adsabs/SciX_UAT_keywords huggingface dataset:
Spectroscopic r-process Abundance Retrieval for Kilonovae. II. Lanthanides in the Inferred Abundance Patterns of Multicomponent Ejecta from the GW170817 Kilonova

In kilonovae, freshly synthesized r-process elements imprint features on optical spectra, as observed in AT2017gfo, the counterpart to the GW170817 binary neutron star merger. However, measuring the r-process compositions of the merger ejecta is computationally challenging. Vieira et al. introduced Spectroscopic r-process Abundance Retrieval for Kilonovae (SPARK), a software tool to infer elemental abundance patterns of the ejecta and associate spectral features with particular species. Previously, we applied SPARK to the 1.4-day spectrum of AT2017gfo and inferred its abundance pattern for the first time, characterized by electron fraction Y e = 0.31, a substantial abundance of strontium, and a dearth of lanthanides and heavier elements. This ejecta is consistent with wind from a remnant hypermassive neutron star and/or accretion disk. We now extend our inference to spectra at 2.4 and 3.4 days and test the need for multicomponent ejecta, where we stratify the ejecta in composition. The ejecta at 1.4 and 2.4 days is described by the same single blue component. At 3.4 days, a new redder component with lower Y e = 0.16 and a significant abundance of lanthanides emerges. This new redder component is consistent with dynamical ejecta and/or neutron-rich ejecta from a magnetized accretion disk. As expected from photometric modeling, this component emerges as the ejecta expands, the photosphere recedes, and the earlier bluer component dims. At 3.4 days, we find an ensemble of lanthanides, with the presence of cerium most concrete. This presence of lanthanides has important implications for the contribution of kilonovae to the r-process abundances observed in the Universe.

Keywords: nuclear abundances; r-process; radiative transfer simulations; spectral line identification
Radial Evolution of the Near-Sun Solar Wind: Parker Solar Probe Observations

A statistical study of the radial evolution of the solar wind within 0.3 au is shown in this Letter based on Parker Solar Probe observations. We show the radial distribution of the main solar wind parameters, including the solar wind speed V sw, magnetic field ∣B∣, the number density of electrons N e , protons N p , and α particles N α , and the temperature of protons T p and α particles T α . The power-law fitting results of these parameters in the near-Sun solar wind are compared with previous radial models. We also show the radial distribution of the angle between the magnetic field B , solar wind V sw, and radial vector R . In the solar wind within 0.3 au, ${\theta }_{{\mathrm{BV}}_{\mathrm{sw}}}$ , and θ BR mainly concentrate around 135°, and ${\theta }_{{\mathrm{RV}}_{\mathrm{sw}}}$ almost concentrates in the region less than 20°. Furthermore, we also present the radial distribution of the relative values between the solar wind parameters, including the electric neutrality estimation ((2 × N α + N p )/N e ≃ 1 within 0.2 au), relative number density ratio (N α /N p ≃ 0.02 in slow solar wind and N α /N p ≃ 0.04 in faster solar wind), relative temperature ratio (T α /T p decreases with the increase of heliocentric distance and its decay rate is larger in faster solar wind), and differential speed (both V α ‑ V p and (V α ‑ V p )/V A are larger in the faster solar wind and decrease as heliocentric distance increases).

Keywords: solar wind; solar evolution; space plasmas
Signatures of a Distant Planet on the Inclination Distribution of the Detached Kuiper Belt

A distant, massive planet in the outer solar system has recently been proposed to explain some observed features of extreme trans-Neptunian objects (TNOs). Here we use N-body simulations of the formation of the Kuiper Belt and Oort cloud as well as a survey simulator to compare models of the solar system with and without a ninth planet to one another as well as to observations. The main mechanism for TNOs to be deposited into the distant (a > 50 au), detached (q > 40 au) region of the Kuiper Belt in the eight-planet model is Kozai-Lidov oscillation of objects in mean motion resonances (MMR) with Neptune. This effect does not deposit low-inclination (i ≲ 20°) objects into this region. However, we find that the ninth planet generates a group of distant, detached TNOs at low inclinations that are not present in the eight-planet model. This disparity between the eight-planet and nine-planet models could provide a strong constraint on a possible planet nine with further detections of TNOs in the distant, detached region of the Kuiper Belt.

Keywords: kuiper belt; resonant kuiper belt objects; trans-neptunian objects
Active Galactic Nucleus Variability in the Age of Rubin

Over the next 10 years, the Vera C. Rubin Observatory (Rubin) will observe ~10 million active galactic nuclei (AGNs) with a regular and high cadence. During this time, the intensities of most of these AGNs will fluctuate stochastically. Here, we explore the prospects to quantify precisely these fluctuations with Rubin measurements of AGN light curves. To do so, we suppose that each light curve is described by a damped random walk with a given fluctuation amplitude and correlation time. Theoretical arguments and some current measurements suggest that the correlation timescale and fluctuation amplitude for each AGN may be correlated with other observables. We use an expected-information analysis to calculate the precision with which these parameters will be inferred from the measured light curves. We find that the measurements will be so precise as to allow the AGNs to be separated into up to ~10 different correlation-timescale bins. We then show that if the correlation time varies as some power of the luminosity, the normalization and power-law index of that relation will be determined to ${ \mathcal O }({10}^{-4} \% )$ . These results suggest that with Rubin, precisely measured variability parameters will take their place alongside spectroscopy in the detailed characterization of individual AGNs and in the study of AGN population statistics. Analogous analyses will be enabled by other time-domain projects, such as CMB-S4.

Keywords: active galactic nuclei; high energy astrophysics; astrostatistics; optical astronomy; time domain astronomy; optical telescopes
Magnetic Field of Molecular Gas Measured with the Velocity Gradient Technique. II. Curved Magnetic Field in kpc-scale Bubble of NGC 628

We report the detection of the ordered alignment between the magnetic field and kpc-scale bubbles in the nearby spiral galaxy, NGC 628. Applying the Velocity Gradient Technique on CO spectroscopic data from the ALMA-PHANGS, the magnetic field of NGC 628 is measured at the scale of 191 pc (∼4″). The large-scale magnetic field is oriented parallel to the spiral arms and curves around the galactic bubble structures in the mid-infrared emission observed by the James Webb Space Telescope. A total of 21 bubble structures have been identified at the edges of spiral arms with scales over 300 pc, which includes two kpc-scale structures. These bubbles are caused by supernova remnants and prolonged star formation and are similar to the outflow chimneys found in neutral hydrogen in galactic disks. At the edge of the bubbles, the shocks traced by the O III emission present a curved magnetic field that parallels the bubble's shell. The magnetic field follows the bubble expansion and binds the gas in the shell to trigger further star formation. By analyzing the larger sample of 1694 bubbles, we found a distinct radial-size distribution of bubbles in NGC 628 indicating the star formation history in the galaxy.

Keywords: extragalactic magnetic fields; interstellar medium; interstellar magnetic fields
Shallow Transits-Deep Learning. II. Identify Individual Exoplanetary Transits in Red Noise using Deep Learning

In a previous paper, we introduced a deep learning neural network that should be able to detect the existence of very shallow periodic planetary transits in the presence of red noise. The network in that feasibility study would not provide any further details about the detected transits. The current paper completes this missing part. We present a neural network that tags samples that were obtained during transits. This is essentially similar to the task of identifying the semantic context of each pixel in an image-an important task in computer vision, called "semantic segmentation," which is often performed by deep neural networks. The neural network we present makes use of novel deep learning concepts such as U-Nets, Generative Adversarial Networks, and adversarial loss. The resulting segmentation should allow further studies of the light curves that are tagged as containing transits. This approach toward the detection and study of very shallow transits is bound to play a significant role in future space-based transit surveys such as PLATO, which are specifically aimed to detect those extremely difficult cases of long-period shallow transits. Our segmentation network also adds to the growing toolbox of deep learning approaches that are being increasingly used in the study of exoplanets; but, so far mainly for vetting transits, rather than their initial detection.

Keywords: exoplanet detection methods; transit photometry; neural networks
Dependencies of Mantle Shock Heating in Pairwise Accretion

The final assembly of planets involves mutual collisions of large similar-sized protoplanets ("giant impacts"), setting the stage for modern geologic and atmospheric processes. However, thermodynamic consequences of impacts in diverse (exo)planetary systems/models are poorly understood. Impact velocity in "self-stirred" systems is proportional to the mass of the colliding bodies (vimp ∝ M1/3), providing a predictable transition to supersonic collisions in roughly Mars-sized bodies. In contrast, nearby larger planets, or migrating gas giants, stir impact velocities, producing supersonic collisions between smaller protoplanets and shifting outcomes to disruption and nonaccretion. Our particle hydrocode simulations suggest that thermodynamic processing can be enhanced in merging collisions more common to calmer dynamical systems due to post-impact processes that scale with the mass of the accreting remnant. Thus, impact heating can involve some contribution from energy scaling, a departure from pure velocity-scaling in cratering scenarios. Consequently, planetary thermal history depends intimately on the initial mass distribution assumptions and dynamical conditions of formation scenarios. In even the gentlest pairwise accretions, sufficiently large bodies feature debris fields dominated by melt and vapor. This likely plays a critical role in the observed diversity of exoplanet systems and certain debris disks. Furthermore, we suggest solar system formation models that involve self-stirred dynamics or only one to a few giant impacts between larger-than-Mars-sized bodies (e.g., "pebble accretion") are more congruent with the "missing mantle problem" for the main belt, as we demonstrate debris would be predominantly vapor and thus less efficiently retained due to solar radiation pressure effects.

Keywords: impact phenomena; hydrodynamical simulations; planet formation; exoplanet formation; exoplanet atmospheres; shocks
The Effect of Interior Heat Flux on the Atmospheric Circulation of Hot and Ultra-hot Jupiters

Many hot and ultra-hot Jupiters have inflated radii, implying that their interiors retain significant entropy from formation. These hot interiors lead to an enhanced internal heat flux that impinges upon the atmosphere from below. In this work, we study the effect of this hot interior on the atmospheric circulation and thermal structure of hot and ultra-hot Jupiters. To do so, we incorporate the population-level predictions from evolutionary models of hot and ultra-hot Jupiters as input for a suite of general circulation models (GCMs) of their atmospheric circulation with varying semimajor axis and surface gravity. We conduct simulations with and without a hot interior, and find that there are significant local differences in temperature of up to hundreds of Kelvin and in wind speeds of hundreds of meters per second or more across the observable atmosphere. These differences persist throughout the parameter regime studied, and are dependent on surface gravity through the impact on photosphere pressure. These results imply that the internal evolution and atmospheric thermal structure and dynamics of hot and ultra-hot Jupiters are coupled. As a result, a joint approach including both evolutionary models and GCMs may be required to make robust predictions for the atmospheric circulation of hot and ultra-hot Jupiters.

Keywords: hot jupiters; exoplanet atmospheres; planetary atmospheres; exoplanet structure; exoplanet atmospheric dynamics
Cosmic Web-halo Connection between Twin Universes

Both simulation and observational data have shown that the spin and shape of dark matter halos are correlated with their nearby large-scale environment. As structure formation on different scales is strongly coupled, it is tricky to disentangle the formation of a halo from that of the large-scale environment, making it difficult to infer which is the driving force behind the correlation between halo spin/shape and the large-scale structure. In this paper, we use N-body simulations to produce twin universes that share the same initial conditions on small scales but that are different on large scales. This is achieved by changing the random seeds for the phase of those k modes smaller than a given scale in the initial conditions. In this way, we are able to disentangle the formation of halo and large-scale structure, making it possible to investigate how halo spin and shape correspond to the change of environment on large scales. We identify matching halo pairs in the twin simulations as those sharing the maximum number of identical particles within them. Using these matched halo pairs, we study the cross match of halo spin and the correlation with the large-scale structure. It is found that when the large-scale environment changes (eigenvector) between the twin simulations, the halo spin has to rotate accordingly, although not significantly, to maintain the universal correlation seen in each simulation. Our results suggest that the large-scale structure is the main factor to drive the correlation between halo properties and their environment.

Keywords: large-scale structure of the universe; cold dark matter; computational methods; astrostatistics; galaxy evolution
Volume Density Structure of the Central Molecular Zone NGC 253 through ALCHEMI Excitation Analysis

We present a spatially resolved excitation analysis for the central molecular zone (CMZ) of the starburst galaxy NGC 253 using the data from the Atacama Large Millimeter/submillimeter Array Comprehensive High-resolution Extragalactic Molecular Inventory, whereby we explore parameters distinguishing NGC 253 from the quiescent Milky Way's Galactic center (GC). Non-LTE analyses employing a hierarchical Bayesian framework are applied to Band 3-7 transitions from nine molecular species to delineate the position-position-velocity distributions of column density ( ${N}_{{{\rm{H}}}_{2}}$ ), volume density ( ${n}_{{{\rm{H}}}_{2}}$ ), and temperature (T kin) at 27 pc resolution. Two distinct components are detected: a low-density component with $({n}_{{{\rm{H}}}_{2}},{T}_{\mathrm{kin}})\sim ({10}^{3.3}\ {\mathrm{cm}}^{-3},85\ {\rm{K}})$ and a high-density component with $({n}_{{{\rm{H}}}_{2}},{T}_{\mathrm{kin}})\,\sim ({10}^{4.4}\ {\mathrm{cm}}^{-3},110\ {\rm{K}})$ , separated at ${n}_{{{\rm{H}}}_{2}}\sim {10}^{3.8}\ {\mathrm{cm}}^{-3}$ . NGC 253 has ~10 times the high-density gas mass and ~3 times the dense-gas mass fraction of the GC. These properties are consistent with their HCN/CO ratio but cannot alone explain the factor of ~30 difference in their star formation efficiencies (SFEs), contradicting the dense-gas mass to star formation rate scaling law. The ${n}_{{{\rm{H}}}_{2}}$ histogram toward NGC 253 exhibits a shallow declining slope up to ${n}_{{{\rm{H}}}_{2}}\sim {10}^{6}\ {\mathrm{cm}}^{-3}$ , while that of the GC steeply drops in ${n}_{{{\rm{H}}}_{2}}\gtrsim {10}^{4.5}\ {\mathrm{cm}}^{-3}$ and vanishes at 105 cm-3. Their dense-gas mass fraction ratio becomes consistent with their SFEs when the threshold ${n}_{{{\rm{H}}}_{2}}$ for the dense gas is taken at ~104.2-4.6 cm-3. The rich abundance of gas above this density range in the NGC 253 CMZ, or its scarcity in the GC, is likely to be the critical difference characterizing the contrasting star formation in the centers of the two galaxies.

Keywords: star formation; giant molecular clouds; starburst galaxies; galactic center; interstellar medium
The POKEMON Speckle Survey of Nearby M Dwarfs. II. Observations of 1125 Targets

Stellar multiplicity is correlated with many stellar properties, yet multiplicity measurements have proven difficult for the M dwarfs-the most common type of star in our galaxy-due to their faintness and the fact that a reasonably complete inventory of later M dwarfs did not exist until recently. We have therefore carried out the Pervasive Overview of "Kompanions" of Every M dwarf in Our Neighborhood (POKEMON) survey, which made use of the Differential Speckle Survey Instrument on the 4.3 m Lowell Discovery Telescope, along with the NN-EXPLORE Exoplanet Stellar Speckle Imager on the 3.5 m WIYN telescope. The POKEMON sample is volume limited from M0V through M9V out to 15 pc, with additional brighter targets at larger distances. In total, 1125 targets were observed. New discoveries were presented in the first paper in the series. In this second paper in the series, we present all detected companions, gauge our astrometric and photometric precision, and compare our filtered and filterless speckle observations. We find that the majority (58.9%) of the companions we detect in our speckle images are not resolved in Gaia, demonstrating the need for high-resolution imaging in addition to long-term astrometric monitoring. Additionally, we find that the majority (73.2%) of simulated stellar companions would be detectable by our speckle observations. Specifically within 100 au, we find that 70.3% of simulated companions are recovered. Finally, we discuss future directions of the POKEMON survey.

Keywords: m dwarf stars; binary stars; high angular resolution; low mass stars; solar neighborhood
Identifying SuperWASP Detected Candidate Variables with TESS

Using Transiting Exoplanet Survey Satellite light curves, I have identified more than 1200 new pulsating variable stars from the SuperWASP-detected but unclassified candidate variables. These include a variety of types of pulsating variable stars, including 125 δ Scuti stars, 235 γ Doradus stars, 302 RR Lyrae stars, and 450+ Mira/SR/IR/LPV variables. I also identified 1300+ rotating variable stars. Additionally, I revealed that 16 of 91 newly identified eclipsing binary systems have pulsating components. These findings will help us to better understand the properties and evolution of pulsating variable stars. *Dedicated to my wife Jingyun Zhang.

Keywords: pulsating variable stars; delta scuti variable stars; gamma doradus variable stars; rr lyrae variable stars; mira variable stars; eclipsing binary stars
Gamma-Ray Spectral Properties of the Galactic Globular Clusters: Constraint on the Number of Millisecond Pulsars

We study the γ-ray spectra of 30 globular clusters (GCs) thus far detected with the Fermi Gamma-ray Space Telescope. Presuming that γ-ray emission of a GC comes from millisecond pulsars (MSPs) contained within the GC, a model that generates spectra for the GCs is built based on the γ-ray properties of the detected MSP sample. We fit the GCs' spectra with the model, and for 27 of them, their emission can be explained as arising from MSPs. The spectra of the other three, NGC 7078, 2MS-GC01, and Terzan 1, cannot be fit with our model, indicating that MSPs' emission should not be the dominant one in the first two and the third one has a unique hard spectrum. We also investigate six nearby GCs that have relatively high encounter rates compared to the comparison cases. The candidate spectrum of NGC 6656 can be fit with that of one MSP, supporting its possible association with the γ-ray source at its position. The five others do not have detectable γ-ray emission. Their spectral upper limits set limits of ≤1 MSPs in them, consistent with the numbers of radio MSPs found in them. The estimated numbers of MSPs in the γ-ray GCs generally match well those reported for radio pulsars. Our studies of the γ-ray GCs and the comparison nearby GCs indicate that the encounter rate should not be the only factor determining the number of γ-ray MSPs a GC contains.

Keywords: globular star clusters; gamma-ray sources; millisecond pulsars
Spatio-temporal Variation of Bright Ephemeral Features on Titan's North Pole

We identify and document the instances of bright ephemeral features (BEF)—bright areas that appear, disappear, and shift from flyby to flyby on Titan's north pole, using the Cassini Visual and Infrared Mapping Spectrometer data set, thereby developing a sense of their spatial distribution and temporal frequency. We find that BEFs have differing geographic location and spatial extents. However, they have similar observation geometries and orders of surface area coverage and are mostly accompanied by specular reflections. We find the BEFs to represent either broad specular reflection off of a recently wetted surface on the north pole of Titan or a near-surface fog—both owing to probable recent rainfalls. Our surface model constrains the surface roughness to be of 9°-15° indicating the approximate vertical relief of the region to be that of cobbles. We also find that within less than two Titan days the BEF (if on the surface) might infiltrate into the subsurface. We hypothesize the parts of BEFs that extend into the maria to be precipitation fog.

Keywords: saturnian satellites
Simulating Metal Mixing of Both Common and Rare Enrichment Sources in a Low-mass Dwarf Galaxy

One-zone models constructed to match observed stellar abundance patterns have been used extensively to constrain the sites of nucleosynthesis with sophisticated libraries of stellar evolution and stellar yields. The metal mixing included in these models is usually highly simplified, although it is likely to be a significant driver of abundance evolution. In this work we use high-resolution hydrodynamics simulations to investigate how metals from individual enrichment events with varying source energies Eej mix throughout the multiphase interstellar medium (ISM) of a low-mass (Mgas = 2 × 106 M⊙), low-metallicity, isolated dwarf galaxy. These events correspond to the characteristic energies of both common and exotic astrophysical sites of nucleosynthesis, including asymptotic giant branch winds (Eej ∼ 1046 erg), neutron star-neutron star mergers (Eej ∼ 1049 erg), supernovae (Eej ∼ 1051 erg), and hypernovae (Eej ∼ 1052 erg). We find the mixing timescales for individual enrichment sources in our dwarf galaxy to be long (100 Myr-1 Gyr), with a clear trend of increasing homogeneity for the more energetic events. Given these timescales, we conclude that the spatial distribution and frequency of events are important drivers of abundance homogeneity on large scales; rare, low-Eej events should be characterized by particularly broad abundance distributions. The source energy Eej also correlates with the fraction of metals ejected in galactic winds, ranging anywhere from 60% at the lowest energy to 95% for hypernovae. We conclude by examining how the radial position, local ISM density, and global star formation rate influence these results.

Keywords: galaxy chemical evolution; dwarf galaxies; chemical enrichment; hydrodynamics