Sazuna/UAT_keywords huggingface dataset:
Electrostatic Bursts Generated by the Ion–Ion Acoustic Instability with Solar Wind Plasma Parameters. This study is motivated by recent observations from the Parker Solar Probe (PSP) mission, which have been identified as ion-acoustic waves from 15 to 25 solar radii. These observations reveal characteristic sequences of narrowband, high-frequency bursts exceeding 100 Hz embedded into a slower evolution around 1 Hz, persisting for several hours. To explore the potential role of the ion-acoustic instability (IAI) in these phenomena, we begin by reviewing classical findings on the IAI within the framework of linear kinetic theory. Focusing on proton distributions comprising both a core and a beam component, we analyze the IAI instability range and growth rates within the parameter regime relevant to PSP observations. Our findings indicate that the IAI can indeed occur in this regime, albeit requiring electron-to-core and beam-to-core temperature ratios slightly different from reported values during electrostatic burst detection. Furthermore, employing one-dimensional kinetic plasma simulations, we validate the growth rates predicted by linear theory and observe the saturation behavior of the instability. The resultant nonlinear structures exhibit trapped proton beam populations and oscillatory signatures comparable to those observed, both in terms of timescales and amplitude.

Keywords: Solar wind
Forecasting Geoffective Events from Solar Wind Data and Evaluating the Most Predictive Features through Machine Learning Approaches. This study addresses the prediction of geomagnetic disturbances by exploiting machine learning techniques. Specifically, the Long Short-term Memory recurrent neural network, which is particularly suited for application over long time series, is employed in the analysis of in situ measurements of solar wind plasma and magnetic field acquired over more than one solar cycle, from 2005 to 2019, at the Lagrangian point L1. The problem is approached as a binary classification aiming to predict 1 hr in advance a decrease in the SYM-H geomagnetic activity index below the threshold of ‑50 nT, which is generally regarded as indicative of magnetospheric perturbations. The strong class imbalance issue is tackled by using an appropriate loss function tailored to optimize appropriate skill scores in the training phase of the neural network. Beside classical skill scores, value-weighted skill scores are then employed to evaluate predictions, suitable in the study of problems, such as the one faced here, characterized by strong temporal variability. For the first time, the content of magnetic helicity and energy carried by solar transients, associated with their detection and likelihood of geoeffectiveness, were considered as input features of the network architecture. Their predictive capabilities are demonstrated through a correlation-driven feature selection method to rank the most relevant characteristics involved in the neural network prediction model. The optimal performance of the adopted neural network in properly forecasting the onset of geomagnetic storms, which is a crucial point for giving real warnings in an operational setting, is finally showed.

Keywords: Space weather, Solar wind, Classification, Neural networks
Natal Kicks from the Galactic Center and Implications on Their Environment and for the Nancy Grace Roman Space Telescope. Most galaxies, including the Milky Way, harbor a central supermassive black hole (SMBH) weighing millions to billions of solar masses. Surrounding these SMBHs are dense regions of stars and stellar remnants, such as neutron stars (NSs) and black holes (BHs). NSs and possibly BHs receive large natal kicks at birth on the order of hundreds of kilometers per second. The natal kicks that occur in the vicinity of an SMBH may redistribute the orbital configuration of the compact objects and alter their underlying density distribution. We model the effects of natal kicks on a Galactic center (GC) population of massive stars and stellar binaries with different initial density distributions. Using observational constraints from stellar orbits near the GC, we place an upper limit on the steepness of the initial stellar profile and find it to be core-like. In addition, we predict that 30%–70% of compact objects become unbound from the SMBH due to their kicks and will migrate throughout the Galaxy. Different BH kick prescriptions lead to distinct spatial and kinematic distributions. We suggest that the Nancy Grace Roman Space Telescope may be able to distinguish between these distributions and thus be able to differentiate between natal kick mechanisms.

Keywords: Galactic center, Binary stars, Stellar dynamics, Gravitational wave sources, Compact objects, Supernovae
A Multiwavelength, Multiepoch Monitoring Campaign of Accretion Variability in T Tauri Stars from the ODYSSEUS Survey. II. Photometric Light Curves. Classical T Tauri stars (CTTSs) are young, low-mass stars that accrete material from their surrounding protoplanetary disk. To better understand accretion variability, we conducted a multiepoch, multiwavelength photometric monitoring campaign of four CTTSs, TW Hya, RU Lup, BP Tau, and GM Aur, in 2021 and 2022, contemporaneous with Hubble Space Telescope UV and optical spectra. We find that all four targets display significant variability in their light curves, generally on days-long timescales (but in some cases year-to-year), often due to periodicity associated with stellar rotation and to stochastic accretion variability. There is a strong connection between mass accretion and photometric variability in all bands, but the relationship varies per target and epoch. Thus, photometry should be used with caution as a direct measure of accretion in CTTSs.

Keywords: Light curves, Classical T Tauri stars, Variable stars, Photometry, Stellar accretion
Constraining the Selection-corrected Luminosity Function and Total Pulse Count for Radio Transients. Studying transient phenomena, such as individual pulses from pulsars, has garnered considerable attention in the era of astronomical big data. Of specific interest to this study are rotating radio transients (RRATs), nulling, and intermittent pulsars. This study introduces a new algorithm named LuNfit, tailored to correct the selection biases originating from the telescope and detection pipelines. Ultimately LuNfit estimates the intrinsic luminosity distribution and nulling fraction of the single pulses emitted by pulsars. LuNfit relies on Bayesian nested sampling so that the parameter space can be fully explored. Bayesian nested sampling also provides the additional benefit of simplifying model comparisons through the Bayes ratio. The robustness of LuNfit is shown through simulations and applying LuNfit onto pulsars with known nulling fractions. LuNfit is then applied to three RRATs, J0012+5431, J1538+1523, and J2355+1523, extracting their intrinsic luminosity distribution and burst rates. We find that their nulling fractions are 0.4(2), 0.749(5), and 0.995(2), respectively. We further find that a log-normal distribution likely describes the single pulse luminosity distribution of J0012+5431 and J1538+1523, while the Bayes ratio for J2355+1523 slightly favors an exponential distribution. We show the conventional method of correcting selection effects by "scaling up" the missed fraction of radio transients can be unreliable when the mean luminosity of the source is faint relative to the telescope sensitivity. Finally, we discuss the limitations of the current implementation of LuNfit while also delving into potential enhancements that would enable LuNfit to be applied to sources with complex pulse morphologies.

Keywords: Radio transient sources, Neutron stars, Compact objects, Radio pulsars
Proper Motions and Orbits of Distant Local Group Dwarf Galaxies from a Combination of Gaia and Hubble Data. We have determined the proper motions (PMs) of 12 dwarf galaxies in the Local Group (LG), ranging from the outer Milky Way (MW) halo to the edge of the LG. We used the Hubble Space Telescope (HST) as the first and Gaia as the second epoch using the GaiaHub software. For Leo A and Sag DIG, we also used multi-epoch HST measurements relative to background galaxies. Orbital histories derived using these PMs show that two-thirds of the galaxies in our sample are on first infall with &gt;90% certainty. The observed star formation histories of these first-infall dwarfs are generally consistent with infalling dwarfs in simulations. The remaining four galaxies have crossed the virial radius of either the MW or M31. When we compare their star formation (SF) and orbital histories we find tentative agreement between the inferred pattern of SF with the timing of dynamical events in the orbital histories. For Leo I, SF activity rises as the dwarf crosses the MW's virial radius, culminating in a burst of SF shortly before pericenter (≈1.7 Gyr ago). The SF then declines after pericenter, but with some smaller bursts before its recent quenching (≈0.3 Gyr ago). This shows that even small dwarfs like Leo I can hold onto gas reservoirs and avoid quenching for several gigayears after falling into their host, which is longer than generally found in simulations. Leo II, NGC 6822, and IC 10 are also qualitatively consistent with this SF pattern in relation to their orbit, but more tentatively due to larger uncertainties.

Keywords: Local Group, Dwarf galaxies, Proper motions
3D-DASH: The Evolution of Size, Shape, and Intrinsic Scatter in Populations of Young and Old Quiescent Galaxies at 0.5 &lt; z &lt; 3. We present a study of the growth of the quiescent galaxy population between 0.5 &lt; z &lt; 3 by tracing the number density and structural evolution of a sample of 4518 old and 583 young quiescent galaxies with log(M ⋆/M ⊙) &gt; 10.4, selected from the COSMOS2020 catalog with complementary Hubble Space Telescope F160W imaging from the 3D-DASH survey. Among the quiescent population at z ∼ 2, roughly 50% are recently quenched galaxies; these young quiescent galaxies become increasingly rare toward lower redshift, supporting the idea that the peak epoch of massive galaxy quenching occurred at z &gt; 2. Our data show that while the effective half-light radius of quiescent galaxies generally increases with time, young quiescent galaxies are significantly smaller than their older counterparts at the same redshift. In this work we investigate the connection between this size difference and other structural properties, including axis ratio, color gradients, stellar mass, and the intrinsic scatter in effective radius. We demonstrate that the size difference is driven by the most massive subpopulation (log(M ⋆/M ⊙) &gt; 11) and does not persist when restricting the sample to intermediate-mass galaxies (10.4 &lt; log(M ⋆/M ⊙) &lt; 11). Interestingly, the intrinsic scatter in physical size shows a strong coevolution over the investigated time period and peaks around z ∼ 2 for both populations, only diverging at z &lt; 1. Taken together, and assuming we are not missing a significant population of lower surface brightness galaxies, while the formation and quenching mechanisms that dominate at higher redshifts yield compact remnants, multiple evolutionary pathways may explain the diverse morphologies of galaxies that quench at z &lt; 1.

Keywords: Galaxy formation, Galaxy structure, High-redshift galaxies, Galaxy evolution
Faraday Tomography with CHIME: The "Tadpole" Feature G137+7. A direct consequence of Faraday rotation is that the polarized radio sky does not resemble the total intensity sky at long wavelengths. We analyze G137+7, which is undetectable in total intensity but appears as a depolarization feature. We use the first polarization maps from the Canadian Hydrogen Intensity Mapping Experiment. Our 400–729 MHz bandwidth and angular resolution,  17‧ – 30‧ , allow us to use Faraday synthesis to analyze the polarization structure. In polarized intensity and polarization angle maps, we find a tail extending 10° from the head and designate the combined object, the tadpole. Similar polarization angles, distinct from the background, indicate that the head and tail are physically associated. The head appears as a depolarized ring in single channels, but wideband observations show that it is a Faraday rotation feature. Our investigations of H I and Hα find no connections to the tadpole. The tail suggests motion of either the gas or an ionizing star through the interstellar medium; the B2(e) star HD 20336 is a candidate. While the head features a coherent, ∼ ‑8 rad m‑2 Faraday depth, Faraday synthesis also identifies multiple components in both the head and tail. We verify the locations of the components in the spectra using QU fitting. Our results show that approximately octave-bandwidth Faraday rotation observations at ∼600 MHz are sensitive to low-density ionized or partially ionized gas, which is undetectable in other tracers.

Keywords: Interstellar dust, Stellar-interstellar interactions, Polarimetry, Interstellar magnetic fields, Warm ionized medium, Interstellar clouds, Proper motions, Interstellar medium, Radio interferometry, Radio astronomy
A Possible Additional Formation Pathway for the Interstellar Diatomic SiS. The formation of silicon monosulfide (SiS) in space appears to be a difficult process, but the present work shows that a previously excluded pathway may contribute to its astronomical abundance. Reaction of the radicals SH + SiH produces SiS with a submerged transition state and generates a stabilizing H2 molecule as a product to dissipate the kinetic energy. Such is a textbook chemical reaction for favorable gas-phase chemistry. While previously proposed mechanisms reacting atomic sulfur and silicon with SiH, SH, and H2S will still be major contributors to the production of SiS, an abundance of SiS in certain regions could be a marker for the presence of SiH where it has previously been unobserved. These quantum chemically computed reaction profiles imply that the silicon-chalcogen chemistry of molecular clouds, shocked regions, or protoplanetary disks may be richer than previously thought. Quantum chemical spectral data for the intermediate cis- and trans-HSiSH are also provided to aid in their potential spectroscopic characterization.

Keywords: Neutral-neutral reactions, Astrochemistry, Quantum-chemical calculations, Shocks, Interdisciplinary astronomy
Observation of Persistent Propagating Waves in a Solar Prominence. Spectropolarimetric observation of a quiescent prominence was performed in He I 1083 nm. With the slit of the spectrograph fixed on the prominence, we obtained a time series of Stokes profiles for a duration of 108 minutes with a cadence of 8 s. Also using imaging spectroscopic data in Hα and extreme-ultraviolet images at 193 Å, we obtained the following results: (1) The prominence harbors persistent waves propagating across its body. (2) The waves are conspicuous in the line-of-sight (LOS) velocity with an amplitude of about 2 km s‑1 but not detectable in the intensity of emission lines or magnetic field. (3) Noticeable periods are about 4 minutes (220 and 260 s) and 15 minutes (910 s), and they propagate with phase speeds of 140 ∼ 200 and ∼24 km s‑1 preferentially in horizontal and vertical directions, respectively. (4) Magnetic field strength was estimated to be about 2.5 G with its LOS component of 0 ± 1 G on average. We interpret the 4 minute oscillation as Alfvénic waves propagating in the corona containing the prominence threads, and it is not a resonant wave trapped in the prominence body but excited by an external source. On the other hand, a 15 minute oscillation is interpreted as Alfvénic waves propagating upward in the prominence body. The prominence was evolving in its height during our observation, and there is a hint that the 15 minute period gradually gets longer during the observation. These waves are thought to be taking place in layers with different field directions and strength superposed in the LOS.

Keywords: Solar prominences
Low-mass Globular Clusters from Stripped Dark Matter Halos. The origin and formation of globular clusters (GCs) has remained a mystery. We present a formation scenario for ancient GC-like objects that form in ultrahigh-resolution simulations (smallest cell size &lt; 0.1 pc, mass resolution M cell = 4 M ⊙). The simulations are cosmological zoom-in simulations of dwarf galaxies within the stellar mass range 106‑7 M ⊙ that match Local Group dwarf properties well. Our investigation reveals GCs hosting ancient stellar populations, characterized by a lack of dark matter (DM) in the present epoch. The clusters exhibit short, episodic star formation histories, occasionally marked by the presence of multiple stellar generations. The metallicity distributions show a widening, encompassing stars in the range of 10‑4 &lt; Z ⋆/Z ⊙ &lt; 1. The presence of these objects is attributable to star formation occurring within low-mass DM halos (M halo ≈ 106 M ⊙) during the early stages of the Universe, preceding reionization (z ≳ 7). As these clusters are accreted into dwarf galaxies, DM is preferentially subjected to tidal stripping, with an average accretion redshift of  z¯≈5 .

Keywords: Globular star clusters, Galaxy dark matter halos, Galaxy formation, Tidal disruption, Star formation, Tidal interaction, Dark matter
APPLE: An Evolution Code for Modeling Giant Planets. We introduce APPLE, a novel planetary evolution code designed specifically for the study of giant exoplanet and Jovian planet evolution in the era of Galileo, Juno, and Cassini. With APPLE, state-of-the-art equations of state for hydrogen, helium, ice, and rock are integrated with advanced features to treat ice/rock cores and metals in the gaseous envelope; models for helium rain and hydrogen/helium immiscibility; detailed atmosphere boundary tables that also provide self-consistent albedos and spectra; and options to address envelope metal gradients and stably stratified regions. Our hope is that these purpose-built features of APPLE will help catalyze the development of the next generation of giant exoplanet and Jovian planet evolutionary models.

Keywords: Exoplanet structure, Exoplanet evolution, Planetary structure, Planetary science
A Detailed Survey of the Parallel Mean Free Path of Solar Energetic Particle Protons and Electrons. In this work, more than a dozen solar energetic particle (SEP) events are identified where the source region is magnetically well connected to at least one spacecraft at 1 au. The observed intensity–time profiles, for all available proton and electron energy channels, are compared to results computed using a numerical one-dimensional SEP transport model in order to derive the parallel mean free paths (pMFPs) as a function of energy (or rigidity) at 1 au. These inversion results are then compared to theoretical estimates of the pMFP, using observed turbulence quantities with observationally motivated variations as input. For protons, a very good comparison between inversion and theoretical results is obtained. It is shown that the observed inter-event variations in the inversion pMFP values can be explained by natural variations in the background turbulence values. For electrons, there is relatively good agreement with pMFPs derived assuming the damping model of dynamical turbulence, although the theoretical values are extremely sensitive to the details of the turbulence dissipation range, which themselves display a high level of variation.

Keywords: Heliosphere, Interplanetary turbulence, Solar energetic particles, Solar wind, Cosmic rays
Particle Acceleration in Relativistic Alfvénic Turbulence. Strong magnetically dominated Alfvénic turbulence is an efficient engine of nonthermal particle acceleration in a relativistic collisionless plasma. We argue that in the limit of strong magnetization, the type of energy distribution attained by accelerated particles depends on the relative strengths of turbulent fluctuations δ B 0 and the guide field B 0. If δ B 0 ≪ B 0, the particle magnetic moments are conserved, and the acceleration is provided by magnetic curvature drifts. Curvature acceleration energizes particles in the direction parallel to the magnetic field lines, resulting in log-normal tails of particle energy distribution functions. Conversely, if δ B 0 ≳ B 0, interactions of energetic particles with intense turbulent structures can scatter particles, creating a population with large pitch angles. In this case, magnetic mirror effects become important, and turbulent acceleration leads to power-law tails of the energy distribution functions.

Keywords: Relativity, Plasma astrophysics, High energy astrophysics, Plasma physics
Detection of a Spatially Extended Stellar Population in M33: A Shallow Stellar Halo?. We analyze the outer regions of M33, beyond 15 kpc in projected distance from its center, using Subaru/Hyper Suprime-Cam multicolor imaging. We identify red giant branch (RGB) stars and red clump (RC) stars using the surface-gravity-sensitive NB515 filter for the RGB sample and a multicolor selection for both samples. We construct the radial surface density profiles of these RGB and RC stars and find that M33 has an extended stellar population with a shallow power-law index of α &gt; ‑3, depending on the intensity of the contamination. This result represents a flatter profile than the stellar halo that was detected by the previous study focusing on the central region, suggesting that M33 may have a double-structured halo component, i.e., inner/outer halos or a very extended disk. Also, the slope of this extended component is shallower than those typically found for halos in large galaxies, implying intermediate-mass galaxies may have different formation mechanisms (e.g., tidal interaction) from large spirals. We also analyze the radial color profiles of RC/RGB stars and detect a radial gradient, consistent with the presence of an old and/or metal-poor population in the outer region of M33, thereby supporting our proposal that the stellar halo extends beyond 15 kpc. Finally, we estimate that the surface brightness of this extended component is μ  V  = 35.72 ± 0.08 mag arcsec‑2. If our detected component is the stellar halo, this estimated value is consistent with the detection limit of previous observations.

Keywords: Galaxy stellar halos, Triangulum Galaxy, Local Group
Young Stellar Objects in NGC 346: A JWST NIRCam/MIRI Imaging Survey. We present a JWST imaging survey with NIRCam and MIRI of NGC 346, the brightest star-forming region in the Small Magellanic Cloud. By combining aperture and point-spread function photometry of 11 wavelength bands across these two instruments, we have detected more than 200,000 unique sources. Using a near-infrared color analysis, we observe various evolved and young populations, including 196 young stellar objects (YSOs) and pre-main-sequence stars suitable for forthcoming spectroscopic studies. We expand upon this work, creating mid-infrared color–magnitude diagrams and determining color cuts to identify 833 reddened sources which are YSO candidates. We observe that these candidate sources are spatially associated with regions of dusty, filamentary nebulosity. Furthermore, we fit model YSO spectral energy distributions to a selection of sources with detections across all of our MIRI bands. We classify with a high degree of confidence 23 YSOs in this sample and estimate their radii, bolometric temperatures, luminosities, and masses. We detect YSOs approaching 1 M ⊙, the lowest-mass extragalactic YSOs confirmed to date.

Keywords: Hertzsprung Russell diagram, Small Magellanic Cloud, Two-color diagrams, Infrared astronomy, Infrared excess, James Webb Space Telescope, Pre-main sequence, Protostars, Metallicity, Near infrared astronomy