adsabs/SciX_UAT_keywords huggingface dataset:
Small-scale Field-aligned Currents in the Magnetopause Boundary Layer

Based on high-resolution measurements from the Magnetospheric Multiscale mission from 2015 May to 2018 June, we statistically investigate the properties of small-scale field-aligned currents (SFACs) in the magnetopause boundary layer. A total of 2235 SFACs are successfully identified. The durations of SFACs mainly fall between 0.2 and 0.3 s. Over 90% of SFACs have a width of less than 1 ion inertia length and are primarily distributed from 5 to 25 electron inertia lengths, implying that the SFACs belong to the kinetic-scale current layer. The main carriers of SFACs are electrons, and over 70% of SFACs exhibit net energy dissipation (i.e., J · E ' > 0) with the majority of energy dissipation taking place in the parallel direction. SFACs are widely distributed spatially, and the occurrence rate of SFACs is higher in the boundary layer closer to the magnetosphere. Additionally, less than half of the total SFACs are identified in well-known structures, including the magnetic reconnection region, flux transfer event, Kelvin–Helmholtz vortex, and exhaust region, and 54% of the SFACs are in the "others" unknown structures. These results improve our comprehension of the current system at the magnetopause and the roles of SFACs in the coupling between the solar wind and magnetosphere.

Keywords: planetary magnetospheres; solar wind; planetary boundary layers
Alfnoor: A Retrieval Simulation of the Ariel Target List

In this work, we present Alfnoor, a dedicated tool optimized for population studies of exoplanet atmospheres. Alfnoor combines the latest version of the retrieval algorithm, TauREx 3, with the instrument noise simulator ArielRad and enables the simultaneous retrieval analysis of a large sample of exo-atmospheres. We applied this tool to the Ariel list of planetary candidates and focus on hydrogen dominated, cloudy atmospheres observed in transit with the Tier-2 mode (medium Ariel resolution). As a first experiment, we randomized the abundances—ranging from 10-7 to 10-2—of the trace gases, which include H2O, CH4, CO, CO2, and NH3. This exercise allowed us to estimate the detection limits for Ariel Tier-2 and Tier-3 modes when clouds are present. In a second experiment, we imposed an arbitrary trend between a chemical species and the effective temperature of the planet. A last experiment was run requiring molecular abundances being dictated by equilibrium chemistry at a certain temperature. Our results demonstrate the ability of Ariel Tier-2 and Tier-3 surveys to reveal trends between the chemistry and associated planetary parameters. Future work will focus on eclipse data, on atmospheres heavier than hydrogen, and will be applied also to other observatories.

Keywords: space telescopes; exoplanet atmospheric composition; transmission spectroscopy
Recent Updates of Gas-phase Chemical Reactions and Molecular Lines of SiS in CLOUDY

Here we present our current update of CLOUDY on gas-phase chemical reactions for the formation and destruction of the SiS molecule, its energy levels, and collisional rate coefficients with H2, H, and He over a wide range of temperatures. As a result, henceforth the spectral synthesis code CLOUDY predicts SiS line intensities and column densities for various astrophysical environments.

Keywords: interstellar medium; molecular physics
X-Ray Characterization of the Pulsar PSR J1849-0001 and Its Wind Nebula G32.64+0.53 Associated with TeV Sources Detected by H.E.S.S., HAWC, Tibet ASγ, and LHAASO

We report on the X-ray emission properties of the pulsar PSR J1849-0001 and its wind nebula (PWN), as measured by Chandra, XMM-Newton, NICER, Swift, and NuSTAR. In the X-ray data, we detected the 38 ms pulsations of the pulsar up to ~60 keV with high significance. Additionally, we found that the pulsar's on-pulse spectral energy distribution displays significant curvature, peaking at ≈60 keV. Comparing the phase-averaged and on-pulse spectra of the pulsar, we found that the pulsar's off-pulse emission exhibits a spectral shape that is very similar to its on-pulse emission. This characterization of the off-pulse emission enabled us to measure the >10 keV spectrum of the faint and extended PWN using NuSTAR's off-pulse data. We measured both the X-ray spectrum and the radial profiles of the PWN's brightness and photon index, and we combined these X-ray measurements with published TeV results. We then employed a multizone emission scenario to model the broadband data. The results of the modeling suggest that the magnetic field within the PWN is relatively low (≈7 μG) and that electrons are accelerated to energies ≳400 TeV within this PWN. The electrons responsible for the TeV emission outside the X-ray PWN may propagate to ~30 pc from the pulsar in ~10 kyr.

Keywords: pulsars; pulsar wind nebulae; rotation powered pulsars; high energy astrophysics; gamma-ray sources; x-ray sources; spectral energy distribution; radiative processes
Pulse Profile Variations Associated with the Glitch of PSR B2021+51

We reported the first glitch of PSR B2021+51 detected with the Shanghai Tian Ma Radio Telescope that occurred around MJD 58289.1 (2018 June 20). The spin frequency and its derivative suffered a jump of about 7.04 × 10-10 Hz and 2.6 × 10-18 s-2, respectively. The pulse width at the 10% intensity level (W10) of the mean pulse profile significantly decreased right before the glitch and then increased after the glitch, accompanied by an enhancement in the trailing peak of the normalized profile. The mean pulse profiles were decomposed into three Gaussian components, i.e., C1, C2, and C3 from left to right by peak phase. The width of C3 (w3) had an apparent maximum right before the glitch and its weighted mean value became slightly smaller than the pre-glitch value after the glitch, while the weighted mean values of both w1 and w2 had no apparent change. The significant decrease of the mean pulse width right before the glitch is mainly due to the movement of C3 toward C1 and C2, while the increase of the mean pulse width after the glitch results from the movement of C2 toward C3. Changes in the widths of mean pulse profiles and in the widths and phase separations of Gaussian components associated with the glitch convinced us of a connection between the changes in characteristics of the pulsar emission zone and the glitch activity. We discuss a possible interpretation invoking the movements of flux tubes in the emission zone.

Keywords: neutron stars; pulsars
The HST Nondetection of SN Ia 2011fe 11.5 yr after Explosion Further Restricts Single-degenerate Progenitor Systems

We present deep Hubble Space Telescope imaging of the nearby Type Ia supernova (SN Ia) 2011fe obtained 11.5 yr after explosion. No emission is detected at the SN location to a 1σ (3σ) limit of F555W > 30.2 (29.0) mag, or equivalently M V > 1.2 (‑0.1) mag, neglecting the distance uncertainty to M101. We constrain the presence of donor stars impacted by the SN ejecta with the strictest limits thus far on compact (i.e., $\mathrm{log}\,g\gtrsim 4$ ) companions. H-rich zero-age main-sequence companions with masses ≥2 M ⊙ are excluded, a significant improvement upon the preexplosion imaging limit of ≈5 M ⊙. Main-sequence He stars with masses ≥1.0 M ⊙ and subgiant He stars with masses ≤0.8 M ⊙ are also disfavored by our late-time imaging. Synthesizing our limits on postimpact donors with previous constraints from preexplosion imaging, early-time radio and X-ray observations, and nebular-phase spectroscopy, essentially all formation channels for SN 2011fe invoking a nondegenerate donor star at the time of explosion are unlikely.

Keywords: type ia supernovae; stellar mass loss; helium-rich stars; interacting binary stars
A Census of Star Formation in the Outer Galaxy. II. The GLIMPSE360 Field

We have conducted a study of star formation in the outer Galaxy from 65°< l < 265° in the region observed by the GLIMPSE360 program. This Spitzer warm mission program mapped the plane of the outer Milky Way with IRAC at 3.6 and 4.5 μm. We combine the IRAC, Wide-field Infrared Survey Explorer (WISE), and Two Micron All Sky Survey catalogs and our previous results from another outer Galaxy survey and identify a total of 47,338 young stellar objects (YSOs) across the field spanning >180° in Galactic longitude. Using the DBSCAN method on the combined catalog, we identify 618 clusters or aggregations of YSOs having five or more members. We identify 10,476 class I, 29,604 class II, and 7325 anemic class II/class III YSOs. The ratio of YSOs identified as members of clusters was 25,528/47,338, or 54%. We found that 100 of the clusters identified have previously measured distances in the WISE H II survey. We used these distances in our spectral energy distribution (SED) fitting of the YSOs in these clusters, of which 96 had YSOs with <3σ fits. We used the derived masses from the SED model fits to estimate the initial mass function (IMF) in the inner and outer Galaxy clusters; dividing the clusters by galactocentric distances, the slopes were Γ = 1.87 ± 0.31 above 3 M⊙ for RGal < 11.5 kpc and Γ = 1.15 ± 0.24 above 3 M⊙ for RGal > 11.5 kpc. The slope of the combined IMF was found to be Γ = 1.92 ± 0.42 above 3 M⊙. These values are consistent with each other within the uncertainties and with literature values in the inner Galaxy high-mass star formation regions. The slopes are likely also consistent with a universal Salpeter IMF.

Keywords: young stellar objects; protoplanetary disks; protostars; stellar mass functions; star formation; milky way galaxy; circumstellar disks; infrared excess
Satellite Alignment. III. Satellite Galaxies' Spatial Distribution and Their Dependence on Redshift with a Novel Galaxy Finder

After being extensively explored, observations and theories have shown that satellites are preferentially aligned with major axes of their host centrals. There are still some unresolved issues on this topic. In this paper, we present studies on satellite spatial distribution. To fairly compare with observations, we develop a novel galaxy finder and reconstruction algorithm in hydrodynamical simulation, which is based on the projected mock image, taking into account the full consideration of the point-spread function, pixel size, surface brightness limit, resolution, and redshift dimming effects. With galaxy samples constructed using such an algorithm, the satellite alignment is examined by comparing with observational results. It is found that the observational alignment can be reproduced for red galaxies, which dominate the sample in this study, but not for blue galaxies. Satellites' radial distribution is also investigated. It exhibits that outer satellites within host halos show stronger alignment signal than satellites in the inner regions, especially for red satellites, which is in contrast with previous studies. The disagreement is mainly due to extra galaxies identified by our new galaxy finder, which are mainly located in the inner region of host halos. Our study illustrates that at lower redshift, the alignment strength becomes stronger, while the radial distribution curve becomes flatter. This suggests differences in the evolution of the angular distribution between satellites residing in the inner and outer halos and implies that the post-infall evolution reduces the original alignment signal and that the impact decreases for satellites with later infall times.

Keywords: galaxy formation; galaxy structure; computational methods; observational astronomy; astrostatistics
The Space Weather Context of the First Extreme Event of Solar Cycle 25, on 2022 September 5

The coronal mass ejection (CME) on 2022 September 5 was the fastest CME yet observed and measured in situ by a spacecraft inside the corona (0.06 au for the Parker Solar Probe). Here we assess the significance of this event for space weather studies by analyzing the source region characteristics and its temporal evolution via a magnetic complexity index. We also examine the kinematics and energetics of the CME. We find that it was a very fast and massive event, with a speed greater than 2200 km s-1 and a mass of 2 × 1016 g. Consequently, this is within the top 1% of all CMEs observed by SOHO/LASCO since 1996. It is therefore natural to ask, "What if this CME was an Earth-directed one?" To answer this question, we put the CME and the associated flare properties in the context of similar previous extreme events (namely, the 2012 July 23 and 2012 March 7 eruptions), discussing the possibility that these trigger a solar energetic particle (SEP) event. We find that 2022 September 5 could have resulted in a high-energy SEP event. We also estimate the transit time and speed of the CME and calculate the likely Dst variations if this was an Earth-directed event.

Keywords: space weather; solar coronal mass ejections; solar coronal mass ejection shocks; solar energetic particles; heliosphere
Intense Whistler-mode Waves at Foreshock Transients: Characteristics and Regimes of Wave-Particle Resonant Interaction

Thermalization and heating of plasma flows at shocks result in unstable charged-particle distributions that generate a wide range of electromagnetic waves. These waves, in turn, can further accelerate and scatter energetic particles. Thus, the properties of the waves and their implication for wave-particle interactions are critically important for modeling energetic particle dynamics in shock environments. Whistler-mode waves, excited by the electron heat flux or a temperature anisotropy, arise naturally near shocks and foreshock transients. As a result, they can often interact with suprathermal electrons. The low background magnetic field typical at the core of such transients and the large wave amplitudes may cause such interactions to enter the nonlinear regime. In this study, we present a statistical characterization of whistler-mode waves at foreshock transients around Earth's bow shock, as they are observed under a wide range of upstream conditions. We find that a significant portion of them are sufficiently intense and coherent (narrowband) to warrant nonlinear treatment. Copious observations of background magnetic field gradients and intense whistler wave amplitudes suggest that phase trapping, a very effective mechanism for electron acceleration in inhomogeneous plasmas, may be the cause. We discuss the implications of our findings for electron acceleration in planetary and astrophysical shock environments.

Keywords: planetary bow shocks
Limiting Behavior of Asteroid Obliquity and Spin Using a Semi-analytic Thermal Model of the YORP Effect

The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect governs the spin evolution of small asteroids. The axial component of YORP, which alters the rotation rate of the asteroid, is mostly independent of its thermal inertia, while the obliquity component is very sensitive to the thermal model of the asteroid. Here, we develop a semi-analytic theory for the obliquity component of YORP. We integrate an approximate thermal model over the surface of an asteroid, and find an analytic expression for the obliquity component in terms of two YORP coefficients. This approach allows us to investigate the overall evolution of asteroid rotation state, and to generalize the results previously obtained in the case of zero thermal inertia. The proposed theory also explains how a nonzero obliquity component of YORP originates even for a symmetric asteroid, due to its finite thermal inertia. In many cases, this causes equatorial planes of asteroids to align with their orbital planes. The studied nontrivial behavior of YORP as a function of thermal model allows for a new kind of rotational equilibria, which can have important evolutionary consequences for asteroids.

Keywords: asteroid dynamics; asteroid rotation
MIRECLE: Science Yield for a Mid-infrared Explorer-class Mission to Study Nontransiting Rocky Planets Orbiting the Nearest M Stars Using Planetary Infrared Excess

Recent investigations have demonstrated the potential for utilizing a new observational and data-analysis technique for studying the atmospheres of nontransiting exoplanets with combined light that relies on acquiring simultaneous, broad-wavelength spectra and resolving planetary infrared emission from the stellar spectrum through simultaneous fitting of the stellar and planetary spectral signatures. This new data-analysis technique, called planetary infrared excess (PIE), holds the potential to open up the opportunity for measuring mid-infrared (MIR) phase curves of nontransiting rocky planets around the nearest stars with a relatively modest telescope aperture. We present simulations of the performance and science yield for a mission and instrument concept that we call the MIR Exoplanet CLimate Explorer, a concept for a moderately sized cryogenic telescope with broad wavelength coverage (1-18 μm) and a low-resolution (R ~ 50) spectrograph designed for the simultaneous wavelength coverage and extreme flux measurement precision necessary to detect the emission from cool rocky planets with PIE. We present exploratory simulations of the potential science yield for PIE measurements of the nearby planet Proxima Centauri b, showing the potential to measure the composition and structure of an Earth-like atmosphere with a relatively modest observing time. We also present overall science yields for several mission architecture and performance metrics, and discuss the technical performance requirements and potential telescope and instrument technologies that could meet these requirements.

Keywords: exoplanet atmospheres; exoplanet astronomy; exoplanets; extrasolar rocky planets; space observatories
On the Contribution of Quiet-Sun Magnetism to Solar Irradiance Variations: Constraints on Quiet-Sun Variability and Grand-minimum Scenarios

While the quiet-Sun magnetic field shows only little variation with the solar cycle, long-term variations cannot be completely ruled out from first principles. We investigate the potential effect of quiet-Sun magnetism on spectral solar irradiance through a series of small-scale dynamo simulations with zero vertical flux imbalance ( $\langle {B}_{z}\rangle =0$) and varying levels of small-scale magnetic field strength, and one weak network case with an additional flux imbalance corresponding to a flux density of $\langle {B}_{z}\rangle =100$ G. From these setups, we compute the dependence of the outgoing radiative energy flux on the mean vertical magnetic field strength in the photosphere at a continuum optical depth τ = 1 ( $\langle | {B}_{z}| {\rangle }_{\tau =1}$). We find that a quiet-Sun setup with a mean vertical field strength of $\langle | {B}_{z}| {\rangle }_{\tau =1}=69$ G is about 0.6% brighter than a non-magnetic reference case. We find a linear dependence of the outgoing radiative energy flux on the mean field strength $\langle | {B}_{z}| {\rangle }_{\tau =1}$ with a relative slope of 1.4 × 10-4 G-1. With this sensitivity, only a moderate change of the quiet-Sun field strength by 10% would lead to a total solar irradiance variation comparable to the observed solar cycle variation. While this does provide strong indirect constraints on possible quiet-Sun variations during a regular solar cycle, it also emphasizes that potential variability over longer timescales could make a significant contribution to longer-term solar irradiance variations.

Keywords: quiet sun; solar spectral irradiance; radiative magnetohydrodynamics; solar photosphere; radiative transfer; solar granulation; solar magnetic fields
Modeling the Spectral Energy Distributions and Spectropolarimetry of Blazars-Application to 4C+01.02 in 2016-2017

The optical radiation emitted by blazars contains contributions from synchrotron radiation by relativistic electrons in the jets, as well as thermal radiation emitted mainly by the accretion disk (AD), the broad-line region (BLR), and the host galaxy. The unpolarized radiation components from the AD, BLR, and host galaxy present themselves by decreasing the total polarization in the optical/ultraviolet (UV) spectrum. A combined model for the spectral energy distribution (SED) and degree of optical/UV polarization is constructed, enabling the disentanglement of the synchrotron and AD components. Our model is applied to the multiwavelength SED and spectropolarimetry observations of the flat-spectrum radio quasar 4C+01.02 (z = 2.1) in its 2016 July-August flaring state and 2017 July-August quiescent state, using data from the Fermi Large Area Telescope, the Southern African Large Telescope, and the Las Cumbres Observatory network of telescopes. By constraining the AD component, the mass of the supermassive black hole is obtained as ~3 × 109 M ⊙. Furthermore, the model retrieves the characteristics of the relativistic electron distribution in the jet and the degree of ordering of the magnetic field. Our results highlight the potential of spectropolarimetry observations for disentangling thermal from nonthermal (jet) emission components, thus revealing the physics of particle acceleration and high-energy emission in active galactic nucleus jets. * Based on observations made with the Southern African Large Telescope (SALT) under program 2016-2-LSP-001 (PI: D. A. H. Buckley).

Keywords: active galaxies; galaxy jets; flat-spectrum radio quasars; spectropolarimetry; blazars; active galactic nuclei
Target Selection and Validation of DESI Quasars

The Dark Energy Spectroscopic Instrument (DESI) survey will measure large-scale structures using quasars as direct tracers of dark matter in the redshift range 0.9 < z < 2.1 and using Lyα forests in quasar spectra at z > 2.1. We present several methods to select candidate quasars for DESI, using input photometric imaging in three optical bands (g, r, z) from the DESI Legacy Imaging Surveys and two infrared bands (W1, W2) from the Wide-field Infrared Survey Explorer. These methods were extensively tested during the Survey Validation of DESI. In this paper, we report on the results obtained with the different methods and present the selection we optimized for the DESI main survey. The final quasar target selection is based on a random forest algorithm and selects quasars in the magnitude range of 16.5 < r < 23. Visual selection of ultra-deep observations indicates that the main selection consists of 71% quasars, 16% galaxies, 6% stars, and 7% inconclusive spectra. Using the spectra based on this selection, we build an automated quasar catalog that achieves a fraction of true QSOs higher than 99% for a nominal effective exposure time of ~1000 s. With a 310 deg-2 target density, the main selection allows DESI to select more than 200 deg-2 quasars (including 60 deg-2 quasars with z > 2.1), exceeding the project requirements by 20%. The redshift distribution of the selected quasars is in excellent agreement with quasar luminosity function predictions.

Keywords: quasars; redshift surveys; sky surveys