Sazuna/UAT_keywords huggingface dataset:
The State of the Heliosphere Revealed by Limb-halo Coronal Mass Ejections in Solar Cycles 23 and 24. We compare the properties of halo coronal mass ejections (CMEs) that originate close to the limb (within a central meridian distance range of 60°-∼90°) during solar cycles 23 and 24 to quantify the effect of the heliospheric state on CME properties. There are 44 and 38 limb halos in cycles 23 and 24, respectively. Normalized to the cycle-averaged total sunspot number, there are 42% more limb halos in cycle 24. Although the limb halos as a population are very fast (average speed ∼1464 km s-1), cycle-24 halos are slower by ∼26% than the cycle-23 halos. We introduce a new parameter, the heliocentric distance of the CME leading edge at the time a CME becomes a full halo; this height is significantly shorter in cycle 24 (by ∼20%) and has a lower cutoff at ∼6 Rs. These results show that cycle-24 CMEs become halos sooner and at a lower speed than the cycle-23 ones. On the other hand, the flare sizes are very similar in the two cycles, ruling out the possibility of eruption characteristics contributing to the differing CME properties. In summary, this study reveals the effect of the reduced total pressure in the heliosphere that allows cycle-24 CMEs to expand more and become halos sooner than in cycle 23. Our findings have important implications for the space-weather consequences of CMEs in cycle 25 (predicted to be similar to cycle 24) and for understanding the disparity in halo counts reported by automatic and manual catalogs.

Keywords: Solar flares, Heliosphere, Solar energetic particles, Radio bursts, Solar coronal mass ejections
Network Jets as the Driver of Counter-streaming Flows in a Solar Filament/Filament Channel. Counter-streaming flows in a small (100″ long) solar filament/filament channel are directly observed in high-resolution Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) extreme-ultraviolet (EUV) images of a region of enhanced magnetic network. We combine images from SDO/AIA, SDO/Helioseismic and Magnetic Imager (HMI), and the Interface Region Imaging Spectrograph (IRIS) to investigate the driving mechanism of these flows. We find that: (I) counter-streaming flows are present along adjacent filament/filament channel threads for ∼2 hr, (II) both ends of the filament/filament channel are rooted at the edges of magnetic network flux lanes along which there are impinging fine-scale opposite-polarity flux patches, (III) recurrent small-scale jets (known as network jets) occur at the edges of the magnetic network flux lanes at the ends of the filament/filament channel, (IV) the recurrent network jet eruptions clearly drive the counter-streaming flows along threads of the filament/filament channel, (V) some of the network jets appear to stem from sites of flux cancelation, between network flux and merging opposite-polarity flux, and (VI) some show brightening at their bases, analogous to the base brightening in coronal jets. The average speed of the counter-streaming flows along the filament/filament channel threads is 70 km s-1. The average widths of the AIA filament/filament channel and the Hα filament are 4″ and 2"5, respectively, consistent with the earlier findings that filaments in EUV images are wider than in Hα images. Thus, our observations show that the continually repeated counter-streaming flows come from network jets, and these driving network jet eruptions are possibly prepared and triggered by magnetic flux cancelation.

Keywords: Jets, Solar magnetic reconnection, Solar chromospheric heating, Solar filaments, Solar magnetic fields, Solar corona, Solar chromosphere
Kinetic Scale Slow Solar Wind Turbulence in the Inner Heliosphere: Coexistence of Kinetic Alfvén Waves and Alfvén Ion Cyclotron Waves. The nature of the plasma wave modes around the ion kinetic scales in highly Alfvénic slow solar wind turbulence is investigated using data from the NASA's Parker Solar Probe taken in the inner heliosphere, at 0.18 au from the Sun. The joint distribution of the normalized reduced magnetic helicity σm (θRB, τ) is obtained, where θRB is the angle between the local mean magnetic field and the radial direction and τ is the temporal scale. Two populations around ion scales are identified: the first population has σm (θRB, τ) &lt; 0 for frequencies (in the spacecraft frame) ranging from 2.1 to 26 Hz for 60° &lt; θRB &lt; 130°, corresponding to kinetic Alfvén waves (KAWs), and the second population has σm (θRB, τ) &gt; 0 in the frequency range [1.4, 4.9] Hz for θRB &gt; 150°, corresponding to Alfvén ion cyclotron waves (ACWs). This demonstrates for the first time the coexistence of KAWs and ACWs in the slow solar wind in the inner heliosphere, which contrasts with previous observations in the slow solar wind at 1 au. This discrepancy between 0.18 and 1 au could be explained either by (I) a dissipation of ACWs via cyclotron resonance during their outward journey, or by (II) the high Alfvénicity of the slow solar wind at 0.18 au that may be favorable for the excitation of ACWs.

Keywords: Slow solar wind, Space plasmas, Heliosphere, Interplanetary turbulence, The Sun, Solar wind, Plasma astrophysics, Alfven waves, Interplanetary magnetic fields
A Dual-band Radio Observation of FRB 121102 with the Deep Space Network and the Detection of Multiple Bursts. The spectra of repeating fast radio bursts (FRBs) are complex and time-variable, sometimes peaking within the observing band and showing a fractional emission bandwidth of about 10%-30%. These spectral features may provide insight into the emission mechanism of repeating FRBs, or they could possibly be explained by extrinsic propagation effects in the local environment. Broadband observations can better quantify this behavior and help to distinguish between intrinsic and extrinsic effects. We present results from a simultaneous 2.25 and 8.36 GHz observation of the repeating FRB 121102 using the 70 m Deep Space Network radio telescope, DSS-43. During the 5.7 hr continuous observing session, we detected six bursts from FRB 121102, which were visible in the 2.25 GHz frequency band. However, none of these bursts were detected in the 8.36 GHz band, despite the larger bandwidth and greater sensitivity in the higher-frequency band. This effect is not explainable by Galactic scintillation and, along with previous multi-band experiments, clearly demonstrates that apparent burst activity depends strongly on the radio frequency band that is being observed.

Keywords: Radio transient sources
Neutral Cr and V in the Atmosphere of Ultra-hot Jupiter WASP-121 b. Ultra-hot Jupiters (UHJs), giant exoplanets with equilibrium temperatures above 2000 K, are ideal laboratories for studying metal compositions of planetary atmospheres. At these temperatures the thermal dissociation of metal-rich molecules into their constituent elements makes these atmospheres conducive for elemental characterization. Several elements, mostly ionized metals, have been detected in UHJs recently using high-resolution transit spectroscopy. Even though a number of neutral transition metals (e.g., Fe, Ti, V, Cr) are expected to be strong sources of optical/near-ultraviolet (NUV) opacity and, hence, influence radiative processes in the lower atmospheres of UHJs, only Fe I has been detected to date. We conduct a systematic search for atomic species in the UHJ WASP-121 b. Using theoretical models we present a metric to predict the atomic species likely to be detectable in such planets with high-resolution transmission spectroscopy. We search for the predicted species in observations of WASP-121 b and report the first detections of neutral transition metals Cr I and V I in an exoplanet at 3.6σ and 4.5σ significance, respectively. We confirm previous detections of Fe I and Fe II. Whereas Fe II was detected previously in the NUV, we detect it in the optical. We infer that the neutral elements Fe I, V I, and Cr I are present in the lower atmosphere, as predicted by thermochemical equilibrium, while Fe II is a result of photoionization in the upper atmosphere. Our study highlights the rich chemical diversity of UHJs.

Keywords: High resolution spectroscopy, Hot Jupiters, Exoplanets, Transmission spectroscopy, Radiative transfer, Exoplanet atmospheres
Comparison of Enhanced Absorption in He I 10830 Šin Observations and Modeling during the Early Phase of a Solar Flare. The He I 10830 Å triplet is a very informative indicator of chromospheric activities as the helium is the second most abundant element in the solar atmosphere. Taking advantage of the high resolution of the 1.6 m Goode Solar Telescope at Big Bear Solar Observatory, previous observations have shown clear evidence of the enhanced absorption, instead of typically observed emission, for two M-class flares. In this study, we analyze the evolution of the He I 10830 Å emission in numerical models and compare it with observations. The models represent the RADYN simulation results obtained from the F-CHROMA database. We consider the models with the injected electron spectra parameters close to observational estimates for the 2013 August 17 flare event (δ = 8, ${E}_{c}=\{15,20\}\,\,\mathrm{keV}$ , $F=\{1\times {10}^{11},3\times {10}^{11}\}\,\mathrm{erg}\,{\mathrm{cm}}^{-2}$ ) in detail, as well as other available models. The modeling results agree well with observations, in the sense of both the maximum intensity decrease (-17.1%, compared with the observed value of -13.7%) and the trend of temporal variation (initial absorption phase followed by the emission). All models demonstrate the increased number densities and decreased ratio of the upper and lower level populations of the He I 10830 Å transition in the initial phase, which enhances the opacity and forms an absorption feature. Models suggest that the temperatures and free electron densities at heights of 1.3-1.5 Mm should be larger than ∼104 K and 6 × 1011 cm-3 thresholds for the line to start being in emission.

Keywords: Solar activity, Solar chromosphere, Solar flares
Being Careful with the Field Formation Interpretation of GW190412. The LIGO/Virgo Scientific Collaboration recently announced the detection of a compact object binary merger, GW190412, as the first asymmetric binary black hole (BBH) merger with mass ratio q ≈ 0.25. Other than the mass ratio, this BBH has been shown to have a positive effective spin of around χeff ≈ 0.28. Assuming a field formation channel, associating this effective spin to either the primary or the secondary black hole (BH) each have implications: if the spin of the BBH comes from the primary BH, it has consequences for the efficiency of angular momentum transport in the formation of the BH. If, on the other hand, the spin is due to the secondary BH through tidal spin-up processes, it should be noted that (I) such processes have very short delay times, and (II) subsequently, their local merger rate is determined by local star formation rate at the assumed formation metallicity of the BBH. We show that the predicted merger rate density from this channel is $\lesssim 0.3\,{\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$ , and is in tension with the rather high local merger rate of such systems, which we estimate from this single event to be $\sim {1.7}_{-1.4}^{+2.5}\,{\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$ (90% confidence interval, and assuming 50 days of observing time). Large natal kicks (V ≳ 500 km s-1) would be required to get such an BBHs with an in-plane spin component to account for the marginal detection of precession in GW190412. However, this would only exacerbate the tension as the estimated local merger rate would be further decreased. Similarly, the formation of such systems through the dynamical assembly is exceedingly rare; consequently, it is difficult to account for this system with the currently accepted paradigms of BBH formation.

Keywords: Black hole physics, Binary stars, Stellar populations, Close binary stars, LIGO
Spin-Orbit Alignment of the β Pictoris Planetary System. A crucial diagnostic that can tell us about processes involved in the formation and dynamical evolution of planetary systems is the angle between the rotation axis of a star and a planet's orbital angular momentum vector ("spin-orbit" alignment or "obliquity"). Here we present the first spin-orbit alignment measurement for a wide-separation exoplanetary system, namely on the directly imaged planet β Pictoris b. We use VLTI/GRAVITY spectro-interferometry with an astrometric accuracy of 1 μas (microarcsecond) in the Brγ photospheric absorption line to measure the photocenter displacement associated with the stellar rotation. Taking inclination constraints from astroseismology into account, we constrain the three-dimensional orientation of the stellar spin axis and find that β Pic b orbits its host star on a prograde orbit. The angular momentum vectors of the stellar photosphere, the planet, and the outer debris disk are well aligned with mutual inclinations ≤3° ± 5°, which indicates that β Pic b formed in a system without significant primordial misalignments. Our results demonstrate the potential of infrared interferometry to measure the spin-orbit alignment for wide-separation planetary systems, probing a highly complementary regime to the parameter space accessible with the Rossiter-McLaughlin effect. If the low obliquity is confirmed by measurements on a larger sample of wide-separation planets, it would lend support to theories that explain the obliquity in Hot Jupiter systems with dynamical scattering and the Kozai-Lidov mechanism.

Keywords: Planetary system formation, Stellar rotation, Interferometers, Dynamical evolution
Betelgeuse Fainter in the Submillimeter Too: An Analysis of JCMT and APEX Monitoring during the Recent Optical Minimum. Betelgeuse, the nearest red supergiant star to Earth, underwent an unusually deep minimum at optical wavelengths during its most recent pulsation cycle. We present submillimeter observations taken by the James Clerk Maxwell Telescope and Atacama Pathfinder Experiment over a time span of 13 yr including the optical dimming. We find that Betelgeuse has also dimmed by ∼20% at these longer wavelengths during this optical minimum. Using radiative-transfer models, we show that this is likely due to changes in the photosphere (luminosity) of the star as opposed to the surrounding dust, as was previously suggested in the literature.

Keywords: Submillimeter astronomy, Variable stars, Time domain astronomy, Red supergiant stars
The Extreme Space Weather Event in 1903 October/November: An Outburst from the Quiet Sun. While the Sun is generally more eruptive during its maximum and declining phases, observational evidence shows certain cases of powerful solar eruptions during the quiet phase of solar activity. Occurring in the weak Solar Cycle 14 just after its minimum, the extreme space weather event in 1903 October-November is one of these cases. Here, we reconstruct the time series of geomagnetic activity based on contemporary observational records. With the mid-latitude magnetograms, the 1903 magnetic storm is thought to be caused by a fast coronal mass ejection (≈1500 km s-1) and is regarded as a superstorm with an estimated minimum of the equivalent disturbance storm time index (Dst') of ≈-531 nT. The reconstructed time series has been compared with the equatorward extension of auroral oval (≈44°1 in invariant latitude) and the time series of telegraphic disturbances. This case study shows that potential threats posed by extreme space weather events exist even during weak solar cycles or near their minima.

Keywords: Geomagnetic fields, Solar flares, Sunspots, Solar coronal mass ejections, Solar-terrestrial interactions, Solar storm
Characteristics and Importance of "ICME-in-sheath" Phenomenon and Upper Limit for Geomagnetic Storm Activity. As an important source for large geomagnetic storms, an "ICME-in-sheath" is a completely shocked interplanetary coronal mass ejection (ICME) stuck in the sheath between a shock and host ejecta. Typical characteristics are identified from coordinated multi-sets of observations: (1) it is usually short in duration and lasts a few hours at 1 au; (2) its solar wind parameters, in particular the magnetic field, seem to keep enhanced for a large range of distances; and (3) common ICME signatures are often lost. The host ejecta could be a single ICME or a complex ejecta, being fast enough to drive a shock. These results clarify previous misinterpretations of this phenomenon as a normal part of a sheath region. The "ICME-in-sheath" phenomenon, together with a preconditioning effect, produced an extreme set of the magnetic field, speed, and density near 1 au in the 2012 July 23 case, all around their upper limits at the same time. This is probably the most extreme solar wind driving at 1 au and enables us to estimate the plausible upper limit for geomagnetic storm activity. With an appropriate modification in the southward field, we suggest that a geomagnetic storm with a minimum Dst of about -2000 nT could occur in principle. The magnetopause would be compressed to about 3.3 Earth radii from the Earth's center, well inside the geosynchronous orbit.

Keywords: Solar-terrestrial interactions, Shocks, Solar wind, Solar coronal mass ejections
Image-based Classification of Variable Stars: First Results from Optical Gravitational Lensing Experiment Data. Recently, machine learning methods have presented a viable solution for the automated classification of image-based data in various research fields and business applications. Scientists require a fast and reliable solution in order to handle increasingly large amounts of astronomical data. However, so far astronomers have been mainly classifying variable starlight curves based on various pre-computed statistics and light curve parameters. In this work we use an image-based Convolutional Neural Network to classify the different types of variable stars. We use images of phase-folded light curves from the Optical Gravitational Lensing Experiment (OGLE)-III survey for training, validating, and testing, and use OGLE-IV survey as an independent data set for testing. After the training phase, our neural network was able to classify the different types between 80% and 99%, and 77%-98%, accuracy for OGLE-III and OGLE-IV, respectively.

Keywords: Periodic variable stars, Delta Scuti variable stars, Light curve classification , Classification, Anomalous Cepheid variable stars, Sky surveys, Convolutional neural networks, Astronomy data analysis, RR Lyrae variable stars, Eclipsing binary stars, Type II Cepheid variable stars
Estimating the Energy Dissipation from Kelvin-Helmholtz Instability Induced Turbulence in Oscillating Coronal Loops. Kelvin-Helmholtz instability induced turbulence is one promising mechanism by which loops in the solar corona can be heated by MHD waves. In this Letter we present an analytical model of the dissipation rate of Kelvin-Helmholtz instability induced turbulence ɛD, finding it scales as the wave amplitude (d) to the third power (ɛD ∝ d3). Based on the concept of steady-state turbulence, we expect the turbulence heating throughout the volume of the loop to match the total energy injected through its footpoints. In situations where this holds, the wave amplitude has to vary as the cube-root of the injected energy. Comparing the analytic results with those of simulations shows that our analytic formulation captures the key aspects of the turbulent dissipation from the numerical work. Applying this model to the observed characteristics of decayless kink waves we predict that the amplitudes of these observed waves are insufficient to turbulently heat the solar corona.

Keywords: Magnetohydrodynamics, Solar coronal heating, Solar coronal waves, Solar corona
Pōniuā'ena: A Luminous z = 7.5 Quasar Hosting a 1.5 Billion Solar Mass Black Hole. We report the discovery of a luminous quasar, J1007+2115 at z = 7.515 ("Pōniuā'ena"), from our wide-field reionization-era quasar survey. J1007+2115 is the second quasar now known at z &gt; 7.5, deep into the reionization epoch. The quasar is powered by a (1.5 ± 0.2) × 109 M☉ supermassive black hole (SMBH), based on its broad Mg II emission-line profile from Gemini and Keck near-IR spectroscopy. The SMBH in J1007+2115 is twice as massive as that in quasar J1342+0928 at z = 7.54, the current quasar redshift record holder. The existence of such a massive SMBH just 700 million years after the Big Bang significantly challenges models of the earliest SMBH growth. Model assumptions of Eddington-limited accretion and a radiative efficiency of 0.1 require a seed black hole of ≳104 M☉ at z = 30. This requirement suggests either a massive black hole seed as a result of direct collapse or earlier periods of rapid black hole growth with hyper-Eddington accretion and/or a low radiative efficiency. We measure the damping wing signature imprinted by neutral hydrogen absorption in the intergalactic medium (IGM) on J1007+2115's Lyα line profile, and find that it is weaker than that of J1342+0928 and two other z ≳ 7 quasars. We estimate an IGM volume-averaged neutral fraction $\langle {X}_{{\rm{H}}{\rm{I}}}\rangle ={0.39}_{-0.13}^{+0.22}$ . This range of values suggests a patchy reionization history toward different IGM sightlines. We detect the 158 μm [C II] emission line in J1007+2115 with the Atacama Large Millimeter/submillimeter Array; this line centroid yields a systemic redshift of z = 7.5149 ± 0.0004 and indicates a star formation rate of ∼210 M☉ yr-1 in its host galaxy.

Keywords: Early universe, Supermassive black holes, Quasar absorption line spectroscopy, Quasars, Intergalactic medium, Reionization
Fine Structure of a Solar Type II Radio Burst Observed by LOFAR. Shock waves in the solar corona are closely associated with coronal mass ejections and flares. The longest-known and frequently studied signatures of coronal shock waves are metric type II radio bursts, which provide information on the shock driver and ambient plasma conditions. We report on outstanding high frequency/time resolution LOw Frequency ARray (LOFAR) observations of a metric type II radio burst. The LOFAR observations show a strong fragmentation of the type II emission, in both the frequency and time domains, during the whole duration of the event. A very unusual splitting of an already-split type II band, which we call the band-split of the band-split, was observed for the first time. The richness of fine structure, observed in both the fundamental and harmonic bands of the type II emission, is unprecedented. Fine structures, morphologically similar to those seen superposed on a type IV continuum, were observed for the first time within a type II burst. We classify the fine structures into three categories: simple narrowband, broadband, and complex fine structures, and discuss their properties. LOFAR observations of fragmented shock-associated radio emission have the potential of bringing new insight into the physics of coronal shock waves, and also new challenges for the theory of electron acceleration by shocks.

Keywords: Solar coronal mass ejection shocks, Solar physics, Solar radio emission, Solar coronal waves, Solar electromagnetic emission, Active solar corona