adsabs/SciX_UAT_keywords huggingface dataset:
SN2019wxt: An Ultrastripped Supernova Candidate Discovered in the Electromagnetic Follow-up of a Gravitational Wave Trigger

We present optical, radio, and X-ray observations of a rapidly evolving transient SN2019wxt (PS19hgw), discovered during the search for an electromagnetic counterpart to the gravitational-wave (GW) trigger S191213g. Although S191213g was not confirmed as a significant GW event in the off-line analysis of LIGO-Virgo data, SN2019wxt remained an interesting transient due to its peculiar nature. The optical/near-infrared (NIR) light curve of SN2019wxt displayed a double-peaked structure evolving rapidly in a manner analogous to currently known ultrastripped supernovae (USSNe) candidates. This double-peaked structure suggests the presence of an extended envelope around the progenitor, best modeled with two components: (i) early-time shock-cooling emission and (ii) late-time radioactive 56Ni decay. We constrain the ejecta mass of SN2019wxt at M ej ≈ 0.20M ⊙, which indicates a significantly stripped progenitor that was possibly in a binary system. We also followed up SN2019wxt with long-term Chandra and Jansky Very Large Array observations spanning ~260 days. We detected no definitive counterparts at the location of SN2019wxt in these long-term X-ray and radio observational campaigns. We establish the X-ray upper limit at 9.93 × 10-17 erg cm-2 s-1 and detect an excess radio emission from the region of SN2019wxt. However, there is little evidence for SN1993J- or GW170817-like variability of the radio flux over the course of our observations. A substantial host-galaxy contribution to the measured radio flux is likely. The discovery and early-time peak capture of SN2019wxt in optical/NIR observations during EMGW follow-up observations highlight the need for dedicated early, multiband photometric observations to identify USSNe.

Keywords: core-collapse supernovae; supernovae; ejecta; stellar remnants; gravitational wave sources; x-ray sources; x-ray astronomy; radio interferometry; extragalactic radio sources; spectral line identification; transient detection; transient sources
A Cross-correlation Study of High-energy Neutrinos and Tracers of Large-scale Structure

The origin of the bulk of the astrophysical neutrinos detected by the IceCube Observatory remains a mystery. Previous source-finding analyses compared the directions of IceCube events and individual sources in astrophysical catalogs. The source association method is technically challenging when the number of source candidates is much larger than the number of the observed astrophysical neutrinos. We show that in this large source number regime, a two-point cross-correlation analysis of neutrino data and source catalog can instead be used to constrain potential source populations for the high-energy astrophysical neutrinos, and provide spatial evidence for the existence of astrophysical neutrinos. We present an analysis of the cross-correlation of the IceCube 2010-2012 point-source data and a WISE-2MASS galaxy sample. While we find no significant detection of cross-correlation with the publicly available neutrino data set, we show that, when applied to the full IceCube data, which has a longer observation time and higher astrophysical neutrino purity, our method has sufficient statistical power to detect a cross-correlation signal if the neutrino sources trace the large-scale structure of the universe.

Keywords: neutrino astronomy; large-scale structure of the universe
Consistently Simulating a Wide Range of Atmospheric Scenarios for K2-18b with a Flexible Radiative Transfer Module

The atmospheres of small, potentially rocky exoplanets are expected to cover a diverse range in composition and mass. Studying such objects therefore requires flexible and wide-ranging modeling capabilities. We present in this work the essential development steps that lead to our flexible radiative transfer module, REDFOX, and validate REDFOX for the solar system planets Earth, Venus, and Mars, as well as for steam atmospheres. REDFOX is a k-distribution model using the correlated-k approach with the random overlap method for the calculation of opacities used in the δ-two-stream approximation for radiative transfer. Opacity contributions from Rayleigh scattering, UV/visible cross sections, and continua can be added selectively. With the improved capabilities of our new model, we calculate various atmospheric scenarios for K2-18b, a super-Earth/sub-Neptune with ∼8 M⊕ orbiting in the temperate zone around an M star, with recently observed H2O spectral features in the infrared. We model Earth-like, Venus-like, and H2-He primary atmospheres of different solar metallicity and show resulting climates and spectral characteristics compared to observed data. Our results suggest that K2-18b has an H2-He atmosphere with limited amounts of H2O and CH4. Results do not support the possibility of K2-18b having a water reservoir directly exposed to the atmosphere, which would reduce atmospheric scale heights, and with it the amplitudes of spectral features, making the latter inconsistent with the observations. We also performed tests for H2-He atmospheres up to 50 times solar metallicity, all compatible with the observations.

Keywords: radiative transfer simulations; radiative transfer; computational methods; exoplanets; extrasolar rocky planets; exoplanet atmospheres; planetary atmospheres; mini neptunes; super earths
The True Nature of the Brightest Local Triple Stellar Candidates within 100 pc in the Galaxy

We present a study of a sample of bright (V ≤ 10 mag) and close (d ≤ 100 pc) triple-stellar system candidates in the galaxy, consisting of eight systems in total. Our aim is to determine their actual multiplicity and the physical properties of each stellar component in the systems. The sample was analyzed using a complex spectrophotometric technique by Al-Wardat that utilizes ATLAS9 line-blanketed plane-parallel model atmospheres. Based on our analysis, we found that five of the systems (HIP 109951, HIP 105947, HIP 40523, HIP 35733, and HIP 23824) are indeed triples, while the remaining three systems (HIP 9642, HIP 59426, and HIP 101227) are more consistent with being quadruples. We estimated the physical properties of the individual components using the most recent parallax measurements from the GAIA Data Release 3 catalog. We also examined the applicability of the well-established Mass-Luminosity (M-L) relation for individual components of all the stellar systems that have been analyzed by the Al-Wardat technique. We found that generally, the components are in good agreement with the established relationship. This further supports the reliability of the method in determining the physical properties of multiple stellar systems. In addition, we investigated the M-L relation for each order of stellar multiplicity (i.e., binary, triple, and quadruple) by performing linear fitting to the data. It was found that the slopes for each multiplicity are consistent with each other. The relations also seem to shift down in luminosity for a given total mass, as the order of multiplicity increases from binary to quadruple.

Keywords: multiple stars; stellar properties; stellar atmospheres; stellar evolution
Revealing the Double Nucleus of NGC 4490

NGC 4490/85 (UGC 7651/48) or Arp 269 is well known for being one of the closest interacting/merging galactic systems. NGC 4490 has a high star formation rate (SFR) and is surrounded by an enormous H I feature stretching about 60 kpc north and south of the optically visible galaxies. Both the driver for the high SFR in NGC 4490 and the formation mechanism of the H I structure are puzzling aspects of this system. We have used mid-infrared Spitzer data to show that NGC 4490 has a double nucleus morphology. One nucleus is visible in the optical, while the other is only visible at infrared and radio wavelengths. We find the optical nucleus and the potential infrared visible nucleus have similar sizes, masses, and luminosities. Both are comparable in mass and luminosity to other nuclei found in interacting galaxy pairs and much more massive and luminous compared with typical nonnuclear star-forming complexes. We examine possible origin scenarios for the infrared feature, and conclude that it is likely that NGC 4490 is itself a merger remnant, which is now interacting with NGC 4485. This earlier encounter provides both a possible driver for extended star formation in NGC 4490, and multiple pathways for the formation of the extended H I plume.

Keywords: galaxy evolution; galaxy mergers; galaxy structure; galaxy formation
Hard X-Ray Emission from an Activated Flux Rope and Subsequent Evolution of an Eruptive Long-duration Solar Flare

In this paper, we present a comprehensive study of the evolutionary phases of a major M6.6 long duration event with special emphasize on its pre-flare phase. The event occurred in NOAA 12371 on 2015 June 22. A remarkable aspect of the event was an active pre-flare phase lasting for about an hour during which a hot EUV coronal channel was in the build-up stage and displayed cospatial hard X-ray (HXR) emission up to energies of 25 keV. This is the first evidence of the HXR coronal channel. The coronal magnetic field configuration based on nonlinear-force-free-field modeling clearly exhibited a magnetic flux rope (MFR) oriented along the polarity inversion line (PIL) and cospatial with the coronal channel. We observed significant changes in the AR's photospheric magnetic field during an extended period of ≈42 hr in the form of rotation of sunspots, moving magnetic features, and flux cancellation along the PIL. Prior to the flare onset, the MFR underwent a slow rise phase (≈14 km s-1) for ≈12 minutes, which we attribute to the faster build-up and activation of the MFR by tether-cutting reconnection occurring at multiple locations along the MFR itself. The sudden transition in the kinematic evolution of the MFR from the phase of slow to fast rise (≈109 km s-1 with acceleration ≈110 m s-2) precisely divides the pre-flare and impulsive phase of the flare, which points toward the feedback process between the early dynamics of the eruption and the strength of the flare magnetic reconnection.

Keywords: solar active regions; solar x-ray emission; solar active region filaments; solar flares; solar magnetic reconnection
Elevated r-process Enrichment in Gaia Sausage and Sequoia

The Gaia Sausage (GS) and the Sequoia represent the major accretion events that formed the stellar halo of the Milky Way. A detailed chemical study of these main building blocks provides a pristine view of the early steps of the Galaxy's assembly. We present the results of the analysis of the UVES high-resolution spectroscopic observations at the 8.2 m VLT of nine Sausage/Sequoia members selected kinematically using Gaia DR2. We season this set of measurements with archival data from Nissen & Schuster and GALAH DR3 (2020). Here, we focus on the neutron-capture process by analyzing Sr, Y, Ba, and Eu behavior. We detect clear enhancement in Eu abundance ([Eu/Fe] ∼ 0.6-0.7) indicative of large prevalence of the r-process in the stellar n-capture makeup. We are also able to trace the evolution of the heavy element production across a wide range of metallicity. The barium to europium changes from a tight, flat sequence with [Ba/Eu] = -0.7 reflecting dominant contribution from exploding massive stars, to a clear upturn at higher iron abundances, betraying the onset of contamination from asymptotic giant branch (AGB) ejecta. Additionally, we discover two clear sequences in the [Fe/H]-[Ba/Fe] plane likely caused by distinct levels of s-process pollution and mixing within the GS progenitor. * Based on observations made with Very Large Telescope (VLT) at Paranal Observatory, Chile, under program 0104.B-0487(B).

Keywords: population ii stars; galaxy formation; halo stars; milky way stellar halo; nuclear astrophysics; nuclear abundances; galaxy chemical evolution; chemical abundances; dwarf galaxies
Constraining PDS 70b's Formation Mechanism with Multi-hydrogen-emission Observations

We present our Keck/OSIRIS observations of the Paβ emission line (1.282 μm) to investigate accretion mechanisms of PDS 70 planetary system. Our spectral differential imaging reduction to remove the stellar PSF resulted in null detection of Paβ at the locations of PDS 70b and c. The 5σ detection limit of Paβ compared with the theoretical model of Aoyama & Ikoma (2019) indicates the gas velocity onto PDS 70b is smaller than 70 km s-1, which suggests MUSE-based H&agr; studies overestimated the gas velocity and the mass of PDS 70b.

Keywords: exoplanet astronomy
JWST-TST Proper Motions. I. High-precision NIRISS Calibration and Large Magellanic Cloud Kinematics

We develop and disseminate effective point-spread functions and geometric-distortion solutions for high-precision astrometry and photometry with the JWST NIRISS instrument. We correct field dependencies and detector effects, and assess the quality and the temporal stability of the calibrations. As a scientific application and validation, we study the proper motion (PM) kinematics of stars in the JWST calibration field near the Large Magellanic Cloud (LMC) center, comparing to a first-epoch Hubble Space Telescope (HST) archival catalog with a 16 yr baseline. For stars with G ~ 20, the median PM uncertainty is ~13 μas yr-1 (3.1 km s-1), better than Gaia DR3 typically achieves for its very best-measured stars. We kinematically detect the known star cluster OGLE-CL LMC 407, measure its absolute PM for the first time, and show how this differs from other LMC populations. The inferred cluster dispersion sets an upper limit of 24 μas yr-1 (5.6 km s-1) on systematic uncertainties. Red-giant-branch stars have a velocity dispersion of 33.8 ± 0.6 km s-1, while younger blue populations have a narrower velocity distribution, but with a significant kinematical substructure. We discuss how this relates to the larger velocity dispersions inferred from Gaia DR3. These results establish JWST as capable of state-of-the-art astrometry, building on the extensive legacy of HST. This is the first paper in a series by our JWST Telescope Scientist Team, in which we will use Guaranteed Time Observations to study the PM kinematics of various stellar systems in the Local Group.

Keywords: astrometry; proper motions; photometry; star clusters; large magellanic cloud
An Evolutionary Study of Volatile Chemistry in Protoplanetary Disks

The volatile composition of a planet is determined by the inventory of gas and ice in the parent disk. The volatile chemistry in the disk is expected to evolve over time, though this evolution is poorly constrained observationally. We present Atacama Large Millimeter/submillimeter Array observations of C18O, C2H, and the isotopologues H13CN, HC15N, and DCN toward five Class 0/I disk candidates. Combined with a sample of 14 Class II disks presented in Bergner et al., this data set offers a view of volatile chemical evolution over the disk lifetime. Our estimates of C18O abundances are consistent with a rapid depletion of CO in the first ∼0.5-1 Myr of the disk lifetime. We do not see evidence that C2H and HCN formation are enhanced by CO depletion, possibly because the gas is already quite under-abundant in CO. Further CO depletion may actually hinder their production by limiting the gas-phase carbon supply. The embedded sources show several chemical differences compared to the Class II stage, which seem to arise from shielding of radiation by the envelope (impacting C2H formation and HC15N fractionation) and sublimation of ices from infalling material (impacting HCN and C18O abundances). Such chemical differences between Class 0/I and Class II sources may affect the volatile composition of planet-forming material at different stages in the disk lifetime.

Keywords: astrochemistry; protoplanetary disks; protostars; interstellar molecules
JWST CEERS and JADES Active Galaxies at z = 4-7 Violate the Local M •-M ⋆ Relation at >3σ: Implications for Low-mass Black Holes and Seeding Models

JWST is revolutionizing our understanding of the high-z Universe by expanding the black hole horizon, looking farther and to smaller masses, and revealing the stellar light of their hosts. By examining JWST galaxies at z = 4-7 that host Hα-detected black holes, we investigate (i) the high-z M •-M ⋆ relation and (ii) the black hole mass distribution, especially in its low-mass range (M • ≲ 106.5 M ⊙). With a detailed statistical analysis, our findings conclusively reveal a high-z M •-M ⋆ relation that deviates at >3σ confidence level from the local relation. The high-z relation is $\mathrm{log}({M}_{\bullet }/\,{M}_{\odot })=-{2.43}_{-0.83}^{+0.83}+{1.06}_{-0.09}^{+0.09}\mathrm{log}({M}_{\star }/\,{M}_{\odot })$ . Black holes are overmassive by ~10-100× compared to their low-z counterparts in galactic hosts of the same stellar mass. This fact is not due to a selection effect in surveys. Moreover, our analysis predicts the possibility of detecting in high-z JWST surveys 5-15× more black holes with M • ≲ 106.5 M ⊙, and 10-30× more with M • ≲ 108.5 M ⊙, compared to local relation's predictions. The lighter black holes preferentially occupy galaxies with a stellar mass of ~107.5-108 M ⊙. We have yet to detect these sources because (i) they may be inactive (duty cycles 1%-10%), (ii) the host overshines the active galactic nucleus (AGN), or (iii) the AGN is obscured and not immediately recognizable by line diagnostics. A search of low-mass black holes in existing JWST surveys will further test the M •-M ⋆ relation. Current JWST fields represent a treasure trove of black hole systems at z = 4-7; their detection will provide crucial insights into their early evolution and coevolution with their galactic hosts.

Keywords: active galaxies; supermassive black holes; galaxy evolution; surveys; early universe
Modified Newtonian Dynamics as an Alternative to the Planet Nine Hypothesis

A new class of Kuiper Belt objects (KBOs) that lie beyond Neptune with semimajor axes greater than 250 astronomical units show orbital anomalies that have been interpreted as evidence for an undiscovered ninth planet. We show that a modified gravity theory known as modified Newtonian dynamics (MOND) provides an alternative explanation for the anomalies using the well-established secular approximation. We predict that the major axes of the orbits will be aligned with the direction toward the Galactic center and that the orbits cluster in phase space, in agreement with observations of KBOs from the new class. Thus, MOND, which can explain galactic rotation without invoking dark matter, might also be observable in the outer solar system.

Keywords: modified newtonian dynamics; kuiper belt
Systematically Measuring Ultradiffuse Galaxies in H I: Results from the Pilot Survey

We present neutral hydrogen (H I) observations using the Robert C. Byrd Green Bank Telescope (GBT) of 70 optically detected UDG candidates in the Coma region from the Systematically Measuring Ultra-Diffuse Galaxies survey (SMUDGes). We detect H I in 18 targets, confirming nine to be gas-rich UDGs and the remainder to be foreground dwarfs. None of our H I-detected UDGs are Coma Cluster members and all but one are in low-density environments. The H I-detected UDGs are bluer and have more irregular morphologies than the redder, smoother candidates not detected in H I, with the combination of optical color and morphology being a better predictor of gas richness than either parameter alone. There is little visual difference between the gas-rich UDGs and the foreground dwarfs in the SMUDGes imaging, and distances are needed to distinguish between them. We find that the gas richnesses of our H I-confirmed UDGs and those from other samples scale with their effective radii in two stellar mass bins, possibly providing clues to their formation. We attempt to place our UDGs on the baryonic Tully-Fisher relation (BTFR) using optical ellipticities and turbulence-corrected H I line widths to estimate rotation velocities, but the potential systematics associated with fitting smooth Sérsic profiles to clumpy, low-inclination disks of low surface brightness precludes a meaningful analysis of potential BTFR offsets. These observations are a pilot for a large campaign now under way at the GBT to use the H I properties of gas-rich UDGs to quantitatively constrain how these galaxies form and evolve.

Keywords: low surface brightness galaxies; galaxy evolution; galaxy formation; dwarf galaxies
SN 2022jox: An Extraordinarily Ordinary Type II SN with Flash Spectroscopy

We present high-cadence optical and ultraviolet (UV) observations of the Type II supernova (SN), SN 2022jox which exhibits early spectroscopic high-ionization flash features of H I, He II, C IV, and N IV that disappear within the first few days after explosion. SN 2022jox was discovered by the Distance Less Than 40 Mpc survey ∼0.75 day after explosion with follow-up spectra and UV photometry obtained within minutes of discovery. The SN reached a peak brightness of M V ∼ ‑17.3 mag, and has an estimated 56Ni mass of 0.04 M ⊙, typical values for normal Type II SNe. The modeling of the early light curve and the strong flash signatures present in the optical spectra indicate interaction with circumstellar material (CSM) created from a progenitor with a mass-loss rate of $\dot{M}\sim {10}^{-3}{\textstyle {\unicode{x02013}}}{10}^{-2}\text{}{M}_{\odot }\,{{\rm{y}}{\rm{r}}}^{-1}$ . There may also be some indication of late-time CSM interaction in the form of an emission line blueward of Hα seen in spectra around 200 days. The mass-loss rate of SN 2022jox is much higher than the values typically associated with quiescent mass loss from red supergiants, the known progenitors of Type II SNe, but is comparable to inferred values from similar core-collapse SNe with flash features, suggesting an eruptive event or a superwind in the progenitor in the months or years before explosion.

Keywords: type ii supernovae; circumstellar matter
Detection of Accretion Shelves Out to the Virial Radius of a Low-mass Galaxy with JWST

We report the serendipitous discovery of an extended stellar halo surrounding the low-mass galaxy Ark 227 (M * = 5 × 109 M ⊙; d = 35 Mpc) in deep JWST NIRCam imaging from the Blue Jay Survey. The F200W–F444W color provides robust star–galaxy separation, enabling the identification of stars at very low density. By combining resolved stars at large galactocentric distances with diffuse emission from NIRCam and Dragonfly imaging at smaller distances, we trace the surface-brightness and color profiles of this galaxy over the entire extent of its predicted dark matter halo, from 0.1 to 100 kpc. Controlled N-body simulations have predicted that minor mergers create "accretion shelves" in the surface-brightness profile at large radius. We observe such a feature in Ark 227 at 10–20 kpc, which, according to models, could be caused by a merger with total mass ratio 1:10. The metallicity declines over this radial range, further supporting the minor merger scenario. There is tentative evidence of a second shelf at μ V ≈ 35 mag arcsec‑2 extending from 50 to 100 kpc, along with a corresponding drop in metallicity. The stellar mass in this outermost envelope is ≈107 M ⊙. These results suggest that Ark 227 experienced multiple mergers with a spectrum of lower-mass galaxies—a scenario that is broadly consistent with the hierarchical growth of structure in a cold-dark-matter-dominated universe. Finally, we identify an ultra-faint dwarf associated with Ark 227 with M * ≈ 105 M ⊙ and μ V,e = 28.1 mag arcsec‑2, demonstrating that JWST is capable of detecting very-low-mass dwarfs to distances of at least ∼30 Mpc.

Keywords: galaxy stellar halos