Sazuna/UAT_keywords huggingface dataset:
Observational Quantification of Three-dimensional Anisotropies and Scalings of Space Plasma Turbulence at Kinetic Scales. A statistical survey of spectral anisotropy of space plasma turbulence is performed using five years of measurements from the Magnetospheric Multiscale mission in the magnetosheath. By measuring the five-point second-order structure functions of the magnetic field, we have for the first time quantified the three-dimensional anisotropies and scalings at sub-ion scales (&lt;100 km). In the local reference frame $({\hat{L}}_{\perp },{\hat{l}}_{\perp },{\hat{l}}_{\parallel })$ defined with respect to local mean magnetic field ${{\boldsymbol{B}}}_{0}$ , the "statistical eddies" are found to be mostly elongated along ${{\boldsymbol{B}}}_{0}$ and shortened in the direction perpendicular to both ${{\boldsymbol{B}}}_{0}$ and local field fluctuations. From several di (ion inertial length) toward ∼0.05 di, the ratio between eddies' parallel and perpendicular lengths features a trend of rise then fall, whereas the anisotropy in the perpendicular plane appears scale-invariant. Specifically, the anisotropy relations for the total magnetic field at 0.1-1.0 di are obtained as ${l}_{\parallel }\simeq 2.44\cdot {l}_{\perp }^{0.71}$ , and ${L}_{\perp }\simeq 1.58\cdot {l}_{\perp }^{1.08}$ , respectively. Our results provide new observational evidence to compare with phenomenological models and numerical simulations, which may help to better understand the nature of kinetic-scale turbulence.

Keywords: Interplanetary turbulence, Space plasmas
Vibrational Spectroscopy of a Potential Interstellar Ion: Protonated Methyl Formate. The abundance of methyl formate (MF, HCOOCH3) in star-forming regions of the interstellar medium (ISM) suggests the presence of protonated MF (H+MF). However, no spectroscopic data exist for isolated H+MF. Here, we address the vibrational properties of H+MF and its H+MF-Ln≤2 clusters (L = Ar/N2) by infrared photodissociation (IRPD) spectroscopy and density functional theory calculations. Protonation of MF occurs at the CO oxygen, resulting in four different isomers arising from the syn/anti (s/a) and cis/trans (c/t) orientation between OCH3 and the excess proton. H+MF photofragments into protonated methanol by CO elimination. The IRPD spectrum exhibits redshifted OH stretch bands of the most stable H+MF(t/s) and H+MF(c/a) conformers because of the high internal energy required for dissociation. Tagging of H+MF with inert ligands drastically reduces both the internal energy and the dissociation threshold. The resulting higher-resolution IRPD spectra allow determination of the most stable H+MF rotamers as (t/s) and (c/a). In the cold H+MF-L dimers, the ligand forms an OH...L hydrogen bond, while bonding to the positively charged 2pz orbital of the carbonyl C atom is less favorable. The latter allows estimation of the free OH stretch fundamental of the most stable H+MF(t/s) rotamer as 3545 ± 5 cm-1. While for neutral MF the more stable syn rotamer MF(s) dominates the population in both the laboratory and the ISM (&gt;99%), the anti conformer is substantially populated for H+MF (∼30%), which is rationalized by protonation-induced isomerization. This mechanism may lead to an enhanced abundance of MF(a) in certain regions of the ISM.

Keywords: Laboratory astrophysics, Molecular spectroscopy, Chemical abundances, Astrochemistry, Interstellar medium, Electron impact ionization
Radio Echo in the Turbulent Corona and Simulations of Solar Drift-pair Radio Bursts. Drift-pair bursts are an unusual type of solar low-frequency radio emission, which appear in the dynamic spectra as two parallel drifting bright stripes separated in time. Recent imaging spectroscopy observations allowed for the quantitative characterization of the drifting pairs in terms of source size, position, and evolution. Here, the drift-pair parameters are qualitatively analyzed and compared with the newly developed Monte Carlo ray-tracing technique simulating radio-wave propagation in the inhomogeneous anisotropic turbulent solar corona. The results suggest that drift-pair bursts can be formed due to a combination of refraction and scattering processes, with the trailing component being the result of turbulent reflection (turbulent radio echo). The formation of drift-pair bursts requires an anisotropic scattering with the level of plasma density fluctuations comparable to that in type III bursts, but with a stronger anisotropy at the inner turbulence scale. The anisotropic radio-wave scattering model can quantitatively reproduce the key properties of drift-pair bursts: the apparent source size and its increase with time at a given frequency, the parallel motion of the source centroid positions, and the delay between the burst components. The trailing component is found to be virtually cospatial and following the main component. The simulations suggest that drift-pair bursts are likely to be observed closer to the disk center and below 100 MHz due to the effects of free-free absorption and scattering. The exciter of drift pairs is consistent with propagating packets of whistlers, allowing for a fascinating way to diagnose the plasma turbulence and the radio emission mechanism.

Keywords: Solar coronal radio emission, Radio spectroscopy
Obliquity of an Earth-like Planet from Frequency Modulation of Its Direct-imaged Lightcurve: Mock Analysis from General Circulation Model Simulation. Direct-imaging techniques of exoplanets have made significant progress recently and will eventually enable monitoring of photometric and spectroscopic signals of Earth-like habitable planets. The presence of clouds, however, would remain as one of the most uncertain components in deciphering such direct-imaged signals of planets. We attempt to examine how the planetary obliquity produces different cloud patterns by performing a series of general circulation model simulation runs using a set of parameters relevant for our Earth. Then we use the simulated photometric lightcurves to compute their frequency modulation that is due to the planetary spin-orbit coupling over an entire orbital period, and we attempt to see to what extent one can estimate the obliquity of an Earth twin. We find that it is possible to estimate the obliquity of an Earth twin within the uncertainty of several degrees with a dedicated 4 m space telescope at 10 pc away from the system if the stellar flux is completely blocked. While our conclusion is based on several idealized assumptions, a frequency modulation of a directly imaged Earth-like planet offers a unique methodology to determine its obliquity.

Keywords: Stellar photometry, Oblique rotators, Hydrodynamics, Earth atmosphere, Atmospheric circulation, Exoplanet surface composition, Direct imaging, Radiative transfer, Biosignatures, Exoplanet atmospheres
Origin of Large Meteoritic SiC Stardust Grains in Metal-rich AGB Stars. Stardust grains that originated in ancient stars and supernovae are recovered from meteorites and carry the detailed composition of their astronomical sites of origin. We present evidence that the majority of large (μm-sized) meteoritic silicon carbide (SiC) grains formed in C-rich asymptotic giant branch (AGB) stars that were more metal-rich than the Sun. In the framework of the slow neutron captures (the s process) that occur in AGB stars, the lower-than-solar ${}^{88}$ Sr/ ${}^{86}$ Sr isotopic ratios measured in the large SiC grains can only be accompanied by Ce/Y elemental ratios that are also lower than solar and predominately observed in metal-rich barium stars—the binary companions of AGB stars. Such an origin suggests that these large grains represent the material from high-metallicity AGB stars needed to explain the s-process nucleosynthesis variations observed in bulk meteorites. In the outflows of metal-rich, C-rich AGB stars, SiC grains are predicted to be small (≃0.2 μm); large (≃μm-sized) SiC grains can grow if the number of dust seeds is 2-3 orders of magnitude lower than the standard value of 10-13 times the number of H atoms. We therefore predict that with increasing metallicity, the number of dust seeds might decrease, resulting in the production of larger SiC grains.

Keywords: Stellar abundances, Asymptotic giant branch stars, Circumstellar dust, Chemically peculiar stars
An Evolutionary Study of Volatile Chemistry in Protoplanetary Disks. The volatile composition of a planet is determined by the inventory of gas and ice in the parent disk. The volatile chemistry in the disk is expected to evolve over time, though this evolution is poorly constrained observationally. We present Atacama Large Millimeter/submillimeter Array observations of C18O, C2H, and the isotopologues H13CN, HC15N, and DCN toward five Class 0/I disk candidates. Combined with a sample of 14 Class II disks presented in Bergner et al., this data set offers a view of volatile chemical evolution over the disk lifetime. Our estimates of C18O abundances are consistent with a rapid depletion of CO in the first ∼0.5-1 Myr of the disk lifetime. We do not see evidence that C2H and HCN formation are enhanced by CO depletion, possibly because the gas is already quite under-abundant in CO. Further CO depletion may actually hinder their production by limiting the gas-phase carbon supply. The embedded sources show several chemical differences compared to the Class II stage, which seem to arise from shielding of radiation by the envelope (impacting C2H formation and HC15N fractionation) and sublimation of ices from infalling material (impacting HCN and C18O abundances). Such chemical differences between Class 0/I and Class II sources may affect the volatile composition of planet-forming material at different stages in the disk lifetime.

Keywords: Interstellar molecules, Protostars, Protoplanetary disks, Astrochemistry
Supervised Convolutional Neural Networks for Classification of Flaring and Nonflaring Active Regions Using Line-of-sight Magnetograms. Solar flares are explosions in the solar atmosphere that release intense bursts of short-wavelength radiation and are capable of producing severe space-weather. Flares release free energy built up in coronal fields, which are rooted in active regions (ARs) on the photosphere, via magnetic reconnection. The exact processes that lead to reconnection are not fully known and therefore reliable forecasting of flares is challenging. Recently, photospheric magnetic-field data has been extensively analyzed using machine learning (ML) and these studies suggest that flare-forecasting accuracy does not strongly depend on how long in advance flares are predicted. Here, we use ML to understand the evolution of AR magnetic fields before and after flares. We explicitly train convolutional neural networks (CNNs) to classify Solar Dynamics Observatory/Helioseismic and Magnetic Imager line-of-sight magnetograms into ARs producing at least one M- or X-class flare or as nonflaring. We find that flaring ARs remain in flare-productive states—marked by recall &gt; 60% with a peak of ∼80%—days before and after flares. We use occlusion maps and statistical analysis to show that the CNN pays attention to regions between the opposite polarities from ARs and the CNN output is dominantly decided by the total unsigned line-of-sight flux of ARs. Using synthetic bipole magnetograms, we find spurious dependencies of the CNN output on magnetogram dimensions for a given bipole size. Our results suggest that it is important to use CNN designs that eliminate such artifacts in CNN applications for processing magnetograms and, in general, solar image data.

Keywords: Convolutional neural networks, Solar flares, Astronomy data analysis
Was GW190412 Born from a Hierarchical 3 + 1 Quadruple Configuration?. The gravitational wave source GW190412 is a binary black hole (BBH) merger with three unique properties: (i) its mass ratio is about 0.28, the lowest found so far, (ii) it has a relatively high positive effective spin parameter ${\chi }_{\mathrm{eff}}=0.25$ , and (iii) it is observed to be precessing due to in-plane projected spin of the binary with an in-plane precession parameter ${\chi }_{{\rm{p}}}=0.3$ . The two main formation channels of BBH formation fail to account for GW190412: field formation scenarios cannot explain the observed precession unless by invoking large natal kicks, and dynamical assembly in dense stellar systems is inefficient in producing such low-mass-ratio BBH mergers. Here, we investigate whether "double mergers" in wide hierarchical quadruple systems in the "3 + 1" configuration could explain the unique properties of GW190412. In this scenario, a compact object quadruple system experiences two mergers: first, two compact objects in the innermost orbit merge due to secular chaotic evolution. At a later time, the merged compact object coalesces with another compact object due to secular Lidov-Kozai oscillations. We find that our scenario is consistent with GW190412. In particular, we find a preferential projected spin around ${\chi }_{{\rm{p}}}=0.2$ . However, the likelihood of a double merger is small and the formation efficiency of these systems is uncertain. If GW190412 originated from a double merger in a 3 + 1 quadruple, we find a strong constraint that the first merger likely occurred between roughly equal-mass BHs in the innermost orbit, since the recoil velocity from unequal-mass BHs would otherwise have disrupted the system.

Keywords: Black hole physics, Gravitational wave sources
Cosmological Model-independent Constraints on Spatial Curvature from Strong Gravitational Lensing and SN Ia Observations. Applying the distance sum rule in strong gravitational lensing (SGL) and SN Ia observations, one can provide an interesting cosmological model-independent method to determine the cosmic curvature parameter Ωk. In this paper, with the newly compiled data sets including 161 galactic-scale SGL systems and 1048 SN Ia data, we place constraints on Ωk within the framework of three types of lens models extensively used in SGL studies. Moreover, to investigate the effect of different mass lens samples on the results, we divide the SGL sample into three subsamples based on the center velocity dispersion of intervening galaxies. In the singular isothermal sphere (SIS) and extended power-law lens models, a flat universe is supported with an uncertainty of about 0.2, while a closed universe is preferred in the power-law lens model. We find that the choice of lens models and the classification of SGL data actually can influence the constraints on Ωk significantly.

Keywords: Cosmology, Strong gravitational lensing, Gravitational lensing, Cosmological parameters
Imaging and Spectral Study on the Null Point of a Fan-spine Structure During a Solar Flare. Using the multi-instrument observations, we make the first simultaneous imaging and spectral study on the null point of a fan-spine magnetic topology during a solar flare. When magnetic reconnection occurs at the null point, the fan-spine configuration brightens in the (extreme-)ultraviolet channels. In the Hα images, the fan-spine structure is partly filled and outlined by the bidirectional material flows ejected from the reconnection site. The extrapolated coronal magnetic field confirms the existence of the fan-spine topology. Before and after the flare peak, the total velocity of the outflows is estimated to be about 60 km s-1. During the flare, the Si IV line profile at the reconnection region is enhanced both in the blue-wing and red-wing. At the flare peak time, the total velocity of the outflows is found to be 144 km s-1. Superposed on the Si IV profile, there are several deep absorption lines with the blueshift of several tens of km s-1. The reason is inferred to be that the bright reconnection region observed in Si IV channel is located under the cooler material appearing as dark features in the Hα line. The blueshifted absorption lines indicate the movement of the cooler material toward the observer. The depth of the absorption lines also depends on the amount of cooler material. These results imply that these kinds of spectral profiles can be used as a tool to diagnose the properties of cooler material above the reconnection site.

Keywords: Solar flares, Solar ultraviolet emission, Solar magnetic reconnection, Solar photosphere, Solar flare spectra, Solar active regions, Solar filaments, Solar magnetic fields, Solar corona, Solar activity, Solar chromosphere
On the Determination of Rotation Velocity and Dynamical Mass of Galaxies Based on Integrated H I Spectra. The integrated 21 cm H I emission profile of a galaxy encodes valuable information on the kinematics, spatial distribution, and dynamical state of its cold interstellar medium. The line width, in particular, reflects the rotation velocity of the galaxy, which, in combination with a size scale, can be used to constrain the dynamical mass of the system. We introduce a new method based on the concept of the curve of growth to derive a set of robust parameters to characterize the line width, asymmetry, and concentration of the integrated H I spectra. We use mock spectra to evaluate the performance of our method, to estimate realistic systematic uncertainties for the proposed parameters, and to correct the line widths for the effects of instrumental resolution and turbulence broadening. Using a large sample of nearby galaxies with available spatially resolved kinematics, we demonstrate that the newly defined line widths can predict the rotational velocities of galaxies to within an accuracy of ≲30 km s-1. We use the calibrated line widths, in conjunction with the empirical relation between the size and mass of H I disks, to formulate a prescription for estimating the dynamical mass within the H I-emitting region of gas-rich galaxies. Our formalism yields dynamical masses accurate to ∼0.3 dex based solely on quantities that can be derived efficiently and robustly from current and future extragalactic H I surveys. We further extend the dynamical mass calibration to the scale of the dark matter halo.

Keywords: Galaxy dynamics, H I line emission, Galaxy kinematics, Interstellar medium, Galaxies
Photohadronic Model for the Neutrino and Gamma-Ray Emission from TXS 0506+056. The detection of a high-energy muon neutrino on 2017 September 22 by the IceCube neutrino detector coincides with the multiwavelength flaring from the BL Lac object TXS 0506+056, most likely confirming an active galactic nucleus as a source of high energy cosmic rays and neutrinos. Using the photohadronic model, we have explained the very high energy γ-rays observed by MAGIC telescopes a few days after the neutrino event and extend the model to calculate the neutrino flux at different windows consistent with the flaring period of TXS 0506+056 and compared with the IceCube and MAGIC estimates. We also use this model to estimate the neutrino flux from the flaring of FSRQ PKS B1424-418, which is believed to be associated with the 2 PeV neutrino event observed by IceCube.

Keywords: BL Lacertae objects, Gamma-ray sources, Neutrino astronomy, Relativistic jets, Particle astrophysics
The Evolutionary Track of H/He Envelopes of the Observed Population of Sub-Neptunes and Super-Earths. The observational detection of a localized reduction in the small planet occurrence rate, sometimes termed a "gap," is an exciting discovery because of the implications for planet evolutionary history. This gap appears to define a transition region in which sub-Neptune planets are believed to have lost their H/He envelopes, potentially by photoevaporation or core powered mass loss, and have thus been transformed into bare core terrestrial planets. Here we investigate the transition between sub-Neptunes and super-Earths using a real sample of observed small close-in planets and applying envelope evolution models of the H/He envelope together with the mass-radius diagram and a photoevaporation model. We find that photoevaporation can explain the H/He envelope loss of most super-Earths in 100 Myr, although an additional loss mechanism appears necessary in some planets. We explore the possibility that these planets' families have different core masses and find a continuum in the primordial population of the strongly irradiated super-Earths and the sub-Neptunes. Our analysis also shows that close-orbiting sub-Neptunes with R &lt; 3.5 R⊕ typically lose ∼30% of their primordial envelope.

Keywords: Extrasolar rocky planets, Exoplanets, Exoplanet structure, Mini Neptunes, Exoplanet atmospheres
No Redshift Evolution in the Broad-line-region Metallicity up to z = 7.54: Deep Near-infrared Spectroscopy of ULAS J1342+0928. We present deep (9 hr) Gemini-N/Gemini Near-InfraRed Spectrograph near-infrared spectroscopic observations of ULAS J1342+0928, a luminous quasar at z = 7.54. Various broad emission lines were detected, as well as the underlying continuum and iron forests over the rest-frame wavelength 970-2930 Å. There is a clear trend that higher-ionization emission lines show larger blueshifts with C IV $\lambda 1549$ exhibiting ${5510}_{-110}^{+240}$ km s-1 blueshift with respect to the systematic redshift from the far-infrared [C II] $158\,\mu {\rm{m}}$ emission line. Those high-ionization lines have wide profiles with FWHM more than 10,000 km s-1. A modest blueshift of ${340}_{-80}^{+110}$ km s-1 is also seen in Mg II, the lowest-ionization line identified in the spectrum. The updated Mg II-based black hole mass of ${M}_{\mathrm{BH}}={9.1}_{-1.3}^{+1.4}\times {10}^{8}{M}_{\odot }$ and the Eddington ratio of ${L}_{\mathrm{bol}}/{L}_{\mathrm{Edd}}={1.1}_{-0.2}^{+0.2}$ confirm that ULAS J1342+0928 is powered by a massive and actively accreting black hole. There is no significant difference in the emission-line ratios such as Si IV/C IV and Al III/C IV when compared to lower-redshift quasars in a similar luminosity range, which suggests early metal pollution of the broad-line-region clouds. This trend also holds for the Fe II/Mg II line ratio, known as a cosmic clock that traces the iron enrichment in the early universe. Different iron templates and continuum fitting ranges were used to explore how the Fe II/Mg II measurement changes as a function of spectral modeling. Quasars at even higher redshift or at fainter luminosity range ( ${L}_{\mathrm{bol}}\lesssim {10}^{46}$ erg s-1) are needed to probe the sites of early metal enrichment and a corresponding change in the Fe II/Mg II ratio.

Keywords: Supermassive black holes, Quasars
Nuclear X-Ray Activity in Low-surface-brightness Galaxies: Prospects for Constraining the Local Black Hole Occupation Fraction with a Chandra Successor Mission. About half of nearby galaxies have a central surface brightness ≥1 mag below that of the sky. The overall properties of these low-surface-brightness galaxies (LSBGs) remain understudied, and in particular we know very little about their massive black hole population. This gap must be closed to determine the frequency of massive black holes at z = 0 as well as to understand their role in regulating galaxy evolution. Here we investigate the incidence and intensity of nuclear, accretion-powered X-ray emission in a sample of 32 nearby LSBGs with the Chandra X-ray Observatory. A nuclear X-ray source is detected in four galaxies (12.5%). Based on an X-ray binary contamination assessment technique developed for normal galaxies, we conclude that the detected X-ray nuclei indicate low-level accretion from massive black holes. The active fraction is consistent with that expected from the stellar mass distribution of the LSBGs, but not their total baryonic mass, when using a scaling relation from an unbiased X-ray survey of normal galaxies. This suggests that their black holes co-evolved with their stellar population. In addition, the apparent agreement nearly doubles the number of galaxies available within ∼100 Mpc for which a measurement of nuclear activity can efficiently constrain the frequency of black holes as a function of stellar mass. We conclude by discussing the feasibility of measuring this occupation fraction to a few percent precision below ≲1010M⊙ with high-resolution, wide-field X-ray missions currently under consideration.

Keywords: Active galactic nuclei, X-ray active galactic nuclei, Low surface brightness galaxies