adsabs/SciX_UAT_keywords huggingface dataset:
Interplay between Anisotropy- and Skewness-driven Whistler Instabilities in the Solar Wind under the Core-Strahlo Model

Temperature anisotropy and field-aligned skewness are commonly observed nonthermal features in electron velocity distributions in the solar wind. These characteristics can act as a source of free energy to destabilize different electromagnetic wave modes, which may alter the plasma state through wave-particle interactions. Previous theoretical studies have mainly focused on analyzing these nonthermal features and self-generated instabilities individually. However, to obtain a more accurate and realistic understanding of the kinetic processes in the solar wind, it is necessary to examine the interplay between these two energy sources. By means of linear kinetic theory, in this paper we investigate the excitation of the parallel propagating whistler mode, when it is destabilized by electron populations exhibiting both temperature anisotropy and field-aligned strahl or skewness. To describe the solar wind electrons, we adopt the core-strahlo model as an alternative approach. This model offers the advantage of representing the suprathermal features of halo and strahl electrons, using a single skew-kappa distribution already known as the strahlo population. Our findings show that when the electron strahlo exhibits an intrinsic temperature anisotropy, this suprathermal population becomes a stronger and more efficient source of free energy for destabilizing the whistler mode. This suggests the greater involvement of the anisotropic strahlo in processes conditioned by wave-particle interactions. The present results also suggest that the contribution of core anisotropy can be safely disregarded when assessing the importance of instabilities driven by the suprathermal population. This allows for a focused study, particularly regarding the regulation of the electron heat flux in the solar wind.

Keywords: solar wind; plasma astrophysics; space plasmas
Imaging of I Zw 18 by JWST. I. Detecting Dusty Stellar Populations

We present a JWST imaging survey of I Zw 18, the archetypal extremely metal-poor, star-forming (SF), blue compact dwarf galaxy. With an oxygen abundance of only ∼3% Z ⊙, it is among the lowest-metallicity systems known in the local Universe, and is, therefore, an excellent accessible analog for the galactic building blocks which existed at early epochs of ionization and star formation. These JWST data provide a comprehensive infrared (IR) view of I Zw 18 with eight filters utilizing both Near Infrared Camera (F115W, F200W, F356W, and F444W) and Mid-Infrared Instrument (F770W, F1000W, F1500W, and F1800W) photometry, which we have used to identify key stellar populations that are bright in the near- and mid-IR. These data allow for a better understanding of the origins of dust and dust-production mechanisms in metal-poor environments by characterizing the population of massive, evolved stars in the red supergiant (RSG) and asymptotic giant branch (AGB) phases. In addition, it enables the identification of the brightest dust-enshrouded young stellar objects (YSOs), which provide insight into the formation of massive stars at extremely low metallicities typical of the very early Universe. This paper provides an overview of the observational strategy and data processing, and presents first science results, including identifications of dusty AGB, RSG, and bright YSO candidates. These first results assess the scientific quality of JWST data and provide a guide for obtaining and interpreting future observations of the dusty and evolved stars inhabiting compact dwarf SF galaxies in the local Universe.

Keywords: stellar populations; evolved stars; asymptotic giant branch stars; red supergiant stars; dust formation; dwarf irregular galaxies; blue compact dwarf galaxies; james webb space telescope; infrared astronomy; infrared photometry
A Multilevel Scheduling Framework for Distributed Time-domain Large-area Sky Survey Telescope Array

Telescope arrays are receiving increasing attention due to their promise of higher resource utilization, greater sky survey area, and higher frequency of full space-time monitoring than single telescopes. Compared with the ordinary coordinated operation of several telescopes, the new astronomical observation mode has an order of magnitude difference in the number of telescopes. It requires efficient coordinated observation by large-domain telescopes distributed at different sites. Coherent modeling of various abstract environmental constraints is essential for responding to multiple complex science goals. Also, due to competing science priorities and field visibility, how the telescope arrays are scheduled for observations can significantly affect observation efficiency. This paper proposes a multilevel scheduling model oriented toward the problem of telescope-array scheduling for time-domain surveys. A flexible framework is developed with basic functionality encapsulated in software components implemented on hierarchical architectures. An optimization metric is proposed to self-consistently weight contributions from time-varying observation conditions to maintain uniform coverage and efficient time utilization from a global perspective. The performance of the scheduler is evaluated through simulated instances. The experimental results show that our scheduling framework performs correctly and provides acceptable solutions considering the percentage of time allocation efficiency and sky coverage uniformity in a feasible amount of time. Using a generic version of the telescope-array scheduling framework, we also demonstrate its scalability and its potential to be applied to other astronomical applications.

Keywords: surveys; astronomical models; astronomical methods; observational astronomy
X-Ray Polarization of the BL Lacertae Type Blazar 1ES 0229+200

We present polarization measurements in the 2-8 keV band from blazar 1ES 0229+200, the first extreme high synchrotron peaked source to be observed by the Imaging X-ray Polarimetry Explorer (IXPE). Combining two exposures separated by about two weeks, we find the degree of polarization to be ΠX = 17.9% ± 2.8% at an electric-vector position angle ψ X = 25.°0 ± 4.°6 using a spectro-polarimetric fit from joint IXPE and XMM-Newton observations. There is no evidence for the polarization degree or angle varying significantly with energy or time on both short timescales (hours) or longer timescales (days). The contemporaneous polarization degree at optical wavelengths was >7× lower, making 1ES 0229+200 the most strongly chromatic blazar yet observed. This high X-ray polarization compared to the optical provides further support that X-ray emission in high-peaked blazars originates in shock-accelerated, energy-stratified electron populations, but is in tension with many recent modeling efforts attempting to reproduce the spectral energy distribution of 1ES 0229+200, which attribute the extremely high energy synchrotron and Compton peaks to Fermi acceleration in the vicinity of strongly turbulent magnetic fields.

Keywords: polarimetry; x-ray quasars; radio galaxies
Supermassive Black Hole Fueling in IllustrisTNG: Impact of Environment

We study the association between active galactic nuclei (AGNs) and environment at scales of 0.01-1 ${h}^{-1}$ Mpc in the IllustrisTNG simulated universe (TNG100). We identify supermassive black hole (BH) pairs and multiples within scales of 0.01, 0.1, and 1 ${h}^{-1}$ Mpc and examine their AGN activity in relation to randomly selected pairs and multiples. The number density of BHs in TNG100 is n = 0.06 h3 Mpc-3 at z ≲ 1.5 (n = 0.02 h3 Mpc-3 at z = 3). About ∼10% and ∼1% of these BHs live in pairs and multiples, respectively, within 0.1 ${h}^{-1}$ Mpc scales. These systems have enhanced likelihood (up to factors of 3-6) of containing high Eddington ratio (η ≳ 0.7) AGNs compared to random pairs and multiples. Conversely, the likelihood of an AGN to live in 0.1 ${h}^{-1}$ Mpc scale BH systems is also higher (by factors ∼4 for η ≳ 0.7) compared to random pairs and multiples. ∼10% of ultra-hard X-ray selected AGNs in TNG100 have detectable 2-10 keV AGN companions on 0.1 ${h}^{-1}$ Mpc scales, consistent with observations. On larger spatial scales (∼1 ${h}^{-1}$ Mpc), however, no significant enhancements in AGN activity exist, even at high Eddington ratios. This implies that small-scale (≲0.1 ${h}^{-1}$ Mpc) AGN enhancement is likely driven by galaxy interactions and mergers. Nonetheless, the overall percentage of AGNs living in ≲0.1 ${h}^{-1}$ Mpc scale multiples is still subdominant (≲40%). Furthermore, the associated Eddington ratio enhancements of BH systems (as well as merging BHs) is only up to factors of ∼2-3. Our results support the existence of merger-AGN connection in TNG100. However, it plays a relatively minor role in fueling the AGN population.

Keywords: supermassive black holes; active galactic nuclei
The Impact of Classical and General Relativistic Obliquity Precessions on the Habitability of Circumstellar Neutron Stars' Planets

Recently, it has been shown that rocky planets orbiting neutron stars can be habitable under plausible circumstances. If a distant, point-like source of visible light, such as a Sun-like main-sequence star or the gravitationally-lensed accretion disk of a supermassive black hole is present, possible temporal variations ${\rm{\Delta }}{\varepsilon }_{{\rm{p}}}\left(t\right)$ of the planet's axial tilt εp to the ecliptic plane should be included in the overall habitability budget since the obliquity determines the insolation at a given latitude on a body' s surface. I point out that, for rather generic initial spin-orbit initial configurations, general relativistic and classical spin variations induced by the post-Newtonian de Sitter and Lense-Thirring components of the field of the host neutron star and by its pull to the planetary oblateness ${J}_{2}^{{\rm{p}}}$ may induce huge and very fast variations of εp that would likely have an impact on the habitability of such worlds. In particular, for a planet's distance of, say, 0.005 au from a 1.4 M⊙ neutron star corresponding to an orbital period Pb = 0.109 day, obliquity shifts Δεp as large as ${\varepsilon }_{{\rm{p}}}^{\max }-{\varepsilon }_{{\rm{p}}}^{\min }\simeq 50^\circ \mbox{--}100^\circ $ over characteristic timescales as short as 10 days ( ${J}_{2}^{{\rm{p}}}$ ) to 3 Myr (Lense-Thirring) may occur for arbitrary orientations of the orbital and spin angular momenta L, Sns, Sp of the planet-neutron star system. In view of this feature of their spins, I dub such hypothetical planets as "nethotrons."

Keywords: exoplanets; neutron stars; general relativity; oblateness; astrobiology; gravitation
Turbulent Reacceleration of Streaming Cosmic Rays

Subsonic, compressive turbulence transfers energy to cosmic rays (CRs), a process known as nonresonant reacceleration. It is often invoked to explain the observed ratios of primary to secondary CRs at ~GeV energies, assuming wholly diffusive CR transport. However, such estimates ignore the impact of CR self-confinement and streaming. We study these issues in stirring box magnetohydrodynamic (MHD) simulations using Athena++, with field-aligned diffusive and streaming CR transport. For diffusion only, we find CR reacceleration rates in good agreement with analytic predictions. When streaming is included, reacceleration rates depend on plasma β. Due to streaming-modified phase shifts between CR and gas variables, they are slower than canonical reacceleration rates in low-β environments like the interstellar medium but remain unchanged in high-β environments like the intracluster medium. We also quantify the streaming energy-loss rate in our simulations. For sub-Alfvénic turbulence, it is resolution dependent (hence unconverged in large-scale simulations) and heavily suppressed compared to the isotropic loss rate v A · ∇P CR/P CR ~ v A/L 0, due to misalignment between the mean field and isotropic CR gradients. Unlike acceleration efficiencies, CR losses are almost independent of magnetic field strength over β ~ 1-100 and are, therefore, not the primary factor behind lower acceleration rates when streaming is included. While this paper is primarily concerned with how turbulence affects CRs, in a follow-up paper we consider how CRs affect turbulence by diverting energy from the MHD cascade, altering the pathway to gas heating and steepening the turbulent spectrum.

Keywords: plasma astrophysics; galaxies; cosmic rays; galactic cosmic rays; magnetohydrodynamical simulations
SOFIA/FIFI-LS Full-disk [C II] Mapping and CO-dark Molecular Gas across the Nearby Spiral Galaxy NGC 6946

We present SOFIA/FIFI-LS observations of the [C II] 158 μm cooling line across the nearby spiral galaxy NGC 6946. We combine these with UV, IR, CO, and H I data to compare [C II] emission to dust properties, star formation rate (SFR), H2, and H I at 560 pc scales via stacking by environment (spiral arms, interarm, and center), radial profiles, and individual, beam-sized measurements. We attribute 73% of the [C II] luminosity to arms, and 19% and 8% to the center and interarm region, respectively. [C II]/TIR, [C II]/CO, and [C II]/PAH radial profiles are largely constant, but rise at large radii (≳ 8 kpc) and drop in the center ("[C II] deficit"). This increase at large radii and the observed decline with the 70 μm/100 μm dust color are likely driven by radiation field hardness. We find a near proportional [C II]-SFR scaling relation for beam-sized regions, though the exact scaling depends on methodology. [C II] also becomes increasingly luminous relative to CO at low SFR (interarm or large radii), likely indicating more efficient photodissociation of CO and emphasizing the importance of [C II] as an H2 and SFR tracer in such regimes. Finally, based on the observed [C II] and CO radial profiles and different models, we find αCO to increase with radius, in line with the observed metallicity gradient. The low αCO (galaxy average ≲ 2 M⊙ pc-2 (K km s-1)-1) and low [C II]/CO ratios (∼400 on average) imply little CO-dark gas across NGC 6946, in contrast to estimates in the Milky Way.

Keywords: spiral galaxies; interstellar medium; interstellar dust; interstellar line emission; galaxy structure
Relation of Microstreams in the Polar Solar Wind to Switchbacks and Coronal X-Ray Jets

Ulysses data obtained at high solar latitudes during periods of minimum solar activity in 1994 and 2007 are examined to determine the relation between velocity structures called microstreams and folds in the magnetic field called switchbacks. A high correlation is found. The possibility of velocity peaks in microstreams originating from coronal X-ray jets is reexamined; we now suggest that microstreams are the consequence of the alternation of patches of switchbacks and quiet periods, where the switchbacks could be generated by minifilament/flux rope eruptions that cause coronal jets.

Keywords: fast solar wind
Discovery of Nine Super Li-rich Unevolved Stars from the LAMOST Survey

Based on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) medium-resolution spectroscopic survey (MRS), we report the discovery of nine super Li-rich unevolved stars with A(Li) > 3.8 dex. These objects show unusually high levels of lithium abundances, up to three times higher than the meteoritic value of 3.3 dex, which indicates that they must have experienced a history of lithium enrichment. It is found that seven of our program stars are fast rotators with v sin i > 9 km s-1, which suggests that the accretion of circumstellar matter may be the main contributor to the lithium enhancement of these unevolved stars; however, other sources cannot be excluded.

Keywords: chemically peculiar stars; lithium stars; circumstellar matter; stellar rotation
Precision Calibration of Radio Interferometers for 21 cm Cosmology with No Redundancy and Little Knowledge of Antenna Beams and the Radio Sky

We introduce CALibration AMITY (CALAMITY), a precision bandpass calibration method for radio interferometry. CALAMITY can solve for direction-independent gains with arbitrary frequency structure to the high precision required for 21 cm cosmology with minimal knowledge of foregrounds or antenna beams and does not require any degree of redundancy (repeated identical measurements of the same baseline). We have achieved this through two key innovations. First, we model the foregrounds on each baseline independently using a flexible and highly efficient set of basis functions that have minimal overlap with 21 cm modes and enforce spectral smoothness in the calibrated foregrounds. Second, we use an off-the-shelf GPU accelerated API (TENSORFLOW) to solve for per-baseline foregrounds simultaneously with per-frequency antenna gains in a single optimization loop. GPU acceleration is critical for our technique to be able to solve for the large numbers of foreground and gain parameters simultaneously across all frequencies for an interferometer with ≳10 antennas in a reasonable amount of time. In this paper, we give an overview of our technique and, using realistic simulations, demonstrate its performance in solving for and removing pathological gain structures down to 4.5 orders of magnitude below the level of foregrounds and consistent with our simulated thermal noise limit. If readers want to start using CALAMITY now, they can find a tutorial notebook online.

Keywords: observational cosmology; radio interferometers
The Behavior of HgMn Stars in the Far-UV-Paper 7: HR 6000

The analysis of nine high resolution SWP spectra of the chemically peculiar star HR 6000 recorded by the International Ultraviolet Explorer reveals low amplitude variations of the far-ultraviolet flux (about 15% at 1500 Å) over the various observations with IUE. These variations could be caused by horizontal gradients of abundances of chemical elements over the surface of HR 6000.

Keywords: chemically peculiar stars
Solar Magnetic Polarity Effect on Neutron Monitor Count Rates: Comparing Latitude Surveys and Antarctic Stations

The Galactic cosmic-ray spectrum manifests pronounced variations over the 11 yr sunspot cycle and more subtle variations over the 22 yr solar magnetic cycle. An important tool to study these variations is repeated latitude surveys with neutron monitors (NMs) on board icebreakers in conjunction with land-based references. We revisit 13 annual latitude surveys from 1994 to 2007 using reference data from the Mawson NM instead of McMurdo NM (which closed in 2017). We then consider two more latitude surveys (2018 and 2019) with a monitor similar to the 3NM64 in the previous surveys but without lead rings around the central tube, a so-called "semi-leaded neutron monitor." The new surveys extend the linear relationship among data taken at different cutoff rigidity ranges. They also confirm the "crossover" measured near solar minima during epochs of opposite solar magnetic polarity and the absence of a crossover for epochs having the same solar magnetic polarity.

Keywords: galactic cosmic rays; solar cycle; solar-terrestrial interactions
Early-forming Massive Stars Suppress Star Formation and Hierarchical Cluster Assembly

Feedback from massive stars plays an important role in the formation of star clusters. Whether a very massive star is born early or late in the cluster formation timeline has profound implications for the star cluster formation and assembly processes. We carry out a controlled experiment to characterize the effects of early-forming massive stars on star cluster formation. We use the star formation software suite Torch, combining self-gravitating magnetohydrodynamics, ray-tracing radiative transfer, N-body dynamics, and stellar feedback, to model four initially identical 104 M ⊙ giant molecular clouds with a Gaussian density profile peaking at 521.5 cm-3. Using the Torch software suite through the AMUSE framework, we modify three of the models, to ensure that the first star that forms is very massive (50, 70, and 100 M ⊙). Early-forming massive stars disrupt the natal gas structure, resulting in fast evacuation of the gas from the star-forming region. The star formation rate is suppressed, reducing the total mass of the stars formed. Our fiducial control model, without an early massive star, has a larger star formation rate and total efficiency by up to a factor of 3, and a higher average star formation efficiency per freefall time by up to a factor of 7. Early-forming massive stars promote the buildup of spatially separate and gravitationally unbound subclusters, while the control model forms a single massive cluster.

Keywords: astronomical simulations; young massive clusters; star forming regions; massive stars
A 2:1 Mean-motion Resonance Super-Jovian Pair Revealed by TESS, FEROS, and HARPS

We report the discovery of a super-Jovian 2:1 mean-motion resonance (MMR) pair around the G-type star TIC 279401253, whose dynamical architecture is a prospective benchmark for planet formation and orbital evolution analysis. The system was discovered thanks to a single-transit event recorded by the Transiting Exoplanet Survey Satellite mission, which pointed to a Jupiter-sized companion with poorly constrained orbital parameters. We began ground-based precise radial velocity (RV) monitoring with HARPS and FEROS within the Warm gIaNts with tEss survey to constrain the transiting body's period, mass, and eccentricity. The RV measurements revealed not one but two massive planets with periods of ${76.80}_{-0.06}^{+0.06}$ and ${155.3}_{-0.7}^{+0.7}$ days, respectively. A combined analysis of transit and RV data yields an inner transiting planet with a mass of ${6.14}_{-0.42}^{+0.39}$ M Jup and a radius of ${1.00}_{-0.04}^{+0.04}$ R Jup, and an outer planet with a minimum mass of ${8.02}_{-0.18}^{+0.18}$ M Jup, indicating a massive giant pair. A detailed dynamical analysis of the system reveals that the planets are locked in a strong first-order, eccentricity-type 2:1 MMR, which makes TIC 279401253 one of the rare examples of truly resonant architectures supporting disk-induced planet migration. The bright host star, V ≈ 11.9 mag, the relatively short orbital period (P b = ${76.80}_{-0.06}^{+0.06}$ days), and pronounced eccentricity (e = 0.448 ${}_{-0.029}^{+0.028}$ ) make the transiting planet a valuable target for atmospheric investigation with the James Webb Space Telescope and ground-based extremely large telescopes. *Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere under ESO programmes 105.20GX.001, 108.22A8.001, 110.23YQ.001, and MPG programmes 0106.A-9014, 0107.A-9003, 0108.A-9003, 0109.A-9003, 0110.A-9011.

Keywords: radial velocity; transit photometry; exoplanets; exoplanet systems; exoplanet dynamics; exoplanet evolution; exoplanet migration; exoplanet astronomy; extrasolar gaseous planets