adsabs/SciX_UAT_keywords huggingface dataset:
Autoencoding Galaxy Spectra. I. Architecture

We introduce the neural network architecture SPENDER as a core differentiable building block for analyzing, representing, and creating galaxy spectra. It combines a convolutional encoder, which pays attention to up to 256 spectral features and compresses them into a low-dimensional latent space, with a decoder that generates a restframe representation, whose spectral range and resolution exceeds that of the observing instrument. The decoder is followed by explicit redshift, resampling, and convolution transformations to match the observations. The architecture takes galaxy spectra at arbitrary redshifts and is robust to glitches like residuals of the skyline subtraction, so that spectra from a large survey can be ingested directly without additional preprocessing. We demonstrate the performance of SPENDER by training on the entire spectroscopic galaxy sample of SDSS-II; show its ability to create highly accurate reconstructions with substantially reduced noise; perform deconvolution and oversampling for a superresolution model that resolves the [O II] doublet; introduce a novel method to interpret attention weights as proxies for important spectral features; and infer the main degrees of freedom represented in the latent space. We conclude with a discussion of future improvements and applications.

Keywords: astronomy data modeling; galaxy spectroscopy
Cosmological Parameter Constraints from the SDSS Density and Momentum Power Spectra

We extract the galaxy density and momentum power spectra from a subset of early-type galaxies in the Sloan Digital Sky Survey (SDSS) DR7 main galaxy catalog. Using galaxy distance information inferred from the improved fundamental plane described in Yoon and Park, we reconstruct the peculiar velocities of the galaxies and generate number density and density-weighted velocity fields, from which we extract the galaxy density and momentum power spectra. We compare the measured values to the theoretical expectation of the same statistics, assuming an input Λ cold dark matter (CDM) model and using a third-order perturbative expansion. After validating our analysis pipeline with a series of mock data sets, we apply our methodology to the SDSS data and arrive at constraints $f{\sigma }_{8}={0.471}_{-0.080}^{+0.077}$ and ${b}_{1}{\sigma }_{8}={0.920}_{-0.070}^{+0.070}$ at a mean redshift $\bar{z}=0.04$ . Our result is consistent with the Planck cosmological best-fit parameters for the ΛCDM model. The momentum power spectrum is found to be strongly contaminated by small-scale velocity dispersion, which suppresses power by $\sim { \mathcal O }(30 \% )$ on intermediate scales k ~ 0.05 h Mpc-1.

Keywords: observational cosmology; large-scale structure of the universe; cosmological parameters
Analytic Model and Magnetohydrodynamic Simulations of Three-dimensional Magnetic Switchbacks

Parker Solar Probe observations reveal that the near-Sun space is almost filled with magnetic switchbacks ("switchbacks" hereinafter), which may be a major contributor to the heating and acceleration of solar wind. Here, for the first time, we develop an analytic model of an axisymmetric switchback with uniform magnetic field strength. In this model, three parameters control the geometry of the switchback: height (length along the background magnetic field), width (thickness along radial direction perpendicular to the background field), and the radial distance from the center of switchback to the central axis, which is a proxy of the size of the switchback along the third dimension. We carry out 3D magnetohydrodynamic simulations to investigate the dynamic evolution of the switchback. Comparing simulations conducted with compressible and incompressible codes, we verify that compressibility, i.e., parametric decay instability, is necessary for destabilizing the switchback. Our simulations also reveal that the geometry of the switchback significantly affects how fast the switchback destabilizes. The most stable switchbacks are 2D-like (planar) structures with large aspect ratios (length to width), consistent with the observations. We show that when plasma beta (β) is smaller than one, the switchback is more stable as β increases. However, when β is greater than 1, the switchback becomes very unstable as the pattern of the growing compressive fluctuations changes. Our results may explain some of the observational features of switchbacks, including the large aspect ratios and nearly constant occurrence rates in the inner heliosphere.

Keywords: solar wind; magnetohydrodynamics; magnetohydrodynamical simulations; alfven waves
(Non)radial Solar Wind Propagation through the Heliosphere

The solar wind nonradial velocity components observed beyond the Alfvén point are usually attributed to waves, the interaction of different streams, or other transient phenomena. However, Earth-orbiting spacecraft as well as monitors at L1 indicate systematic deviations of the wind velocity from the radial direction. Since these deviations are of the order of several degrees, the calibration of the instruments is often questioned. This paper investigates for the first time the evolution of nonradial components of the solar wind flow along the path from ≈0.17 to 10 au. A comparison of observations at 1 au with those closer to or farther from the Sun based on measurements of many spacecraft at different locations in the heliosphere (Parker Solar Probe, Helios 1 and 2, Wind, Advanced Composition Explorer, Spektr-R, Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) probes, Mars Atmosphere and Volatile Evolution (MAVEN), Voyagers 1 and 2) shows that (I) the average values of nonradial components are not zero and vary in a systematic manner with the distance from the Sun and (II) their values significantly depend on the solar wind radial velocity.

Keywords: heliosphere; solar wind; fast solar wind
Bursts from High-magnetic-field Pulsars Swift J1818.0-1607 and PSR J1846.4-0258

The detection of magnetar-like bursts from highly magnetic (B > 1013 G) rotation-powered pulsars (RPPs) opened the magnetar population to yet another group of neutron stars. At the same time the question arose as to whether magnetar-like bursts from high-B RPPs have similar characteristics to bursts from known magnetar sources. We present here our analyses of the Fermi Gamma-ray Burst Monitor (GBM) data from two magnetar candidates, Swift J1818.0-1607 (a radio-loud magnetar) and PSR J1846.4-0258. Both sources entered active bursting episodes in 2020 triggering Fermi-GBM in 2020 and in early 2021. We searched for untriggered bursts from both sources and performed temporal and spectral analyses on all events. Here, we present the results of our comprehensive burst search and analyses. We identified 37 and 58 bursts that likely originated from Swift J1818.0-1607 and PSR J1846.4-0258, respectively. We find that the bursts from these sources are shorter on average than typical magnetar bursts. In addition, their spectra are best described with a single blackbody function with kT ~ 10-11 keV; several relatively bright events, however, show higher energy emission that could be modeled with a cutoff power-law model. We find that the correlation between the blackbody emitting area and the spectral temperature for the burst ensemble of each pulsar deviates from the ideal Stefan-Boltzmann law, as it does for some burst-active magnetars. We interpret this characteristic as being due to the significant radiation anisotropy expected from optically thick plasmas in very strong magnetic fields.

Keywords: magnetars; x-ray bursts; neutron stars; rotation powered pulsars
Heliospheric Maps from Cassini INCA Early in the Cruise to Saturn

We present new energetic neutral atom (ENA) maps from the Ion and Neutral Camera (INCA) instrument on Cassini from the year 2000, prior to Cassini's encounter with Jupiter. These maps are the first produced for the year 2000 and are the only maps with comprehensive spatial coverage from the peak of solar cycle 23. These ENA maps span the energy range from 5.2 to 55 keV covering the pickup to suprathermal energy range. These maps represent a novel glimpse into the influence of the solar cycle on the structure of the outer heliosphere, specifically on the heliosheath where pickup and suprathermal ions dominate. The observations are consistent with the picture of the heliosheath from previous observations by the Cassini, Interstellar Boundary Explorer (IBEX), and Voyager missions. These maps have some consistent spatial features to maps produced by Cassini during solar cycle 24 such as reduced intensities in the mid-latitude basins. These maps also have distinct spatial features such as enhanced intensities at the poles and reduced intensities at the low-latitude flanks. These maps do not indicate a strong intensity increase in the regions adjacent to the nose and also show an intensity increase in the regions adjacent to the tailward direction.

Keywords: heliosphere; heliosheath; solar wind
Superorbital Modulation in the High-mass X-Ray Binary 4U 1538-52 and Possible Modulation in IGR J16393-4643

Hard X-ray observations with the Neil Gehrels Swift Observatory Burst Alert Telescope (BAT) reveal superorbital modulation in the wind-accreting supergiant high-mass X-ray binary (HMXB) 4U 1538-52 at a period of 14.9130 ± 0.0026 days that is consistent with four times the 3.73 day orbital period. These periods agree with a previously suggested correlation between superorbital and orbital periods in similar HMXBs. During the ∼14 yr of observations the superorbital modulation changes amplitude, and since ∼MJD 57,650 it was no longer detected in the power spectrum, although a peak near the second harmonic of this was present for some time. Measurements of the spin period of the neutron star in the system with the Fermi Gamma-ray Burst Monitor show a long-term spin-down trend, which halted toward the end of the light curve, suggesting a connection between ${\dot{P}}_{\mathrm{spin}}$ and superorbital modulation, as proposed for 2S 0114+650. However, an earlier torque reversal from INTEGRAL observations was not associated with superorbital modulation changes. B- and V-band photometry from the Las Cumbres Observatory reveals orbital ellipsoidal photometric variability, but no superorbital optical modulation. However the photometry was obtained when the 14.9130 day period was no longer detected in the BAT power spectrum. We revisit possible superorbital modulation in BAT observations of IGR J16393-4643 but cannot conclusively determine whether this is present, although it is not persistent. We consider superorbital modulation mechanisms, and suggest that the corotating interaction region model, with small deviations from orbital synchronization, appears promising.

Keywords: high mass x-ray binary stars; neutron stars; x-ray binary stars; ob supergiant stars; bondi accretion; accretion
Probing the Inner Edge of Dead Zones in Protoplanetary Disks with ALMA and Next Generation Very Large Array

The discovery of substructures in protoplanetary disks by the Atacama Large Millimeter/submillimeter Array (ALMA) has provided us with key insights into the formation of planets. However, observational constraints on the formation of rocky planets have been still sparse, especially because of the limited spatial resolution. The inner edge of the so-called dead zone is one of the preferential sites of rocky planet formation. We investigate the capabilities of ALMA and Next Generation Very Large Array (ngVLA) for observing a dust concentration expected at the inner edge of the dead zone around a Herbig star. Herbig Ae/Be stars are useful laboratories for exploring the evolution of rocky grains in protoplanetary disks because of their high luminosity that pushes the dead zone inner edge outward. We find that, thanks to its unprecedented angular resolution and sensitivity, ngVLA can detect the dust concentration at the dead zone inner edge, with a reasonable integration time of 10 hr at λ = 3, 7 mm, and 1 cm. The dust concentration is expected to be optically thick at the ALMA wavelengths and cannot be spatially resolved due to its limited resolution. On the other hand, the flux density from the inner disk regions (~3-4 au) observed with current VLA is higher for disks with a dust ring, and hence would be a useful indicator that helps us choose potential candidates of disks having a dust concentration at the innermost region. With these observations we can characterize the process of dust concentration in the innermost disk regions, where rocky planets can form.

Keywords: protoplanetary disks; planet formation
High-frequency Waves in Chromospheric Spicules

Using high-cadence observations from the Hydrogen-alpha Rapid Dynamics camera imaging system on the Dunn Solar Telescope, we present an investigation of the statistical properties of transverse oscillations in spicules captured above the solar limb. At five equally separated atmospheric heights, spanning approximately 4900-7500 km, we have detected a total of 15,959 individual wave events, with a mean displacement amplitude of 151 ± 124 km, a mean period of 54 ± 45 s, and a mean projected velocity amplitude of 21 ± 13 km s-1. We find that both the displacement and velocity amplitudes increase with height above the solar limb, ranging from 132 ± 111 km and 17.7 ± 10.6 km s-1 at ≈4900 km, and 168 ± 125 km and 26.3 ± 14.1 km s-1 at ≈7500 km, respectively. Following the examination of neighboring oscillations in time and space, we find 45% of the waves to be upwardly propagating, 49% to be downwardly propagating, and 6% to be standing, with mean absolute phase velocities for the propagating waves on the order of 75-150 km s-1. While the energy flux of the waves propagating downwards does not appear to depend on height, we find the energy flux of the upwardly propagating waves decreases with atmospheric height at a rate of -13,200 ± 6500 W m-2/Mm. As a result, this decrease in energy flux as the waves propagate upwards may provide significant thermal input into the local plasma.

Keywords: solar spicules; solar oscillations; solar chromosphere; solar atmosphere
Physical Characterization of Interstellar Comet 2I/2019 Q4 (Borisov)

We present a study of interstellar comet 2I/2019 Q4 (Borisov) using both preperihelion and postperihelion observations spanning late September 2019 through late January 2020. The intrinsic brightness of the comet was observed to continuously decline throughout the timespan, likely due to the decreasing effective scattering cross-section as a result of volatile sublimation with a slope of -0.43 ± 0.02 km2 d-1. We witnessed no significant change in the slightly reddish color of the comet, with mean values of $\left\langle g-r\right\rangle =0.68\pm 0.04$ , $\left\langle r-i\right\rangle =0.23\pm 0.03$ , and the normalized reflectivity gradient across the g and i bands $\overline{S^{\prime} }\left(g,i\right)=\left(10.6\pm 1.4\right)$ % per 103 Å, all unremarkable in the context of solar system comets. Using the available astrometric observations, we confidently detect the nongravitational acceleration of the comet following a shallow heliocentric distance dependence of ${r}_{{\rm{H}}}^{-1\pm 1}$ . Accordingly, we estimate that the nucleus is most likely $\lesssim 0.4$ km in radius, and that a fraction of ≳0.2% of the total mass of the nucleus has been eroded due to the sublimation activity since the earliest observation of the comet in 2018 December by the time of perihelion. Our morphology simulation suggests that the dust ejection speed increased from ∼4 m s-1 in 2019 September to ∼7 m s-1 around perihelion for the optically dominant dust grains with $\beta \sim 0.01$ , and that the observable dust grains are no smaller than micron size.

Keywords: comets
Gamma-Ray Flares in the Long-term Light Curve of 3C 454.3

3C 454.3 is frequently observed in the flaring state. The long-term light curve of this source has been analyzed with 9 yr (2008 August-2017 July) of data from the Fermi-LAT detector. We have identified five flares and one quiescent state. The flares have substructures with many peaks during the flaring phase. We have estimated the rise and decay time of the flares and compared with flares of other similar sources. The modeling of gamma-ray spectral energy distributions shows in most cases that a log-parabola function gives the best fit to the data. We have done time-dependent leptonic modeling of two of the flares, for which simultaneous multiwavelength data are available. These two long-lasting flares, Flare-2A and Flare-2D, continued for 95 and 133 days, respectively. We have used the average values of Doppler factor, injected luminosity in electrons, size of the emission region, and the magnetic field in the emission region in modeling these flares. The emission region is assumed to be in the broad-line region in our single-zone model. The energy losses (synchrotron, synchrotron self-Compton, external Compton) and escape of electrons from the emission region have been included while doing the modeling. Although the total jet powers required to model these flares with the leptonic model are higher compared to other sources, they are always found to be lower than the Eddington luminosity of 3C 454.3. We also select some flaring peaks and show that the time variation of the Doppler factor or the injected luminosity in electrons over short timescales can explain their light curves.

Keywords: galactic and extragalactic astronomy; extragalactic astronomy; quasars; active galactic nuclei; blazars; jets
Magnetic Hump Associated with Electron Vortex at Dipolarization Front

As the plasma boundary between two distinct plasma populations, dipolarization fronts (DFs) host abundant kinetic-scale substructures that change their normal directions and thus cause their deformation. However, studies on such deformation caused by an electron vortex have been lacking. Here, we present novel observations of a subion-scale magnetic hump (MHu) associated with an oblique electron vortex at a DF through strengthening three components of the magnetic field. A radial electric field in the MHu, showing bipolar variation, is also associated with the electron vortex as it is mainly ascribed to the electron convection term. There is apparent energy conversion ( $\overrightarrow{J}\cdot \overrightarrow{E}$ ~-0.3 nw m-3) from the particles to the electromagnetic field in the MHu's leading part, which is accompanied by inflow and outflow of electromagnetic energy (nonzero ${\rm{\nabla }}\cdot \overrightarrow{S}$ ). The other regions of the DF host opposite energy conversion ( $\overrightarrow{J}\cdot \overrightarrow{E}$ > 0). Broadband parallel electrostatic waves are also observed in the MHu. Our study provides insights into the kinetic-scale processes at DFs.

Keywords: space weather; space plasmas; planetary magnetospheres
An Exploration of an Early Gravity Transition in Light of Cosmological Tensions

We study a step-like transition in the value of the effective Planck mass (or effective gravitational constant) on cosmological scales prior to recombination. We employ cosmic microwave background, baryon acoustic oscillations, and Type Ia supernova data and find they are sufficient to strongly constrain our implementation of the effective field theory of dark energy and modified gravity, used to model the transition, to a limited parameter space. The data prefer a ~5% shift in the value of the effective Planck mass (<10% at 2σ) prior to recombination. This Transitional Planck Mass (TPM) model is free to undergo its transition at any point over multiple decades of scale factor prior to recombination, ${\mathrm{log}}_{10}(a)=-{5.32}_{-0.72}^{+0.96}$ (68% confidence level). This lowers the sound horizon at last scattering, which increases the Hubble constant to 71.09 ± 0.75 km s-1 Mpc-1 with a combination of local measurements as prior and to ${69.22}_{-0.86}^{+0.67}$ km s-1 Mpc-1 when the prior is excluded. The TPM model improves χ 2 with respect to ΛCDM by Δχ 2 = -23.72 with the H 0 prior and Δχ 2 = -4.8 without the prior. The model allows for both H 0 > 70 kms-1 Mpc-1 and S 8 < 0.80 simultaneously with lower values of S 8 due to a reduction in the matter density Ω m to offset the increase in H 0 relative to ΛCDM. While this is a particular modified gravity model, studying other variants of modified gravity may be a productive path for potentially resolving cosmological tensions while avoiding the need for a cosmological constant.

Keywords: cosmology; dark energy; cosmological parameters
Galaxy–Galaxy Lensing Data: f(T) Gravity Challenges General Relativity

We use galaxy–galaxy lensing data to test general relativity and f(T) gravity at galaxy scales. We consider an exact spherically symmetric solution of f(T) theory, which is obtained from an approximate quadratic correction, and thus it is expected to hold for every realistic deviation from general relativity. Quantifying the deviation by a single parameter Q, and following the post-Newtonian approximation, we obtain the corresponding deviation in the gravitational potential, shear component, and effective excess surface density profile. We used five stellar mass samples and divided them into blue and red galaxies to test the model dependence on galaxy color, and we modeled the excess surface density profiles using the Navarro–Frenk–White profiles. Based on the group catalog from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) we finally extract Mpc‑2 at 1σ confidence. This result indicates that f(T) corrections on top of general relativity are favored. Finally, we apply information criteria, such as the Akaike and Bayesian ones, and although the dependence of f(T) gravity on the off-center effect implies that its optimality needs to be carefully studied, our analysis shows that f(T) gravity is more efficient in fitting the data compared to general relativity and the ΛCDM paradigm, and thus it offers a challenge to the latter.

Keywords: weak gravitational lensing; cosmology; non-standard theories of gravity
Geologic History of the Amundsen Crater Region Near the Lunar South Pole: Basis for Future Exploration

We provide the first detailed 1:100,000 scale geomorphologic map of the ∼100 km Amundsen crater region, which is of high scientific relevance for future exploration, e.g., NASA's VIPER mission, the Artemis program, and the Chinese International Lunar Research Station. We investigated the complex geological history of the region before and after the formation of Amundsen crater on the rims of the South Pole–Aitken (SPA) and Amundsen–Ganswindt basins. We present a new Amundsen crater formation age of ∼4.04 Ga, which, in contrast to previously derived ages, is based on non-light-plains terrain. The estimated maximum excavation depth for Amundsen crater is ∼8 km, and elevated concentrations of FeO near the crater suggest that Amundsen may have redistributed SPA-derived materials. Plains materials of various kinds were observed both inside and outside Amundsen crater and are estimated to be up to 350 m thick and ∼3.8 Ga old. A less cratered, tens of meters thick mantling unit indicates a resurfacing event ∼3.7 Ga ago. We highlight five potential exploration sites that satisfy technical constraints (such as shallow slopes, solar illumination, and Earth visibility), provide materials that can be sampled, and are capable of addressing multiple science objectives. Due to its accessibility and traversability, combined with its geologic diversity, proximity of permanently shadowed regions for studying volatile processes, and ability to address multiple science objectives, we confirm and reinforce the Amundsen crater region as a high-priority landing and exploration site.

Keywords: planetary geology; the moon; planetary polar regions; planetary mineralogy; planetary surfaces; lunar craters; lunar geochronology; lunar science; lunar surface