adsabs/SciX_UAT_keywords huggingface dataset:
Figuring Out Gas & Galaxies in Enzo (FOGGIE). VI. The Circumgalactic Medium of L ∗ Galaxies Is Supported in an Emergent, Nonhydrostatic Equilibrium

The circumgalactic medium (CGM) is often assumed to exist in or near hydrostatic equilibrium, with the regulation of accretion and the effects of feedback treated as perturbations to a stable balance between gravity and thermal pressure. We investigate global hydrostatic equilibrium in the CGM using four highly resolved L * galaxies from the Figuring Out Gas & Galaxies in Enzo (FOGGIE) project. The FOGGIE simulations were specifically targeted at fine spatial and mass resolution in the CGM (Δx ≲ 1 kpc h -1 and M ≃ 200M ⊙). We develop a new analysis framework that calculates the forces provided by thermal pressure gradients, turbulent pressure gradients, ram pressure gradients of large-scale radial bulk flows, centrifugal rotation, and gravity acting on the gas in the CGM. Thermal and turbulent pressure gradients vary strongly on scales of ≲5 kpc throughout the CGM. Thermal pressure gradients provide the main supporting force only beyond ~0.25R 200, or ~50 kpc at z = 0. Within ~0.25R 200, turbulent pressure gradients and rotational support provide stronger forces than thermal pressure. More generally, we find that global equilibrium models are neither appropriate nor predictive for the small scales probed by absorption line observations of the CGM. Local conditions generally cannot be derived by assuming a global equilibrium, but an emergent global equilibrium balancing radially inward and outward forces is obtained when averaging over the nonequilibrium local conditions on large scales in space and time. Approximate hydrostatic equilibrium holds only at large distances from galaxies, even when averaging out small-scale variations.

Keywords: circumgalactic medium
Bright, Months-long Stellar Outbursts Announce the Explosion of Interaction-powered Supernovae

Interaction-powered supernovae (SNe) explode within an optically thick circumstellar medium (CSM) that could be ejected during eruptive events. To identify and characterize such pre-explosion outbursts, we produce forced-photometry light curves for 196 interacting SNe, mostly of Type IIn, detected by the Zwicky Transient Facility between early 2018 and 2020 June. Extensive tests demonstrate that we only expect a few false detections among the 70,000 analyzed pre-explosion images after applying quality cuts and bias corrections. We detect precursor eruptions prior to 18 Type IIn SNe and prior to the Type Ibn SN 2019uo. Precursors become brighter and more frequent in the last months before the SN and month-long outbursts brighter than magnitude -13 occur prior to 25% (5-69%, 95% confidence range) of all Type IIn SNe within the final three months before the explosion. With radiative energies of up to 1049 erg, precursors could eject ∼1 M⊙ of material. Nevertheless, SNe with detected precursors are not significantly more luminous than other SNe IIn, and the characteristic narrow hydrogen lines in their spectra typically originate from earlier, undetected mass-loss events. The long precursor durations require ongoing energy injection, and they could, for example, be powered by interaction or by a continuum-driven wind. Instabilities during the neon- and oxygen-burning phases are predicted to launch precursors in the final years to months before the explosion; however, the brightest precursor is 100 times more energetic than anticipated.

Keywords: eruptive phenomena; stellar mass loss; circumstellar matter; late stellar evolution; stellar flares; core-collapse supernovae
The Low Earth Orbit Satellite Population and Impacts of the SpaceX Starlink Constellation

I discuss the current low Earth orbit artificial satellite population and show that the proposed "megaconstellation" of circa 12,000 Starlink Internet satellites would dominate the lower part of the Earth orbit, below 600 km, with a latitude-dependent areal number density of between 0.005 and 0.01 objects per square degree at airmass <2. Such large, low-altitude satellites appear visually bright to ground observers, and the initial Starlinks are naked-eye objects. I model the expected number of illuminated satellites as a function of latitude, time of year, and time of night and summarize the range of possible consequences for ground-based astronomy. In winter at lower latitudes typical of major observatories, the satellites will not be illuminated for six hours in the middle of the night. However, at low elevations near twilight at intermediate latitudes (45°-55°, e.g., much of Europe) hundreds of satellites may be visible at once to naked-eye observers at dark sites.

Keywords: artificial satellites; night sky brightness; astronomical site protection; ground-based astronomy
Morphological Reconstruction of a Small Transient Observed by Parker Solar Probe on 2018 November 5

On 2018 November 5, about 24 hr before the first close perihelion passage of Parker Solar Probe (PSP), a coronal mass ejection (CME) entered the field of view of the inner detector of the Wide-field Imager for Solar PRobe (WISPR) instrument on board PSP, with the northward component of its trajectory carrying the leading edge of the CME off the top edge of the detector about four hours after its first appearance. We connect this event to a very small jetlike transient observed from 1 au by coronagraphs on both the SOlar and Heliospheric Observatory (SOHO) and the A component of the Solar TErrestrial RElations Observatory mission (STEREO-A). This allows us to make the first three-dimensional reconstruction of a CME structure considering both observations made very close to the Sun and images from two observatories at 1 au. The CME may be small and jetlike as viewed from 1 au, but the close-in vantage point of PSP/WISPR demonstrates that it is not intrinsically jetlike but instead has a structure consistent with a flux rope morphology. Based on its appearance in the SOHO and STEREO-A images, the event belongs in the "streamer blob" class of transients, but its kinematic behavior is very unusual, with a more impulsive acceleration than previously studied blobs.

Keywords: solar coronal mass ejections; solar k corona; solar coronal transients
Magnetic Connectivity of the Ecliptic Plane within 0.5 au: Potential Field Source Surface Modeling of the First Parker Solar Probe Encounter

We compare magnetic field measurements taken by the FIELDS instrument on board Parker Solar Probe (PSP) during its first solar encounter to predictions obtained by potential field source surface (PFSS) modeling. Ballistic propagation is used to connect the spacecraft to the source surface. Despite the simplicity of the model, our results show striking agreement with PSP's first observations of the heliospheric magnetic field from ∼0.5 au (107.5 R⊙) down to 0.16 au (35.7 R⊙). Further, we show the robustness of the agreement is improved both by allowing the photospheric input to the model to vary in time, and by advecting the field from PSP down to the PFSS model domain using in situ PSP/Solar Wind Electrons Alphas and Protons measurements of the solar wind speed instead of assuming it to be constant with longitude and latitude. We also explore the source surface height parameter (RSS) to the PFSS model, finding that an extraordinarily low source surface height (1.3-1.5 R⊙) predicts observed small-scale polarity inversions, which are otherwise washed out with regular modeling parameters. Finally, we extract field line traces from these models. By overlaying these on extreme ultraviolet images we observe magnetic connectivity to various equatorial and mid-latitude coronal holes, indicating plausible magnetic footpoints and offering context for future discussions of sources of the solar wind measured by PSP.

Keywords: heliosphere; solar corona; solar wind; solar magnetic fields; magnetic fields; open source software; interplanetary magnetic fields
Rotational Evolution of Classical T Tauri Stars: Models and Observations

We developed a grid of stellar rotation models for low-mass and solar-type classical T Tauri stars (CTTS; 0.3M ⊙ < M * < 1.2M ⊙). These models incorporate the star–disk interaction and magnetospheric ejections to investigate the evolution of the stellar rotation rate as a function of the mass of the star M *, the magnetic field (B *), and stellar wind ( ). We compiled and determined stellar parameters for 208 CTTS, such as projected rotational velocity , mass accretion rate , stellar mass M *, ages, and estimated rotational periods using Transiting Exoplanet Survey Satellite (TESS) data. We also estimated a representative value of the mass-loss rate for our sample using the [O I] λ 6300 spectral line. Our results confirm that measurements in CTTS agree with the rotation rates provided by our spin models in the accretion-powered stellar winds picture. In addition, we used the approximate Bayesian computation technique to explore the connection between the model parameters and the observational properties of CTTS. We find that the evolution of with age might be regulated by variations in (1) the intensity of B * and (2) the fraction of the accretion flow ejected in magnetic winds, removing angular momentum from these systems. The youngest stars in our sample (∼1 Myr) show a median branching ratio and median B * ∼ 2000 G, in contrast to ∼0.01 and 1000 G, respectively, for stars with ages ≳3 Myr.

Keywords: classical t tauri stars; stellar evolution; stellar magnetic fields; stellar properties; stellar rotation; stellar winds
WISE J135501.90-825838.9 is a Nearby, Young, Extremely Low-mass Substellar Binary

We present a parallax solution for WISE J135501.90-825838.9, a spectral binary with spectral types L7+T7.5 and a candidate AB Doradus member. Using Wide-field Infrared Survey Explorer (WISE) astrometry, we obtain a distance of d = 16.7 ± 5.3 pc. This preliminary parallax solution provides further evidence that WISE J135501.90-825838.9 is a member of AB Doradus (130-200 Myr), and when combined with evolutionary models predicts masses of 11 MJup and 9 MJup for each component.

Keywords: binary stars; brown dwarfs; low mass stars; astrometry; trigonometric parallax; parallax; close binary stars
Two-dimensional Particle-in-cell Simulations of Axisymmetric Black Hole Magnetospheres

We investigate the temporal evolution of an axisymmetric magnetosphere around a rapidly rotating stellar-mass black hole by applying a two-dimensional particle-in-cell simulation scheme. Adopting homogeneous pair production and assuming that the mass accretion rate is much less than the Eddington limit, we find that the black hole's rotational energy is preferentially extracted from the middle latitudes and that this outward energy flux exhibits an enhancement that lasts approximately 160 dynamical timescales. It is demonstrated that the magnetohydrodynamic approximations cannot be justified in such a magnetically dominated magnetosphere because Ohm's law completely breaks down and the charge-separated electron-positron plasmas are highly nonneutral. An implication is given regarding the collimation of relativistic jets.

Keywords: kerr black holes; astronomical simulations; stellar magnetic fields; general relativity
Do Type Ia Supernovae Explode inside Planetary Nebulae?

The nature of Type Ia supernova (SN Ia) explosions remains an open issue, with several contending progenitor scenarios actively being considered. One such scenario involves an SN Ia explosion inside a planetary nebula (PN) in the aftermath of a stellar merger triggered by a common envelope (CE) episode. We examine this scenario using hydrodynamic and nonequilibrium ionization simulations of the interaction between the SN ejecta and the PN cocoon into the supernova remnant (SNR) phase, focusing on the impact of the delay between the CE episode and the SN explosion. We compare the bulk dynamics and X-ray spectra of our simulated SNRs to the observed properties of known Type Ia SNRs in the Milky Way and the Magellanic Clouds. We conclude that models where the SN explosion happens in the immediate aftermath of the CE episode (with a delay ≲1000 yr) are hard to reconcile with the observations, because the interaction with the dense PN cocoon results in ionization timescales much higher than those found in any known Type Ia SNR. Models with a longer delay between the CE episode and the SN explosion (∼10,000 yr) are closer to the observations, and may be able to explain the bulk properties of some Type Ia SNRs.

Keywords: supernova remnants; type ia supernovae; planetary nebulae; common envelope evolution; x-ray astronomy
Improving Astronomical Time-series Classification via Data Augmentation with Generative Adversarial Networks

Due to the latest advances in technology, telescopes with significant sky coverage will produce millions of astronomical alerts per night that must be classified both rapidly and automatically. Currently, classification consists of supervised machine-learning algorithms whose performance is limited by the number of existing annotations of astronomical objects and their highly imbalanced class distributions. In this work, we propose a data augmentation methodology based on generative adversarial networks (GANs) to generate a variety of synthetic light curves from variable stars. Our novel contributions, consisting of a resampling technique and an evaluation metric, can assess the quality of generative models in unbalanced data sets and identify GAN-overfitting cases that the Fréchet inception distance does not reveal. We applied our proposed model to two data sets taken from the Catalina and Zwicky Transient Facility surveys. The classification accuracy of variable stars is improved significantly when training with synthetic data and testing with real data with respect to the case of using only real data.

Keywords: variable stars; rr lyrae variable stars; cepheid variable stars; delta scuti variable stars; long period variable stars; eclipsing binary stars; astroinformatics; astrostatistics; neural networks; time series analysis; light curve classification; surveys
The GALPROP Cosmic-ray Propagation and Nonthermal Emissions Framework: Release v57

The past decade has brought impressive advances in the astrophysics of cosmic rays (CRs) and multiwavelength astronomy, thanks to the new instrumentation launched into space and built on the ground. Modern technologies employed by those instruments provide measurements with unmatched precision, enabling searches for subtle signatures of dark matter and new physics. Understanding the astrophysical backgrounds to better precision than the observed data is vital in moving to this new territory. A state-of-the-art CR propagation code, called GALPROP, is designed to address exactly this challenge. Having 25 yr of development behind it, the GALPROP framework has become a de facto standard in the astrophysics of CRs, diffuse photon emissions (radio to γ-rays), and searches for new physics. GALPROP uses information from astronomy, particle physics, and nuclear physics to predict CRs and their associated emissions self-consistently, providing a unifying modeling framework. The range of its physical validity covers 18 orders of magnitude in energy, from sub-keV to PeV energies for particles and from μeV to PeV energies for photons. The framework and the data sets are public and are extensively used by many experimental collaborations and by thousands of individual researchers worldwide for interpretation of their data and for making predictions. This paper details the latest release of the GALPROP framework and updated cross sections, further developments of its initially auxiliary data sets for models of the interstellar medium that grew into independent studies of the Galactic structure-distributions of gas, dust, radiation, and magnetic fields-as well as the extension of its modeling capabilities. Example applications included with the distribution illustrating usage of the new features are also described.

Keywords: galactic cosmic rays; gamma-rays; diffuse radiation; gamma-ray astronomy; non-thermal radiation sources
RAM: Rapid Advection Algorithm on Arbitrary Meshes

The study of many astrophysical flows requires computational algorithms that can capture high Mach number flows, while resolving a large dynamic range in spatial and density scales. In this paper we present a novel method, RAM: Rapid Advection Algorithm on Arbitrary Meshes. RAM is a time-explicit method to solve the advection equation in problems with large bulk velocity on arbitrary computational grids. In comparison with standard upwind algorithms, RAM enables advection with larger time steps and lower truncation errors. Our method is based on the operator splitting technique and conservative interpolation. Depending on the bulk velocity and resolution, RAM can decrease the numerical cost of hydrodynamics by more than one order of magnitude. To quantify the truncation errors and speed-up with RAM, we perform one- and two-dimensional hydrodynamics tests. We find that the order of our method is given by the order of the conservative interpolation and that the effective speed-up is in agreement with the relative increment in time step. RAM will be especially useful for numerical studies of disk-satellite interaction, characterized by high bulk orbital velocities and nontrivial geometries. Our method dramatically lowers the computational cost of simulations that simultaneously resolve the global disk and potential well inside the Hill radius of the secondary companion.

Keywords: algorithms; hydrodynamics; accretion; protoplanetary disks
A Value-added COSMOS2020 Catalog of Physical Properties: Constraining Temperature-dependent Initial Mass Function

This work presents and releases a catalog of new photometrically derived physical properties for the ~105 most well-measured galaxies in the COSMOS field on the sky. Using a recently developed technique, spectral energy distributions are modeled assuming a stellar initial mass function (IMF) that depends on the temperature of gas in star-forming regions. The method is applied to the largest current sample of high-quality panchromatic photometry, the COSMOS2020 catalog, that allows for testing this assumption. It is found that the galaxies exhibit a continuum of IMF and gas temperatures, most of which are bottom-lighter than measured in the Milky Way. As a consequence, the stellar masses and star formation rates of most galaxies here are found to be lower than those measured by traditional techniques in the COSMOS2020 catalog by factors of ~1.6-3.5 and 2.5-70.0, respectively, with the change being the strongest for the most active galaxies. The resulting physical properties provide new insights into variation of the IMF-derived gas temperature along the star-forming main sequence and at quiescence, produce a sharp and coherent picture of downsizing, as seen from the stellar mass functions, and hint at a possible high-temperature and high-density stage of early galactic evolution.

Keywords: catalogs; initial mass function; galaxy evolution; galaxy properties; galaxy masses; high-redshift galaxies; stellar mass functions
Modeling the Optical to Ultraviolet Polarimetric Variability from Thomson Scattering in Colliding-wind Binaries

Massive-star binaries are critical laboratories for measuring masses and stellar wind mass-loss rates. A major challenge is inferring viewing inclination and extracting information about the colliding-wind interaction (CWI) region. Polarimetric variability from electron scattering in the highly ionized winds provides important diagnostic information about system geometry. We combine for the first time the well-known generalized treatment of Brown et al. for variable polarization from binaries with the semianalytic solution for the geometry and surface density CWI shock interface between the winds based on Cantó et al. Our calculations include some simplifications in the form of inverse-square law wind densities and the assumption of axisymmetry, but in so doing they arrive at several robust conclusions. One is that when the winds are nearly equal (e.g., O+O binaries) the polarization has a relatively mild decline with binary separation. Another is that despite Thomson scattering being a gray opacity, the continuum polarization can show chromatic effects at ultraviolet wavelengths but will be mostly constant at longer wavelengths. Finally, when one wind dominates the other, as, for example, in WR+OB binaries, the polarization is expected to be larger at wavelengths where the OB component is more luminous and generally smaller at wavelengths where the WR component is more luminous. This behavior arises because, from the perspective of the WR star, the distortion of the scattering envelope from spherical is a minor perturbation situated far from the WR star. By contrast, the polarization contribution from the OB star is dominated by the geometry of the CWI shock.

Keywords: spectropolarimetry; stellar winds; massive stars
Diffuse Synchrotron Emission Associated with the Starburst in the Circumnuclear Disk of NGC 1275

Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations found a positive correlation between the mass of dense molecular gas in the circumnuclear disks (CNDs) and accretion rate to the active galactic nuclei (AGNs). This indicates that star formation activity in the CNDs is essential for triggering the accretion of mass to AGNs. Although the starburst-driven turbulence is a key mechanism for the transfer of angular momentum and the resultant mass accretion from the CND scale to the inner radius, the observational evidence is lacking. We report the very-long-baseline-interferometry detection of the diffuse synchrotron emission on a scale of several tens of parsecs coinciding spatially with the molecular gas disk recently discovered by ALMA observations in NGC 1275. The synchrotron emissions most likely resulted from the relativistic electrons produced by the supernova explosions. This is unambiguous evidence of the star formation activity in a CND. The turbulent velocity and the scale height of the CND predicted from the supernova-driven turbulence model agree with the observations, although the model-predicted accretion rate disagrees with the bolometric luminosity. This might indicate that additional mechanisms to enhance the turbulence are required for the inner disk. We discuss the multiphase nature of the CND by combining the information of the CO emission, synchrotron emission, and free-free absorption.

Keywords: low-luminosity active galactic nuclei; radio active galactic nuclei; radio galaxies; perseus cluster; galaxy accretion disks; radio interferometry; very long baseline interferometry
Centimeter-sized Grains in the Compact Dust Ring around Very-low-mass Star CIDA 1

We examined the grain size in the dust ring encircling the 0.19 M ☉ T Tauri star CIDA 1 using the Karl G. Jansky Very Large Array at multiple centimeter wavelengths, with a spatial resolution of 0.″2-0.″9. We detected distinct partial-ring structures at these wavelengths around CIDA 1. Based on spatial distributions and spectral indices, we determined that these centimeter emissions originated from dust, rather than free-free or synchrotron emissions. To estimate the maximum grain size ( ${a}_{\max }$ ) within the ring, we compared the observed spectral energy distribution (SED) with SEDs calculated for different ${a}_{\max }$ values using radiative transfer calculations. Our findings indicate an ${a}_{\max }$ value of approximately 2.5 cm in the ring, assuming that the dust opacity can be approximated by the DSHARP models. These results suggest that grain growth took place within the CIDA 1 ring, potentially facilitating more efficient planet formation through pebble accretion scenarios involving centimeter-sized pebbles.

Keywords: protoplanetary disks