Sazuna/UAT_keywords huggingface dataset:
Advanced Composition Explorer Observations of Turbulence from 1998 through 2002: Data Intervals. We have published several papers describing solar wind turbulence at 1 au using data from the Advanced Composition Explorer spacecraft. In an oversight that we regret, we never published the list of data intervals that constitute the database of observations. As we have recently returned to this database of observations in comparisons of turbulent observations by the Voyager spacecraft against established results from 1 au, we wish to now correct our oversight and publish the list of intervals that constitute the 1 au observations. Along with this, we show the distribution of some common solar wind parameters as contained within the database.

Keywords: Magnetohydrodynamics, Solar wind, Heliosphere
In the Trenches of the Solar-Stellar Connection. I. Ultraviolet and X-Ray Flux-Flux Correlations across the Activity Cycles of the Sun and Alpha Centauri AB. This study focuses on high-energy proxies of stellar magnetic activity over long-term starspot cycles of three low-activity Sun-like stars: α Centauri A (HD 128620: G2 V), α Cen B (HD 128621: K1 V), and the Sun itself. Data sets include: daily solar ultraviolet irradiance spectra and X-ray fluxes from the Solar Radiation and Climate Experiment, during recent sunspot Cycles 23 and 24; Interface Region Imaging Spectrograph long-slit stigmatic imaging of solar Mg II h (2803 Å) and k (2796 Å) in quiet and active regions; and Hubble Space Telescope Imaging Spectrograph ultraviolet, and Chandra X-ray, campaigns on α Cen AB. Established stellar "flux-flux" relations, for example X-rays (T ∼ 1 MK) versus Mg II (T ∼ 8000 K), showed increasing power-law slopes with increasing formation temperature, but these give way on the Sun to bent power laws, and surprising inversions in the activity hierarchy: Si III is more "active" (steeper power laws) than N V, despite the latter's four times higher formation temperature. The Sun's flux-flux behavior, nevertheless, remarkably parallels its low-activity solar twin α Cen A. In contrast, the cooler, somewhat more active, K dwarf companion displays correlations more in line with the previous stellar paradigm. The new flux-flux relations offer a way to vet numerical spectral simulations and proxy-based irradiance models, and extrapolate solar global activity indices into regimes below or above the grasp of contemporary records, or to exoplanet hosts at the low end of the Sun-like activity ladder.

Keywords: Solar cycle, Solar analogs, Solar ultraviolet emission, Quiet sun, Stellar chromospheres, Active sun, Solar x-ray emission, Stellar activity, Stellar physics, Time domain astronomy, Stellar coronae, Stellar spectral lines
The Next Generation Virgo Cluster Survey. XXXIV. Ultracompact Dwarf Galaxies in the Virgo Cluster. We present a study of ultracompact dwarf (UCD) galaxies in the Virgo cluster based mainly on imaging from the Next Generation Virgo Cluster Survey (NGVS). Using ∼100 deg2 of u*giz imaging, we have identified more than 600 candidate UCDs, from the core of Virgo out to its virial radius. Candidates have been selected through a combination of magnitudes, ellipticities, colors, surface brightnesses, half-light radii, and, when available, radial velocities. Candidates were also visually validated from deep NGVS images. Subsamples of varying completeness and purity have been defined to explore the properties of UCDs and compare to those of globular clusters and the nuclei of dwarf galaxies with the aim of delineating the nature and origins of UCDs. From a surface density map, we find the UCDs to be mostly concentrated within Virgo's main subclusters, around its brightest galaxies. We identify several subsamples of UCDs—i.e., the brightest, largest, and those with the most pronounced and/or asymmetric envelopes—that could hold clues to the origin of UCDs and possible evolutionary links with dwarf nuclei. We find some evidence for such a connection from the existence of diffuse envelopes around some UCDs and comparisons of radial distributions of UCDs and nucleated galaxies within the cluster.

Keywords: Globular star clusters, Galaxy formation, Virgo Cluster, Dwarf elliptical galaxies, Galaxy nuclei, Ultracompact dwarf galaxies
ALMA High-frequency Long-baseline Campaign in 2017: A Comparison of the Band-to-band and In-band Phase Calibration Techniques and Phase-calibrator Separation Angles. The Atacama Large Millimeter/submillimeter Array (ALMA) obtains spatial resolutions of 15 to 5 mas at 275-950 GHz (0.87-0.32 mm) with 16 km baselines. Calibration at higher frequencies is challenging as ALMA sensitivity and quasar density decrease. The band-to-band (B2B) technique observes a detectable quasar at a lower frequency that is closer to the target, compared to one at the target high frequency. Calibration involves a nearly constant instrumental phase offset between the frequencies and the conversion of the temporal phases to the target frequency. The instrumental offsets are solved with a differential gain calibration (DGC) sequence, consisting of alternating low- and high-frequency scans of strong quasars. Here we compare B2B and in-band phase referencing for high frequencies (&gt;289 GHz) using 2-15 km baselines and calibrator separation angles between ∼0°68 and ∼11°65. The analysis shows the following: (1) DGC for B2B produces a coherence loss &lt;7% for DGC phase rms residuals &lt;30°. (2) B2B images using close calibrators (&lt;1°67) are superior to in-band images using distant ones (&gt;2°42). (3) For more distant calibrators, B2B is preferred if it provides a calibrator ∼2° closer than the best in-band calibrator. (4) Decreasing image coherence and poorer image quality occur with increasing phase-calibrator separation angle because of uncertainties in the antenna positions and suboptimal phase referencing. (5) To achieve &gt;70% coherence for long-baseline (16 km) band 7 (289 GHz) observations, calibrators should be within ∼4° of the target.

Keywords: Submillimeter astronomy, Long baseline interferometry, Phase error
Panning for Gold: New Emission Lines from UV-VIS Spectroscopy of Au I and Au II. The recent detection of a neutron star merger by the LIGO collaboration has renewed interest in laboratory studies of r-process elements. Accurate modeling and interpretation of the electromagnetic transients following the mergers requires computationally expensive calculations of both the structure and opacity of all trans-iron elements. To date, the necessary atomic data to benchmark structure codes are incomplete or, in some cases, absent entirely. Within the available laboratory studies, the literature on Au I and Au II provides incomplete reports of the emission lines and level structures. We present a new study of Au I and Au II lines and levels by exposing a solid gold target to plasma in the Compact Toroidal Hybrid (CTH) experiment at Auburn University. A wavelength range from 187 to 800 nm was studied. In Au I, 86 lines are observed, 43 of which are unreported in the literature, and the energies of 18 $5{d}^{9}6s6p$ levels and 16 of the 18 known $5{d}^{9}6s6d$ levels are corroborated by a least-squares level energy optimization. In Au II, 76 emission lines are observed, and 51 of the lines are unreported in the literature. For both Au I and Au II, the new lines predominantly originate from the most energetic of the known levels, and over half of the new Au II lines have wavelengths longer than 300 nm. For the estimated electron parameters of CTH plasmas at the gold target (ne ∼ 1012 cm-3, Te ∼ 10 eV), two-electron transitions are similar in intensity to LS-allowed one-electron transitions.

Keywords: Spectral line lists, Spectral line identification, Laboratory astrophysics, R-process, Atomic spectroscopy, Chemically peculiar stars
A Search for Rotation Periods in 1000 TESS Objects of Interest. The high-quality light curves from the Transiting Exoplanet Survey Satellite (TESS) represent a unique laboratory for the study of stellar rotation, which is a fundamental observable driving stellar and planetary evolution, including planetary atmospheres and impacting habitability conditions and the genesis of life around stars. As of 2020 April 14, this mission delivered public light curves for 1000 TESS objects of interest (TOIs), observed with a 2 minute cadence during the first 20 months of the mission. Here, we present a search for rotation signatures in these TOIs, using fast Fourier transform, Lomb-Scargle, and wavelet techniques, accompanied by a rigorous visual inspection. This effort revealed 163 targets with rotation signatures, 131 of which present unambiguous rotation periods ranging from 0.321 and 13.219 days, whereas 32 of them present dubious rotation periodicities. Of these stars, 109 show flux fluctuations whose root cause is not clearly identified. For 714 TOIs, the light curves show a noisy behavior, corresponding to typically low-amplitude signals. Our analysis has also revealed 10 TOI stars with pulsation periodicities ranging from 0.049 to 2.995 days and four eclipsing binaries. With upcoming TESS data releases, our periodicity analysis will be expanded to almost all TOI stars, thereby contributing in defining criteria for follow-up strategy itself, and the study of star-planet interactions, surface dynamic of host stars, and habitability conditions in planets, among other aspects. In this context, a living catalog is maintained on the Filtergraph visualization portal at https://filtergraph.com/tess_rotation_tois.

Keywords: Stellar photometry, Exoplanet catalogs, Stellar pulsations, Variable stars, Stellar rotation
Simulating the Cosmic Neutrino Background Using Collisionless Hydrodynamics. The cosmic neutrino background is an important component of the universe that is difficult to include in cosmological simulations due to the extremely large velocity dispersion of neutrino particles. We develop a new approach to simulate cosmic neutrinos that decomposes the Fermi-Dirac phase space into shells of constant speed and then evolves those shells using hydrodynamic equations. These collisionless hydrodynamic equations have fluxes that match linear theory but retain the full nonlinear gravitational source terms. We implement this method into the information-optimized cosmological N-body code CUBE and demonstrate that neutrino perturbations can be accurately resolved to at least k ∼ 1 h Mpc-1. This technique allows for neutrino memory requirements to be decreased by up to $\sim {10}^{3}$ compared to traditional N-body methods.

Keywords: Cosmology, Cosmological neutrinos, N-body simulations, Large-scale structure of the universe
Upgraded GMRT Observations of the Coma Cluster of Galaxies: The Observations. We have used the upgraded Giant Metrewave Radio Telescope to map the Coma cluster of galaxies at 250-500 MHz and 1050-1450 MHz bands. These 6"26 and 2"18 resolutions observations allow detailed radio structures to be determined of all detected radio sources that show both discrete pointlike and extended morphologies. We present images of a subset of 32 brightest (Sν ≳ 30 mJy) and dominant sources, and several sources show discrete pointlike radio morphologies. We find the steepening of the spectra consistent with synchrotron cooling in the majority of sources and the median for spectral indices is -0.78, suggesting that ∼59% sources have steep spectra. The nature and the statistical properties of the radio sources in the Coma cluster will be discussed in subsequent papers.

Keywords: Galaxy clusters, Radio jets, Active galaxies, Coma Cluster, Radio continuum emission, Radio active galactic nuclei
AstroSat UVIT Detections of Chandra X-Ray Sources in M31. An ultraviolet (UV) survey of M31 has been carried out during 2017-19 with the Ultra-Violet Imaging Telescope (UVIT) instrument on board the AstroSat Observatory. Here we match the M31 UVIT source catalog with the Chandra source catalog. We find 67 UVIT/Chandra sources detected in a varying number of UV and X-ray bands. The UV and X-ray photometry is analyzed using power-law and blackbody models. The X-ray types include 15 low-mass X-ray binaries (LMXBs) and five active galactic nuclei. Crossmatches with catalogs of stars, clusters, and other source types yield the following: 20 of the UVIT/Chandra sources match with M31 globular clusters, and nine with foreground stars. Three more globular clusters and two more foreground stars are consistent with the UVIT source positions although outside the Chandra match radius of 1″. The UV emission of the UVIT/Chandra sources associated with globular clusters is consistent with emission from blue horizontal branch stars rather than from the X-ray source. The LMXBs in globular clusters are among the most luminous globular clusters in M31. Comparison with stellar evolutionary tracks shows that the UVIT/Chandra sources with high UV blackbody temperatures are consistent with massive (10-30 M⊙) stars in M31.

Keywords: Ultraviolet sources, Globular star clusters, X-ray sources, Low-mass x-ray binary stars, Andromeda Galaxy
The Spectroscopic Follow-up of the QUBRICS Bright Quasar Survey. We present the results of the spectroscopic follow-up of the QUasars as BRIght beacons for Cosmology in the Southern Hemisphere (QUBRICS; Calderone et al. 2019) survey. The selection method is based on a machine-learning approach applied to photometric catalogs, covering an area of ∼12,400 deg2 in the Southern Hemisphere. The spectroscopic observations started in 2018 and identified 55 new, high-redshift (z ≥ 2.5), bright (i ≤ 18) quasi-stellar objects (QSOs), with the catalog published in late 2019. Here we report the current status of the survey, bringing the total number of bright QSOs at z ≥ 2.5 identified by QUBRICS to 224. The success rate of the QUBRICS selection method, in its most recent training, is estimated to be 68%. The predominant contaminant turns out to be lower-z QSOs at z &lt; 2.5. This survey provides a unique sample of bright QSOs at high z available for a number of cosmological investigations. In particular, carrying out the redshift drift measurements (Sandage Test) in the Southern Hemisphere, using the High Resolution Spectrograph at the 39 m Extremely Large Telescope appears to be possible with less than 2500 hr of observations spread over 30 targets in 25 yr.

Keywords: Cosmology, Quasars, Surveys, Active galaxies, Redshift surveys, Catalogs
Inference of the Local Interstellar Spectra of Cosmic-Ray Nuclei Z ≤ 28 with the GALPROP-HELMOD Framework. Composition and spectra of Galactic cosmic rays (CRs) are vital for studies of high-energy processes in a variety of environments and on different scales, for interpretation of γ-ray and microwave observations, for disentangling possible signatures of new phenomena, and for understanding of our local Galactic neighborhood. Since its launch, AMS-02 has delivered outstanding-quality measurements of the spectra of $\bar{p}$ , ${e}^{\pm }$ , and nuclei: 1H-8O, 10Ne, 12Mg, 14Si. These measurements resulted in a number of breakthroughs; however, spectra of heavier nuclei and especially low-abundance nuclei are not expected until later in the mission. Meanwhile, a comparison of published AMS-02 results with earlier data from HEAO-3-C2 indicates that HEAO-3-C2 data may be affected by undocumented systematic errors. Utilizing such data to compensate for the lack of AMS-02 measurements could result in significant errors. In this paper we show that a fraction of HEAO-3-C2 data match available AMS-02 measurements quite well and can be used together with Voyager 1 and ACE-CRIS data to make predictions for the local interstellar spectra (LIS) of nuclei that are not yet released by AMS-02. We are also updating our already-published LIS to provide a complete set from 1H-28Ni in the energy range from 1 MeV nucleon-1 to ∼100-500 TeV nucleon-1, thus covering 8-9 orders of magnitude in energy. Our calculations employ the GALPROP-HELMOD framework, which has proved to be a reliable tool in deriving the LIS of CR $\bar{p}$ , e-, and nuclei 1H-8O.

Keywords: Interplanetary medium, Heliosphere, Cosmic ray detectors, Galactic cosmic rays, Cosmic ray sources, Interstellar medium
The Coronal Global Evolutionary Model: Using HMI Vector Magnetogram and Doppler Data to Determine Coronal Magnetic Field Evolution. The Coronal Global Evolutionary Model (CGEM) provides data-driven simulations of the magnetic field in the solar corona to better understand the build-up of magnetic energy that leads to eruptive events. The CGEM project has developed six capabilities. CGEM modules (1) prepare time series of full-disk vector magnetic field observations to (2) derive the changing electric field in the solar photosphere over active-region scales. This local electric field is (3) incorporated into a surface flux transport model that reconstructs a global electric field that evolves magnetic flux in a consistent way. These electric fields drive a (4) 3D spherical magnetofrictional (SMF) model, either at high resolution over a restricted range of solid angles or at lower resolution over a global domain to determine the magnetic field and current density in the low corona. An SMF-generated initial field above an active region and the evolving electric field at the photosphere are used to drive (5) detailed magnetohydrodynamic (MHD) simulations of active regions in the low corona. SMF or MHD solutions are then used to compute emissivity proxies that can be compared with coronal observations. Finally, a lower-resolution SMF magnetic field is used to initialize (6) a global MHD model that is driven by an SMF electric field time series to simulate the outer corona and heliosphere, ultimately connecting Sun to Earth. As a demonstration, this report features results of CGEM applied to observations of the evolution of NOAA Active Region 11158 in 2011 February.

Keywords: Solar activity, Solar magnetic fields, Solar corona
Search for Nearby Earth Analogs .III. Detection of 10 New Planets, 3 Planet Candidates, and Confirmation of 3 Planets around 11 Nearby M Dwarfs. Earth-sized planets in the habitable zones of M dwarfs are good candidates for the study of habitability and detection of biosignatures. To search for these planets, we analyze all available radial velocity data and apply four signal detection criteria to select the optimal candidates. We find 10 strong candidates satisfying these criteria and three weak candidates showing inconsistency over time due to data samplings. We also confirm three previous planet candidates and improve their orbital solutions through combined analyses of updated data sets. Among the strong planet candidates, HIP 38594 b is a temperate super-Earth with a mass of 8.2 ± 1.7 M⊕ and an orbital period of 60.7 ± 0.1 days, orbiting around an early-type M dwarf. Early-type M dwarfs are less active and thus are better hosts for habitable planets than mid-type and late-type M dwarfs. Moreover, we report the detection of five two-planet systems, including two systems made up of a warm or cold Neptune and a cold Jupiter, consistent with a positive correlation between these two types of planets. We also detect three temperate Neptunes, four cold Neptunes, and four cold Jupiters, contributing to a rarely explored planet population. Due to their proximity to the Sun, these planets on wide orbits are appropriate targets for direct imaging by future facilities such as the Habitable Exoplanet Observatory and the Extremely Large Telescope.

Keywords: M dwarf stars, Exoplanet detection methods, High-resolution microlensing event imaging, Astrostatistics, Exoplanet astronomy, Radial velocity
On Neural Architectures for Astronomical Time-series Classification with Application to Variable Stars. Despite the utility of neural networks (NNs) for astronomical time-series classification, the proliferation of learning architectures applied to diverse data sets has thus far hampered a direct intercomparison of different approaches. Here we perform the first comprehensive study of variants of NN-based learning and inference for astronomical time series, aiming to provide the community with an overview on relative performance and, hopefully, a set of best-in-class choices for practical implementations. In both supervised and self-supervised contexts, we study the effects of different time-series-compatible layer choices, namely the dilated temporal convolutional neural network (dTCNs), long-short term memory NNs, gated recurrent units and temporal convolutional NNs (tCNNs). We also study the efficacy and performance of encoder-decoder (i.e., autoencoder) networks compared to direct classification networks, different pathways to include auxiliary (non-time-series) metadata, and different approaches to incorporate multi-passband data (i.e., multiple time series per source). Performance—applied to a sample of 17,604 variable stars (VSs) from the MAssive Compact Halo Objects (MACHO) survey across 10 imbalanced classes—is measured in training convergence time, classification accuracy, reconstruction error, and generated latent variables. We find that networks with recurrent NNs generally outperform dTCNs and, in many scenarios, yield to similar accuracy as tCNNs. In learning time and memory requirements, convolution-based layers perform better. We conclude by discussing the advantages and limitations of deep architectures for VS classification, with a particular eye toward next-generation surveys such as the Legacy Survey of Space and Time, the Roman Space Telescope, and Zwicky Transient Facility.

Keywords: Periodic variable stars, Light curve classification , Neural networks, Light curves, Variable stars
The 2017 September 6 Flare: Radio Bursts and Pulsations in the 22-5000 MHz Range and Associated Phenomena. For the 2017 September 6 flare (SOL2017-Sep-06T11:53) we present not only unusual radio bursts but also their interesting time association with the other flare phenomena observed in extreme ultraviolet (EUV), white-light, X-ray, and γ-ray emissions. Using our new method based on wavelets we found quasi-periodic pulsations (QPPs) in several locations of the whole time-frequency domain of the analyzed radio spectrum (11:55-12:07 UT and 22-5000 MHz). Among them the drifting QPPs are new and the most interesting, especially a bidirectional QPP at the time of the hard X-ray and γ-ray peaks and a sunquake start. In the pre-impulsive phase we show an unusual drifting pulsation structure (DPS) in association with the EUV brightenings caused by the interaction of magnetic ropes. In the flare impulsive phase we found an exceptional radio burst drifting from 5000 to 800 MHz. In connection with this drifting burst, we show a U burst at about the onset time of an EUV writhed structure and a drifting radio burst as a signature of a shock wave at high frequencies (1050-1350 MHz). In the peak flare phase we found an indication of an additional energy-release process located at higher altitudes in the solar atmosphere. These phenomena are interpreted considering a rising magnetic rope, magnetosonic waves, and particle beams. Using a density model we estimated the density, wave velocities, and source heights for the bidirectionally drifting QPPs, the density for the pre-impulsive DPS and U burst, and the density and magnetic field strength for the drifting radio burst.

Keywords: Solar oscillations, Solar radio flares, The Sun