado, A. Singh, P. García, G. S. Stringfellow, L. Sabin, J. Toalá, R. Orozco Duarte, A. M. Jones

Solar and Stellar Astrophysics

Gaia white dwarfs with infrared excess I. The 100 pc catalogue

R. Murillo-Ojeda, F. M. Jiménez-Esteban, A. Rebassa-Mansergas et al. (+1 more)

The presence of infrared excess flux observed in white dwarfs (WDs) is related to the existence of debris disks or substellar companions. These systems provide important clues in the study of extrasolar planetary material and binary evolution. However, fully characterising their properties requires a statistically significant, complete sample. This work aims to identify a complete sample of WDs with infrared excess emission within 100 pc of the Sun. We built the spectral energy distributions (SEDs) of the WDs using synthetic photometry in 56 optical filters of the J-PAS system, generated from Gaia Data Release 3 low-resolution spectra and complemented with the latest infrared photometry available at the Virtual Observatory (VO). VOSA was used to fit the SEDs with different atmospheric WD models depending on the source spectral type. We visually checked optical and infrared images to identify contaminated photometry. We built a catalogue of 456 infrared excess WDs, of which 292 are robust identifications, and 164 are candidates. 351 ($\sim$75%) are new identifications. This implies a fraction of infrared excess WDs between 5.9$\pm$0.3% and 9.2$\pm$0.4%, higher than previous works, but in agreement with some more recent estimates. Furthermore, for the sample of infrared excess WDs, the fraction of sources with non-hydrogen atmosphere increases with the Gaia GBP-GRP colour, contrary to the general WD population. However, this result should be interpreted with caution. Additionally, a thorough comparison of our catalogue with those of previous studies was performed. The sample of WDs with infrared excess emission within 100 pc presented in this work is the largest, most complete and reliable to date. Due to their proximity, they are ideal targets for follow-up studies aimed at characterising circumstellar disks, substellar companions, and the composition of accreted planetary material.
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All authors R. Murillo-Ojeda, F. M. Jiménez-Esteban, A. Rebassa-Mansergas, S. Torres

Cosmology and Nongalactic Astrophysics

Dark Energy Survey Year 6 Results: Cosmological Constraints from Cosmic Shear

DES Collaboration: T. M. C. Abbott, M. Aguena, A. Alarcon et al. (+125 more)

We present legacy cosmic shear measurements and cosmological constraints using six years of Dark Energy Survey imaging data. From these data, we study ~140 million galaxies (8.29 galaxies/arcmin$^2$) that are 50% complete at i=24.0 and extend beyond z=1.2. We divide the galaxies into four redshift bins, and obtain cosmic shear measurement with a signal-to-noise of 83, a factor of 2 higher than the Year 3 analysis. We model the uncertainties due to shear and redshift calibrations, and discard measurements on small angular scales to mitigate baryon feedback and other small-scale uncertainties. We consider two fiducial models to account for the intrinsic alignment (IA) of the galaxies. We conduct a blind analysis in the context of the $\Lambda$CDM model and find $S_8 \equiv \sigma_8(\Omega_m/0.3)^{0.5}=0.798^{+0.014}_{-0.015}$ (marginalized mean with 68% CL) when using the non-linear alignment model (NLA) and $S_{8} = 0.783^{+0.019}_{-0.015}$ with the tidal alignment and tidal torque model (TATT), providing 1.8% and 2.5% uncertainty on $S_8$. Compared to constraints from the cosmic microwave background from Planck 2018, ACT DR6 and SPT-3G DR1, we find consistency in the full parameter space at 1.1$\sigma$ (1.7$\sigma$) and in $S_8$ at 2.0$\sigma$ (2.3$\sigma$) for NLA (TATT). The result using the NLA model is preferred according to the Bayesian evidence. We find that the model choice for IA and baryon feedback can impact the value of our $S_8$ constraint up to $1\sigma$. For our fiducial model choices, the resultant uncertainties in $S_8$ are primarily degraded by the removal of scales, as well as the marginalization over the IA parameters. We demonstrate that our result is internally consistent and robust to different choices in calibrating the data, owing to methodological improvements in shear and redshift measurement, laying the foundation for next-generation cosmic shear programs.
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All authors DES Collaboration: T. M. C. Abbott, M. Aguena, A. Alarcon, O. Alves, A. Amon, D. Anbajagane, F. Andrade-Oliveira, W. d'Assignies, S. Avila, D. Bacon, J. Beas-Gonzalez, K. Bechtol, M. R. Becker, G. M. Bernstein, J. Blazek, S. Bocquet, D. Brooks, H. Camacho, G. Camacho-Ciurana, R. Camilleri, G. Campailla, A. Campos, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, F. J. Castander, R. Cawthon, C. Chang, A. Choi, J. M. Coloma-Nadal, C. Conselice, L. N. da Costa, M. Costanzi, M. Crocce, T. M. Davis, J. De Vicente, D.L. DePoy, J. DeRose, S. Desai, H.T. Diehl, P. Doel, C. Doux, A. Drlica-Wagner, T. F. Eifler, S. Everett, A. E. Evrard, A. Ferté, B. Flaugher, P. Fosalba, O. Friedrich, J. Frieman, J. García-Bellido, M. Gatti, G. Giannini, P. Giles, K. Glazebrook, D. Gruen, R. A. Gruendl, G. Gutierrez, I. Harrison, W. G. Hartley, K. Herner, S. R. Hinton, D. L. Hollowood, K. Honscheid, D. Huterer, B. Jain, D. J. James, M. Jarvis, N. Jeffrey, T. Jeltema, T. Kacprzak, S. Kent, E. Krause, O. Lahav, S. Lee, E.Legnani, H. Lin, J. L. Marshall, S. Mau, J. Mena-Fernández, F. Menanteau, R. Miquel, J. J. Mohr, J. Muir, J. Myles, R. C. Nichol, R. L. C. Ogando, A. Palmese, M. Paterno, W. J. Percival, D. Petravick, A. A. Plazas Malagón, A. Porredon, J. Prat, C. Preston, M. Raveri, M. Rodriguez-Monroy, A. K. Romer, A. Roodman, E. S. Rykoff, S. Samuroff, C. Sánchez, E. Sanchez, D. Sanchez Cid, T. Schutt, I. Sevilla-Noarbe, E. Sheldon, T. Shin, M. E. da Silva Pereira, M. Smith, M. Soares-Santos, E. Suchyta, M. E. C. Swanson, M. Tabbutt, G. Tarle, D. Thomas, C. To, M. A. Troxel, V. Vikram, M. Vincenzi, N. Weaverdyck, J. Weller, P. Wiseman, M. Yamamoto, B. Yanny, B. Yin, J. Zuntz

Instrumentation and Methods for Astrophysics

Operational Mass Measurement for Flyby Reconnaissance Missions of Potentially Hazardous Asteroid

Justin A. Atchison, Gael Cascioli, Anivid Pedros-Faura et al. (+5 more)

This study evaluates a technique for determining the mass of a potentially hazardous asteroid from a high-speed flyby in the context of a rapid reconnaissance planetary defense scenario. We consider a host spacecraft that dispenses a small CubeSat, which acts as a test-mass. Both spacecraft perform approach maneuvers to target their flyby locations, with the host targeting a close proximity flyby and the CubeSat targeting a distant flyby. By incorporating short-range intersatellite measurements between the host and the CubeSat, the mass measurement sensitivity is substantially improved. We evaluate a set of proposed host and CubeSat hardware options against the 2023 and 2025 Planetary Defense Conference hypothetical threats, as well as a hypothetical flyby of 2024 YR4. These scenarios differ predominantly in their flyby speeds, which span from 1.7 to 22 km/s. Based on these scenarios, we demonstrate that a typical radio-frequency intersatellite measurement is ineffective for asteroids with diameters relevant to planetary defense (i.e., 50 - 500 m). However, we find that augmenting the system with a laser-based intersatellite ranging system or a high-precision Doppler system can enable mass measurements of asteroids as small as 100 m across all cases, and as small as 50 m for the slower (< 8 km/s) cases. The results are very sensitive to the timing of the final maneuver, which is used to target the low-altitude flyby point. This presents an operational challenge for the smallest objects, where optical detection times are comparatively late and the optical navigation targeting knowledge converges too slowly.
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All authors Justin A. Atchison, Gael Cascioli, Anivid Pedros-Faura, Erwan Mazarico, Rylie A. Bull, Jay McMahon, Evan J. Smith, Daniel R. Cremons

High Energy Astrophysical Phenomena

The supernova remnant J0450.4-7050 possesses a jets-shaped point-symmetric morphology

Noam Soker

By examining recently published images in different wavelengths, I identify a point-symmetric morphology in the Large Magellanic Cloud core-collapse supernova (CCSN) remnant (CCSNR) J0450.4-7050 (SNR 0450-70.9; nicknamed Veliki), which I attribute to at least three pairs of energetic jets that participated in the explosion of the progenitor in the framework of the jittering jets explosion mechanism (JJEM). Two pairs of ears, a pair of blowouts in the north and south along the long axis of this SNR, and a pair of dents compose the point symmetric morphology. The fact that the symmetry axes of two pairs include pairs of opposite structural features in the inner ejecta implies that the shaping is by jets and not due to an interaction with an ambient material. While the JJEM predicts such morphologies, the competing neutrino-driven mechanism cannot account for point-symmetric morphologies. This study provides strong support for the claim that the JJEM is the primary CCSN explosion mechanism.
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Astrophysics of Galaxies

Physical properties of circumnuclear ionising clusters. IV. NGC 1097

Sandra Zamora, Angeles I. Díaz and Asier Castrillo

The circumnuclear star-forming ring of the barred spiral galaxy NGC 1097 provides a unique laboratory to study star formation under extreme conditions. This work aims to derive the physical properties of the circumnuclear star-forming regions (CNSFRs) using MUSE integral field spectroscopy observations. A total of 24 individual ionised HII are identified and analysed within its ring, which spans from $\sim$385 pc to $\sim$1.3 kpc. Despite the complex nuclear activity, all HII regions are found to be purely photoionised. Directly derived abundances reveal supersolar metallicities, with the highest one exceeding five times the solar value (12+log(S/H) = 7.875 $\pm$ 0.353, T$_e$([SIII]) = 3912 $\pm$ 567 K), and representing the highest abundance reported to date. In this high-metallicity regime, we find a break in the ionisation parameter-[SII]/[SIII] relation, which can be explained by changes in the ionisation structure and line emissivities, as confirmed by photoionisation models that successfully reproduce the observed emission-line ratios. Our results also indicate that the local gas supply regulates the star formation activity within the ring, with the young stars ionising 8 % of the total gas in the ring. Furthermore, our findings support a propagating starburst scenario, originating in the galaxy nucleus and extending towards the ends of the bar and into the circumnuclear ring through bar-driven shocks, this being consistent with the results of previous multi-wavelength studies. Finally, we likely detect optical signatures associated with one of the two known jets in this galaxy. This finding, together with the radio core emission previously found at sub-parsec scales, reflects the presence of feedback processes operating even on small galactic disc scales.
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Solar and Stellar Astrophysics

Chromospheric Flashes in a Solar Pore: Insights from Multi-line Spectropolarimetric Diagnostics

Sandeep Dubey, Christian Beck, Rahul Yadav et al. (+2 more)

Solar pores are strongly magnetized regions lacking a photospheric penumbra and characterized by predominantly vertical magnetic fields. We present a multi-line study of flashes in a solar pore using high-resolution observations from the Swedish 1-m Solar Telescope in Fe~i~6302~Å, Ca~ii~8542~Å\ and K, and H-$\beta$, complemented by (E)UV data from IRIS and SDO/AIA. Bisector analysis and spectral inversions with SIR and NICOLE were used to infer stratifications of temperature, line-of-sight velocity, and magnetic field. Flashes, confined to one half of the pore, exhibit cooler photospheric temperatures ($\Delta T \approx 400$~K), stronger magnetic fields ($\Delta B \approx 250$~G), larger inclinations ($\sim25^{\circ}$ versus $\sim18^{\circ}$), and persistent upflows ($\sim0.5$~km~s$^{-1}$) compared to the quiescent pore. They are co-spatial with enhanced 3- and 5-minute power in the photosphere, while only 3-minute power persists in the chromosphere. Flashes are detected down to $\sim50\%$ line depth in Ca~ii~8542~Å\ intensity and show central chromospheric upflows ($\sim1$~km~s$^{-1}$) flanked by strong downflows ($\sim8$~km~s$^{-1}$). Temperature enhancements reach $\sim500$~K at $\log\tau \approx -5$ and $\sim2500$~K at $\log\tau \approx -6$, with a bimodal velocity distribution. Flashes correspond one-to-one with radially outward running waves near the pore boundary (5–15~km~s$^{-1}$). Strong Ca~ii core emission, occasional Stokes~$V$ reversals, and H-$\beta$ enhancements indicate that pore flashes are confined to the lower and mid-chromosphere, with little influence on higher atmospheric layers.
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All authors Sandeep Dubey, Christian Beck, Rahul Yadav, Tobias Felipe, Shibu K Mathew

Solar and Stellar Astrophysics

A Detailed Study of the Physical and Orbital Characteristics, and Eclipse Timing Variations of the Post Common Envelope Binary DD CrB

Özgür Baştürk, Ezgi Sertkan, Furkan Akar et al. (+10 more)

We present an in-depth analysis of the eclipsing binary DD CrB, composed of a B-type subdwarf primary and an M-type main-sequence secondary, with the main goal of investigating its eclipse timing variations (ETVs). Our new multi-color photometric observations, radial velocity measurements, and precise eclipse timings from TESS allow us to constrain the system parameters. The Romer delay between primary and secondary minima yields a mass ratio of $q = 0.299 \pm 0.009$, enabling robust simultaneous modeling of the light and radial velocity curves with phoebe 2.17. By fixing the albedo of the secondary to its maximum physically plausible value (A$_2 = 1.0$), despite the degeneracy between albedo, surface temperature, and radius, we obtained a satisfactory fit, resulting in a significantly lower temperature ($T_2 \sim 2360$ K) and a radius ($R_2 \sim 0.16$ R$_\odot$) in agreement with literature values. Using the total mass of the components and the orbital size derived from this modeling, we interpret the ETVs and find them best explained by a Jupiter-mass tertiary companion on a $\sim13$-year orbit in all competing models, while the eccentric (e $\sim0.46$) models perform better in terms of fit statistics.
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All authors Özgür Baştürk, Ezgi Sertkan, Furkan Akar, Ulisse Munari, Bar{\i}ş Güler, Ekrem M. Esmer, Selim O. Selam, Ahmet C. Kutluay, Marek Wolf, Petr Zasche, Hanna Kučáková, Miloslav Zejda, Özlem Şimşir

Instrumentation and Methods for Astrophysics

Reference File Updates Following the Application of New Geometric Distortion and Walk Corrections I: Overview

Nick Indriolo, William J. Fischer, Elaine Frazer et al. (+8 more)

The calibration of Cosmic Origins Spectrograph (COS) data is performed by the data processing pipeline known as CalCOS. CalCOS utilizes several reference files that store information required for data processing (e.g., dispersion solutions), and these reference files can be updated for the purpose of improving calibrated data products. In 2024 a major effort to improve the far-ultraviolet (FUV) geometric distortion, delta-geometric, and walk corrections was completed. Those three corrections occur early in the CalCOS workflow and shift photon events into the corrected reference frame ((XCORR, YCORR) coordinate system) in which subsequent calibration steps-and their reference files-are defined. This change necessitated the re-derivation of all "downstream" reference files in use at the time. Here we summarize the effort to create new versions of 56 reference files applicable to lifetime positions 1 through 6 and intended for use with the new geometric distortion, delta geometric, and walk corrections. The primary outcome of this work is improved wavelength and flux calibrations for COS FUV spectra.
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All authors Nick Indriolo, William J. Fischer, Elaine Frazer, David French, Sten Hasselquist, Jaquline Hernandez, Christian I. Johnson, Darshan Kakkad, Lauren P. Miller, Marc Rafelski, Ravi Sankrit

High Energy Astrophysical Phenomena

In-flight calibration of the INTEGRAL/IBIS Compton mode: Application to the Crab Nebula polarization

Tristan Bouchet, Philippe Laurent, Floriane Cangemi et al. (+1 more)

The INTEGRAL satellite explored the gamma-ray sky since its launch on October 17, 2002, and until the end of its scientific operation on February 28, 2025. A large fraction of the available data is still largely untouched, due to the complexity of analysis. We describe the latest in-flight calibration of the Compton mode of the INTEGRAL/IBIS telescope, taking into account more than twenty years of data. The spectroscopy and polarization of the standard candle that is the Crab Nebula is analyzed in detail. We operate the IBIS telescope as a Coded mask Compton telescope, using the Crab Nebula to refine the calibration, as is usually done for high-energy instruments. We have determined the spectroscopic and polarimetric properties of the IBIS Compton mode and their evolution along the entire duration of the mission. In addition, the long-term evolution of the Crab Nebula's polarization has been successfully measured and compared with other high-energy experiments. We could estimate the energy dependence of the Crab Nebula polarization in four bands between 200 keV and 1 MeV. In particular, the detection of polarized emissions strictly above 400 keV makes it the highest energy measurement ever performed for the Crab Nebula. A Python library was also made publicly available to analyze processed data.
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All authors Tristan Bouchet, Philippe Laurent, Floriane Cangemi, Jérôme Rodriguez

Astrophysics of Galaxies

Resolved Dust Emission and CO Isotopologues in Giant Molecular Clouds of the Andromeda Galaxy

Chloe Bosomworth, Jan Forbrich, Charles J. Lada et al. (+1 more)

Dust emission at submillimeter wavelengths can be used to reliably trace the basic properties of molecular clouds. Early results from a recent Submillimeter Array (SMA) survey of the Andromeda Galaxy (M31) include the first detections of resolved dust continuum emission from individual giant molecular clouds (GMCs) in an external spiral galaxy. This paper updates on the now-complete SMA survey of 80 Herschel-identified giant molecular associations (GMAs) in M31. The SMA survey simultaneously probes dust continuum emission at 230 GHz and the $J = 2 \rightarrow 1$ transitions of the CO isotopologues, $^{12}\rm CO$, $^{13}\rm CO$, and $\rm C^{18}O$ at a spatial resolution of $\lesssim 15~\mathrm{pc}$. Dust continuum emission was detected in 71 cloud cores, of which 26 were resolved. This more than doubles the size of the previous sample. By comparing dust and CO observations with identical astrometry, we directly measure the dust mass to-light ratios, $\rm \alpha^{\prime}_{^{12}CO}$, and $\rm \alpha^{\prime}_{^{13}CO}$. We derive $<\alpha^{\prime}_{\rm ^{12}\rm CO}>~=~0.070~\pm~0.031~M_{\odot}\,(\rm K~km~s^{-1}~pc^{2})^{-1}$ and $<\alpha^{\prime}_{\rm ^{13}\rm CO}>~=~0.37~\pm~0.20~M_{\odot}\,(\rm K~km~s^{-1}~pc^{2})^{-1}$ for the increased sample, which are in agreement with previously reported values. From virial analysis, we find that 80% of the GMC regions traced by resolved dust emission are bound and close to virial equilibrium. Finally, we update our analysis on the metallicity dependence of $\rm \alpha^{\prime}_{\rm CO}$ by combining SMA observations with existing MMT/Hectospec optical spectroscopy toward H II regions. We find no trend in $\rm \alpha^{\prime}_{\rm CO}$ with metallicity, supporting the previous findings.
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All authors Chloe Bosomworth, Jan Forbrich, Charles J. Lada, Glen Petitpas

Solar and Stellar Astrophysics

A comparison of G-band brightness as a proxy-magnetometer in various magnetic configurations

Malay Shukla, Sneha Pandit and Nitin Yadav

We investigate the diagnostic potential of the G-band at 430.4 nm for probing small-scale magnetic fields in the solar photosphere. Combining three-dimensional MHD simulations from the MURaM code and spectral synthesis via the RH 1.5D code, we evaluate the intensity contrast in the G-band filtergrams by comparing the filter centered at 430.4 nm in comparison to the conventional 430.5 nm. Our results show that filtergrams centered at 430.4 nm provide higher contrast across varying magnetic environments, particularly at narrow filter widths. This enhancement arises from its slightly higher formation height and greater sensitivity to temperature variations in magnetized regions. These findings indicate that G-band filtergrams centered at 430.4 nm show enhanced diagnostic potential under the assumptions of the present modeling. The obtained results are also relevant and suggest potential applications in stellar contexts, where molecular bands are often used as proxies for magnetic activity.
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Solar and Stellar Astrophysics

Investigating the Nested Structure of the Outflow from the Low Luminosity Protostar IRAS 16253-2429 using JWST and ALMA

Mayank Narang, Himanshu Tyagi, Nagayoshi Ohashi et al. (+37 more)

Understanding the earliest stage of star and planet formation requires detailed observations to address the connection and interplay between the accretion, outflow and disk evolution. We present results from the observations of the low luminosity ($L_\mathrm{bol}\sim~0.2~L_\odot$) and mass (M$_*\sim$\,0.15~M$_\odot$) Class~0 protostar IRAS 16253$-$2429, conducted as part of the eDisk ALMA large program and the JWST cycle-1 GO program IPA. Observations reveal a wide hourglass-shaped continuum cavity traced in scattered light (at $\leq$~5~$\mu$m), with a brighter, extended northern side. We detect 15 pure rotational H$_2$ transitions (E$_\mathrm{up}$:~1015–21411~K), revealing a wide-angle molecular outflow. {The outflow width (as traced in H$_2$~0-0~S(11)) at the protostellar location measures $\leq$35 au, slightly larger than the dust and Keplerian disk diameters ($\sim$30 au) but wider than the 20–23~au jet width in [Fe II].} {The opening angle narrows from 40–35\arcdeg{} for the low-J H$_2$ lines (up to S(5)) and the cold gas component (ALMA $^{12}$CO) to $\sim$28–19\arcdeg{} for the high-J H$_2$ lines (S(7)–S(11)).} Position-velocity diagrams of H$_2$ reveal higher velocities for higher E$_{up}$, ranging from ~12.5 km~s$^{-1}$ for H$_2$~0-0~S(1) and S(2) to ~28.5 km~s$^{-1}$ for H$_2$~0-0~S(5)~and~S(7) with respect to the mean flow velocity. The nested excitation and velocity structure of the collimated jet and wide angle wind suggest a magnetohydrodynamic wind as a likely launching mechanism, similar to the findings in other protostars and Class II sources. The lower velocity mm CO may be gas from the infalling envelope accelerated outwards by the wide angle wind along the cavity walls.
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All authors Mayank Narang, Himanshu Tyagi, Nagayoshi Ohashi, P. Manoj, S. Thomas Megeath, John J. Tobin, Ewine F. van Dishoeck, Neal J. Evans II, Dan M. Watson, Alessio Caratti o Garatti, Jes K. Jørgensen, Robert Gutermuth, Yusuke Aso, Henrik Beuther, Leslie W. Looney, David A. Neufeld, Guillem Anglada, Mayra Osorio, Adam E. Rubinstein, Samuel Federman, Lee W. Hartmann, Pooneh Nazari, Nicole Karnath, Hendrik Linz, Thomas Stanke, Tyler L. Bourke, Yao-Lun Yang, Rolf Kuiper, Joel Green, Pamela Klaassen, Wafa Zakri, Nolan Habel, Nashanty Brunken, James Muzerolle, Katerina Slavicinska, Amelia M. Stutz, Lukasz Tychoniec, Scott Wolk, Will R. M. Rocha, William J. Fischer

Solar and Stellar Astrophysics

Searching for rotational X-ray modulation on TIC 277539431

Desmond Dsouza, Katja Poppenhaeger and Ekaterina Ilin

TIC 277539431, a fast rotating M7 dwarf, was detected to host the highest latitude flare to date at $81^\circ$. Magnetic activity like stellar flares occurring at high latitude indicate occurrence of coronal loops at these latitudes on fully-convective M dwarfs. In contrast, sunspots usually occur below $30^\circ$. In our study we look for modulation on the X-ray signal occurring due to occultation of coronal loops by the star due to stellar rotation. We report an updated rotation period for this star as $P_{\text{rot}}=273.593$ min based on TESS sectors 12, 37, 39, 64 and 65. We conducted $\chi^2_{\textrm{red}}$ fits by varying the amplitude and the phase of a sinusoidally modulated signal derived from the new rotation period. We find no evidence of rotational modulation in the X-ray signal. This could be due to multiple scenarios, such as lack of a stable coronal loop during observation or the modulated signal being too weak, however given the dataset, individual scenarios cannot be distinguished.
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Instrumentation and Methods for Astrophysics

The Pollux European instrument concept for HWO: a high-resolution spectrograph and spectropolarimeter from the far-UV to the near-IR

Coralie Neiner, Jean-Claude Bouret, Luca Fossati et al. (+4 more)

Pollux is a high-resolution spectrograph and spectropolarimeter working from 100 nm to 1.8 microns proposed for HWO by a European consortium. Pollux will allow us to study stellar and (exo)planetary systems, as well as cosmic ecosystems. For example, Pollux will provide new insights on exoplanet formation and evolution, characterization of the atmospheres and magnetospheres of stars and planets, and star-planet interactions. It will also allow us to resolve narrow UV emission and absorption lines, enabling us to follow the baryon cycle over cosmic time – from galaxies forming stars out of interstellar gas and grains, and planets forming in circumstellar disks, to the various forms of feedback into the interstellar and intergalactic medium – and from active galactic nuclei. The most innovative characteristic of Pollux is its unique spectropolarimetric capability in the UV, which will open a new parameter space. Its very high spectral resolution (~70000 to ~100000) and stability over a very large wavelength range will also be a major asset. In this paper, we summarize the main scientific drivers of Pollux and present its current design, technological challenges, and the Pollux consortium organization.
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All authors Coralie Neiner, Jean-Claude Bouret, Luca Fossati, David le Mignant, Eduard Muslimov, Ana Ines Gomez de Castro, Frédéric Marin

Solar and Stellar Astrophysics

Estimating Electron Densities in the Middle Solar Corona using White-light and Radio Observations

Surajit Mondal, Shaheda Begum Shaik, Russell A. Howard et al. (+45 more)

The electron density of the solar corona is a fundamental parameter in many areas of solar physics. Traditionally, routine estimates of coronal density have relied exclusively on white-light observations. However, these density estimates, obtained by inverting the white-light data, require simplifying assumptions, which may affect the robustness of the measurements. Hence, to improve the reliability of coronal density measurements, it is highly desirable to explore other complementary methods. In this study, we estimate the coronal electron densities in the middle corona, between approximately $1.7-3.5R_\odot$, using low-frequency radio observations from the recently commissioned Long Wavelength Array at the Owens Valley Radio Observatory (OVRO-LWA). The results demonstrate consistency with those derived from white-light coronagraph data and predictions from theoretical models. We also derive a density model valid between 1.7–3.5 $r_\odot$ and is given by $\rho (r')=1.27r'^{-2}+29.02r'^{-4}+71.18r'^{-6}$, where $r'=r/R_\odot$, and $r$ is the heliocentric distance. OVRO-LWA is a solar-dedicated radio interferometer that provides science-ready images with low latency, making it well-suited for generating regular and independent estimates of coronal densities to complement existing white-light techniques.
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All authors Surajit Mondal, Shaheda Begum Shaik, Russell A. Howard, Peijin Zhang, Bin Chen, Xingyao Chen, Sijie Yu, Dale Gary, Marin M. Anderson, Judd D. Bowman, Ruby Byrne, Morgan Catha, Sherry Chhabra, Larry D Addario, Ivey Davis, Jayce Dowell, Gregg Hallinan, Charlie Harnach, Greg Hellbourg, Jack Hickish, Rick Hobbs, David Hodge, Mark Hodges, Yuping Huang, Andrea Isella, Daniel C. Jacobs, Ghislain Kemby, John T. Klinefelter, Matthew Kolopanis, Nikita Kosogorov, James Lamb, Casey Law, Nivedita Mahesh, Brian O Donnell, Corey Posner, Travis Powell, Vinand Prayag, Andres Rizo, Andrew Romero Wolf, Jun Shi, Greg Taylor, Jordan Trim, Mike Virgin, Akshatha Vydula, Sandy Weinreb, Scott White, David Woody, Thomas Zentmeyer

Astrophysics of Galaxies

Analysis of Galactic cirrus filaments in HSC-SSP high-resolution deep images using artificial neural networks

Denis M. Poliakov, Anton A. Smirnov, Sergey S. Savchenko et al. (+6 more)

The existence of Galactic optical cirrus poses a challenge for observing faint objects within our Galaxy and dim extragalactic structures. To investigate individual cirrus filaments in the Hyper Suprime-Cam Subaru Strategic Program public data release 3 (HSC-SSP DR3) we use a technique based on convolutional neural networks and ensemble learning. This approach allows us to distinguish cirrus filaments from foreground and background objects across the entire HSC-SSP, using optical images in the $g$, $r$, and $i$ wavebands. A comparison with previous work using deep Sloan Digital Sky Survey Stripe~82 (SDSS Stripe~82) data reveals that the cirrus clouds identified in this study are highly consistent in location within the overlapping survey region. However, in the deeper HSC-SSP dataset, we were able to detect $4.5$ times more cirrus clouds. Our study indicates that the sky background in HSC-SSP coadd images is over-subtracted, as evidenced by the surface brightness distribution in cirrus filaments and surrounding regions. Objects with surface brightness of $m = 29~\mbox{mag~arcsec}^{-2}$ near large filaments can be dimmed by over-subtraction of $0.5$ magnitude in the $r$ band. This suggests that cirrus clouds should be taken into account in algorithms for estimating the sky background. For practical use, we provide a catalog of filaments and a framework that allows one to train neural network models for segmenting cirri in HSC-SSP coadd images.
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All authors Denis M. Poliakov, Anton A. Smirnov, Sergey S. Savchenko, Alexander A. Marchuk, Aleksandr V. Mosenkov, Vladimir B. Ilin, George A. Gontcharov, Daria G. Turichina, Andrey D. Panasyuk

Solar and Stellar Astrophysics

Characterisation of an EXor outburst SPICY 97589

Aaron Labdon and Rik Claes

Stellar outbursts from variable or periodic accretion are thought to be ubiquitous across young stellar populations. However, relatively few outbursting objects have been discovered to date. Here, we present the characterisation of a new EXor-type episodic accretor. We aim to characterise the nature of the 2023 outburst of SPICY 97589/Gaia23bab and characterise the stellar source for the first time, while exploring how an accretion outburst contributes to disk evolution. We employ multi-waveband medium-resolution spectroscopy with UVB-VIS-NIR coverage during the peak of the 2023 outburst and the post-outburst quiescent object. The broad wavelength coverage of the dataset allows for robust measurements of the accretion rate using known line tracers. The addition of quiescent spectra provides a good estimation of stellar parameters of the central star while also informing us on the evolution of the disk during outburst phases. We find the stellar source to be a 3410\,K, M3.0 type star with a luminosity of 0.41 $L_\odot$ and an estimated stellar mass of 0.29 $M_\odot$. We measure the accretion rate of SPICY 97589 to be $\dot M = 2.38\pm0.58\times10^{-7}\,\mathrm{M_\odot yr^{-1}}$. This value is at two orders of magnitude greater than the quiescent accretion rate. Thus, we confirm that the 2023 outburst was driven by an influx of material from the surrounding environment to the central star, an accretion outburst. The spectral fingerprint of emission lines is also characteristic of an outbursting EXor-type source, including variable disk winds.
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Astrophysics of Galaxies

Massive disk galaxies with high surface brightness plus low surface brightness stellar disks, hosted by massive dark matter halo – a TNG50 simulation study

Suchira Sarkar and Kanak Saha

We study massive disk galaxies (total stellar mass$>=10^{11}$ $\mathrm{M_{\odot}}$) from IllustrisTNG50 simulation, and perform 2-D structural decomposition of the galaxies using their idealised, synthetic SDSS images for z=0. We find an interesting sample of galaxies having a central high surface brightness (HSB) stellar disk, surrounded by an extended low surface brightness (LSB) stellar disk, similar to giant LSB galaxies. These massive, double-exponential disk galaxies are found to be hosted by dark matter haloes of $\sim 10^{12} \mathrm{M_{\odot}}$ in agreement to observations of such galaxies. Their maximum rotation velocity, an approximate measure of their dynamical mass, lies within $\sim$ (300-500) km/s. The stellar-to-dark matter mass ratio and the baryon-to-dark matter mass ratio of the sample lies in the range of $\sim$ (0.04 - 0.46) and $\sim$ (0.07 - 0.47) respectively. Our results show that cosmological simulations are able to form disc galaxies with HSB plus LSB disks, as in observations.
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Cosmology and Nongalactic Astrophysics

Non-minimally Coupled Running Curvaton for DESI-motivated Dynamical Dark Energy

Bichu Li and Lei-Hua Liu

Recent DESI BAO data combined with CMB and supernova measurements suggest a dynamical dark energy that can cross the phantom divide. We show that introducing a non-minimal coupling $\xi\chi^2R$ to the running-curvaton framework allows a single field to drive early-universe curvature perturbations and late-time phantom-crossing cosmic acceleration without ghost instabilities. Using MCMC background likelihoods with DESI DR2 BAO, Pantheon+ SNe, and a reduced CMB prior, we constrain the cosmological parameters: $H_0 = 67.88^{+0.53}_{-0.61}\,{\rm km\,s^{-1}\,Mpc^{-1}}$, $\Omega_m = 0.3072^{+0.0059}_{-0.0054}$, $w_0 = -0.922^{+0.055}_{-0.063}$, and $w_a = -0.205^{+0.173}_{-0.182}$. Parameter degeneracies leave the coupling constants weakly constrained, highlighting the need for full perturbation-level analysis using CMB spectra and lensing.
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Astrophysics of Galaxies

Stellar-mass black holes in young massive and open stellar clusters – VII. Comparisons with gravitational-wave events until LVK-O4a and Gaia compact binaries

Sambaran Banerjee

Gravitational-wave (GW) detections by the LIGO-Virgo-KAGRA (LVK) observatories suggest multiple formation channels for GW compact binary mergers. Here I assess the role of young massive clusters (YMC) evolving into old open clusters (OC) - the YMC/OC channel - to the GW merger population. A homogeneous grid of 90 N-body evolutionary model star clusters, spanning initial masses of $10^4M_\odot\leq M_{cl}(0)\leq10^5M_\odot$, half-mass radii of 1-3 pc, and metallicities between 0.0002-0.02 is computed with the direct, post-Newtonian N-body code NBODY7. The N-body simulations include primordial binaries, delayed stellar-remnant model forming black holes (BH) and neutron stars (NS), BH spin prescriptions, and GW recoil kicks, and they are evolved until BH depletion. Most GW mergers from the cluster models are dynamically assembled binary black holes (BBH) that merge within their host clusters. Merger mass ratios reach 0.1-0.2 despite an overall bias toward nearly symmetric pairs. The GW merger efficiency varies non-monotonically with cluster mass, peaking around $M_{cl}(0)=7.5\times10^4M_\odot$ and also for $M_{cl}(0)\leq3.0\times10^4M_\odot$. The computed mergers reproduce some of the key features of the latest observed GW event catalogue, including asymmetric low-mass mergers, misaligned events among highly spinning, massive BHs, and an excess of $30M_\odot$ primaries, though they under-produce $10M_\odot$ primaries, hinting at contributions from other channels. The model merger rate density accounts for a fiducial 25%-33% of the observed rate; it increases with redshift somewhat faster than the cosmic star formation, consistently with LVK's inferences. The model effective spin distribution is positively asymmetric at zero redshift and broadens with redshift. The models yield field BH- and NS-main sequence star binaries with parameters consistent with the Gaia-discovered candidates. [Abgd]
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Solar and Stellar Astrophysics

A Deep Precursor-Dip-Main Superoutburst Sequence in VW Hydri Observed with TESS: High-Cadence Constraints on the Thermal-Tidal Instability Model

Bisi Bernard Ogunwale, Shara Michael, Avi Shporer et al. (+2 more)

We present 120s cadence TESS observations of three superoutbursts of the SU UMa-type dwarf nova VW Hydri. Two events (SO2 in Sectors 87+88 and SO3 in Sector 93) exhibit a pronounced, temporally pronounced precursor-dip followed by a rapid rise into the main superoutburst plateau. This morphology, previously seen in Kepler light curves of V1504 Cyg and V344 Lyr, is a key prediction of the thermal-tidal instability (TTI) model when a normal (precursor) outburst expands the disk only marginally beyond the 3:1 resonance radius, allowing the tidal instability to grow slowly and produce a deep dip approaching quiescence before rapid amplification drives the main superoutburst. A sliding-window time-frequency analysis reveals superhump power already during the decline and near minimum light, with a smooth period evolution across the dip and stabilization after the system returns to the hot state, consistent with the growth and saturation of disk eccentricity at the 3:1 resonance. From the stabilized Stage A superhump periods, we infer a representative mass ratio $q = 0.131 \pm 0.002$. Combined with either a typical SU UMa white-dwarf mass prior or the semi-empirical donor sequence at an orbital period of 107~min, the implied component masses are $M_1 \simeq 0.6$–$1.0\,M_\odot$ and $M_2 \simeq 0.08$–$0.14\,M_\odot$, ruling out a brown-dwarf donor and establishing VW~Hyi as a benchmark system for testing tidal-instability models in low-$q$ dwarf novae.
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All authors Bisi Bernard Ogunwale, Shara Michael, Avi Shporer, Dafne Guetta, Lev Tal-Or

Astrophysics of Galaxies

Two-dimensional metallicity distribution of the ionized gas in NGC 628 and NGC 6946

Bernabé Cedrés, Jordi Cepa, Ángel Bongiovanni et al. (+3 more)

We present here two H II region catalogues with azimuthal resolution for the two grand design galaxies NGC 628 and NGC 6946. With the help of these catalogues, we study several properties of the star-forming processes occurring in spiral galaxies. We obtained direct imaging in the narrow-band filters centred at H{\alpha}, He̱ta}, [O II]{\lambda}3727, and [O III]{\lambda}{\lambda}4959, 5007 and their respective continua. After the calibration and correction of the data, we obtained for each H II region the de-reddened fluxes in the aforementioned lines, the size, the H{\alpha} equivalent width, and, using two different empirical calibrations, the metallicity. Employing a method based on the Delaunay triangulation, a two-dimensional (2D) representation of the metallicity was obtained. Data for 209 H II regions of NGC 628 and 226 H II regions of NGC 6946 are obtained. The radial behaviours of the H{\alpha} equivalent width, the excitation, and the oxygen abundance are derived. Two-dimensional representations of the metallicity and the excitation are calculated for the galaxies in the study. The two empirical calibrations of the metallicity are compared. The oxygen abundance gradients obtained in this study agree with previously published values. However, more regions were examined than in previous studies. We find a difference of about 0.6 dex between the two empirical calibrations employed. Finally, the 2D representations of the metallicity reveal high metallicity knots in NGC 628, and for NGC 6946 a high metallicity azimuthal structure is discovered. These high metallicity regions seem to be linked to the arms of the galaxies and are probably produced by an increase in the temperature of the ionizing clusters in the H II regions, which may be linked to variations in the initial mass functions of the galaxies between the arm and interarm regions.
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All authors Bernabé Cedrés, Jordi Cepa, Ángel Bongiovanni, Héctor Castañeda, Miguel Sánchez-Portal, A. Tomita

Instrumentation and Methods for Astrophysics

Talking with the Latents – how to convert your LLM into an astronomer

Ilay Kamai, Marc-Huertas Company, Mike J. Smith et al. (+1 more)

Recent advances in Large Language Models (LLMs) offer unique opportunities for scientific tasks, yet their ability to reason over complex numerical data remains largely unexplored. We propose a simple mechanism to introduce domain-specific physical knowledge into LLMs by fusing pre-trained latent physical features with a pre-trained language model. Our method employs a teacher-student knowledge distillation framework where a large LLM (teacher) generates synthetic question-answer supervision to transfer physical reasoning to a smaller LLM (student). The student is conditioned on latent physical features and trained via a lightweight adapter and Low-Rank Adaptation (LoRA). We demonstrate that this approach, applied to models with 1B, 8B, and 32B parameters, enables effective reasoning over real scientific data. Our models substantially outperform strong baselines, such as Gemini 3 Pro, across multiple downstream tasks without task-specific fine-tuning. We show that the model combines latent information with general physical understanding to predict complex properties and can be "steered" by identifying physically meaningful directions in the latent space. This allows for explicit physical manipulation and natural language interpretation of latent structures. While our experiments focus on astrophysics, the framework is domain-agnostic and applicable to various scientific fields. Our main contribution is a general framework for using LLMs as interpretable interfaces to scientific latent spaces, enabling a single model to perform diverse tasks through natural language guidance. This work marks a step toward developing scientifically capable and useful LLMs.
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All authors Ilay Kamai, Marc-Huertas Company, Mike J. Smith, Hagai B. Perets

Astrophysics of Galaxies

Global statistical entropy and its implications for the main sequences of stars and galaxies

David Elbaz

In a dissipative system such as star or a galaxy, the emitted photons are decoupled from matter particles and may therefore be considered as part of a closed system to which the Second Law of Thermodynamics applies. In the present paper, we define a global entropy using a statistical approach that accounts for the contributions of both matter particles and photons. The statistical contribution of radiation is described as a photon gas in the definition of this global entropy. The increase in global entropy can foster structure formation – rather than disorder – because structures such as stars and galaxies are efficient at dissipating energy in the form of photons, and thus at producing entropy. We show that stars generate a nearly equal amount of specific entropy, and therefore a comparable number of photons per unit mass, over their lifetime on the main sequence of the Hertzsprung-Russell (HR) diagram. This suggests that the main sequence of the HR diagram constitutes a locus of convergence toward a universal specific entropy production by stars. We then examine the implications of this approach for the star-formation main sequence in galaxies, and find a similar result. The emergence of organized structures in cosmic history reflects the second law, as organized matter is efficient at generating entropy through the slicing of energy into lower-frequency photons. This is also reflected in the dominant contribution of low-frequency photons to the extragalactic background light. Finally, we briefly discuss how this perspective may inform us on the possibility of the existence of life elsewhere in the universe.
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Astrophysics of Galaxies

EMU Radio Observations of Barred Spiral Galaxy NGC 5938 (Araish)

H. Zakir, M.D. Filipović, L. Barnes et al. (+14 more)

We present multi-wavelength observations of the nearby spiral galaxy NGC 5938 (Araish) to investigate the origin of its radio emission, specifically the contribution from active galactic nucleus (AGN) activity and star formation. Using Evolutionary Map of the Universe (EMU) data, we detect extended radio emission extending outwards to the galactic axis, with a steep non-thermal spectral index ($\alpha = -1.2 \pm 0.2$) indicative of synchrotron radiation from an AGN jet. The jet has a physical extent of $\approx 8.2\,kpc$ (angular length of $64^{\prime\prime}$). Multi-wavelength data from The Dark Energy Camera Plane Survey 2 (DECaPS2), Wide-field Infrared Survey Explorer (WISE), and extended Roentgen Survey with an Imaging Telescope Array (eROSITA) provide further support for this interpretation. The colour-colour diagram presenting WISE infrared observations suggests the presence of dust and young stars that trace the galaxy's disk structure. Our analysis reveals a radio jet, alongside star formation traced by infrared emission, demonstrating the complex interplay of AGN activity and star formation in this well-resolved galaxy. Intriguingly, the spatial relationship reveals the brighter X-ray emission to be largely adjacent to and enveloping the extended radio emission. This suggests that the radio jet, while extending at a significant angle to the galactic disk, is confined by the larger X-ray gas halo, similar to other systems (i.e., ESO 295-IG022, Centaurus A) and may indicate jet collimation and channelling effects.
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All authors H. Zakir, M.D. Filipović, L. Barnes, R. Z. E. Alsaberi, T. An, K. Dage, S. W. Duchesne, A. M. Hopkins, A. Kapinska, B. Koribalski, S. Lazarević, D. Leahy, Z. Liu, R. P. Norris, A. Rau, Z.J. Smeaton, T. Jarrett

Astrophysics of Galaxies

Organic Acid Chemistry in ISM: Detection of Formic Acid and its Prebiotic Chemistry in Hot Core G358.93$-$0.03 MM1

Arijit Manna, Sabyasachi Pal, Sekhar Sinha et al. (+1 more)

In the interstellar medium, formic acid (HCOOH) plays a significant role in the synthesis of the simplest amino acid, glycine (NH$_{2}$CH$_{2}$COOH). The presence of HCOOH suggests that oxygen-bearing molecules may be directly involved in the chemical and physical evolution of star formation regions, particularly in hot molecular cores. This paper presents the first detection of the rotational emission lines of the $trans$-conformer of HCOOH toward the hot molecular core G358.93$-$0.03 MM1, located in the massive star formation region G358.93$-$0.03. This study employed high-resolution observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 7. The column density and excitation temperature of $t$-HCOOH are determined as $(8.13\pm0.72)\times10^{15}$ cm$^{-2}$ and $120\pm15$ K, respectively. The fractional abundance of $t$-HCOOH relative to H$_{2}$ is $(2.62\pm 0.29)\times 10^{-9}$. The column density ratios of $t$-HCOOH/CH$_{3}$OH and $t$-HCOOH/H$_{2}$CO are $(1.56 \pm 0.12)\times 10^{-2}$ and $(1.16 \pm 0.12)$, respectively. We computed a three-phase warm-up chemical model of HCOOH using the gas-grain chemical code UCLCHEM. We found that the observed and modelled abundances of HCOOH are almost identical, within a factor of 0.89. Based on chemical modelling, we showed that HCOOH may be formed through the reaction between HCO and OH on the grain surface, which is further released in the gas-phase.
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All authors Arijit Manna, Sabyasachi Pal, Sekhar Sinha, Sushanta Kumar Mondal

Earth and Planetary Astrophysics

Comet 73P/Schwassmann-Wachmann 3's Dust Trail as a Source of Pickup Ions

Samuel R. Grant, Geraint H. Jones and Antoinette B. Galvin

73P/Schwassmann-Wachmann 3 is a short-period comet that has undergone multiple fragmentation events in the last few decades. During May-June 2006, while passing near Earth, multiple fragments of comet 73P passed sunward of Sun-Earth Lagrange Point 1, while cometary pickup ions were detected concurrently by instruments on both the ACE and Wind spacecraft, implying the crossing of one or more ion tail. Additionally, during August 2011, a fragment of 73P passed directly sunward of spacecraft STEREO-B. A detection of cometary ions is shown to originate at fragment 73P-AM. Solar wind velocity measurements are used to extrapolate the flow of the solar wind in 3 dimensions and, when compared with the positions of known comets and cometary fragments, estimate the separation between the cometary ion tail and the spacecraft. Using this technique, it is shown that the alignment of the major cometary fragments with the spacecraft was poor for the transport of cometary ions via the solar wind, but the encounter was near enough for immersion in the diffuse ion tail surrounding an extended dust trail within which the nucleus fragments reside. This implies that, at this distance, the extended trail of cometary debris was a significant source of cometary ions in the case of comet 73P.
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Cosmology and Nongalactic Astrophysics

Highly suppressed tensor-to-scalar ratio from a modified Lennard-Jones inflationary potential

Panagiotis G. Stavros, Spyros Basilakos and Emmanuel N. Saridakis

The increasingly stringent observational bounds on primordial gravitational waves strongly constrain inflationary model building, favoring scenarios that predict highly suppressed tensor perturbations. While many viable constructions rely on non-canonical kinetic terms, non-minimal couplings, or modifications of gravity, it remains an open question whether comparably small tensor amplitudes can emerge within a minimal, single-field framework driven solely by potential dynamics. In this work we propose a novel inflationary scenario based on a modified Lennard-Jones potential. Inspired by a well-known interaction potential in molecular physics, the proposed form naturally combines a smooth minimum with an extended flat plateau at large field values. This intrinsic structure supports slow-roll inflation and ensures a graceful exit without introducing additional degrees of freedom. We perform a detailed analysis of the inflationary dynamics and confront the model with current observational constraints. We find that the scalar spectral index is fully consistent with CMB data, while the tensor-to-scalar ratio is predicted to be extremely small, reaching values as low as $r\sim10^{-7}$. Finally, the running of the scalar spectral index is also found to be small, well withing the 1$\sigma$ recent observational bounds from Atacama Cosmology Telescope.
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