Sazuna/UAT_keywords huggingface dataset:
Dalek: A Deep Learning Emulator for TARDIS. Supernova spectral time series contain a wealth of information about the progenitor and explosion process of these energetic events. The modeling of these data requires the exploration of very high dimensional posterior probabilities with expensive radiative transfer codes. Even modest parameterizations of supernovae contain more than 10 parameters and a detailed exploration demands at least several million function evaluations. Physically realistic models require at least tens of CPU minutes per evaluation putting a detailed reconstruction of the explosion out of reach of traditional methodology. The advent of widely available libraries for the training of neural networks combined with their ability to approximate almost arbitrary functions with high precision allows for a new approach to this problem. Instead of evaluating the radiative transfer model itself, one can build a neural network proxy trained on the simulations but evaluating orders of magnitude faster. Such a framework is called an emulator or surrogate model. In this work, we present an emulator for the TARDIS supernova radiative transfer code applied to Type Ia supernova spectra. We show that we can train an emulator for this problem given a modest training set of 100,000 spectra (easily calculable on modern supercomputers). The results show an accuracy on the percent level (that are dominated by the Monte Carlo nature of TARDIS and not the emulator) with a speedup of several orders of magnitude. This method has a much broader set of applications and is not limited to the presented problem.

Keywords: Supernovae, Radiative transfer, Neural networks
Discovery of Double-ring Structure in the Supernova Remnant N103B: Evidence for Bipolar Winds from a Type Ia Supernova Progenitor. The geometric structure of supernova remnants (SNR) provides a clue to unveiling the pre-explosion evolution of their progenitors. Here we present an X-ray study of N103B (0509-68.7), a Type Ia SNR in the Large Magellanic Cloud, that is known to be interacting with dense circumstellar matter (CSM). Applying our novel method for feature extraction to deep Chandra observations, we have successfully resolved the CSM, Fe-rich ejecta, and intermediate-mass element (IME) ejecta components, and revealed each of their spatial distributions. Remarkably, the IME ejecta component exhibits a double-ring structure, implying that the SNR expands into an hourglass-shape cavity and thus forms bipolar bubbles of the ejecta. This interpretation is supported by more quantitative spectroscopy that reveals a clear bimodality in the distribution of the ionization state of the IME ejecta. These observational results can be naturally explained if the progenitor binary system had formed a dense CSM torus on the orbital plane prior to the explosion, providing further evidence that the SNR N103B originates from a single-degenerate progenitor.

Keywords: Supernova remnants
Proxy-based Prediction of Solar Extreme Ultraviolet Emission Using Deep Learning. High-energy radiation from the Sun governs the behavior of Earth's upper atmosphere and such radiation from any planet-hosting star can drive the long-term evolution of a planetary atmosphere. However, much of this radiation is unobservable because of absorption by Earth's atmosphere and the interstellar medium. This motivates the identification of a proxy that can be readily observed from the ground. Here, we evaluate absorption in the near-infrared 1083 nm triplet line of neutral orthohelium as a proxy for extreme ultraviolet (EUV) emission in the 30.4 nm line of He II and 17.1 nm line of Fe IX from the Sun. We apply deep learning to model the nonlinear relationships, training and validating the model on historical, contemporaneous images of the solar disk acquired in the triplet He I line by the ground-based SOLIS observatory and in the EUV by the NASA Solar Dynamics Observatory. The model is a fully convolutional neural network that incorporates spatial information and accounts for the projection of the spherical Sun to 2d images. Using normalized target values, results indicate a median pixelwise relative error of 20% and a mean disk-integrated flux error of 7% on a held-out test set. Qualitatively, the model learns the complex spatial correlations between He I absorption and EUV emission has a predictive ability superior to that of a pixel-by-pixel model; it can also distinguish active regions from high-absorption filaments that do not result in EUV emission.

Keywords: Convolutional neural networks, Ground-based astronomy, Solar extreme ultraviolet emission, Neural networks
Minidisk Dynamics in Accreting, Spinning Black Hole Binaries: Simulations in Full General Relativity. We perform magnetohydrodynamic simulations of accreting, equal-mass binary black holes in full general relativity focusing on the impact of black hole spin on the dynamical formation and evolution of minidisks. We find that during the late inspiral the sizes of minidisks are primarily determined by the interplay between the tidal field and the effective innermost stable orbit around each black hole. Our calculations support that a minidisk forms when the Hill sphere around each black hole is significantly larger than the black hole's effective innermost stable orbit. As the binary inspirals, the radius of the Hill sphere decreases, and minidisks consequently shrink in size. As a result, electromagnetic signatures associated with minidisks may be expected to gradually disappear prior to merger when there are no more stable orbits within the Hill sphere. In particular, a gradual disappearance of a hard electromagnetic component in the spectrum of such systems could provide a characteristic signature of merging black hole binaries. For a binary of given total mass, the timescale to minidisk "evaporation" should therefore depend on the black hole spins and the mass ratio. We also demonstrate that accreting binary black holes with spin have a higher efficiency for converting accretion power to jet luminosity. These results could provide new ways to estimate black hole spins in the future.

Keywords: Accretion, Black hole physics, High energy astrophysics, Gravitation, Gravitational wave sources, Astrophysical black holes
Rotational Mass Shedding from Asteroid (6478) Gault. The ∼4 km diameter main belt asteroid 6478 Gault has ejected dust intermittently since at least 2013. The character of the emission, including its episodic nature and the low speed of the ejected particles (V ∼ 0.15 m s-1), is most consistent with mass loss from a body rotating near rotational breakup. Owing to dust contamination of the nucleus signal, this conclusion had not yet been confirmed. To test this idea, we have obtained new images of Gault in 2020 August in the absence of dust. Our photometry shows a lightcurve with a very small amplitude (maximum ∼0.05 mag) and a periodicity of 2.55 ± 0.10 hr. The new observations are consistent with a model in which Gault is rotating near breakup, with centrifugal forces responsible for its episodic mass loss. Approximated as a strengthless (fluid) spherical body, the implied density is ρ = 1700 kg m-3. We use the Froude number Fr, defined here as the ratio between centrifugal force and gravitational force, as a way to investigate mass-loss regimes in fast-spinning asteroids and find that mass shedding starts at Fr ∼ 0.5.

Keywords: Small Solar System bodies, Asteroids
Hubble Space Telescope Observations of the Old Pulsar PSR J0108-1431. We present results of optical-UV observations of the 200 Myr old rotation-powered radio pulsar J0108-1431 with the Hubble Space Telescope. We found a putative candidate for the far-UV (FUV) pulsar counterpart, with the flux density fν = 9.0 ± 3.2 nJy at λ = 1528 Å. The pulsar was not detected, however, at longer wavelengths, with 3σ upper limits of 52, 37, and 87 nJy at λ = 4326, 3355, and 2366 Å, respectively. Assuming that the pulsar counterpart was indeed detected in FUV, and the previously reported marginal U and B detections with the Very Large Telescope were real, the optical-UV spectrum of the pulsar can be described by a power-law model with a nearly flat fν spectrum. Similar to younger pulsars detected in the optical, the slope of the nonthermal spectrum steepens in the X-ray range. The pulsar's luminosity in the 1500-6000 Å wavelength range, L ∼ 1.2 × 1027(d/210 pc)2 erg s-1, corresponds to a high efficiency of conversion of pulsar rotation energy-loss rate $\dot{E}$ &lt;!-- --&gt; to the optical-UV radiation, $\eta =L/\dot{E}\sim (1\mbox{--}6)\times {10}^{-4}$ &lt;!-- --&gt; , depending on somewhat uncertain values of distance and spectral slope. The brightness temperature of the bulk neutron star surface does not exceed 59,000 K (3σ upper bound), as seen by a distant observer. If we assume that the FUV flux is dominated by a thermal component, then the surface temperature can be in the range of 27,000-55,000 K, Requiring a heating mechanism to operate in old neutron stars. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #14249.

Keywords: Neutron stars, Pulsars
The Causes of Peripheral Coronal Loop Contraction and Disappearance Revealed in a Magnetohydrodynamic Simulation of Solar Eruption. The phenomenon of peripheral coronal loop contraction during solar flares and eruptions, recently discovered in observations, has gradually drawn the attention of solar physicists. However, its underlying physical mechanism is still uncertain. One possible mechanism is Hudson's implosion conjecture, which attributes the contraction of peripheral coronal loops to magnetic pressure reduction in the magnetic energy liberation core, while other researchers proposed alternative explanations. In previous observational studies we also note the disappearance of peripheral shrinking loops in the late phase, of which there is a lack of investigation and interpretation. In this paper, we exploit a full MHD simulation of solar eruption to study the causes of the two phenomena. It is found that the loop motion in the periphery is well correlated with magnetic energy accumulation and dissipation in the core, and the loop shrinkage is caused by a more significant reduction in magnetic pressure gradient force than in magnetic tension force, consistent with the implosion conjecture. The peripheral contracting loops in the late phase act as inflow to reconnect with central erupting structures, which destroys their identities and naturally explains their disappearance. We also propose a positive feedback between the peripheral magnetic reconnection and the central eruption.

Keywords: Solar active region magnetic fields, Magnetohydrodynamics, Solar corona, Magnetohydrodynamical simulations
Downstream Depolarization in the Sausage Relic: A 1-4 GHz Very Large Array Study. Radio relics are elongated sources related to shocks driven by galaxy cluster merger events. Although these objects are highly polarized at GHz frequencies (≳20%), high-resolution studies of their polarization properties are still lacking. We present the first high-resolution and high-sensitivity polarimetry study of the merging galaxy cluster CIZA J2242.8+5301 in the 1-4 GHz frequency band. We use the QU-fitting approach to model the Stokes I, Q, and U emission, obtaining best-fit intrinsic polarization fraction (p0), intrinsic polarization angle (χ0), rotation measure (RM), and wavelength-dependent depolarization (σRM) maps of the cluster. Our analysis focuses on the northern relic (RN). For the first time in a radio relic, we observe a decreasing polarization fraction in the downstream region. Our findings are possibly explained by geometrical projections and/or by decreasing of the magnetic field anisotropy toward the cluster center. From the amount of depolarization of the only detected background radio galaxy, we estimate a turbulent magnetic field strength of Bturb ∼ 5.6 μG in the relic. Finally, we observe RM fluctuations of about 30 rad m-2 around the median value of 140.8 rad m-2 at the relic position.

Keywords: Galaxy clusters, Plasma astrophysics, Galactic and extragalactic astronomy, Shocks, Intracluster medium, Polarimetry
Radio Spectral Imaging of an M8.4 Eruptive Solar Flare: Possible Evidence of a Termination Shock. Solar flare termination shocks have been suggested as one of the viable mechanisms for accelerating electrons and ions to high energies. Observational evidence of such shocks, however, remains rare. Using radio dynamic spectroscopic imaging of a long-duration C1.9 flare obtained by the Karl G. Jansky Very Large Array (VLA), Chen et al. suggested that a type of coherent radio bursts, referred to as "stochastic spike bursts," were radio signatures of nonthermal electrons interacting with myriad density fluctuations at the front of a flare termination shock. Here we report another stochastic spike burst event recorded during the extended energy release phase of a long-duration M8.4-class eruptive flare on 2012 March 10. VLA radio spectroscopic imaging of the spikes in 1.0-1.6 GHz shows that, similar to the case of Chen et al., the burst centroids form an extended, ∼10″-long structure in the corona. By combining extreme-ultraviolet imaging observations of the flare from two vantage points with hard X-ray and ultraviolet observations of the flare ribbon brightenings, we reconstruct the flare arcade in three dimensions. The results show that the spike source is located at ∼60 Mm above the flare arcade, where a diffuse supra-arcade fan and multitudes of plasma downflows are present. Although the flare arcade and ribbons seen during the impulsive phase do not allow us to clearly understand how the observed spike source location is connected to the flare geometry, the cooling flare arcade observed 2 hr later suggests that the spikes are located in the above-the-loop-top region, where a termination shock presumably forms.

Keywords: Solar flares, Solar magnetic reconnection, Solar radio flares, Solar radio emission, Non-thermal radiation sources, Solar coronal mass ejections, Shocks
ALMA Observations of the Asymmetric Dust Disk around DM Tau. We report an analysis of the dust disk around DM Tau, newly observed with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm. The ALMA observations with high sensitivity (8.4 μJy beam-1) and high angular resolution (35 mas, 5.1 au) detect two asymmetries on the ring at r ∼ 20 au. They could be two vortices in early evolution, the destruction of a large-scale vortex, or double continuum emission peaks with different dust sizes. We also found millimeter emissions with ∼50 μJy (a lower-limit dust mass of 0.3 MMoon) inside the 3 au ring. To characterize these emissions, we modeled the spectral energy distribution (SED) of DM Tau using a Monte Carlo radiative transfer code. We found that an additional ring at r = 1 au could explain both the DM Tau SED and the central point source. The disk midplane temperature at the 1 au ring calculated in our modeling is less than the typical water sublimation temperature of 150 K, prompting the possibility of forming small icy planets there.

Keywords: Protoplanetary disks
Mass Ejection in Failed Supernovae: Equation of State and Neutrino Loss Dependence. A failed core-collapse supernova from a nonrotating progenitor can eject mass due to a weakening of gravity associated with neutrino emission from the protoneutron star. This mechanism yields observable transients and sets an upper limit on the mass of the black hole (BH) remnant. Previous global simulations of this mechanism have included neutrino losses parametrically, however, with direct implications for the ejecta mass and energy. Here we evolve the inner supernova core with a spherically symmetric, general-relativistic neutrino radiation-hydrodynamic code until BH formation. We then use the result in a Newtonian code that follows the response of the outer layers of the star to the change in gravity and resolves the surface pressure scale height. We find that the dense-matter equation of state (EOS) can introduce a factor of ∼2 variation in gravitational mass lost to neutrinos, with a stiff EOS matching previous parametric results and a soft EOS yielding lower ejecta masses and energies by a factor of several. This difference is caused primarily by the longer time to BH formation in stiffer EOSs. With a soft EOS, our red and yellow supergiant progenitors fail to unbind mass if hydrogen recombination energy is not included. Using a linear ramp in time for mass-energy lost to neutrinos (with suitable parameters) yields a stellar response within ∼10% of that obtained using the detailed history of neutrino losses. Our results imply quantitative but not qualitative modifications to previous predictions for shock breakout, plateau emission, and final BH masses from these events.

Keywords: Supernova neutrinos, Black holes, Hydrodynamics, Core-collapse supernovae, Gravitation, Shocks
The Hawaii Infrared Parallax Program. V. New T-dwarf Members and Candidate Members of Nearby Young Moving Groups. We present a search for new planetary-mass members of nearby young moving groups (YMGs) using astrometry for 694 T and Y dwarfs, including 447 objects with parallaxes, mostly produced by recent large parallax programs from UKIRT and Spitzer. Using the BANYAN Σ and LACEwING algorithms, we identify 30 new candidate YMG members, with spectral types of T0-T9 and distances of 10-43 pc. Some candidates have unusually red colors and/or faint absolute magnitudes compared to field dwarfs with similar spectral types, providing supporting evidence for their youth, including four early-T dwarfs. We establish one of these, the variable T1.5 dwarf 2MASS J21392676+0220226, as a new planetary-mass member ( ${14.6}_{-1.6}^{+3.2}$ &lt;!-- --&gt; MJup) of the Carina-Near group (200 ± 50 Myr) based on its full six-dimensional kinematics, including a new parallax measurement from CFHT. The high-amplitude variability of this object is suggestive of a young age, given the coexistence of variability and youth seen in previously known YMG T dwarfs. Our four latest-type (T8-T9) YMG candidates, WISE J031624.35+430709.1, ULAS J130217.21+130851.2, WISEPC J225540.74-311841.8, and WISE J233226.49-432510.6, if confirmed, will be the first free-floating planets (≍2-6 MJup) whose ages and luminosities are compatible with both hot-start and cold-start evolutionary models, and thus overlap with the properties of the directly imaged planet 51 Eri b. Several of our early/mid-T candidates have peculiar near-infrared spectra, indicative of heterogenous photospheres or unresolved binarity. Radial velocity measurements needed for final membership assessment for most of our candidates await upcoming 20-30 m class telescopes. In addition, we compile all 15 known T7-Y1 benchmarks and derive a homogeneous set of their effective temperatures, surface gravities, radii, and masses.

Keywords: Free floating planets, Stellar associations, T dwarfs
Testing the Jeans, Toomre, and Bonnor-Ebert Concepts for Planetesimal Formation: 3D Streaming-instability Simulations of Diffusion-regulated Formation of Planetesimals. We perform streaming-instability simulations at Hill density and beyond to demonstrate that planetesimal formation is not completed when pebble accumulations exceed the local Hill density. We find that Hill density is not a sufficient criterion for further gravitational collapse of a pebble cloud into a planetesimal, but that additionally the accumulated mass has to be large enough to overcome turbulent diffusion. A Toomre analysis of the system indicates that linear self-gravity modes play no role on the scale of our numerical simulation. We nevertheless find that self-gravity, by vertically contracting the pebble layer, increases the strength of turbulence, which is either an indication of Kelvin-Helmholtz instability or a boost of the streaming instability. We furthermore determine the Bonnor-Ebert central density to which a pebble cloud of a given mass has to be compressed before it would be able to continue contraction against internal diffusion. As the equivalent "solid body" size of the pebble cloud scales with the central density to the power of -1/6, it is much easier to have a pebble cloud of 100 km equivalent size to collapse than one of 10 km for the same level of turbulent diffusion. This can explain the lack of small bodies in the solar system and predicts small objects will form at large pebble-to-gas ratios, so either in the outskirts of the solar nebula or at late times of generally reduced gas mass.

Keywords: Hydrodynamical simulations, Solar system formation, Small Solar System bodies, Classical Kuiper belt objects, Asteroids, Circumstellar disks, Protoplanetary disks, Planetesimals, Trans-Neptunian objects
Avoiding the Geometric Boundary Effect in Shear Measurement. In image processing, source detections are inevitably affected by the presence of the geometric boundaries in the images, including the physical boundaries of the CCD, and the boundaries of masked regions due to column defects, bright diffraction spikes, etc. These boundary conditions make the source detection process not statistically isotropic and can lead to additive shear bias near the boundaries. We build a phenomenological model to understand the bias, and propose a simple method to effectively eliminate the influence of geometric boundaries on shear measurement. We demonstrate the accuracy and efficiency of this method using both simulations and the z-band imaging data from the third data release of the DECam Legacy Survey.

Keywords: Gravitational lensing
A Stochastic Theory of the Hierarchical Clustering. II. Halo Progenitor Mass Function and Large-scale Bias. We generalize the stochastic theory of hierarchical clustering presented in Paper I by Lapi &amp; Danese to derive the (conditional) halo progenitor mass function and the related large-scale bias. Specifically, we present a stochastic differential equation that describes fluctuations in the mass growth of progenitor halos of given descendant mass and redshift, as driven by a multiplicative Gaussian white noise involving the power spectrum and the spherical collapse threshold of density perturbations. We demonstrate that, as cosmic time passes, the noise yields an average drift of the progenitors toward larger masses, which quantitatively renders the expectation from the standard extended Press and Schechter (EPS) theory. We solve the Fokker-Planck equation associated with the stochastic dynamics, and obtain as an exact, stationary solution, the EPS progenitor mass function. Then we introduce a modification of the stochastic equation in terms of a mass-dependent collapse threshold modulating the noise, and solve analytically the associated Fokker-Planck equation for the progenitor mass function. The latter is found to be in excellent agreement with the outcomes of N-body simulations; even more remarkably, this is achieved with the same shape of the collapse threshold used in Paper I to reproduce the halo mass function. Finally, we exploit the above results to compute the large-scale halo bias, and find it in pleasing agreement with the N-body outcomes. All in all, the present paper illustrates that the stochastic theory of hierarchical clustering introduced in Paper I can describe effectively not only halos' abundance, but also their progenitor distribution and their correlation with the large-scale environment across cosmic times.

Keywords: Cosmology, Dark matter