Sazuna/UAT_keywords huggingface dataset:
Deriving X-Ray Line Profiles for Massive-star Winds from Momentum-conserving Dynamical Working Surface Solutions. We present a general procedure for deriving a line-profile model for massive-star X-ray spectra that captures the dynamics of the wind more directly. The basis of the model is the analytic solution to the problem of variable jets in Herbig–Haro objects given by Cantó et al. In deriving our model, we generalize this jet solution to include flows with a prescribed nonzero acceleration for the context of radiatively driven winds. We provide example line profiles generated from our model for the case of sinusoidal velocity and mass-ejection variations. The example profiles show the expected shape of massive-star X-ray emission lines, as well as interesting but complicated trends with the model parameters. This establishes the possibility that observed X-rays could be a result of temporal variations seeded at the wind base, rather than purely generated intrinsically within the wind volume, and can be described via a quantitative language that connects with the physical attributes of those variations, consistently with the downstream momentum-conserving nature of radiatively cooled shocked radial flows.

Keywords: X-ray astronomy, Massive stars, Analytical mathematics, Stellar winds
Winds and Disk Turbulence Exert Equal Torques on Thick Magnetically Arrested Disks. The conventional accretion disk lore is that magnetized turbulence is the principal angular momentum transport process that drives accretion. However, when dynamically important large-scale magnetic fields thread an accretion disk, they can produce mass and angular momentum outflows, known as winds, that also drive accretion. Yet, the relative importance of turbulent and wind-driven angular momentum transport is still poorly understood. To probe this question, we analyze a long-duration (1.2 × 105 r  g /c) simulation of a rapidly rotating (a = 0.9) black hole feeding from a thick (H/r ∼ 0.3), adiabatic, magnetically arrested disk (MAD), whose dynamically important magnetic field regulates mass inflow and drives both uncollimated and collimated outflows (i.e., winds and jets, respectively). By carefully disentangling the various angular momentum transport processes within the system, we demonstrate the novel result that disk winds and disk turbulence both extract roughly equal amounts of angular momentum from the disk. We find cumulative angular momentum and mass accretion outflow rates of $\dot{L}\propto {r}^{0.9}$ and $\dot{M}\propto {r}^{0.4}$ , respectively. This result suggests that understanding both turbulent and laminar stresses is key to understanding the evolution of systems where geometrically thick MADs can occur, such as the hard state of X-ray binaries, low-luminosity active galactic nuclei, some tidal disruption events, and possibly gamma-ray bursts.

Keywords: Accretion, Black holes, High energy astrophysics, Relativistic jets, Relativistic disks
The Sun Remains Relatively Refractory Depleted: Elemental Abundances for 17,412 Gaia RVS Solar Analogs and 50 Planet Hosts. The element abundances of stars, particularly the refractory elements (e.g., Fe, Si, and Mg), play an important role in connecting stars to their planets. Most Sun-like stars do not have refractory abundance measurements since obtaining a large sample of high-resolution spectra is difficult with oversubscribed observing resources. In this work we infer abundances for C, N, O, Na, Mn, Cr, Si, Fe, Ni, Mg, V, Ca, Ti, Al, and Y for solar analogs with Gaia Radial Velocity Spectrometer (RVS) spectra (R = 11,200) using TheCannon, a data-driven method. We train a linear model on a reference set of 34 stars observed by Gaia RVS with precise abundances measured from previous high-resolution spectroscopic efforts (R &gt; 30,000–110,000). We then apply this model to several thousand Gaia RVS solar analogs. This yields abundances with average upper limit precisions of 0.04–0.1 dex for 17,412 stars, 50 of which are identified planet (candidate) hosts. We subsequently test the relative refractory depletion of these stars with increasing element condensation temperature compared to the Sun. The Sun remains refractory depleted compared to other Sun-like stars regardless of our current knowledge of the planets they host. This is inconsistent with theories of various types of planets locking up or sequestering refractories. Furthermore, we find no significant abundance differences between identified close-in giant planet hosts, giant planet hosts, and terrestrial/small planet hosts with the rest of the sample within our precision limits. This work demonstrates the utility of data-driven learning for future exoplanet composition and demographics studies.

Keywords: Solar abundances, Stellar abundances, Solar system formation
A Channel to Form Fast-spinning Black Hole–Neutron Star Binary Mergers as Multimessenger Sources. II. Accretion-induced Spin-up. In this work, we investigate an alternative channel for the formation of fast-spinning black hole–neutron star (BHNS) binaries, in which super-Eddington accretion is expected to occur in accreting BHs during the stable mass transfer phase within BH-stripped helium (BH–He-rich) star binary systems. We evolve intensive MESA grids of close-orbit BH–He-rich star systems to systematically explore the projected aligned spins of BHs in BHNS binaries, as well as the impact of different accretion limits on the tidal disruption probability and electromagnetic (EM) signature of BHNS mergers. Most of the BHs in BHNS mergers cannot be effectively spun up through accretion if the accretion rate is limited to $\lesssim 10\,{\dot{M}}_{\mathrm{Edd}}$ , where ${\dot{M}}_{\mathrm{Edd}}$ is the standard Eddington accretion limit. In order to reach high spins (e.g., χ BH ≳ 0.5), the BHs are required to be born less massive (e.g., ≲3.0 M ⊙) in binary systems with initial periods of ≲0.2–0.3 days and accrete material at $\sim 100\,{\dot{M}}_{\mathrm{Edd}}$ . However, even under this high accretion limit, ≳6 M ⊙ BHs are typically challenging to significantly spin up and generate detectable associated EM signals. Our population simulations suggest that different accretion limits have a slight impact on the ratio of tidal disruption events. However, as the accretion limit increases, the EM counterparts from the cosmological BHNS population can become bright overall.

Keywords: Close binary stars, Neutron stars, Gravitational waves, Black holes
Radiation Process in Relativistic MHD Waves: The Case of Circularly Polarized Alfvén Waves. Turbulence in highly magnetized plasma can be relativistic and induce an electric field comparable to the background magnetic field. Such a strong electric field can affect the emission process of nonthermal electrons. As the first step toward elucidating the emission process in relativistic turbulence, we study the radiation process of electrons in relativistic circularly polarized Alfvén waves. While the induced electric field boosts the average energy of low-energy electrons with a Larmor radius smaller than the wavelength, the emissivity for such electrons is suppressed because of the elongated gyromotion trajectory. The trajectory of high-energy electrons is shaken by the small-scale electric field, which enhances the emissivity. Since the effective Lorentz factor of E × B drift is $\simeq \sqrt{2}$ in the circularly polarized Alfvén waves, the deviation from the standard synchrotron emission is not so prominent. However, a power-law energy injection in the waves can produce a concave photon spectrum, which is similar to the GeV extra component seen in GRB spectra. If the turbulence electric field is responsible for the GeV extra component in GRBs, the estimates of the typical electron energy and magnetic field should be largely altered.

Keywords: Gamma-ray bursts
[C II] Emission in a Self-regulated Interstellar Medium. The [C II] 157.74 μm fine-structure transition is one of the brightest and most well-studied emission lines in the far-infrared, produced in the interstellar medium (ISM) of galaxies. We study its properties in subparsec-resolution hydrodynamical simulations for an ISM patch with gas surface density of Σ g  = 10 M ⊙ pc‑2, coupled with time-dependent chemistry, far-ultraviolet dust and gas shielding, star formation, photoionization and supernova feedback, and full line radiative transfer. We find a [C II]-to-H2 conversion factor that scales weakly with metallicity   ${X}_{[{\rm{C}}\,{\rm\small{II}}]}=6.31\times {10}^{19}\ {Z}^{{\prime} \ 0.17}\ {\mathrm{cm}}^{-2}\ {({\rm{K}}\ \mathrm{km}\ {{\rm{s}}}^{-1})}^{-1}$  , where   ${Z}^{{\prime} }$   is the normalized metallicity relative to solar. The majority of [C II] originates from atomic gas with hydrogen number density n ∼ 10 cm‑3. The [C II] line intensity positively correlates with the star formation rate (SFR), with a normalization factor that scales linearly with metallicity. We find that this is broadly consistent with z ∼ 0 observations. As such, [C II] is a good SFR tracer even in metal-poor environments where molecular lines might be undetectable. Resolving the clumpy structure of the dense (n = 10‑103 cm‑3) ISM is important, as it dominates [C II] 157.74 μm emission. We compare our full radiative transfer computation with the optically thin limit and find that the [C II] line becomes marginally optically thick only at supersolar metallicity for our assumed gas surface density.

Keywords: Hydrodynamical simulations, Interstellar medium, Astrochemistry
Impact of Anisotropic Cosmic-Ray Transport on the Gamma-Ray Signatures in the Galactic Center. The very high energy (VHE) emission of the central molecular zone (CMZ) is rarely modeled in 3D. Most approaches describe the morphology in 1D or simplify the diffusion to the isotropic case. In this work, we show the impact of a realistic 3D magnetic field configuration and gas distribution on the VHE γ-ray distribution of the CMZ. We solve the 3D cosmic-ray transport equation with an anisotropic diffusion tensor using the approach of stochastic differential equations as implemented in the CRPropa framework. We test two different source distributions for five different anisotropies of the diffusion tensor, covering the range of effectively fieldline-parallel diffusion to isotropic diffusion. Within the tested magnetic field configuration, the anisotropy of the diffusion tensor is close to the isotropic case, and three point sources within the CMZ are favored. Future missions such as the upcoming CTA will reveal more small-scale structures that are not yet included in the model. Therefore, a more detailed 3D gas distribution and magnetic field structure will be needed.

Keywords: Galactic cosmic rays, Galactic center, Gamma-rays
TESS Observations of Outbursts on Polars—Superflares. Flare events are magnetic activities on the stellar surface, which can provide us with information about the accretion behavior and evolution of polars. In this paper, we search for flare events on polars from all the available 2 minute cadence TESS data through visual inspection, and identify six flare events on five flaring stars from 185 polars. All the flares have bolometric energies above 1034 erg, with a median of ∼1035 erg, so they are superflares. Among them, two flares are followed by a brightness enhancement, which may suggest an accretion burst on the white dwarf caused by a coronal mass ejection. A completeness analysis of the detections demonstrates that the flare activities on the low-mass red dwarfs of polars are very similar to those on M dwarfs, which indicates that the highly magnetic fields of the white dwarfs have no significant effect on the magnetic activities on polars. We estimate that another ∼20–30 polars include a magnetically active secondary star, and more intensive searching for flares on polars is encouraged in further work.

Keywords: M dwarf stars, Magnetic stars, AM Herculis stars
Latitude-dependent Atmospheric Waves and Long-period Modulations in Luhman 16 B from the Longest Light Curve of an Extrasolar World. In this work, we present the longest photometric monitoring of up to 1200 hr of the strongly variable brown dwarf binaries Luhman 16 AB and provide evidence of ±5% variability on a timescale of several to hundreds of hours for this object. We show that short-period rotational modulation around 5 hr (k = 1 wavenumber) and 2.5 hr (k = 2 wavenumber) dominate the variability under 10 hr, where the planetary-scale wave model composed of k = 1 and k = 2 waves provides good fits to both the periodograms and light curve. In particular, models consisting of three to four sine waves could explain the variability of the light-curve durations up to 100 hr. We show that the relative range of the k = 2 periods is narrower compared to the k = 1 periods. Using simple models of zonal banding in solar system giants, we suggest that the difference in period range arises from the difference in wind-speed distribution at low and mid-to-high latitudes in the atmosphere. Last, we show that Luhman 16 AB also exhibits long-period ±5% variability, with periods ranging from 15 hr up to 100 hr over the longest monitoring of this object. Our results for the k = 1 and k = 2 waves and long-period evolution are consistent with previous 3D atmosphere simulations, demonstrating that both latitude-dependent waves and slow-varying atmospheric features are potentially present in Luhman 16 AB atmospheres and are a significant contribution to the light-curve modulation over hundreds of rotations.

Keywords: Broad band photometry, Brown dwarfs, Exoplanet atmospheres, Atmospheric circulation
Probing 3D Magnetic Fields Using Thermal Dust Polarization and Grain Alignment Theory. Magnetic fields are ubiquitous in the Universe and are thought to play an important role in various astrophysical processes. Polarization of thermal emission from dust grains aligned with the magnetic field is widely used to measure the 2D magnetic field projected onto the plane of the sky, but its component along the line of sight is not yet constrained. Here, we introduce a new method to infer 3D magnetic fields using thermal dust polarization and grain alignment physics. We first develop a physical model of thermal dust polarization using the modern grain alignment theory based on the magnetically enhanced radiative torque alignment theory. We then test this model with synthetic observations of magnetohydrodynamic simulations of a filamentary cloud with our updated POLARIS code. Combining the tested physical polarization model with synthetic polarization, we show that the B-field inclination angles can be accurately constrained by the polarization degree from synthetic observations. Compared to the true 3D magnetic fields, our method based on grain alignment physics is more accurate than the previous methods that assume uniform grain alignment. This new technique paves the way for tracing 3D B-fields using thermal dust polarization and grain alignment theory and for constraining dust properties and grain alignment physics.

Keywords: Interstellar dust, Star forming regions, Astrophysical dust processes, Interstellar magnetic fields, Starlight polarization, Star formation
Photocleavage of Aliphatic C–C Bonds in the Interstellar Medium. Ultraviolet (UV) processing in the interstellar medium (ISM) induces the dehydrogenation of hydrocarbons. Aliphatics, including alkanes, are present in different interstellar environments, being prevalently formed in evolved stars; thus, the dehydrogenation by UV photoprocessing of alkanes plays an important role in the chemistry of the ISM, leading to the formation of unsaturated hydrocarbons and eventually to aromatics, the latter ubiquitously detected in the ISM. Here, through combined experimental results and ab initio calculations, we show that UV absorption (mainly at the Lyα emission line of hydrogen at 121.6 nm) promotes an alkane to an excited Rydberg state from where it evolves toward fragmentation, inducing the formation of olefinic C=C bonds, which are necessary precursors of aromatic hydrocarbons. We show that the photochemistry of aliphatics in the ISM does not primarily produce direct hydrogen elimination but preferential C–C photocleavage. Our results provide an efficient synthetic route for the formation of unsaturated aliphatics, including propene and dienes, and suggest that aromatics could be formed in dark clouds by a bottom-up mechanism involving molecular fragments produced by UV photoprocessing of aliphatics.

Keywords: Dust physics, Laboratory astrophysics, Dense interstellar clouds, Astrochemistry, Molecular physics, Interstellar medium, Interstellar dust processes
A Coronal Mass Ejection Impacting Parker Solar Probe at 14 Solar Radii. The relationship between CME properties in the corona and their interplanetary counterparts is not well understood. Until recently, a wide spatial gap existed between the two regions, which prevented us from disentangling the spatial and temporal evolution of CMEs. NASA's Parker Solar Probe (PSP) has imaged multiple CMEs since its launch in 2018, but these events either intercepted the spacecraft far from the corona or completely missed it. Here we describe one of the first CMEs observed simultaneously by remote sensing and in situ instruments, and compare the corresponding measured properties, such as orientation, cross section diameter, density, and speed. The CME encounter occurred on 2022 June 2, while PSP was around 14 solar radii from the Sun center. We reconstruct the CME with forward modeling and determine its morphology and kinematics. The reconstruction suggests that PSP misses the CME apex but encounters its flank. The encounter time matches the period when the PSP in situ measurements indicate the passage of a CME. We also reconstruct the flux rope diameter and orientation using the in situ magnetic field measurements. The results are consistent with the CME reconstruction from imaging data. The close agreement between remote sensing and in situ analyses suggests that discrepancies found in past studies are more likely associated with the CME temporal evolution. We also find that the magnetic field of the CME flank extrapolated to 1 au is well below the average solar wind background and likely indistinguishable from it. This point could explain past events where the CMEs' interplanetary counterparts were not identified.

Keywords: Interplanetary medium, Space plasmas, Solar coronal transients, Solar wind, Interplanetary magnetic fields, Solar corona, Solar coronal mass ejections
Magnetic Flux in the Sun Emerges Unaffected by Supergranular-scale Surface Flows. Magnetic flux emergence from the convection zone into the photosphere and beyond is a critical component of the behavior of large-scale solar magnetism. Flux rarely emerges amid field-free areas at the surface, but when it does, the interaction between the magnetism and plasma flows can be reliably explored. Prior ensemble studies have identified weak flows forming near emergence locations, but the low signal-to-noise ratio (S/N) required averaging over the entire data set, erasing information about variation across the sample. Here, we apply deep learning to achieve an improved S/N, enabling a case-by-case study. We find that these associated flows are dissimilar across instances of emergence and also occur frequently in the quiet convective background. Our analysis suggests the diminished influence of supergranular-scale convective flows and magnetic buoyancy on flux rise. Consistent with numerical evidence, we speculate that small-scale surface turbulence and/or deep convective processes play an outsized role in driving flux emergence.

Keywords: Solar active region magnetic fields, Solar magnetic flux emergence, Solar convective zone, Convolutional neural networks, Solar active regions
Absorption and Self-absorption of [C II] and [O I] Far Infrared Lines toward a Bright Bubble in the Nessie Infrared Dark Cloud. Using the upGREAT instrument on board the Stratospheric Observatory for Infrared Astronomy, we imaged [C II] 157.74 and [O I] 63.18 μm line emission from a bright photodissociation region (PDR) associated with an ionized bubble located in the Nessie Nebula, a filamentary infrared dark cloud. A comparison with Australia Telescope Compact Array data reveals a classic photodissociation region (PDR) structure, with a uniform progression from ionized gas, to photodissociated gas, and to molecular gas from the bubble's interior to its exterior. [O I] line emission from the bubble's PDR reveals self-absorption features. Toward a far-IR bright protostar, both [O I] and [C II] show an absorption feature at a velocity of ‑18 km s‑1, the same velocity as an unrelated foreground molecular cloud. Since the gas density in typical molecular clouds is well below the [O I] and [C II] critical densities, the excitation temperatures for both lines are low (∼20 K). The Meudon models demonstrate that the surface of a molecular cloud, externally illuminated by a standard G 0 = 1 interstellar radiation field, can produce absorption features in both transitions. Thus, the commonly observed [O I] and [C II] self-absorption and absorption features plausibly arise from the subthermally excited, externally illuminated photodissociated envelopes of molecular clouds. The luminous young stellar object AGAL337.916-00.477, located precisely where the expanding bubble strikes the Nessie filament, is associated with two shock tracers: NH3 (3,3) maser emission and SiO 2‑1 emission, indicating an interaction between the bubble and the filament. The interaction of the expanding bubble with its parental dense filament has triggered star formation.

Keywords: Interstellar line absorption, Photodissociation regions, Star formation, Interstellar medium, H II regions
PEARLS: NuSTAR and XMM-Newton Extragalactic Survey of the JWST North Ecliptic Pole Time-domain Field II. We present the second NuSTAR and XMM-Newton extragalactic survey of the JWST north ecliptic pole (NEP) time-domain field (TDF). The first NuSTAR NEP-TDF survey had 681 ks total exposure time executed in NuSTAR cycle 5 in 2019 and 2020. This second survey, acquired from 2020 to 2022 in cycle 6, adds 880 ks of NuSTAR exposure time. The overall NuSTAR NEP-TDF survey is the most sensitive NuSTAR extragalactic survey to date, and a total of 60 sources were detected above the 95% reliability threshold. We constrain the hard X-ray number counts,   $\mathrm{log}N$  ─  $\mathrm{log}S$  , down to 1.7 × 10−14 erg cm−2 s−1 at 8─24 keV and detect an excess of hard X-ray sources at the faint end. About 47% of the NuSTAR-detected sources are heavily obscured (N H &gt; 1023 cm−2), and   ${18}_{-8}^{+20}$  % of the NuSTAR-detected sources are Compton-thick (N H &gt; 1024 cm−2). These fractions are consistent with those measured in other NuSTAR surveys. Four sources presented &gt;2σ variability in the 3 yr survey. In addition to NuSTAR, a total of 62 ks of XMM-Newton observations were taken during NuSTAR cycle 6. The XMM-Newton observations provide soft X-ray (0.5─10 keV) coverage in the same field and enable more robust identification of the visible and infrared counterparts of the NuSTAR-detected sources. A total of 286 soft X-ray sources were detected, out of which 214 XMM-Newton sources have secure counterparts from multiwavelength catalogs.

Keywords: Active galactic nuclei, X-ray surveys