adsabs/SciX_UAT_keywords huggingface dataset:
Eppur è piatto? The Cosmic Chronometers Take on Spatial Curvature and Cosmic Concordance

The question of whether cosmic microwave background (CMB) temperature and polarization data from Planck favor a spatially closed universe with curvature parameter ΩK < 0 has been the subject of recent intense discussions. Attempts to break the geometrical degeneracy combining Planck data with external data sets such as baryon acoustic oscillation (BAO) measurements all point toward a spatially flat universe at the cost of significant tensions with Planck, which makes the resulting data set combination problematic. Settling this issue requires identifying a data set that can break the geometrical degeneracy while avoiding these tensions. We argue that cosmic chronometers (CCs), measurements of the expansion rate H(z) from the relative ages of massive early-type passively evolving galaxies, are the data set we are after. Furthermore, CCs come with the additional advantage of being virtually free of cosmological model assumptions. Combining Planck 2018 CMB temperature and polarization data with the latest CCs, we break the geometrical degeneracy and find ΩK = -0.0054 ± 0.0055, consistent with a spatially flat universe and competitive with the Planck+BAO constraint. Our results are stable against minimal parameter space extensions and CC systematics, and we find no substantial tension between Planck and CC data within a nonflat universe, making the resulting combination reliable. Our results allow us to assert with confidence that the universe is spatially flat to the ${ \mathcal O }({10}^{-2})$ level, a finding that might possibly settle the ongoing spatial curvature debate and lends even more support to the already very successful inflationary paradigm.

Keywords: observational cosmology; cosmic background radiation; galaxy ages; cosmological parameters; galaxies
The Dependence of the Location and Pressure Variations of the Martian Magnetic Pileup Boundary on the Interplanetary Magnetic Field: An MHD Simulation Study

In this paper, using a three-dimensional multispecies MHD model, we study the effect of the interplanetary magnetic field (IMF) intensity and orientation on the subsolar standoff distance of the Martian magnetic pileup boundary (r 0) and the pressure balance across it. The results show that: (1) with the increasing magnitude of the Y- or Z-component of the IMF, B Y or B Z , r 0 increases, while the radial IMF component, B X , has little effect. With the increasing magnitude of B Y or B Z , the compression degree of the magnetic field (f) increases, while the solar wind pressure coefficient (k) remains unchanged, resulting in the enhancement of r 0. (2) Under the same IMF intensity, B t , the impact of the IMF cone angle on r 0 and f is controlled by the ratio of the IMF Y- and Z-components to B t , $\sqrt{{B}_{Y}^{2}+{B}_{Z}^{2}}/{B}_{t}$ . When the ratio is enhanced, both r 0 and f increase, while k generally remains unchanged. Compared with the IMF cone angle, the influence of the IMF clock angle is relatively less. We suggest that the stronger magnetic pileup process controlled by the perpendicular IMFs (B Y or B Z ) causes the larger r 0, while the weaker magnetic pileup under the radial IMF leads to the smaller r 0. The difference in the IMF effect on the size of the Martian magnetic pileup boundary and the terrestrial magnetopause reveals different solar wind interactions with a magnetized and unmagnetized planet. Last, the location of the intense crustal field can also affect r 0 and the pressure balance condition, and the specific impact needs to be further studied.

Keywords: mars; interplanetary magnetic fields; planetary magnetospheres; solar wind
Deciphering Solar Coronal Heating: Energizing Small-scale Loops through Surface Convection

The solar atmosphere is filled with clusters of hot small-scale loops commonly known as coronal bright points (CBPs). These ubiquitous structures stand out in the Sun by their strong X-ray and/or extreme-ultraviolet (EUV) emission for hours to days, which makes them a crucial piece when solving the solar coronal heating puzzle. In addition, they can be the source of coronal jets and small-scale filament eruptions. Here we present a novel 3D numerical model using the Bifrost code that explains the sustained CBP heating for several hours. We find that stochastic photospheric convective motions alone significantly stress the CBP magnetic field topology, leading to important Joule and viscous heating concentrated around the CBP's inner spine at a few megameters above the solar surface. We also detect continuous upflows with faint EUV signals resembling observational dark coronal jets and small-scale eruptions when Hα fibrils interact with the reconnection site. We validate our model by comparing simultaneous CBP observations from the Solar Dynamics Observatory (SDO) and the Swedish 1‑m Solar Telescope (SST) with observable diagnostics calculated from the numerical results for EUV wavelengths as well as for the Hα line using the Multi3D synthesis code. Additionally, we provide synthetic observables to be compared with Hinode, Solar Orbiter, and the Interface Region Imaging Spectrograph (IRIS). Our results constitute a step forward in the understanding of the many different facets of the solar coronal heating problem.

Keywords: magnetohydrodynamics; computational methods; observational astronomy; solar atmosphere; solar chromosphere; solar corona
Magnetospheric Multiscale Mission Observations of Lower-hybrid Drift Waves in Terrestrial Magnetotail Reconnection with Moderate Guide Field and Asymmetric Plasma Density

Utilizing high-resolution data from the Magnetospheric Multiscale mission, we present new observations of lower-hybrid drift waves (LHDWs) in terrestrial magnetotail reconnection with guide field levels of ~70% and asymmetric plasma density (N high/N low ~ 2.5). The LHDWs, driven by lower-hybrid drift instability, were observed in correlation with magnetic field and density gradients at separatrices on both sides of the reconnection current sheet. The properties of the LHDWs at both sides of the separatrices are different: (1) At high-density side separatrices, the LHDWs with wavelength kρ e ~ 0.41 propagated away from the X-line mainly in the L-M plane; (2) at the low-density side separatrices, the LHDWs with wavelengths kρ e ~ 0.76 and kρ e ~ 0.35 propagated mainly along the outflow direction and current sheet normal. It is also found that the perpendicular magnetic field fluctuations were comparable to the parallel component. Wave potential of the LHDWs was 20% ~ 35% of the electron temperature. The LHDWs contributed to electron demagnetization and energy dissipation. Our study can promote understanding of properties of LHDWs during magnetic reconnection.

Keywords: space plasmas; solar magnetic reconnection
From Feast to Famine: A Systematic Study of Accretion onto Oblique Pulsars with 3D GRMHD Simulations

Disk-fed accretion onto neutron stars can power a wide range of astrophysical sources ranging from X-ray binaries, to accretion-powered millisecond pulsars, ultraluminous X-ray sources, and gamma-ray bursts. A crucial parameter controlling the gas-magnetosphere interaction is the strength of the stellar dipole. In addition, coherent X-ray pulsations in many neutron star systems indicate that the star's dipole moment is oblique relative to its rotation axis. Therefore, it is critical to systematically explore the 2D parameter space of the star's magnetic field strength and obliquity, which is what this work does, for the first time, in the framework of 3D general-relativistic magnetohydrodynamics. If the accretion disk carries its own vertical magnetic field, this introduces an additional factor: the relative polarity of the disk and stellar magnetic fields. We find that depending on the strength of the stellar dipole and the star-disk relative polarity, the neutron star's jet power can either increase or decrease with increasing obliquity. For weak dipole strength (equivalently, high accretion rate), the parallel polarity results in a positive correlation between jet power and obliquity, whereas the antiparallel orientation displays the opposite trend. For stronger dipoles, the relative-polarity effect disappears, and jet power always decreases with increasing obliquity. The influence of the relative polarity gradually disappears as obliquity increases. Highly oblique pulsars tend to have an increased magnetospheric radius, a lower mass accretion rate, and enter the propeller regime at lower magnetic moments than aligned stars.

Keywords: neutron stars; pulsars; general relativity; magnetohydrodynamical simulations
Revealing the Spectral State Transition of the Clocked Burster, GS 1826-238, with NuSTAR StrayCats

We present the long-term analysis of GS 1826-238, a neutron star X-ray binary known as the Clocked Burster, using data from NuSTAR StrayCats. StrayCats, a catalog of NuSTAR stray light data, contains data from bright, off-axis X-ray sources that have not been focused by the NuSTAR optics. We obtained stray light observations of the source from 2014-2021, reduced and analyzed the data using nustar-gen-utils Python tools, demonstrating the transition of the source from the island atoll state to a banana branch. We also present the light-curve analysis of Type I X-ray bursts from the Clocked Burster and show that the bursts from the banana/soft state are systematically shorter in duration than those from the island/hard state and have a higher burst fluence. From our analysis, we note an increase in the mass accretion rate of the source, and a decrease in burst frequency with the transition.

Keywords: neutron stars; compact objects; low-mass x-ray binary stars; x-ray astronomy
Retrieving C and O Abundance of HR 8799 c by Combining High- and Low-resolution Data

The formation and evolution pathway for the directly imaged multiplanetary system HR 8799 remains mysterious. Accurate constraints on the chemical composition of the planetary atmosphere(s) are key to solving the mystery. We perform a detailed atmospheric retrieval on HR 8799 c to infer the chemical abundances and abundance ratios using a combination of photometric data along with low- and high-resolution spectroscopic data (R ~ 20-35,000). We specifically retrieve [C/H], [O/H], and C/O and find them to be ${0.55}_{-0.39}^{+0.36}$ , ${0.47}_{-0.32}^{+0.31}$ , and ${0.67}_{-0.15}^{+0.12}$ at 68% confidence. The superstellar C and O abundances, yet a stellar C/O ratio, reveal a potential formation pathway for HR 8799 c. Planet c, and likely the other gas giant planets in the system, formed early on (likely within ~1 Myr), followed by further atmospheric enrichment in C and O through the accretion of solids beyond the CO ice line. The enrichment either preceded or took place during the early phase of the inward migration to the current planet locations.

Keywords: exoplanet atmospheres
The Sparse Atmospheric Model Sampling Analysis (SAMOSA) Intercomparison: Motivations and Protocol Version 1.0: A CUISINES Model Intercomparison Project

Planets in synchronous rotation around low-mass stars are the most salient targets for current ground- and space-based missions to observe and characterize. Such model calculations can help to prioritize targets for observation with current and future missions; however, intrinsic differences in the complexity and physical parameterizations of various models can lead to different predictions of a planet's climate state. Understanding model differences is necessary if such models are to guide target selection and aid in the analysis of observations. This paper presents a protocol to intercompare models of a hypothetical planet with a 15-day synchronous rotation period around a 3000 K blackbody star across a parameter space of surface pressure and incident instellation. We conduct a sparse sample of 16 cases from a previously published exploration of this parameter space with the ExoPlaSim model. By selecting particular cases across this broad parameter space, the SAMOSA intercomparison will identify areas where simpler models are sufficient, as well as areas where more complex GCMs are required. Our preliminary comparison using ExoCAM shows general consistency between the climate state predicted by ExoCAM and ExoPlaSim except in regions of the parameter space most likely to be in a steam atmosphere or incipient runaway greenhouse state. We use this preliminary analysis to define several options for participation in the intercomparison by models of all levels of complexity. The participation of other GCMs is crucial to understand how the atmospheric states across this parameter space differ with model capabilities.

Keywords: exoplanet atmospheres; planetary climates; planetary atmospheres
YunMa: Enabling Spectral Retrievals of Exoplanetary Clouds

In this paper, we present YunMa, an exoplanet cloud simulation and retrieval package, which enables the study of cloud microphysics and radiative properties in exoplanetary atmospheres. YunMa simulates the vertical distribution and sizes of cloud particles and their corresponding scattering signature in transit spectra. We validated YunMa against results from the literature. When coupled to the TauREx 3 platform, an open Bayesian framework for spectral retrievals, YunMa enables the retrieval of the cloud properties and parameters from transit spectra of exoplanets. The sedimentation efficiency (f sed), which controls the cloud microphysics, is set as a free parameter in retrievals. We assess the retrieval performances of YunMa through 28 instances of a K2-18 b-like atmosphere with different fractions of H2/He and N2, and assuming water clouds. Our results show a substantial improvement in retrieval performances when using YunMa instead of a simple opaque cloud model and highlight the need to include cloud radiative transfer and microphysics to interpret the next-generation data for exoplanet atmospheres. This work also inspires instrumental development for future flagships by demonstrating retrieval performances with different data quality.

Keywords: exoplanets; atmospheric clouds; exoplanet atmospheres; transmission spectroscopy
Dynamical Stellar Mass-to-light Ratio Gradients: Evidence for Very Centrally Concentrated IMF Variations in ETGs?

Evidence from different probes of the stellar initial mass function (IMF) of massive early-type galaxies (ETGs) has repeatedly converged on IMFs more bottom heavy than in the Milky Way (MW). This consensus has come under scrutiny due to often contradictory results from different methods on the level of individual galaxies. In particular, a number of strong lensing probes are ostensibly incompatible with a non-MW IMF. Radial gradients of the IMF-related to gradients of the stellar mass-to-light ratio ϒ-can potentially resolve this issue. We construct Schwarzschild models allowing for ϒ-gradients in seven massive ETGs with MUSE and SINFONI observations. We find dynamical evidence that ϒ increases toward the center for all ETGs. The gradients are confined to subkiloparsec scales. Our results suggest that constant-ϒ models may overestimate the stellar mass of galaxies by up to a factor of 1.5. For all except one galaxy, we find a radius where the total dynamical mass has a minimum. This minimum places the strongest constraints on the IMF outside the center and appears at roughly 1 kpc. We consider the IMF at this radius characteristic for the main body of each ETG. In terms of the IMF mass-normalization α relative to a Kroupa IMF, we find on average an MW-like IMF <α main> = 1.03 ± 0.19. In the centers, we find concentrated regions with increased mass normalizations that are less extreme than previous studies suggested, but still point to a Salpeter-like IMF, <α cen> = 1.54 ± 0.15.

Keywords: galaxy evolution; early-type galaxies; galaxy dynamics; galaxy kinematics; supermassive black holes; mass-to-light ratio; stellar mass functions
Observations of the Crab Nebula and Pulsar with the Large-sized Telescope Prototype of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a next-generation ground-based observatory for gamma-ray astronomy at very high energies. The Large-Sized Telescope prototype (LST-1) is located at the CTA-North site, on the Canary Island of La Palma. LSTs are designed to provide optimal performance in the lowest part of the energy range covered by CTA, down to ≃20 GeV. LST-1 started performing astronomical observations in 2019 November, during its commissioning phase, and it has been taking data ever since. We present the first LST-1 observations of the Crab Nebula, the standard candle of very-high-energy gamma-ray astronomy, and use them, together with simulations, to assess the performance of the telescope. LST-1 has reached the expected performance during its commissioning period-only a minor adjustment of the preexisting simulations was needed to match the telescope's behavior. The energy threshold at trigger level is around 20 GeV, rising to ≃30 GeV after data analysis. Performance parameters depend strongly on energy, and on the strength of the gamma-ray selection cuts in the analysis: angular resolution ranges from 0.°12-0.°40, and energy resolution from 15%-50%. Flux sensitivity is around 1.1% of the Crab Nebula flux above 250 GeV for a 50 hr observation (12% for 30 minutes). The spectral energy distribution (in the 0.03-30 TeV range) and the light curve obtained for the Crab Nebula agree with previous measurements, considering statistical and systematic uncertainties. A clear periodic signal is also detected from the pulsar at the center of the Nebula.

Keywords: gamma-ray astronomy; gamma-ray sources; astronomy data analysis; pulsar wind nebulae; pulsars
Constraints on Circumgalactic Media from Sunyaev-Zel'dovich Effects and X-Ray Data

We use observational measurements of thermal and kinetic Sunyaev-Zel'dovich effects, as well as soft X-ray emission associated with galaxy groups, to constrain the gas density and temperature in the circumgalactic medium for dark matter halos with masses above 1012.5 M⊙. A number of generic models are used together with a Bayesian scheme to make model inferences. We find that gas with a single temperature component cannot provide a consistent model to match the observational data. A simple two-phase model assuming a hot component and an ionized warm component can accommodate all three observations. The total amount of the gas in individual halos is inferred to be comparable to the universal baryon fraction corresponding to the halo mass. The inferred temperature of the hot component is comparable to the halo virial temperature. The fraction of the hot component increases from (15-40)% for 1012.5M⊙ halos to (40-60)% for 1014.5M⊙ halos, where the ranges reflect uncertainties in the assumed gas density profile. Our results suggest that a significant fraction of the halo gas is in a nonthermalized component with the temperature much lower than the virial temperature.

Keywords: sunyaev-zeldovich effect; bayesian statistics; galaxy formation; galaxy evolution; circumgalactic medium
Stacked Periodograms as a Probe of Exoplanetary Populations

Ongoing, extreme-precision Doppler radial-velocity (RV) surveys seek planets with masses less than several M ⊕; population-level studies to determine the distribution of planetary masses, however, remain difficult due to the required observational time investment, as well as challenges associated with robustly detecting the lowest-mass planets. We outline a novel approach that leverages extensive, existing RV data sets to constrain masses of exoplanet populations: stacking periodograms of RV time series across many targets. We show that an exoplanet population may be statistically identifiable in the stacked periodogram, even when individual planets do not pass the threshold of detection. We discuss analytical, statistical properties of the stacked periodogram, perform simulations to demonstrate the efficacy of the method, and investigate the influence of semistructured window functions and stellar activity. Analysis of the Lick-Carnegie Exoplanet Survey data set reveals a marginally significant (1.6σ) signal consistent with a population of exoplanets occupying 3-7 days periods with typical K between 1.6-5.1 m s-1. More detailed investigation of signals associated with stellar activity and yearly systematics may be necessary to confirm this result or detect other underlying Keplerian contributions.

Keywords: exoplanet detection methods; radial velocity; lomb-scargle periodogram
Long-timescale X-Ray Variability of BAL and Mini-BAL Quasars

We investigated the rest-frame ≈0.1-5 yr X-ray variability properties of an unbiased and uniformly selected sample of 24 broad absorption line (BAL) and 35 mini-BAL quasars, making it the largest representative sample used to investigate such variability. We find that the distributions of X-ray variability amplitudes of these quasar populations are statistically similar to that of non-BAL, radio-quiet (typical) quasars.

Keywords: quasars; broad-absorption line quasar; x-ray quasars
Exploring TeV Candidates of Fermi Blazars through Machine Learning

In this work, we make use of a supervised machine-learning algorithm based on Logistic Regression (LR) to select TeV blazar candidates from the 4FGL-DR2/4LAC-DR2, 3FHL, 3HSP, and 2BIGB catalogs. LR constructs a hyperplane based on a selection of optimal parameters, named features, and hyperparameters whose values control the learning process and determine the values of features that a learning algorithm ends up learning, to discriminate TeV blazars from non-TeV blazars. In addition, it gives the probability (or logistic) that a source may be considered a TeV blazar candidate. Non-TeV blazars with logistics greater than 80% are considered high-confidence TeV candidates. Using this technique, we identify 40 high-confidence TeV candidates from the 4FGL-DR2/4LAC-DR2 blazars and we build the feature hyperplane to distinguish TeV and non-TeV blazars. We also calculate the hyperplanes for the 3FHL, 3HSP, and 2BIGB. Finally, we construct the broadband spectral energy distributions for the 40 candidates, testing for their detectability with various instruments. We find that seven of them are likely to be detected by existing or upcoming IACT observatories, while one could be observed with extensive air shower particle detector arrays.

Keywords: blazars
Full Velocities and Propagation Directions of Coronal Mass Ejections Inferred from Simultaneous Full-disk Imaging and Sun-as-a-star Spectroscopic Observations

Coronal mass ejections (CMEs) are violent ejections of magnetized plasma from the Sun that can trigger geomagnetic storms, endanger satellite operations, and destroy electrical infrastructures on the Earth. After systematically searching Sun-as-a-star spectra observed by the Extreme Ultraviolet Variability Experiment on board the Solar Dynamics Observatory (SDO) from 2010 May to 2022 May, we identified eight CMEs associated with flares and filament eruptions by analyzing the blue-wing asymmetry of the O III 52.58 nm line profiles. Combined with images simultaneously taken by the 30.4 nm channel of the Atmospheric Imaging Assembly on board SDO, the full velocity and propagation direction for each of the eight CMEs are derived. We find a strong correlation between geomagnetic indices (Kp and Dst) and the angle between the CME propagation direction and the Sun-Earth line, suggesting that Sun-as-a-star spectroscopic observations at extreme-ultraviolet wavelengths can potentially help to improve the prediction accuracy of the geoeffectiveness of CMEs. Moreover, an analysis of synthesized long-exposure Sun-as-a-star spectra implies that it is possible to detect CMEs from other stars through blue-wing asymmetries or blueshifts of spectral lines.

Keywords: solar coronal mass ejections; stellar coronal mass ejections; solar filament eruptions; spectroscopy; space weather