Sazuna/UAT_keywords huggingface dataset:
Katachi (形): Decoding the Imprints of Past Star Formation on Present-day Morphology in Galaxies with Interpretable CNNs. The physical processes responsible for shaping how galaxies form and quench over time leave imprints on both the spatial (galaxy morphology) and temporal (star formation history; SFH) tracers that we use to study galaxies. While the morphology–SFR connection is well studied, the correlation with past star formation activity is not as well understood. To quantify this, we present Katachi (形), an interpretable convolutional neural network framework that learns the connection between the factors regulating star formation in galaxies on different spatial and temporal scales. Katachi is trained on 9904 galaxies at 0.02 &lt; z &lt; 0.1 in the SDSS-IV MaNGA DR17 sample to predict stellar mass (M *; root mean square error (RSME) 0.22 dex), current star formation rate (SFR; RMSE 0.31 dex), and half-mass time (t 50; RMSE 0.23 dex). This information allows us to reconstruct nonparametric SFHs for each galaxy from gri imaging alone. To quantify the morphological features informing the SFH predictions, we use SHAP (SHapley Additive exPlanations). We recover the expected trends of M * governed by the growth of galaxy bulges, as well as those of SFR correlating with spiral arms and other star-forming regions. We also find that the SHAP maps of D4000 are more complex than those of M * and SFR, and that morphology is correlated with t 50 even at fixed mass and SFR. Katachi serves as a scalable public framework to predict galaxy properties from large imaging surveys including Rubin, Roman, and Euclid, with large data sets of high signal-to-noise ratio imaging across limited photometric bands. * https://github.com/juanpabloalfonzo/Katachi

Keywords: Convolutional neural networks, Astronomy data analysis, Galaxy classification systems, Galaxy evolution, Extragalactic astronomy
Two Repeated Transient Quasiperiodic Oscillations in the γ-Ray Emission from the Blazar 3C 279. In this work, we report for the first time two repeated transient quasiperiodic oscillations (QPOs) in the γ-ray light curve of the TeV blazar 3C 279. We search for the periodicity in the light curve and estimate its confidence level using the weighted wavelet Z-transform, the Lomb–Scargle periodogram, and the REDFIT techniques. The main results are as follows: (1) a QPO of ∼33 days (&gt;2.5σ) is found during the flare of 117 days (MJD 55008–55125) from 2009 June to November. Interestingly, the same QPO (∼39 days) reappeared in the flaring duration from MJD 59430 to 59585, with the confidence level of &gt;4σ. (2) Another transient QPO of ∼91 days with a significance of &gt;3.8σ is found during a period with 455 days (MJD 58430–58985) from 2019 February to 2020 May. Under the premise of considering the QPOs reported in the literature, the QPO of ∼40 days is repeated three times and the QPO of ∼91 days is repeated twice. We discuss several physical models explaining the QPOs of this blazar. Our study may suggest that the two QPOs originate from the twin jets of the binary black holes at the center of 3C 279. The repeated occurrence of QPOs of a similar scale strongly supports the geometric scenario of a blob spiraling within the jet. Furthermore, the hypothesis of a sheath in the jet may also be a potential explanation for the repetitive γ-ray flare patterns observed in the light curve.

Keywords: Blazars
Modified Temperature–Redshift Relation and Ultra-high-energy Cosmic Ray Propagation. We reexamine the interactions of ultra-high-energy cosmic rays (UHECRs) with photons from the cosmic microwave background (CMB) under a changed, locally nonlinear temperature–redshift relation T(z). This changed temperature–redshift relation has recently been suggested by the postulate of subjecting thermalized and isotropic photon gases such as the CMB to an SU(2) rather than a U(1) gauge group. This modification of ΛCDM is called SU(2)CMB, and some cosmological parameters obtained by SU(2)CMB seem to be in better agreement with local measurements of the same quantities, in particular H 0 and S8. In this work, we apply the reduced CMB photon density under SU(2)CMB to the propagation of UHECRs. This leads to a higher UHECR flux just below the ankle in the cosmic ray spectrum and slightly more cosmogenic neutrinos under otherwise equal conditions for emission and propagation. Most prominently, the proton flux is significantly increased below the ankle (5 × 1018 eV) for hard injection spectra and without considering the effects of magnetic fields. The reduction in CMB photon density also favors a decreased cosmic ray source evolution than the best fit using ΛCDM. In consequence, it seems that SU(2)CMB favors sources that evolve like the star formation rate, such as starburst galaxies and gamma-ray bursts, over active galactic nuclei as origins of UHECRs. We conclude that the question about the nature of primary sources of UHECRs is directly affected by the assumed temperature–redshift relation of the CMB.

Keywords: Cosmology, Cosmological neutrinos, Ultra-high-energy cosmic radiation
Enhancing Pulsar Candidate Identification with Self-tuning Pseudolabeling Semisupervised Learning. In the field of astronomy, machine-learning technologies are becoming increasingly crucial for identifying radio pulsars. However, the process of acquiring labeled data, which is both time-consuming and potentially biased, poses a significant limitation to current methodologies. In response to these challenges, this study proposes and validates a self-tuning pseudolabeling semisupervised learning approach. This approach synthesizes a vast unlabeled data set with a considerably smaller set of labeled data, markedly enhancing classifier performance and effectuating a transition from traditional fully supervised learning methods to more efficient radio pulsar detection strategies. Our experimental outcomes demonstrate that even with a training set comprised of only 100 labeled pulsar candidates, this method can attain a recall rate of 92.35% and an F1 score of 93.89%. When the number of labeled examples is increased to 800, we observe a further improvement in performance, with the recall rate rising to 97.50% and the F1 score reaching 97.16%. The utility of the semisupervised learning approach is evident even with minimal labeled data, which is a common scenario in the search for pulsars, including in environments like globular clusters. What stands out is the method's capacity to detect pulsar candidates effectively with only a limited number of labeled examples. This emphasizes the robust potential of our approach to facilitate early-stage pulsar surveys and highlights its capability to yield substantial results even when labeled data are in short supply.

Keywords: Astronomy data modeling, Astronomical object identification, Convolutional neural networks, Astronomy data analysis, Pulsars, Radio pulsars
GRBs from Collapse of Thorne─Żytkow─like Objects as the Aftermath of WD-NS Coalescence. The Type II gamma-ray burst (GRB) 200826A challenges collapsar models by questioning how they can generate a genuinely short-duration event. The other Type I GRB 211211A confused us with a kilonova signature observed in the afterglow of a long burst. Here, we propose a comprehensive model in which both bursts are the results of the collapse of Thorne─Żytkow─like objects (TZlOs). The TZlO consists of a central neutron star (NS), with a dense white dwarf (WD) material envelope, which is formed as the aftermath of a WD-NS coalescence. We find that the characteristics of the resultant GRBs depend on whether the TZlO collapses immediately following the WD-NS merger or not. Additionally, the observational properties of the consequent GRBs manifest variations contingent upon whether the collapse of the TZlO results in a magnetar or a black hole. We also show that our model is consistent with the observations of GRB 211211A and GRB 200826A. Specifically, the optical excess in GRB 211211A can be attributed to an engine-fed kilonova, while the supernova bump in GRB 200826A is likely due to the collision between the ejecta and the disk wind shell.

Keywords: Neutron stars, White dwarf stars, Gamma-ray bursts
Polarized Light from Massive Protoclusters (POLIMAP). I. Dissecting the Role of Magnetic Fields in the Massive Infrared Dark Cloud G28.37+0.07. Magnetic fields may play a crucial role in setting the initial conditions of massive star and star cluster formation. To investigate this, we report SOFIA-HAWC+ 214 μm observations of polarized thermal dust emission and high-resolution GBT-Argus C18O(1-0) observations toward the massive Infrared Dark Cloud (IRDC) G28.37+0.07. Considering the local dispersion of B-field orientations, we produce a map of the B-field strength of the IRDC, which exhibits values between ∼0.03 and 1 mG based on a refined Davis–Chandrasekhar–Fermi method proposed by Skalidis &amp; Tassis. Comparing to a map of inferred density, the IRDC exhibits a B–n relation with a power-law index of 0.51 ± 0.02, which is consistent with a scenario of magnetically regulated anisotropic collapse. Consideration of the mass-to-flux ratio map indicates that magnetic fields are dynamically important in most regions of the IRDC. A virial analysis of a sample of massive, dense cores in the IRDC, including evaluation of magnetic and kinetic internal and surface terms, indicates consistency with virial equilibrium, sub-Alfvénic conditions, and a dominant role for B-fields in regulating collapse. A clear alignment of magnetic field morphology with the direction of the steepest column density gradient is also detected. However, there is no preferred orientation of protostellar outflow directions with the B-field. Overall, these results indicate that magnetic fields play a crucial role in regulating massive star and star cluster formation, and therefore they need to be accounted for in theoretical models of these processes.

Keywords: Star forming regions, Magnetic fields, Polarimetry, Infrared dark clouds
High Mass Inner Regions Found in Five Outbursting Sources. Young stellar objects are thought to commonly undergo sudden accretion events that result in a rise in bolometric luminosity. These outbursts likely coincide with the onset of planet formation and could impact the formation of planets. The reason behind this dramatic enhancement of accretion is an active area of research, and the mass of the system is a critical parameter. Using the Northern Extended Millimeter Array, we survey five outbursting sources (three FU Ori, one EX Or, and one "peculiar" source) with the primary goal of determining the system's mass using an optically thin line of CO. We estimate the mass of a central region for each object that using both continuum emission and C17O J = 2-1. The C17O emission likely includes both disk and inner envelope material, thus acts as an upper limit on the disk mass, ranging from 0.33 to 3.4 M⊙ for our sources. These derived masses suggest that the inner ∼1000 au contains enough mass along the line of sight for these sources to be gravitationally unstable.

Keywords: FU Orionis stars, Young stellar objects, Protoplanetary disks, Submillimeter astronomy, Interferometry
Is the Compact Object Associated with HESS J1731-347 a Strange Quark Star? A Possible Astrophysical Scenario for Its Formation. The analysis of the central compact object within the supernova (SN) remnant HESS J1731-347 suggests that it has a small radius and, even more interestingly, a mass of the order or smaller than 1 M ☉. This raises the question of which astrophysical process could lead to such a small mass, since the analysis of various types of SN explosions indicate that is it not possible to produce a neutron star with a mass smaller than about 1.17 M ☉. Here we show that masses of the order or smaller than 1 M ☉ can be obtained in the case of strange quark stars and that it is possible to build a coherent model explaining not only the mass and the radius of that object, but also its slow cooling suggested in various analyses. We also show that an astrophysical path exists, which leads to the formation of such an object, and we discuss the role played in that scenario by strangelets assumed to constitute the dark matter.

Keywords: Neutron stars, Baryonic dark matter, Dark matter, Compact objects
Gravitational-wave Radiation from the Magnetar-driven Supernovae. Rapidly spinning magnetars are potential candidates for the energy source of supernovae (SNe) and gamma-ray bursts and the most promising sources for continuous gravitational waves (GWs) detected by ground-based GW detectors. Continuous GWs can be radiated from magnetars due to magnetic-induced deformation or fluid oscillations, compatible with magnetic dipole (MD) radiation for spin-down energy. In this paper, we investigate the diverse light curves of magnetar-driven SNe in the scenario that the spin-down is dominated by GW radiation and/or MD radiation. By simulating the light curves of SNe and employing the Markov Chain Monte Carlo method, we constrain the parameters of the magnetars and SN explosions and show that the signature of GW radiation may be indicated by the bolometric luminosity curves of SNe Ic-BL 2007ru and 2009bb. We find that the ellipticity of magnetars in the order of 10‑3 can be induced by the magnetic field of ∼1016 G. If such continuous GWs associated with SNe can be detected in the future by the Advanced LIGO and Virgo detectors, this would be a smoking gun for a magnetar engine powering SNe.

Keywords: Magnetars, Supernovae, Gravitational waves
Discovery and Characterization of Two Ultrafaint Dwarfs outside the Halo of the Milky Way: Leo M and Leo K. We report the discovery of two ultrafaint dwarf galaxies, Leo M and Leo K, that lie outside the halo of the Milky Way (MW). Using Hubble Space Telescope imaging of the resolved stars, we create color–magnitude diagrams reaching the oldest main-sequence turnoff of each system and (i) fit for structural parameters of the galaxies; (ii) measure their distances using the luminosity of the horizontal branch stars; (iii) estimate integrated magnitudes and stellar masses; and (iv) reconstruct the star formation histories. Based on their location in the Local Group, neither galaxy is currently within the halo of the MW although Leo K is located ∼26 kpc from the low-mass galaxy Leo T and these two systems may have had a past interaction. Leo M and Leo K have stellar masses of M ⊙ and 1.2 ± 0.2 × 104 M ⊙, and were quenched Gyr and Gyr ago, respectively. Given that the galaxies are at farther distances from the MW, it is unlikely that they were quenched by environmental processing. Instead, given their low stellar masses, their early quenching timescales are consistent with the scenario that a combination of reionization and stellar feedback shut down star formation at early cosmic times.

Keywords: Local Group, Hertzsprung Russell diagram, Stellar populations, Hubble Space Telescope, Dwarf galaxies, Galaxy quenching, Reionization
Global Coronal Plasma Diagnostics Based on Multislit Extreme-ultraviolet Spectroscopy. Full-disk spectroscopic observations of the solar corona are highly desired to forecast solar eruptions and their impact on planets and to uncover the origin of solar wind. In this paper, we introduce a new multislit design (five slits) to obtain extreme-ultraviolet (EUV) spectra simultaneously. The selected spectrometer wavelength range (184–197 Å) contains several bright EUV lines that can be used for spectral diagnostics. The multislit approach offers an unprecedented way to efficiently obtain the global spectral data but the ambiguity from different slits should be resolved. Using a numerical simulation of the global corona, we primarily concentrate on the optimization of the disambiguation process, with the objective of extracting decomposed spectral information of six primary lines. This subsequently facilitates a comprehensive series of plasma diagnostics, including density (Fe XII 195.12/186.89 Å), Doppler velocity (Fe XII 193.51 Å), line width (Fe XII 193.51 Å), and temperature diagnostics (Fe VIII 185.21 Å, Fe X 184.54 Å, Fe XI 188.22 Å, and Fe XII 193.51 Å). We find a good agreement between the forward modeling parameters and the inverted results at the initial eruption stage of a coronal mass ejection, indicating the robustness of the decomposition method and its immense potential for global monitoring of the solar corona.

Keywords: Solar atmosphere, Solar extreme ultraviolet emission, Solar active regions, Spectroscopy, Solar instruments
Mass–Radius Relationships and Contraction of Condensed Planets by Cooling or Despinning. Condensed planets contract or expand as their temperature changes. With the exception of the effect of phase changes, this phenomenon is generally interpreted as being solely related to the thermal expansivity of the planet's components. However, changes in density affect pressure and gravity and, consequently, the planet's compressibility. A planet's radius is also linked to its rate of rotation. Here again, changes in pressure, gravity, and compressibility are coupled. In this article we clarify how the radius of a condensed planet changes with temperature and rotation, using a simple and rigorous thermodynamic model. We consider condensed materials to obey a simple equation of state which generalizes a polytopic EoS as temperature varies. Using this equation, we build simple models of condensed planet's interiors including exoplanets, derive their mass–radius relationships, and study the dependence of their radius on temperature and rotation rate. We show that it depends crucially on the value of ρ  s  gR/K  s  (ρ  s  being surface density, g gravity, R radius, K  s  surface incompressibility). This nondimensional number is also the ratio of the dissipation number which appears in compressible convection and the Gruneïsen mineralogic parameter. While the radius of small planets depends on temperature, this is not the case for large planets with large dissipation numbers; Earth and a super-Earth like CoRoT-7b are in something of an intermediate state, with a moderately temperature-dependent radius. Similarly, while the radius of these two planets is a function of their rotation rates, this is not the case for smaller or larger planets.

Keywords: Extrasolar rocky planets, Solar system terrestrial planets, Planetary thermal histories
Maser Activity of Organic Molecules toward Sgr B2(N). At centimeter wavelengths, single-dish observations have suggested that the Sagittarius (Sgr) B2 molecular cloud at the Galactic Center hosts weak maser emission from several organic molecules, including CH2NH, HNCNH, and HCOOCH3. However, the lack of spatial distribution information on these new maser species has prevented us from assessing the excitation conditions of the maser emission as well as their pumping mechanisms. Here, we present a mapping study toward Sgr B2 north (N) to locate the region where the complex maser emission originates. We report the first detection of the Class I methanol (CH3OH) maser at 84 GHz and the first interferometric map of the methanimine (CH2NH) maser at 5.29 GHz toward this region. In addition, we present a tool for modeling and fitting the unsaturated molecular maser signals with non-LTE radiative transfer models and Bayesian analysis using the Markov Chain Monte Carlo approach. These enable us to quantitatively assess the observed spectral profiles. The results suggest a two-chain-clump model for explaining the intense CH3OH Class I maser emission toward a region with low continuum background radiation. By comparing the spatial origin and extent of maser emission from several molecular species, we find that the 5.29 GHz CH2NH maser has a close spatial relationship with the 84 GHz CH3OH Class I masers. This relationship serves as observational evidence to suggest a similar collisional pumping mechanism for these maser transitions.

Keywords: Spectral line identification, Galactic center, Radiative transfer, Interstellar masers
The Low-mass Stellar Initial Mass Function in Nearby Ultrafaint Dwarf Galaxies. The stellar initial mass function (IMF) describes the distribution of stellar masses that form in a given star formation event. The long main-sequence lifetimes of low-mass stars mean that the IMF in this regime (below ∼ 1 M ☉) can be investigated through star counts. Ultrafaint dwarf galaxies are low-luminosity systems with ancient, metal-poor stellar populations. We investigate the low-mass IMF in four such systems (Reticulum II, Ursa Major II, Triangulum II, and Segue 1), using Hubble Space Telescope imaging data that reaches to ≲ 0.2 M ☉ in each galaxy. The analysis techniques that we adopt depend on the number of low-mass stars in each sample. We use Kolmogorov─Smirnov tests for all four galaxies to determine whether their observed apparent magnitude distributions can reject a given combination of IMF parameters and binary fraction for the underlying population. We forward model 1000 synthetic populations for each combination of parameters, and reject those parameters only if each of the 1000 realizations reject the null hypothesis. We find that all four galaxies reject a variety of IMFs, and the IMFs that they cannot reject include those that are identical, or similar, to that of the stellar populations of the Milky Way. We determine the best-fit parameter values for the IMF in Reticulum II and Ursa Major II and find that the IMF in Reticulum II is generally consistent with that of the Milky Way, while the IMF in Ursa Major II is more bottom heavy. The interpretation of the results for Ursa Major II is complicated by possible contamination from two known background galaxy clusters.

Keywords: Local Group, Initial mass function, Low mass stars, Dwarf spheroidal galaxies
Measuring White Dwarf Variability from Sparsely Sampled Gaia DR3 Multi-epoch Photometry. White dwarf stars are ubiquitous in the Galaxy, and are essential to understanding stellar evolution. While most white dwarfs are photometrically stable and reliable flux standards, some can be highly variable, which can reveal unique details about the endpoints of low-mass stellar evolution. In this study, we characterize a sample of high-confidence white dwarfs with multi-epoch photometry from Gaia Data Release 3. We compare these Gaia light curves with light curves from the Zwicky Transiting Facility and the Transiting Exoplanet Survey Satellite to see when Gaia data independently can accurately measure periods of variability. From this sample, 105 objects have variability periods measured from the Gaia light curves independently, with periods as long as roughly 9.5 days and as short as 256.2 s (roughly 4 minutes), including seven systems with periods shorter than 1000 s. We discover 86 new objects from the 105 target samples, including pulsating, spotted, and binary white dwarfs, and even a new 68.4 minute eclipsing cataclysmic variable. The median amplitude of the absolute photometric variability we confirm from Gaia independently is 1.4%, demonstrating that Gaia epoch photometry is capable of measuring short-term periods even when observations are sparse.

Keywords: Light curves, White dwarf stars, Periodic variable stars