adsabs/SciX_UAT_keywords huggingface dataset:
High-resolution Chemical Abundances of the Nyx Stream

Nyx is a nearby, prograde, and high-eccentricity stellar stream physically contained in the thick disk, but its origin is unknown. Nyx could be the remnant of a disrupted dwarf galaxy, in which case the associated dark matter substructure could affect terrestrial dark matter direct-detection experiments. Alternatively, Nyx could be a signature of the Milky Way's disk formation and evolution. To determine the origin of Nyx, we obtained high-resolution spectroscopy of 34 Nyx stars using Keck/HIRES and Magellan/MIKE. A differential chemical abundance analysis shows that most Nyx stars reside in a metal-rich ([Fe/H] > -1) high-α component that is chemically indistinguishable from the thick disk. This rules out the originally suggested scenario that Nyx is the remnant of a single massive dwarf galaxy merger. However, we also identify 5 substantially more metal-poor stars ([Fe/H] ~ -2.0) whose chemical abundances are similar to those of the metal-weak thick disk. It remains unclear how stars that are chemically identical to the thick disk can be on such prograde, high-eccentricity orbits. We suggest two most likely scenarios: that Nyx is the result of an early minor dwarf galaxy merger, or that it is a record of the early spin-up of the Milky Way disk-although neither perfectly reproduces the chemodynamic observations. The most likely formation scenarios suggest that future spectroscopic surveys should find Nyx-like structures outside of the solar neighborhood.

Keywords: stellar abundances; stellar kinematics; milky way formation; dark matter
Constraining the Metallicities of Damped Lyα Systems Using Extinction Curves

In this paper, we present a new method to constrain the metallicities of high-redshift damped Lyα (DLA) absorbers using observed extinction curves. This is the first time such an approach is employed to constrain the metallicities of extragalactic absorbers. To demonstrate our method, we use the spectra of 13 quasars and one gamma-ray burst (GRB) with DLA absorbers detected along their sightlines. By using the Kramers-Kronig (KK) relation, which relates the wavelength-integrated extinction to the total volume occupied by dust per hydrogen nucleon, we set some robust lower limits on the metallicity of the DLAs. The resulting lower limits are all consistent with the DLA metallicities from the literature. The GRB extinction curve exhibits a very strong 2175 Å extinction bump. We try to constrain the metallicity of the GRB DLA by modeling the GRB extinction curve using dust models with two (graphite and silicates) and three (polycyclic aromatic hydrocarbon, hydrogenated amorphous carbon, and silicates) dust components. The two-component model results in a metallicity of Z ∼ -0.45, while the three-component model gives Z ∼ -0.50. However, the lower limit from the KK approach for this DLA is Z ≥ -0.60. Modeling a large sample of extinction curves with a 2175 Å extinction bump and measured DLA metallicities would allow a thorough comparison between the KK and the model-dependent approach. In cases where the precise measurement of the metallicity of a DLA is not possible (e.g., due to the saturation of important absorption lines), the approach presented in this paper can be used to constrain the metallicity.

Keywords: extinction; ultraviolet extinction; galaxies; gamma-ray bursts; quasar absorption line spectroscopy
Recovering the Star Formation Histories of Recently Quenched Galaxies: The Impact of Model and Prior Choices

Accurate models of the star formation histories (SFHs) of recently quenched galaxies can provide constraints on when and how galaxies shut down their star formation. The recent development of nonparametric SFH models promises the flexibility required to make these measurements. However, model and prior choices significantly affect derived SFHs, particularly for post-starburst galaxies (PSBs), which have sharp changes in their recent SFH. In this paper, we create mock PSBs, then use the Prospector SED fitting software to test how well four different SFH models recover key properties. We find that a two-component parametric model performs well for our simple mock galaxies, but is sensitive to model mismatches. The fixed- and flexible-bin nonparametric models included in Prospector are able to rapidly quench a major burst of star formation, but systematically underestimate the post-burst age by up to 200 Myr. We develop a custom SFH model that allows for additional flexibility in the recent SFH. Our flexible nonparametric model is able to constrain post-burst ages with no significant offset and just ~90 Myr of scatter. Our results suggest that while standard nonparametric models are able to recover first-order quantities of the SFH (mass, SFR, average age), accurately recovering higher-order quantities (burst fraction, quenching time) requires careful consideration of model flexibility. These mock recovery tests are a critical part of future SFH studies. Finally, we show that our new, public SFH model is able to accurately recover the properties of mock star-forming and quiescent galaxies and is suitable for broader use in the SED fitting community. https://github.com/bd-j/prospector

Keywords: galaxy evolution; galaxy formation; galaxy ages; post-starburst galaxies; galaxy quenching
The Coma Cluster at LOw Frequency ARray Frequencies. I. Insights into Particle Acceleration Mechanisms in the Radio Bridge

Radio synchrotron emission from the bridges of low-density gas connecting galaxy clusters and groups is a challenge for particle acceleration processes. In this work, we analyze the Coma radio bridge using new LOw Frequency ARray (LOFAR) observations at 144 MHz. LOFAR detects the bridge and its substructures with unprecedented sensitivity and resolution. We found that the radio emission peaks on the NGC 4839 group. Toward the halo, in front of the NGC 4839 group, the radio brightness decreases and streams of radio emission connect the NGC 4839 group to the radio relic. Using X-ray observations, we found that thermal and non-thermal plasma are moderately correlated with a sublinear scaling. We use archival radio data at 326 MHz to constrain the spectral index in the bridge, and quantify the distribution of particles and magnetic field at different frequencies. We found that the spectrum is steeper than -1.4 ± 0.2, and that the emission is clumpier at 326 MHz than at 144 MHz. Using cosmological simulations and a simplified approach to compute particle acceleration, we derive under which conditions turbulent acceleration of mildly relativistic electrons generate the radio emission in the bridge. Assuming that the initial energy ratio of the seed electrons is 3 · 10-4 with respect to the thermal gas, we are able to reproduce the observed luminosity. Our results suggest that the seed electrons released by radio galaxies in the bridge and the turbulence generated by the motion of gas and galaxies are essential to producing the radio emission.

Keywords: galaxy clusters; coma cluster; intracluster medium; intergalactic medium; radio continuum emission; extragalactic magnetic fields; plasma astrophysics
Constraining the Densities of the Three Kepler-289 Planets with Transit Timing Variations

Kepler-289 is a three-planet system containing two sub-Neptunes and one cool giant planet orbiting a young, Sun-like star. All three planets exhibit transit timing variations (TTVs), with both adjacent planet pairs having orbital periods close to the 2:1 orbital resonance. We observe two transits of Kepler-289c with the Wide-field InfraRed Camera on the 200″ Hale Telescope at Palomar Observatory, using diffuser-assisted photometry to achieve space-like photometric precision from the ground. These new transit observations extend the original four-year Kepler TTV baseline by an additional 7.5 yr. We rereduce the archival Kepler data with an improved stellar activity correction and carry out a joint fit with the Palomar data to constrain the transit shapes and derive updated transit times. We then model the TTVs to determine the masses of the three planets and constrain their densities and bulk compositions. Our new analysis improves on previous mass and density constraints by a factor of two or more for all three planets, with the innermost planet showing the largest improvement. Our updated atmospheric mass fractions for the inner two planets indicate that they have hydrogen-rich envelopes, consistent with their location on the upper side of the radius valley. We also constrain the heavy element composition of the outer Saturn-mass planet, Kepler-289c, for the first time, finding that it contains 30.5 ± 6.9 M ⊕ of metals. We use dust evolution models to show that Kepler-289c must have formed beyond 1 au, and likely beyond 3 au, and then migrated inward.

Keywords: infrared photometry; transit timing variation method; transits
Plasma Heating and Nanoflare Caused by Slow-mode Wave in a Coronal Loop

We present a detailed analysis of a reflecting intensity perturbation in a large coronal loop that appeared as a sloshing oscillation and lasted for at least one and a half periods. The perturbation is initiated by a microflare at one footpoint of the loop, propagates along the loop, and is eventually reflected at the remote footpoint where significant brightenings are observed in all of the Atmospheric Imaging Assembly extreme-ultraviolet channels. This unique observation provides us with the opportunity to better understand not only the thermal properties and damping mechanisms of the sloshing oscillation but also the energy transfer at the remote footpoint. Based on differential emission measures analysis and the technique of coronal seismology, we find that (1) the calculated local sound speed is consistent with the observed propagation speed of the perturbation during the oscillation, which is suggestive of a slow magnetoacoustic wave; (2) thermal conduction is the major damping mechanism of the wave but an additional damping mechanism such as anomalous enhancement of compressive viscosity or wave leakage is also required to account for the rapid decay of the observed waves; (3) the wave produced a nanoflare at the remote footpoint, with a peak thermal energy of ~1024-1025 erg. This work provides a consistent picture of the magnetoacoustic wave propagation and reflection in a coronal loop, and reports the first solid evidence of a wave-induced nanoflare. The results reveal new clues for further simulation studies and may help with solving the coronal heating problem.

Keywords: solar flares; solar coronal waves; solar coronal heating; solar coronal loops; solar extreme ultraviolet emission
Independent Core Rotation in Massive Filaments in Orion

We present high-angular-resolution Atacama Large Millimeter/submillimeter Array images of N2H+ (1-0) that have been combined with those from the Nobeyama telescope toward the Orion Molecular Cloud (OMC)-2 and OMC-3 filamentary regions. The filaments (with typical widths of ∼0.1 pc) and dense cores are resolved. The measured 2D velocity gradients of cores are between 1.3 and 16.7 km s-1 pc-1, corresponding to a specific angular momentum (J/M) between 0.0012 and 0.016 pc km s-1. With respect to the core size R, the specific angular momentum follows a power law J/M ∝ R1.52±0.14. The ratio (β) between the rotational energy and gravitational energy ranges from 0.00041 to 0.094, indicating insignificant support from rotation against gravitational collapse. We further focus on the alignment between the cores' rotational axes, which is defined to be perpendicular to the direction of the velocity gradient (θG), and the direction of elongation of filaments (θf) in this massive star-forming region. The distribution of the angle between θf and θG was found to be random, I.e., the cores' rotational axes have no discernible correlation with the elongation of their hosting filament. This implies that, in terms of angular momentum, the cores have evolved to be dynamically independent from their natal filaments.

Keywords: interstellar medium; interstellar filaments; interstellar clouds; interstellar dynamics; interstellar molecules
Impact of Self-shielding Minihalos on the Lyα Forest at High Redshift

Dense gas in minihalos with masses of 106‑108 M ⊙ can shield themselves from reionization for ∼100 Myr after being exposed to the UV background. These self-shielded systems, often unresolved in cosmological simulations, can introduce strong absorption in quasar spectra. This paper is the first systematic study on the impact of these systems on the Lyα forest. We first derive the H I column density profile of photoevaporating minihalos by conducting 1D radiation–hydrodynamics simulations. We utilize these results to estimate the Lyα opacity from minihalos in a large-scale simulation that cannot resolve self-shielding. When the ionization rate of the background radiation is 0.03 × 10‑12 s‑1, as expected near the end of reionization at z ∼ 5.5, we find that the incidence rate of damped Lyα absorbers increases by a factor of ∼2‑4 compared to at z = 4.5. The Lyα flux is, on average, suppressed by ∼3% of its mean due to minihalos. The absorption features enhance the 1D power spectrum up to ∼5% at k ∼ 0.1 h Mpc‑1 (or 10‑3 km‑1 s), which is comparable to the enhancement caused by inhomogeneous reionization. The flux is particularly suppressed in the vicinity of large halos along the line-of-sight direction at separations of up to 10 h ‑1 Mpc at r ⊥ ≲ 2 h ‑1 Mpc. However, these effects become much smaller for higher ionizing rates (≳0.3 × 10‑12 s‑1) expected in the post-reionization Universe. Our findings highlight the need to consider minihalo absorption when interpreting the Lyα forest at z ≳ 5.5. Moreover, the sensitivity of these quantities to the ionizing background intensity can be exploited to constrain the intensity itself.

Keywords: lyman alpha forest; reionization; radiative transfer simulations; hydrodynamical simulations
Does Intelligence Matter? An Interdisciplinary Guidance Statement on the Search for Extraterrestrial Intersections

Attendees at the 2023 Penn State SETI Symposium participated in a workshop series entitled "The Moral Relevance of Intelligence in the Search for Extraterrestrial Life." This breakout series focused interdisciplinary dialogs on the role intelligence plays in the search for extraterrestrials. A moderated inquiry took place over the course of two days, resulting in a Guiding Statement on Extraterrestrial Intersections in support of interdisciplinary, ethics-informed engagement and research related to the search for extraterrestrials.

Keywords: search for extraterrestrial intelligence; technosignatures; biosignatures
ZTFJ0038+2030: A Long-period Eclipsing White Dwarf and a Substellar Companion

In a search for eclipsing white dwarfs using the Zwicky Transient Facility lightcurves, we identified a deep eclipsing white dwarf with an orbital period of 10.4 hr and an undetected substellar companion. We obtained high-speed photometry and radial velocity measurements to characterize the system. The white dwarf has a mass of 0.50 ± 0.02 M⊙ and a temperature of 10,900 ± 200 K. The companion has a mass of 0.059 ± 0.004 M⊙ and is a brown dwarf. It has a radius of 0.0783 ± 0.0013 R⊙, and is one of the physically smallest transiting brown dwarfs known and likely old, ≳8 Gyr. The ZTF discovery efficiency of substellar objects transiting white dwarfs is limited by the number of epochs and as ZTF continues to collect data we expect to find more of these systems.

Keywords: white dwarf stars; eclipsing binary stars; brown dwarfs; extrasolar gaseous giant planets
Kozai Migration Naturally Explains the White Dwarf Planet WD1856 b

The Jovian-sized object WD 1856 b transits a white dwarf (WD) in a compact 1.4 day orbit. Unlikely to have endured stellar evolution in its current orbit, WD 1856 b is thought to have migrated from much wider separations. Because the WD is old, and a member of a well-characterized hierarchical multiple, the well-known Kozai mechanism provides an effective migration channel for WD 1856 b. The tidal dissipation that makes this mechanism possible is sensitive to the mass of WD 1856 b, which remains unconstrained by observations. Moreover, the lack of tides in the star allows us to directly connect the current semimajor axis to the pre-migration one, from which we can infer the initial conditions of the system. By further requiring that planets must survive all previous phases of stellar evolution before migrating, we are able to constrain the main-sequence semimajor axis of WD 1856 b to have been ∼2.5 au, and its mass to be ≃0.7-3MJ. These mass limits put WD 1856 b firmly within the planet category. Furthermore, our inferred values imply that WD 1856 b was born a typical gas giant. We further estimate the occurrence rate of Kozai-migrated planets around WDs to be ${ \mathcal O }({10}^{-3}-{10}^{-4})$ , suggesting that WD 1856 b is the only one in the TESS sample, but implying ${ \mathcal O }({10}^{2})$ future detections by the LSST survey. In a sense, WD 1856 b was an ordinary Jovian planet that underwent an extraordinary dynamical history.

Keywords: binary stars; white dwarf stars; exoplanet dynamics; exoplanet evolution; multiple stars
Earth's Polar Night Boundary Layer as an Analog for Dark Side Inversions on Synchronously Rotating Terrestrial Exoplanets

A key factor in determining the potential habitability of synchronously rotating planets is the strength of the atmospheric boundary layer inversion between the dark side surface and the free atmosphere. Here we analyze data obtained from polar night measurements at the South Pole and Alert Canada, which are the closest analogs on Earth to conditions on the dark sides of synchronously rotating exoplanets without and with a maritime influence, respectively. On Earth, such inversions rarely exceed 30 K in strength, because of the effect of turbulent mixing induced by phenomena such as so-called "mesoscale slope winds," which have horizontal scales of 10-100 s of km, suggesting a similar constraint to near-surface dark side inversions. We discuss the sensitivity of inversion strength to factors such as orography and the global-scale circulation, and compare them to a simulation of the planet Proxima Centauri b. Our results demonstrate the importance of comparisons with Earth data in exoplanet research, and highlight the need for further studies of the exoplanet atmospheric collapse problem using mesoscale and eddy-resolving models.

Keywords: exoplanets; habitable planets; atmospheric science; exoplanet atmospheres; exoplanet atmospheric variability; planetary boundary layers; planetary atmospheres; exoplanet surface variability; land-atmosphere interactions; exoplanet surface characteristics; exoplanet atmospheric composition
Saddle-shaped Solar Flare Arcades

Arcades of flare loops form as a consequence of magnetic reconnection powering solar flares and eruptions. We analyze the morphology and evolution of flare arcades that formed during five well-known eruptive flares. We show that the arcades have a common saddle-like shape. The saddles occur despite the fact that the flares were of different classes (C to X), occurred in different magnetic environments, and were observed in various projections. The saddles are related to the presence of longer, relatively higher, and inclined flare loops, consistently observed at the ends of the arcades, which we term "cantles." Our observations indicate that cantles typically join straight portions of flare ribbons with hooked extensions of the conjugate ribbons. The origin of the cantles is investigated in stereoscopic observations of the 2011 May 9 eruptive flare carried out by the Atmospheric Imaging Assembly and Extreme Ultraviolet Imager. The mutual separation of the instruments led to ideal observational conditions allowing for simultaneous analysis of the evolving cantle and the underlying ribbon hook. Based on our analysis we suggest that the formation of one of the cantles can be explained by magnetic reconnection between the erupting structure and its overlying arcades. We propose that the morphology of flare arcades can provide information about the reconnection geometries in which the individual flare loops originate.

Keywords: solar coronal mass ejections; solar magnetic reconnection; solar extreme ultraviolet emission; solar flares; solar filament eruptions
Spectroscopic Constraints on the Mid-infrared Attenuation Curve. I. Attenuation Model Using Polycyclic Aromatic Hydrocarbon Emission

We introduce a novel model to spectroscopically constrain the mid-infrared (MIR) extinction/attenuation curve from 3–17 μm, using polycyclic aromatic hydrocarbon (PAH) emission drawn from an AKARI–Spitzer extragalactic cross-archival data set. Currently proposed MIR extinction curves vary significantly in their slopes toward the near-infrared, and the variation in the strengths and shapes of the 9.7 μm and 18 μm silicate absorption features make MIR spectral modeling and interpretation challenging, particularly for heavily obscured galaxies. By adopting the basic premise that PAH bands have relatively consistent intrinsic ratios within dusty starbursting galaxies, we can, for the first time, empirically determine the overall shape of the MIR attenuation curve by measuring the differential attenuation at specific PAH wavelengths. Our attenuation model shows PAH emission in most (ultra)luminous infrared galaxies is unambiguously subjected to attenuation, and we find strong evidence that PAH bands undergo differential attenuation as obscuration increases. Compared to preexisting results, the MIR attenuation curve derived from the model favors relatively gray continuum absorption from 3–8 μm and silicate features with intermediate strength at 9.7 μm but with stronger than typical 18 μm opacity.

Keywords: interstellar dust extinction; polycyclic aromatic hydrocarbons; starburst galaxies; luminous infrared galaxies; ultraluminous infrared galaxies
2023 DZ2 Planetary Defense Campaign

We present the results of a fourth planetary defense exercise, focused this time on the small near-Earth asteroid (NEA) 2023 DZ2 and conducted during its close approach to the Earth in 2023 March. The International Asteroid Warning Network (IAWN), with support from NASA's Planetary Defense Coordination Office (PDCO), has been coordinating planetary defense observational campaigns since 2017 to test the operational readiness of the global planetary defense capabilities. The last campaign focused on the NEA Apophis, and an outcome of that exercise was the need for a short burst campaign to replicate a real-life near-Earth object impact hazard scenario. The goal of the 2023 DZ2 campaign was to characterize the small NEA as a potential impactor and exercise the planetary defense system including observations, hypothetical risk assessment and risk prediction, and hazard communication with a short notice of just 24 hr. The entire campaign lasted about 10 days. The campaign team was divided into several working groups based on the characterization method: photometry, spectroscopy, thermal IR photometry and optical polarimetry, radar, and risk assessment. Science results from the campaign show that 2023 DZ2 has a rotation period of 6.2745 ± 0.0030 minutes; visible wavelength color photometry/spectroscopy/polarimetry and near-IR spectroscopy all point to an E-type taxonomic classification with surface composition analogous to aubrite meteorites; and radar observations show that the object has a diameter of 30 ± 10 m, consistent with the high albedo (0.49) derived from polarimetric and thermal IR observations.

Keywords: asteroids; achondrites; near-earth objects; small solar system bodies; close encounters