Sazuna/UAT_keywords huggingface dataset:
Dust Clumping in Outer Protoplanetary Disks: The Interplay among Four Instabilities. Dust concentration in protoplanetary disks (PPDs) is the first step toward planetesimal formation, a crucial yet highly uncertain stage in planet formation. Although the streaming instability (SI) is widely recognized as a powerful mechanism for planetesimal formation, its properties can be sensitive to the gas dynamical environment. The outer region of PPDs is subject to the vertical shear instability (VSI), which could further induce the Rossby wave instability (RWI) to generate numerous vortices. In this work, we use the multifluid dust module in Athena++ to perform a 3D global simulation with mesh refinement to achieve an adequate domain size and resolution to resolve and accommodate all these instabilities. The VSI mainly governs the overall gas dynamics, which are dominated by the breathing mode due to dust mass loading. The dust strongly settles to the midplane layer, which is much more densely populated with small vortices compared to the dust-free case. Strong dust clumping is observed, which is likely owing to the joint action of the SI and dusty RWI, and those sufficient for planetesimal formation reside only in a small fraction of such vortices. Dust clumping becomes stronger with increasing resolution, and has not yet achieved numerical convergence in our exploration. In addition, we find evidence of the Kelvin–Helmholtz instability operating at certain parts of the dust–gas interface, which may contribute to the temporary destruction of dust clumps.

Keywords: Hydrodynamical simulations, Astrophysical fluid dynamics, Protoplanetary disks, Hydrodynamics
A New Spectral Class of Brown Dwarfs at the Bottom of the IMF in IC 348. In a previous study, we used James Webb Space Telescope (JWST) to identify three new brown dwarfs in the center of a nearby star-forming cluster, IC 348. The faintest object had an estimated mass of 3–4 MJup, making it a contender for the least massive brown dwarf confirmed with spectroscopy. Two of the new brown dwarfs also exhibited absorption features from an unidentified aliphatic hydrocarbon, which were not predicted by atmospheric models and were not previously detected in atmospheres outside of the solar system. We have used JWST to perform a deeper survey for brown dwarfs across a larger field in IC 348. We have identified 39 brown dwarf candidates in NIRCam images and have obtained spectra for 15 of them with Near-Infrared Spectrograph (NIRSpec), nine of which are classified as substellar members of the cluster. The faintest new members have mass estimates of ∼2 MJup, providing a new constraint on the minimum mass of the IMF. Two new members (∼2 and 10 MJup) exhibit large excess emission from circumstellar disks, demonstrating that they harbor the raw materials for planet formation. Finally, eight of the nine new brown dwarfs and one known member that is newly observed with NIRSpec show the aforementioned hydrocarbon features. Among the total of 11 brown dwarfs in IC 348 that have hydrocarbon detections, the features are stronger at fainter magnitudes, indicating that the hydrocarbon is a natural constituent of the atmospheres of the coolest newborn brown dwarfs. We propose a new spectral class "H" that is defined by the presence of the 3.4 μm fundamental band of the hydrocarbon.

Keywords: Brown dwarfs, Initial mass function, Star forming regions, L dwarfs, James Webb Space Telescope, Star formation, Circumstellar disks
High-resolution Observations of a C9.3 White-light Flare and Its Impact on the Solar Photosphere. We present a detailed analysis of a C9.3 white-light flare using high-resolution observations from the New Vacuum Solar Telescope. The flare occurred near the eastern solar limb on 2023 September 11, within NOAA AR 13431, and produced beam electrons with energies just below 50 keV as observed by the Hard X-ray Imager onboard the Advanced Space-based Solar Observatory. Two white-light flare kernels were detected in the TiO band, connected by filamentary brightenings aligned with penumbral fibrils, suggesting a photospheric contribution to the white-light emission. Notably, the impact of the flare on the solar photosphere was characterized by sudden vortex flows and significant amplification of the magnetic field in the white-light flare kernel region. We infer that this impact is driven by the propagation of flare-generated Alfvén wave pulses, which deposited energy into the photosphere. These observations support the potential role of the Alfvén wave mechanism in driving energy transport and heating during white-light flares.

Keywords: Solar activity, Solar active regions, Solar flares
Spectroscopic Observations of Supra-arcade Downflows. Despite their somewhat frequent appearance in extreme-ultraviolet (EUV) imaging of off-limb flares, the origins of supra-arcade downflows (SADs) remain a mystery. Appearing as dark, tendril-like downflows above growing flare loop arcades, SADs themselves are yet to be tied into the standard model of solar flares. The uncertainty of their origin is, in part, due to a lack of spectral observations, with the last published SAD spectral observations dating back to the Solar and Heliospheric Observatory/Solar Ultraviolet Measurements of Emitted Radiation era in 2003. In this work, we present new observations of SADs within an M-class solar flare on 2022 April 2, observed by the Hinode EUV Imaging Spectrometer (EIS) and the NASA Solar Dynamics Observatory. We measure Fe XXIV 192.02 Å Doppler downflows and nonthermal velocities in the low-intensity SAD features, exceeding values measured in the surrounding flare fan. The ratio of temperature-sensitive Fe XXIV 255.11 Å and Fe XXIII 263.41 Å lines also allows the measurement of electron temperature, revealing temperatures within the range of the surrounding flare fan. We compare EIS line-of-sight Doppler velocities with plane-of-sky velocities measured by Atmospheric Imaging Assembly, to construct the 3D velocity profile of four prominent SADs, finding evidence for their divergence above the flare loop arcade—possibly related to the presence of a high-altitude termination shock. Finally, we detect "stealth" SADs, which produce SAD-like Doppler signals, yet with no change in intensity.

Keywords: Solar flares, Solar magnetic reconnection, Solar extreme ultraviolet emission, Solar flare spectra, Solar physics, Active solar corona
The Sulfur Plume in the Horsehead Nebula: New Detections of S<SUB>2</SUB>H, SH<SUP>+</SUP>, and CO<SUP>+</SUP>. Sulfur is essential for life, but its abundance and distribution in the interstellar medium remain uncertain, with over 90% of sulfur undetected in cold molecular clouds. Sulfur allotropes (Sn) have been proposed as possible reservoirs, but the only detected interstellar molecule with a disulfide bond is S2H in the Horsehead Nebula, making the estimation of sulfur chains abundances difficult. Here we present total-power Atacama Large Millimeter/submillimeter Array images of H2S, S2H, SO2, CO+, and SH+ toward the Horsehead Nebula. These observations, with unprecedented sensitivity (rms ∼1.5 mK), provide the first detections of SH+ and CO+ in this region, together with the identification of a new S2H line. The comparison of the spectroscopic images of H2S, S2H, SO2, CO+, and SH+ shows that the S2H emission originates from a warm gas layer adjacent to the photodissociation front. The emission peak of S2H is offset from those of reactive ions such as SH+, CO+, and SO+, suggesting that gas-phase reactions involving SH+ and H2S are not the dominant formation pathway of S2H. Instead, we propose that S2H is desorbed from irradiated grain surfaces by nonthermal processes. The SH+ detection indicates that sulfur is not significantly depleted at the UV-irradiated edge of the molecular cloud, arguing against a major refractory sulfur reservoir in the interior of molecular clouds.

Keywords: Molecular clouds, Chemical abundances, Photodissociation regions, Astrochemistry
Candidate Dark Galaxy-2: Validation and Analysis of an Almost Dark Galaxy in the Perseus Cluster. Candidate Dark Galaxy-2 (CDG-2) is a potential dark galaxy consisting of four globular clusters (GCs) in the Perseus cluster, first identified in D. Li et al. through a sophisticated statistical method. The method searched for overdensities of GCs from a Hubble Space Telescope (HST) survey targeting Perseus. Using the same HST images and new imaging data from the Euclid survey, we report the detection of extremely faint but significant diffuse emission around the four GCs of CDG-2. We thus have exceptionally strong evidence that CDG-2 is a galaxy. This is the first galaxy detected purely through its GC population. Under the conservative assumption that the four GCs make up the entire GC population, preliminary analysis shows that CDG-2 has a total luminosity of LV,gal = 6.2 ± 3.0 × 106 L⊙ and a minimum GC luminosity of LV,GC = 1.03 ± 0.2 × 106 L⊙. Our results indicate that CDG-2 is one of the faintest galaxies having associated GCs, while at least ∼16.6% of its light is contained in its GC population. This ratio is likely to be much higher (∼33%) if CDG-2 has a canonical GC luminosity function (GCLF). In addition, if the previously observed GC-to-halo mass relations apply to CDG-2, it would have a minimum dark matter halo mass fraction of 99.94% to 99.98%. If it has a canonical GCLF, then the dark matter halo mass fraction is ≳99.99%. Therefore, CDG-2 may be the most GC dominated galaxy and potentially one of the most dark matter dominated galaxies ever discovered.

Keywords: Globular star clusters, Perseus Cluster, Low surface brightness galaxies
HDO Ice Detected toward an Isolated Low-mass Protostar with JWST. Water is detected in environments representing every stage of star and solar system formation, but its chemical evolution throughout these stages remains poorly constrained. Deuterium ratios offer a means of probing chemical links between water in different cosmic regions because of their sensitivity to physicochemical conditions. Here, we present the first detection of the 4.1 μm HDO ice feature with JWST toward a low-mass protostar, L1527 IRS, which may eventually grow to a Sun-like mass. We measure an ice HDO/H2O ratio of 4.4 -1.7+3.7  × 10‑3, where the reported error is dominated by uncertainties in continuum definition and ice band strengths. This fraction is similar to the gas HDO/H2O ratios measured in the warm (&gt;100 K) inner cores of other low-mass protostellar envelopes and protoplanetary disks found in comparably isolated star-forming regions. Such a similarity tentatively supports the assumption that water vapor detected in these regions is not significantly altered by gas-phase reactions following ice sublimation. It also supports the hypothesis that pre- and protostellar water ice is largely inherited in a chemically unaltered state by outer protoplanetary disks. However, the fraction is a factor of ∼4–10 times higher than the gas HDO/H2O ratios measured toward comets and low-mass protostars in clustered star-forming regions. This difference may be due to either gas-phase water reprocessing in protostellar envelopes and protoplanetary disks or differences between prestellar conditions of isolated dense cores and the clustered star-forming regions that are more analogous to the environment in which our Sun formed.

Keywords: Isotopic abundances, Infrared spectroscopy, Ice spectroscopy, Astrochemistry, Protostars
Helioseismic Signature of Parker Fragmentation of Magnetic Flux beneath Sunspot Photospheres. Standard local helioseismic diagnostics of large sunspots show the signature of anomalously strong compact scatterers of p-modes within about 1 Mm beneath their photospheres. We applied standard "subjacent-vantage phase-correlation helioseismic holography" to the major sunspot umbra and inner penumbra in NOAA AR12192 as it crossed central solar meridian on 2014 October 23. This diagnostic delivers diffraction-limited maps of the phase delay in the echos of p-mode noise in the 2.5–4.5 mHz acoustic spectrum impinging upward from the underlying solar interior into the sunspot photosphere. What we recognize as the nominal sunspot umbra sends its echos back into the solar interior up to about 1.2 minutes ahead of those reflected from the quiet Sun. In addition to this, we find multiple compact regions approximately 5 Mm in horizontal diameter whose echos are expedited by a further 30 s ahead of the nominal umbral echos. These "strong acoustic scatterers" appear in both umbrae and inner penumbrae, but in a sunspot whose umbra is large enough to accommodate several of them, they show a decided affinity for the boundary separating the two. Standard focus–defocus depth diagnostics pin the anomalies to within about 1 Mm of the base of the photosphere. We propose that the strong acoustic scatterers are the helioseismic signature of fragmentation of magnetic flux beneath sunspot photospheres predicted by E. N. Parker 4.5 decades ago as a crucial accommodation for the stability of sunspot magnetic flux subject to warpage by a precipitous ambient vertical pressure gradient.

Keywords: Helioseismology, Solar physics, Sunspots
Evidence of Gaia Enceladus Experiencing at Least Two Passages around the Milky Way. One of the major recent breakthroughs has been the discovery of the last major merger to happen in the history of the Milky Way. Around 10 Gyr ago, the galaxy Gaia Enceladus with an estimated ∼10% of the Milky Way mass, fell into the potential of our Galaxy, bringing a large amount of stars that can be identified through their unique chemical and kinematic signatures. Simulations have long predicted that a galaxy of this size should experience several passages through the disk of the Milky Way before eventually being fully dispersed. For the first time, we present observational evidence to support this. We identify two subpopulations accreted from Gaia Enceladus: (1) stars that today have large kinematic energy, which originated from the outskirts of Gaia Enceladus and were accreted during early passages; (2) stars with low kinetic energy accreted at later passages, originating from the inner parts of Gaia Enceladus. Through the use of high-precision chemical abundances, crucially including new aluminum measurements, we show that in all observed abundance ratios ([Fe/H], [Al/Fe], [Mg/Fe], and [Mg/Ba]), stars with high energy show evidence of coming from a less chemically evolved outer region of Gaia Enceladus, compared to the stars with low energy. We therefore conclude that Gaia Enceladus experienced several passages before merging with the main body of our Galaxy. This discovery has wide implications for our understanding of this event and consolidates Gaia Enceladus as a benchmark for studying galaxy mergers and hierarchical galaxy formation in extraordinary detail. *Based on observations collected at the European Southern Observatory under ESO program IDs 109.22VP and 110.240W, as obtained from the ESO Science Archive Facility.

Keywords: Local Group, Galaxy chemical evolution, Stellar kinematics, Stellar abundances, Galactic archaeology, Galaxy interactions, Chemical abundances, Milky Way stellar halo, Galaxy mergers, Galaxy evolution, Milky Way Galaxy
The First Detection of Molecular Activity in the Largest Known Oort Cloud Comet: ALMA Imaging of C/2014 UN271 (Bernardinelli─Bernstein) at 16.6 au from the Sun. We report observations of comet C/2014 UN271 (Bernardinelli─Bernstein) carried out on UT 2024 March 8 and 17 at a heliocentric distance (rH) of 16.6 au using the Atacama Large Millimeter/submillimeter Array (ALMA). The CO (J = 2─1) line at 230 GHz was detected along with continuum emission from its dust coma and large (∼140 km) nucleus, revealing the nature of the activity drivers and outgassing kinematics of the largest Oort cloud comet discovered to date. This work presents spectrally integrated flux maps, autocorrelation spectra, production rates, and parent scale lengths for CO and a stringent upper limit for the H2CO production rate. CO outgassing displayed multiple active jets that evolved from one epoch to the next. The continuum emission was compact and spatially unresolved and is consistent with thermal emission from the large nucleus and a tentative detection of a dust coma. Complementary optical observations provided activity context for the ALMA epochs, indicating that UN271 underwent an outburst in late February before returning to a quiescent brightness in mid- to late March. These results represent the first secure detection of molecular activity reported in the literature for C/2014 UN271 and highlight the dynamic nature of this distantly active small world.

Keywords: High resolution spectroscopy, Comae, Molecular spectroscopy, Comets, Radio interferometry, Radio astronomy
Spectropolarimetry of a Nuclear Transient AT2023clx: Revealing the Geometrical Alignment between the Transient Outflow and the Nuclear Dusty Region. AT2023clx, which occurred in NGC 3799 with a low-ionization nuclear emission-line region (LINER), is one of the most nearby nuclear transients classified as a tidal disruption event (TDE). We present three-epoch spectropolarimetric follow-up observations of AT2023clx. We detected two polarization components; one is a constant polarization of ∼1% originating from an aspherical outflow associated with the transient, while the other is a blue-excess polarization toward ∼2% originating from a nuclear dusty environment via light echoes. The polarization angle flipped by 90° between the two epochs, indicating that the outflow direction was perpendicular to the dust plane. Furthermore, the polarized flux might suggest that the nuclear dust favors relatively large grains, potentially offering constraints on its physical properties. Such polarization features—the blue excess and the 90° flip—have never been observed in previous TDE polarization samples, highlighting unique mechanisms behind AT2023clx. We propose possible scenarios: the disruption of a star formed within or captured by a nuclear dusty cloud. Given the LINER nature of NGC3799, the dusty region may possibly be linked to a torus or disk associated with a weak active galactic nucleus (AGN). Furthermore, as a more speculative scenario, the event might have been triggered by AGN-like activity, potentially linked to changing-look AGNs or ambiguous nuclear transients. These findings highlight the power of time-series spectropolarimetry of TDEs, not only in probing the origins of nuclear transients but also in investigating the physical properties of nuclear dust.

Keywords: Tidal disruption, Polarimetry, Galaxy nuclei, Spectropolarimetry
Potential-driven Metal Cycling: JADES Census of Gas-phase Metallicity for Galaxies at 1 &lt; z &lt; 7. The gravitational potential is established as a critical determinant of gas-phase metallicity (12+log(O/H)) in low-redshift galaxies, whereas its influence remains unconfirmed at high redshifts. We investigate the correlation between gas-phase metallicity and effective radius (Re) for a sample of galaxies with redshifts ranging from 1 to 7, drawn from JWST Advanced Deep Extragalactic Survey Data Release 3. We calculate the metallicities using four strong-line methods: N2S2Hα, R23, N2, and O3N2. After taking out the evolution of size, we find that the offsets of the mass─size relation ( ∆logRe ) are significantly negatively correlated with the offset of the mass─metallicity relation ( ∆log(O/H) ) for the four metallicity tracers. Regardless of the metallicity tracer used, we obtain Spearman rank p-values much less than 0.01, rejecting the null hypothesis that the observed correlation is statistically nonsignificant and attributable to random chance. This is also true for galaxies with z &gt; 3, with p-values less than 0.05 for the four metallicity tracers. We for the first time find evidence of size playing a key role in determining gas-phase metallicity toward cosmic dawn, suggesting that the gravitational potential influences galaxies' material-exchange processes with the surrounding environment in the very early Universe.

Keywords: Galaxy chemical evolution, Chemical abundances, Galaxy evolution, Metallicity, High-redshift galaxies
A Tale of Dynamical Instabilities and Giant Impacts in the Exoplanet Radius Valley. The size distribution of planets with radii between 1R⊕ and 4R⊕ peaks near 1.4R⊕ and 2.2R⊕, with a dip around 1.8R⊕—the so-called "radius valley." Recent statistical analyses suggest that planets within this valley (1.5 &lt; R &lt; 2R⊕) tend to have slightly higher orbital eccentricities than those outside it. The origin of this dynamical signature remains unclear. We revisit the "breaking the chains" formation model and propose that late dynamical instabilities—occurring after disk dispersal—may account for the elevated eccentricities observed in the radius valley. Our simulations show that subvalley planets (R &lt; 2R⊕) are generally rocky, while those beyond the valley (R &gt; 2R⊕) are typically water-rich. Rocky planets that undergo strong dynamical instabilities and numerous late giant impacts have their orbits excited and their radii increased, ultimately placing them into the radius valley. In contrast, the larger, water-rich planets just beyond the valley experience weaker instabilities and fewer impacts, resulting in lower eccentricities. This contrast leads to a peak in the eccentricity distribution within the valley. The extent to which planets in the radius valley are dynamically excited depends sensitively on the orbital architecture before the orbital instability. Elevated eccentricities among radius valley planets arise primarily in scenarios that form a sufficiently large number of rocky planets within 100 days (typically ≳5) prior to instability, and that also host external perturbers (P &gt; 100 days), which further amplify the strength of dynamical instabilities.

Keywords: Exoplanet dynamics, Extrasolar rocky planets, Planetary system evolution, Exoplanet systems, Planetary system formation, Exoplanet evolution, Planetesimals, Exoplanet formation, Planetary dynamics, Planet formation
NIRCam Yells at Cloud: JWST MIRI Imaging Can Directly Detect Exoplanets of the Same Temperature, Mass, Age, and Orbital Separation as Saturn and Jupiter. NIRCam and MIRI coronagraphy has successfully demonstrated the ability to directly image young sub-Jupiter-mass and mature gas giant exoplanets. However, these modes struggle to reach the sensitivities needed to find the population of cold giant planets that are similar to our own solar system's giant planets (Teff = 60–125 K, a = 5–30 au). For the first time, we explore the high-contrast imaging capabilities of MIRI imaging rather than coronagraphy. Using data from the JWST GO 6122: Cool Kids on the Block program, which targets nearby (&lt;6 pc) M dwarfs with NIRCam coronagraphy and MIRI imaging, we demonstrate that 21 μm MIRI imaging can detect planets with the same temperature, mass, age, and orbital separations as Saturn and Jupiter. For systems within 3 pc, 21 μm MIRI imaging reaches the sensitivity needed to detect planets colder than Saturn (&lt;95 K). NIRCam coronagraphy can achieve similar results only in the unlikely case that a cold giant planet is cloud-free. Motivated by these compelling findings, we extend our analysis to evaluate the measured performance of MIRI F2100W imaging versus NIRCam F444W coronagraphy to 70 pc and conclude that MIRI imaging offers the advantage for systems within 20 pc. Microlensing surveys predict an occurrence rate as high as one to two low-mass giant exoplanets per star, suggesting that JWST MIRI imaging surveys of nearby systems may be poised to uncover a substantial population. This breakthrough enables a path toward the first direct characterization of cold giant exoplanets that are analogous to the solar system giant planets.

Keywords: High contrast techniques, Extrasolar ice giants, James Webb Space Telescope, Direct imaging, Extrasolar gaseous giant planets