Sazuna/UAT_keywords huggingface dataset:
Breaking Gyrochronology through the Collapse of Coronal Winds. Gyrochronology, a method for dating aged field stars (≳a few Gyr) based on their rotation rate, has recently been shown to fail for many stars older than the Sun. The explanation most often put forth is that a shutdown or mode change in the stellar dynamo leads to a sharp decrease in angular momentum loss in magnetized coronal winds. In this paper, we explore an alternate possibility, namely, a collapse of the wind itself through a reduction of coronal heating. We show that in the low coronal temperature (T0) limit, even at solar-like low rotation rates (Ω) and coronal magnetic field strength (Br0), magnetocentrifugal effects are important and preclude expression of the mass and angular momentum loss rates as power laws of T0 or Ω when T0 drops below ≃1.5 MK. Mass loss is found to scale linearly with power input into the wind at all coronal temperatures. Introducing an ad hoc power-law relationship  T0∝Br0σ  while retaining the "standard" dynamo relationship Br0 ∝ Ω, we show that reproducing the observed break in gyrochronology requires an exponent σ ≳ 1.5, which is associated with a drop by over 3 orders of magnitude in power input into the quiet corona. This appears physically unrealistic, given current observations of chromospheric and coronal nonthermal emission in aged solar-type stars.

Keywords: Solar wind, Solar coronal heating, Stellar magnetic fields, Stellar physics, Stellar winds, Stellar rotation, Stellar coronae
Development of Turbulence in Postshock Regions. Supersonic isothermal turbulence is ubiquitous in the interstellar medium. This work presents high-resolution AREPO hydrodynamical simulations of isolated shocks moving through supersonic turbulence to study the development and evolution of turbulence in the pre- and postshock regions. We find that shocks can amplify turbulent energy in the postshock region while inducing a preferential orientation for the vorticity. This results in the creation of anisotropic turbulence in the postshock region. Turbulent energy and dissipation are also strongly enhanced near the shock front. By applying typical scalings from the cold neutral medium to simulations, we find that shocks moving into turbulence on the scale of superbubbles can generate compressive flows on the order of 103 M⊙ Myr─1. Our results also show good agreement with related studies on turbulent fluctuations generated by shocks in pure fluid mechanics.

Keywords: Shocks, Hydrodynamical simulations, Star formation, Interstellar medium
Reexamining the Power-law Relationship between Global Solar X-Ray Luminosity and Total Unsigned Magnetic Flux. The mechanism heating the solar corona remains unclear but is generally hypothesized to involve magnetic fields. One probe of this hypothesis is a statistical study relating coronal emission to magnetic flux. A. A. Pevtsov et al. conducted such a survey relating X-ray luminosity (LX) to unsigned photospheric magnetic flux (Φm) for a variety of heated plasmas, ranging from solar quiet regions to T Tauri stars. They reported that a power-law relationship,  LX∼Φm1.15 , described the entire collection but found that the subset from solar disk─integrated flux was better fit by a broken power law. Several parameters entering the calculations of LX and Φm have the potential to impact this analysis. The present study uses more recent data to reanalyze the flux─luminosity relationship for the full solar disk and examines its dependence on parameters. We find the most significant effects from two parameters: the cutoff field strength used in computation of Φm and the range of wavelengths defining LX. We find further that lower choices of cutoff yield a broken power law, while an optimal choice yields a single power law and minimizes the fitting residual. The critical cutoff is well above the magnetogram noise level, suggesting that weaker fields may not contribute significantly to the X-ray corona. We also find that LX defined by decreasing wavelength ranges requires an increasing critical cutoff. The resulting power-law indices vary, but all fall around 1.2.

Keywords: Solar spectral irradiance, Solar coronal heating, Solar magnetic fields
Transport of Mirror Mode Structures through Saturn's Magnetopause Reconnection. Magnetopause reconnection plays a significant role in transferring plasma and energy from the solar wind to planetary magnetospheres. Using a Cassini measurement, we reported a magnetopause reconnection at Saturn, identified by the Hall magnetic field and the mixture of magnetosheath electron population and magnetosphere electron population near the X-line. Then, the mirror mode (MM) structures are identified both in the magnetosheath and the magnetosphere. Further analysis suggests that the MM structures were generated in the magnetosheath and traveled across the magnetopause. We infer that MM structures enter the magnetosphere through the magnetopause reconnection. This result provides a possible source for the MM structures in the magnetosphere. These observations and analyses also help to further understand the influence of Saturn's magnetopause reconnection on the magnetosphere dynamics.

Keywords: Space plasmas, Saturn
Transiting Planetary Debris near the Roche Limit of a White Dwarf on a 4.97 hr Orbit—and its Vanishing. We present the discovery of deep, irregular, periodic transits toward the white dwarf ZTF J1944+4557 using follow-up time-series photometry and spectroscopy from Palomar, Keck, McDonald, Perkins, and Lowell observatories. We find a predominant period of 4.9704 hr, consistent with an orbit near the Roche limit of the white dwarf, with individual dips over 30% deep and lasting between 15 and 40 minutes. Similar to the first known white dwarf with transiting debris, WD 1145+017, the transit events are well-defined with prominent out-of-transit phases where the white dwarf appears unobscured. Spectroscopy concurrent with transit photometry reveals that the average Ca K equivalent width remains constant in and out of transit. The broadening observed in several absorption features cannot be reproduced by synthetic photospheric models, suggesting the presence of circumstellar gas. Simultaneous g + r- and g + i-band light curves from the CHIMERA instrument reveal no color dependence to the transit depths, requiring transiting dust grains to have sizes s ≳ 0.2 μm. The transit morphologies appear to be constantly changing at a rate faster than the orbital period. Overall transit activity varies in the system, with transit features completely disappearing during the seven months between our 2023 and 2024 observing seasons and then reappearing in 2025 March, still repeating at 4.9704 hr. Our observations of the complete cessation and resumption of transit activity provide a novel laboratory for constraining the evolution of disrupted debris and processes like disk exhaustion and replenishment timescales at white dwarfs.

Keywords: Transits, White dwarf stars, Tidal disruption, Variable stars, Debris disks
Evolution of Large-scale Structures in the Energetic Neutral Atom Sky Maps in Energy and Solar Activity. The heliospheric energetic neutral atoms (ENAs) are products of charge exchange between solar wind and pick-up ions and interstellar neutral atoms. They are created in different regions of the heliosphere and its boundary region with the interstellar medium, constituting different ENA populations, and they carry information about their parent populations and production processes. Thus, ENAs enable mapping of the global structure of the heliosphere and the processes within and at its edge. Three instruments have provided sky maps of the heliospheric ENAs from 200 eV up to 44 keV over the solar activity cycle. The IBEX-Lo and IBEX-Hi instruments on board the Interstellar Boundary Explorer (IBEX) have provided ENA sky maps from 200 eV to 4.3 keV (central energy) from 2009 throughout Solar Cycle 24. The Ion and Neutral Camera (INCA) on board the Cassini─Huygens mission provided sky maps of the ENAs from 8─44 keV (central energy) on the spacecraft route to and in orbit around Saturn through Solar Cycles 23 and 24. We compare large-scale structures of ENA enhancements present across the sky maps in a wide energy range based on IBEX-Lo, IBEX-Hi, and INCA. They include Ribbon, heliotail lobes, and upwind ENA enhancement. We report on similarities and differences observed, including the evolution of the Ribbon from low to higher energies, and the presence of confined north and south heliotail lobes up to 44 keV.

Keywords: Heliosphere, Particle physics
On the Formation of Star-forming Galaxies Having Anomalously Low-metallicity Regions: The Role of Galaxy Interaction and Circumgalactic Medium/Intergalactic Medium Accretion. Gas accretion from both the circumgalactic medium (CGM)/intergalactic medium (IGM) and interacting companion galaxy can dilute the gas phase metallicity of a galaxy. However, their relative contribution to the chemical evolution of galaxies remains to be quantified. To this end, in this work we study a sample of 510 star-forming galaxies (SFGs) having anomalously low-metallicity (ALM) regions selected from the MaNGA data available in the Data Release 17 from the Sloan Digital Sky Survey. ALM regions are defined as those having gas-phase metallicities that are at least ∼2σ lower than the empirical relation between stellar mass surface density (Σ*) and gas phase metallicity, i.e., the Σ*─Z relation. We find that ALM galaxies have higher star formation rates and H I gas fractions than normal SFGs at fixed M*. Also, ∼25% of the ALM galaxies exhibit tidal features, while the tidal fraction is only ∼12% for normal SFGs, indicating that galaxy interaction is an important factor responsible for the ALM phenomenon. To explore the origin of nontidal ALM galaxies, we compare their morphologies and environments with those of mass-matched normal SFGs. We find that nontidal ALM galaxies tend to have more disk-dominated morphologies and reside in less-dense environment. These findings suggest that cold gas accretion from the CGM/IGM is the primary cause for the ALM phenomenon, while galaxy interaction plays a minor but nonnegligible role.

Keywords: Galaxy abundances, Star formation, Galaxy evolution
Fermi Detection of γ-Rays from the Radio-quiet Seyfert Galaxy NGC 3281. We report the detection of significant γ-ray emission with the Fermi Large Area Telescope from the radio-quiet Seyfert 2 galaxy NGC 3281, with a luminosity of 5.9 (±1.7) × 1041erg s−1 at a significance of 6.22σ (TS = 42.81). The power-law photon index is 2.61 (±0.24), indicative of a soft spectrum. The star formation activity in NGC 3281 is insufficient to explain its γ-ray luminosity based on the empirical relation between the infrared and γ-ray luminosities observed in other sources. The multiwavelength spectrum can be explained as due to inverse Compton scattering by relativistic electrons in the corona or the jet of seed photons from the corona, disk, and torus. The source is Compton thick, and attenuation of GeV photons due to pair production in the corona is nonnegligible (with an optical depth of about 10). The intrinsic γ-ray luminosity is inferred to be 3.4 × 1042 and 2.2 × 1041 erg s−1 for the corona and jet model, respectively. The observed γ-ray and radio luminosities are roughly consistent with the known correlation between the two quantities, among the lowest-luminosity regime. The jet origin is valid only if the radio emission is dominated by the jet.

Keywords: Active galactic nuclei, Gamma-rays, High energy astrophysics
Unions with UNIONS: Using Galaxy─Galaxy Lensing to Probe Galaxy Mergers. We use galaxy─galaxy lensing to investigate how the dark matter (DM) haloes and stellar content of galaxies with 0.012 ≤ z ≤ 0.32 and  10≤log10(M⋆/M⊙)≤12  change as a result of the merger process. To this end, we construct two samples of galaxies obtained from the Ultraviolet Near Infrared Optical Northern Survey, comprising 1623 postmergers and ∼30,000 nonmerging controls, that live in low-density environments to use as our lenses. These samples are weighted to share the same distributions of stellar mass, redshift, and geometric mean distance to a galaxy's three nearest neighbors to ensure differences in the lensing signal are due to the merger process itself. We do not detect a statistically significant difference in the excess surface density profile of postmergers and nonmerging controls with current data. Fitting haloes composed of a pointlike stellar mass component and an extended DM structure described by a Navarro─Frenk─White profile to the lensing measurements yields, for both samples, halo masses of Mhalo ∼ 4 × 1012 M⊙ and a moderately negative correlation between Mhalo and concentration c. This allows us to rule out, at the 95% confidence level, merger-induced starbursts in which more than 60% of the stellar mass is formed in the burst. The application of our methods to upcoming surveys that are able to provide samples ∼10× larger than our current catalog is expected to detect the weak-lensing signatures of mergers and further constrain their properties.

Keywords: Weak gravitational lensing, Galaxy dark matter halos, Galaxy evolution
Evaluating the Limits of Rotation Period Recovery Through Gyrochronology Criteria. Contamination from nearby sources often compromises stellar rotation periods derived from photometric light curves, particularly in data with large pixel scales such as The Transiting Exoplanet Survey Satellite (TESS). This problem is compounded when both the target and contaminant are intrinsically variable, a scenario that challenges deblending algorithms, which often assume constant contaminants. We assess the reliability of rotation period detections using wide binary systems, whose components share a common age and rotational history. By applying gyrochronology constraints, we identify period combinations that yield consistent ages between components, helping to isolate true rotation signals. Simulating blends with degraded Kepler data, our method recovers correct rotation periods with an 88% success rate for periods &lt;12 days, where TESS detections are most reliable. Applying this framework to nearly 300 wide binaries observed by TESS, we find that, despite significant contamination, a subset of pairs shows consistent gyrochronological ages. We establish a practical detection threshold for TESS blended observations, finding that periods shorter than ∼8 days are reliably recovered, while those longer than ∼10 days become significantly more challenging and often remain inconclusive. As expected, rotation periods are more often recovered when the highest-amplitude periodogram peak is linked to the brighter star and the second to the dimmer star. However, many cases deviate from this pattern, indicating it cannot always be assumed. Our results highlight the limitations of standard deblending methods and demonstrate that astrophysical constraints, such as gyrochronology, provide a valuable tool for extracting reliable rotation periods from complex photometric blends.

Keywords: Binary stars, Stellar ages, Stellar astronomy, Stellar physics, Wide binary stars, Stellar rotation
Multifidelity Emulator for Large-scale 21 cm Lightcone Images: A Few-shot Transfer Learning Approach with Generative Adversarial Network. Emulators using machine learning techniques have emerged to efficiently generate mock data matching the large survey volume for upcoming experiments, as an alternative approach to large-scale numerical simulations. However, high-fidelity emulators have become computationally expensive as the simulation volume grows to hundreds of megaparsecs. Here, we present a multifidelity emulation of large-scale 21 cm lightcone images from the epoch of reionization, which is realized by applying the few-shot transfer learning to training generative adversarial networks (GAN) from small-scale to large-scale simulations. Specifically, a GAN emulator is first trained with a huge number of small-scale simulations, and then transfer-learned with only a limited number of large-scale simulations, to emulate large-scale 21 cm lightcone images. We test the precision of our transfer-learned GAN emulator in terms of representative statistics including global 21 cm brightness temperature history, 2D power spectrum, and scattering transform coefficients. We demonstrate that the lightcone images generated by the transfer-learned GAN emulator can reach the percentage level precision in most cases on small scales, and the error on large scales only increases mildly to the level of a few tens of percent. Nevertheless, our multifidelity emulation technique saves a significant portion of computational resources that are mostly consumed for generating training samples for GAN. On estimate, the computational resource by training GAN completely with large-scale simulations would be 1 to 2 orders of magnitude larger than using our multifidelity technique. This implies that our technique allows for emulating high-fidelity, traditionally computationally prohibitive, images in an economic manner.

Keywords: Interdisciplinary astronomy, Reionization, Astrostatistics techniques, Astrostatistics
Starspot Temperature of CoRoT-2 from Multiwavelength Observations with SPARC4. Measuring starspot temperatures is crucial for understanding stellar magnetic activity as it affects stellar brightness variations, influences exoplanet transit measurements, and provides constraints on the physical conditions and energy transport in active regions, offering insights into stellar dynamos. Our goal is to determine the temperature of starspots on the active star CoRoT-2 to enhance our understanding of magnetic activity in young, solar-like stars. Multiwavelength observations were conducted using the Simultaneous Polarimeter and Rapid Camera in Four bands instrument on the 1.6 m telescope at Pico dos Dias Observatory (Brazil), capturing simultaneous transit data in four photometric bands (g, r, i, and z). The ECLIPSE model, combined with Markov Chain Monte Carlo fitting, was used to model spot characteristics during the planetary transit of CoRoT-2 b. The spot intensities were analyzed considering three different methods: the assumption of blackbody emission, the PHOENIX atmospheric model, and multiwavelength fitting assuming the same spot parameters for all wavelengths. Two starspots were detected in the residuals of the light curve, yielding temperature estimates of 5040─5280 K based on the three different methods. These values align more closely with the temperatures of solar penumbrae than with typical umbral temperatures, suggesting relatively moderate magnetic activity. The radius of the spots ranged from 0.34 to 0.61 the planetary radius, or equivalently (38─69) × 106 m, much larger than sunspots. This study provides a method to estimate spot temperatures on active stars using multiband photometry, with results indicating penumbral-like temperatures on CoRoT-2. The methodology enhances precision in starspot temperature estimation, beneficial for studies of stellar activity and exoplanet characterization.

Keywords: Starspots, Stellar activity
Vibrational Spectroscopy of <inline-formula> <mml:math><mml:msubsup><mml:mrow><mml:mi>C</mml:mi></mml:mrow><mml:mrow><mml:mn>60</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math> </inline-formula> and <inline-formula> <mml:math><mml:msubsup><mml:mrow><mml:mi>C</mml:mi></mml:mrow><mml:mrow><mml:mn>70</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math> </inline-formula> in the Mid-infrared: A Comparison with Astronomical Observations. In recent years, astronomical observations, in combination with laboratory spectra and theoretical modeling, have confirmed the presence of C60,  C60+  and C70 across a broad range of astrophysical objects. Despite expectations that  C70+  should also be present in space, its detection is difficult to confirm due to both the lack of laboratory gas-phase IR spectra and challenges in calculating its vibrational spectrum. This study presents gas-phase IR spectroscopy of  C70+  between 6 and 9 μm (1100−1625 cm−1) under astrochemically relevant conditions. The large discrepancies between the experimental and theoretical spectra of  C70+  highlight the challenges of calculating the complex vibrational spectrum of this ion and emphasize the need for laboratory data for comparison to astronomical observations. Additionally, new spectroscopic data of  C60+  are provided, showing the mid-IR spectra of both fullerene cations are dominated by features around 7 μm, where strong emission from planetary nebulae is observed. These results are compared with emission from SMP LMC 56 and Tc 1, providing a foundation to search for  C70+  in space.

Keywords: Infrared spectroscopy, Fullerenes, Molecular spectroscopy, Astrochemistry, Molecular physics, Interstellar medium
Central Massive Black Holes Are Not Ubiquitous in Local Low-mass Galaxies. The black hole occupation fraction (focc) defines the fraction of galaxies that harbor central massive black holes (MBHs), irrespective of their accretion activity level. While it is widely accepted that focc is nearly 100% in local massive galaxies with stellar masses M⋆ ≳ 1010 M⊙, it is not yet clear whether MBHs are ubiquitous in less-massive galaxies. In this work, we present new constraints on focc based on over 20 yr of Chandra imaging data for 1606 galaxies within 50 Mpc. We employ a Bayesian model to simultaneously constrain focc and the specific accretion-rate distribution function, p(λ), where the specific accretion rate is defined as λ = LX/M⋆, where LX is the MBH accretion luminosity in the 2─10 keV range. Notably, we find that p(λ) peaks around  1028ergs−1M⊙−1 ; above this value, p(λ) decreases with increasing λ, following a power law that smoothly connects with the probability distribution of bona fide active galactic nuclei. We also find that the occupation fraction decreases dramatically with decreasing M⋆: in high-mass galaxies (M⋆ ≍ 1011−12 M⊙), the occupation fraction is &gt;93% (a 2σ lower limit), and then declines to  66%−7%+8%  (1σ errors) between M⋆ ≍ 109−10 M⊙, and to  33%−9%+13%  in the dwarf galaxy regime between M⋆ ≍ 108−9 M⊙. Our results have significant implications for the normalization of the MBH mass function over the mass range most relevant for tidal disruption events, extreme mass ratio inspirals, and MBH merger rates that upcoming facilities are poised to explore.

Keywords: Dwarf galaxies, Astrophysical black holes, Galaxy nuclei