adsabs/SciX_UAT_keywords huggingface dataset:
Impact of Differential Dust Settling on the SED and Polarization: Application to the Inner Region of the HL Tau Disk

The polarimetric observations of the protoplanetary disk around HL Tau have shown the scattering-induced polarization at ALMA Band 7, which indicates that the maximum dust size is ∼100 μm, while the spectral energy distribution (SED) has suggested that the maximum dust size is approximately a millimeter. To solve the contradiction, we investigate the impact of differential settling of dust grains on the SED and polarization. If the disk is optically thick, a longer observing wavelength traces more interior layers, which would be dominated by larger grains. We find that the SED of the center part of the HL Tau disk can be explained with millimeter-sized grains for a broad range of turbulence strength, while 160 μm-sized grains cannot be explained unless the turbulence strength parameter αt is lower than 10-5. We also find that the observed polarization fraction can be potentially explained with a maximum dust size of 1 mm if αt ≲ 10-5, although models with 160 μm-sized grains are also acceptable. However, if the maximum dust size is ∼3 mm, the simulated polarization fraction is too low to explain the observations even if the turbulence strength is extremely small, indicating a maximum dust size of ≲1 mm. The degeneracy between 100 μm- and millimeter-sized grains can be solved by improving the ALMA calibration accuracy or polarimetric observations at (sub)centimeter wavelengths.

Keywords: protoplanetary disks; planet formation
Advanced γ-Ray Emission Studies of G15.4+0.1 with Fermi-LAT: Evidence of Escaping Cosmic Rays Interacting with Surrounding Molecular Clouds

We present an analysis of γ-ray emission in the direction of supernova remnant (SNR) G15.4+0.1 with 13 yr Fermi Large Area Telescope data. There are three point-like GeV sources in this region: one is spatially coincident with the TeV source HESS J1818-154 and is interpreted as the counterpart of HESS J1818-154. Its γ-ray spectrum can be well fitted by a single power law with an index of 2.3. The other two sources with log-parabola spectra are spatially coincident with dense regions of surrounding molecular clouds revealed by CO observations. Their γ-ray emission originates from hadronic π 0 decay due to inelastic collisions between nuclei in the clouds and cosmic rays accelerated in and escaping from SNR G15.4+0.1. The total energy of the escaping protons is about 1048 erg, assuming a point-like instantaneous injection. However, the inferred diffusion coefficients are lower than the typical Galactic value.

Keywords: gamma-ray sources; gamma-ray astronomy; supernova remnants
Binary Vision: The Mass Distribution of Merging Binary Black Holes via Iterative Density Estimation

Binary black hole (BBH) systems detected via gravitational-wave emission are a recently opened astrophysical frontier with many unknowns and uncertainties. Accurate reconstruction of the binary distribution with as few assumptions as possible is desirable for inference of formation channels and environments. Most population analyses have, though, assumed a power law in binary mass ratio q, and/or assumed a universal q distribution regardless of primary mass. Methods based on kernel density estimation allow us to dispense with such assumptions and directly estimate the joint binary mass distribution. We deploy a self-consistent iterative method to estimate this full BBH mass distribution, finding local maxima in primary mass consistent with previous investigations and a secondary mass distribution with a partly independent structure, inconsistent both with a power law and with a constant function of q. We find a weaker preference for near-equal-mass binaries than in most previous investigations; instead, the secondary mass has its own "spectral lines" at slightly lower values than the primary, and we observe an anticorrelation between primary and secondary masses around the ~10 M ⊙ peak.

Keywords: gravitational waves
Signatures of Velocity-dependent Dark Matter Self-interactions in Milky Way-mass Halos

We explore the impact of elastic, anisotropic, velocity-dependent dark matter (DM) self-interactions on the host halo and subhalos of Milky Way (MW)-mass systems. We consider a generic self-interacting dark matter (SIDM) model parameterized by the masses of a light mediator and the DM particle. The ratio of these masses, w, sets the velocity scale above which momentum transfer due to DM self-interactions becomes inefficient. We perform high-resolution zoom-in simulations of an MW-mass halo for values of w that span scenarios in which self-interactions either between the host and its subhalos or only within subhalos efficiently transfer momentum, and we study the effects of self-interactions on the host halo and on the abundance, radial distribution, orbital dynamics, and density profiles of subhalos in each case. The abundance and properties of surviving subhalos are consistent with being determined primarily by subhalo-host halo interactions. In particular, subhalos on radial orbits in models with larger values of the cross section at the host halo velocity scale are more susceptible to tidal disruption owing to mass loss from ram pressure stripping caused by self-interactions with the host. This mechanism suppresses the abundance of surviving subhalos relative to collisionless DM simulations, with stronger suppression for larger values of w. Thus, probes of subhalo abundance around MW-mass hosts can be used to place upper limits on the self-interaction cross section at velocity scales of $\sim 200\ \mathrm{km}\,{{\rm{s}}}^{-1}$, and combining these measurements with the orbital properties and internal dynamics of subhalos may break degeneracies among velocity-dependent SIDM models.

Keywords: dark matter; milky way dark matter halo; galaxy abundances; computational methods
Wave Generation and Energetic Electron Scattering in Solar Flares

We conduct two-dimensional particle-in-cell simulations to investigate the scattering of electron heat flux by self-generated oblique electromagnetic waves. The heat flux is modeled as a bi-kappa distribution with a T ∥ > T ⊥ temperature anisotropy maintained by continuous injection at the boundaries. The anisotropic distribution excites oblique whistler waves and filamentary-like Weibel instabilities. Electron velocity distributions taken after the system has reached a steady state show that these instabilities inhibit the heat flux and drive the total distributions toward isotropy. Electron trajectories in velocity space show a circular-like diffusion along constant energy surfaces in the wave frame. The key parameter controlling the scattering rate is the average speed, or drift speed v d , of the heat flux compared with the electron Alfvén speed v Ae, with higher drift speeds producing stronger fluctuations and a more significant reduction of the heat flux. Reducing the density of the electrons carrying the heat flux by 50% does not significantly affect the scattering rate. A scaling law for the electron scattering rate versus v d /v Ae is deduced from the simulations. The implications of these results for understanding energetic electron transport during energy release in solar flares are discussed.

Keywords: active solar corona; plasma physics; solar coronal waves; solar flares
Hubble Space Telescope Transmission Spectroscopy for the Temperate Sub-Neptune TOI-270 d: A Possible Hydrogen-rich Atmosphere Containing Water Vapor

TOI-270 d is a temperate sub-Neptune discovered by the Transiting Exoplanet Survey Satellite (TESS) around a bright (J = 9.1 mag) M3V host star. With an approximate radius of 2 R ⊕ and equilibrium temperature of 350 K, TOI-270 d is one of the most promising small exoplanets for atmospheric characterization using transit spectroscopy. Here we present a primary transit observation of TOI-270 d made with the Hubble Space Telescope Wide Field Camera 3 (WFC3) spectrograph across the 1.126-1.644 μm wavelength range, and a 95% credible upper limit of 8.2 × 10-14 erg s-1 cm-2 Å-1 arcsec-2 for the stellar Lyα emission obtained using the Space Telescope Imaging Spectrograph. The transmission spectrum derived from the TESS and WFC3 data provides evidence for molecular absorption by a hydrogen-rich atmosphere at 4σ significance relative to a featureless spectrum. The strongest evidence for any individual absorber is obtained for H2O, which is favored at 3σ significance. When retrieving on the WFC3 data alone and allowing for the possibility of a heterogeneous stellar brightness profile, the detection significance of H2O is reduced to 2.8σ. Further observations are therefore required to robustly determine the atmospheric composition of TOI-270 d and assess the impact of stellar heterogeneity. If confirmed, our findings would make TOI-270 d one of the smallest and coolest exoplanets to date with detected atmospheric spectral features.

Keywords: exoplanet astronomy; exoplanet atmospheres; exoplanet atmospheric composition
Probing Interstellar Grain Growth through Polarimetry in the Taurus Cloud Complex

The optical and near-infrared (OIR) polarization of starlight is typically understood to arise from the dichroic extinction of that light by dust grains whose axes are aligned with respect to a local magnetic field. The size distribution of the aligned-grain population can be constrained by measurements of the wavelength dependence of the polarization. The leading physical model for producing the alignment is that of radiative alignment torques (RATs), which predicts that the most efficiently aligned grains are those with sizes larger than the wavelengths of light composing the local radiation field. Therefore, for a given grain-size distribution, the wavelength at which the polarization reaches a maximum ( ${\lambda }_{\max }$ ) should correlate with the characteristic reddening along the line of sight between the dust grains and the illumination source. A correlation between ${\lambda }_{\max }$ and reddening has been previously established for extinctions up to ${A}_{V}\approx 4$ mag. We extend the study of this relationship to a larger sample of stars in the Taurus cloud complex, including extinctions ${A}_{V}\gt 10$ mag. We confirm the earlier results for ${A}_{V}\lt 4$ mag but find that the ${\lambda }_{\max }$ versus AV relationship bifurcates above ${A}_{V}\approx 4$ mag, with part of the sample continuing the previously observed relationship. The remaining sample exhibits a steeper rise in ${\lambda }_{\max }$ versus AV. We propose that the data exhibiting the steep rise represent lines of sight of high-density "clumps," where grain coagulation has taken place. We present RAT-based modeling supporting these hypotheses. These results indicate that multiband OIR polarimetry is a powerful tool for tracing grain growth in molecular clouds, independent of uncertainties in the dust temperature and emissivity.

Keywords: starlight polarization; interstellar dust; polarimetry; spectropolarimetry; interstellar dust extinction; interstellar clouds; interstellar medium
The Encounter of the Parker Solar Probe and a Comet-like Object Near the Sun: Model Predictions and Measurements

The Parker Solar Probe (PSP) aims to explore the nascent solar wind close to the Sun. Meanwhile, PSP is also expected to encounter small objects like comets and asteroids. In this work, we survey the ephemerides to find the chance of a recent encounter and then model the interaction between released dusty plasmas and solar wind plasmas. On 2019 September 2, a comet-like object, the 322P/Solar and Heliosphere Observatory, just passed its perihelion flying to a heliocentric distance of 0.12 au and swept by PSP at a relative distance as close as 0.025 au. We present the dynamics of the dust particles released from 322P, forming a curved dust tail. Along the path of PSP in the simulated inner heliosphere, the states of plasma and magnetic field are sampled and illustrated, with the magnetic field sequences from simulation results being compared directly with the in situ measurements from PSP. Through the comparison, we suggest that 322P might be at a deficient activity level releasing limited dusty plasmas on its way to becoming a "rock comet." We also present images of solar wind streamers as recorded by the Wide-field Imager for Solar Probe Plus, showing an indication of dust bombardment for the images superposed with messy trails. We observe from the Large Angle and Spectrometric Coronagraph that 322P was transiting from a dimming region to a relatively bright streamer during its perihelion passage, and perform a simulation to confirm that 322P was flying from relatively faster to slower solar wind streams, modifying the local plasma states of the streams.

Keywords: solar wind; comet tails; interplanetary dust; asteroids
8.9 hr Rotation in the Partly Burnt Runaway Stellar Remnant LP 40-365 (GD 492)

We report the detection of 8.914 hr variability in both optical and ultraviolet light curves of LP 40-365 (also known as GD 492), the prototype for a class of partly burnt runaway stars that have been ejected from a binary due to a thermonuclear supernova event. We first detected this 1.0% amplitude variation in optical photometry collected by the Transiting Exoplanet Survey Satellite (TESS). Reanalysis of observations from the Hubble Space Telescope at the TESS period and ephemeris reveal a 5.8% variation in the ultraviolet of this 9800 K stellar remnant. We propose that this 8.914 hr photometric variation reveals the current surface rotation rate of LP 40-365, and is caused by some kind of surface inhomogeneity rotating in and out of view, though a lack of observed Zeeman splitting puts an upper limit on the magnetic field of <20 kG. We explore ways in which the present rotation period can constrain progenitor scenarios if angular momentum was mostly conserved, which suggests that the survivor LP 40-365 was not the donor star but was most likely the bound remnant of a mostly disrupted white dwarf that underwent advanced burning from an underluminous (Type Iax) supernova.

Keywords: supernova remnants; white dwarf stars; stellar rotation
Evolution of Magnetic Field of the Quasar 1604+159 at parsec Scale

We have analyzed the total intensity, spectral index, linear polarization, and rotation measure (RM) distributions at the parsec scale for the quasar 1604+159. The source was observed at 5.0, 8.4, and 15.4 GHz in 2002 and 4.6, 5.1, 6.0, 7.8, 12.2, 15.2, and 43.9 GHz in 2020 with the American Very Long Baseline Array (VLBA). Combining the polarization results of Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments at 15 GHz from 2009 to 2013, we studied the evolution of magnetic field at the parsec scale for the source. We detected a core-jet structure. The jet extends to the distance of ∼25 mas from the core at a direction of ∼66° north by east. The shape of the jet derived from 15 GHz data varies slightly with time and could be described by a straight line. Based on the linear polarization distribution in 2002, we divided the source structure into the central region and the jet region. In the jet region, we find the polarized emission varies with time. The flatter spectral index values and electric vector position angle direction indicate the possible existence of shocks, contributing to the variation of polarization in the jet with time. In the central region, the derived core shift index k r values indicate that the core in 2002 is close to the equipartition case, while it deviated from the case in 2020. The measured magnetic field strength in 2020 is 2 orders of magnitude lower than that in 2002. We detected transverse RM gradients, evidence of a helical magnetic field, in the core. The polarized emission orients in general toward the jet direction in the core. At 15 GHz, in the place close to the jet base, the polarization direction changes significantly with time from perpendicular to parallel to the jet direction. The evolution of RM and magnetic field structure are potential reasons for the observed polarization change. The core ∣RM∣ in 2020 increases with frequency following a power law with index a = 2.7 ± 0.5, suggesting a fast electron density falloff in the medium with distance from the jet base.

Keywords: galaxy magnetic fields; active galactic nuclei; galaxies; jets; extragalactic magnetic fields
Gas Kinematics and Dynamics of Carina Pillars: A Case Study of G287.76-0.87

We study the kinematics of a pillar, namely G287.76-0.87, using three rotational lines of 12CO(5-4), 12CO(8-7), 12CO(11-10), and a fine structure line of [O I] 63 μm in southern Carina observed by SOFIA/GREAT. This pillar is irradiated by the associated massive star cluster Trumpler 16, which includes η Carina. Our analysis shows that the relative velocity of the pillar with respect to this ionization source is small, ∼1 km s‑1, and the gas motion in the tail is more turbulent than in the head. We also performed analytical calculations to estimate the gas column density in local thermal equilibrium (LTE) conditions, which yields N CO as (∼0.2–5) × 1017 cm‑2. We further constrain the gas's physical properties in non-LTE conditions using RADEX. The non-LTE estimations result in and N CO ≃ 1016 cm‑2. We found that the thermal pressure within the G287.76-0.87 pillar is sufficiently high to make it stable for the surrounding hot gas and radiation feedback if the winds are not active. While they are active, stellar winds from the clustered stars sculpt the surrounding molecular cloud into pillars within the giant bubble around η Carina.

Keywords: interstellar clouds; interstellar medium; photodissociation regions
A Revisit of the Mass–Metallicity Trends in Transiting Exoplanets

The two prevailing planet formation scenarios, core accretion and disk instability, predict distinct planetary mass–metallicity relations. Yet, the detection of this trend remains challenging due to inadequate data on planet atmosphere abundance and inhomogeneities in both planet and host stellar abundance measurements. Here we analyze high-resolution spectra for the host stars of 19 transiting exoplanets to derive the C, O, Na, S, and K abundances, including planetary types from cool mini-Neptunes to hot Jupiters (T eq ∼ 300–2700 K; planet radius ∼0.1–2 R J). Our Monte Carlo simulations suggest that the current data set, updated based on Welbanks et al., is unable to distinguish between a linear relation and an independent distribution model for the abundance-mass correlation for water, Na, or K. To detect a trend with strong evidence (Bayes factor > 10) at the 2σ confidence interval, we recommend a minimum sample of 58 planets with Hubble Space Telescope measurements of water abundances coupled with [O/H] of the host stars, or 45 planets at the JWST precision. Coupled with future JWST or ground-based high-resolution data, this well-characterized sample of planets with precise host-star abundances constitute an important ensemble of planets to further probe the abundance-mass correlation.

Keywords: exoplanet astronomy; exoplanet atmospheres; exoplanet formation; planet hosting stars
Exploiting Machine Learning and Disequilibrium in Galaxy Clusters to Obtain a Mass Profile

We use 3D k-means clustering to characterize galaxy substructure in the A2146 cluster of galaxies (z = 0.2343). This method objectively characterizes the cluster's substructure using projected position and velocity data for 67 galaxies within a 2.305 Mpc circular region centered on the cluster's optical center. The optimal number of substructures is found to be four. Four distinct substructures with rms velocity typical of galaxy groups or low-mass subclusters, when compared to cosmological simulations of galaxy cluster formation, suggest that A2146 is in the early stages of formation. We utilize this disequilibrium, which is so prevalent in galaxy clusters at all redshifts, to construct a radial mass distribution. Substructures are bound but not virialized. This method is in contrast to previous kinematical analyses, which have assumed virialization, and ignored the ubiquitous clumping of galaxies. The best-fitting radial mass profile is much less centrally concentrated than the well-known Navarro–Frenk–White profile, indicating that the dark-matter-dominated mass distribution is flatter pre-equilibrium, becoming more centrally peaked in equilibrium through the merging of the substructure.

Keywords: galaxy clusters; astroinformatics; large-scale structure of the universe; dark matter distribution
The Collimation of Relativistic Jets in Post-Neutron Star Binary Merger Simulations

The gravitational waves from the binary neutron star merger GW170817 were accompanied by a multiwavelength electromagnetic counterpart, which confirms the association of the merger with a short gamma-ray burst (sGRB). The afterglow observations implied that the event was accompanied by a narrow, ~5°, and powerful, ~1050 erg, jet. We study the propagation of a Poynting flux-dominated jet within the merger ejecta (kinematic, neutrino-driven, and magnetorotational instability turbulence-driven) of a neutrino-radiation-GRMHD simulation of two coalescing neutron stars. We find that the presence of a postmerger low-density/low-pressure polar cavity, which arose due to angular momentum conservation, is crucial to let the jet break out. At the same time the ejecta collimates the jet to a narrow opening angle. The collimated jet has a narrow opening angle of ~4°-7° and an energy of 1049-1050 erg, in line with the observations of GW170817 and other sGRBs.

Keywords: relativistic jets; neutron stars; gamma-ray bursts
Large-scale Mapping Observations of DCN and DCO+ toward Orion KL

We present emission maps ( $1\buildrel{\,\prime}\over{.} 5\,\times \,1\buildrel{\,\prime}\over{.} 5$ scale, corresponding to 0.18 pc) of the DCN (J = 2 ‑ 1) and DCO+ (J = 2 ‑ 1) lines in the 2 mm band toward the Orion KL region obtained with the 2 mm receiver system named B4R installed on the Large Millimeter Telescope. The DCN emission shows a peak at the Orion KL hot core position, whereas no DCO+ emission has been detected there. The DCO+ emission shows enhancement at the west side of the hot core, which is well shielded from the UV radiation from OB massive stars in the Trapezium cluster. We have derived the abundance ratio of DCN/DCO+ at three representative positions where both species have been detected. The gas components with V LSR ≈ 7.5–8.7 km s‑1 are associated with low abundance ratios of ∼4–6, whereas much higher abundance ratios (∼22–30) are derived for the gas components with V LSR ≈ 9.2–11.6 km s‑1. We have compared the observed abundance ratio to our chemical models and found that the observed differences in the DCN/DCO+ abundance ratios are explained by different densities.

Keywords: astrochemistry; star forming regions; interstellar molecules