Sazuna/UAT_keywords huggingface dataset:
Detecting Atmospheric CO<SUB>2</SUB> Trends as Population-level Signatures for Long-term Stable Water Oceans and Biotic Activity on Temperate Terrestrial Exoplanets. Identifying key observables is essential for enhancing our knowledge of exoplanet habitability and biospheres, as well as improving future mission capabilities. While currently challenging, future observatories such as the Large Interferometer for Exoplanets (LIFE) will enable atmospheric observations of a diverse sample of temperate terrestrial worlds. Using thermal emission spectra that represent conventional predictions of atmospheric CO2 variability across the habitable zone (HZ), we assess the ability of the LIFE mission—as a specific concept for a future space-based interferometer—to detect CO2 trends indicative of the carbonate–silicate (Cb–Si) weathering feedback, a well-known habitability marker and potential biological tracer. Therefore, we explore the feasibility of differentiating between CO2 trends in biotic and abiotic planet populations. We create synthetic exoplanet populations based on geochemistry-climate predictions and perform retrievals on simulated thermal emission observations. The results demonstrate the robust detection of population-level CO2 trends in both biotic and abiotic scenarios for population sizes as small as 30 exo-Earth candidates (EECs) and the lowest assessed spectrum quality in terms of signal-to-noise ratio, S/N = 10, and spectral resolution, R = 50. However, biased CO2 partial pressure constraints hinder accurate differentiation between biotic and abiotic trends. If these biases were corrected, accurate differentiation could be achieved for populations with ≥100 EECs. We conclude that LIFE can effectively enable population-level characterization of temperate terrestrial atmospheres and detect CO2 trends driven by the Cb–Si cycle as habitability indicators. Nevertheless, the identified biases underscore the importance of testing atmospheric characterization performance against the broad diversity expected for planetary populations.

Keywords: Infrared spectroscopy, Exoplanet atmospheric variability, Space telescopes, Biosignatures, Habitable zone, Exoplanet atmospheres
The Peak Flux of Long Gamma-Ray Bursts in the E<SUB>p,i</SUB>–L<SUB>iso</SUB> Diagram and in the Classification. The Ep,i–Liso correlation of long gamma-ray bursts (LGRBs) is regarded as a fundamental correlation for standardizing LGRBs to probe cosmology and constrain LGRB physics. However, this correlation may be affected by potential selection effects, which are likely overlooked in the current small LGRB redshift sample. In this work, we simulate a large LGRB sample that reflects the observed situation, aiming to study the impact of peak flux P on the observed LGRB Ep,i–Liso correlation. We find that the overall Ep,i and Liso distribution, which will directly affect the best-fit result of the correlation, is significantly dependent on the value of P. This indicates that the impact of peak flux selection should be carefully considered in the studies and applications of the Ep,i–Liso correlation. Notably, we show that our simulated data can reproduce the observed P distribution only if some dependence between Ep,i and Liso is included in the simulation. This is an indication that the Ep,i–Liso connection is a crucial property of LGRBs. We also find that GRBs with high peak flux in the low-Ep,i and Liso region are not the straightforward extrapolation of the GRB population in the higher-Ep,i and Liso region. Selecting four bursts with Liso ≤ 1050 erg s‑1, Ep,i ≤ 102.5 keV, and P ≥ 100.5 ph cm‑2 s‑1, we find two bursts, GRB 060614 and GRB 191019A, which may not be associated with the theoretical massive-star origin of LGRBs. This suggests that combining P with the position in the Ep,i–Liso diagram may be used to indicate alternative LGRB origins.

Keywords: Gamma-ray bursts
Forecasting Geomagnetic Disturbances in Solar Cycle 25 for Space Weather Prediction. Accurate forecasting of geomagnetic disturbances is essential for mitigating space weather effects on critical infrastructure. We present an optimized Long Short-term Memory neural network (LSTM+), refined through a reforecast procedure and hyperparameter tuning using data from Solar Cycle 24, achieving high predictive skill. For Solar Cycle 24, the model demonstrates a Nash–Sutcliffe efficiency of 0.95 for Ap and 0.78 for Dst, with Pearson correlation coefficients of 0.983 and 0.901, respectively. Furthermore, the error rate for predicting the peak Ap and trough Dst values was low, at 4.16% and 7.77%, respectively. This LSTM+ model is used to predict the Ap and Dst indices for Solar Cycle 25. The model forecasts a peak in Ap around 2026 January and a trough in Dst around 2026 February, consistent with the observed lag of up to 3 yr between geomagnetic indices and the sunspot number maximum in prior cycles. Validation against historical data confirms the model's reliability in capturing these temporal offsets. These projections offer a predictive framework for improving space weather preparedness and safeguarding technological systems.

Keywords: Geomagnetic fields
Kinetic Simulation of Magnetic Reconnection with Pickup Ions: Shell Stability and Reconnection Rate Analysis. Collisionless magnetic reconnection is postulated to be active in many regions of the heliosphere, where the physics and formation of heliospheric structures are influenced by pickup ions (PUIs). Recent investigations suggest that the presence of PUIs may enhance the reconnection rate due to PUI-induced turbulence. Our investigation from particle-in-cell simulations with seed PUI shell velocity distributions reveals that the distributions remain quasi-stable within the reconnection exhaust region. The reconnection rate is rather suppressed as compared with non-PUI reconnection simulations. The PUI population eventually responds to the reconnection dynamics and forms a thicker current sheet layer. Both PUI and regular ion populations develop sub-ion-Alfvénic outflow jets, although PUI outflows are slower in comparison and extend beyond the separatrix surface. We predict that a future Interstellar Probe mission may encounter reconnecting current sheet layers in the outer heliosphere that demonstrate an initial slow modulation followed by a sharp rotation of the reconnecting magnetic field toward the center of the layer.

Keywords: Pickup ions, Solar magnetic reconnection, Heliosphere
X-Ray Spectral Variability as a Probe of Multimessenger Emission in Blazar 5BZB J0630−2406. X-ray observations are essential for understanding the multimessenger emission mechanisms of active galactic nuclei (AGN). Blazars, a subset of AGN whose X-ray emission predominantly originates from relativistic jets, have been proposed as promising high-energy neutrino sources. In this work, we study the candidate neutrino-emitting blazar 5BZB J0630-2406, which has been observed over multiple epochs with the XMM-Newton, NuSTAR, Neil Gehrels Swift-XRT, and eROSITA observatories. Analysis of the X-ray spectra in the 2.0─10.0 keV band shows significant variability, with high-flux states adhering to a power-law model indicative of jet emission. However, during low-flux states, the spectrum reveals an additional component in hard X-rays, indicating a transition from jet-dominated to multicomponent X-ray emission, possibly associated with hadronic processes. To investigate this spectral evolution, we tested various models and found it to be consistent with coronal emission or photoionized absorption processes typically observed in obscured AGN. The identification of the X-ray spectral variability in 5BZB J0630-2406, combined with its potential for neutrino production, opens new perspectives in multimessenger astrophysics of blazars, highlighting the synergies between the mechanisms of the jet and the nuclear environment.

Keywords: Neutrino astronomy, Non-thermal radiation sources, Active galactic nuclei, Quasars
He Awa Whiria: The Tidal Streams of Interstellar Objects. Upcoming surveys are likely to discover a new sample of interstellar objects (ISOs) within the solar system, but questions remain about the origin and distribution of this population within the Galaxy. ISOs are ejected from their host systems with a range of velocities, spreading out into tidal streams—analogous to the stellar streams routinely observed from the disruption of star clusters and dwarf galaxies. We create a simulation of ISO streams orbiting in the Galaxy, deriving a simple model for their density distribution over time. We then construct a population model to predict the properties of the streams in which the Sun is currently embedded. We find that the number of streams encountered by the Sun is quite large, ∼106 or more. However, the wide range of stream properties means that for reasonable future samples of ISOs observed in the solar system, we may see ISOs from the same star ("siblings"), and we are likely to see ISOs from the same star cluster ("cousins"). We also find that ISOs are typically not traceable to their parent star, though this may be possible for ISO siblings. Any ISOs observed with a common origin will come from younger, dynamically colder streams.

Keywords: Small Solar System bodies, Stellar streams, Milky Way dynamics, Milky Way disk, Interstellar objects, Milky Way Galaxy, Star clusters
Breaking the Degeneracy between Warps and Radial Flows in External Galaxies. Observations of the line-of-sight (LOS) component of emitter velocities in galaxies are valuable for reconstructing their two-dimensional (2D) velocity fields, albeit requiring certain assumptions. A common one is that radial flows can be neglected in the outer regions of galaxies, while their geometry can be deformed by a warp. A specular approach assumes that galactic disks are flat but allows for the presence of radial flows. This approach enables the reconstruction of 2D velocity maps that encompass both the transversal and radial velocity fields. Through the study of velocity fields in toy disk models, we find that the presence of warps is manifested as a dipolar correlation between the two velocity components obtained by assuming a flat disk. This shows that the analysis of angular velocity anisotropies provides an effective tool for breaking the degeneracy between warps and radial flows. We have applied these findings to the analysis of velocity fields of the galaxies from the THINGS sample and M33. Many of these galaxies exhibit such a dipolar correlation, indicating the presence of warps. However, we have found that the warp alone cannot explain all variations in the velocity field, suggesting that intrinsic perturbations are common. Furthermore, we have observed that the spatial distribution of the LOS velocity dispersion may correlate with both velocity components, providing independent evidence of nontrivial velocity fields. These findings offer a robust approach to reconstructing the velocity fields of galaxies, allowing us to distinguish between the presence of warps and complex velocity structures by assessing their relative amplitude.

Keywords: Spiral galaxies, Galaxy dynamics, Galaxy rotation, Galaxy kinematics, Galaxy rotation curves
Modified Gravity Realizations of Quintom Dark Energy after DESI DR2. We investigate the realization of quintom scenario for dynamical dark energy within modified gravity theories that can efficiently fit the recent observational data sets. Starting from a general effective field theory formulation of dark energy in metric-affine geometry, we derive the background action in unitary gauge and we demonstrate how both f(T) and f(Q) gravity can naturally realize quintom behavior through appropriate forms and parameter choices. Additionally, using the Gaussian process reconstruction of the latest Dark Energy Spectroscopic Instrument DR2 baryon acoustic oscillation data combined with Type Ia supernovae and cosmic microwave background observations, we extract the reconstructed dark-energy equation-of-state parameter, showing that it exhibits quintom-type evolution, crossing the phantom divide from below. Moreover, through detailed parameter estimations and application of information criteria, we compare the model with the quadratic one and the ΛCDM model. Our results show that, due to its rich structure, modified gravity stands as one of the main candidates for the realization of the data-favored dynamical dark energy.

Keywords: Non-standard theories of gravity, Dark energy
The Rotating Bulge and Halo in the Milky Way: Evidence of Angular Momentum Transferred from the Decelerating Bar. Recent observations indicate that both the Milky Way bulge and inner halo exhibit angular momentum, although the origin and evolution of this prograde signature remain ambiguous. One plausible scenario involves secular evolution induced by the central bar and spiral arms. In this study, we identified a component consisting of 1,175,737 stars with net rotation through the application of a neural network (NN) method. To investigate the composition of this rotating sample and the origin of its rotation, we conducted a test particle simulation incorporating an equilibrium axisymmetric background potential together with a central decelerating bar. The test particles were generated using a distribution function model derived from observational constraints. Our results indicate that the decelerating bar transfers angular momentum to the pseudo-stars, and the rotational profile from our simulation shows strong agreement with observational data. These findings suggest that the rotating sample identified by our NN model is predominantly comprised of bulge, halo, and thick disk stars, and that the central decelerating bar is pivotal in shaping the inner Galaxy's kinematics through angular momentum transfer.

Keywords: Milky Way stellar halo, Milky Way dynamics, Galactic bulge, Galactic bar
The Angular Momentum of Stars Reflects the Relationship between Star-forming Environment and Galactic Evolution History. This study focuses on stars with masses above the Kraft break in the Kepler field. Their rotational angular momenta are essentially the same as those at the zero-age main sequence. The angular momentum dissipation experienced by these stars during their pre-main sequence (PMS) phase is also relatively weak, so their rotational angular momentum can reflect the parameters of their parental molecular clouds. The reliability of angular momentum measurements was evaluated based on the phenomenon of angular momentum conservation observed in stars before and after the turnoff point in observational data. We find that stars with masses between 1.4M⊙ and 1.8M⊙ show an inverse proportionality between angular momentum and isochrone age. We propose that the angular momentum–age correlation reflects changes in the star-forming environment in the Milky Way's history. Besides, the observed inverse proportionality implies that as the Milky Way has evolved, the stars formed within it tend to possess greater rotational angular momenta. This trend would promote the fragmentation of stars during the PMS phase and inhibit the formation of massive stars, providing a useful perspective for explaining variations in the initial mass function.

Keywords: Stellar kinematics, Stellar rotation, Galaxy evolution
Varstrometry for Off-nucleus and Dual Sub-Kpc AGN (VODKA): Long-slit Optical Spectroscopic Follow-up with Gemini/GMOS and Hubble Space Telescope/STIS. High spatial and spectral resolution observations are essential for identifying subarcsecond dual and lensed quasars and confirming their redshifts. We present Gemini/Gemini Multi-Object Spectrograph and Hubble Space Telescope/STIS optical spectra for 27 dual quasar candidates selected based on their variability-induced astrometric noise or double detections in Gaia (the Varstrometry for Off-nucleus and Dual sub-Kpc AGN (VODKA) project). From this follow-up, we spectroscopically identify 11 star superpositions and seven dual/lensed quasars. Among the remaining targets, two are likely dual/lensed quasars based on additional radio imaging, while the rest are quasars with unknown companions. Without prior photometric or spectroscopic selection, we find the star contamination rate to be 41%─67%, while the dual/lensed quasar fraction is ≳26% in the follow-up VODKA sample. However, when combined with existing unresolved spectra and spatially resolved two-band color cuts, the dual/lensed quasar fraction can be increased to ≳67%. Our study highlights the need for high-quality spectral data, including a signal-to-noise ratio of at least 20, spatial resolution that is at least twice finer than the source separation, and a spectral resolution of R ≳ 1000, in order to separate close sources, exclude stellar superpositions, and reliably identify dual quasars.

Keywords: Double quasars, Supermassive black holes, Quasars, Strong gravitational lensing, Active galactic nuclei, Spectroscopy
Coevolution of Dwarf Galaxies and Their Circumgalactic Medium Across Cosmic Time. Dwarf galaxies (DGs) are thought of as the building blocks of large galaxies such as our Milky Way. This paper presents new high-resolution hydrodynamical simulations of DGs and their intergalactic medium with the GIZMO code. Our simulations consider the key physical processes of galaxy evolution, such as gas cooling, chemistry, and stellar and black hole feedback. Unlike previous work, the initial conditions of our simulations take DGs of 2─5 × 1010 M⊙ from the realistic cosmology simulations of IllustrisTNG. We further increase the original resolution of IllustrisTNG by a factor of ∼100 via a particle-splitting scheme. Our results show that the evolution of the complex multiphase circumgalactic medium (CGM) and its metal content is sensitive to the redshift of DGs. The accretion of the CGM into DGs plays a key role, providing 20%─50% of the star-forming gas and replenishing 40%─70% of the total mass in the galactic disk. Furthermore, the accretion histories of the supermassive black holes (SMBHs) at the centers of high-z DGs shows episodic patterns, with high-accreting states close to ∼10% of the Eddington mass accretion rate, implying the rapid growth of SMBHs in the early Universe, which may be revealed by coming observations from the James Webb Space Telescope.

Keywords: Computational astronomy, Galaxy evolution, Galaxy accretion, Circumgalactic medium
The Age and High-energy Environment of the Very Young Transiting Exoplanet TOI 1227b. The mid-M star TOI 1227 hosts among the youngest known transiting exoplanets. We have conducted new X-ray imaging and optical spectroscopic observations of TOI 1227 aimed at ascertaining its age and the influence of its high-energy radiation on the exoplanet, TOI 1227b. We obtained a definitive X-ray detection of TOI 1227 with the Chandra/High Resolution Camera-I (HRC-I), and measured its Li and Hα lines using the Australian National University's Siding Spring Observatory 2.3 m telescope (WiFeS) spectroscopy. Through spatiokinematic, isochronal, and spectral energy distribution-based modeling, we have constrained the age of TOI 1227 as lying between 5 and 12 Myr, with a best estimate of ∼8 Myr. In the context of this age, we model the evolution of the transiting exoplanet TOI 1227b, using the X-ray luminosity derived from Chandra HRC-I imaging. Our modeling suggests that TOI 1227b is currently undergoing rapid atmospheric mass loss at rates on the order of ∼1012 g s−1. The modeling demonstrates that the exoplanet's predicted future evolution depends sensitively on assumptions for total and core planet mass, highlighting the importance of follow-up observations of the TOI 1227 star─exoplanet system to enable measurements of both planetary mass and mass-loss rate.

Keywords: X-ray astronomy, Star-planet interactions, Pre-main sequence stars, Exoplanet atmospheres
Using the Coolest Ae Stars to Constrain Circumstellar Disk Viscosity. Classical Ae (CAe) stars are main-sequence, A-type stars with Hα emission but no signature of dust. They are thought to be the cool extension of the classical Be stars to lower masses. Recent surveys based on Hα spectroscopy have significantly increased the number of known CAe stars, with the population extending to spectral types as cool as A4 (Teff ≈ 8500 K). We compute the temperature structure of gaseous, circumstellar disks around A-type stars, including both radiative heating from the central star and viscous shear heating from the disk's rotation. We find that shear heating can become important for spectral types A2 and later and can act to increase the low temperatures predicted by purely radiatively heated disks. Our modeling indicates that the presence and strength of Hα emission for spectral types A2 and later significantly increases with the amount of shear heating included, and we propose that this dependence can be used to constrain the α viscosity parameter appropriate for CAe star disks.

Keywords: Circumstellar matter, Be stars, Emission line stars, Early-type stars
Inferring Kilonova Ejecta Photospheric Properties from Early Blackbody Spectra. We present simple analytic corrections to the standard blackbody fitting used for early kilonova emission. We consider a spherical, relativistically expanding shell that radiates thermally at a single temperature in its own rest frame. Due to relativistic effects, including Doppler boosting, time delay, and temperature evolution, the observed temperature is smeared across different polar angles by approximately ∼10%. While the observed spectrum remains roughly consistent with a single-temperature blackbody, neglecting relativistic effects leads to significant systematic inaccuracies: the inferred photospheric velocity and temperature are overestimated by up to ∼50% for mildly relativistic velocities. By applying our analytic corrections, these deviations are reduced to within 10%, even in cases where the photosphere is receding and cooling is considered. Applying our corrections to observed kilonovae (AT2017gfo and the thermal component of GRB 211211A) reveals that standard blackbody fitting overestimated the inferred velocities and temperatures by 10%–40%; such deviations can alter the inferred formation of heavy elements.

Keywords: Neutron stars, Ultraviolet transient sources, Gravitational wave sources, Relativistic fluid dynamics
Radio Continuum Studies of Ultracompact and Short Orbital Period X-Ray Binaries. We present the radio continuum counterparts to the enigmatic ultracompact X-ray binaries (UCXBs): a black hole or neutron star accreting from a hydrogen-deficient white dwarf donor star with short orbital periods (&lt;80 minutes). For the sample of UCXBs hosted by globular clusters (GCs), we search for whether certain GC properties are more likely to enhance UCXB formation. We determine that GCs that host UCXBs are drawn from a distinct population in terms of cluster concentration, core radius, and half-light radius, but are similar to other well-studied GCs in metallicity and cluster mass. In particular, UCXB-hosting GCs tend to be on average more compact, with a higher concentration than other GCs, with significantly higher encounter rates. We investigate whether a correlation exists between radio luminosity and orbital period, using new and archival observations. We determine that there is not a clear connection between the two observable quantities.

Keywords: Neutron stars, Black holes, Galactic radio sources, White dwarf stars, Low-mass x-ray binary stars