Sazuna/UAT_keywords huggingface dataset:
Sparse Identification of Variable Star Dynamics. Variable stars play a crucial role as standard candles and provide valuable insights into stellar physics. They can be modeled either through fully fledged hydrodynamical simulations or analytically as systems of coupled differential equations describing the evolution of relevant physical quantities. Typically, such equations are arrived at by simplified physical assumptions concerning the conservation laws governing stellar interiors. Here we apply a data-driven technique-sparse identification of nonlinear dynamics (SINDy)-to automatically learn governing equations from observed light curves. We apply SINDy to 3100 light curves of three different variable types from the Catalina Sky Survey. The success rate depends systematically on variable type, with possible implications for variable star classification; however, it does not obviously depend on amplitude or period. Successful models can be reduced to the generalized Lienard equation $\ddot{x}+(a+{bx}+c\dot{x})\dot{x}+x=0$ . Members of the Lienard class of ordinary differential equations, such as the well-studied van der Pol oscillator, already saw some application to variable star modeling. For a, b = 0 the equation can be solved exactly, and it admits both periodic and nonperiodic solutions. We find a condition on the coefficients of the general equation for the presence of a limit cycle, which is also observed numerically in several instances.

Keywords: Delta Scuti variable stars, Pulsating variable stars, RRc variable stars, RR Lyrae variable stars, RRab variable stars
Global Mapping of Surface Composition on an Exo-Earth Using Sparse Modeling. The time series of light reflected from exoplanets by future direct imaging can provide spatial information with respect to the planetary surface. We apply sparse modeling to the retrieval method that disentangles the spatial and spectral information from multiband reflected light curves termed as spin-orbit unmixing. We use the ℓ 1-norm and the total squared variation norm as regularization terms for the surface distribution. Applying our technique to a toy model of cloudless Earth, we show that our method can infer sparse and continuous surface distributions and also unmixed spectra without prior knowledge of the planet surface. We also apply the technique to the real Earth data as observed by DSCOVR/EPIC. We determined the representative components that can be interpreted as cloud and ocean. Additionally, we found two components that resembled the distribution of land. One of the components captures the Sahara Desert, and the other roughly corresponds to vegetation, although their spectra are still contaminated by clouds. Sparse modeling significantly improves the geographic retrieval, in particular, of clouds and leads to higher resolutions for other components when compared with spin-orbit unmixing using Tikhonov regularization.

Keywords: Astroinformatics, Exoplanet surface composition, Exoplanet astronomy, Astrobiology, Direct imaging, Exoplanet surfaces, Exoplanet surface characteristics
The Coherent Differential Imaging on Speckle Area Nulling (CDI-SAN) Method for High-contrast Imaging under Speckle Variation. Differential imaging is a postprocessing method to obtain high contrast, often used for exoplanet searches. The coherent differential imaging on speckle area nulling (CDI-SAN) method was developed to detect a faint exoplanet lying beneath residual speckles of a host star. It utilizes image acquisitions faster than the stellar speckle variation synchronized with five shapes of a deformable mirror repeatedly. By using only the integrated values of each of the five images and square differences for a long interval of observations, the light of the exoplanet could be separated from the stellar light. The achievable contrast would reach almost the photon-noise limit of the residual speckle intensities under appropriate conditions. CDI-SAN can be applied to both ground-based and space telescopes.

Keywords: Exoplanet detection methods, Coronagraphic imaging, Direct imaging, Exoplanets
High-energy Studies of the 3HWC J1954+286 Region: Likely Gamma-Ray Detection of the Supernova Remnant G65.1+0.6. We carry out high-energy studies of the region of the Galactic TeV source 3HWC J1954+286, whose location coincides with those of PSR J1954+2836 and supernova remnant (SNR) G65.1+0.6. Analyzing the GeV γ-ray data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope, we are able to separate the pulsar's emission from that of the region. Excess power-law-like emission of a ~6σ significance level at the region is found, which we explain as arising from the SNR G65.1+0.6. Given the low-significance detection, either a hadronic or a leptonic model can provide a fit to the power-law spectrum. Considering the properties of the pulsar and the SNR, we discuss the possible origin of the TeV source, and suggest that it is likely to be the TeV halo associated with the pulsar.

Keywords: Supernova remnants, Gamma-rays, Pulsars
A Study of Dimmings, CMEs, and Flares during the STEREO-SOHO Quadrature. During the quadrature period (2010 December-2011 August) the STEREO-A and B satellites were approximately at right angles to the SOHO satellite. This alignment was particularly advantageous for determining the coronal mass ejection (CME) properties, since the closer a CME propagates to the plane of sky, the smaller the measurement inaccuracies are. Our primary goal was to study dimmings and their relationship to CMEs and flares during this time. We identified 53 coronal dimmings using STEREO/EUVI 195 Å observations, and linked 42 of the dimmings to CMEs (observed with SOHO/LASCO/C2) and 23 to flares. Each dimming in the catalog was processed with the Coronal Dimming Tracker which detects transient dark regions in extreme ultraviolet images directly, without the use of difference images. This approach allowed us to observe footpoint dimmings: the regions of mass depletion at the footpoints of erupting magnetic flux rope structures. Our results show that the CME mass has a linear, moderate correlation with dimming total EUV intensity change, and a monotonic, moderate correlation with dimming area. These results suggest that the more the dimming intensity drops and the larger the erupting region is, the more plasma is evacuated. We also found a strong correlation between the flare duration and the total change in EUV intensity. The correlation between dimming properties showed that larger dimmings tend to be brighter; they go through more intensity loss and generally live longer-supporting the hypothesis that larger transient open regions release more plasma and take longer to close down and refill with plasma.

Keywords: Solar ultraviolet emission, Solar flares, Solar coronal mass ejections
UV Counterpart of an X-Ray Ultrafast Outflow in IRAS 17020+4544. We report on the discovery of a UV absorption counterpart of a low-ionization X-ray ultrafast outflow (UFO) in the narrow-line Seyfert 1 galaxy IRAS 17020+4544. This UV signature of the UFO is seen as a narrow and blueshifted Lyα absorption feature in the far-UV spectrum, taken with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). The Lyα feature is found to be outflowing with a velocity of -23,430 km s-1 (0.078 c). We carry out high-resolution UV spectroscopy and photoionization modeling to study the UFO that is seen in the HTS/COS spectrum. The results of our modeling show that the UV UFO corresponds to a low-ionization, low-velocity component of the X-ray UFO found previously with XMM-Newton's Reflection Grating Spectrometer. The other higher-velocity and higher-ionization components of the X-ray UFOs are not significantly detected in the HST/COS spectrum, consistent with predictions of our photoionization calculations. The multiple ionization and velocity components of the UFOs in IRAS 17020+4544 suggest a scenario where a powerful primary UFO entrains and shocks the ambient medium, resulting in formation of weaker secondary UFO components, such as the one found in the UV band.

Keywords: High resolution spectroscopy, High energy astrophysics, Ultraviolet observatories, Seyfert galaxies, Active galactic nuclei, X-ray observatories
Neutral-charged-particle Collisions as the Mechanism for Accretion Disk Angular Momentum Transport. The matter in an accretion disk must lose angular momentum when moving radially inwards but how this works has long been a mystery. By calculating the trajectories of individual colliding neutrals, ions, and electrons in a weakly ionized 2D plasma containing gravitational and magnetic fields, we numerically simulate accretion disk dynamics at the particle level. As predicted by Lagrangian mechanics, the fundamental conserved global quantity is the total canonical angular momentum, not the ordinary angular momentum. When the Kepler angular velocity and the magnetic field have opposite polarity, collisions between neutrals and charged particles cause: (i) ions to move radially inwards, (ii) electrons to move radially outwards, (iii) neutrals to lose ordinary angular momentum, and (iv) charged particles to gain canonical angular momentum. Neutrals thus spiral inward due to their decrease of ordinary angular momentum while the accumulation of ions at small radius and accumulation of electrons at large radius produces a radially outward electric field. In 3D, this radial electric field would drive an out-of-plane poloidal current that produces the magnetic forces that drive bidirectional astrophysical jets. Because this neutral angular momentum loss depends only on neutrals colliding with charged particles, it should be ubiquitous. Quantitative scaling of the model using plausible disk density, temperature, and magnetic field strength gives an accretion rate of 3 × 10-8 solar mass per year, which is in good agreement with observed accretion rates.

Keywords: Accretion, Jets, Plasma jets, Plasma astrophysics, Protoplanetary disks, Stellar accretion, Circumstellar disks
Eruption of the Envelope of Massive Stars by Energy Injection with Finite Duration. A significant fraction of supernovae show signatures of dense circumstellar material (CSM). While multiple scenarios for creating a dense CSM exist, mass eruption due to injection of energy at the base of the outer envelope is a likely possibility. We carry out radiation hydrodynamical simulations of eruptive mass loss from a typical red supergiant progenitor with an initial mass of 15 M ⊙, for the first time focusing on the timescale of the injection as well as energy. We find that not only sufficient injection energy but also sufficient rate of energy injection per unit time, L min ~ 8 × 1040 erg s-1 in this particular model, is required for eruption of unbound CSM. This result suggests that the energy injection rate needs to be greater than the binding energy of the envelope divided by the dynamical timescale for the eruption. The density profile of the resulting CSM, whose shape was analytically and numerically predicted in the limit of instantaneous energy injection, similarly holds for a finite injection timescale. We discuss our findings in the framework of proposed mass outburst scenarios, specifically wave-driven outbursts and common-envelope ejection.

Keywords: Stellar mass loss
Simultaneous Evidence of Edge Collapse and Hub-filament Configurations: A Rare Case Study of a Giant Molecular Filament, G45.3+0.1. We study multiwavelength and multiscale data to investigate the kinematics of molecular gas associated with the star-forming complexes G045.49+00.04 (G45E) and G045.14+00.14 (G45W) in the Aquila constellation. An analysis of the FUGIN 13CO(1-0) line data unveils the presence of a giant molecular filament (GMF G45.3+0.1; length ~75 pc, mass ~1.1 × 106 M ⊙) having a coherent velocity structure at [53, 63] km s-1. The GMF G45.3+0.1 hosts G45E and G45W complexes at its opposite ends. We find large-scale velocity oscillations along GMF G45.3+0.1, which also reveals the linear velocity gradients of -0.064 and +0.032 km s-1 pc-1 at its edges. The photometric analysis of point-like sources shows the clustering of young stellar object (YSO) candidate sources at the filament's edges where the presence of dense gas and H II regions are also spatially observed. The Herschel continuum maps along with the CHIMPS 13CO(3-2) line data unravel the presence of parsec scale hub-filament systems (HFSs) in both sites, G45E and G45W. Our study suggests that the global collapse of GMF G45.3+0.1 is end dominated, with the addition to the signature of global nonisotropic collapse at the edges. Overall, GMF G45.3+0.1 is the first observational sample of filament where the edge-collapse and the hub-filament configurations are simultaneously investigated. These observations open the new possibility of massive star formation, including the formation of HFSs.

Keywords: Star forming regions, Molecular clouds, Giant molecular clouds, Interstellar emissions, Pre-main sequence stars, Star formation, Interstellar clouds, Interstellar medium, Dust continuum emission, Young stellar objects, H II regions
The Dense Gas Mass Fraction and the Relationship to Star Formation in M51. Observations of 12CO J = 1 - 0 and HCN J = 1 - 0 emission from NGC 5194 (M51) made with the 50 m Large Millimeter Telescope and the SEQUOIA focal plane array are presented. Using the HCN-to-CO ratio, we examine the dense gas mass fraction over a range of environmental conditions within the galaxy. Within the disk, the dense gas mass fraction varies along the spiral arms but the average value over all spiral arms is comparable to the mean value of interarm regions. We suggest that the near-constant dense gas mass fraction throughout the disk arises from a population of density-stratified, self-gravitating molecular clouds and the required density threshold to detect each spectral line. The measured dense gas fraction significantly increases in the central bulge in response to the effective pressure, P  e , from the weight of the stellar and gas components. This pressure modifies the dynamical state of the molecular cloud population and, possibly, the HCN-emitting regions in the central bulge from self-gravitating to diffuse configurations in which P  e  is greater than the gravitational energy density of individual clouds. Diffuse molecular clouds comprise a significant fraction of the molecular gas mass in the central bulge, which may account for the measured sublinear relationships between the surface densities of the star formation rate and molecular and dense gas.

Keywords: Galaxy environments, Star forming regions, Interstellar clouds, Dense interstellar clouds
Disk Evolution Study through Imaging of Nearby Young Stars (DESTINYS): A Panchromatic View of DO Tau's Complex Kilo-astronomical-unit Environment. While protoplanetary disks are often treated as isolated systems in planet formation models, observations increasingly suggest that vigorous interactions between Class II disks and their environments are not rare. DO Tau is a T Tauri star that has previously been hypothesized to have undergone a close encounter with the HV Tau system. As part of the DESTINYS ESO Large Programme, we present new Very Large Telescope (VLT)/SPHERE polarimetric observations of DO Tau and combine them with archival Hubble Space Telescope (HST) scattered-light images and Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO isotopologues and CS to map a network of complex structures. The SPHERE and ALMA observations show that the circumstellar disk is connected to arms extending out to several hundred astronomical units. HST and ALMA also reveal stream-like structures northeast of DO Tau, some of which are at least several thousand astronomical units long. These streams appear not to be gravitationally bound to DO Tau, and comparisons with previous Herschel far-IR observations suggest that the streams are part of a bridge-like structure connecting DO Tau and HV Tau. We also detect a fainter redshifted counterpart to a previously known blueshifted CO outflow. While some of DO Tau's complex structures could be attributed to a recent disk-disk encounter, they might be explained alternatively by interactions with remnant material from the star formation process. These panchromatic observations of DO Tau highlight the need to contextualize the evolution of Class II disks by examining processes occurring over a wide range of size scales.

Keywords: Radio interferometry, Polarimetry, Protoplanetary disks, Planet formation
Simultaneous View of FRB 180301 with FAST and NICER during a Bursting Phase. FRB 180301 is one of the most actively repeating fast radio bursts (FRBs) that has shown polarization angle changes in its radio burst emission, an indication for their likely origin in the magnetosphere of a highly magnetized neutron star. We carried out a multiwavelength campaign with the FAST radio telescope and NICER X-ray observatory to investigate any possible X-ray emission temporally coincident with the bright radio bursts. The observations took place on 2021 March 4, 9 and 19. We detected five bright radio bursts with FAST, four of which were strictly simultaneous with the NICER observations. The peak flux density of the radio bursts ranged between 28 and 105 mJy, the burst fluence between 27 and 170 mJy ms, and the burst durations between 1.7 and 12.3 ms. The radio bursts from FRB 180301 exhibited a complex time domain structure, and subpulses were detected in individual bursts, with no significant circular polarization. The linear degree of polarization in the L band reduced significantly compared to the 2019 observations. We do not detect any X-ray emission in excess of the background during the 5, 10, 100 ms, 1 and 100 s time intervals at/around the radio-burst barycenter-corrected arrival times, at a &gt; 5σ confidence level. The 5σ upper limits on the X-ray (a) persistent flux is &lt;7.64 × 10-12 erg cm-2 s-1, equivalent to L X &lt; 2.50 × 1045 erg s-1 and (b) 5 ms fluence is &lt;2 × 10-11 erg cm-2, at the radio burst regions. Using the 5 ms X-ray fluence upper limit, we can estimate the radio efficiency η  R/X  ≡ L radio/L X-ray ≳ 10-8. The derived lower limit on η  R/X  is consistent with both magnetospheric models and synchrotron maser models involving relativistic shocks.

Keywords: Radio transient sources
Misaligned Spinning Binary Black Hole Mergers in Hot Magnetized Plasma. We present general relativistic magnetohydrodynamical simulations of equal-mass spinning black hole binary mergers embedded in a magnetized gas cloud. We focus on the effect of the spin orientation relative to the orbital angular momentum on the flow dynamics, mass accretion rate, and Poynting luminosity. We find that, across the inspiral, the gas accreting onto the individual black holes concentrates into disklike overdensities whose angular momenta are oriented toward the spin axes and that persist until merger. We identify quasiperiodic modulations occurring in the mass accretion rate at the level of ~1%-20%, evolving in parallel with the gravitational-wave chirp. The similarity between the accretion rate time series and the gravitational strain is a consequence of the interplay between strong, dynamical gravitational fields and magnetic fields in the vicinity of the inspiraling black holes. This result suggests that quasiperiodicity in the premerger accretion rate of massive binaries is not exclusive of environments in which the black holes are embedded in a circumbinary accretion disk and could provide an additional useful signature of electromagnetic emission concurrent to low-frequency gravitational-wave detection.

Keywords: Black hole physics, Supermassive black holes, Gravitational wave sources, General relativity, Gravitational waves, Rotating black holes, Magnetohydrodynamical simulations
On the Potential of Bright, Young Pulsars to Power Ultrahigh Gamma-Ray Sources. The recent discovery of a new population of ultrahigh-energy gamma-ray sources with spectra extending beyond 100 TeV revealed the presence of Galactic PeVatrons-cosmic-ray factories accelerating particles to PeV energies. These sources, except for the one associated with the Crab Nebula, are not yet identified. With an extension of 1° or more, most of them contain several potential counterparts, including supernova remnants, young stellar clusters, and pulsar wind nebulae (PWNe), which can perform as PeVatrons and thus power the surrounding diffuse ultrahigh-energy gamma-ray structures. In the case of PWNe, gamma-rays are produced by electrons, accelerated at the pulsar wind termination shock, through the inverse Compton scattering of 2.7 K cosmic microwave background (CMB)radiation. The high conversion efficiency of pulsar rotational power to relativistic electrons, combined with the short cooling timescales, allow gamma-ray luminosities up to the level of ${L}_{\gamma }\sim 0.1\dot{E}$ . The pulsar spin-down luminosity, $\dot{E}$ , also determines the absolute maximum energy of individual photons: ${E}_{\gamma ,max}\approx 0.9{\dot{E}}_{36}^{0.65}\,\,{\rm{PeV}}$ . This fundamental constraint dominates over the condition set by synchrotron energy losses of electrons for young PWNe with typical magnetic field of ≈100 μG with $\dot{E}\lesssim {10}^{37}\ \mathrm{erg}\,{{\rm{s}}}^{-1}$ . We discuss the implications of Eγ ,max by comparing it with the highest-energy photons reported by LHAASO from a dozen of ultrahigh-energy sources. Whenever a PWN origin of the emission is possible, we use the LHAASO measurements to set upper limits on the nebular magnetic field.

Keywords: High energy astrophysics, Rotation powered pulsars, Gamma-ray sources, Pulsars, Pulsar wind nebulae
ALMA Discovery of a Disk around the Planetary-mass Companion SR 12 c. We report an Atacama Large Millimeter/submillimeter Array 0.88 mm (Band 7) continuum detection of the accretion disk around SR 12 c, an ~11 M Jup planetary-mass companion (PMC) orbiting its host binary at 980 au. This is the first submillimeter detection of a circumplanetary disk around a wide PMC. The disk has a flux density of 127 ± 14 μJy and is not resolved by the ~0.″1 beam, so the dust disk radius is likely less than 5 au and can be much smaller if the dust continuum is optically thick. If, however, the dust emission is optically thin, then the SR 12 c disk has a comparable dust mass to the circumplanetary disk around PDS 70 c but is about five times lower than that of the ~12 M Jup free-floating OTS 44. This suggests that disks around bound and unbound planetary-mass objects can span a wide range of masses. The gas mass estimated with an accretion rate of 10-11 M ☉ yr-1 implies a gas-to-dust ratio higher than 100. If cloud absorption is not significant, a nondetection of 12CO(3-2) implies a compact gas disk around SR 12 c. Future sensitive observations may detect more PMC disks at 0.88 mm flux densities of ≲100 μJy.

Keywords: Radio continuum emission, Radio interferometry, Accretion, Extrasolar gaseous giant planets