Sazuna/UAT_keywords huggingface dataset:
Population-level Hypothesis Testing with Rocky Planet Emission Data: A Tentative Trend in the Brightness Temperatures of M-Earths. Determining which rocky exoplanets have atmospheres, and why, is a key goal for the James Webb Space Telescope. So far, emission observations of individual rocky exoplanets orbiting M stars (M-Earths) have not provided definitive evidence for atmospheres. Here, we synthesize emission data for M-Earths and find a trend in measured brightness temperatures (ratioed to its theoretical maximum value) as a function of instellation. However, the statistical evidence of this trend is dependent on the choice of stellar model, and we consider its identification tentative. We show that this trend can be explained by either the onset of thin/tenuous (&lt;1 bar) CO2-rich atmospheres on colder worlds, or a population of bare rocks with stronger space weathering and/or coarser regolith on closer-in worlds. Such grain coarsening may be caused by sintering near the melting point of rock or frequent volcanic resurfacing. Furthermore, we highlight considerations when testing rocky planet hypotheses at the population level, including the choice of instrument, stellar modeling, and how brightness temperatures are derived. We also find that fresh (unweathered) fine-grained surfaces can serve as a false positive to the detection of moderate atmospheric heat redistribution through eclipse observations. However, we argue that such surfaces are unlikely given the ubiquity of space weathering in the solar system, the low albedo of solar system airless bodies, and the high stellar wind environments of M-Earths. Emission data from a larger sample of M-Earths will be able to confirm or reject this tentative trend and diagnose its cause through spectral characterization.

Keywords: Extrasolar rocky planets, Exoplanets, Exoplanet surface composition, Exoplanet surfaces, Exoplanet surface characteristics, Exoplanet atmospheres
"Oh FUors, Where Art Thou?": A Search for Long-lasting Young Stellar Object Outbursts Hiding in Infrared Surveys. Long-lasting episodes of high accretion can strongly impact stellar and planetary formation. However, the universality of these events during the formation of young stellar objects (YSOs) is still under debate. Accurate statistics of strong outbursts (FUors) are necessary to understand the role of episodic accretion bursts. In this work, we search for a population of FUors that may have gone undetected in the past because they either (a) went into outburst before the start of modern monitoring surveys and are now slowly fading back into quiescence or (b) are slow-rising outbursts that would not commonly be classified as candidate FUors. We hypothesize that the light curves of these outbursts should be well fitted by linear models with negative (declining) or positive (rising) slopes. The analysis of the infrared light curves and photometry of ∼99,000 YSO candidates from SPICY yields 717 candidate FUors. Infrared spectroscopy of 20 candidates, from both the literature and obtained by our group, confirms that 18 YSOs are going through long-term outbursts and identifies two evolved sources as contaminants. The number of candidate FUors combined with previously measured values of the frequency of FUor outbursts yields average outburst decay times that are 2.5 times longer than the rise times. In addition, a population of outbursts with rise timescales between 2000 and 5000 days must exist to obtain our observed number of YSOs with positive slopes. Finally, we estimate a mean-burst lifetime of between 45 and 100 yr.

Keywords: Protostars, Young stellar objects, Eruptive variable stars, FU Orionis stars
Bioverse: Potentially Observable Exoplanet Biosignature Patterns under the UV Threshold Hypothesis for the Origin of Life. A wide variety of scenarios for the origin of life have been proposed, with many influencing the prevalence and distribution of biosignatures across exoplanet populations. This relationship suggests these scenarios can be tested by predicting biosignature distributions and comparing them with empirical data. Here, we demonstrate this approach by focusing on the cyanosulfidic origins-of-life scenario and investigating the hypothesis that a minimum near-ultraviolet (NUV) flux is necessary for abiogenesis. Using Bayesian modeling and the Bioverse survey simulator, we constrain the probability of obtaining strong evidence for or against this "UV Threshold Hypothesis" with future biosignature surveys. Our results indicate that a correlation between past NUV flux and current biosignature occurrence is testable for sample sizes of ≳50 planets. The diagnostic power of such tests is critically sensitive to the intrinsic abiogenesis rate and host star properties, particularly maximum past NUV fluxes. Surveys targeting a wide range of fluxes, and planets orbiting M dwarfs enhance the chances of conclusive results, with sample sizes ≳100 providing ≳80% likelihood of strong evidence if abiogenesis rates are high and the required NUV fluxes are moderate. For required fluxes exceeding a few hundred erg s‑1 cm‑2, both the fraction of inhabited planets and the diagnostic power sharply decrease. Our findings demonstrate the potential of exoplanet surveys to test origins-of-life hypotheses. Beyond specific scenarios, this work underscores the broader value of realistic survey simulations for future observatories (e.g., Habitable Worlds Observatory, LIFE, Extremely Large Telescopes, Nautilus) in identifying testable science questions, optimizing mission strategies, and advancing theoretical and experimental studies of abiogenesis.

Keywords: Extrasolar rocky planets, Bayesian statistics, Transits, Near ultraviolet astronomy, Astronomical simulations, Transit photometry, Astrobiology, Parametric hypothesis tests, Biosignatures, Habitable planets, Pre-biotic astrochemistry, Astrostatistics strategies
Investigating Silicate, Carbon, and Water in the Diffuse Interstellar Medium: The First Shots from WISCI. The dusty interstellar medium (ISM) of the Milky Way is distributed in a complex, cloudy structure. It is fundamental to the radiation balance within the Milky Way, provides a reaction surface to form complex molecules, and is the feedstock for future generations of stars and planets. The life cycle of interstellar dust is not completely understood, and neither are its structure nor composition. The abundance, composition, and structure of dust in the diffuse ISM can be determined by combining infrared, optical, and ultraviolet spectroscopy. JWST enables measurement of the faint absorption of ISM dust grains against bright stars at kiloparsec distances across the infrared spectrum. Here we present an overview of the project "Webb Investigation of Silicates, Carbons, and Ices" (WISCI) along with interpretation of two targets, GSC 08152-02121 and CPD-59 5831. Observations of 12 WISCI target stars were taken by JWST, the Hubble Space Telescope, Himalayan Chandra Telescope, and the Very Large Telescope. We use these to characterize the targets' spectral types and calculate their line-of-sight extinction parameters, AV and RV. We find absorption in the JWST spectra of GSC 08152-02121 and CPD-59 5831 associated with carbonaceous dust around 3.4 and 6.2 μm and amorphous silicates at 9.7 μm. In GSC 08152-02121, we also find indications of absorption by trapped water around 3 μm. This first look from WISCI demonstrates the line-of-sight variability within the sample, and the program's potential to identify and correlate features across ultraviolet to mid-infrared wavelengths.

Keywords: Interstellar dust, Silicate grains, Optical astronomy, Interstellar dust extinction, Infrared astronomy, Stellar classification, OB stars, Interstellar absorption, Ultraviolet astronomy, Carbonaceous grains, Spectroscopy, Interstellar medium
Exploring Compact Symmetric Objects with Complex Morphologies. Compact symmetric objects (CSOs) are a unique class of jetted active galactic nuclei defined by subkiloparsec radio emission, showing radio structure on both sides of the central engine. CSOs tend to exhibit little to no relativistic beaming, thereby allowing us to determine their physical characteristics, such as the magnetic field strength and particle energy density. Selected with a literature search, we describe very long baseline interferometry observations, imaging, and analyses of 167 CSO candidates. We identified 65 new bona fide CSOs, thus almost doubling the number of known bona fide CSOs to 144. With our greater breadth of sources, we confirm that edge-dimmed CSOs (CSO-1s) may represent a more diverse population than originally expected. We highlight a number of CSOs with complex morphologies, including candidates for supermassive binary black holes and CSOs that appear to have morphologies akin to wide-angle tail galaxies, which could perhaps indicate that some CSOs are experiencing a galactic merger.

Keywords: Active galaxies, Active galactic nuclei, Relativistic jets
Continuous Habitable Zone Metric for Prioritizing Habitable Worlds Observatory Targets. Future direct imaging space telescopes, such as NASA's Habitable Worlds Observatory (HWO), will be the first capable of both detecting and characterizing terrestrial exoplanets in the habitable zones (HZs) of nearby Sun-like stars. Since this will require a significant amount of time and resources for even a single system or exoplanet, the likelihood that a system will host detectable life should be considered when prioritizing observations. One method of prioritization is to estimate the likelihood that an exoplanet has remained continuously within the HZ long enough for life to emerge and make a detectable impact on the atmosphere. We utilize a Bayesian method to calculate the likelihood that a given orbital radius around a star is currently in the 2 Gyr continuous habitable zone (CHZ2), the approximate time it took life on Earth to significantly oxygenate the atmosphere. We apply this method to the 164 stars in the NASA Exoplanet Exploration Program Mission Star List for HWO, representing a preliminary sample of Sun-like stars with HZs most accessible to a future direct imaging mission. By considering the CHZ2 likelihood at all orbital radii outside a hypothetical inner working angle for HWO, we define a metric for prioritizing targets according to the accessibility and total extent of the CHZ2. We find that the CHZ2 metric peaks between 3 and 4 Gyr for late F and early G dwarfs, but tentatively determine that stars earlier than ∼F3 or hotter than ∼6600 K are unlikely to have a CHZ2 at the time of observation.

Keywords: Exoplanets, Astrobiology, Space telescopes, Habitable zone, Stellar evolution
Debiasing Structure Function Estimates from Sparse Time Series of the Solar Wind: A Data-driven Approach. Structure functions (SFs), which quantify the moments of increments of a stochastic process, are essential complementary statistics to power spectra for analyzing the self-similar behavior of a time series. However, many real-world data sets, such as those from spacecraft monitoring the solar wind, contain gaps, which inevitably corrupt the statistics. The nature of this corruption for SFs remains poorly understood—indeed, often overlooked. In this study, we simulate gaps in a large set of Parker Solar Probe magnetic field intervals to characterize how missing data affect SFs of solar wind turbulence. We find that linear interpolation systematically underestimates the true SF, and we introduce a simple, empirically derived correction factor to address this bias. Learned from data from a single spacecraft, the correction generalizes well to solar wind measured elsewhere in the heliosphere. Compared to conventional gap-handling methods, our approach reduces the mean error for missing data fractions above 20%, and the overall error is reduced by nearly 50% when averaged across all missing fractions tested. We apply the correction to Voyager intervals from the inner heliosheath and local interstellar medium (60%–85% missing) and recover spectral indices consistent with previous studies. The correction factor is released as an open-source Python package, enabling more accurate analysis of scaling in gapped solar wind data sets.

Keywords: Interplanetary turbulence, Solar wind, Time series analysis
Oort Cloud Formation and Evolution in Star Clusters. It is unknown whether an Oort cloud reaches its maximum mass within its star's birth cluster or millions of years later. Complicating the Oort cloud evolution process is the fact that comets can be stripped from orbit due to perturbations from passing stars. We explore how a star's cluster escape time (tesc) and the time its Oort cloud reaches maximum mass (t max ) affect the Oort cloud's ability to survive via N-body simulations. In a 14 M⊙ pc–3 cluster, we identify 50 stars of 1 M⊙ with a range of tesc to host Oort clouds, each with 1000 comets at t max . For each host, we consider Oort clouds that reach maximum mass 0, 50, and 250 Myr after the cluster's formation. Each Oort cloud's evolution is simulated in the cluster from t max  to tesc. Only a fraction of comets tend to remain in orbit, with this amount depending on t max  and tesc. We observe that 12%, 22%, and 32% of Oort clouds with a t max  of 0, 50, and 250 Myr retain &gt;50% of their comets at tesc, respectively. We find that the fraction of comets stripped has the relationship  f=mlog10tesc‑tmaxMyr , where m = 0.32 ± 0.04, indicating that the longer the Oort cloud remains in the cluster, the more comets are stripped, with this fraction increasing logarithmically at approximately the same rate for each t max .

Keywords: Small Solar System bodies, Oort cloud, Comet dynamics, Stellar dynamics, Orbital evolution, Comets, Star clusters
Three-dimensional Orbital Architectures and Detectability of Adjacent Companions to Hot Jupiters. The orbital properties of the (as yet) small population of hot Jupiters with nearby planetary companions provide valuable constraints on the past migration processes of these systems. In this work, we explore the likelihood that dynamical perturbations could cause nearby inner or outer companions to a hot Jupiter to leave the transiting plane, potentially leaving these companions undetected despite their presence at formation. Using a combination of analytical and numerical models, we examine the effects of stellar evolution on hot Jupiter systems with nearby companions and identify several possible outcomes. We find that while inner companions are generally unlikely to leave the transiting plane, outer companions are more prone to decoupling from the hot Jupiter and becoming nontransiting, depending on the system's initial orbital architecture. Additionally, we observe a range of dynamical behaviors, including overall stability, inclination excitation, and, in some cases, instability leading to the ejection or collision of planets. We also show that the effect of stellar obliquity (with respect to the mean planet of the planets) is to amplify these effects and potentially cause outer companions to attain nonmutually transiting configurations more often. Our results highlight the complex dynamical pathways shaping the architectures of hot Jupiter systems.

Keywords: Exoplanet dynamics, Exoplanet evolution, Exoplanet formation, Exoplanet systems
Large-amplitude Whistler Precursors and &gt;MeV Particles Observed at a Weak Interplanetary Shock by Parker Solar Probe. We report observations of an interplanetary (IP) shock observed by Parker Solar Probe (PSP) on 2024 September 29 at ∼07:50:29 UTC. PSP was only ∼17.07 Rs from the Sun, making this one of the closest observed IP shocks to date. The IP shock was a weak (Mf ∼ 1.2), quasi-perpendicular (θBn ∼ 50°), and of moderate speed (Vshn ∼ 465 km s‑1). The standard shock acceleration mechanisms (e.g., Fermi acceleration) predict that such an unremarkable shock cannot generate energetic particles (i.e., over 4 orders of magnitude above thermal energies), which is supported by decades of IP shock observations near 1 au. However, ∼MeV energy protons with an inverse velocity arrival and synchrotron radiation (due to ∼MeV energy electrons) were observed upstream. This raised the question of what was different about this shock. One observation was that of a fast/magnetosonic-whistler precursor with peak-to-peak magnetic field amplitudes &gt;700 nT, electric fields &gt;2000 mV m‑1, and Poynting fluxes &gt;230 mW m‑2. These are 2 orders of magnitude larger than any previously observed whistler precursor. To put the amplitudes in context, the lower bound Poynting flux estimates are &gt;200 times what is necessary to drive the terrestrial aurora. Note that the normalized wave parameters (e.g., frequency) were found to be consistent with previous studies near 1 au. Thus, the precursors cannot likely generate a larger fraction of energetic particles than similar precursors near 1 au. However, the much larger amplitudes would allow for higher maximum energies. This raises important questions about inaccessible shocks in more extreme astrophysical environments and what potential energization they may have in light of these observations.

Keywords: Solar coronal mass ejection shocks, Solar wind, Interplanetary shocks, The Sun
Investigating the Possible Contribution of Helicity Condensation to the Ambient Increase in Solar Open Flux. The Sun's Open Flux plays a vital role in heliospheric physics and for the origin of the solar wind. A key problem faced by global magnetic field models of the solar corona is that they consistently underestimate the amount of Open Flux compared to in situ measurements. The purpose of the present paper is to consider if statistically averaged helicity condensation (SAHC) can reduce this discrepancy by increasing the simulated Open Flux found in potential field source surface (PFSS) models. We consider each Carrington rotation from 1646–2149 (1976 September to 2014 April). For each rotation, we hold the photosphere fixed, construct a PFSS model, and inject nonpotentiality into the coronal field by applying SAHC at different angular rotation rates, ω. When ω exceeds 2.5 × 10‑6 s‑1, both ambient and sporadic enhancements of Open Flux are found within the Carrington rotation timescale. As ω increases, the amount of ambient Open Flux increases, along with the frequency of sporadic events. These enhancements are accompanied by increased footpoint area of open field lines, where the open field locations at each pole expand by up to 3∘–6∘ of latitude. A solar cycle dependence is found with higher increases in ambient Open Flux at solar maximum compared to solar minimum. Comparing our results with 27 day averaged OMNI spacecraft measurements, our highest value of ω = 10 × 10‑6 s‑1 can resolve just under 50% of the discrepancy between in situ Open Flux measurements and PFSS models. Although helicity condensation cannot fully resolve the discrepancy, it can significantly contribute toward reducing it.

Keywords: Heliosphere, Solar wind, Solar physics, Solar magnetic fields, Solar corona, Solar evolution
GULP. II. Hierarchical Distribution and Evolution of Young Stellar Structures in NGC 4449. We investigate the hierarchical distribution and evolution of young stellar structures in the dwarf starburst galaxy NGC 4449 using data from the GULP survey. By analyzing the spatial distribution of field stars younger than 100 Myr, we identify large-scale stellar complexes and substructures using HDBSCAN—a density-based clustering algorithm—and trace their evolution over time. While comparing these stellar structures in different regions of the galaxy, we find that the central bar-like region shows a clear expansion of the structures within the first ∼60 Myr, while the arm-like structure in the northeast shows no discernible trend, possibly due to external perturbations from tidal interactions with a neighboring galaxy. An age-dependent two-point correlation function (TPCF) analysis shows that young stars exhibit a strong hierarchical distribution, with clustering strength decreasing over time. The power-law slope of the TPCF, which starts at α ∼ 0.65 for stars younger than 5 Myr, shows a slight decline to α ∼ 0.4 for stars older than 50 Myr, though it does not reach a completely flat (random) distribution. This trend indicates a subtle weakening of structural hierarchy among young (&lt;100 Myr) stars, which is primarily driven by internal stellar motions. Future work will extend this analysis to the remaining 26 galaxies in the GULP survey to better constrain the role of the galactic environment in shaping the hierarchical evolution of young stellar populations.

Keywords: Starburst galaxies, Galaxies, Stellar structures, Two-point correlation function, Hierarchical models, Stellar associations, Star clusters
Pulse Profiles of Accreting Neutron Stars from GRMHD Simulations. The pulsed X-ray emission from the neutron star surface acts as a window to study the state of matter in the neutron star interior. For accreting millisecond pulsars, the surface X-ray emission is generated from the "hotspots" formed due to the magnetically channeled accretion flow hitting the stellar surface. The emission from these hotspots is modulated by stellar rotation, giving rise to pulsations. Using global three-dimensional general relativistic magnetohydrodynamic (GRMHD) simulations of the star-disk system, we investigate the accretion hotspots and the corresponding X-ray pulse properties of accreting millisecond pulsars with dipolar magnetic fields. The accretion spot morphologies in our simulations are entirely determined by the accretion columns and vary as a function of the stellar magnetic inclination. For lower magnetic inclinations, the hotspots are shaped like crescents around the magnetic axis and are transformed into elongated bars for higher inclinations. We model the X-ray pulses resulting from the simulated hotspots using general-relativistic ray-tracing calculations and quantify the variability of the pulsed signal. The pulse amplitudes in our simulations usually range between 1% and 12% rms and are consistent with the observed values. We find that the turbulent accretion flow in the GRMHD simulations introduces significant broadband variability on a timescale similar to the stellar rotational period. We also explore the impact of electron scattering absorption and show that, along with being a key factor in determining the pulse characteristics, this also introduces significant additional variability and higher harmonics in the bolometric light curve of the accreting sources.

Keywords: Neutron stars, Accretion, Magnetohydrodynamics, Pulsars, Compact objects, Low-mass x-ray binary stars
Nonlinear Coupling between Magnetar QPOs. The quasiperiodic oscillations (QPOs) observed in the tails of magnetar giant γ-ray flares have long been interpreted as normal oscillation modes of these stars. However, most studies modeling QPOs have neglected some key features in the analyses of the signals, namely that QPOs appear to be detectable only intermittently and exhibit drifts in their frequencies. These are typical characteristics of nonlinear mode coupling, where, at leading order, the modes couple and evolve collectively as triplets. Using a representative triplet of modes, we solve the system's nonlinear equations of motion analytically and argue that the coupling is likely axial-axial-polar in nature, with the observed intermittence and frequency drifts providing a way to infer details of the magnetar's internal magnetic field geometry.

Keywords: Neutron stars, Neutron star cores, Stellar oscillations, Stellar pulsations, Polytropes, Stellar magnetic fields, Analytical mathematics, Soft gamma-ray repeaters, Non-radial pulsations, Pulsation modes, Magnetars, Magnetic fields