Sazuna/UAT_keywords huggingface dataset:
Estimating the Mean Free Paths of Energetic Protons Using Differential Intensity Spectra. An analytical calculation is presented to derive the mean free paths of energetic protons in large western solar energetic particle (SEP) events during the first 12 hr after the event onset utilizing the differential spectra averaged over successive time intervals of 3 hr. The model assumes diffusive transport of energetic particles in a radial magnetic flux tube and neglects solar wind convection and adiabatic cooling. The model further assumes that particles over the considered energies (&gt;10 MeV) are injected instantaneously near the Sun. Using the model, we reproduce the differential spectra averaged over successive time intervals after event onset and derive the radial mean free paths (λmfp) for protons at the energies where the two spectra over successive time intervals intersect. We then select eight western SEP events during the past solar cycle and apply the scheme. The derived λmfp ranges from 0.016 to 0.149 au. Our method finds smaller mean free paths than the lower limit of the "Palmer consensus" (0.04 au) in approximately 35% of the cases. We also combine differential intensity spectra and fluence to estimate the number of crossings (Nc) of particles passing through 1 au at applicable energies. The average Nc, excluding a twin-CME event, is 17.7, which indicates that diffusive transport of SEPs is capable of elevating the fluence observed at 1 au by one order of magnitude compared to if particles stream through 1 au nearly scatter-free.

Keywords: Solar energetic particles, Interplanetary physics
Very Large Telescope Spectroscopy of Ultra-faint Dwarf Galaxies. I. Boötes I, Leo IV, and Leo V. We perform consistent reductions and measurements for three ultra-faint dwarf galaxies (UFDs): Boötes I, Leo IV, and Leo V. Using the public archival data from the GIRAFFE spectrograph on the Very Large Telescope (VLT), we locate new members and provide refined measurements of physical parameters for these dwarf galaxies. We identify nine new Leo IV members and four new Leo V members, and perform a comparative analysis of previously discovered members. Additionally, we identify one new binary star in both Leo IV and Leo V. After removing binary stars, we recalculate the velocity dispersions of Boötes I and Leo IV to be ${5.1}_{-0.8}^{+0.7}$ and ${3.4}_{-0.9}^{+1.3}$ km s-1, respectively; we do not resolve the Leo V velocity dispersion. We identify a weak velocity gradient in Leo V that is ~4× smaller than the previously calculated gradient and that has a corresponding position angle that differs from the value in the literature by ~120°. Combining the VLT data with previous values from the literature, we reanalyze the Boötes I metallicity distribution function and find that a model including infall of pristine gas, while Boötes I was forming stars' best fits the data. Our analysis of Leo IV, Leo V, and other UFDs will enhance our understanding of these enigmatic stellar populations and contribute to future dark matter studies. This is the first in a series of papers examining 13 UDFs observed with VLT/GIRAFFE between 2009 and 2017. Similar analyses of the remaining 10 UFDs will be presented in forthcoming papers.

Keywords: Local Group, Binary stars, Stellar kinematics, Stellar abundances, Stellar populations, Dwarf galaxies, Metallicity, Dark matter
The Stellar Initial Mass Function and Population Properties of M89 from Optical and NIR Spectroscopy: Addressing Biases in Spectral Index Analysis. The complexity of constraining the stellar initial mass function (IMF) in early-type galaxies cannot be overstated, given the necessity of very high signal-to-noise ratio (S/N) data and the difficulty of breaking the strong degeneracies that occur among several stellar population parameters, including age, metallicity, and elemental abundances. With this paper, the second in a series, we present a detailed analysis of the biases that can occur when retrieving the IMF shape by exploiting both optical and near-IR IMF-sensitive spectral indices. As a test case, here we analyze data for the nearby galaxy M89, for which we have high-S/N spectroscopic data that cover the 3500-9000 Å spectral region and allow us to study the radial variation of the stellar population properties out to 1Re. Carrying out parallel simulations that mimic the retrieval of all of the explored stellar parameters from a known input model, we quantify the amount of bias at each step of our analysis. From more general simulations, we conclude that to accurately retrieve the IMF, it is necessary to retrieve accurate estimates not only of the age and metallicity but also of all of the elemental abundances that the spectral index fits are sensitive to. With our analysis technique applied to M89, we find consistency with a bottom-heavy IMF with a negative gradient from the center to half Re when using the Conroy et al. and Vazdekis et al. EMILES stellar population models. We find agreement with both a parallel full spectral fitting of the same data and literature results. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Initial mass function, Early-type galaxies
The Consistency of Chemical Clocks among Coeval Stars. The abundance ratios of some chemical species have been found to correlate with stellar age, leading to the possibility of using stellar atmospheric abundances as stellar age indicators. These chemical clocks have already been calibrated with solar twins and open clusters, but it remains to be seen whether they can be effective at identifying coeval stars in a population that spans a broad parameter space (i.e., the promise of chemical tagging). Since the components of wide binaries are known to be stars of common origins, they constitute ideal laboratories for testing the usefulness of chemical clocks for the age dating of field stars. Using a combination of our new measurements and literature data on wide binaries, we show for the first time that chemical clocks are even more consistent among the components of wide binaries than their individual abundances. Moreover, the special case of HIP 34426/HIP 34407 may indicate that chemical clocks are consistent for coeval stars even when those individual abundances are not. If the assumption that chemical clocks are reliable age indicators is correct, this would constitute the first statistically significant evidence that the components of wide binaries are indeed coeval, validating a large body of published work that relies on that to be the case. Furthermore, our results provide strong evidence that chemical clocks indeed carry important information about stellar birthplaces and chemical evolution, and thus we propose that including them in chemical tagging efforts may facilitate the identification of now-dissolved stellar groups.

Keywords: Binary stars, Solar analogs, Galaxy chemical evolution, Solar neighborhood, Chemical abundances, Spectroscopy
The MOSDEF-LRIS Survey: Probing the ISM/CGM Structure of Star-forming Galaxies at z   2 Using Rest-UV Spectroscopy. The complex structure of gas, metals, and dust in the interstellar and circumgalactic medium (ISM and CGM, respectively) in star-forming galaxies can be probed by Lyα emission and absorption, low-ionization interstellar (LIS) metal absorption, and dust reddening E(B - V). We present a statistical analysis of the mutual correlations among Lyα equivalent width (EWLyα), LIS equivalent width (EWLIS), and E(B - V) in a sample of 157 star-forming galaxies at z ~ 2.3. With measurements obtained from individual deep rest-UV spectra and spectral energy distribution modeling, we find that the tightest correlation exists between EWLIS and E(B - V), although correlations among all three parameters are statistically significant. These results signal a direct connection between dust and metal-enriched H I gas and that they are likely cospatial. By comparing our results with the predictions of different ISM/CGM models, we favor a dusty ISM/CGM model where dust resides in H I gas clumps and Lyα photons escape through the low H I covering fraction/column density intraclump medium. Finally, we investigate the factors that potentially contribute to the intrinsic scatter in the correlations studied in this work, including metallicity, outflow kinematics, Lyα production efficiency, and slit loss. Specifically, we find evidence that scatter in the relationship between EWLyα and E(B - V) reflects the variation in the metal-to-H I covering fraction ratio as a function of metallicity and the effects of outflows on the porosity of the ISM/CGM. Future simulations incorporating star formation feedback and the radiative transfer of Lyα photons will provide key constraints on the spatial distributions of neutral hydrogen gas and dust in the ISM/CGM structure.

Keywords: Interstellar medium, Circumgalactic medium, Extragalactic astronomy, Galaxy spectroscopy, High-redshift galaxies
DirtyGrid II: An Analysis of the Dust and Stellar Properties in Nearby Star-forming Galaxies. We study the dust and stellar properties of the Spitzer Infrared Nearby Galaxies Survey galaxies by fitting the ultraviolet (UV) to far-infrared (FIR) spectral energy distributions using the DIRTYGrid stellar and dust radiative transfer models. We find a minimum of two components of different stellar ages are needed, representing a young and an old stellar population, in order to obtain good fits for most of the galaxies. Our total dust masses agree with literature dust masses to within a factor of 2, and the residuals correlate most strongly with the stellar mass surface density of the old component. The LMC-2 dust grain model best describes the dust found in these normal star-forming galaxies. The derived attenuation curves are steeper than those found previously for starburst galaxies, and possess a weak 2175 Å feature. The relative contribution of the young and old stellar components as a function of wavelength reveals that the young component dominates the far-UV and MIPS24 bands, the old component dominates the optical/near-IR bands, and both components are important for the FIR bands. The DIRTYGrid star formation rates (SFRs) are consistent with a number of literature SFR indicators within a factor of 2. The differences we find are primarily due to the influence of the old stellar population that are accounted for by the DIRTYGrid SFRs fitting on a galaxy-by-galaxy basis using the information present in the full UV-FIR spectral energy distribution.

Keywords: Interstellar dust, Star formation, Spectral energy distribution, Radiative transfer, Galaxies
The Nuclear Star Cluster and Nuclear Stellar Disk of the Milky Way: Different Stellar Populations and Star Formation Histories. The Milky Way's nuclear stellar disk (NSD) and nuclear star cluster (NSC) are the main features of the Galactic center. Nevertheless, their observation is hampered by the extreme source crowding and high extinction. Hence, their relation and formation scenario are not fully clear yet. We aim to detect the stellar populations from the NSC and the NSD along the line of sight toward the NSC and assess whether they have different stellar populations and star formation histories. We analyzed the color-magnitude diagram, Ks versus H-Ks, of a region of 8'2 × 2'8 centered on the NSC, and detected two different stellar groups with different extinctions. We studied their red clumps to find the features associated with each of the stellar populations. We obtained that the two groups of stars correspond to the NSD and the NSC and found that they have significantly different stellar populations and star formation histories. We detected a double red clump for the NSD population, in agreement with previous work, whereas the NSC presents a more complex structure well fitted by three Gaussian features. We created extinction maps to analyze the extinction variation between the detected stellar groups. We found that the high-extinction layer varies on smaller scales (arcseconds) and that there is a difference of ${A}_{{K}_{s}}$ ~ 0.6 mag between both extinction layers. Finally, we obtained that the distance toward each of the stellar populations is compatible with the Galactic center distance and found some evidence of a slightly closer distance for the NSD stars (~360 ± 200 pc).

Keywords: Galaxy structure, Galactic center, Interstellar dust extinction, Red giant clump
Core Mass Estimates in Strong Lensing Galaxy Clusters: A Comparison between Masses Obtained from Detailed Lens Models, Single-halo Lens Models, and Einstein Radii. The core mass of galaxy clusters is both an important anchor of the radial mass distribution profile and a probe of structure formation. With thousands of strong lensing galaxy clusters being discovered by current and upcoming surveys, timely, efficient, and accurate core mass estimates are needed. We assess the results of two efficient methods to estimate the core mass of strong lensing clusters: the mass enclosed by the Einstein radius (M(&lt;θE), where θE is approximated from arc positions, and a single-halo lens model (MSHM), compared with measurements from publicly available detailed lens models (MDLM) of the same clusters. We use data from the Sloan Giant Arc Survey, the Reionization Lensing Cluster Survey, the Hubble Frontier Fields, and the Cluster Lensing and Supernova Survey with Hubble. We find a scatter of 18.1% (8.2%) with a bias of -7.1% (1.0%) between ${M}_{\mathrm{corr}}\left(\lt {\theta }_{\mathrm{arcs}}\right)$ (MSHM) and MDLM. Last, we compare the statistical uncertainties measured in this work to those from simulations. This work demonstrates the successful application of these methods to observational data. As the effort to efficiently model the mass distribution of strong lensing galaxy clusters continues, we need fast, reliable methods to advance the field.

Keywords: Galaxy clusters, Strong gravitational lensing
Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph. I. An Accurate Look at the L-to-T Transition at  300 Myr from Optical Through Mid-infrared Spectrophotometry. We present Spitzer IRS 5-14 μm spectra and 16 μm and 22 μm photometry of the T2.5 companion to the ~300 Myr old G0V star HN Peg. We incorporate previous 0.8-5 μm observations to obtain the most comprehensive spectral energy distribution (SED) of an intermediate-gravity L/T-transition dwarf that, together with an accurate Gaia EDR3 parallax of the primary, enables us to derive precise fundamental parameters. We find that young (≍0.1-0.3 Gyr) early-T dwarfs on average have ≍140 K lower effective temperatures, ≍20% larger radii, and similar bolometric luminosities compared to ≳1 Gyr old field dwarfs with similar spectral types. Our accurate infrared spectrophotometry offers new detail at wavelengths where the dominant carbon-bearing molecules have their strongest transitions: at 3.4 μm for methane and at 4.6 μm for carbon monoxide. We assess the performance of various widely available photospheric models and find that models with condensates and/or clouds better reproduce the full SED of this moderately young early-T dwarf. However, cloud-free models incorporating a more general convective instability treatment reproduce at least the low-resolution near-infrared spectrum similarly well. Our analysis of R ≍ 2300 J-band spectra shows that the near-infrared potassium absorption lines in HN Peg B have similar strengths to those seen in both younger and older T2-T3 dwarfs. We conclude that while alkali lines are well established as surface gravity indicators for L-type or warmer stars, they are insensitive to surface gravity in early-T dwarfs.

Keywords: Brown dwarfs
A New Reconstruction of the Sun's Magnetic Field and Total Irradiance since 1700. We model the Sun's large-scale magnetic field and total solar irradiance (TSI) since 1700 by combining flux transport simulations with empirical relationships between facular brightening, sunspot darkening, and the total photospheric flux. The photospheric field is evolved subject to the constraints that (1) the flux emergence rate scales as the yearly sunspot numbers, and (2) the polar field strength at solar minimum is proportional to the amplitude of the following cycle. Simulations are performed using both the recently revised sunspot numbers and an average of these numbers and the Hoyt-Schatten group numbers. A decrease (increase) in the polar field strength from one cycle to the next is simulated either by increasing (decreasing) the poleward flow speed, or by decreasing (increasing) the average axial tilts of active regions; the resulting photospheric field evolution is very similar whichever parameter is varied. Comparisons between irradiance data and both the simulated and observed photospheric field suggest that TSI and facular brightness increase less steeply with the field strength at solar minimum than at other phases of the cycle, presumably because of the dominance of small-scale ephemeral regions when activity is very low. This relative insensitivity of the irradiance to changes in the large-scale field during cycle minima results in a minimum-to-minimum increase of annual TSI from 1700 to 1964 (2008) of 0.2 (0.06) W m-2, a factor of 2-3 smaller than predicted in earlier reconstructions where the relation between facular brightness and field strength was assumed to be independent of cycle phase.

Keywords: Solar cycle, Sunspots, Solar dynamo, Solar faculae, Galactic cosmic rays, Solar active regions, Interplanetary magnetic fields, Solar magnetic fields, Ephemeral active regions, Solar radiation, Solar-terrestrial interactions
Generation of He I 1083 nm Images from SDO AIA Images by Deep Learning. In this study, we generate He I 1083 nm images from Solar Dynamic Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images using a novel deep learning method (pix2pixHD) based on conditional Generative Adversarial Networks (cGAN). He I 1083 nm images from National Solar Observatory (NSO)/Synoptic Optical Long-term Investigations of the Sun (SOLIS) are used as target data. We make three models: single-input SDO/AIA 19.3 nm image for Model I, single-input 30.4 nm image for Model II, and double-input (19.3 and 30.4 nm) images for Model III. We use data from 2010 October to 2015 July except for June and December for training and the remaining one for test. Major results of our study are as follows. First, the models successfully generate He I 1083 nm images with high correlations. Second, Model III shows better results than those with one input image in terms of metrics such as correlation coefficient (CC) and root mean square error (RMSE). CC and RMSE between real and synthetic ones for model III with 4 by 4 binnings are 0.88 and 9.49, respectively. Third, synthetic images show well observational features such as active regions, filaments, and coronal holes. This work is meaningful in that our model can produce He I 1083 nm images with higher cadence without data gaps, which would be useful for studying the time evolution of the chromosphere and transition region.

Keywords: The Sun, Convolutional neural networks, Solar filaments, Solar coronal holes, Solar chromosphere
Is Flare Ribbon Fine Structure Related to Tearing in the Flare Current Sheet?. Observations of solar flare ribbons show significant fine structure in the form of breaking wavelike perturbations and spirals. The origin of this structure is not well understood, but one possibility is that it is related to the tearing instability in the flare current sheet. Here we study this connection by constructing an analytical 3D magnetic field representative of an erupting flux rope with a flare current sheet below it. We introduce small-scale flux ropes representative of those formed during a tearing instability in the current layer, and use the squashing factor on the solar surface to identify the shape of the presumed flare ribbons and fine structure. Our analysis suggests there is a direct link between flare ribbon fine structure and flare current sheet tearing, with the majority of the ribbon fine structure related to oblique tearing modes. Depending upon the size, location, and twist of the small-scale flux ropes, breaking wavelike and spiral features within the hooks and straight sections of the flare ribbon can be formed that are qualitatively similar to observations. We also show that the handedness of the spirals/waves must be the same as the handedness of the hooks of the main ribbon. We conclude that tearing in the flare current layer is a likely explanation for spirals and wavelike features in flare ribbons.

Keywords: Solar flares, Solar magnetic reconnection, Solar physics, Solar corona, Solar chromosphere
Planck Galactic Cold Clumps at High Galactic Latitude-a Study with CO Lines. Gas at high Galactic latitude is a relatively little noticed component of the interstellar medium. In an effort to address this, 41 Planck Galactic Cold Clumps at high Galactic latitude (HGal; ∣b∣ &gt; 25°) were observed in 12CO, 13CO, and C18O J = 1-0 lines, using the Purple Mountain Observatory 13.7 m telescope. 12CO (1-0) and 13CO (1-0) emission was detected in all clumps, while C18O (1-0) emission was only seen in 16 clumps. The highest and average latitudes are 71°4 and 37°8, respectively. Fifty-one velocity components were obtained, and then each was identified as a single clump. Thirty-three clumps were further mapped at 1' resolution, and 54 dense cores were extracted. Among dense cores, the average excitation temperature Tex of 12CO is 10.3 K. The average line widths of thermal and nonthermal velocity dispersions are 0.19 and 0.46 km s-1, respectively, suggesting that these cores are dominated by turbulence. Distances of the HGal clumps given by Gaia dust reddening are about 120-360 pc. The ratio of X13/X18 is significantly higher than that in the solar neighborhood, implying that HGal gas has a different star formation history compared to the gas in the Galactic disk. HGal cores with sizes from 0.01 to 0.1 pc show no notable Larson's relation, and the turbulence remains supersonic down to a scale of slightly below 0.1 pc. None of the HGal cores that bear masses from 0.01 to 1 M⊙ are gravitationally bound, and all appear to be confined by outer pressure.

Keywords: Interstellar molecules, Dark interstellar clouds, Star formation
The Resolved Sunyaev-Zel'dovich Profiles of Nearby Galaxy Groups. Many of the baryons in galaxy groups are thought to have been driven out to large distances (≳R500) by feedback, but there are few constraining observations of this extended gas. This work presents the resolved Sunyaev-Zel'dovich (SZ) profiles for a stacked sample of 10 nearby galaxy groups within the mass range ${\mathrm{log}}_{10}({M}_{500}[{M}_{\odot }])=13.6\mbox{--}13.9$ . We measured the SZ profiles using the publicly available y-map from the Planck Collaboration as well as our own y-maps constructed from more recent versions of Planck data. The y-map extracted from the latest data release yielded a significant SZ detection out to 3 R500. In addition, the stacked profile from these data was consistent with simulations that included AGN feedback. Our best-fit model using the latest Planck data suggested a baryon fraction ≈5.6% within R500. This is significantly lower than the cosmic value of ≈16%, supporting the idea that baryons have been driven to large radii by AGN feedback. Lastly, we discovered a significant (~3σ) "bump" feature near ~2 R500 that is most likely the signature of internal accretion shocks.

Keywords: Active galactic nuclei, Intracluster medium, Sunyaev-Zeldovich effect, Galaxy groups