adsabs/SciX_UAT_keywords huggingface dataset:
Preventing Anomalous Torques in Circumbinary Accretion Simulations

Numerical experiments are the primary method of studying the evolution of circumbinary disks due to the strong nonlinearities involved. Many circumbinary simulations also require the use of numerical mass sinks: source terms that prevent gas from unphysically accumulating around the simulated point masses by removing gas at a given rate. However, special care must be taken when drawing physical conclusions from such simulations to ensure that results are not biased by numerical artifacts. We demonstrate how improved sink methods reduce some of these biases, using simulations of aspect ratio 0.1 accretion disks around binaries with mass ratios between 0.1 and 1. We show that sink terms that do not reduce the angular momentum of gas relative to the accreting object (1) reduce the dependence on the sink rate of quantities such as the torque on the binary, distribution of accretion between binary components, and evolution of the binary semimajor axis; (2) reduce the degree to which the sink rate affects the structure of the accretion disks around each binary component; (3) alter the variability of accretion onto the binary, regularizing it in time. We also investigate other potential sources of systematic error, such as gravitational softening and simplifications to the viscous stress tensor. Because of the strong dependence of binary orbital evolution on both the torque and the distribution of mass between binary components, the sink method influences the orbital evolution of the binary at all mass ratios, with mass ratios below ~0.3 most affected.

Keywords: accretion; astrophysical fluid dynamics; computational methods; circumstellar disks; active galactic nuclei; black holes
VERITAS and Fermi-LAT Constraints on the Gamma-Ray Emission from Superluminous Supernovae SN2015bn and SN2017egm

Superluminous supernovae (SLSNe) are a rare class of stellar explosions with luminosities ~ 10-100 times greater than ordinary core-collapse supernovae. One popular model to explain the enhanced optical output of hydrogen-poor (Type I) SLSNe invokes energy injection from a rapidly spinning magnetar. A prediction in this case is that high-energy gamma-rays, generated in the wind nebula of the magnetar, could escape through the expanding supernova ejecta at late times (months or more after optical peak). This paper presents a search for gamma-ray emission in the broad energy band from 100 MeV to 30 TeV from two Type I SLSNe, SN2015bn, and SN2017egm, using observations from Fermi-LAT and VERITAS. Although no gamma-ray emission was detected from either source, the derived upper limits approach the putative magnetar's spin-down luminosity. Prospects are explored for detecting very-high-energy (VHE; 100 GeV-100 TeV) emission from SLSNe-I with existing and planned facilities such as VERITAS and CTA.

Keywords: shocks; gamma-rays; particle astrophysics; supernovae; magnetars; millisecond pulsars; rotation powered pulsars
Reconnection-driven Particle Acceleration in Relativistic Shear Flows

Particle energization in shear flows is invoked to explain nonthermal emission from the boundaries of relativistic astrophysical jets. Yet the physics of particle injection, i.e., the mechanism that allows thermal particles to participate in shear-driven acceleration, remains unknown. With particle-in-cell simulations, we study the development of Kelvin-Helmholtz (KH) instabilities seeded by the velocity shear between a relativistic magnetically dominated electron-positron jet and a weakly magnetized electron-ion ambient plasma. We show that, in their nonlinear stages, KH vortices generate kinetic-scale reconnection layers, which efficiently energize the jet particles, thus providing a first-principles mechanism for particle injection into shear-driven acceleration. Our work lends support to spine-sheath models of jet emission—with a fast core/spine surrounded by a slower sheath—and can explain the origin of radio-emitting electrons at the boundaries of relativistic jets.

Keywords: relativistic jets; plasma astrophysics; non-thermal radiation sources; high energy astrophysics
JWST Identification of Extremely Low C/N Galaxies with [N/O] ≳ 0.5 at z 6-10 Evidencing the Early CNO-cycle Enrichment and a Connection with Globular Cluster Formation

We present chemical abundance ratios of 70 star-forming galaxies at z ~ 4-10 observed by the JWST/NIRSpec Early Release Observations, GLASS, and CEERS programs. Among the 70 galaxies, we have pinpointed two galaxies, CEERS_01019 at z = 8.68 and GLASS_150008 at z = 6.23, with extremely low C/N ([C/N] ≲ -1), evidenced with C III]λλ1907,1909, N III]λ1750, and N IV]λλ1483,1486, which show high N/O ratios ([N/O] ≳ 0.5) comparable with the one of GN-z11, regardless of whether stellar or active galactic nucleus radiation is assumed. Such low C/N and high N/O ratios found in CEERS_01019 and GLASS_150008 (additionally identified in GN-z11) are largely biased toward the equilibrium of the CNO cycle, suggesting that these three galaxies are enriched by metals processed by the CNO cycle. On the C/N versus O/H plane, these three galaxies do not coincide with Galactic H II regions, normal star-forming galaxies, and nitrogen-loud quasars with asymptotic giant branch stars, but with globular-cluster (GC) stars, indicating a connection with GC formation. We compare the C/O and N/O of these three galaxies with those of theoretical models and find that these three galaxies are explained by scenarios with dominant CNO-cycle materials, i.e., Wolf-Rayet stars, supermassive (103-105 M ⊙) stars, and tidal disruption events, interestingly with a requirement of frequent direct collapses. For all the 70 galaxies, we present measurements of Ne/O, S/O, and Ar/O, together with C/O and N/O. We identify four galaxies with very low Ne/O, log(Ne/O) < -1.0, indicating abundant massive (≳30 M ⊙) stars.

Keywords: high-redshift galaxies; galaxy chemical evolution; galaxy formation; star formation
Conditions for Proton Temperature Anisotropy to Drive Instabilities in the Solar Wind

Using high-resolution data from Solar Orbiter, we investigate the plasma conditions necessary for the proton temperature-anisotropy-driven mirror-mode and oblique firehose instabilities to occur in the solar wind. We find that the unstable plasma exhibits dependencies on the angle between the direction of the magnetic field and the bulk solar wind velocity which cannot be explained by the double-adiabatic expansion of the solar wind alone. The angle dependencies suggest that perpendicular heating in Alfvénic wind may be responsible. We quantify the occurrence rate of the two instabilities as a function of the length of unstable intervals as they are convected over the spacecraft. This analysis indicates that mirror-mode and oblique firehose instabilities require a spatial interval of length greater than 2-3 unstable wavelengths in order to relax the plasma into a marginally stable state and thus closer to thermodynamic equilibrium in the solar wind. Our analysis suggests that the conditions for these instabilities to act effectively vary locally on scales much shorter than the correlation length of solar wind turbulence.

Keywords: solar wind; space plasmas; interplanetary turbulence; plasma physics; alfven waves; heliosphere
Late-time Observations of Calcium-rich Transient SN 2019ehk Reveal a Pure Radioactive Decay Power Source

We present multiband Hubble Space Telescope imaging of the calcium-rich supernova (SN) SN 2019ehk at 276-389 days after explosion. These observations represent the latest B-band to near-IR photometric measurements of a calcium-rich transient to date and allow for the first opportunity to analyze the late-time bolometric evolution of an object in this observational SN class. We find that the late-time bolometric light curve of SN 2019ehk can be described predominantly through the radioactive decay of 56Co for which we derive a mass of M(56Co) = (2.8 ± 0.1) × 10-2 M⊙. Furthermore, the rate of decline in bolometric luminosity requires the leakage of γ-rays on timescale tγ = 53.9 ± 1.30 days, but we find no statistical evidence for incomplete positron trapping in the SN ejecta. While our observations cannot constrain the exact masses of other radioactive isotopes synthesized in SN 2019ehk, we estimate a mass ratio limit of M(57Co)/M(56Co) ≤ 0.030. This limit is consistent with the explosive nucleosynthesis produced in the merger of low-mass white dwarfs, which is one of the favored progenitor scenarios in early-time studies of SN 2019ehk.

Keywords: supernovae; type ib supernovae; white dwarf stars; nuclear abundances; nucleosynthesis
RZ Piscium Hosts a Compact and Highly Perturbed Debris Disk

RZ Piscium (RZ Psc) is well known in the variable star field because of its numerous irregular optical dips in the past 5 decades, but the nature of the system is heavily debated in the literature. We present multiyear infrared monitoring data from Spitzer and WISE to track the activities of the inner debris production, revealing stochastic infrared variability as short as weekly timescales that is consistent with destroying a 90 km sized asteroid every year. ALMA 1.3 mm data combined with spectral energy distribution modeling show that the disk is compact (~0.1-13 au radially) and lacks cold gas. The disk is found to be highly inclined and has a significant vertical scale height. These observations confirm that RZ Psc hosts a close to edge-on, highly perturbed debris disk possibly due to migration of recently formed giant planets that might be triggered by the low-mass companion RZ Psc B if the planets formed well beyond the snowlines.

Keywords: circumstellar matter; debris disks; infrared excess; extrasolar rocky planets; exoplanet migration
Tests of Disk-locking in T Tauri Stars of the Orion Nebula Cluster

We look for specific correlations predicted by magnetospheric accretion models for young stars that assume disk-locking using stellar and accretion parameters derived from low-resolution HST-STIS spectra of 33 T Tauri stars in the Orion Nebula Cluster. Our results provide strong support for the correlation predicted by a model that does not constrain the stellar magnetic field to a specific geometry, while little support is found for the correlation that assumes a dipolar stellar field geometry. These results support the conclusions from similar studies of older T Tauri stars in Taurus and NGC 2264 and underscore the role that trapped flux plays in regulating a young star's angular momentum as detailed by Ostriker & Shu. While our targets were all selected to be accreting young stars based on photometric indices, approximately half of the observed stars show no significant signs of accretion in our spectra, illustrating the difficulty in using photometric indices to find accreting stars and the possible role that variability has in the appearance of spectra in young stars. Although values of accretion luminosity derived from our models agree well with those derived from Hβ luminosity for strongly accreting stars, we find that accretion luminosity derived from Hβ luminosity is not a reliable parameter for discriminating between weakly accreting and nonaccreting T Tauri stars due to chromospheric emission that is likely present in all T Tauri stars.

Keywords: pre-main sequence stars; t tauri stars; low mass stars; variable stars; fundamental parameters of stars
A Radial Limit on Polar Circumbinary Orbits from General Relativity

A particle orbiting a misaligned eccentric orbit binary undergoes nodal precession either around the binary angular momentum vector (a circulating orbit) or around a stationary inclination (a librating orbit). In the absence of general relativity (GR), the stationary inclination is inclined by 90° to the binary angular momentum vector (aligned with the binary eccentricity vector) and does not depend on the particle semimajor axis. GR causes apsidal precession of the binary orbit. Close to the binary, the behavior of the particle is not significantly affected, and a librating particle precesses with the binary. However, we find that the stationary inclination and the minimum inclination required for libration both increase with the particle semimajor axis. There is a critical radius beyond which there are no librating orbits, only circulating orbits, and therefore there is a maximum orbital radius for a stationary polar-orbiting body. The critical radius is within planet-forming regions around binaries with a semimajor axis ≲1 au. This has implications for the search for misaligned circumbinary planets and the radial extent of polar circumbinary disks.

Keywords: binary stars; celestial mechanics; planet formation
Firefly: A Browser-based Interactive 3D Data Visualization Tool for Millions of Data Points

We present Firefly, a new browser-based interactive tool for visualizing 3D particle data sets. On a typical personal computer, Firefly can simultaneously render and enable real-time interactions with ≳10 million particles, and can interactively explore data sets with billions of particles using the included custom-built octree render engine. Once created, viewing a Firefly visualization requires no installation and is immediately usable in most modern internet browsers simply by visiting a URL. As a result, a Firefly visualization works out-of-the-box on most devices including smartphones and tablets. Firefly is primarily developed for researchers to explore their own data, but can also be useful to communicate results to researchers and/or collaborators and as an effective public outreach tool. Every element of the user interface can be customized and disabled, enabling easy adaptation of the same visualization for different audiences with little additional effort. Creating a new Firefly visualization is simple with the provided Python data preprocessor that translates input data to a Firefly-compatible format and provides helpful methods for hosting instances of Firefly both locally and on the internet. In addition to visualizing the positions of particles, users can visualize vector fields (e.g., velocities) and also filter and color points by scalar fields. We share three examples of Firefly applied to astronomical data sets: (1) the FIRE cosmological zoom-in simulations, (2) the SDSS galaxy catalog, and (3) Gaia Data Release 3. A gallery of additional interactive demos is available at alexbgurvi.ch/Firefly.

Keywords: astronomy data visualization; open source software
Hit-and-stick Dust Collisions: Rotating Aggregate Targets

Current models of dust aggregation in early planet formation describe numerous collision mechanisms in detail, but this research evaluates the impact of an idea that has not yet been explored: the effect of rotating targets on the probability of aggregate growth. Rotating target surfaces decrease the probability of successful sticking collisions due to an increased relative velocity between the colliding surfaces. A model has been developed to quantify this effect for use in dust evolution models. Curiously, the decrease in probability was found to almost exactly correlate to a quadratic function of the target angular velocity. For the range of target angular velocities between 0 and 100 rad s-1, the decrease in probability of sticking was calculated to be between 0% and 25% lower than predicted in a model that does not consider rotation, suggesting that dust may accumulate slower than previously thought in streaming stabilities.

Keywords: protoplanetary disks; planetary system formation
The Coronal Mass Ejection Visibility Function of Modern Coronagraphs

We analyze the detection capability of coronal mass ejections (CMEs) for all currently operating coronagraphs in space. We define as CMEs events that propagate beyond 10 solar radii with morphologies broadly consistent with a magnetic flux-rope presence. We take advantage of multi-viewpoint observations over five month-long intervals, corresponding to special orbital configurations of the coronagraphs aboard the Solar Terrestrial Relations Observatory (STEREO) and Solar and Heliospheric Observatory missions. This allows us to sort out CMEs from other outward-propagating features (e.g., waves or outflows), and thus to identify the total number of unique CMEs ejected during those periods. We determine the CME visibility functions (VFs) of the STEREO COR2-A/B and LASCO C2/C3 coronagraphs directly as the ratio of observed to unique CMEs. The VFs range from 0.71 to 0.92 for a 95% confidence interval. By comparing detections between coronagraphs on the same spacecraft and from multiple spacecraft, we assess the influence of field of view (FOV), instrument performance, and projection effects on the CME detection ability without resorting to proxies, such as flares or radio bursts. We find that no major CMEs are missed by any of the coronagraphs, that a few slow halo-like events may be missed in synoptic cadence movies, and that narrow FOV coronagraphs have difficulties discriminating between CMEs and other ejections, leading to "false" detection rates. We conclude that CME detection can only be validated with multi-viewpoint imaging—two coronagraphs in quadrature offer adequate detection capability. Finally, we apply the VFs to observed CME rates resulting in upward corrections of 40%.

Keywords: active solar corona; solar coronal mass ejections; sunspot number; coronagraphic imaging
Time Evolution of the CMB Quadrupole

I show that the quadrupole of the Cosmic Microwave Background (CMB) evolves more rapidly than previously expected, as a result of the acceleration of the Sun toward the Galactic center. The acceleration, measured most recently by Gaia EDR3, implies a fractional change in the quadrupole of ~10-9 per year, an order of magnitude larger than expected from the evolution in the last scattering surface of the CMB.

Keywords: cosmic microwave background radiation
Probing the Origin of Diffuse Radio Emission in the Cool Core of the Phoenix Galaxy Cluster

Cool core galaxy clusters are considered to be dynamically relaxed clusters with regular morphology and highly X-ray luminous central region. However, cool core clusters can also be sites for merging events that exhibit cold fronts in X-ray and minihalos in radio. We present recent radio/X-ray observations of the Phoenix Cluster or South Pole Telescope (SPT)-CL J2344-4243 at the redshift of z = 0.596. Using archival Chandra X-ray observations, we detect spiraling cool gas around the cluster core as well as discover two cold fronts near the core. This is perhaps the most distant galaxy cluster to date known to host cold fronts. Also, we present JVLA8 1.52 GHz observations of the minihalo, previously discovered at 610 MHz with GMRT9 observations in the center of the Phoenix galaxy cluster. The minihalo flux density at 1.52 GHz is 9.65 ± 0.97 mJy with the spectral index between 610 MHz and 1.52 GHz being -0.98 ± 0.16.10 A possible origin of these radio sources is turbulence induced by sloshing of the gas in the cluster core.

Keywords: galaxy clusters; intracluster medium; non-thermal radiation sources; x-ray sources; cool cores; extended radiation sources
Refractive Index and Extinction Coefficient of Vapor-deposited Water Ice in the UV-vis Range

Laboratory results of the optical properties of vapor-deposited water ice, specifically the refractive index and extinction coefficient, are available mainly for a selective set of wavelengths and a limited number of deposition temperatures. Experimental limitations are the main reason for the lack of broadband data, which is unfortunate as these quantities are needed to interpret and predict astronomical and planetary observations. The goal of this work is to address these lacking data, using an experimental broadband method that is capable of rapidly providing reliable water ice data across the entire UV-visible range. This approach combines the simultaneous use of a monochromatic HeNe laser and a broadband Xe-arc lamp to record interference fringes of water ice during deposition at astronomically relevant ice temperatures. The ice thickness is typically more than 20 μm. Analyzing the period and intensity patterns combining both the monochromatic and broadband interference patterns allows the determination of the wavelength-dependent refractive index and extinction coefficient. We present accurate refractive index and extinction coefficient graphs for wavelengths between 250 and 750 nm and ices deposited between 30 and 160 K. From our data, we find a possible structural change in the ice in the 110-130 K region that has not been reported before. We also discuss that the data presented in this paper can be used to interpret astronomical observations of icy surfaces.

Keywords: laboratory astrophysics; experimental techniques; surface ices
Clustering Properties of Intermediate and High-mass Young Stellar Objects

We have selected 337 intermediate- and high-mass young stellar objects (YSOs; 1.5-20 M ⊙) well-characterized with spectroscopy. By means of the clustering algorithm HDBSCAN, we study their clustering and association properties in the Gaia DR3 catalog as a function of stellar mass. We find that the lower-mass YSOs (1.5-4 M ⊙) have clustering rates of 55%-60% in Gaia astrometric space, a percentage similar to that found in the T Tauri regime. However, intermediate-mass YSOs in the range 4-10 M ⊙ show a decreasing clustering rate with stellar mass, down to 27%. We find tentative evidence suggesting that massive YSOs (>10 M ⊙) often (yet not always) appear clustered. We put forward the idea that most massive YSOs form via a mechanism that demands many low-mass stars around them. However, intermediate-mass YSOs form in a classical core-collapse T Tauri way, yet they do not appear often in the clusters around massive YSOs. We also find that intermediate- and high-mass YSOs become less clustered with decreasing disk emission and accretion rate. This points toward an evolution with time. For those sources that appear clustered, no major correlation is found between their stellar properties and the cluster sizes, number of cluster members, cluster densities, or distance to cluster centers. In doing this analysis, we report the identification of 55 new clusters. We tabulated all of the derived cluster parameters for the considered intermediate- and high-mass YSOs. * Table is also available online at the CDS in the VizieR archive service.

Keywords: star formation; clustering; young star clusters; star clusters; young stellar objects; herbig ae/be stars; massive stars; t tauri stars; emission line stars; protoplanetary disks
Exponential Fluctuations in the Modes of Orthogonal Polarization in Pulsar Radio Emission

A statistical model for the polarization of pulsar radio emission is enhanced to account for the heavy modulation of the emission, the possible covariance of the Stokes parameters, and the observed asymmetries in the distributions of total intensity, polarization, and fractional polarization, by treating the intensities of the orthogonal polarization modes as exponential random variables. The model is used to derive theoretical distributions to compare with what is observed. The resulting distributions are unimodal and generally asymmetric. The unimodality arises from the model's fundamental assumption that the orthogonal modes are superposed. The asymmetry originates primarily from different fluctuations in mode intensities. The distributions of fractional polarization are truncated at the degree of linear and circular polarization intrinsic to the modes. A number of observable parameters that quantify the statistical properties of the emission and its polarization are derived and are shown to be functions only of the ratio of the modes' mean intensities, M, suggesting their spectra coevolve according to the frequency dependence of M. This particular implementation of the model requires the modes to fluctuate differently in order to replicate the observations. Given that a single underlying emission mechanism seems unlikely to selectively modulate the mode intensities, the different fluctuations are attributed either to different emission mechanisms for the modes or to mode-dependent propagation or scattering effects in the pulsar magnetosphere.

Keywords: radio pulsars