adsabs/SciX_UAT_keywords huggingface dataset:
Scaling Anisotropy with Stationary Background Field in Near-Sun Solar Wind Turbulence

The scaling of magnetic fluctuations provides crucial information for the understanding of solar wind turbulence. However, the observed magnetic fluctuations contain not only turbulence but also magnetic structures, leading to the violation of time stationarity. This violation would conceal the true scaling and influence the determination of the sampling angle with respect to the local background magnetic field. Here, to investigate scaling anisotropy, we utilize a simple but effective criterion ϕ < 10° to ensure the time stationarity of the magnetic field, where ϕ is the angle between the two averaged magnetic fields after cutting the interval into two halves. We study the scaling anisotropy using higher-order statistics of structure functions under the condition of stationarity for near-Sun solar wind turbulence for the first time based on measurements obtained from the Parker Solar Probe at 0.17 au. We find that the scaling indices ξ of the magnetic field show a linear dependence on the order p close to ξ(p) = p/4. The multifractal scaling of the magnetic-trace structure functions becomes monoscaling close to ξ(p) = p/3 with the local magnetic field perpendicular to the sampling direction and close to ξ(p) = p/4 with the local magnetic field parallel to the sampling direction when measured with the stationary background magnetic field. The scaling of the velocity-trace structure functions has similar but less significant changes. The near-Sun solar wind turbulence displays different scaling anisotropies from the near-Earth solar wind turbulence, suggesting the evolution of the nonlinear interaction process during solar wind expansion.

Keywords: solar wind; interplanetary turbulence; magnetic fields
On the Influence of the Ionization-Recombination Processes on the Hydrogen Plasma Polytropic Index

An analytical approximation for the polytropic index of a hydrogen gas has been derived. The derived expressions can be useful for theoretical work and numerical calculations. These results open the possibility of direct computation of these thermodynamic quantities, rather than interpolating from tables. Additionally, the polytropic index is graphically represented as a function of temperature and density. It is concluded that the partially ionized hydrogen plasma cannot be exactly polytropic. The calculated deviations from the monoatomic value 5/3 are significant and measurable. The present theory supposes that hydrogen molecules are completely dissociated, and this analytical result for pure hydrogen plasma can be applied for the solar chromosphere, where He ionization is negligible and H2 dissociation is almost complete. These two conditions define the ranges of applicability of temperatures and densities. The analytical result for pure hydrogen plasma is a test example of how this approach can be extended for an arbitrary gas cocktail.

Keywords: solar chromospheric heating; ionization; recombination
Non-Markovian Pitch-angle Scattering as the Origin of Particle Superdiffusion Parallel to the Magnetic Field

We develop a theoretical model for particle superdiffusive transport parallel to the average magnetic field, due to the pitch-angle scattering times having a non-Markovian, power-law probability distribution. We show that a non-Markovian Fokker-Planck equation can be derived, where the traditional time derivative is changed for a fractional time derivative. By solving the fractional Fokker-Planck equation, with the time-dependent part having solutions that are expressed by the Mittag-Leffler functions, it is found that an initial pitch-angle distribution slowly decays toward isotropy. This leads to a parallel velocity autocorrelation function that also has a slow power-law decay in time, thus implying superdiffusive transport in the direction parallel to the background magnetic field. In this framework, we derive for the first time the anomalous diffusion coefficient as a function of physical parameters like the background magnetic field, the resonant turbulence level, and the particle speed.

Keywords: cosmic rays; particle astrophysics; interplanetary turbulence; solar energetic particles; astrophysical processes
Magellan/IMACS Spectroscopy of Grus I: A Low Metallicity Ultra-faint Dwarf Galaxy

We present a chemodynamical study of the Grus I ultra-faint dwarf galaxy (UFD) from medium-resolution (R ~ 11,000) Magellan/IMACS spectra of its individual member stars. We identify eight confirmed members of Grus I, based on their low metallicities and coherent radial velocities, and four candidate members for which only velocities are derived. In contrast to previous work, we find that Grus I has a very low mean metallicity of <[Fe/H]> = -2.62 ± 0.11 dex, making it one of the most metal-poor UFDs. Grus I has a systemic radial velocity of -143.5 ± 1.2 km s-1 and a velocity dispersion of ${\sigma }_{\mathrm{rv}}={2.5}_{-0.8}^{+1.3}$ km s-1, which results in a dynamical mass of ${M}_{1/2}({r}_{h})={8}_{-4}^{+12}\times {10}^{5}$ M ⊙ and a mass-to-light ratio of M/L V = ${440}_{-250}^{+650}$ M ⊙/L ⊙. Under the assumption of dynamical equilibrium, our analysis confirms that Grus I is a dark-matter-dominated UFD (M/L > 80 M ⊙/L ⊙). However, we do not resolve a metallicity dispersion (σ [Fe/H] < 0.44 dex). Our results indicate that Grus I is a fairly typical UFD with parameters that agree with mass-metallicity and metallicity-luminosity trends for faint galaxies. This agreement suggests that Grus I has not lost an especially significant amount of mass from tidal encounters with the Milky Way, in line with its orbital parameters. Intriguingly, Grus I has among the lowest central densities ( ${\rho }_{1/2}\sim {3.5}_{-2.1}^{+5.7}\times {10}^{7}$ M ⊙ kpc-3) of the UFDs that are not known to be tidally disrupting. Models of the formation and evolution of UFDs will need to explain the diversity of these central densities, in addition to any diversity in the outer regions of these relic galaxies. *This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: dwarf galaxies; population ii stars
Supplement: "An Isolated Mass-gap Black Hole or Neutron Star Detected with Astrometric Microlensing" (2022, ApJL, 933, L23)

This supplement provides supporting material for Lam et al. We briefly summarize past gravitational microlensing searches for black holes (BHs) and present details of the observations, analysis, and modeling of five BH candidates observed with both ground-based photometric microlensing surveys and Hubble Space Telescope astrometry and photometry. We present detailed results for four of the five candidates that show no or low probability for the lens to be a BH. In these cases, the lens masses are <2 M ⊙, and two of the four are likely white dwarfs or neutron stars. We also present detailed methods for comparing the full sample of five candidates to theoretical expectations of the number of BHs in the Milky Way (~108).

Keywords: astrometry; astrometric microlensing effect; astrophysical black holes; stellar populations
Machine Learning Classification to Identify Catastrophic Outlier Photometric Redshift Estimates

We present results of using a basic binary classification neural network model to identify likely catastrophic outlier photometric redshift estimates of individual galaxies, based only on the galaxies' measured photometric band magnitude values. We find that a simple implementation of this classification can identify a significant fraction of galaxies with catastrophic outlier photometric redshift estimates while falsely categorizing only a much smaller fraction of non-outliers. These methods have the potential to reduce the errors introduced into science analyses by catastrophic outlier photometric redshift estimates.

Keywords: redshift surveys; astrostatistics techniques; neural networks
Hunting Gravitational Wave Black Holes with Microlensing

Gravitational microlensing is a powerful tool to search for a population of invisible black holes (BHs) in the Milky Way (MW), including isolated BHs and binary BHs at wide orbits that are complementary to gravitational wave observations. By monitoring highly populated regions of source stars like the MW bulge region, one can pursue microlensing events due to these BHs. We find that if BHs have a Salpeter-like mass function extended beyond 30M⊙ and a similar velocity and spatial structure to stars in the Galactic bulge and disk regions, the BH population is a dominant source of microlensing events at long timescales of the microlensing light curve ≳100 days. This is due to a boosted sensitivity of the microlensing event rate to lens mass, given as M2, for such long-timescale events. A monitoring observation of 2 × 1010 stars in the bulge region over 10 yr with the Rubin Observatory Legacy Survey of Space and Time (LSST) would enable one to find about 6 × 105 BH microlensing events. We evaluate the efficiency of potential LSST cadences for characterizing the light curves of BH microlensing and find that nearly all events of long timescales can be detected.

Keywords: gravitational microlensing; microlensing event rate; microlensing optical depth; gravitational wave sources
A Common Origin for Low-mass Ratio Events Observed by LIGO and Virgo in the First Half of the Third Observing Run

In its third observing run, the Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo Collaboration has announced a potential neutron star-black hole (NS-BH) merger candidate, GW190426_152155. Together with GW190814, these two events belong to a class of binaries with a secondary mass less than 3 M⊙. While the secondary system in GW190426_152155 is consistent with being a neutron star (NS) with a mass of ${1.5}_{-0.5}^{+0.8}\,{\text{}}\,{M}_{\odot }$ , that of GW190814 is a ${2.59}_{-0.09}^{+0.08}\,{\text{}}\,{M}_{\odot }$ object and counts as the first confirmed detection of a mass-gap object. Here we argue that these two events could have a common origin as follows: both are formed as NS-BH systems; however, the larger escape velocity of a system with more massive primary black hole (BH) increases the bound fraction of the ejecta material from the supernova explosion leading to the formation of a NS. This bound material forms a disk, which is preferentially accreted onto the NS. This scenario predicts the secondary component mass should correlate with the primary component mass, which is consistent with GW190426_152155 and GW190814. If this hypothesis is corroborated by upcoming observations, GW190814-like events can be excluded from the binary BH population when inferring their global characteristics.

Keywords: ligo; accretion; neutron stars; astrophysical black holes; supernova remnants; ejecta; compact objects
The Substructures in Disks Undergoing Vertical Shear Instability. II. Observational Predictions for the Dust Continuum

High-angular resolution observations at submillimeter/millimeter wavelengths of disks surrounding young stars have shown that their morphology is made of azimuthally symmetric or point-symmetric substructures, in some cases with spiral arms or localized spur- or crescent-shaped features. The majority of theoretical studies with the aim of interpreting the observational results have focused on disk models with planets under the assumption that the disk substructures are due to disk-planet interaction. However, so far, only in very few cases have exoplanets been detected in these systems. Furthermore, some substructures are expected to appear before planets form, as they are necessary to drive the concentration of small solids which can lead to the formation of planetesimals. In this work we present observational predictions from high-resolution 3D radiative hydrodynamical models that follow the evolution of gas and solids in a prototoplanetary disk. We focus on substructures in the distribution of millimeter-sized and smaller solid particles produced by the vertical shear instability. We show that their characteristics are compatible with some of the shallow gaps detected in recent observations at sub-mm/mm wavelengths and present predictions for future observations with better sensitivity and angular resolution with ALMA and a Next Generation Very Large Array.

Keywords: protoplanetary disks
The Variable Detection of Atmospheric Escape around the Young, Hot Neptune AU Mic b

Photoevaporation is a potential explanation for several features within exoplanet demographics. Atmospheric escape observed in young Neptune-sized exoplanets can provide insight into and characterize which mechanisms drive this evolution and at what times they dominate. AU Mic b is one such exoplanet, slightly larger than Neptune (4.19 R ⊕). It closely orbits a 23 Myr pre-main-sequence M dwarf with an orbital period of 8.46 days. We obtained two visits of AU Mic b at Lyα with Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph. One flare within the first HST visit is characterized and removed from our search for a planetary transit. We present a nondetection in our first visit, followed by the detection of escaping neutral hydrogen ahead of the planet in our second visit. The outflow absorbed ~30% of the star's Lyα blue wing 2.5 hr before the planet's white-light transit. We estimate that the highest-velocity escaping material has a column density of 1013.96 cm-2 and is moving 61.26 km s-1 away from the host star. AU Mic b's large high-energy irradiation could photoionize its escaping neutral hydrogen in 44 minutes, rendering it temporarily unobservable. Our time-variable Lyα transit ahead of AU Mic b could also be explained by an intermediate stellar wind strength from AU Mic that shapes the escaping material into a leading tail. Future Lyα observations of this system will confirm and characterize the unique variable nature of its Lyα transit, which, combined with modeling, will tune the importance of stellar wind and photoionization.

Keywords: exoplanets; hot neptunes; exoplanet atmospheric variability; exoplanet atmospheric dynamics
COSMIC: An Ethernet-based Commensal, Multimode Digital Backend on the Karl G. Jansky Very Large Array for the Search for Extraterrestrial Intelligence

The primary goal of the search for extraterrestrial intelligence is to gain an understanding of the prevalence of technologically advanced beings (organic or inorganic) in the Galaxy. One way to approach this is to look for technosignatures: remotely detectable indicators of technology, such as temporal or spectral electromagnetic emissions consistent with an artificial source. With the new Commensal Open-Source Multimode Interferometer Cluster (COSMIC) digital backend on the Karl G. Jansky Very Large Array (VLA), we aim to conduct a search for technosignatures that is significantly more comprehensive, sensitive, and efficient than previously attempted. The COSMIC system is currently operational on the VLA, recording data and designed with the flexibility to provide user-requested modes. This paper describes the hardware system design, the current software pipeline, and plans for future development.

Keywords: gpu computing; astrobiology; search for extraterrestrial intelligence
Evolution of the Size–Mass Relation of Star-forming Galaxies Since z = 5.5 Revealed by CEERS

We combine deep imaging data from the CEERS early release JWST survey and Hubble Space Telescope imaging from CANDELS to examine the size–mass relation of star-forming galaxies and the morphology–quenching relation at stellar masses M ⋆ ≥ 109.5 M ⊙ over the redshift range 0.5 < z < 5.5. In this study with a sample of 2450 galaxies, we separate star-forming and quiescent galaxies based on their star formation activity and confirm that star-forming and quiescent galaxies have different morphologies out to z = 5.5, extending the results of earlier studies out to higher redshifts. We find that star-forming and quiescent galaxies have typical Sérsic indices of n ∼ 1.3 and n ∼ 4.3, respectively. Focusing on star-forming galaxies, we find that the slope of the size–mass relation is nearly constant with redshift, as was found previously, but shows a modest increase at z ∼ 4.2. The intercept in the size–mass relation declines out to z = 5.5 at rates that are similar to what earlier studies found. The intrinsic scatter in the size–mass relation is relatively constant out to z = 5.5.

Keywords: galaxy structure; galaxy evolution; high-redshift galaxies; galaxy photometry
NGDEEP Epoch 1: The Faint End of the Luminosity Function at z 9-12 from Ultradeep JWST Imaging

We present a robust sample of very high redshift galaxy candidates from the first epoch of JWST/NIRCam imaging from the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) survey. The NGDEEP NIRCam imaging, spanning 9.7 arcmin2 in the Hubble Ultra Deep Field Parallel Field 2, reaches m = 30.4 (5σ, point-source, 2″ diameter apertures corrected to total) in F277W, making it the deepest public JWST GO imaging data set to date. We describe our detailed data reduction process of the six-filter broadband JWST/NIRCam imaging, incorporating custom corrections for systematic effects to produce high-quality calibrated images. Using robust photometric redshift selection criteria, we identify a sample of 38 z ≳ 9 galaxy candidates. These objects span a redshift range of z = 8.5-15.8 and apparent magnitudes of m F277W = 27-30.5 AB mag, reaching ~1.5 mag deeper than previous public JWST imaging surveys. We calculate the rest-frame ultraviolet luminosity function at z ~ 9 and 11 and present a new measurement of the luminosity function faint-end slope at z ~ 11. We find a faint-end slope of α = -2.5 ± 0.4 and -2.2 ± 0.2 at z ~ 9 and 11, respectively. This is consistent with no significant evolution in the faint-end slope and number density from z = 9 to 11. Comparing our results with theoretical predictions, we find that some models produce better agreement at the faint end than the bright end. These results will help to constrain how stellar feedback impacts star formation at these early epochs.

Keywords: early universe; galaxy evolution; galaxy formation; high-redshift galaxies
Magnetic Flux in the Sun Emerges Unaffected by Supergranular-scale Surface Flows

Magnetic flux emergence from the convection zone into the photosphere and beyond is a critical component of the behavior of large-scale solar magnetism. Flux rarely emerges amid field-free areas at the surface, but when it does, the interaction between the magnetism and plasma flows can be reliably explored. Prior ensemble studies have identified weak flows forming near emergence locations, but the low signal-to-noise ratio (S/N) required averaging over the entire data set, erasing information about variation across the sample. Here, we apply deep learning to achieve an improved S/N, enabling a case-by-case study. We find that these associated flows are dissimilar across instances of emergence and also occur frequently in the quiet convective background. Our analysis suggests the diminished influence of supergranular-scale convective flows and magnetic buoyancy on flux rise. Consistent with numerical evidence, we speculate that small-scale surface turbulence and/or deep convective processes play an outsized role in driving flux emergence.

Keywords: solar active regions; convolutional neural networks; solar convective zone; solar active region magnetic fields; solar magnetic flux emergence
Observations of Instability-driven Nanojets in Coronal Loops

The recent discovery of nanojets by Antolin et al. represents magnetic reconnection in a braided field, thus clearly identifying reconnection-driven nanoflares. Due to their small scale (500 km in width, 1500 km in length) and short timescales (<15 s), it is unclear how pervasive nanojets are in the solar corona. In this paper, we present Interface Region Imaging Spectrograph and Solar Dynamics Observatory observations of nanojets found in multiple coronal structures, namely, in a coronal loop powered by a blowout jet, and in two other coronal loops with coronal rain. In agreement with previous findings, we observe that nanojets are accompanied by small nanoflare-like intensity bursts in the (E)UV, have velocities of 150-250 km s-1 and occur transversely to the field line of origin, which is sometimes observed to split. However, we find a variety of nanojet directions in the plane transverse to the loop axis. These nanojets are found to have kinetic and thermal energies within the nanoflare range, and often occur in clusters. In the blowout jet case study, the Kelvin-Helmholtz instability (KHI) is directly identified as the reconnection driver. For the other two loops, we find that both, KHI and Rayleigh-Taylor instability (RTI) are likely to be the drivers. However, we find that KHI and RTI are each more likely in one of the other two cases. These observations of nanojets in a variety of structures and environments support nanojets being a general result of reconnection that are driven here by dynamic instabilities.

Keywords: the sun; solar corona; solar magnetic fields; solar prominences; magnetohydrodynamics
The BANANA Project. VI. Close Double Stars are Well Aligned with Noticeable Exceptions; Results from an Ensemble Study Using Apsidal Motion and Rossiter-McLaughlin Measurements

Here we present an ensemble study of spin-orbit alignment in 43 close double star systems. We determine spin-orbit angles, obliquities, in 31 of these systems making use of recently improved apsidal motion rate measurements and apsidal motion constants. In the remaining 12 systems researchers have constrained spin-orbit alignment by different combinations of measurements of apsidal motion rates, projected obliquities, and stellar inclinations. Of the 43 systems 40 are consistent with alignment albeit with some measurements having large uncertainties. A Fisher distribution with mean zero and a concentration factor κ = 6.1 represents this ensemble well. Indeed employing a bootstrapping resampling technique we find our data on these 40 systems are consistent with perfect alignment. We also confirm significant misalignment in two systems that travel on eccentric orbits and where misalignments have been reported on before; namely DI Her and AS Cam. The third misaligned system CV Vel orbits on a circular orbit. So while there are some glaring exceptions, the majority of close double star systems for which data are available appear to be well aligned.

Keywords: close binary stars; apsidal motion; binary stars; eclipsing binary stars; oblique rotators
TEMPLATES: A Robust Outlier Rejection Method for JWST/NIRSpec Integral Field Spectroscopy

We describe a custom outlier rejection algorithm for JWST/NIRSpec integral field spectroscopy. This method uses a layered sigma clipping approach that adapts clipping thresholds based upon the spatial profile of the science target. We find that this algorithm produces a robust outlier rejection while simultaneously preserving the signal of the science target. Originally developed as a response to unsatisfactory initial performance of the jwst pipeline outlier detection step, this method works either as a standalone solution, or as a supplement to the current pipeline software. Comparing leftover (i.e., not flagged) artifacts with the current pipeline's outlier detection step, we find that our method results in one fifth as many residual artifacts as the jwst pipeline. However, we find a combination of both methods removes nearly all artifacts—an approach that takes advantage of both our algorithm's robust outlier rejection and the pipeline's use of individual dithers. This combined approach is what the TEMPLATES Early Release Science team has converged upon for our NIRSpec observations. Finally, we publicly release the code and Jupyter notebooks for the custom outlier rejection algorithm.

Keywords: spectroscopy; astronomy data reduction; astronomical techniques