Sazuna/UAT_keywords huggingface dataset:
Haze Seasonal Variations of Titan's Upper Atmosphere during the Cassini Mission. This study presents a 13 yr survey of haze UV extinction profiles, monitoring the temporal evolution of the detached haze layer (DHL) in Titan's upper atmosphere (350-600 km). As reported by West et al. (GRL vol.38, L06204) at the equator, we show that the DHL was present at all latitudes below 55°N during the northern winter (2004-2009). Subsequently, it globally sunk and disappeared in 2012. No permanent DHL was observed between 2012 and 2015. Only in late 2015 did a new structure emerge from the Northern hemisphere, and propagate to the equator. This new DHL is not as pronounced as that observed in 2004, and is much more complex. In one specific sequence, in 2005, we were able to investigate the short timescale variability of the DHL, and no major changes were observed. When both sides of the limb were visible (dawn/dusk), we notice that the extinction of the DHL is slightly higher on the dawn side. Moreover, during a polar flyby in 2009, we observed the longitudinal variability of the DHL and spotted some local inhomogeneities. Finally, comparisons with UVIS stellar occultations and General Climate Models are both consistent with our findings. However, we noticed that the timing of the DHL main pattern predicted by the GMCs can be off by up to 30° in solar longitude. All these observations offer new perspectives on the seasonal cycle of Titan's upper atmosphere, the evolution of the DHL and its interaction with the dynamics.

Keywords: Saturnian satellites, Radiative transfer
Variation of Dust Properties with Cosmic Time Implied by Radiative Torque Disruption. Dust properties within a galaxy are known to change from the diffuse medium to dense clouds due to increased local gas density. However, the question of whether dust properties change with redshift remains elusive. In this paper, using the fact that the mean radiation intensity of the interstellar medium (ISM) of star-forming galaxies increases with redshift, we show that dust properties should change due to increasing efficiency of rotational disruption by radiative torques, an effect named radiative torque disruption (RATD). We first show that because of RATD, the size distribution of interstellar dust varies with redshift, for instance, dust grains become smaller at higher z. We model the extinction curves and find that the curve becomes steeper with increasing redshift. The ratio of total-to-selective extinction, RV, decreases with redshift and achieves low values of RV ∼ 1.5-2.5 for grains having a composite structure. We also find that dust properties change with the local gas density because of RATD, but the change is dominated by the radiation field for the diffuse ISM. The low values of RV implied by RATD of interstellar dust could reproduce anomalous dust extinction observed toward supernovae Ia and Small Magellanic Cloud-like extinction curves with a steep far-UV rise toward high-z galaxies. Fluctuations in RV due to interstellar turbulence and varying radiation intensity may resolve the tension in measurements of the Hubble constant using supernovae Ia. We finally discuss the implications of evolving dust properties for high-z astrophysics.

Keywords: Interstellar dust, Interstellar dust extinction, Type Ia supernovae, Interstellar medium, High-redshift galaxies
A Semianalytic Model of the Pairwise Velocity Distribution between Dark Matter Halos. We study the probability distribution function (PDF) of relative velocity between two different dark matter halos (i.e., pairwise velocity) with high-resolution cosmological N-body simulations. We revisit a non-Gaussian framework to predict pairwise velocity statistics developed in Tinker. We investigate the pairwise velocity PDFs over a wide range of halo masses of 1012.5 ≲ M [h-1 M⊙] ≲ 1015 and redshifts of 0 &lt; z &lt; 1. At a given set of masses, redshift, and separation length between two halos, our model requires three parameters to set the pairwise velocity PDF, whereas previous non-Gaussian models in the literature assumed four or more free parameters. At length scales of 5 &lt; r [h-1 Mpc] &lt; 40, our model predicts the mean and dispersion of the pairwise velocity for dark matter halos with masses of 1012.5 ≲ M [h-1 M⊙] ≲ 1013.5 at 0.3 &lt; z &lt; 1 with a 5%-level precision. We demonstrate that our model of the pairwise velocity PDF provides an accurate mapping of the two-point clustering of massive-galaxy-sized halos at scales of O(10)h-1 Mpc between redshift and real space for a given real-space correlation function. For a mass-limited halo sample with masses greater than 1013.5 h-1 M⊙ at z = 0.55, our model can explain the monopole and quadrupole moments of the redshift-space two-point correlations with a precision better than 5% at the scales of 5-40 and 10-30 h-1 Mpc, respectively. Our model of the pairwise velocity PDF will give a detailed explanation of the statistics of massive galaxies at intermediate scales in redshift surveys.

Keywords: Cosmology, Galaxy dark matter halos, Large-scale structure of the universe
On the Connection between Solar Surface Magnetic Flux and the Total Solar Irradiance. Solar surface magnetic flux evolution plays a dominant role in the variability of total solar irradiance (TSI). Different proxies of magnetic activity have been introduced to correlate solar variability and TSI. We present the daily strong flux densities (SFDs) and weak flux densities (WFDs) defined with three magnetic thresholds calculated from the Solar Dynamic Observatory/Helioseismic Magnetic Imager. TSI measurements are from the radiometers of the Variability of Solar Irradiance and Gravity Oscillations experiment on the Solar and Heliosphere Observatory, and sunspot area (SSA) is from the National Oceanic and Atmospheric Administration. We characterize the influence of the magnetic flux density variation on the TSI using the Pearson, Spearman, and percentage bend correlations and wavelet analysis between the TSI and the flux density. The Pearson's correlation shows that the TSI is negatively and strongly correlated with SFD and moderately with SSA; Spearman and 20% bend correlation shows that the TSI is moderately correlated with SFD and weakly with SSA on solar maximum, but weakly correlated on solar minimum. However, the TSI is not correlated with WFD during solar maximum and minimum. The bootstrapping tests also confirm that the influence of SFD on TSI is more significant than that of SSA. Finally, a wavelet analysis supports the idea that the SFD and TSI have a causality linkage and that the SFD dominantly influences the TSI variability on the rotational timescale.

Keywords: Solar active region magnetic fields, Solar magnetic flux emergence, Solar magnetic reconnection, Solar physics, Solar active regions, Solar magnetic fields
Kernel Phase and Coronagraphy with Automatic Differentiation. The accumulation of aberrations along the optical path in a telescope produces distortions and speckles in the resulting images, limiting the performance of cameras at high angular resolution. It is important to achieve the highest possible sensitivity to faint sources, using both hardware and data analysis software. While analytic methods are efficient, real systems are better modeled numerically, but numerical models of complicated optical systems with many parameters can be hard to understand, optimize, and apply. Automatic differentiation or "backpropagation" software developed for machine-learning applications now makes calculating derivatives with respect to aberrations in arbitrary planes straightforward for any optical system. We apply this powerful new tool to the problem of high-angular-resolution astronomical imaging. Self-calibrating observables such as the "closure phase" or "bispectrum" have been widely used in optical and radio astronomy to mitigate optical aberrations and achieve high-fidelity imagery. Kernel phases are a generalization of closure phases valid in the limit of small phase errors. Using automatic differentiation, we reproduce existing kernel phase theory within this framework and demonstrate an extension to the case of a Lyot coronagraph, which is found to have self-calibrating combinations of speckles. which are resistant to phase noise, but only in the very high-wave-front-quality regime. As an illustrative example, we reanalyze Palomar adaptive optics observations of the binary α Ophiuchi, finding consistency between the new pipeline and the existing standard. We present a new Python package MORPHINE that incorporates these ideas, with an interface similar to the popular package POPPY, for optical simulation with automatic differentiation. These methods may be useful for designing improved astronomical optical systems by gradient descent.

Keywords: Optical interferometry, Astronomy data analysis, Coronagraphic imaging, Direct imaging, Astronomical simulations
From Pseudostreamer Jets to Coronal Mass Ejections: Observations of the Breakout Continuum. The magnetic breakout model, in which reconnection in the corona leads to destabilization of a filament channel, explains numerous features of eruptive solar events, from small-scale jets to global-scale coronal mass ejections (CMEs). The underlying multipolar topology, pre-eruption activities, and sequence of magnetic-reconnection onsets (first breakout, then flare) of many observed fast CMEs/eruptive flares are fully consistent with the model. Recently, we demonstrated that most observed coronal-hole jets in fan/spine topologies also are induced by breakout reconnection at the null point above a filament channel (with or without a filament). For these two types of eruptions occurring in similar topologies, the key question is, why do some events generate jets while others form CMEs? We focused on the initiation of eruptions in large bright points/small active regions that were located in coronal holes and clearly exhibited null-point (fan/spine) topologies: such configurations are referred to as pseudostreamers. We analyzed and compared Solar Dynamics Observatory/Atmospheric Imaging Assembly, Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph Experiment, and Reuven Ramaty High Energy Solar Spectroscopic Imager observations of three events. Our analysis of the events revealed two new observable signatures of breakout reconnection prior to the explosive jet/CME outflows and flare onset: coronal dimming and the opening up of field lines above the breakout current sheet. Most key properties were similar among the selected erupting structures, thereby eliminating region size, photospheric field strength, magnetic configuration, and pre-eruptive evolution as discriminating factors between jets and CMEs. We consider the factors that contribute to the different types of dynamic behavior, and conclude that the main determining factor is the ratio of the magnetic free energy associated with the filament channel compared to the energy associated with the overlying flux inside and outside the pseudostreamer dome.

Keywords: Solar magnetic reconnection, Solar active regions, Solar filaments, Solar coronal mass ejections, Solar coronal holes, Solar coronal streamers
Terahertz Water Masers. II. Further SOFIA/GREAT Detections Toward Circumstellar Outflows, and a Multitransition Analysis. Following up on our discovery of terahertz water masers, reported in 2017, we report two further detections of water maser emission at frequencies above 1 THz. Using the GREAT instrument on SOFIA, we have detected emission in the 1.296411 THz 827 - 734 transition of water toward two additional oxygen-rich evolved stars, omicron Ceti (Mira) and R Crateris, and obtained an upper limit on the 1.296 THz line emission from U Orionis. Toward these three sources, and toward the red supergiant star VY Canis Majorae from which 1.296 THz line emission was reported previously, we have also observed several lower-frequency (sub)millimeter water maser transitions using the APEX 12 m telescope along with the 22 GHz transition using the Effelsberg 100 m telescope. We have used a simple model to analyze the multitransition data thereby obtained. Adopting, as a prior, independent literature estimates of the mass-loss rates in these four sources and in W Hydrae, we infer water abundances in a remarkably narrow range: n(H2O)/n(H2) = 1.4-2.5 × 10-4. For o Cet, VY CMa, and W Hya, the model is successful in predicting the maser line fluxes to within a typical factor ∼1.6-3. For R Crt and U Ori, the model is less successful, with typical line flux predictions lying an order of magnitude above or below the observations; such discrepancies are perhaps unsurprising given the exponential nature of maser amplification. * GREAT, the German REceiver for Astronomy at Terahertz frequencies, is a development by the MPI für Radioastronomie and the KOSMA/Universität zu Köln, in cooperation with the DLR Institut für Optische Sensorsysteme.

Keywords: Submillimeter astronomy, Circumstellar envelopes, Astrophysical masers
A Proper Discretization of Hydrodynamic Equations in Cylindrical Coordinates for Astrophysical Simulations. Cylindrical coordinates are often used in computational fluid dynamics, particularly when one is considering gas flow accreting onto a central object. Although cylindrical coordinates have several advantages in describing rotation, they have apparent singularity along the axis at the coordinate origin (z-axis). This singularity introduces difficulties in numerical simulations. First, it is difficult to reproduce the flow across the z-axis. Second, the time step is extremely shortened by the CFL condition near the z-axis because the numerical cell thereof is narrow in the azimuthal direction for a given angular resolution. Here, we propose a new discretization scheme to overcome these difficulties. In our new scheme, we consider changes in the direction of the unit vector within a cell when evaluating the flux across each cell surface. Besides, we evaluate the source term in the radial component of the momentum equation from the thermal and dynamic pressures acting on the azimuthal cell surface. The new scheme is designed to be free-stream-preserving so that flow with uniform density, pressure, and velocity is an exact solution of the discretized equation. These improvements are essential to using a lower angular resolution in the innermost area and thus to elongating each time step. Our examples demonstrate that the innermost circular region around the axis can be resolved by only six numerical cells. We present an application to an accreting compact star surrounded by a disk, in addition to Sod shock tube and rotating outflow tests.

Keywords: Hydrodynamical simulations, Hydrodynamics, Astronomical simulations
Removing Astrophysics in 21 cm Maps with Neural Networks. Measuring temperature fluctuations in the 21 cm signal from the epoch of reionization and the cosmic dawn is one of the most promising ways to study the universe at high redshifts. Unfortunately, the 21 cm signal is affected by both cosmology and astrophysics processes in a nontrivial manner. We run a suite of 1000 numerical simulations with different values of the main astrophysical parameters. From these simulations we produce tens of thousands of 21 cm maps at redshifts 10 ≤ z ≤ 20. We train a convolutional neural network to remove the effects of astrophysics from the 21 cm maps and output maps of the underlying matter field. We show that our model is able to generate 2D matter fields not only that resemble the true ones visually but whose statistical properties agree with the true ones within a few percent down to scales ≃2 Mpc-1. We demonstrate that our neural network retains astrophysical information that can be used to constrain the value of the astrophysical parameters. Finally, we use saliency maps to try to understand which features of the 21 cm maps the network is using in order to determine the value of the astrophysical parameters.

Keywords: Cosmology, Dark matter distribution, Cosmological evolution, Large-scale structure of the universe, Cold dark matter, Convolutional neural networks, H I line emission, Intergalactic medium, Dark matter
Combined Analysis of X-Ray Spectra of NGC 3227. The 1.5 Seyfert galaxy NGC 3227 has been observed by several X-ray missions. We carried out a combined analysis of the data obtained by more recent major observations of this source—two observations performed by XMM-Newton in 2000 and 2006 and six observations performed by Suzaku in 2008. A unified model, which is consistent with all eight of the observations by the two satellites with large intensity and spectral changes, was constructed. The model consists of a hard power law with the spectral index of ΓHard = 1.4-1.7, which is interpreted as the Comptonized emission from the corona above an accretion disk. In the high-flux states, an additional soft excess component dominates, which is consistent with a model with either a steeper power law with ΓSoft = 3.3-3.85 or the warm Comptonization component. These emissions from the central engine are absorbed by a partial covering material and warm absorbers. A reflection component and several emission lines are also present. We examined the relationship between the intrinsic luminosity and the absorbers' physical parameters such as the column density, which suggests that the source expanded significantly during the bright states when the soft excess is greatly enhanced.

Keywords: Accretion, Galaxy accretion disks, Active galaxies, Seyfert galaxies, Active galactic nuclei, X-ray active galactic nuclei
Far-infrared Polarization Spectrum of the OMC-1 Star-forming Region. We analyze the wavelength dependence of the far-infrared polarization fraction toward the OMC-1 star-forming region using observations from HAWC+/SOFIA at 53, 89, 154, and 214 μm. We find that the shape of the far-infrared polarization spectrum is variable across the cloud and that there is evidence of a correlation between the slope of the polarization spectrum and the average line-of-sight temperature. The slope of the polarization spectrum tends to be negative (falling toward longer wavelengths) in cooler regions and positive or flat in warmer regions. This is very similar to what was discovered in ρ Oph A via SOFIA polarimetry at 89 and 154 μm. Like the authors of this earlier work, we argue that the most natural explanation for our falling spectra is line-of-sight superposition of differing grain populations, with polarized emission from the warmer regions and less-polarized emission from the cooler ones. In contrast with the earlier work on ρ Oph A, we do not find a clear correlation of polarization spectrum slope with column density. This suggests that falling spectra are attributable to variations in grain alignment efficiency in a heterogeneous cloud consistent with radiative torques theory. Alternative explanations in which variations in grain alignment efficiency are caused by varying gas density rather than by varying radiation intensity are disfavored.

Keywords: Interstellar dust, Interstellar magnetic fields, Polarimetry, Molecular clouds
Difference in Chemical Composition between the Bright and Faint Red Clump Stars in the Milky Way Bulge. The double red clump (RC) observed in color-magnitude diagrams of the Milky Way bulge is at the heart of the current debate on the structure and formation origin of the bulge. This feature can be explained by the difference between the two RCs either in distance ("X-shaped scenario") or in chemical composition ("multiple-population scenario"). Here we report our high-resolution spectroscopy for the RC and red giant branch stars in a high-latitude field (b ∼ -8.5°) of the bulge. We find a difference in [Fe/H] between the stars in the bright and faint RC regimes, in the sense that the bright stars are enhanced in [Fe/H] with respect to the faint stars by 0.149 ± 0.036 dex. The stars on the bright RC are also enhanced in [Na/Fe] but appear to be depleted in [Al/Fe] and [O/Fe], although more observations are required to confirm the significance of these differences. Interestingly, these chemical patterns are similar to those observed among multiple stellar populations in the metal-rich bulge globular cluster Terzan 5. In addition, we find a number of Na-rich stars, which would corroborate the presence of multiple populations in the bulge. Our results support an origin of the double RC from dissolved globular clusters that harbor multiple stellar populations. Thus, our study suggests that a substantial fraction of the outer bulge stars would have originated from the assembly of such stellar systems in the early phase of the Milky Way formation.

Keywords: Globular star clusters, Galaxy formation, Red giant clump, Stellar abundances, Galaxy bulges, Spectroscopy
Unveiling the Architecture of a Pulsar-Binary Black Hole Triple System with Pulsar Arrival Time Analysis. A large number of binary black holes (BBHs) with longer orbital periods are supposed to exist as progenitors of BBH mergers recently discovered with gravitational wave (GW) detectors. In our previous papers, we proposed to search for such BBHs in triple systems through the radial velocity modulation of the tertiary orbiting star. If the tertiary is a pulsar, high-precision and high-cadence observations of its arrival time enable an unambiguous characterization of the pulsar-BBH triples located at several kiloparsecs, which are inaccessible with the radial velocity of stars. The present paper shows that such inner BBHs can be identified through the short-term Rømer delay modulation, on the order of 10 ms for our fiducial case, a triple consisting of a 20 M⊙ BBH and 1.4 M⊙ pulsar with Pin = 10 days and Pout = 100 days. If the relativistic time delays are measured as well, one can determine basically all the orbital parameters of the triple. For instance, this method is applicable to inner BBHs of down to ∼1 hr orbital periods if the orbital period of the tertiary pulsar is around several days. Inner BBHs with ≲1 hr orbital period emit the GW detectable by future space-based GW missions, including LISA, DECIGO, and BBO, and very short inner BBHs with subsecond orbital period can be even probed by the existing ground-based GW detectors. Therefore, our proposed methodology provides a complementary technique to search for inner BBHs in triples, if they exist at all, in the near future.

Keywords: Multiple stars, Black holes, Pulsar timing method, Compact binary stars, Pulsars, Celestial mechanics, Three-body problem, Gravitational waves
Scintillation Arcs in Pulsar B0450-18. We report on Green Bank Telescope observations of interstellar scintillation from the pulsar B0450-18 at 340 and 825 MHz, revealing prominent arcs in the secondary spectra at both frequencies. The arcs are successfully modeled by one-dimensional angular brightness distributions, estimated by two independent techniques. The distributions do not follow the expected shape for a Kolmogorov plasma density spectrum, and their overall angular widths follow a scaling law, versus frequency, that is slightly slower than the inverse square law expected from plasma dispersion. They also exhibit discrete peaks that are the cause of the occasional reverse sub-arcs. Over a narrow (5%) frequency range these peaks do not participate in the overall spreading, having angular positions that are fixed on the sky. However, the peaks do evolve over a wider range of frequencies and cannot be traced from 825 to 340 MHz. Our conclusions add further evidence for a widespread distribution of highly localized regions of interstellar plasma with small-scale structure that is either elongated or flattened.

Keywords: Interstellar scintillation, Radio pulsars, Interstellar medium, Interstellar plasma