adsabs/SciX_UAT_keywords huggingface dataset:
Photometry of Outer Solar System Objects from the Dark Energy Survey. I. Photometric Methods, Light-curve Distributions, and Trans-Neptunian Binaries

We report the methods of and initial scientific inferences from the extraction of precision photometric information for the >800 trans-Neptunian objects (TNOs) discovered in the images of the Dark Energy Survey (DES). Scene-modeling photometry is used to obtain shot-noise-limited flux measures for each exposure of each TNO, with background sources subtracted. Comparison of double-source fits to the pixel data with single-source fits are used to identify and characterize two binary TNO systems. A Markov Chain Monte Carlo method samples the joint likelihood of the intrinsic colors of each source as well as the amplitude of its flux variation, given the time series of multiband flux measurements and their uncertainties. A catalog of these colors and light-curve amplitudes A is included with this publication. We show how to assign a likelihood to the distribution q(A) of light-curve amplitudes in any subpopulation. Using this method, we find decisive evidence (i.e., evidence ratio <0.01) that cold classical (CC) TNOs with absolute magnitude 6 < H r < 8.2 are more variable than the hot classical (HC) population of the same H r , reinforcing theories that the former form in situ and the latter arise from a different physical population. Resonant and scattering TNOs in this H r range have variability consistent with either the HCs or CCs. DES TNOs with H r < 6 are seen to be decisively less variable than higher-H r members of any dynamical group, as expected. More surprising is that detached TNOs are decisively less variable than scattering TNOs, which requires them to have distinct source regions or some subsequent differential processing.

Keywords: kuiper belt; trans-neptunian objects; photometry; asteroid satellites
Axion Oscillations in Binary Systems: Angle-action Surgery

Scalar, tensor waves induce oscillatory perturbations in Keplerian systems that can be probed with measurements of pulsar timing residuals. In this paper, we consider the imprint of coherent oscillations produced by ultralight axion dark matter on the Roemer time delay. We use the angle-action formalism to calculate the time evolution of the observed signal and its dependence on the orbital parameters and the axion phase. We derive exact analytical expressions for arbitrary binary pulsar mass ratio and eccentricity, alleviating the need for long numerical integrations. We emphasize the similarity of the expected signal-to-noise ratio with the response of a harmonic oscillator to an external oscillatory driving. We validate our theoretical predictions with numerical simulations. Our results furnish a useful benchmark for numerical codes and analysis procedures and, hopefully, will motivate the search for such imprints in real data.

Keywords: dark matter; binary pulsars; milky way dark matter halo; celestial mechanics; perturbation methods
Evidence of Extended Emission in GRB 181123B and Other High-redshift Short GRBs

We study the high-energy properties of GRB 181123B, a short gamma-ray burst (sGRB) at redshift z ≈ 1.75. We show that, despite its nominal short duration with T90 < 2 s, this burst displays evidence of a temporally extended emission (EE) at high energies and that the same trend is observed in the majority of sGRBs at z ≳ 1. We discuss the impact of instrumental selection effects on the GRB classification, stressing that the measured T90 is not an unambiguous indicator of the burst physical origin. By examining their environment (e.g., stellar mass, star formation, offset distribution), we find that these high-z sGRBs share many properties of long GRBs at a similar distance and are consistent with a short-lived progenitor system. If produced by compact binary mergers, these sGRBs with EE may be easier to localize at large distances and herald a larger population of sGRBs in the early universe.

Keywords: gamma-ray bursts; neutron stars; nucleosynthesis; chemical abundances; gravitational waves
Far-infrared Polarization Spectrum of the OMC-1 Star-forming Region

We analyze the wavelength dependence of the far-infrared polarization fraction toward the OMC-1 star-forming region using observations from HAWC+/SOFIA at 53, 89, 154, and 214 μm. We find that the shape of the far-infrared polarization spectrum is variable across the cloud and that there is evidence of a correlation between the slope of the polarization spectrum and the average line-of-sight temperature. The slope of the polarization spectrum tends to be negative (falling toward longer wavelengths) in cooler regions and positive or flat in warmer regions. This is very similar to what was discovered in ρ Oph A via SOFIA polarimetry at 89 and 154 μm. Like the authors of this earlier work, we argue that the most natural explanation for our falling spectra is line-of-sight superposition of differing grain populations, with polarized emission from the warmer regions and less-polarized emission from the cooler ones. In contrast with the earlier work on ρ Oph A, we do not find a clear correlation of polarization spectrum slope with column density. This suggests that falling spectra are attributable to variations in grain alignment efficiency in a heterogeneous cloud consistent with radiative torques theory. Alternative explanations in which variations in grain alignment efficiency are caused by varying gas density rather than by varying radiation intensity are disfavored.

Keywords: polarimetry; interstellar dust; molecular clouds; interstellar magnetic fields
On the Temperature Profiles and Emission Spectra of Mini-Neptune Atmospheres

Atmospheric observations of mini-Neptunes orbiting M dwarfs are beginning to provide constraints on their chemical and thermal properties, while also providing clues about their interiors and potential surfaces. With their relatively large scale heights and large planet-star contrasts, mini-Neptunes are currently ideal targets toward the goal of characterizing temperate low-mass exoplanets. Understanding the thermal structures and spectral appearances of mini-Neptunes is important to understand various aspects of their atmospheres, including radiative/convective energy transport, boundary conditions for the interior, and their potential habitability. In the present study, we explore these aspects of mini-Neptunes using self-consistent models of their atmospheres. We begin by exploring the effects of irradiation, internal flux, metallicity, clouds, and hazes on the atmospheric temperature profiles and thermal emission spectra of temperate mini-Neptunes. In particular, we investigate the impact of these properties on the radiative-convective boundary and the thermodynamic conditions in the lower atmosphere, which serves as the interface with the interior and/or a potential surface. Building on recent suggestions of habitability of the mini-Neptune K2-18 b, we find a range of physically motivated atmospheric conditions that allow for liquid water under the H2-rich atmospheres of such planets. We find that observations of thermal emission with JWST/MIRI spectrophotometry can place useful constraints on the habitability of temperate mini-Neptunes such as K2-18 b and provide more detailed constraints on the chemical and thermal properties of warmer planets such as GJ 3470 b. Our results underpin the potential of temperate mini-Neptunes such as K2-18 b as promising candidates in the search for habitable exoplanets.

Keywords: exoplanets; mini neptunes; spectroscopy; exoplanet atmospheres; radiative transfer; habitable planets
From Seeds to Supermassive Black Holes: Capture, Growth, Migration, and Pairing in Dense Protobulge Environments

The origins and mergers of supermassive black holes (SMBHs) remain a mystery. We describe a scenario from a novel multiphysics simulation featuring rapid (≲1 Myr) hyper-Eddington gas capture by a ∼1000 M ⊙ "seed" black hole (BH) up to supermassive (≳106 M ⊙) masses in a massive, dense molecular cloud complex typical of high-redshift starbursts. Due to the high cloud density, stellar feedback is inefficient, and most of the gas turns into stars in star clusters that rapidly merge hierarchically, creating deep potential wells. Relatively low-mass BH seeds at random positions can be "captured" by merging subclusters and migrate to the center in ∼1 freefall time (vastly faster than dynamical friction). This also efficiently produces a paired BH binary with ∼0.1 pc separation. The centrally concentrated stellar density profile (akin to a "protobulge") allows the cluster as a whole to capture and retain gas and build up a large (parsec-scale) circumbinary accretion disk with gas coherently funneled to the central BH (even when the BH radius of influence is small). The disk is "hypermagnetized" and "flux-frozen": dominated by a toroidal magnetic field with plasma β ∼ 10‑3, with the fields amplified by flux-freezing. This drives hyper-Eddington inflow rates ≳1 M ⊙ yr‑1, which also drive the two BHs to nearly equal masses. The late-stage system appears remarkably similar to recently observed high-redshift "little red dots." This scenario can provide an explanation for rapid SMBH formation, growth, and mergers in high-redshift galaxies.

Keywords: accretion; black hole physics; intermediate-mass black holes; giant molecular clouds; star formation
A Tale of Two Grains: Impact of Grain Size on Ring Formation via Nonideal Magnetohydrodynamic Processes

Substructures in protoplanetary disks (PPDs), whose ubiquity was unveiled by recent Atacama Large Millimeter/submillimeter Array observations, are widely discussed regarding their possible origins. We carry out global 2D magnetohydrodynamic (MHD) simulations in axisymmetry, coupled with self-consistent ray-tracing radiative transfer, thermochemistry, and nonideal MHD diffusivities. The abundance profiles of grains are also calculated based on the global dust evolution calculation, including sintering effects. We found that dust size plays a crucial role in the ring formation around the snow lines of PPDs through the accretion process. Disk ionization structures and thus tensorial conductivities depend on the size of grains. When grains are significantly larger than polycyclic aromatic hydrocarbons (PAHs), the nonideal MHD conductivities change dramatically across each snow line of major volatiles, leading to a sudden change in the accretion process across the snow lines and the subsequent formation of gaseous rings/gaps there. Specific layout of magnetic fields can suppress wind launching in certain regions by canceling out different stress components. On the other hand, the variations of conductivities are a lot less with only PAH-sized grains in disks and then these disks retain smoother radial density profiles across snow lines.

Keywords: stellar accretion disks; protoplanetary disks; magnetohydrodynamics; planet formation
Small Electron Events Observed by Parker Solar Probe/IS⊙IS during Encounter 2

The current understanding of the characteristics of solar and inner heliospheric electron events is inferred almost entirely from observations made by spacecraft located at 1 astronomical unit (au). Previous observations within 1 au of the Sun, by the Helios spacecraft at ∼0.3-1 au, indicate the presence of electron events that are not detected at 1 au or may have merged during transport from the Sun. Parker Solar Probe's close proximity to the Sun at perihelion provides an opportunity to make the closest measurements yet of energetic electron events. We present an overview of measurements of electrons with energies between ∼17 keV and ∼1 MeV made by the Parker Solar Probe Integrated Science Investigation of the Sun (IS⊙IS) instrument suite during Encounter 2 (2019 March 31-April 10 with perihelion of ∼0.17 au), including several small electron events. We examine these events in the context of the electromagnetic and solar wind environment measured by the FIELDS and SWEAP instruments on Parker Solar Probe. We find most of these electron enhancements to be associated with type III radio emissions that reach the local plasma frequency and one enhancement that appears to be primarily associated with abrupt changes in the local magnetic field. Together, these associations suggest that these are indeed the first measurements of energetic electron events within 0.2 au.

Keywords: solar flares; solar energetic particles; solar particle emission; radio bursts; solar physics
Hydrodynamic Winds from Twin-star Binaries

Stellar winds shape the evolution of stars through the loss of mass. In binary systems, they also shape the stars' evolution by modifying the orbit. In this paper, we use hydrodynamic simulations to study the emergence of nearly isothermal winds from identical twin binaries. We vary the degree to which model stars fill their Roche lobes and the temperature of the wind. Initialized at rest on the stellar surfaces, winds accelerate away from the binary components through a sonic surface to supersonic outward velocities. In cases where the binary fills its Roche lobe, a shared subsonic region surrounds both components. We find that mass loss rates from close twin-star binaries are enhanced relative to the expectation from two single-object winds. This binary enhancement is best modeled as a function of the ratio of wind velocity to orbital velocity. Similarly, we find that the specific angular momentum with which winds emerge can vary between that of the binary components and that of the outer Lagrange points depending on the ratio of wind velocity to orbital velocity. Given that mass and angular momentum loss can be modeled as simple functions of wind velocity, our results may be broadly applicable to the evolution of close, equal-mass binaries. One particularly important potential application is to massive, close binaries, which may be progenitors of binary black hole mergers through the chemically homogeneous evolution channel.

Keywords: binary stars; close binary stars; stellar winds; hydrodynamics
The Role of Magnetic Shear in Reconnection-driven Flare Energy Release

Using observations from the Solar Dynamics Observatory's Atmosphere Imaging Assembly and the Ramaty High Energy Solar Spectroscopic Imager, we present novel measurements of the shear of post-reconnection flare loops (PRFLs) in SOL20141218T21:40 and study its evolution with respect to magnetic reconnection and flare emission. Two quasi-parallel ribbons form adjacent to the magnetic polarity inversion line (PIL), spreading in time first parallel to the PIL and then mostly in a perpendicular direction. We measure the magnetic reconnection rate from the ribbon evolution, and also the shear angle of a large number of PRFLs observed in extreme ultraviolet passbands (≲1 MK). For the first time, the shear angle measurements are conducted using several complementary techniques allowing for cross validation of the results. In this flare, the total reconnection rate is much enhanced before a sharp increase in the hard X-ray emission, and the median shear decreases from 60°-70° to 20°, on a timescale of 10 minutes. We find a correlation between the shear-modulated total reconnection rate and the nonthermal electron flux. These results confirm the strong-to-weak shear evolution suggested in previous observational studies and reproduced in numerical models, and also confirm that, in this flare, reconnection is not an efficient producer of energetic nonthermal electrons during the first 10 minutes when the strongly sheared PRFLs are formed. We conclude that an intermediate shear angle, ≤40°, is needed for efficient particle acceleration via reconnection, and we propose a theoretical interpretation.

Keywords: solar magnetic reconnection; solar flares; solar x-ray emission; solar ultraviolet emission
A Large Population of Luminous Active Galactic Nuclei Lacking X-Ray Detections: Evidence for Heavy Obscuration?

We present a large sample of infrared-luminous candidate active galactic nuclei (AGNs) that lack X-ray detections in Chandra, XMM-Newton, and NuSTAR fields. We selected all optically detected SDSS sources with redshift measurements, combined additional broadband photometry from WISE, UKIDSS, 2MASS, and GALEX, and modeled the spectral energy distributions (SEDs) of our sample sources. We parameterize nuclear obscuration in our SEDs with $E{\left(B-V\right)}_{\mathrm{AGN}}$ and uncover thousands of powerful obscured AGNs that lack X-ray counterparts, many of which are identified as AGN candidates based on straightforward WISE photometric criteria. Using the observed luminosity correlation between rest-frame 2-10 keV ( ${L}_{{\rm{X}}}$ ) and rest-frame AGN $6\,\mu {\rm{m}}$ ( ${L}_{\mathrm{MIR}}$ ), we estimate the intrinsic X-ray luminosities of our sample sources and combine these data with flux limits from X-ray catalogs to determine lower limits on nuclear obscuration. Using the ratio of intrinsic-to-observed X-ray luminosity ( ${R}_{{L}_{{\rm{X}}}}$ ), we find a significant fraction of sources with column densities approaching ${N}_{{\rm{H}}}\gt {10}^{24}$ cm-2, suggesting that multiwavelength observations are necessary to account for the population of heavily obscured AGNs. We simulate the underlying ${N}_{{\rm{H}}}$ distribution for the X-ray non-detected sources in our sample through survival analysis, and confirm the presence of AGN activity via X-ray stacking. Our results point to a considerable population of extremely obscured AGNs undetected by current X-ray observatories.

Keywords: active galaxies; infrared galaxies; quasars; surveys
On the Stability of Tidal Streams in Action Space

In the Gaia era it is increasingly apparent that traditional static, parameterized models are insufficient to describe the mass distribution of our complex, dynamically evolving Milky Way (MW). In this work, we compare different time-evolving and time-independent representations of the gravitational potentials of simulated MW-mass galaxies from the FIRE-2 suite of cosmological-baryonic simulations. Using these potentials, we calculate actions for star particles in tidal streams around three galaxies with varying merger histories at each snapshot from 7 Gyr ago to the present day. We determine the action-space coherence preserved by each model using the Kullback-Leibler divergence to gauge the degree of clustering in actions and the relative stability of the clusters over time. We find that all models produce a clustered action space for simulations with no significant mergers. However, a massive (mass ratio prior to infall more similar than 1:8) interacting galaxy not present in the model will result in mischaracterized orbits for stars most affected by the interaction. The locations of the action space clusters (i.e., the orbits of the stream stars) are only preserved by the time-evolving model, while the time-independent models can lose significant amounts of information as soon as 0.5-1 Gyr ago, even if the system does not undergo a significant merger. Our results imply that reverse-integration of stream orbits in the MW using a fixed potential is likely to give incorrect results if integrated longer than 0.5 Gyr into the past.

Keywords: stellar streams; dark matter; galaxy interactions
Photometry of Type II Supernova SN 2023ixf with a Worldwide Citizen Science Network

We present highly sampled photometry of the supernova (SN) 2023ixf, a Type II SN in M101, beginning 2 days before its first known detection. To gather these data, we enlisted the global Unistellar Network of citizen scientists. These 252 observations from 115 telescopes show the SN's rising brightness associated with shock emergence followed by gradual decay. We measure a peak M V = - 18.18 ± 0.09 mag at 2023 May 25 21:37 UTC in agreement with previously published analyses.

Keywords: core-collapse supernovae; supernovae; type ii supernovae
Suspicious Siblings: The Distribution of Mass and Spin across Component Black Holes in Isolated Binary Evolution

The LIGO and Virgo gravitational-wave detectors have uncovered binary black hole systems with definitively nonzero spins, as well as systems with significant spin residing in the more massive black hole of the pair. We investigate the ability of isolated binary evolution in forming such highly spinning, asymmetric-mass systems through both accretion onto the first-born black hole and tidal spin-up of the second-born black hole using a rapid population synthesis approach with detailed considerations of spin-up through tidal interactions. Even with the most optimistic assumptions regarding the efficiency at which an accreting star receives material from a donor, we find that it is difficult to form systems with significant mass asymmetry and moderate or high spins in the primary black hole component. Assuming efficient angular momentum transport within massive stars and Eddington-limited accretion onto black holes, we find that >1.5% of systems in the underlying binary black hole population have a primary black hole spin greater than 0.2 and a mass asymmetry of greater than 2:1 in our most optimistic models, with most models finding that this criteria is only met in ~0.01% of systems. The production of systems with significant mass asymmetries and spin in the primary black hole component is thus an unlikely byproduct of isolated evolution unless highly super-Eddington accretion is invoked or angular momentum transport in massive stars is less efficient than typically assumed.

Keywords: gravitational wave sources; astrophysical black holes; binary stars
Walkaway Star Candidates in IC 348 and Their Possible Birthplaces

Observations and theories reveal that star-forming regions eject their members during the early evolution of the cluster. We present an initial search for stars ejected from the young cluster IC 348 based on an analysis of Gaia EDR3 astrometry of previously identified members. We identify six candidate walkaway stars with projected velocities of 5-8 km s-1. The candidate with properties most consistent with a walkaway star, V701 Per, was likely ejected from a small group to the west of IC 348. Three candidates are currently located or have proper motions that trace back to the center of IC 348, though their classification as walkaway stars may also be affected by large astrometric errors. Two other candidate walkaway stars were likely born in other subgroups around IC 348 within the Perseus star-forming region. Since our search criteria are restricted to previously identified members of IC 348, we did not identify any stars that were ejected at high velocities and traveled far from the cluster. Our study suggests that ejections have potentially occurred in both the central region of IC 348 and other subgroups in Perseus. Extending the search range will lead to more candidate ejections and constrain the dynamic properties and evolution of IC 348 by comparing with simulations.

Keywords: pre-main sequence stars; stellar dynamics; proper motions