adsabs/SciX_UAT_keywords huggingface dataset:
The Effects of Three-dimensional Radiative Transfer on the Resonance Polarization of the Ca I 4227 Å Line

The sizable linear polarization signals produced by the scattering of anisotropic radiation in the core of the Ca I 4227 Å line constitute an important observable for probing the inhomogeneous and dynamic plasma of the lower solar chromosphere. Here we show the results of a three-dimensional (3D) radiative transfer complete frequency redistribution investigation of the line's scattering polarization in a magnetohydrodynamical 3D model of the solar atmosphere. We take into account not only the Hanle effect produced by the model's magnetic field but also the symmetry breaking caused by the horizontal inhomogeneities and macroscopic velocity gradients. The spatial gradients of the horizontal components of the macroscopic velocities produce very significant forward scattering polarization signals without the need of magnetic fields, while the Hanle effect tends to depolarize them at the locations where the model's magnetic field is stronger than about 5 G. The standard 1.5D approximation is found to be unsuitable for understanding the line's scattering polarization, but we introduce a novel improvement to this approximation that produces results in qualitative agreement with the full 3D results. The instrumental degradation of the calculated polarization signals is also investigated, showing what we can expect to observe with the Visible Spectro-Polarimeter at the upcoming Daniel K. Inouye Solar Telescope.

Keywords: radiative transfer; quiet solar chromosphere; spectropolarimetry
A Quasi-linear Diffusion Model for Resonant Wave-Particle Instability in Homogeneous Plasma

In this paper, we develop a model to describe the generalized wave-particle instability in a quasi-neutral plasma. We analyze the quasi-linear diffusion equation for particles by expressing an arbitrary unstable and resonant wave mode as a Gaussian wave packet, allowing for an arbitrary direction of propagation with respect to the background magnetic field. We show that the localized energy density of the Gaussian wave packet determines the velocity-space range in which the dominant wave-particle instability and counteracting damping contributions are effective. Moreover, we derive a relation describing the diffusive trajectories of resonant particles in velocity space under the action of such an interplay between the wave-particle instability and damping. For the numerical computation of our theoretical model, we develop a mathematical approach based on the Crank-Nicolson scheme to solve the full quasi-linear diffusion equation. Our numerical analysis solves the time evolution of the velocity distribution function under the action of a dominant wave-particle instability and counteracting damping and shows a good agreement with our theoretical description. As an application, we use our model to study the oblique fast-magnetosonic/whistler instability, which is proposed as a scattering mechanism for strahl electrons in the solar wind. In addition, we numerically solve the full Fokker-Planck equation to compute the time evolution of the electron-strahl distribution function under the action of Coulomb collisions with core electrons and protons after the collisionless action of the oblique fast-magnetosonic/whistler instability.

Keywords: space plasmas; solar wind; plasma astrophysics
Origin and Extent of the Opacity Challenge for Atmospheric Retrievals of WASP-39 b

As the James Webb Space Telescope (JWST) came online last summer, we entered a new era of astronomy. This new era is supported by data products of unprecedented information content that require novel reduction and analysis techniques. Recently, Niraula et al. (N22) highlighted the need for upgraded opacity models to prevent facing a model-driven accuracy wall when interpreting exoplanet transmission spectra. Here, we follow the same approach as N22 to explore the sensitivity of inferences on the atmospheric properties of WASP-39 b to the opacity models used. We find that the retrieval of the main atmospheric properties from this first JWST exoplanet spectrum is mostly unaffected by the current state of the community's opacity models. Abundances of strong opacity sources like water and carbon dioxide are reliably constrained within ~0.30 dex, beyond the 0.50 dex accuracy wall reported in N22. Assuming the completeness and accuracy of line lists, N22's accuracy wall is primarily driven by model uncertainties on broadening coefficients and far-wing behaviors, which we find to have marginal consequences for interpreting the transmission spectra of large, hot, high-metallicity atmospheres such as WASP-39 b, in opposition to emission spectra and climate modeling, which depend on deeper parts of a planetary atmosphere. The origin of the opacity challenge in the retrieval of metal-rich hot Jupiters via transmission spectroscopy will thus mostly stem from the incompleteness and inaccuracy of line lists.

Keywords: transmission spectroscopy; exoplanet atmospheric composition; exoplanet atmospheres
Free Core Nutation and Its Relation to the Spin-over Mode

The time-varying response of Earth's and other planets' rotation to external gravitational torques depends strongly on their internal structure. In particular, the existence of the mode known as the free core nutation in the fluid core is known to amplify the forced nutations in the near-diurnal retrograde frequency band (as measured in the planetary frame of reference). Due to their proximity in shape and frequency, this mode is sometimes equated with the so-called spin-over mode, which denotes the free oscillation of a steadily rotating ellipsoidal fluid core. Through a careful study of the freely rotating two-layer planetary model with a rigid mantle and an inviscid fluid core, we show that the spin-over mode frequency corresponds to that where the sum of the external and internal torques on the mantle is balanced, causing it to rotate steadily. The presence of dissipation at the core-mantle boundary causes the free core nutation to become damped and slightly offsets its resonance frequency. We show that this offset, which is ≈-1 day for Earth, can be interpreted as the result of the proximity of the free core nutation frequency to that of the spin-over mode, which now corresponds to a minimum in the magnitude of the transfer function for nutations. We also show how this proximity leads to a slightly lower quality factor for the resonance than that computed from the usual formula. We conclude by discussing possible implications of this mechanism for Mars, the Moon, and the long-term evolution of Earth.

Keywords: earth (planet); solar system; mars; the moon; geodesics; lunar geodesy
Rotation of Low-mass Stars in Upper Centaurus-Lupus and Lower Centaurus-Crux with TESS

We present stellar rotation rates derived from Transiting Exoplanet Survey Satellite (TESS) light curves for stars in Upper Centaurus-Lupus (UCL; ~136 pc, ~16 Myr) and Lower Centaurus-Crux (LCC; ~115 pc, ~17 Myr). We find spot-modulated periods (P) for ~90% of members. The range of light-curve and periodogram shapes echoes that found for other clusters with K2, but fewer multiperiod stars may be an indication of the different noise characteristics of TESS, or a result of the source selection methods here. The distribution of P as a function of color as a proxy for mass fits nicely in between that for both older and younger clusters observed by K2, with fast rotators being found among both the highest and lowest masses probed here, and a well-organized distribution of M-star rotation rates. About 13% of the stars have an infrared excess, suggesting a circumstellar disk; this is well matched to expectations, given the age of the stars. There is an obvious pileup of disked M stars at P ~ 2 days, and the pileup may move to shorter P as the mass decreases. There is also a strong concentration of disk-free M stars at P ~ 2 days, hinting that perhaps these stars have recently freed themselves from their disks. Exploring the rotation rates of stars in UCL/LCC has the potential to help us understand the beginning of the end of the influence of disks on rotation, and the timescale on which stars respond to unlocking.

Keywords: stellar rotation; stellar associations; low mass stars
Barred Galaxies in the IllustrisTNG Simulation

Almost two-thirds of disk galaxies in the local universe host bars, which serve as important drivers of secular evolutionary processes. While cosmological simulations are powerful tools to study the formation and evolution of galaxies, they have often struggled to generate reasonable bar populations. We measure the fraction, size, and strength of bars in 3866 disk galaxies from the TNG100 run of the advanced cosmological simulation IllustrisTNG. Consistent with observations, about 55% of disk galaxies with stellar mass ${M}_{* }\approx {10}^{10.6}\,{M}_{\odot }$ are barred, and the relation between bar size and total stellar mass is similar to that found in near-infrared surveys. However, the formation of bars is suppressed in galaxies with ${M}_{* }\lt {10}^{10.6}\,{M}_{\odot }$ , which may result from the difficulty TNG100 has in resolving short bars with radius $\lt 1.4\,\mathrm{kpc}$ . In contrast, up to 75% of massive disk galaxies with ${M}_{* }\gt {10}^{10.6}\,{M}_{\odot }$ have bars, ∼10%-20% higher than observed. TNG100 overproduces relatively short bars (radius ∼1.4-3 kpc) with respect to the mass-bar size relation observed in near-infrared surveys. Tracing the progenitors of z = 0 massive galaxies we find that the bar fraction increases from 25% to 63% between z = 1 and 0. Instead if we select all disk galaxies during z = 0-1 with a constant mass cut of ${M}_{* }\geqslant {10}^{10.6}\,{M}_{\odot }$ we find that the bar fraction is a nearly constant 60%.

Keywords: barred spiral galaxies; astronomical simulations
KMT-2019-BLG-0842Lb: A Cold Planet below the Uranus/Sun Mass Ratio

We report the discovery of a cold planet with a very low planet/host mass ratio of q = (4.09 ± 0.27) × 10-5, which is similar to the ratio of Uranus/Sun (q = 4.37 × 10-5) in the solar system. The Bayesian estimates for the host mass, planet mass, system distance, and planet-host projected separation are Mhost = 0.76 ± 0.40M⊙, Mplanet = 10.3 ± 5.5M⊕, DL = 3.3 ± 1.3 kpc, and a⊥ = 3.3 ± 1.4 au, respectively. The consistency of the color and brightness expected from the estimated lens mass and distance with those of the blend suggests the possibility that the most blended light comes from the planet host, and this hypothesis can be established if high-resolution images are taken during the next (2020) bulge season. We discuss the importance of conducting optimized photometry and aggressive follow-up observations for moderately or very high magnification events to maximize the detection rate of planets with very low mass ratios.

Keywords: gravitational microlensing; gravitational microlensing exoplanet detection
Probing Cosmic Reionization and Molecular Gas Growth with TIME

Line intensity mapping (LIM) provides a unique and powerful means to probe cosmic structures by measuring the aggregate line emission from all galaxies across redshift. The method is complementary to conventional galaxy redshift surveys that are object based and demand exquisite point-source sensitivity. The Tomographic Ionized-carbon Mapping Experiment (TIME) will measure the star formation rate during cosmic reionization by observing the redshifted [C II] 158 μm line (6 ≲ z ≲ 9) in the LIM regime. TIME will simultaneously study the abundance of molecular gas during the era of peak star formation by observing the rotational CO lines emitted by galaxies at 0.5 ≲ z ≲ 2. We present the modeling framework that predicts the constraining power of TIME on a number of observables, including the line luminosity function and the auto- and cross-correlation power spectra, including synergies with external galaxy tracers. Based on an optimized survey strategy and fiducial model parameters informed by existing observations, we forecast constraints on physical quantities relevant to reionization and galaxy evolution, such as the escape fraction of ionizing photons during reionization, the faint-end slope of the galaxy luminosity function at high redshift, and the cosmic molecular gas density at cosmic noon. We discuss how these constraints can advance our understanding of cosmological galaxy evolution at the two distinct cosmic epochs for TIME, starting in 2021, and how they could be improved in future phases of the experiment.

Keywords: reionization; interstellar medium; molecular gas; large-scale structure of the universe; observational cosmology; high-redshift galaxies
Zwicky Transient Facility and Globular Clusters: The Period-Luminosity and Period-Wesenheit Relations for Type II Cepheids

We present the first gri-band period-luminosity (PL) and period-Wesenheit (PW) relations for 37 Type II Cepheids (TIICs) located in 18 globular clusters based on photometric data from the Zwicky Transient Facility. We also updated BVIJHK-band absolute magnitudes for 58 TIICs in 24 globular clusters using the latest homogeneous distances to the globular clusters. The slopes of g/r/i- and B/V/I-band PL relations are found to be statistically consistent when using the same sample of distance and reddening. We employed the calibration of ri-band PL/PW relations in globular clusters to estimate a distance to M31 based on a sample of ~270 TIICs from the PAndromeda project. The distance modulus to M31, obtained using calibrated ri-band PW relation, agrees well with the recent determination based on classical Cepheids. However, distance moduli derived using the calibrated r- and i-band PL relations are systematically smaller by ~0.2 mag, suggesting there are possible additional systematic errors on the PL relations. Finally, we also derive the period-color (PC) relations and for the first time the period-Q-index (PQ) relations, where the Q-index is reddening free, for our sample of TIICs. The PC relations based on (r - i) and near-infrared colors and the PQ relations are found to be relatively independent of the pulsation periods.

Keywords: type ii cepheid variable stars; globular star clusters; distance indicators; sky surveys; wide-field telescopes
Dissecting the Crab Nebula with JWST: Pulsar Wind, Dusty Filaments, and Ni/Fe Abundance Constraints on the Explosion Mechanism

We present JWST observations of the Crab Nebula, the iconic remnant of the historical SN 1054. The observations include NIRCam and MIRI imaging mosaics plus MIRI/MRS spectra that probe two select locations within the ejecta filaments. We derive a high-resolution map of dust emission and show that the grains are concentrated in the innermost, high-density filaments. These dense filaments coincide with multiple synchrotron bays around the periphery of the Crab's pulsar wind nebula (PWN). We measure synchrotron spectral index changes in small-scale features within the PWN's torus region, including the well-known knot and wisp structures. The index variations are consistent with Doppler boosting of emission from particles with a broken power-law distribution, providing the first direct evidence that the curvature in the particle injection spectrum is tied to the acceleration mechanism at the termination shock. We detect multiple nickel and iron lines in the ejecta filaments and use photoionization models to derive nickel-to-iron abundance ratios that are a factor of 3–8 higher than the solar ratio. We also find that the previously reported order-of-magnitude higher Ni/Fe values from optical data are consistent with the lower values from JWST when we reanalyze the optical emission using updated atomic data and account for local extinction from dust. We discuss the implications of our results for understanding the nature of the explosion that produced the Crab Nebula and conclude that the observational properties are most consistent with a low-mass Fe core-collapse supernova, even though an electron-capture explosion cannot be ruled out.

Keywords: supernova remnants; pulsar wind nebulae; pulsars; supernovae; core-collapse supernovae
Synthesis of the 4400-4600 Å Spectral Range for the A2.5V star HD 176687 (ζ Sagitarii A)

The synthesis of a high resolution high signal-to-noise spectrum of HD 176687 from 4400 to 4600 Å allows the determination of LTE abundances for magnesium, calcium, scandium, titanium, chromium, iron, nickel and barium. This A2.5V star has recently been found to be the most massive star in a triple system. Magnesium and calcium are found to have a solar abundance. Scandium and titanium are depleted by a factor of 0.50, chromium, nickel by a factor of 0.70 and iron by 0.60 compared to their respective solar abundances. Barium is overabundant by a factor of 7.50. The found abundances fit well within the abundance pattern previously found for a few normal A stars. There is no sign of the recently discovered companion to HD 176687 in the spectrum analyzed.

Keywords: a stars
From the Fermi Blazar Sequence to the Relation between Fermi Blazars and γ-Ray Narrow-line Seyfert 1 Galaxies

We use the third catalog of blazars detected by Fermi/LAT (3LAC) and γ-ray narrow-line Seyfert 1 Galaxies (γ-NLSy1s) to study the blazar sequence and relationship between them. Our results are as follows. (i) There is a weak anticorrelation between synchrotron peak frequency and peak luminosity for both Fermi blazars and γ-NLSy1s, which supports the blazar sequence. However, after Doppler correction, the inverse correlation disappeared, which suggests that anticorrelation between synchrotron peak frequency and peak luminosity is affected by the beaming effect. (ii) There is a significant anticorrelation between jet kinetic power and synchrotron peak frequency for both Fermi blazars and γ-NLSy1s, which suggests that the γ-NLSy1s could fit well into the original blazar sequence. (iii) According to previous work, the relationship between synchrotron peak frequency and synchrotron curvature can be explained by statistical or stochastic acceleration mechanisms. There are significant correlations between synchrotron peak frequency and synchrotron curvature for whole sample, Fermi blazars and BL Lac objects, respectively. The slopes of the correlation are consistent with statistical acceleration. For FSRQs, LBLs, IBLs, HBLs, and γ-NLS1s, we also find a significant correlation, but in these cases the slopes cannot be explained by previous theoretical models. (iv) The slope of the relation between synchrotron peak frequency and synchrotron curvature in γ-NLS1s is larger than that of FSRQs and BL Lac objects. This result may imply that the cooling dominates over the acceleration process for FSRQs and BL Lac objects, while γ-NLS1s is the opposite.

Keywords: active galactic nuclei; blazars; seyfert galaxies
The Streaming Instability Cannot Form Planetesimals from Millimeter-size Grains in Pressure Bumps

We present evidence that it is unlikely that the streaming instability (SI) can form planetesimals from millimeter grains inside axisymmetric pressure bumps. We conducted the largest simulation of the SI so far (7 million CPU hours), consisting of a large slice of the disk with millimeter grains, a solar-like dust-to-gas ratio (Z = 0.01), and the largest pressure bump that does not cause gravitational instability (GI) in the particle layer. We used a high resolution of 1000/H to resolve as many SI unstable modes as possible. The simulation produced a long-lived particle overdensity far exceeding the SI criteria (i.e., a critical solid abundance to headwind parameter ratio Z/Π) where strong clumping would occur if these conditions were present over an extended region of the disk; yet we observed none. The likely reason is that the time it takes particles to cross the high-Z/Π region (t cross) is shorter than the growth timescale of the SI (t grow). We propose an added criterion for planetesimal formation by the SI-that t cross > t grow. We show that any bump larger than the one in this run would form planetesimals by the GI instead of the SI. Our results significantly restrict the pathways to planet formation: either protoplanetary disks regularly form grains larger than 1 mm, or planetesimals do not form by the SI in axisymmetric pressure bumps. Since bumps large enough to induce the GI are likely Rossby-wave unstable, we propose that millimeter grains may only form planetesimals in vortices.

Keywords: planet formation; planetesimals
Dust Coagulation in Oxygen-rich Circumstellar Outflows

We show that the inefficient growth of SiO molecules on (SiO) x dust grains prolongs the period of maximum dust nucleation in circumstellar outflows resulting in a several orders-of-magnitude increase in the dust density near the star. This increase in dust density powers dust coagulation and results in the formation of large fractal aggregates that should be extremely efficient per unit mass in coupling to both the stellar radiation field and to the ambient gas.

Keywords: circumstellar dust; stellar winds
Observation of Anomalous Electron Fluxes Induced by GRB221009A on CSES-01 Low-energy Charged Particle Detector

High-energy, long gamma-ray bursts (GRBs) can be generated by the core collapse of massive stars at the end of their lives. When they happen in the close-by universe they can be exceptionally bright, as seen from the Earth in the case of the recent, giant, long-lasting GRB221009A. GRB221009A was produced by a collapsing star with a redshift of 0.152: this event was observed by many gamma-ray space experiments, which also detected an extraordinary long gamma-ray afterglow. The exceptionally large fluence of the prompt emission of about 0.013 erg cm-2 illuminated a large geographical region centered on India and including Europe and Asia. We report in this paper the observation of sudden electron flux changes correlated with GRB221009A and measured by the HEPP-L charged particle detector on board the China Seismo-Electromagnetic Satellite, which was orbiting over Europe at the time of the GRB event. The time structure of the observed electron flux closely matches the very distinctive time dependence of the photon flux associated with the main part of the emission at around 13:20 UTC on 2022 October 9. To test the origin of these signals, we set up a simplified simulation of one HEPP-L subdetector: the results of this analysis suggest that the signals observed are mostly due to electrons created within the aluminum collimator surrounding the silicon detector, providing real-time monitoring of the very intense photon fluxes. We discuss the implications of this observation for existing and forthcoming particle detectors on low Earth orbits.

Keywords: particle astrophysics; gamma-ray bursts; astronomical detectors