adsabs/SciX_UAT_keywords huggingface dataset:
Suprathermal Population Associated with Stream Interaction Regions Observed by STEREO-A: New Insights

Stream interaction regions (SIRs) are often thought to be responsible for the generation of suprathermal population in the interplanetary medium. Even though the source is the same, wide variations in the spectral indices of suprathermal populations are observed at 1 au during SIRs. This poses a significant uncertainty in understanding the generation of suprathermal ion populations by SIRs and indicates an interplay of multiple source mechanisms. By analyzing variations in suprathermal 4He, O, and Fe for 20 SIR events recorded by STEREO-A during 2007-2014, we find that the spectral indices of these elements vary in the range of 2.06-4.08, 1.85-4.56, and 2.11-4.04 for 19 events. However, in one special case, all three suprathermal elements show nearly identical (~1.5) spectral indices. We describe possible mechanisms that might cause significant variations in the spectral indices of suprathermal particles. More importantly, we show the possible role of merging and/or contraction of small-scale magnetic islands near 1 au in producing nearly identical spectral indices for three different elements with different first ionization potentials and mass-to-charge ratios. The occurrence of these magnetic islands near 1 au also supports the minimal modulation in the spectral indices of these particles. We also suggest that a possible solar flare may have played a role in generating these magnetic islands near the heliospheric current sheet.

Keywords: solar wind; interplanetary shocks; corotating streams; solar energetic particles; solar flares
Optimal Prediction of Atmospheric Turbulence by Means of the Weather Research and Forecasting Model

The performance of ground-based astronomical observations and free-space optical communication (FSOC) systems suffers from atmospheric turbulence and meteorological conditions. The a priori knowledge of atmospheric conditions several hours before observations allows the programming of astronomical observations (flexible scheduling) to be optimized. In this paper, we present a prediction study based on the Weather Research and Forecasting (WRF) model. It allows the prediction and characterization of a useful set of meteorological parameters relevant to atmospheric physics (e.g., pressure, temperature, relative humidity, wind speed, and direction). Predicted parameters are then injected into an optical turbulence (OT) model to compute the refractive index structure constant C n 2. We performed sets of simulations for Cerro Pachon Observatory in Chile, using the data from the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR). The main goal is to quantify how accurately numerical weather prediction models can reproduce conditions over the complex terrain of the Cerro Pachon area. In order to produce a reliable forecast, meteorological prognostic skills need accurate representations of the physical parameterization options. Three widely used Planetary Boundary Layer (PBL) schemes and two Land Surface Models (LSM) were tested, analyzed, and compared in order to find the optimal WRF configuration. Predictions are compared to in situ measurements coming from balloon-borne radiosoundings. It is determined that the predicted C n 2 are in good agreement with the radiosoundings measurements with a mean relative error (MRE) under 6.4% at all altitudes when using balloon measurements to deduce some parameters such as the outer scale of turbulence L 0, which is used in the OT model. For a fully operational prediction, the MREs between the predictions and the measurements range from 1.4% to 8% according to the different ways to estimate the L 0 profiles. Seasonal statistics are also presented for different meteorological and turbulence parameters.

Keywords: atmospheric effects; optical observation; planetary boundary layers; observatories; astronomical seeing; astronomical instrumentation
Can Chameleon Fields Be the Source of the Dark Energy Dipole and the Cosmic Microwave Background Dipole?

Recent research reveals that the Local Group is in motion toward (l, b) = (276, 30) relative to the cosmic background radiation, manifesting a velocity of 600 km s‑1, a phenomenon recognized as the cosmic background radiation dipole or cosmic microwave background dipole. Despite its well-documented nature, the precise cause of this peculiar motion remains elusive. High mass–density regions, such as galactic superclusters, stand out among the potential contributors to this cosmic flow. This paper employs chameleon fields to investigate anisotropies on both small and large scales. The data utilized in this study comprise Type Ia supernovae from the Pantheon catalog, totaling 1048 supernovae within the redshift range of 0.015 < z < 2.3. The analysis of the bulk flow at various redshifts has yielded noteworthy discoveries. On a smaller scale (less than 150 Mpc), the movement direction of the Local Group coincides with that of the bulk flow. On a larger scale, the bulk flow direction corresponds to the direction of the dark energy dipole. This implies that the anisotropy at the local scale originates from the same source as the anisotropy observed on a larger scale.

Keywords: dark energy; virgo supercluster
Possible Ongoing Merger Discovered by Photometry and Spectroscopy in the Field of the Galaxy Cluster PLCK G165.7+67.0

We present a detailed study of the Planck-selected binary galaxy cluster PLCK G165.7+67.0 (G165; z = 0.348). A multiband photometric catalog is generated incorporating new imaging from the Large Binocular Telescope/Large Binocular Camera and Spitzer/IRAC to existing imaging. To cope with the different image characteristics, robust methods are applied in the extraction of the matched-aperture photometry. Photometric redshifts are estimated for 143 galaxies in the 4 arcmin2 field of overlap covered by these data. We confirm that strong-lensing effects yield 30 images of 11 background galaxies, of which we contribute new photometric redshift estimates for three image multiplicities. These constraints enable the construction of a revised lens model with a total mass of M 600 kpc = (2.36 ± 0.23) × 1014 M ⊙. In parallel, new spectroscopy using MMT/Binospec and archival data contributes thirteen galaxies that meet our velocity and transverse radius criteria for cluster membership. The two cluster components have a pair-wise velocity of ≲100 km s-1, favoring an orientation in the plane of the sky with a transverse velocity of 100-1700 km s-1. At the same time, the brightest cluster galaxy (BCG) is offset in velocity from the systemic mean value, suggesting dynamical disturbance. New LOFAR and Very Large Array data uncover head-tail radio galaxies in the BCG and a large red galaxy in the northeast component. From the orientation and alignment of the four radio trails, we infer that the two cluster components have already traversed each other, and are now exiting the cluster.

Keywords: large-scale structure of the universe; gravitational lensing; strong gravitational lensing; galaxies; high-redshift galaxies; galaxy clusters
Radio Polarization of Millisecond Pulsars with Multipolar Magnetic Fields

NICER has observed a few millisecond pulsars where the geometry of the X-ray-emitting hotspots on the neutron star have been analyzed in order to constrain the mass and radius from X-ray light-curve modeling. One example, PSR J0030 + 0451, has been shown to possibly have significant multipolar magnetic fields at the stellar surface. Using force-free simulations of the magnetosphere structure, it has been shown that the radio, X-ray, and γ-ray light curves can be modeled simultaneously with an appropriate field configuration. An even more stringent test is to compare predictions of the force-free magnetosphere model with observations of radio polarization. This paper attempts to reproduce the radio polarization of PSR J0030 + 0451 using a force-free magnetospheric solution. As a result of our modeling, we can reproduce certain features of the polarization well.

Keywords: millisecond pulsars; radio astronomy; magnetic fields
Imaging Molecular Outflow in Massive Star-forming Regions with HNCO Lines

Protostellar outflows are considered a signpost of star formation. These outflows can cause shocks in the molecular gas and are typically traced by the line wings of certain molecules. HNCO (4-3) has been regarded as a shock tracer because of the high abundance in shocked regions. Here we present the first imaging results of HNCO (4-3) line wings toward nine sources in a sample of 23 massive star-forming regions using the Instituto de Radioastronomía Milimétrica 30 m Telescope. We adopt the velocity range of the full width of HC3N (10-9) and H13CO+ (1-0) emissions as the central emission values, beyond which the emission from HNCO (4-3) is considered to be from line wings. The spatial distributions of the red and/or blue lobes of HNCO (4-3) emission nicely associate with those lobes of HCO+ (1-0) in most of the sources. High-intensity ratios of HNCO (4-3) to HCO+ (1-0) are obtained in the line wings. The derived column density ratios of HNCO to HCO+ are consistent with those previously observed toward massive star-forming regions. These results provide direct evidence that HNCO could trace outflow in massive star-forming regions. This work also implies that the formation of some HNCO molecules is related to shock, either on the grain surface or within the shocked gas.

Keywords: interstellar medium; interstellar clouds; interstellar molecules; star formation; star forming regions
Long-term Evolution of Massive-star Post-common-envelope Circumbinary Disks and the Environments of Fast Luminous Transients

If the envelope of a massive star is not entirely removed during common envelope (CE) interaction with an orbiting compact (e.g., black hole (BH) or neutron star (NS)) companion, the residual bound material eventually cools, forming a centrifugally supported disk around the binary containing the stripped He core. We present a time-dependent height-integrated model for the long-term evolution of post-CE circumbinary disks (CBDs), accounting for mass and angular momentum exchange with the binary, irradiation heating by the He core, and photoevaporation wind mass loss. A large fraction of the CBD's mass is accreted prior to its outwards viscous spreading and wind dispersal on a timescale of ~104-105 yr, driving significant orbital migration, even for disks containing ~10% of the original envelope mass. Insofar that the CBD lifetime is comparable to the thermal (and, potentially, nuclear) timescale of the He core, over which a second mass-transfer episode onto the companion can occur, the presence of the CBD could impact the stability of this key phase. Disruption of the core by the BH/NS would result in a jetted energetic explosion into the dense gaseous CBD (≲1015 cm) and its wind (≳1016 cm), consistent with the environments of luminous fast blue optical transients like AT2018cow. Evolved He cores that undergo core collapse still embedded in their CBD could generate Type Ibn/Icn supernovae. Thousands of dusty wind-shrouded massive-star CBDs may be detectable as extragalactic luminous infrared sources with the Roman Space Telescope; synchrotron radio nebulae powered by the CBD-fed BH/NS may accompany these systems.

Keywords: common envelope evolution; common envelope binary stars; supernovae; x-ray transient sources; stellar accretion disks; protoplanetary disks
ALMA High-frequency Long-baseline Campaign in 2017: A Comparison of the Band-to-band and In-band Phase Calibration Techniques and Phase-calibrator Separation Angles

The Atacama Large Millimeter/submillimeter Array (ALMA) obtains spatial resolutions of 15 to 5 mas at 275-950 GHz (0.87-0.32 mm) with 16 km baselines. Calibration at higher frequencies is challenging as ALMA sensitivity and quasar density decrease. The band-to-band (B2B) technique observes a detectable quasar at a lower frequency that is closer to the target, compared to one at the target high frequency. Calibration involves a nearly constant instrumental phase offset between the frequencies and the conversion of the temporal phases to the target frequency. The instrumental offsets are solved with a differential gain calibration (DGC) sequence, consisting of alternating low- and high-frequency scans of strong quasars. Here we compare B2B and in-band phase referencing for high frequencies (>289 GHz) using 2-15 km baselines and calibrator separation angles between ∼0°68 and ∼11°65. The analysis shows the following: (1) DGC for B2B produces a coherence loss <7% for DGC phase rms residuals <30°. (2) B2B images using close calibrators (<1°67) are superior to in-band images using distant ones (>2°42). (3) For more distant calibrators, B2B is preferred if it provides a calibrator ∼2° closer than the best in-band calibrator. (4) Decreasing image coherence and poorer image quality occur with increasing phase-calibrator separation angle because of uncertainties in the antenna positions and suboptimal phase referencing. (5) To achieve >70% coherence for long-baseline (16 km) band 7 (289 GHz) observations, calibrators should be within ∼4° of the target.

Keywords: long baseline interferometry; submillimeter astronomy; phase error
Gaia EDR3 Confirms that Westerlund 1 is Closer and Older than Previously Thought

Using Gaia Early Data Release 3 (EDR3) parallaxes and Bayesian inference, we infer a parallax of the Westerlund 1 (Wd1) cluster. We find a parallax of 0.34 ± 0.05 mas corresponding to a distance of ${2.8}_{-0.6}^{+0.7}$ kpc. The new Gaia EDR3 distance is consistent with our previous result using Gaia Data Release 2 (DR2) parallaxes. This confirms that Wd1 is less massive and older than previously assumed. Compared to DR2, the EDR3 individual parallax uncertainties for each star decreased by 30%. However, the aggregate parallax uncertainty for the cluster remained the same. This suggests that the uncertainty is dominated by systematics, which is possibly due to crowding, motions within the cluster, or motions due to binary orbits.

Keywords: massive stars; stellar types; luminous blue variable stars; bayesian statistics; open star clusters; star clusters
The Warm-Hot, Extended, Massive Circumgalactic Medium of NGC 3221: An XMM-Newton Discovery

Using Suzaku data, we had found a 3.4σ evidence for the X-ray emitting warm-hot circumgalactic medium (CGM) in the L⋆ galaxy NGC 3221. Here we present XMM-Newton data and outline an efficient, rigorous, and well-defined method to extract the faint CGM signal. We confirm the CGM detection at 4σ significance within 30-200 kpc of the galaxy. We claim with 99.62% confidence that the CGM is extended beyond 150 kpc. The average temperature of the CGM is ${2.0}_{-0.3}^{+0.2}\times {10}^{6}$ K, but it is not isothermal. We find suggestive evidence for a declining temperature gradient out to 125 kpc and for supervirial temperature within 100 kpc. While a supervirial temperature component has been detected in the Milky Way CGM, this is the first time a temperature gradient has been observed in the warm-hot CGM of any spiral galaxy. The emission measure profile is well-fit with either a β-model or a constant-density profile. Deeper data are required to constrain the temperature and density profiles. We also confirm the Suzaku result that the warm-hot CGM is one of the most massive baryon components of NGC 3221 and can account for the missing galactic baryons.

Keywords: x-ray astronomy; extragalactic astronomy; hot ionized medium; diffuse radiation; circumgalactic medium; galaxy environments; diffuse x-ray background; missing mass
Public Release of A-SLOTH: Ancient Stars and Local Observables by Tracing Halos

The semianalytical model A-SLOTH (Ancient Stars and Local Observables by Tracing Halos) is the first public code that connects the formation of the first stars and galaxies to observables. After several successful projects with this model, we publish the source code (https://gitlab.com/thartwig/asloth) and describe the public version in this paper. The model is based on dark matter merger trees that can either be generated based on Extended Press-Schechter theory or be imported from dark matter simulations. On top of these merger trees, A-SLOTH applies analytical recipes for baryonic physics to model the formation of both metal-free and metal-poor stars and the transition between them with unprecedented precision and fidelity. A-SLOTH samples individual stars and includes radiative, chemical, and mechanical feedback. It is calibrated based on six observables, such as the optical depth to Thomson scattering, the stellar mass of the Milky Way and its satellite galaxies, the number of extremely metal-poor stars, and the cosmic star formation rate density at high redshift. A-SLOTH has versatile applications with moderate computational requirements. It can be used to constrain the properties of the first stars and high-z galaxies based on local observables, predicts properties of the oldest and most metal-poor stars in the Milky Way, can serve as a subgrid model for larger cosmological simulations, and predicts next-generation observables of the early universe, such as supernova rates or gravitational wave events.

Keywords: population iii stars; population ii stars; high-redshift galaxies; astronomical simulations; milky way formation; open source software
The Equilibrium Tide: An Updated Prescription for Population Synthesis Codes

We present an updated prescription for the equilibrium tides suitable for population synthesis codes. A grid of 1D evolutionary models was created and the viscous timescale was calculated for each detailed model. A metallicity-dependent power-law relation was fitted to both the convective cores and convective envelopes of the models. The prescription was implemented into the population synthesis code Binary Star Evolution and predicts a 16.5% reduction in the overall number of merges, with those involving main-sequence stars most affected. The new prescription also reduces the overall supernova rate by 3.6% with individual channels being differently affected. The single degenerate Ia supernova occurrence is reduced by 12.8%. The merging of two carbon oxygen white dwarfs to cause a Ia supernova occurs 16% less frequently. The number of subsynchronously rotating stars in close binaries is substantially increased with our prescription, as is the number of noncircularized systems at the start of common-envelope evolution.

Keywords: binary stars; tidal interaction; stellar populations; stellar evolutionary models
Near-infrared Search for Fundamental-mode RR Lyrae Stars toward the Inner Bulge by Deep Learning

Aiming to extend the census of RR Lyrae stars to highly reddened low-latitude regions of the central Milky Way, we performed a deep near-IR variability search using data from the VISTA Variables in the Vía Láctea (VVV) survey of the bulge, analyzing the photometric time series of over a hundred million point sources. In order to separate fundamental-mode RR Lyrae (RRab) stars from other periodically variable sources, we trained a deep bidirectional long short-term memory recurrent neural network (RNN) classifier using VVV survey data and catalogs of RRab stars discovered and classified by optical surveys. Our classifier attained a ∼99% precision and recall for light curves with signal-to-noise ratio above 60, and is comparable to the best-performing classifiers trained on accurate optical data. Using our RNN classifier, we identified over 4300 hitherto unknown bona fide RRab stars toward the inner bulge. We provide their photometric catalog and VVV $J,H,{K}_{s}$ photometric time series.

Keywords: rr lyrae variable stars; light curve classification; neural networks; near infrared astronomy; catalogs; surveys
Line-of-sight Elongation and Hydrostatic Mass Bias of the Frontier Fields Galaxy Cluster Abell 370

We present a detailed weak-lensing and X-ray study of the Frontier Fields galaxy cluster Abell 370, one of the most massive known lenses on the sky, using wide-field BR C z' Subaru/Suprime-Cam and Chandra X-ray observations. By combining two-dimensional (2D) shear and azimuthally averaged magnification constraints derived from Subaru data, we perform a lensing mass reconstruction in a free-form manner, which allows us to determine both the radial structure and 2D morphology of the cluster mass distribution. In a triaxial framework assuming a Navarro-Frenk-White density profile, we constrain the intrinsic structure and geometry of the cluster halo by forward modeling the reconstructed mass map. We obtain a halo mass M 200 = (1.54 ± 0.29) ×1015 h -1 M ⊙, a halo concentration c 200 = 5.27 ± 1.28, and a minor-major axis ratio q a = 0.62 ± 0.23 with uninformative priors. Using a prior on the line-of-sight alignment of the halo major axis derived from binary merger simulations constrained by multi-probe observations, we find that the data favor a more prolate geometry with lower mass and lower concentration. From triaxial lens modeling with the line-of-sight prior, we find a spherically enclosed gas mass fraction of f gas = (8.4 ± 1.0)% at 0.7 h -1 Mpc ~ 0.7r 500. When compared to the hydrostatic mass estimate (M HE) from Chandra observations, our triaxial weak-lensing analysis yields spherically enclosed mass ratios of 1 - b ≡ M HE/M WL = 0.56 ± 0.09 and 0.51 ± 0.09 at 0.7 h -1 Mpc with and without using the line-of-sight prior, respectively. Since the cluster is in a highly disturbed dynamical state, this represents the likely maximum level of hydrostatic bias in galaxy clusters.

Keywords: galaxy clusters; weak gravitational lensing; dark matter distribution; cold dark matter; intracluster medium; x-ray astronomy
Kinetic Simulations of Instabilities and Particle Acceleration in Cylindrical Magnetized Relativistic Jets

Relativistic magnetized jets, such as those from AGN, GRBs, and XRBs, are susceptible to current- and pressure-driven MHD instabilities that can lead to particle acceleration and nonthermal radiation. Here, we investigate the development of these instabilities through 3D kinetic simulations of cylindrically symmetric equilibria involving toroidal magnetic fields with electron-positron pair plasma. Generalizing recent treatments by Alves et al. and Davelaar et al., we consider a range of initial structures in which the force due to toroidal magnetic field is balanced by a combination of forces due to axial magnetic field and gas pressure. We argue that the particle energy limit identified by Alves et al. is due to the finite duration of the fast magnetic dissipation phase. We find a rather minor role of electric fields parallel to the local magnetic fields in particle acceleration. In all investigated cases, a kink mode arises in the central core region with a growth timescale consistent with the predictions of linearized MHD models. In the case of a gas-pressure-balanced (Z-pinch) profile, we identify a weak local pinch mode well outside the jet core. We argue that pressure-driven modes are important for relativistic jets, in regions where sufficient gas pressure is produced by other dissipation mechanisms.

Keywords: high energy astrophysics; jets