adsabs/SciX_UAT_keywords huggingface dataset:
Ion Acceleration and the Development of a Power-law Energy Spectrum in Magnetic Reconnection

How charged particles are accelerated efficiently and form a power-law energy spectrum in magnetic reconnection is a problem that is not well understood. In a previous paper, it was shown that the electron Kelvin-Helmholtz instability (EKHI) in force-free magnetic reconnection generates fast-expanding vortices that can accelerate electrons in a few tens of ion gyroperiods (less than 1 ms in the solar corona) to form a power-law energy distribution. In this paper, we present a particle-in-cell (PIC) simulation study of ion acceleration in force-free magnetic reconnection in the presence of the EKHI-induced turbulence. We find that ions are not significantly accelerated by the EKHI-induced stochastic electric field until the magnetic vortices expand to sizes comparable to the ion gyroradius. The Alfvén waves generated by the EKHI couple with the magnetic vortices, leading to resonance between the ions inside the magnetic vortices and Alfvén waves and enhanced ion heating. The induced Alfvén wave resonance results in a broken power-law energy spectrum with a breakpoint at $\sim {m}_{i}{v}_{A}^{2}$ , where vA is the Alfvén velocity. We show that the process that forms the nonthermal tail is a second-order Fermi mechanism and the mean spectral index is α = (1 + 4a2D/R)/2, where D is the spatial scale of the inductive electric field, R is that of vortices, and a = Bg/B0, with ratio of guide field Bg and asymptotic B0.

Keywords: solar magnetic reconnection; solar energetic particles; spectral energy distribution
Radio Propagation Studies of the Solar Wind in the Era of Parker Solar Probe

The NASA Parker Solar Probe mission is providing unprecedented measurements of solar wind plasma and plasma turbulence at heliocentric distances as small as 0.125 au, or 26.9 solar radii. Radioastronomical remote sensing measurements of the coronal and solar wind plasma have been made since the 1960s over a heliocentric distance range that overlaps with and extends that of Parker Solar Probe. This paper will compare radio scintillation and Parker Solar Probe results on the heliocentric-distance-dependence of the plasma density variance (where there may be an inconsistency between the two techniques), the speed at which turbulence density irregularities move radially with respect to the Sun, and other topics.

Keywords: solar wind; solar corona; space plasmas
Classification and Jet Power of Fermi Blazars

In this work, we compile a sample of 449 Fermi blazars with the luminosity of the broadline region, the black hole mass, the beam radio luminosity, and the jet power; obtain the beam power and the black hole spin; investigate the dividing line between BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars (FSRQs) to identify the discrepancies in their dominant mechanisms; and revisit the dependence of the jet power on the disk accretion luminosity, the black hole mass, and the black hole spin. We come to the following conclusions. (1) A boundary of log (L BLR/L Edd) = -3.14, separating the BL Lacs and the FSRQs, is obtained from the Bayesian analysis, which is consistent with the results from the literature. We employ the boundary to divide the blazar candidates of uncertain types into candidates for BL Lacs or FSRQs, and we find five changing-look blazars at the same time. (2) A strong correlation is found between black hole mass and intrinsic γ-ray luminosity, but a weaker correlation is found between black hole mass and observed γ-ray luminosity. The latter is weakened by jet effects: it is apparently weak for BL Lacs that have disordered amplification of the Doppler factor, since their mechanism is dominated by jets, while it is moderate for FSRQs, since their mechanism is dominated by accretion processes. (3) The jets of both FSRQs and BL Lacs are likely governed by the Blandford-Znajek mechanism.

Keywords: active galactic nuclei; blazars; jets; black holes; accretion
Evolution of the Outflow in the Water Fountain Source IRAS 18043-2116

We present the spectral and spatial evolution of H2O masers associated with the water fountain source IRAS 18043-2116, found in observations with the Nobeyama 45 m Telescope and the Australia Telescope Compact Array. We have found new highest-velocity components of the H2O masers (at the redshifted side V LSR ≃ 376 km s-1 and at the blueshifted side V LSR ≃ -165 km s-1), and the resulting velocity spread of ≃540 km s-1 breaks the speed record of fast jets/outflows in this type of sources. The locations of those components have offsets from the axis joining the two major maser clusters, indicating a large opening angle of the outflow (~60°). The evolution of the maser cluster separation of ~2.9 mas yr-1 and the compact (~0.″2) CO emission source mapped with the Atacama Large Millimeter-submillimeter Array suggest a very short (~30 yr) timescale of the outflow. We also confirmed an increase in the flux density of the 22 GHz continuum source. The properties of the jet and the continuum sources and their possible evolution in the transition to the planetary nebula phase are further discussed. *Released on 2021 March 1.

Keywords: water masers; asymptotic giant branch stars; astrophysical masers; post-asymptotic giant branch stars; stellar jets
Evidence for a Cosmic-Ray Gradient in the IM Lup Protoplanetary Disk

Protoplanetary disk evolution is strongly impacted by ionization from the central star and local environment, which collectively have been shown to drive chemical complexity and are expected to impact the transport of disk material. Nonetheless, ionization remains a poorly constrained input to many detailed modeling efforts. We use new and archival ALMA observations of N2H+ 3-2 and H13CO+ 3-2 to derive the first observationally motivated ionization model for the IM Lup protoplanetary disk. Incorporating ionization from multiple internal and external sources, we model N2H+ and H13CO+ abundances under varying ionization environments and compare these directly to the imaged ALMA observations by performing non-LTE radiative transfer, visibility sampling, and imaging. We find that the observations are best reproduced using a radially increasing cosmic-ray (CR) gradient, with low CR ionization in the inner disk, high CR ionization in the outer disk, and a transition at ∼80-100 au. This location is approximately coincident with the edge of spiral structure identified in millimeter emission. We also find that IM Lup shows evidence for enhanced UV-driven formation of HCO+, which we attribute to the disk's high flaring angle. In summary, IM Lup represents the first protoplanetary disk with observational evidence for a CR gradient, which may have important implications for IM Lup's ongoing evolution, especially given the disk's young age and large size.

Keywords: protoplanetary disks; planet formation; astrochemistry; radio interferometry
Multiband Spectropolarimetry of Lunar Maria, Pyroclastics, Fresh Craters, and Swirl Materials

Imaging polarimetry is a well-known method for examining the small-scale structure of the surface regolith of airless celestial bodies. In this study, we examine (for the first time) the wavelength-dependent polarization behavior of selected lunar areas, including maria, highlands, fresh craters, pyroclastic deposits, and the Reiner Gamma swirl, based on telescopic multiband UBVRI imaging polarimetry at phase angles within the range of the positive polarization branch. The terrain-dependent spectropolarimetric behavior is studied for the first time in this work. For each study area, we conduct a mapping of the relative regolith grain size, an analysis of the exponent of the Umov law, and the wavelength dependence of the degree of linear polarization. Furthermore, we perform area-specific principal component analyses of the degree of linear polarization, followed by unsupervised machine learning (clustering) to segment different terrain types. We find that fresh mare craters and high-titanium pyroclastic deposits have an increased regolith grain size, whereas crater ray material, low-titanium pyroclastic material, and the Reiner Gamma swirl are more finely grained than the average regolith. The degree of linear polarization decreases with increasing wavelength-dependent albedo according to a power law whose exponent is itself positively correlated with the albedo. For a constant albedo and grain size, the degree of linear polarization increases linearly with wavelength. The clustering step yields a library of terrain-dependent prototype spectra of the degree and angle of linear polarization.

Keywords: the moon; polarimetry; spectropolarimetry; lunar impacts; lunar maria; volcanism; lunar magnetic fields; astronomy data analysis; astronomy image processing
Disentangling the Hadronic Components in NGC 1068

The recent detection of high-energy neutrinos by IceCube in the direction of the nearby Seyfert/starburst galaxy NGC 1068 implies that radio-quiet active galactic nuclei can accelerate cosmic-ray ions. Dedicated multimessenger analyses suggest that the interaction of these high-energy ions with ambient gas or photons happens in a region of the galaxy that is highly opaque for GeV-TeV gamma rays. Otherwise, the GeV-TeV emission would violate existing constraints provided by the Fermi Large Area Telescope (LAT) and the Major Atmospheric Gamma Imaging Cherenkov. The conditions of high optical depth are realized near the central supermassive black hole (SMBH). At the same time, the GeV emission detected by the Fermi LAT is likely related to the galaxy's sustained star formation activity. In this work, we derive a 20 MeV-1 TeV spectrum of NGC 1068 using 14 yr of Fermi LAT observations. We find that the starburst hadronic component is responsible for NGC 1068's emission above ~500 MeV. However, below this energy, an additional component is required. In the 20-500 MeV range, the Fermi LAT data are consistent with hadronic emission initiated by non-thermal ions interacting with gas or photons in the vicinity of the central SMBH. This highlights the importance of the MeV band to discover hidden cosmic-ray accelerators.

Keywords: gamma-ray astronomy; agn host galaxies; cosmological neutrinos
Two Bright M Dwarfs Hosting Ultra-Short-Period Super-Earths with Earth-like Compositions

We present observations of two bright M dwarfs (TOI-1634 and TOI-1685: J = 9.5-9.6) hosting ultra-short-period (USP) planets identified by the TESS mission. The two stars are similar in temperature, mass, and radius (Teff ≈ 3500 K, M⋆ ≈ 0.45-0.46 M⊙, and R⋆ ≈ 0.45-0.46 R⊙), and the planets are both super-Earth size (1.25 R⊕ < Rp < 2.0 R⊕). For both systems, light curves from ground-based photometry exhibit planetary transits, whose depths are consistent with those from the TESS photometry. We also refine the transit ephemerides based on the ground-based photometry, finding the orbital periods of P = 0.9893436 ± 0.0000020 days and P = 0.6691416 ± 0.0000019 days for TOI-1634b and TOI-1685b, respectively. Through intensive radial velocity (RV) observations using the InfraRed Doppler (IRD) instrument on the Subaru 8.2 m telescope, we confirm the planetary nature of the TOIs and measure their masses: 10.14 ± 0.95 M⊕ and 3.43 ± 0.93 M⊕ for TOI-1634b and TOI-1685b, respectively, when the observed RVs are fitted with a single-planet circular-orbit model. Combining those with the planet radii of Rp = 1.749 ± 0.079 R⊕ (TOI-1634b) and 1.459 ± 0.065 R⊕ (TOI-1685b), we find that both USP planets have mean densities consistent with an Earth-like internal composition, which is typical for small USP planets. TOI-1634b is currently the most massive USP planet in this category, and it resides near the radius valley, which makes it a benchmark planet in the context of discussing the size limit of rocky planet cores as well as testing the formation scenarios for USP planets. Excess scatter in the RV residuals for TOI-1685 suggests the presence of a possible secondary planet or unknown activity/instrumental noise in the RV data, but further observations are required to check those possibilities. * Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Keywords: high resolution spectroscopy; radial velocity; super earths; extrasolar rocky planets; transit photometry
Study of Variability in Long-term Multiwavelength Optical Lightcurves of Blazar AO 0235+164

We present a long-term and intraday variability study of optical multiwaveband (U BV RI) data from the blazar AO 0235+164 collected by various telescopes for ~44 yr (1975-2019). The blazar was found to be significantly variable over the years in all wave bands with a variation of about 6 mag between its low and active states. The variations in the different wave bands are highly correlated without any time lag. We did not observe any significant trend in color variation with time, but we observed a bluer-when-brighter trend between the B - I color index and the R magnitude. Optical BV R-band spectral energy distributions always show a convex shape. Significant intraday variability was frequently seen in the quasi-simultaneous observations of AO 0235+164 made on 22 nights in the R and V bands by the CASLEO and CAHA telescopes during 1999-2019. We also estimated a central supermassive black hole mass of 7.9 × 107 M ⊙ by analyzing the broad Mg II emission line in AO 0235+164's spectrum. We briefly explore the probable physical scenarios responsible for the observed variability.

Keywords: galaxies; active galaxies; bl lacertae objects; quasars
Spitzer Publication Statistics

We present statistics on the number of refereed astronomy journal articles that used data from NASA's Spitzer Space Telescope through the end of the calendar year 2020. We discuss the various types of science programs and science categories that were used to collect data during the mission and discuss how operational changes brought on by the depletion of cryogen in 2009 May, including the resulting budget cuts, impacted the publication rate. The post-cryogenic (warm) mission produced fewer papers than the cryogenic mission, but the percentage of the exposure time published did not appreciably change between the warm and cryogenic missions. This was mostly because in the warm mission the length of observations increased, so that each warm paper on average uses more data than the cryogenic papers. We also discuss the speed of publication, archival usage, and the tremendous efficacy of the Legacy and Exploration Science programs (large, coherent investigations), including the value of having well-advertised enhanced data products hosted in centralized archives. We also identify the observations that have been published the largest number of times, and sort them by a variety of metrics (including program type, instrument used, and observation length). Data that have the highest reuse rates in publications were taken early in the Spitzer mission, or belong to one of the large surveys (large either in number of objects, in number of hours observed, or in area covered on the sky). We also assess how often authors have cited the Spitzer fundamental papers or have correctly referenced the Spitzer data they used, finding that as many as 40% of papers have failed to cite the papers, and 15% have made it impossible to identify the data they used.

Keywords: infrared observatories; observatories; space telescopes; surveys; astronomical reference materials; astronomy databases
The Variability of Star Formation Rate in Galaxies. II. Power Spectrum Distribution on the Main Sequence

We constrain the temporal power spectrum of the specific star formation rate of star-forming galaxies, using a well-defined sample of main sequence galaxies from MaNGA and our earlier measurements of the ratio of the star formation rate averaged within the last 5 Myr to that averaged over the last 800 Myr. We explore the assumptions of stationarity and ergodicity that are implicit in this approach. We assume a single power-law form of the power spectrum distribution (PSD) but introduce an additional free parameter, the "intrinsic scatter", to try to account for any non-ergodicity introduced from various sources. We analyze both an "integrated" sample consisting of global measurements of all of the galaxies, as well as 25 subsamples obtained by considering five radial regions and five bins of integrated stellar mass. Assuming that any intrinsic scatter is not the dominant contribution to the main sequence dispersion of galaxies, we find that the PSDs have slopes between 1.0 and 2.0, indicating that the power (per log interval of frequency) is mostly contributed by longer-timescale variations. We find a correlation between the returned PSDs and the inferred gas depletion times ( ${\tau }_{\mathrm{dep},\mathrm{eff}}$ ) obtained from application of the extended Schmidt Law, such that regions with shorter gas depletion times show larger integrated power and flatter PSD. Intriguingly, it is found that shifting the PSDs by the inferred ${\tau }_{\mathrm{dep},\mathrm{eff}}$ causes all 25 PSDs to closely overlap, at least in the region where the PSD is best constrained and least affected by uncertainties about any intrinsic scatter. A possible explanation for these results is the dynamical response of the gas-regulator system of Lilly et al. to a uniform time-varying inflow, as previously proposed in Wang et al.

Keywords: star formation; galaxy evolution
A 3D Numerical Study of Anisotropies in Supernova Remnants

We develop a suite of 3D hydrodynamic models of supernova remnants (SNRs) expanding against the circumstellar medium (CSM). We study the Rayleigh-Taylor instability forming at the expansion interface by calculating an angular power spectrum for each of these models. The power spectra of young SNRs are seen to exhibit a dominant angular mode, which is a diagnostic of their ejecta density profile as found by previous studies. The steep scaling of power at smaller modes and the time evolution of the spectra are indicative of the absence of a turbulent cascade. Instead, as the time evolution of the spectra suggests, they may be governed by an angular mode-dependent net growth rate. We also study the impact of anisotropies in the ejecta and in the CSM on the power spectra of velocity and density. We confirm that perturbations in the density field (whether imposed on the ejecta or the CSM) do not influence the anisotropy of the remnant significantly unless they have a very large amplitude and form large-scale coherent structures. In any case, these clumps can only affect structures on large angular scales. The power spectrum on small angular scales is completely independent of the initial clumpiness and governed only by the growth and saturation of the Rayleigh-Taylor instability.

Keywords: hydrodynamics; shocks; hydrodynamical simulations; supernova remnants
Sp1149. I. Constraints on the Balmer L–σ Relation for H II Regions in a Spiral Galaxy at Redshift z = 1.49 Strongly Lensed by the MACS J1149 Cluster

The luminosities (L) and velocity dispersions (σ) of the extinction-corrected Balmer emission lines of giant H II regions in nearby galaxies exhibit a tight correlation (∼0.35 dex scatter). There are few constraints, however, on whether giant H II regions at significant look-back times follow an L–σ relation, given the angular resolution and sensitivity required to study them individually. We measure the luminosities and velocity dispersions of Hα and Hβ emission from 11 H II regions in Sp1149, a spiral galaxy at redshift (z) z = 1.49 multiply imaged by the MACS J1149 galaxy cluster. Sp1149 is also the host galaxy of the first-known strongly lensed supernova with resolved images, SN Refsdal. We employ archival Keck I OSIRIS observations, and newly acquired Keck I MOSFIRE and Large Binocular Telescope LUCI long-slit spectra of Sp1149. When we use the GLAFIC simply parameterized lens model, we find that the Hα luminosities of the H II regions at z = 1.49 are a factor of brighter than predicted by the low-redshift L–σ relation we measure from Very Large Telescope MUSE spectroscopy. If the lens model is accurate, then the H II regions in Sp1149 differ from their low-redshift counterparts. We identify an H II region in Sp1149 that is dramatically brighter (by 2.03 ± 0.44 dex) than our low-redshift L–σ relation predicts given its low velocity dispersion. Finally, the H II regions in Sp1149 are consistent, perhaps surprisingly, with the z ≈ 0 star-forming locus on the Baldwin–Phillips–Terlevich diagram.

Keywords: gravitational lensing; galactic and extragalactic astronomy; galaxy clusters; h ii regions; high-redshift galaxies
A Perturbative Treatment of the Retrograde Co-orbital Motion

An important area of research in celestial mechanics is the analysis of dynamics in mean-motion resonances (MMR). In this paper, we consider a retrograde MMR 1:1 corresponding to a co-orbital motion, in which the asteroid and the planet revolve around the Sun in opposite directions. The motivation was provided by the recent discovery of real celestial bodies moving in such resonances with giant planets (the most famous example being 514107 Ka'epaoka'awela, a retrograde co-orbital asteroid of Jupiter). Our study is conducted in the context of a spatial restricted circular three-body problem. Applying double numerical averaging, we construct the equations describing the secular evolution of the asteroid's orbit and generate phase portraits in an e - ω space. In some cases, the averaging procedure is complicated by the coexistence of several modes of resonant motion. It leads to different scenarios of the long-term behavior and, consequently, to the splitting of the phase portrait into several sheets.

Keywords: asteroids; orbital resonances; orbital motion; three-body problem; celestial mechanics; perturbation methods
Long- and Short-term Variability of Galactic Cosmic-Ray Radial Intensity Gradients between 1 and 9.5 au: Observations by Cassini, BESS, BESS-Polar, PAMELA, and AMS-02

Spatial gradients of galactic cosmic-ray (GCR) fluxes are important for studying charged particle transport in the heliosphere. Little is known so far about how these gradients evolve with time. Here we present how the radial gradient (Gr) evolves between 2006 January and 2017 September using Cassini measurements of >300 MeV protons, which we combine with proton spectra obtained by advanced observatories at Earth (BESS, BESS-Polar, PAMELA, and AMS-02). All gradient calculations were performed for a nearly constant heliocentric distance of Cassini from Earth's orbit and near the ecliptic, thus revealing only how Gr changes with time. The variability patterns of Gr are well established as they rely on a single data set for ∼9.5 au and accurately cross-calibrated GCR spectra for Earth at 1 au. We show that over solar-cycle timescales, Gr is regulated by both the polarity of the solar magnetic field and the solar-cycle phase. During the negative-polarity phase (A < 0, 2006-2014), gradients are stronger and more stable with an average of Gr = 3.5 ± 0.3%/au and with evidence of a minimum around the 2009 solar minimum. The gradient peaks at ∼4%/au around the solar maximum and subsequently experiences a gradual drop to ∼2%/au in the A > 0 phase (2014-2017). Regular Gr enhancements over yearly or biennial timescales are also observed, in phase with quasi-biennial oscillations in GCR intensity. While all aforementioned results are based on Cassini measurements that are integral in energy, they are most representative for GCR protons in the low gigaelectronvolt range.

Keywords: galactic cosmic rays; heliosphere; solar system gas giant planets; solar cycle