Sazuna/UAT_keywords huggingface dataset:
Testing the Solar Activity Paradigm in the Context of Exoplanet Transits. Transits of exoplanets across cool stars contain blended information about structures on the stellar surface and about the planetary body and atmosphere. To advance understanding of how this information is entangled, a surface-flux transport code, based on observed properties of the Sun's magnetic field, is used to simulate the appearance of hypothetical stellar photospheres from the visible near 4000 Å to the near-IR at 1.6 μm by mapping intensities characteristic of faculae and spots onto stellar disks. Stellar appearances are computed for a Sun-like star of solar activity up to a star with a mean magnetic flux density that is ∼30× higher. Simulated transit signals for a Jupiter-class planet are compared with observations. This (1) indicates that the solar paradigm is consistent with transit observations for stars throughout the activity range explored, provided that infrequent large active regions with fluxes up to ∼3 × 1023 Mx are included in the emergence spectrum, (2) quantitatively confirms that for such a model, faculae brighten relatively inactive stars while starspots dim more-active stars, and suggests (3) that large starspots inferred from transits of active stars are consistent with clusters of more compact spots seen in the model runs, (4) that wavelength-dependent transit-depth effects caused by stellar magnetic activity for the range of activity and the planetary diameter studied here can introduce apparent changes in the inferred exoplanetary radii across wavelengths from a few hundred to a few thousand kilometers, increasing with activity, and (5) that activity-modulated distortions of broadband stellar radiance across the visible to near-IR spectrum can reach several percent.

Keywords: Solar spectral irradiance, Stellar activity, Exoplanet astronomy, Transit photometry, Solar activity, Stellar photospheres
Absolute Calibration Strategies for the Hydrogen Epoch of Reionization Array and Their Impact on the 21 cm Power Spectrum. We discuss absolute calibration strategies for Phase I of the Hydrogen Epoch of Reionization Array (HERA), which aims to measure the cosmological 21 cm signal from the Epoch of Reionization. HERA is a drift-scan array with a 10° wide field of view, meaning bright, well-characterized point-source transits are scarce. This, combined with HERA's redundant sampling of the uv plane and the modest angular resolution of the Phase I instrument, make traditional sky-based and self-calibration techniques difficult to implement with high dynamic range. Nonetheless, in this work, we demonstrate calibration for HERA using point-source catalogs and electromagnetic simulations of its primary beam. We show that unmodeled diffuse flux and instrumental contaminants can corrupt the gain solutions and present a gain-smoothing approach for mitigating their impact on the 21 cm power spectrum. We also demonstrate a hybrid sky and redundant calibration scheme and compare it to pure sky-based calibration, showing only a marginal improvement to the gain solutions at intermediate delay scales. Our work suggests that the HERA Phase I system can be well calibrated for a foreground avoidance power spectrum estimator by applying direction-independent gains with a small set of degrees of freedom across the frequency and time axes.

Keywords: Cosmology, Reionization, Astronomy data analysis
Analysis of Multi-hour Continuous Observations of Seven Millisecond Pulsars. Precision pulsar timing can be used for a variety of astrophysical tests, from the detection of gravitational waves to probing the properties of the interstellar medium. Here we analyze various noise contributions to pulsar timing residuals from continuous multi-hour observations of seven millisecond pulsars (MSPs). We present scintillation bandwidth measurements for all MSPs in the sample, some for the first time. We also present scintillation timescale measurements and lower limits for all MSPs for the first time. In addition, we present upper limits on the contribution of pulse phase jitter to the timing residual error for all MSPs. These long observations also allow us to constrain variations in dispersion measures (DMs) on hour-long timescales for several millisecond pulsars. We find that there are no apparent DM variations in any of the MSPs studied on these timescales, as expected. In light of new radio telescopes, such as the Canadian Hydrogen Intensity Mapping Experiment, which will be able to time many pulsars for a short time each day, we search for differences in timing precisions from continuous pulse times of arrival (TOAs) and from equivalent length time-discontinuous TOAs. We find no differences in the precision for any of the MSPs in our sample, as expected. We conclude that the TOA variations are consistent with the expected breakdown into template-fitting, jitter, and scintillation errors.

Keywords: Interstellar medium, Interstellar scintillation, Pulsars, Millisecond pulsars
A Comparison of Flare Forecasting Methods. IV. Evaluating Consecutive-day Forecasting Patterns. A crucial challenge to successful flare prediction is forecasting periods that transition between "flare-quiet" and "flare-active." Building on earlier studies in this series in which we describe the methodology, details, and results of flare forecasting comparison efforts, we focus here on patterns of forecast outcomes (success and failure) over multiday periods. A novel analysis is developed to evaluate forecasting success in the context of catching the first event of flare-active periods and, conversely, correctly predicting declining flare activity. We demonstrate these evaluation methods graphically and quantitatively as they provide both quick comparative evaluations and options for detailed analysis. For the testing interval 2016-2017, we determine the relative frequency distribution of two-day dichotomous forecast outcomes for three different event histories (I.e., event/event, no-event/event, and event/no-event) and use it to highlight performance differences between forecasting methods. A trend is identified across all forecasting methods that a high/low forecast probability on day 1 remains high/low on day 2, even though flaring activity is transitioning. For M-class and larger flares, we find that explicitly including persistence or prior flare history in computing forecasts helps to improve overall forecast performance. It is also found that using magnetic/modern data leads to improvement in catching the first-event/first-no-event transitions. Finally, 15% of major (I.e., M-class or above) flare days over the testing interval were effectively missed due to a lack of observations from instruments away from the Earth-Sun line.

Keywords: Solar active region magnetic fields, Astrostatistics tools, Solar flares, The Sun, Sunspots, Astronomy data analysis, Solar magnetic fields, Solar x-ray flares, Solar activity, Astronomy data visualization
Hot Subdwarf All Southern Sky Fast Transit Survey with the Evryscope. We have conducted a survey of candidate hot subdwarf (HSD) stars in the southern sky searching for fast transits, eclipses, and sinusoidal-like variability in the Evryscope light curves. The survey aims to detect transit signals from Neptune-size planets to gas giants, and eclipses from M-dwarfs and brown dwarfs. The other variability signals are primarily expected to be from compact binaries and reflection effect binaries. Due to the small size of HSDs (R ≈ 0.2 R⊙), transit and eclipse signals are expected to last only ≈20 minutes, but with large signal depths (up to completely eclipsing if the orientation is edge on). With its 2 minute cadence and continuous observation, the Evryscope is well placed to recover these fast transits and eclipses. The very large field of view (8150 deg2) is critical to obtain enough HSD targets, despite their rarity. We identified ≈11,000 potential HSDs from the 9.3 M Evryscope light curves for sources brighter than mg = 15. With our machine-learning spectral classifier, we flagged high confidence targets and estimate the total HSDs in the survey to be ≈1400. The light-curve search detected three planet transit candidates, shown to have stellar companions from follow-up analysis. We discovered several new compact binaries (including two with unseen degenerate companions), two eclipsing binaries with M-dwarf companions, as well as new reflection effect binaries and others with sinusoidal-like variability. Four of the discoveries are being published in separate follow-up papers, and we discuss the follow-up potential of the other discoveries.

Keywords: Subdwarf stars, Surveys, B subdwarf stars, Stellar classification, Photometry, Spectroscopy, O subdwarf stars
Simulating Turbulence-aided Neutrino-driven Core-collapse Supernova Explosions in One Dimension. The core-collapse supernova (CCSN) mechanism is fundamentally 3D, with instabilities, convection, and turbulence playing crucial roles in aiding neutrino-driven explosions. Simulations of CCNSe including accurate treatments of neutrino transport and sufficient resolution to capture key instabilities remain among the most expensive numerical simulations in astrophysics, prohibiting large parameter studies in 2D and 3D. Studies spanning a large swath of the incredibly varied initial conditions of CCSNe are possible in 1D, though such simulations must be artificially driven to explode. We present a new method for including the most important effects of convection and turbulence in 1D simulations of neutrino-driven CCSNe, called Supernova Turbulence In Reduced-dimensionality, or STIR. Our new approach includes crucial terms resulting from the turbulent and convective motions of the flow. We estimate the strength of convection and turbulence using a modified mixing-length theory approach, introducing a few free parameters to the model that are fit to the results of 3D simulations. For sufficiently large values of the mixing-length parameter, turbulence-aided neutrino-driven explosions are obtained. We compare the results of STIR to high-fidelity 3D simulations and perform a parameter study of CCSN explosion using 200 solar-metallicity progenitor models from 9 to 120 ${M}_{\odot }$ . We find that STIR is a better predictor of which models will explode in multidimensional simulations than other methods of driving explosions in 1D. We also present a preliminary investigation of predicted observable characteristics of the CCSN population from STIR, such as the distributions of explosion energies and remnant masses.

Keywords: Hydrodynamical simulations, Supernova neutrinos, Stellar convective zones, Core-collapse supernovae, Massive stars, Supernovae
Detection of Irregular, Submillimeter Opaque Structures in the Orion Molecular Clouds: Protostars within 10,000 yr of Formation?. We report Atacama Large Millimeter/submillimeter Array and Very Large Array continuum observations that potentially identify the four youngest protostars in the Orion Molecular Clouds taken as part of the Orion VANDAM program. These are distinguished by bright, extended, irregular emission at 0.87 and 8 mm and are optically thick at 0.87 mm. These structures are distinct from the disk or point-like morphologies seen toward the other Orion protostars. The 0.87 mm emission implies temperatures of 41-170 K, requiring internal heating. The bright 8 mm emission implies masses of 0.5-1.2 M☉ assuming standard dust opacity models. One source has a Class 0 companion, while another exhibits substructure indicating a companion candidate. Three compact outflows are detected, two of which may be driven by companions, with dynamical times of ∼300 to ∼1400 yr. The slowest outflow may be driven by a first hydrostatic core. These protostars appear to trace an early phase when the centers of collapsing fragments become optically thick to their own radiation and compression raises the gas temperature. This phase is thought to accompany the formation of hydrostatic cores. A key question is whether these structures are evolving on freefall times of ∼100 yr, or whether they are evolving on Kelvin-Helmholtz times of several thousand years. The number of these sources imply a lifetime of ∼6000 yr, in closer agreement with the Kelvin-Helmholtz time. In this case, rotational and/or magnetic support could be slowing the collapse.

Keywords: Protostars, Stellar jets, Star formation
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. II. A Statistical Characterization of Class 0 and Class I Protostellar Disks. We have conducted a survey of 328 protostars in the Orion molecular clouds with the Atacama Large Millimeter/submillimeter Array at 0.87 mm at a resolution of ∼0"1 (40 au), including observations with the Very Large Array at 9 mm toward 148 protostars at a resolution of ∼0"08 (32 au). This is the largest multiwavelength survey of protostars at this resolution by an order of magnitude. We use the dust continuum emission at 0.87 and 9 mm to measure the dust disk radii and masses toward the Class 0, Class I, and flat-spectrum protostars, characterizing the evolution of these disk properties in the protostellar phase. The mean dust disk radii for the Class 0, Class I, and flat-spectrum protostars are ${44.9}_{-3.4}^{+5.8}$ , ${37.0}_{-3.0}^{+4.9}$ , and ${28.5}_{-2.3}^{+3.7}$ au, respectively, and the mean protostellar dust disk masses are 25.9 ${}_{-4.0}^{+7.7}$ , ${14.9}_{-2.2}^{+3.8}$ , ${11.6}_{-1.9}^{+3.5}$ ${M}_{\oplus }$ , respectively. The decrease in dust disk masses is expected from disk evolution and accretion, but the decrease in disk radii may point to the initial conditions of star formation not leading to the systematic growth of disk radii or that radial drift is keeping the dust disk sizes small. At least 146 protostellar disks (35% of 379 detected 0.87 mm continuum sources plus 42 nondetections) have disk radii greater than 50 au in our sample. These properties are not found to vary significantly between different regions within Orion. The protostellar dust disk mass distributions are systematically larger than those of Class II disks by a factor of &gt;4, providing evidence that the cores of giant planets may need to at least begin their formation during the protostellar phase.

Keywords: Protostars, Young stellar objects, Star formation, Protoplanetary disks
GROWTH on S190814bv: Deep Synoptic Limits on the Optical/Near-infrared Counterpart to a Neutron Star-Black Hole Merger. On 2019 August 14, the Advanced LIGO and Virgo interferometers detected the high-significance gravitational wave (GW) signal S190814bv. The GW data indicated that the event resulted from a neutron star-black hole (NSBH) merger, or potentially a low-mass binary BH merger. Due to the low false-alarm rate and the precise localization (23 deg2 at 90%), S190814bv presented the community with the best opportunity yet to directly observe an optical/near-infrared counterpart to an NSBH merger. To search for potential counterparts, the GROWTH Collaboration performed real-time image subtraction on six nights of public Dark Energy Camera images acquired in the 3 weeks following the merger, covering &gt;98% of the localization probability. Using a worldwide network of follow-up facilities, we systematically undertook spectroscopy and imaging of optical counterpart candidates. Combining these data with a photometric redshift catalog, we ruled out each candidate as the counterpart to S190814bv and placed deep, uniform limits on the optical emission associated with S190814bv. For the nearest consistent GW distance, radiative transfer simulations of NSBH mergers constrain the ejecta mass of S190814bv to be Mej &lt; 0.04 M⊙ at polar viewing angles, or Mej &lt; 0.03 M⊙ if the opacity is κ &lt; 2 cm2g-1. Assuming a tidal deformability for the NS at the high end of the range compatible with GW170817 results, our limits would constrain the BH spin component aligned with the orbital momentum to be χ &lt; 0.7 for mass ratios Q &lt; 6, with weaker constraints for more compact NSs.

Keywords: Neutron stars, Black hole physics, Observational astronomy, Binary stars, Transient sources, Gravitational wave sources, Gravitational waves
Role of Intervening Mg II Absorbers on the Rotation Measure and Fractional Polarization of the Background Quasars. We probed the magnetic fields in high-redshift galaxies using excess extragalactic contribution to residual rotation measure (RRM) for quasar sightlines with intervening Mg II absorbers. Based on a large sample of 1132 quasars, we have computed RRM distributions broadening using median absolute deviation from the mean ( ${\sigma }_{\mathrm{rrm}}^{\mathrm{md}}$ ), and found it to be 17.1 ± 0.7 rad m-2 for 352 sightlines having Mg II intervening absorbers in comparison to its value of 15.1 ± 0.6 rad m-2 for 780 sightlines without such absorbers, resulting in an excess broadening ( ${\sigma }_{\mathrm{rrm}}^{\mathrm{ex}}$ ) of 8.0 ± 1.9 rad m-2 among these two subsamples. This value of ${\sigma }_{\mathrm{rrm}}^{\mathrm{ex}}$ , has allowed us to constrain the average strength of magnetic field (rest frame) in high-redshift galaxies responsible for these Mg II absorbers, to be ∼1.3 ± 0.3 μG at a median redshift of 0.92. This estimate of magnetic field is consistent with the reported estimate in earlier studies based on radio-infrared correlation and energy equipartition for galaxies in the local universe. A similar analysis on subsample split based on the radio spectral index, α (with Fν ∝ να), for flat (α ≥ -0.3; 315 sources) and steep (α ≤ -0.7; 476 sources) spectrum sources shows a significant ${\sigma }_{\mathrm{rrm}}^{\mathrm{ex}}$ (at 3.5σ level) for the former and absent in the latter. An anticorrelation found between the ${\sigma }_{\mathrm{rrm}}^{\mathrm{md}}$ and percentage polarization (p) with a similar Pearson correlation of -0.62 and -0.87 for subsamples with and without Mg II, respectively, suggests the main contribution for decrements in the p value to be intrinsic to the local environment of quasars.

Keywords: Extragalactic astronomy, Magnetic fields, Galaxies, Quasars
Stellar Characterization of M Dwarfs from the APOGEE Survey: A Calibrator Sample for M-dwarf Metallicities. We present spectroscopic determinations of the effective temperatures, surface gravities, and metallicities for 21 M dwarfs observed at high resolution (R ∼ 22,500) in the H band as part of the Sloan Digital Sky Survey (SDSS)-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The atmospheric parameters and metallicities are derived from spectral syntheses with 1D LTE plane-parallel MARCS models and the APOGEE atomic/molecular line list, together with up-to-date H2O and FeH molecular line lists. Our sample range in Teff from ∼3200 to 3800 K, where 11 stars are in binary systems with a warmer (FGK) primary, while the other 10 M dwarfs have interferometric radii in the literature. We define an ${M}_{{K}_{S}}$ M K S -radius calibration based on our M-dwarf radii derived from the detailed analysis of APOGEE spectra and Gaia DR2 distances, as well as a mass-radius relation using the spectroscopically derived surface gravities. A comparison of the derived radii with interferometric values from the literature finds that the spectroscopic radii are slightly offset toward smaller values, with Δ = -0.01 ± 0.02 R⋆/R⊙. In addition, the derived M-dwarf masses based upon the radii and surface gravities tend to be slightly smaller (by ∼5%-10%) than masses derived for M-dwarf members of eclipsing binary systems for a given stellar radius. The metallicities derived for the 11 M dwarfs in binary systems, compared to metallicities obtained for their hotter FGK main-sequence primary stars from the literature, show excellent agreement, with a mean difference of [Fe/H](M dwarf - FGK primary) = +0.04 ± 0.18 dex, confirming the APOGEE metallicity scale derived here for M dwarfs.

Keywords: M dwarf stars, Fundamental parameters of stars, Stellar abundances, Solar neighborhood, Low mass stars, Metallicity
Are Large Sunspots Dominant in Naked-eye Sunspot Observations for 1819-1918?. This article explores the sizes of sunspots as determined by naked-eye sunspot observations (NSOs). The international sunspot number (ISN), the group sunspot number, and the Greenwich photo-heliographic results (GPR) were utilized. According to the ISN results, 64% of NSOs from 1819 to 1918 have been identified as large sunspots. We found that the sunspot sizes had been considerably underestimated using the ISN data (compared to using the GPR data). About 40% of NSOs from 1819 to 1918 have been identified as giant sunspots, which have ranks of sunspot areas smaller than 5%. The results in this article indicate that the majority of NSOs are large sunspots. This calls into question the previous understanding that NSOs include sunspots of all sizes above the visibility limit.

Keywords: Maunder minimum, Sunspots, Sunspot number, Sunspot cycle
Detecting and Locating Electromagnetic Counterparts to Gravitational Wave Sources Using Galactic Dust Scattering Halos. We discuss a technique for detecting and locating rapid transient electromagnetic counterparts to gravitational wave sources that affords a reprieve of several hours after the gravitational wave event. The technique relies on detecting a scattering halo produced if X-rays emitted at the gravitational wave event scatter off Galactic dust clouds. The travel-time delay of these scattered photons makes them detectable up to several hours after the prompt event; the location of the gravitational wave source will be at the geometric center of the halo, which can be determined with precision sufficient to allow the host galaxy to be identified.

Keywords: X-ray astronomy, Gravitational waves, Black holes
Two Ultra-faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey. We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238-4054), is identified as a resolved overdensity of old and metal-poor stars with a heliocentric distance of ${\text{}}{D}_{\odot }={116.3}_{-0.6}^{+0.6}\,\mathrm{kpc}$ , a half-light radius of ${r}_{h}={2.3}_{-0.3}^{+0.4}\,\mathrm{arcmin}$ , an age of $\tau \gt 12.85\,\mathrm{Gyr}$ , a metallicity of $Z={0.0002}_{-0.0002}^{+0.0001}$ , and an absolute magnitude of ${M}_{V}=-{5.55}_{-0.11}^{+0.11}\,\mathrm{mag}$ . This characterization is consistent with the population of ultra-faint satellites and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630-0058), is identified as a resolved overdensity of stars with a heliocentric distance of ${\text{}}{D}_{\odot }={19.0}_{-0.6}^{+0.5}\,\mathrm{kpc}$ , a half-light radius of ${r}_{h}={0.97}_{-0.17}^{+0.24}\,\mathrm{arcmin}$ , an age of $\tau ={12.5}_{-0.7}^{+1.0}\,\mathrm{Gyr}$ , a metallicity of $Z={0.0005}_{-0.0001}^{+0.0002}$ , and an absolute magnitude of ${M}_{V}=-{0.2}_{-0.6}^{+0.8}\,\mathrm{mag}$ , consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.

Keywords: Local Group, Dwarf galaxies, Milky Way Galaxy, Star clusters