Sazuna/UAT_keywords huggingface dataset:
Chicago–Carnegie Hubble Program: A Multiwavelength Search for the Effects of Metallicity on the Cepheid Distance Scale. II. Theoretical Models and Synthetic Spectra. This is the second of two papers exploring the effects of metallicity on the multiwavelength properties of Cepheids in terms of their multiwavelength period–luminosity (PL) relations, impacting their use as extragalactic distance indicators and underpinning one of the most popular paths to estimating the expansion rate of the Universe, H0. In Paper I, we presented five tests for the influence of metallicity on galactic and extragalactic Cepheid PL relations, spanning nearly 2 dex in metallicity and inspecting PL relations from the optical (BVI), through the near-infrared (JHK), and into the mid-infrared (at 3.4 and 4.5 μm). And in no case were any statistically significant results forthcoming. Here we interrogate published spectral energy distributions constructed from theoretical (static) stellar atmospheres, covering the surface gravity and temperature ranges attributed to classical (supergiant, F and K spectral type) Cepheid variables, and explore the differential effects of changing the atmospheric metallicity, down by 2 dex from solar (a factor of 100 below the average Milky Way value) and then up from solar by 0.5 dex (i.e., a factor of 3× above the Milky Way value). The theoretical models clearly show that metallicity systematically impacts each of the bandpasses differentially: the level of this effect is largest in the ultraviolet (where line blanketing is most intense), reversing sign in the optical (due to flux redistribution from the UV), and then asymptotically falling back to zero from the red to the far-infrared. The discovered effects of metallicity are systematic, but they are small, and as such, they do not contradict the findings of Paper I, but they do explain why the problem has been so hard to resolve given the low level of precision of the photometry for all but the very nearest and apparently brightest Cepheids. The most interesting (and useful) result of this investigation is that from a close examination of the models, we have discovered infrared regions in Cepheid spectral energy distributions that allow for the simultaneous correction for extinction and metallicity differences by the judicious combination of only two filters: one in the near-infrared and one in the mid-infrared, the former centered at 1.2 μm and the other centered at 3.6 μm. Even more exciting and promising is the fact that both of these bands can be simultaneously observed in single exposures using the dual-channel imager, NIRCam on JWST.

Keywords: Cepheid variable stars, Metallicity, Cepheid distance, Distance indicators
The GeV γ-Ray Emission from the Composite Supernova Remnant CTB 87. We report the GeV γ-ray emission around the composite supernova remnant (SNR) CTB 87 with more than 16 yr of PASS 8 data recorded by the Fermi Large Area Telescope. Two separate point sources with different GeV spectra are identified in this region: one has a soft γ-ray spectrum, likely due to interactions between the SNR shock and molecular clouds, and another source with a hard GeV γ-ray spectrum aligns with the TeV spectrum of VER J2016+371, suggesting it as the GeV counterpart. Considering the observations of CTB 87 in the radio and X-ray bands, VER J2016+371 is proposed to originate from the pulsar wind nebula (PWN) associated with PSR J2016+3711. A leptonic model with a broken power-law electron distribution could explain the multiwavelength data of VER J2016+371, with fitted parameters matching typical γ-ray PWNe. Deeper searching for the SNR shock of CTB 87 in other bands and the future TeV observations by LHAASO and Cherenkov Telescope Array are crucial to reveal the nature of CTB 87.

Keywords: Supernova remnants, Gamma-ray sources, Pulsar wind nebulae
Magnetic Interactions in White Dwarf Binaries as Mechanism for Long-period Radio Transients. A growing population of long-period radio transients has been discovered, and their physical origin is still up for debate. Recently, a new such source named ILT J1101+5521 was discovered, which is in a white dwarf (WD)–red dwarf (RD) binary system, with the observed 125.5 minutes period in radio emission being identified as the orbital period and the radio emission occurs at the inferior conjunction of the WD. We suggest that the radio emission properties of the system can be well explained within the framework of the unipolar inductor magnetic interaction model between the magnetized WD and the RD with low magnetization, with a relativistic version of electron cyclotron maser emission being the most likely radiation mechanism. We suggest that this mechanism can interpret at least some long-period radio transients, especially the ultra-long-period subpopulation. Within this model, high energy emission in X-rays via relativistically boosted cyclotron radiation and γ-rays via inverse Compton scattering off stellar light are expected, but the predicted luminosities are relatively low. This model likely applies to the ultra-long-period population of LPRTs. The short-period population of LPRTs is likely powered by other engines, such as slow magnetars.

Keywords: Close binary stars, Non-thermal radiation sources
Helium Pickup Ion Velocity Distributions Observed in Interplanetary Coronal Mass Ejection Structures. The velocity distribution functions (VDFs) of He+ pickup ions (PUIs) through two interplanetary coronal mass ejection (ICME) events associated with two interplanetary shocks are examined. Their specific properties in pitch-angle space were used as tracers of the local physical processes. These VDFs were studied using observations from the PLasma And SupraThermal Ion Composition instrument on board the Solar Terrestrial Relations Observatory with 10 minutes cadence and full energy and angular resolutions. The analysis focuses on pitch angle distributions and their average/deviation to evaluate heating/cooling, acceleration/deceleration, and pitch angle diffusion. For an ICME accompanied by the quasi-perpendicular shock, (a) reflected and energized particles were found in the upstream, and pitch angle scattering and suprathermal particle production were conspicuous in the downstream; (b) strong heating was observed in the sheath region; (c) suprathermal particles were found in the sheath region and attributed to the velocity fluctuation within the solar wind; and (d) universal pitch angle scattering was found throughout the ICME. For an ICME accompanied by a quasi-parallel shock, (a) localized heating and acceleration were found around the shock location; (b) power-law suprathermal tail distributions were found near the shock, suggesting diffusive shock acceleration processes; (c) weak or no sheath heating was observed; and (d) pitch angle scattering was correlated with magnetic field power spectral density. In the magnetic cloud for this event, pitch angle diffusion consistent with the scattering by counterpropagating Alfvén waves was found. This type of analysis can be applied to study shock injection processes and PUI transport/diffusion processes under active conditions.

Keywords: Pickup ions, Interplanetary shocks, Solar coronal mass ejections, Space plasmas
Inverse Raman Scattering and the Diffuse Interstellar Bands: An Exploration of the Systemic Interconnections between Spontaneous and Inverse Raman Scattering and Extended Red Emission, Red Rectangle Bands, and Diffuse Interstellar Bands. First identified in 1964, inverse Raman scattering (IRS) is a nonlinear stimulated phenomenon that induces Raman-scattered absorptions where Raman emissions would be expected. This paper highlights the significance of IRS in analyzing the spectra of stars located in the distant background of H I interstellar clouds. Specifically, ultraviolet emission lines Raman scattered by atomic hydrogen, typically observed in emission at wide scattering angles in the optical spectra of symbiotic stars and nebulae, should appear as IRS absorptions in the optical spectra of the background stars. I show that all known interstellar Raman-scattered emission lines in the Hα wavelength region are detected in absorption as diffuse interstellar bands (DIBs) in the spectra of reddened stars, and conclude that IRS by atomic hydrogen resolves the long-standing DIB puzzle. This sheds new light on the perplexing relationship between DIBs and the Red Rectangle nebula emission bands (RRBs). The conditions under which either DIBs or RRBs are detected emphasize the importance of considering the physical relationship between the observer, the H I medium, and the direction of the illuminating radiation field (i.e., the geometry of the observation) in observations of H I interstellar matter. Observing in the direction of the radiation field or on its side determines whether IRS, yielding DIBs and the 2200 Å bump, or spontaneous Raman scattering at wide scattering angles, resulting in extended red emission, Raman-scattered emission lines (including RRBs), and unidentified infrared bands, will be observed.

Keywords: Diffuse interstellar bands
Prediction of Halo Coronal Mass Ejections Using SDO/HMI Vector Magnetic Data Products and a Transformer Model. We present a transformer model, named DeepHalo, to predict the occurrence of halo coronal mass ejections (CMEs). Our model takes as input an active region (AR) and a profile, where the profile contains a time series of data samples in the AR that are collected 24 hr before the beginning of a day, and predicts whether the AR would produce a halo CME during that day. Each data sample contains physical parameters, or features, derived from photospheric vector magnetic field data taken by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We survey and match CME events in the Space Weather Database Of Notification, Knowledge, Information and the Large Angle and Spectrometric Coronagraph CME Catalog, and we compile a list of CMEs, including halo CMEs and nonhalo CMEs, associated with ARs in the period between 2010 November and 2023 August. We use the information gathered above to build the labels (positive vs. negative) of the data samples and profiles at hand, where the labels are needed for machine learning. Experimental results show that DeepHalo with a true skill statistic (TSS) score of 0.907 outperforms a closely related long short-term memory network with a TSS score of 0.821. To our knowledge, this is the first time that the transformer model has been used for halo CME prediction.

Keywords: Solar active regions, Astronomy data analysis, Solar coronal mass ejections
GECKO Follow-up Observations of the Binary Neutron Star–Black Hole Merger Candidate S230518h. The gravitational-wave (GW) event S230518h is a potential binary neutron star–black hole merger (NSBH) event that was detected during engineering run 15, which served as the commissioning period before the LIGO–Virgo–KAGRA O4a observing run. Despite its low probability of producing detectable electromagnetic emissions, we performed extensive follow-up observations of this event using the Gravitational-wave Electromagnetic Counterpart Korean Observatories (GECKO) telescopes in the Southern Hemisphere. Our observations covered 61.7% of the 90% credible region, a 284 deg2 area accessible from the Southern Hemisphere, reaching a median limiting magnitude of R = 21.6 mag. In these images, we conducted a systematic search for an optical counterpart of this event by combining a convolutional-neural-network-based classifier and human verification. We identified 128 transient candidates, but no significant optical counterpart was found that could have caused the GW signal. Furthermore, we provide feasible kilonova properties that are consistent with the upper limits of the observations. Although no optical counterpart was found, our result demonstrates both GECKO's efficient wide-field follow-up capabilities and usefulness for constraining properties of kilonovae from NSBH mergers at distances of ∼200 Mpc.

Keywords: Neutron stars, Optical observation, Stellar mergers, Wide-field telescopes, Optical identification, Transient sources, Gravitational wave sources, Gravitational wave astronomy, Time domain astronomy, Gravitational waves, Supernovae, Time series analysis
A Very Long Baseline Interferometry Calibrator Grid at 600 MHz for Fast Radio Transient Localizations with CHIME/FRB Outriggers. The Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Project has a new very long baseline interferometry (VLBI) Outrigger at the Green Bank Observatory (GBO), which forms a 3300 km baseline with CHIME operating at 400─800 MHz. Using 100 ms long full-array baseband "snapshots" collected commensally during FRB and pulsar triggers, we perform a shallow, wide-area VLBI survey covering a significant fraction of the northern sky targeted at the positions of compact sources from the Radio Fundamental Catalog. In addition, our survey contains calibrators detected from two 1 s long trial baseband snapshots for a deeper survey with CHIME and GBO. In this paper, we present the largest catalogue of compact calibrators suitable for 30 mas scale VLBI observations at subgigahertz frequencies to date. Our catalogue consists of 200 total calibrators in the Northern Hemisphere that are compact on 30 mas scales with fluxes above 100 mJy. This calibrator grid will enable the precise localization of hundreds of FRBs a year with CHIME/FRB Outriggers.

Keywords: Surveys, Very long baseline interferometry, Active galactic nuclei, Radio interferometry, Radio transient sources
On a Critical Acceleration Scale of Dark Matter in ΛCDM and Dynamical Dark Energy. Universal acceleration a0 emerges in various empirical laws, yet its fundamental nature remains unclear. Using Illustris and Virgo N-body simulations, we focus on the velocity and acceleration fluctuations in collisionless dark matter involving long-range gravity. For comparison, in the kinetic theory of gases, molecules undergo random elastic collisions involving short-range interactions, where only velocity fluctuations are relevant. Hierarchical structure formation proceeds through the merging of smaller halos to form larger halos, which facilitates a continuous energy cascade from small to large halos at a constant rate ɛu ≈ ‑10‑7 m2 s‑3. Velocity fluctuations involve a critical velocity uc ∝ (1 + z)‑3/4. Acceleration fluctuations involve a critical acceleration ac ∝ (1 + z)3/4. Two critical quantities are related by the rate of energy cascade ɛu ≈ ‑acuc/[2(3π)2], where factor 3π is from the angle of incidence during merging. With critical velocity uc on the order of 300 km s‑1 at z = 0, the critical acceleration is determined to be ac0 ≡ ac(z = 0) ≈ 10‑10 m s‑2, suggesting ac might explain the universal acceleration a0 ≈ 10‑10 m s‑2 in the empirical Tully–Fisher relation or modified Newtonian dynamics. The redshift evolution ac ∝ (1 + z)3/4 is in good agreement with Magneticum and EAGLE simulations and in reasonable agreement with limited observations. This suggests a larger a0 at a higher redshift such that galaxies of fixed mass rotate faster at a higher redshift. Note that for dark energy (DE) density  J m‑3, we postulate an entropic origin of the DE from acceleration fluctuations of dark matter, analogous to the gas pressure from velocity fluctuations. This leads to a dynamical DE coupled to the structure evolution involving a relatively constant DE density followed by a slow weakening phase, suggesting possible deviations from the standard ΛCDM paradigm.

Keywords: Galaxy dark matter halos, Hydrodynamical simulations, Cold dark matter, Galaxy dynamics, Galaxy rotation, Galaxy evolution, N-body simulations, Galaxy rotation curves, Modified Newtonian dynamics, Dark matter, Astronomical simulations, Dark energy
Considerations on the Origin of IRAS 19312+1950 Based on Long-term Maser Observations. IRAS source 19312+1950 (hereafter I19312) is an infrared point source with maser emissions of SiO, H2O, and OH molecules. Although initial observations suggested that I19312 might be an evolved star, its characteristics are not fully consistent with this classification. This study aims to further investigate the nature of I19312 by conducting long-term monitoring of its maser emissions and comparing the results with other known astrophysical objects. We conducted long-term monitoring of SiO, H2O, and OH maser emissions using single-dish radio telescopes. The results were then compared with historical maser data and the characteristics of similar objects to infer the possible origin of I19312. The SiO maser emissions from I19312 were detected over a wide velocity range and exhibited significant time variability. The OH maser lines suggest characteristics of an evolved star, while the H2O maser lines indicate molecular outflows. These features suggest that I19312 could be a candidate for a water fountain star, though there are inconsistencies, such as the large molecular gas mass, that challenge this hypothesis. The possibility of I19312 being a red nova remnant (RNR) is also considered, but this remains speculative due to the lack of direct evidence. The evolutionary stage of I19312 remains unclear, but it shares multiple characteristics with both evolved stars with peculiar properties and RNRs. Further long-term monitoring and high-resolution interferometric observations are required to better constrain the nature of this object.

Keywords: Circumstellar envelopes, Circumstellar masers, Molecular spectroscopy, Radio astronomy
Effects of Martian Dust Storms on Ionospheric Peak Altitudes. The effects of Martian dust storms on the atmosphere and ionosphere is one of the hot topics in Mars research. This paper reports on the effects of a local dust storm on the ionospheric peak altitude based on electron density profile observations from the Mars Global Surveyor Radio Science experiment during a dust storm event in late 2004. By employing a profile fitting technique, we determined the peak altitudes of both the M1 and M2 layers. A statistical analysis of different dust storm phases was conducted in conjunction with changes in atmospheric dust opacity. The results indicate that during the phase of rapid increase in global opacity, the peak altitudes of the two layers are elevated differently. After the opacity reaches saturation, the peak altitudes start to decrease slowly, with distinct decreasing trends for each layer. This suggests that dust storms exert different effects across various altitudes within the Martian ionosphere and atmosphere, which require the introduction of new physical processes for explanation. The discussion of the relationship between opacity and peak altitude contributes to a deeper understanding of the dynamics by which dust storms influence the Martian atmosphere and ionosphere, offering new insights for dust storm observation and future forecasting efforts.

Keywords: Mars, Aeronomy
The Puzzling Superorbital Period Variation of the Low-mass X-Ray Binary 4U 1820–30. Because of the previously observed stability of the 171 days period, the superorbital modulation of the low-mass X-ray binary 4U 1820–30 was considered a consequence of a third star orbiting around the binary. This study aims to further verify this triple model by testing the stability of the superorbital period using the light curves collected by X-ray sky-monitoring/scanning telescopes from 1987 to 2023. Both power spectral and phase analysis results indicate a significant change in the superorbital period, from 171 to 167 days, over this 36 yr span. The evolution of the superorbital phase suggests that the superorbital period may have experienced an abrupt change between early 2001 and mid 2003 or changed gradually with a period derivative of   day day‑1. We conclude that the superorbital period of 4U 1820–30 was not as stable as anticipated by the triple model, which strongly challenges this hypothesis. Instead, we propose an irradiation-induced mass-transfer instability scenario to explain the superorbital modulation of 4U 1820–30.

Keywords: Low-mass x-ray binary stars, Stellar accretion disks, Close binary stars, X-ray bursters
Double Layers in the Martian Magnetosheath. The observation of electrostatic double layers in Martian magnetosheath plasma is reported, based on medium-frequency (100 Hz–32 kHz) electric field data recorded by the Langmuir Probe and Waves on board the Mars Atmosphere and Volatile Evolution spacecraft on 2021 January 1. A total of six burst mode events were scrutinized, revealing the occurrence of double layer structures. Overall, 79 double layers were identified, with their absolute amplitudes and widths found to be in the ranges of 0.4–3.3 mV m‑1 and 0.6–6.4 ms, respectively. The dominant frequency associated with the observed excitations lies well above the ion plasma frequency (fpi). The identified structures were observed at 2600–4400 km altitude in the dusk sector (17–19 LT). Extensive analysis based on a nonlinear multifluid plasma model shows that the observed structures are electron-acoustic double layers. A comparison of theory and observations indicates that these double layers have spatial scales in the range of 0.4–10 km. This is the first detailed study to give conclusive evidence of the occurrence of double layers in the Martian plasma environment.

Keywords: Planetary magnetospheres, Space plasmas
Bilateral Constraints on Proton Lorentz Violation Effects. Since the early reports of events beyond the Greisen–Zatsepin–Kuzmin (GZK) cutoff, the investigation of ultrahigh-energy cosmic rays has emerged as a fundamental method for testing Lorentz invariance violation (LV) effects. Recent advances in observational capabilities have resulted in more stringent constraints on LV parameters. This study delves into the potentially anomalous phenomena arising from subluminal and superluminal LV effects, encompassing aspects such as proton decay and atypical threshold behavior of photo-pion production from protons within the GZK region. High-energy proton observations via cosmic rays have imposed stringent constraints on superluminal proton LV effects, while the confirmation of the GZK cutoff has established a robust boundary for the anomalous phenomena associated with subluminal proton LV effects. The research provides rigorously bilateral constraints on proton LV effects from both subluminal and superluminal standpoints.

Keywords: High energy astrophysics, Particle physics, Particle astrophysics, Cosmic rays