Sazuna/UAT_keywords huggingface dataset:
Advancing CO<SUB>2</SUB><SUP>++</SUP> Modeling in the Martian Dayside Ionosphere: Insights from Natural Lifetime Analysis. The molecular dication CO2++ has, as previously reported, been detected in the Martian ionosphere by the Neutral Gas and Ion Mass Spectrometer on the Mars Atmosphere and Volatile Evolution (MAVEN) mission. Photochemical models have also been developed to reproduce the CO2++ density in the Martian dayside ionosphere but underestimate significantly the observations. In this study, we examine the influence of the CO2++ natural lifetime against spontaneous dissociation on its modeled density. We show that extending the assumed CO2++ lifetime significantly reduces the discrepancy between the photochemical model predictions and MAVEN observations. Specifically, when treating CO2++ as stable against natural dissociation, instead of invoking a lifetime of 4 s as done in previous studies, the data-to-model ratio comes close to unity throughout the altitude range 160–220 km. We argue that stability of CO2++ against natural dissociation does not necessarily conflict with results from a frequently cited experimental investigation. Our study provides new insights for advancing photochemical modeling of the Martian ionosphere and underscores the need for further laboratory measurements targeting fundamental properties of doubly charged ions.

Keywords: Space plasmas, Mars, Planetary ionospheres, Ionization
Magnetic Flux Emergence and Solar Eruptions in Partially Ionized Plasmas. We have performed 3D MHD simulations to study the effect of partial ionization in the process of magnetic flux emergence in the Sun. In fact, we continue previous work, and we now focus (1) on the emergence of the magnetic fields above the solar photosphere and (2) on the eruptive activity that follows the emergence into the corona. We find that in the simulations with partial ionization (PI), the structure of the emerging field consists of arch-like field lines with very little twist since the axis of the initial rising field remains below the photosphere. The plasma inside the emerging volume is less dense, and it is moving faster compared to the fully ionized (FI) simulation. In both cases, new flux ropes (FR) are formed due to reconnection between emerging field lines, and they eventually erupt in an ejective manner toward the outer solar atmosphere. We are witnessing three major eruptions in both simulations. At least for the first eruption, the formation of the eruptive FR occurs in the low atmosphere in the FI case and at coronal heights in the PI case. Also, in the first PI eruption, part of the eruptive FR carries neutrals in the high atmosphere for a short period of time. Overall, the eruptions are relatively faster in the PI case, while a considerable amount of axial flux is found above the photosphere during the eruptions in both simulations.

Keywords: Solar physics, Solar magnetic flux emergence, Solar magnetic fields
Local 2D Simulations of the Ignition of a Helium Shell Detonation on a White Dwarf by an Impacting Stream. The double detonation model is one of the prevalent explosion mechanisms of Type Ia supernovae (SNe Ia) wherein an outer helium shell detonation triggers a core detonation in the white dwarf (WD). The dynamically driven double degenerate double detonation (D6) is the double detonation of the more massive WD in a binary WD system where the localized impact of the mass transfer stream from the companion sets off the initial helium shell detonation. To have high numerical resolution and control over the stream parameters, we have implemented a study of the local interaction of the stream with the WD surface in 2D. In cases with lower base density of the shell, the stream's impact can cause surface detonation soon after first impact. With higher base densities, after the stream hits the surface, hot material flows around the star and interacts with the incoming stream to produce a denser and narrower impact. Our results therefore show that (1) a directly impacting stream for both a relatively high resolution and for a range of stream parameters can produce a surface detonation, (2) thinner helium shells ignite more promptly via impact, doing so sooner, and (3) there are lower limits on ignition in both shell density and incoming stream speed with lower limits on density being well below those shown by other work to be required for normal appearing SN Ia. This supports stream ignition and therefore the D6 scenario, as a viable mechanism for normal SNe Ia.

Keywords: White dwarf stars, Type Ia supernovae, Supernova dynamics
Einasto Profile as the Halo Model Solution Coupled to the Depletion Radius. We constrain the halo profiles outside the halo boundaries by solving for the matching profiles required by the halo model. In the halo model framework, the matter distribution in the Universe can be decomposed into the spatial distribution of halos convolved with their internal structures. This leads to a set of linear equations in Fourier space that uniquely determines the matching halo profiles for any given halo catalog. In this work, we construct three halo catalogs with different boundary definitions and solve for the matching profiles in each case using measurements of halo–matter and halo–halo power spectra. Our results show that for a given halo field, there is always a set of matching profiles to accurately reconstruct the input statistics of the matter field, even though it might be complex to model the profiles analytically. Comparing the solutions from different halo catalogs, we find that their mass distributions inside the inner depletion radii are nearly identical, while they deviate from each other on larger scales, with a larger boundary resulting in a more extended profile. For the depletion-radius-based catalog, the numerical solution agrees well with the Einasto profile. Coupling the Einasto profile with the depletion catalog, the resulting halo model can simultaneously predict the halo–matter power spectra to 10% and the matter–matter power spectrum to 5%, improving over conventional models in both interpretability and versatility. The conditions and limitations of using the Navarro–Frenk–White profile in the halo model are also discussed.

Keywords: Galaxy dark matter halos, Dark matter distribution, Large-scale structure of the universe
Characterizing Multiband Optical Emission and Variability of 1ES 1215+303 on Diverse Timescales. This study presents analyses of the optical variability of the 1ES 1215+303 on diverse timescales using multiband observations, including observations in the optical BVRI bands carried out with the 0.6 and 1.0 m telescopes located at the Tübitak National Observatory (TUG) from 2022 to 2024 and Zwicky Transient Facility (ZTF) gri data from 2018 to 2023. Investigation of variability on intraday timescales revealed amplitudes of 4.0% and 5.6% on two nights, with a calculated duty cycle of 63%. We determined a minimum timescale of ~92 minutes from these observations, leading us to limit the radius for the optical emission region and the mass of the black hole. The blazar exhibits moderate short- and long-term variability, with variability amplitudes reaching up to 120% and decreasing as the wavelength shortens. Correlation analysis revealed a strong correlation between the optical multiband emissions without any time lag. Analysis of 109 nightly spectral energy distributions yielded spectral indices ranging from 0.772 to 1.413. The consistent trend of both spectral indices and color with respect to brightness suggests a mild bluer when brighter trend persists throughout the observation period, in contrast to the intraday timescale. Utilizing the weighted wavelet z-transform and Lomb–Scargle methods, we analyzed recurrent optical emission patterns on the combined R-band light curves from TUG, ZTF, and Tuorla observations, revealing a quasiperiodic signal at around 1000 days and a secondary signal at approximately 300 days. These signals were found to be insignificant after accounting for the stochastic process and the trial factor.

Keywords: BL Lacertae objects
The Effect of Donor Star Rejuvenation on Common Envelope Evolution. In close binary star systems, common envelope evolution (CEE) may occur after a previous phase of mass transfer. Some isolated formation channels for double neutron star binaries suggest that the donor of CEE was the accretor of a previous phase of stable mass transfer. Accretion should substantially alter the structure of the donor, particularly by steepening the density gradient at the core-envelope interface and rejuvenating the star. We study the CEE of a donor that was the accretor of a previous phase of stable mass transfer and has a rejuvenated structure. We perform 3D hydrodynamics simulations of the CEE of an 18 M⊙ supergiant with a 1.4 M⊙ companion using rejuvenated and non-rejuvenated 1D stellar models for the donor. We compare the two simulations to characterize the effect of the rejuvenation on the outcome of the common envelope phase and the shape of the ejecta. We find that accounting for a previous phase of mass transfer reduces the duration of the inspiral phase by a factor of two, likely due to the different structures in the outer layers of the donor. In the rejuvenated case, the simulations show more equatorially concentrated and asymmetric ejecta, though both cases display evidence for the formation of a pressure-supported thick circumbinary disk. During the dynamical inspiral phase, the impact of rejuvenation on the unbinding of the envelope is unclear; we find that rejuvenation decreases the amount of unbound mass by 20%–40% depending on the energy criterion used.

Keywords: Hydrodynamical simulations, Hydrodynamics, Interacting binary stars, Common envelope evolution, Common envelope binary stars
Nuclear and Star Formation Activities in Nearby Galaxies: Roles of Gas Supply and Active Galactic Nucleus Feedback. We analyze a sample of ~113,000 galaxies (z &lt; 0.3) from the Sloan Digital Sky Survey, divided into star-forming, composite, Seyfert, and LINER types, to explore the relationships between UV-to-optical colors (u ─ r), star formation rates (SFRs), specific SFRs (sSFRs), stellar velocity dispersions (σ*), mass accretion rates onto the black hole ( ), and Eddington ratios. Star-forming galaxies predominantly feature young, blue stars along the main-sequence (MS) line, while composite, Seyfert, and LINER galaxies deviate from this line, displaying progressively older stellar populations and lower SFRs. The   and Eddington ratios are highest in Seyfert galaxies, moderate in composite galaxies, and lowest in LINERs, with higher ratios associated with bluer colors, indicating a younger stellar population and stronger active galactic nucleus (AGN) activity. These trends suggest a strong correlation between sSFRs and Eddington ratios, highlighting a close connection between AGN and star formation activities. These results may imply an evolutionary sequence where galaxies transition from blue star-forming galaxies to red LINERs, passing through the composite and Seyfert phases, driven primarily by gas supply, with AGN feedback playing a secondary role. While both the radio luminosities (L1.4 GHz) and Eddington ratios correlate with SFRs, their trends differ on the SFR−stellar-mass (M*) plane, with the radio luminosities increasing with stellar mass along the MS line and no direct connection between the radio luminosities and Eddington ratios. These findings may provide new insights into the interplay between star formation, AGN activity, and radio emission in galaxies, shedding light on their evolutionary pathways.

Keywords: Active galaxies, Star formation
Investigating the Lower Limit of Metallicity for the Galactic Thin Disk. We explore the metal-poor regime of the Galactic disk on the distribution of stars in the [α/M]–Vϕ plane, to identify the most metal-poor thin disk (MPTnD) stars belonging to the low-α sequence. Chemical abundances and velocities of sample stars are either taken or derived from APOGEE DR17 and Gaia DR3 catalogs. We find the existence of a well-separated extension of the kinematically thin disk stars in the metallicity range of ‑1.2 &lt; [M/H] &lt; ‑0.8 dex. Based on two-by-two distributions of [Mg/Mn], [Al/Fe] and [C+N/Fe], we further confirmed 56 high-possibility metal-poor thin disk (HP-MPTnD) giant stars and suggested the lower metallicity limit of the thin disk below ‑0.95 dex. A comparative analysis of the HP-MPTnD sample with other Galactic components revealed its chemo-dynamical similarities with canonical thin disk stars. These low-α metal-poor stars are predominantly located in the outer disk region and formed in the early stage of the formation of thin disk. Their existence provides compelling support for the two-infall model of the Milky Way's disk formation. Moreover, these stars impose observational constraints on the timing and metallicity of the second gas infall event.

Keywords: Galaxy formation, Galaxy dynamics, Galaxy stellar content, Galaxy disks, Galaxy abundances, Galaxy kinematics
Comparison of Bar Formation Mechanisms. I. Does a Tidally Induced Bar Rotate Slower than an Internally Induced Bar?. Galactic bars can form via the internal bar instability or external tidal perturbations by other galaxies. We systematically compare the properties of the bars formed through the two mechanisms with a series of controlled N-body simulations that form bars through internal or external mechanisms. We create three disk galaxy models with different dynamical "hotness" and evolve them in isolation and under flyby interactions. In the cold- and warm-disk models, where bars can form spontaneously in isolation, tidally induced bars are promoted to a more "advanced" evolutionary stage. However, these bars have similar pattern speeds to those formed spontaneously within the same disk. Bars formed from both mechanisms have similar distributions in pattern-speed–bar-strength (Ωp ‑ A2) space and exhibit comparable ratios of corotation radius to bar length ( ). Dynamical analyses suggest that the inner stellar disk loses the same amount of angular momentum, irrespective of the presence or intensity of the perturbation, which possibly explains the resemblance between tidally and spontaneously formed bars. In the hot-disk model, which avoids the internal bar instability in isolation, a bar forms only under perturbations and rotates more slowly than those in the cold and warm disks. Thus, if "tidally induced bars" refer exclusively to those in galaxies that are otherwise stable against bar instability, they indeed rotate slower than internally induced ones. However, the pattern speed difference is due to the difference in the internal properties of the bar host galaxies, not the different formation mechanisms.

Keywords: Galaxy bars, Galaxy structure, Galaxy dynamics, Galaxy kinematics, Barred spiral galaxies
On Disk Formation around Isolated Black Holes via Stream Accretion. We investigate accretion onto an isolated black hole from uniform winds. If the winds are directed toward the black hole, then the accretion process can be well described by the classical Bondi–Hoyle–Lyttleton or BHL accretion. If the wind is not directed toward the black hole and flows past it, then a smaller fraction of the flow can be attracted by the black hole, and this type of accretion cannot be described by the classical BHL, and we coin the second kind as the lateral BHL. We show that the classical BHL cannot form an accretion disk, while lateral BHL can form transient accretion disks. To describe the thermodynamics of the flow, we have used a variable adiabatic index equation of state which depends on the temperature of the flow as well as the composition of the gas. We show that the electron-proton gas forms an accretion disk, which disappears and forms a shock cone, only to form the disk again at a later time, while for flows with fewer protons, the accretion disk, once lost, does not reappear again. Only when the flow is pair-dominated does it form a persistent accretion disk. We also show that a shock cone is less luminous than the accretion disk.

Keywords: Accretion, Hydrodynamical simulations, Shocks, Astrophysical black holes
Observational Study of Recurrent Jets: Evolution of Magnetic Flux, Current, and Helicity. We observed three recurrent blowout jets in an active region with the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory. Using Helioseismic Magnetic Imager data we found that the magnetic flux of an emerging negative pole increases steadily before declining just as the jets erupt. Certain physical quantities, such as the total unsigned vertical current, align with the periodicity of the jets. The differential affine velocity of vector magnetograms reveals strong shear around the negative pole. The Doppler velocity map, calculated from the Hα spectra observed by the Chinese Hα Solar Explorer, shows upflows with large initial velocity before they can be observed by AIA. The magnetic field derived from the nonlinear force-free field (NLFFF) model suggests a topology akin to a fan─spine structure, consistent with AIA images. We calculated the evolution of the volumetric helicity ratio using the NLFFF model and found its phase aligns with the jet flux in AIA 171 Å. These results suggest that recurrent jets may be triggered by the accumulation and release of energy and helicity, driven by emergence, shearing, and cancellation of photospheric magnetic field.

Keywords: Solar ultraviolet emission, Solar magnetic flux emergence, Solar magnetic fields, Solar magnetic reconnection
Identifying Coronal Mass Ejection Active Region Sources: An Automated Approach. Identifying the source regions of coronal mass ejections (CMEs) is crucial for understanding their origins and improving space weather forecasting. We present an automated algorithm for matching CMEs detected by the Large Angle Spectrometric Coronagraph with their source active regions, specifically Space Weather HMI Active Region Patches (SHARPs), between 2010 May and 2019 January. Our method uses posteruptive signatures, including flares and coronal dimmings, to associate CMEs with potential source regions. Out of 4190 CMEs, we successfully match 1132, achieving a recall rate of ~57% for frontside events. We find that the algorithm performs better for complex SHARP regions containing multiple NOAA regions and for faster CMEs, consistent with expectations that more energetic events produce stronger eruption signatures. We find that CME–flare association rates increase with flare intensity, aligning with previous studies. While our approach has limitations, such as focusing exclusively on SHARP regions and relying on a limited set of posteruptive signatures, it significantly reduces the time required for CME source identification while providing transparent, reproducible results. We encourage the solar physics community to build upon this work, developing improved automated tools for CME source identification. The resulting catalog of CME–source region associations is made publicly available, offering a valuable resource for statistical studies and machine learning applications in solar physics and space weather forecasting.

Keywords: Solar active region magnetic fields, Solar flares, Solar physics, Solar active regions, Solar coronal mass ejections, Solar activity, Catalogs
A Simulated Galaxy Laboratory: Exploring the Observational Effects on UV Spectral Absorption Line Measurements. Ultraviolet absorption line spectroscopy is a sensitive diagnostic for the properties of interstellar and circumgalactic gas. Down-the-barrel observations, where the absorption is measured against the galaxy itself, are commonly used to study feedback from galactic outflows and to make predictions about the leakage of H I ionizing photons into the intergalactic medium. Nonetheless, the interpretation of these observations is challenging, and observational compromises are often made in terms of signal-to-noise ratio, spectral resolution, or the use of stacking analyses. In this paper, we present a novel quantitative assessment of UV absorption line measurement techniques by using mock observations of a hydrodynamical simulation. We use a simulated galaxy to create 22,500 spectra in the commonly used Si II lines while also modeling the signal-to-noise ratio and spectral resolution of recent rest-frame UV galaxy surveys at both high and low redshifts. We show that the residual flux of absorption features is easily overestimated for single line measurements and for stacked spectra. Additionally, we explore the robustness of the partial covering model for estimating column densities from spectra and find underpredictions on an average of 1.25 dex. We show that the underprediction is likely caused by high-column-density sight lines that are optically thick to dust making them invisible in UV spectra.

Keywords: Galactic winds, Hydrodynamical simulations, Ultraviolet spectroscopy, Ultraviolet astronomy, Galaxy evolution, Radiative transfer simulations, Galaxy spectroscopy
Examining Turbulence in Galactic Molecular Clouds. I. A Statistical Analysis of Velocity Structures. We present a systematic analysis of the velocity structure functions (VSFs) of 167 molecular clouds with angular sizes greater than ~176 arcmin2 in three sectors of the Galactic midplane. We calculated the first-to-third-order VSFs and found that 60% of the VSFs exhibit power-law distributions. The relative power-law exponents are consistent with predictions from intermittent turbulence models. Column density weighting reduces the proportion of power-law VSFs and steepens the VSF slopes, implying a reduction of turbulent energy in high-density regions. All clouds show small-scale intermittency, with slightly stronger intermittency in those molecular clouds showing "none" power-law VSFs. Negative VSF exponents that may indicate gravitational collapse are not observed in our sample. The scaling exponents of the observed VSFs do not correlate with the virial parameters of the molecular clouds. These two observations suggest that gravity-dominated scales in molecular clouds still need further investigation. Consistent VSF scaling exponents for the molecular clouds with significant power-law VSFs suggest large-scale external driving of turbulence in these molecular clouds. However, the driving mechanisms are likely not universal, as the power-law scaling coefficients in our results show relatively large scatter. The fact that nearly 40% of the VSFs deviate to some extent from power-law distributions suggests that the influence of local environments on the internal turbulence of molecular clouds may not be negligible.

Keywords: Surveys, Molecular clouds, Star formation, Interstellar clouds, Interstellar medium, Astrophysical fluid dynamics