adsabs/SciX_UAT_keywords huggingface dataset:
The Decline and Fall of the Youngest Planetary Nebula

The Stingray Nebula, a.k.a. Hen3-1357, appeared for the first time in 1990 when bright nebular lines and radio emission that had not been observed before were unexpectedly discovered. In the ensuing years, the nebula faded precipitously. We report changes in shape and large decreases in its nebular emission-line fluxes based on well-calibrated images obtained by the Hubble Space Telescope in 1996 and 2016. Hen3-1357 is now a "recombination nebula."

Keywords: post-asymptotic giant branch stars; planetary nebulae; ionization
Interacting Kilonovae: Long-lasting Electromagnetic Counterparts to Binary Mergers in the Accretion Disks of Active Galactic Nuclei

We investigate the dynamics and electromagnetic (EM) signatures of neutron star-neutron star (NS-NS) or neutron star-black hole (NS-BH) merger ejecta that occur in the accretion disk of an active galactic nucleus (AGN). We find that the interaction between ejecta and disk gas leads to important effects on the dynamics and radiation. We show five stages of the ejecta dynamics: gravitational slowing down, coasting, Sedov-Taylor deceleration in the disk, reacceleration after the breakout from the disk surface, and momentum-conserved snowplow phase. Meanwhile, the radiation from the ejecta is so bright that its typical peak luminosity reaches a few times 1043-1044 erg s-1. Since most of the radiation energy has converted from the kinetic energy of merger ejecta, we call such an explosive phenomenon an interacting kilonova (IKN). It should be emphasized that IKNe are very promising, bright EM counterparts to NS-NS/BH-NS merger events in AGN disks. The bright peak luminosity and long rising time (i.e., 10 to 20 days in UV bands, 30 to 50 days in optical bands, and 100 days to hundreds of days in IR bands) allow most survey telescopes to have ample time to detect an IKN. However, the peak brightness, peak time, and evolution pattern of the light curve of an IKN are similar to a superluminous supernova in a galactic nucleus and a tidal disruption event making it difficult to distinguish between them. But it also suggests that IKNe might have been present in recorded AGN transients.

Keywords: active galactic nuclei; gamma-ray bursts; gravitational wave sources; high energy astrophysics; neutron stars
Detecting Multiplanetary Systems with Gravitational Microlensing and the Roman Space Telescope

It is plausible that most of the Stars in the Milky Way Galaxy, like the Sun, consist of planetary systems, instead of a single planet. Out of the estimately discovered 3980 planet-hosting stars, about 860 of them are known to be multiplanetary systems (as of 2023 June). Gravitational microlensing, which is the magnification in the light of a source star, due to a single or several lenses, has proven to be one of the most useful astrophysical phenomena with many applications. Until now, many extrasolar planets (exoplanets) have been discovered through binary microlensing, where the lens system consists of a star with one planet. In this paper, we discuss and explore the detection of multiplanetary systems that host two exoplanets via microlensing. This is done through the analysis and modeling of possible triple-lens configurations (one star and two planets) of a microlensing event. Furthermore, we examine different magnifications and caustic areas of the second planet, by comparing the magnification maps of triple and binary models in different settings. We also discuss the possibility of detecting the corresponding light curves of such planetary systems with the future implementation of the Nancy Grace Roman (Roman) Space Telescope and its Galactic Time Domain survey.

Keywords: exoplanet detection methods; gravitational microlensing; gravitational microlensing exoplanet detection
Arrival Directions of Cosmic Rays above 32 EeV from Phase One of the Pierre Auger Observatory

A promising energy range to look for angular correlations between cosmic rays of extragalactic origin and their sources is at the highest energies, above a few tens of EeV (1 EeV ≡ 1018 eV). Despite the flux of these particles being extremely low, the area of ~3000 km2 covered at the Pierre Auger Observatory, and the 17 yr data-taking period of the Phase 1 of its operations, have enabled us to measure the arrival directions of more than 2600 ultra-high-energy cosmic rays above 32 EeV. We publish this data set, the largest available at such energies from an integrated exposure of 122,000 km2 sr yr, and search it for anisotropies over the 3.4π steradians covered with the Observatory. Evidence for a deviation in excess of isotropy at intermediate angular scales, with ~15° Gaussian spread or ~25° top-hat radius, is obtained at the 4σ significance level for cosmic-ray energies above ~40 EeV.

Keywords: ultra-high-energy cosmic radiation; cosmic ray astronomy; clustering; active galaxies; starburst galaxies
The Interplay between the Initial Mass Function and Star Formation Efficiency through Radiative Feedback at High Stellar Surface Densities

The observed rest-UV luminosity function at cosmic dawn (z ∼ 8–14) measured by JWST revealed an excess of UV-luminous galaxies relative to many prelaunch theoretical predictions. A high star formation efficiency (SFE) and a top-heavy initial mass function (IMF) are among the mechanisms proposed for explaining this excess. Although a top-heavy IMF has been proposed for its ability to increase the light-to-mass ratio (ΨUV), the resulting enhanced radiative pressure from young stars could decrease the SFE, potentially driving galaxy luminosities back down. In this Letter, we use idealized radiation hydrodynamic simulations of star cluster formation to explore the effects of a top-heavy IMF on the SFE of clouds typical of the high-pressure conditions found at these redshifts. We find that the SFE in star clusters with solar-neighborhood-like dust abundance decreases with increasingly top-heavy IMFs—by ∼20% for an increase of a factor of 4 in ΨUV and by 50% for a factor of ∼10 in ΨUV. However, we find that an expected decrease in the dust-to-gas ratio (∼0.01 × solar) at these redshifts can completely compensate for the enhanced light output. This leads to a (cloud-scale; ∼10 pc) SFE that is ≳70% even for a factor of 10 increase in ΨUV, implying that highly efficient star formation is unavoidable for high surface density and low-metallicity conditions. Our results suggest that a top-heavy IMF, if present, likely coexists with efficient star formation in these galaxies.

Keywords: stellar feedback; radiative transfer simulations; star formation; gas-to-dust ratio; young star clusters; initial mass function; starburst galaxies
Properties of Interplanetary Fast Shocks Close to the Martian Environment

Magnetic field and plasma measurements from the Mars Atmosphere and Volatile EvolutioN mission in orbit around Mars are analyzed for interplanetary fast shock properties and drivers from 2014 October to 2018 November. We identified 52 fast shocks, including 39 fast forward (FF) shocks and 13 fast reverse (FR) shocks. Most (79%) of the FF shocks are driven by stream interaction regions (SIRs) with only a few cases being driven by interplanetary coronal mass ejections, and all of the FR shocks are driven by SIRs. A total of 92% of the identified shocks are quasi-perpendicular shocks. On average, the shock strengths of SIR-driven forward and reverse shocks are comparable, and they are greater than that of ICME-driven forward shocks. The shock strengths show no systematic dependence on the shock locations relative to the Martian bow shock. We find no evidence that the shock shapes are affected by Mars and its bow shock as an obstacle in the propagating medium. The results can help us understand the nature of interplanetary shocks propagating in different environments.

Keywords: heliosphere; solar wind; shocks; mars; interplanetary shocks
Coagulation-Fragmentation Equilibrium for Charged Dust: Abundance of Submicron Grains Increases Dramatically in Protoplanetary Disks

Dust coagulation in protoplanetary disks is not straightforward and is subject to several slowdown mechanisms, such as bouncing, fragmentation, and radial drift to the star. Furthermore, dust grains in UV-shielded disk regions are negatively charged due to collisions with the surrounding electrons and ions, which leads to their electrostatic repulsion. For typical disk conditions, the relative velocities between micron-sized grains are small, and their collisions are strongly affected by the repulsion. On the other hand, collisions between pebble-sized grains can be too energetic, leading to grain fragmentation. The aim of the present paper is to study the combined effect of the electrostatic and fragmentation barriers on dust evolution. We numerically solve the Smoluchowski coagulation-fragmentation equation for grains whose charging occurs under conditions typical for the inner disk regions, where thermal ionization operates. We find that dust fragmentation efficiently resupplies the population of small grains under the electrostatic barrier. As a result, the equilibrium abundance of submicron grains is enhanced by several orders of magnitude compared to the case of neutral dust. For some conditions with fragmentation velocities of ~1 m s-1, macroscopic grains are completely destroyed.

Keywords: protoplanetary disks; circumstellar dust; interstellar dust; young stellar objects; circumstellar disks; dust physics
The Global Structure of the Milky Way's Stellar Halo Based on the Orbits of Local Metal-poor Stars

We analyze the global structure of the Milky Way (MW)'s stellar halo, including its dominant subcomponent, Gaia-Sausage-Enceladus (GSE). The method for reconstructing the global distribution of this old stellar component is to employ the superposition of the orbits covering the large MW's space, where each of the orbit-weighting factors is assigned following the probability that the star is located at its currently observed position. The selected local, metal-poor sample with [Fe/H] <-1, using Gaia Early Data Release 3 and Sloan Digital Sky Survey Data Release 16, shows that the global shape of the halo is systematically rounder at all radii in more metal-poor ranges, such that an axial ratio, q, is nearly 1 for [Fe/H] <-2.2 and ~0.7 for -1.4 < [Fe/H] < -1.0. It is also found that a halo in the relatively metal-rich range of [Fe/H] >-1.8 actually shows a boxy/peanut-like shape, suggesting a major merger event. The distribution of azimuthal velocities shows a disk-like flattened structure at -1.4 < [Fe/H] < -1.0, which is thought to be the metal-weak thick disk. For the subsample of stars showing GSE-like kinematics, at [Fe/H] >-1.8, its global density distribution has an axis ratio of 0.9, which is more spherical than the general halo sample, and an outer ridge at r ~ 20 kpc. This spherical shape is consistent with the features of accreted halo components, and the ridge suggests that the orbit of GSE's progenitor had an apocenter of ~20 kpc. Implications for the formation of the stellar halo are also presented.

Keywords: milky way stellar halo
High-precision Atmospheric Characterization of a Y Dwarf with JWST NIRSpec G395H Spectroscopy: Isotopologue, C/O Ratio, Metallicity, and the Abundances of Six Molecular Species

The launch of the James Webb Space Telescope (JWST) marks a pivotal moment for precise atmospheric characterization of Y dwarfs, the coldest brown dwarf spectral type. In this study, we leverage moderate spectral resolution observations (R ∼ 2700) with the G395H grating of the Near-Infrared Spectrograph (NIRSpec) on board JWST to characterize the nearby (9.9 pc) Y dwarf WISEPA J182831.08+265037.8. With the NIRSpec G395H 2.88–5.12 μm spectrum, we measure the abundances of CO, CO2, CH4, H2S, NH3, and H2O, which are the major carbon-, nitrogen-, oxygen-, and sulfur-bearing species in the atmosphere. Based on the retrieved volume mixing ratios with the atmospheric retrieval framework CHIMERA, we report that the C/O ratio is 0.45 ± 0.01, close to the solar C/O value of 0.458, and the metallicity is +0.30 ± 0.02 dex. Comparison between the retrieval results and the forward modeling results suggests that the model bias for C/O and metallicity could be as high as 0.03 and 0.97 dex, respectively. We also report a lower limit of the 12CO/13CO ratio of >40, being consistent with the nominal solar value of 90. Our results highlight the potential for JWST to measure the C/O ratios down to percent-level precision and characterize isotopologues of cold planetary atmospheres similar to WISE 1828.

Keywords: brown dwarfs; y dwarfs; exoplanet atmospheres; planetary atmospheres
The Luminosity Phase Space of Galactic and Extragalactic X-Ray Transients Out to Intermediate Redshifts

We present a detailed compilation and analysis of the X-ray phase space of low- to intermediate-redshift (0 ≤ z ≤ 1) transients that consolidates observed light curves (and theory where necessary) for a large variety of classes of transient/variable phenomena in the 0.3-10 keV energy band. We include gamma-ray burst afterglows, supernovae, supernova shock breakouts and shocks interacting with the environment, tidal disruption events and active galactic nuclei, fast blue optical transients, cataclysmic variables, magnetar flares/outbursts and fast radio bursts, cool stellar flares, X-ray binary outbursts, and ultraluminous X-ray sources. Our overarching goal is to offer a comprehensive resource for the examination of these ephemeral events, extending the X-ray duration-luminosity phase space (DLPS) to show luminosity evolution. We use existing observations (both targeted and serendipitous) to characterize the behavior of various transient/variable populations. Contextualizing transient signals in the larger DLPS serves two primary purposes: to identify areas of interest (i.e., regions in the parameter space where one would expect detections, but in which observations have historically been lacking), and to provide initial qualitative guidance in classifying newly discovered transient signals. We find that while the most luminous (largely extragalactic) and least luminous (largely Galactic) part of the phase space is well populated at t > 0.1 days, intermediate-luminosity phenomena (L X = 1034-1042 erg s-1) represent a gap in the phase space. We thus identify L X = 1034-1042 erg s-1 and t = 10-4 to 0.1 days as a key discovery phase space in transient X-ray astronomy.

Keywords: x-ray astronomy; x-ray telescopes; x-ray transient sources; high energy astrophysics; transient sources; time domain astronomy
PicSat's Enduring Legacy. Probing the Flight of a Small Astronomical Satellite

Observation of planetary transits and other cutting-edge scientific missions can take advantage of affordable nanosatellites to probe interesting stellar targets. PicSat, a CubeSat dedicated to observing the Beta Pictoris star system, was designed to provide high-precision star pointing, a critical requirement for planetary transit detection. PicSat's Attitude Determination and Control System, responsible for delivering high-accuracy spacecraft pointing, requires dedicated development based on dynamic simulators. This paper presents a dynamic attitude and orbit propagation simulator for CubeSats in low Earth orbit, as well as for its de-tumbling mode. Validation has been performed through PicSat's in-flight data. High-precision dynamic models have been obtained for both attitude and orbit. Such models are well suited to the different mission phases, from spacecraft design to data exploitation. It is, therefore, a crucial tool to minimize the chance of failure of both the platform and the payload, especially in satellites such as PicSat, whose pointing depends on both. PicSat left an enduring legacy: its platform data allow us to obtain flight models that will be valuable for future missions.

Keywords: artificial satellites; astronomical instrumentation
Turbulent Magnetic Field Amplification by the Interaction of a Shock Wave and Inhomogeneous Medium

Magnetic fields of the order of 100 μG observed in young supernova remnants cannot be amplified by shock compression alone. To investigate the amplification caused by a turbulent dynamo, we perform three-dimensional MHD simulations of the interaction between a shock wave and an inhomogeneous density distribution with a shallow spectrum in the preshock medium. The postshock turbulence is mainly driven by the strongest preshock density contrast and follows the Kolmogorov scaling. The resulting turbulence amplifies the postshock magnetic field. The time evolution of the magnetic fields agrees with the prediction of the nonlinear turbulent dynamo theory of Xu & Lazarian. When the initially weak magnetic field is perpendicular to the shock normal, the maximum amplification of the field's strength reaches a factor of ≈200, which is twice as large as that for a parallel shock. We find that the perpendicular shock exhibits a smaller turbulent Alfvén Mach number in the vicinity of the shock front than the parallel shock. However, the strongest magnetic field has a low volume filling factor and is limited by the turbulent energy due to the reconnection diffusion taking place in a turbulent and magnetized fluid. The magnetic field strength averaged along the z-axis is reduced by a factor ≳10. We decompose the turbulent velocity and magnetic field into solenoidal and compressive modes. The solenoidal mode is dominant and evolves to follow the Kolmogorov scaling, even though the preshock density distribution has a shallow spectrum. When the preshock density distribution has a Kolmogorov spectrum, the turbulent velocity's compressive component increases.

Keywords: interstellar dynamics; interstellar magnetic fields; interstellar medium; supernova remnants; magnetohydrodynamics
The Late-time Afterglow Evolution of Long Gamma-Ray Bursts GRB 160625B and GRB 160509A

We present post-jet-break Hubble Space Telescope, Very Large Array, and Chandra observations of the afterglow of the long γ-ray bursts GRB 160625B (between 69 and 209 days) and GRB 160509A (between 35 and 80 days). We calculate the post-jet-break decline rates of the light curves and find the afterglow of GRB 160625B is inconsistent with a simple t-3/4 steepening over the break, expected from the geometric effect of the jet edge entering our line of sight. However, the favored optical post-break decline ( ${f}_{\nu }\propto {t}^{-1.96\pm 0.07}$ ) is also inconsistent with the fν ∝ t-p decline (where p ≈ 2.3 from the pre-break light curve), which is expected from exponential lateral expansion of the jet; perhaps suggesting lateral expansion that only affects a fraction of the jet. The post-break decline of GRB 160509A is consistent with both the t-3/4 steepening and with fν ∝ t-p. We also use BOXFIT to fit afterglow models to both light curves and find both to be energetically consistent with a millisecond magnetar central engine, but the magnetar parameters need to be extreme (I.e., E ∼ 3 × 1052 erg). Finally, the late-time radio light curves of both afterglows are not reproduced well by BOXFIT and are inconsistent with predictions from the standard jet model; instead, both are well represented by a single power-law decline (roughly fν ∝ t-1) with no breaks. This requires a highly chromatic jet break ( ${t}_{j,\mathrm{radio}}\gt 10\times {t}_{j,\mathrm{optical}}$ ) and possibly a two-component jet for both bursts.

Keywords: gamma-ray bursts; relativistic jets
Large Amplitude Switchback Turbulence: Possible Magnetic Velocity Alignment Structures

Switchbacks are widely acknowledged phenomena observed by the Parker Solar Probe and appear to occur in patches. Previous studies focused on the fluctuations at the magnetic reversals. However, the nature of the fluctuations inside the switchbacks remains unknown. Here we utilize the magnetic field data and plasma data measured by the Parker Solar Probe in the first four encounters. We investigate the fluctuations in the switchback intervals of 100 s with ${B}_{R}\gt 0$ at every instant and compare them to the fluctuations in the nonswitchback intervals of 100 s with ${\theta }_{\mathrm{RB}}\gt 160^\circ $ at every instant. We calculate normalized cross-helicity ${\sigma }_{{\rm{c}}}$ , normalized residual energy ${\sigma }_{{\rm{r}}}$ , correlation coefficient Cvb between ${\boldsymbol{\delta }}{{\boldsymbol{v}}}_{{\rm{A}}}$ and ${\boldsymbol{\delta }}{\boldsymbol{v}}$ , Alfvén ratio rA, and the amplitude of magnetic and kinetic fluctuations. We find that the switchback intervals exhibit a distribution of ${\sigma }_{{\rm{c}}}$ similar with the nonswitchback intervals. However, the rA of switchback intervals is around 0.35, while the nonswitchback intervals have rA around 0.65, indicating the fluctuations in the switchbacks are more magnetically dominated. We also find that the distribution pattern of pixel average amplitude of both ${\boldsymbol{\delta }}{{\boldsymbol{v}}}_{{\rm{A}}}$ and ${\boldsymbol{\delta }}{\boldsymbol{v}}$ of switchback intervals in the Cvb- ${\sigma }_{{\rm{r}}}$ plane show a vertical stripe feature at ${C}_{\mathrm{vb}}\gt 0.8$ , illustrating the possible magnetically dominant magnetic-velocity alignment structure. These results will help us to understand the nature and the formation of the switchback turbulence.

Keywords: solar wind; interplanetary turbulence
Extragalactic Magnetism with SOFIA (SALSA Legacy Program). VII. A Tomographic View of Far-infrared and Radio Polarimetric Observations through MHD Simulations of Galaxies

The structure of magnetic fields in galaxies remains poorly constrained, despite the importance of magnetism in the evolution of galaxies. Radio synchrotron and far-infrared (FIR) polarization and polarimetric observations are the best methods to measure galactic scale properties of magnetic fields in galaxies beyond the Milky Way. We use synthetic polarimetric observations of a simulated galaxy to identify and quantify the regions, scales, and interstellar medium (ISM) phases probed at FIR and radio wavelengths. Our studied suite of magnetohydrodynamical cosmological zoom-in simulations features high-resolutions (10 pc full-cell size) and multiple magnetization models. Our synthetic observations have a striking resemblance to those of observed galaxies. We find that the total and polarized radio emission extends to approximately double the altitude above the galactic disk (half-intensity disk thickness of h I radio ∼ h PI radio = 0.23 ± 0.03 kpc) relative to the total FIR and polarized emission that are concentrated in the disk midplane (h I FIR ∼ h PI FIR = 0.11 ± 0.01 kpc). Radio emission traces magnetic fields at scales of ≳300 pc, whereas FIR emission probes magnetic fields at the smallest scales of our simulations. These scales are comparable to our spatial resolution and well below the spatial resolution (<300 pc) of existing FIR polarimetric measurements. Finally, we confirm that synchrotron emission traces a combination of the warm neutral and cold neutral gas phases, whereas FIR emission follows the densest gas in the cold neutral phase in the simulation. These results are independent of the ISM magnetic field strength. The complementarity we measure between radio and FIR wavelengths motivates future multiwavelength polarimetric observations to advance our knowledge of extragalactic magnetism.

Keywords: extragalactic magnetic fields; astrophysical magnetism; dust continuum emission; radio continuum emission; spiral galaxies; disk galaxies; astronomical simulations; magnetohydrodynamical simulations; galaxy formation; galaxy evolution