adsabs/SciX_UAT_keywords huggingface dataset:
Fermi-type Particle Acceleration from Magnetic Reconnection at the Termination Shock of a Relativistic Striped Wind

An oblique-rotating pulsar generates a relativistic striped wind in a pulsar wind nebula (PWN). The termination shock of the PWN compresses the Poynting-flux-dominated flow and drives magnetic reconnection. By carrying out particle-in-cell simulations of the termination shock of the PWN, we study the shock structure as well as the energy conversion processes and particle acceleration mechanisms. With the recent advances in the numerical methods, we extend the simulations to the ultrarelativistic regime with a bulk Lorentz factor of up to γ0 = 106. Magnetic reconnection at the termination shock is highly efficient at converting magnetic energy to particle kinetic energy and accelerating particles to high energies. Similar to earlier studies, we find that the resulting energy spectra crucially depend on λ/de (λ is the wavelength of the striped wind and de is the relativistic plasma skin depth). When λ/de is large (λ ≳ 40de), the downstream particle spectra form a power-law distribution in the magnetically dominated relativistic wind regime. By analyzing particle trajectories and statistical quantities relevant to particle energization, we find that Fermi-type mechanism dominates the particle acceleration and power-law formation. We find that the results for particle acceleration are scalable as γ0 and σ0 increase to large values. The maximum energy for electrons and positrons can reach hundreds of TeV if the wind has a bulk Lorentz factor of γ0 ≈ 106 and a magnetization parameter of σ0 = 10, which can explain the recent observations of high-energy gamma rays from PWNe.

Keywords: high energy astrophysics; plasma astrophysics
The Power Spectrum and Structure Function of the Gamma-Ray Emission from the Large Magellanic Cloud

The Fermi-LAT observational data of the diffuse γ ray emission from the Large Magellanic Cloud (LMC) were examined to test for the existence of underlying long-range correlations. A statistical test applied to the data indicated that the probability that data are random is extremely small. Thus we proceeded and have used the counts-number data to compute 2D spatial autocorrelation, power spectrum, and structure function. The most important result of the present study is a clear indication for large-scale spatial underlying correlations. This is evident in all the functions mentioned above. The 2D power spectrum has a logarithmic slope of -3 on large spatial scales and a logarithmic slope of -4 on small spatial scales. The structure function has logarithmic slopes equaling 1 and 2 for the large and small scales, respectively. The logarithmic slopes of the structure function and the power spectrum are consistent. A plausible interpretation of these results is the existence of a large-scale supersonic compressible turbulence with a 3D logarithmic slope of -4 extending over scales comparable to the size of the LMC. Both the power spectrum and structure function exhibit steeper logarithmic slopes for smaller spatial scales. This is interpreted as an indication that the turbulent region has an effective depth of about 1.5 kpc.

Keywords: galaxies; interstellar medium
The PhotoDissociation Region Toolbox: Software and Models for Astrophysical Analysis

The PhotoDissociation Region Toolbox provides comprehensive, easy-to-use, public software tools and models that enable an understanding of the interaction of the light of young, luminous, massive stars with the gas and dust in the Milky Way and in other galaxies. It consists of an open-source Python toolkit and photodissociation region (PDR) models for analysis of infrared and millimeter/submillimeter line and continuum observations obtained by ground-based and suborbital telescopes, and astrophysics space missions. PDRs include all of the neutral gas in the interstellar medium where far-ultraviolet photons dominate the chemistry and/or heating. In regions of massive star formation, PDRs are created at the boundaries between the H II regions and neutral molecular cloud, as photons with energies 6 eV < h ν < 13.6 eV photodissociate molecules and photoionize metals. The gas is heated by photoelectrons from small grains and large molecules and cools mostly through far-infrared (FIR) fine-structure lines like [O I] and [C II]. The models are created from state-of-the art PDR codes that include molecular freeze-out; recent collision, chemical, and photorates; new chemical pathways, such as oxygen chemistry; and allow for both clumpy and uniform media. The models predict the emergent intensities of many spectral lines and FIR continuum. The tools find the best-fit models to the observations and provide insight into the physical conditions and chemical makeup of the gas and dust. The PDR Toolbox enables novel analysis of data from telescopes such as the Infrared Space Observatory, Spitzer, Herschel, the Stratospheric Terahertz Observatory, the Stratospheric Observatory for Infrared Astronomy, the Submillimeter Wave Astronomy Satellite, the Atacama Pathfinder Experiment, the Atacama Large Millimeter/submillimeter Array, and the JWST.

Keywords: photodissociation regions; astronomy software; molecular gas; interstellar atomic gas
Phase Shift of Planetary Waves and Wave-Jet Resonance on Tidally Locked Planets

Recent studies found that atmospheric superrotation (i.e., west-to-east winds over the equator) on tidally locked planets can modify the phase of planetary waves. But a clear relationship between the superrotation and the magnitude of the phase shift was not examined. In this study, we re-investigate this problem using a 2D linear shallow-water model with a specified uniform zonal flow. We find that the degree of the phase shift is a monotonic but nonlinear function of the strength of the mean flow and the phase shift has two limits of -π and +π. The existence of these limits can be explained using the energy balance of the whole system. We further show that a resonance between the Rossby wave and the mean flow occurs when the speed of an eastward jet approaches to the westward phase speed of the Rossby wave, or a resonance between the Kelvin wave and the mean flow happens when the speed of a westward jet approaches to the eastward phase speed of the Kelvin wave. The resonance mechanism is the same as that found in the previous studies on Earth and hot Jupiters. Moreover, in the spin-up period of a 3D global atmospheric general circulation simulation for tidally locked rocky planet, we also find these two phenomena: phase shift and wave-jet resonance. This study improves the understanding of wave-mean-flow interactions on tidally locked planets.

Keywords: planetary atmospheres; transit photometry; analytical mathematics; exoplanet atmospheres; exoplanets; earth atmosphere; atmospheric circulation; atmospheric science
Mass Segregation as a New Indicator of Binary, IMBH, and Stellar-mass Black Hole Systems in Globular Clusters

This study presents the mass segregation of 35 Galactic globular clusters (GCs) through the radial profile of the mean mass of main-sequence stars. Most of them are found to be mass segregated due to two-body relaxation effects. The GCs with a larger core to half-mass-radius ratio tend to be less mass segregated. Recent simulations show that energy sources can quench mass segregation in relaxed GCs. Combining mass segregation and core binary fractions (fc), we find a moderate anticorrelation between them when fc is below 0.15. Four GCs that have a small amount of mass segregation are selected as possible intermediate-mass black hole holders. However, none of them are strong candidates considering their half-mass relaxation times.

Keywords: globular star clusters; binary stars; intermediate-mass black holes; stellar mass black holes; stellar kinematics; star clusters
Energy Dependence of the Line Ratio I(233.9 Å)/I(243.8 Å) in Fe xv Observed with an Electron Beam Ion Trap

We present the energy dependence of the intensity ratio between the 3s3p 3 P 2-3s3d 3 D 3 transition at 233.9 Å and the 3s3p 1 P 1-3s3d 1 D 2 transition at 243.8 Å in Fe XV studied with an electron beam ion trap over an energy range that spans resonance excitation regions. Clear resonance structures are observed in the electron energy range of 400-600 eV. The energy dependence obtained in the experiment is compared with a collisional-radiative model calculation, including resonance excitations, and overall agreement is found. It is shown that the ratio strongly reflects the population of the 3s3p 3 P 2 metastable state, which is the lower state of the 233.9 Å transition.

Keywords: solar transition region; solar corona; solar flares; solar ultraviolet emission; solar atmosphere; stellar atmospheres; solar extreme ultraviolet emission
Unveiling the Formation of the Massive DR21 Ridge

We present new 13CO (1-0), C18O (1-0), HCO+ (1-0), and H13CO+ (1-0) maps from the IRAM 30 m telescope and a spectrally resolved [C II] 158 μm map observed with the SOFIA telescope toward the massive DR21 cloud. This traces the kinematics from low- to high-density gas in the cloud, which allows us to constrain the formation scenario of the high-mass star-forming DR21 ridge. The molecular line data reveal that the subfilaments are systematically redshifted relative to the dense ridge. We demonstrate that [C II] unveils the surrounding CO-poor gas of the dense filaments in the DR21 cloud. We also show that this surrounding gas is organized in a flattened cloud with curved redshifted dynamics perpendicular to the ridge. The subfilaments thus form in this curved and flattened mass reservoir. A virial analysis of the different lines indicates that self-gravity should drive the evolution of the ridge and surrounding cloud. Combining all results, we propose that bending of the magnetic field, due to the interaction with a mostly atomic colliding cloud, explains the velocity field and resulting mass accretion on the ridge. This is remarkably similar to what was found for at least two nearby low-mass filaments. We tentatively propose that this scenario might be a widespread mechanism to initiate star formation in the Milky Way. However, in contrast to low-mass clouds, gravitational collapse plays a role on the parsec scale of the DR21 ridge because of the higher density. This allows more effective mass collection at the centers of collapse and should facilitate massive cluster formation.

Keywords: molecular clouds; interstellar medium; star formation
The Orbit of Warm Jupiter WASP-106 b is Aligned with its Star

Understanding orbital obliquities, or the misalignment angles between a star's rotation axis and the orbital axis of its planets, is crucial for unraveling the mechanisms of planetary formation and migration. In this study, we present an analysis of Rossiter-McLaughlin (RM) observations of the warm Jupiter exoplanet WASP-106 b. The high-precision radial velocity measurements were made with HARPS and HARPS-N during the transit of this planet. We aim to constrain the orientation of the planet's orbit relative to its host star's rotation axis. The RM observations are analyzed using a code which models the RM anomaly together with the Keplerian orbit given several parameters in combination with a Markov chain Monte Carlo implementation. We measure the projected stellar obliquity in the WASP-106 system for the first time and find λ = (-1 ± 11)°, supporting the theory of quiescent migration through the disk.

Keywords: exoplanet evolution; exoplanet migration; radial velocity; photometry; transits
Solar Wind Streams and Stream Interaction Regions Observed by the Parker Solar Probe with Corresponding Observations at 1 au

Several fast solar wind streams and stream interaction regions (SIRs) were observed by the Parker Solar Probe (PSP) during its first orbit (2018 September-2019 January). During this time, several recurring SIRs were also seen at 1 au at both L1 (Advanced Composition Explorer (ACE) and Wind) and the location of the Solar Terrestrial Relations Observatory-Ahead (STEREO-A). In this paper, we compare four fast streams observed by PSP at different radial distances during its first orbit. For three of these fast stream events, measurements from L1 (ACE and Wind) and STEREO-A indicated that the fast streams were observed by both PSP and at least one of the 1 au monitors. Our associations are supported by simulations made by the ENLIL model driven by GONG-(ADAPT-)WSA, which allows us to contextualize the inner heliospheric conditions during the first orbit of PSP. Additionally, we determine which of these fast streams are associated with an SIR and characterize the SIR properties for these events. From these comparisons, we find that the compression region associated with the fast-speed streams overtaking the preceding solar wind can form at various radial distances from the Sun in the inner heliosphere inside 0.5 au, with the suprathermal ion population (energies between 30 and 586 keV) observed as isolated enhancements suggesting localized acceleration near the SIR stream interface at ∼0.3 au, which is unlike those seen at 1 au, where the suprathermal enhancements extend throughout and behind the SIR. This suprathermal enhancement extends further into the fast stream with increasing distance from the Sun.

Keywords: fast solar wind; heliosphere; interplanetary particle acceleration
High-resolution Transmission Spectroscopy of the Terrestrial Exoplanet GJ 486b

Terrestrial exoplanets orbiting M-dwarf stars are promising targets for transmission spectroscopy with existing or near-future instrumentation. The atmospheric composition of such rocky planets remains an open question, especially given the high X-ray and ultraviolet flux from their host M dwarfs that can drive atmospheric escape. The 1.3 R ⊕ exoplanet GJ 486b (T eq ~ 700 K), orbiting an M3.5 star, is expected to have one of the strongest transmission spectroscopy signals among known terrestrial exoplanets. We observed three transits of GJ 486b using three different high-resolution spectrographs: IRD on Subaru, IGRINS on Gemini-South, and SPIRou on the Canada-France-Hawai'i Telescope. We searched for atmospheric absorption from a wide variety of molecular species via the cross-correlation method, but did not detect any robust atmospheric signals. Nevertheless, our observations are sufficiently sensitive to rule out several clear atmospheric scenarios via injection and recovery tests, and extend comparative exoplanetology into the terrestrial regime. Our results suggest that GJ 486b does not possess a clear H2/He-dominated atmosphere, nor a clear 100% water-vapor atmosphere. Other secondary atmospheres with high mean molecular weights or H2/He-dominated atmospheres with clouds remain possible. Our findings provide further evidence suggesting that terrestrial planets orbiting M-dwarf stars may experience significant atmospheric loss.

Keywords: exoplanet atmospheres; planetary atmospheres; exoplanets; exoplanet atmospheric composition
Model-independent Estimations for the Cosmic Curvature from the Latest Strong Gravitational Lensing Systems

Model-independent measurements for the cosmic spatial curvature, which is related to the nature of cosmic spacetime geometry, play an important role in cosmology. On the basis of the distance sum rule in the Friedmann-Lemaître-Robertson-Walker metric, (distance ratio) measurements of strong gravitational lensing (SGL) systems, together with distances from SNe Ia observations, have been proposed to directly estimate the spatial curvature without any assumptions for the theories of gravity and contents of the universe. However, previous studies indicated that a spatially closed universe was strongly preferred. In this paper, we re-estimate the cosmic curvature with the latest SGL data, which includes 163 well-measured systems. In addition, possible factors, e.g., a combination of SGL data from different surveys and stellar masses of the lens galaxy, which might affect estimations for the spatial curvature, are considered in our analysis. We find that, except for the case where only SGL systems from the Sloan Lens ACS Survey are considered, a spatially flat universe is consistently favored at very high confidence levels by the latest observations. It has been suggested that an increasing number of well-measured strong lensing events might significantly reduce the bias of estimation for the cosmic curvature.

Keywords: cosmological parameters; observational cosmology; galaxy distances; gravitational lensing
HATS-47b, HATS-48Ab, HATS-49b, and HATS-72b: Four Warm Giant Planets Transiting K Dwarfs

We report the discovery of four transiting giant planets around K dwarfs. The planets HATS-47b, HATS-48Ab, HATS-49b, and HATS-72b have masses of ${0.369}_{-0.021}^{+0.031} ${M}_{{\rm{J}}}, ${0.243}_{-0.030}^{+0.022} ${M}_{{\rm{J}}}, ${0.353}_{-0.027}^{+0.038} ${M}_{{\rm{J}}}, and $0.1254\pm 0.0039 ${M}_{{\rm{J}}}, respectively, and radii of $1.117\pm 0.014 ${R}_{{\rm{J}}}, $0.800\pm 0.015 ${R}_{{\rm{J}}}, $0.765\pm 0.013 ${R}_{{\rm{J}}}, and $0.7224\pm 0.0032 ${R}_{{\rm{J}}}, respectively. The planets orbit close to their host stars with orbital periods of $3.9228 days, $3.1317 days, $4.1480 days, and $7.3279 days, respectively. The hosts are main-sequence K dwarfs with masses of ${0.674}_{-0.012}^{+0.016} ${M}_{\odot }, $0.7279\,\pm 0.0066 ${M}_{\odot }, $0.7133\pm 0.0075 ${M}_{\odot }, and $0.7311\pm 0.0028, and with V-band magnitudes of $V=14.829\pm 0.010, $14.35\pm 0.11, $14.998\pm 0.040 and $12.469\pm 0.010 . The super-Neptune HATS-72b (a.k.a. WASP-191b and TOI 294.01) was independently identified as a transiting planet candidate by the HATSouth, WASP, and TESS surveys, and we present a combined analysis of all of the data gathered by each of these projects (and their follow-up programs). An exceptionally precise mass is measured for HATS-72b thanks to high-precision radial velocity (RV) measurements obtained with VLT/ESPRESSO, FEROS, HARPS, and Magellan/PFS. We also incorporate TESS observations of the warm Saturn-hosting systems HATS-47 (a.k.a. TOI 1073.01), HATS-48A, and HATS-49. HATS-47 was independently identified as a candidate by the TESS team, while the other two systems were not previously identified from the TESS data. The RV orbital variations are measured for these systems using Magellan/PFS. HATS-48A has a resolved $5\buildrel{\prime\prime}\over{.} 4 neighbor in Gaia DR2, which is a common-proper-motion binary star companion to HATS-48A with a mass of 0.22 ${M}_{\odot } and a current projected physical separation of ∼1400 au.

Keywords: exoplanets; extrasolar gaseous giant planets; hot jupiters; transits
Generation of He I 1083 nm Images from SDO AIA Images by Deep Learning

In this study, we generate He I 1083 nm images from Solar Dynamic Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images using a novel deep learning method (pix2pixHD) based on conditional Generative Adversarial Networks (cGAN). He I 1083 nm images from National Solar Observatory (NSO)/Synoptic Optical Long-term Investigations of the Sun (SOLIS) are used as target data. We make three models: single-input SDO/AIA 19.3 nm image for Model I, single-input 30.4 nm image for Model II, and double-input (19.3 and 30.4 nm) images for Model III. We use data from 2010 October to 2015 July except for June and December for training and the remaining one for test. Major results of our study are as follows. First, the models successfully generate He I 1083 nm images with high correlations. Second, Model III shows better results than those with one input image in terms of metrics such as correlation coefficient (CC) and root mean square error (RMSE). CC and RMSE between real and synthetic ones for model III with 4 by 4 binnings are 0.88 and 9.49, respectively. Third, synthetic images show well observational features such as active regions, filaments, and coronal holes. This work is meaningful in that our model can produce He I 1083 nm images with higher cadence without data gaps, which would be useful for studying the time evolution of the chromosphere and transition region.

Keywords: the sun; solar chromosphere; convolutional neural networks; solar filaments; solar coronal holes
Dynamical Mass of the Ophiuchus Intermediate-mass Stellar System S1 with DYNAMO-VLBA

We report dynamical mass measurements of the individual stars in the most luminous and massive stellar member of the nearby Ophiuchus star-forming region, the young tight binary system S1. We combine 28 archival data sets with seven recent proprietary Very Long Baseline Array (VLBA) observations obtained as part of the Dynamical Masses of Young Stellar Multiple Systems with the VLBA project (DYNAMO–VLBA), to constrain the astrometric and orbital parameters of the system, and recover high-accuracy dynamical masses. The primary component, S1A, is found to have a mass of 4.11 ± 0.10 M ⊙, significantly lower than the typical value ∼6 M ⊙ previously reported in the literature. We show that the spectral energy distribution (SED) of S1A can be reproduced by a reddened blackbody with a temperature between roughly 14,000 and 17,000 K. According to evolutionary models, this temperature range corresponds to stellar masses between 4 M ⊙ and 6 M ⊙, so the SED is not a priori inconsistent with the dynamical mass of S1A. The luminosity of S1 derived from SED fitting, however, is only consistent with models for stellar masses above 5 M ⊙. Thus, we cannot reconcile the evolutionary models with the dynamical mass measurement of S1A: The models consistent with the location of S1A in the Hertzsprung-Russel diagram correspond to masses higher by 25% at least than the dynamical mass. For the secondary component, S1B, a mass of 0.831 ± 0.014 M ⊙ is determined, consistent with a low-mass young star. While the radio flux of S1A remains roughly constant throughout the orbit, the flux of S1B is found to be higher near apastron.

Keywords: radio astrometry; star formation; stellar kinematics; close binary stars
The Pitch-angle Distributions of Suprathermal Ions near an Interplanetary Shock

We present a case study of the pitch-angle distributions (PADs) of suprathermal H+, He2+ at ∼10-40 keV/nuc and He+ at ∼8-20 keV/nuc near a reverse shock of a stream interaction region observed by the Plasma and Suprathermal Ion Composition instrument on board the Solar Terrestrial Relations Observatory Ahead spacecraft on 2008 March 9. We find that in both the downstream and upstream region close to the shock, the shocked particles of all three species appear to have a power-law-like spectrum at these suprathermal energies. The PADs of these three species show very similar behavior: in the downstream region, the phase space density appears to be significantly higher in the direction perpendicular to the interplanetary magnetic field (IMF) than in the parallel direction, along which particles accelerated at the shock front are supposed to escape into the downstream region. In the upstream region, the PADs of all three species show a clear beam in the direction antiparallel to the IMF due to the escaping particles from the shock into the upstream region. In addition, we find that suprathermal He+ shows a signature of bidirectional beams in the upstream region very close to the shock. These results suggest that H+, He2+ at ∼10-40 keV/nuc and He+ at ∼8-20 keV/nuc could be accelerated similarly at interplanetary shocks and that shock drift acceleration likely plays an important role in the in situ acceleration of low-energy suprathermal ions.

Keywords: interplanetary particle acceleration; interplanetary shocks; solar wind; corotating streams