adsabs/SciX_UAT_keywords huggingface dataset:
Black Hole Formation in the Lower Mass Gap through Mergers and Accretion in AGN Disks

The heaviest neutron stars and lightest black holes expected to be produced by stellar evolution leave the mass range 2.2 M ${}_{\odot }\lesssim m\lesssim 5$ ${M}_{\odot }$ largely unpopulated. Objects found in this so-called lower mass gap likely originate from a distinct astrophysical process. Such an object, with mass 2.6 M ${}_{\odot }$ was recently detected in the binary merger GW190814 through gravitational waves by LIGO/Virgo. Here we show that black holes in the mass gap are naturally assembled through mergers and accretion in active galactic nucleus (AGN) disks, and can subsequently participate in additional mergers. We compute the properties of AGN-assisted mergers involving neutron stars and black holes, accounting for accretion. We find that mergers in which one of the objects is in the lower mass gap represent up to 4% of AGN-assisted mergers detectable by LIGO/Virgo. The lighter object of GW190814, with mass 2.6 M ${}_{\odot }$ , could have grown in an AGN disk through accretion. We find that the unexpectedly high total mass of 3.4 M ${}_{\odot }$ observed in the neutron star merger GW190425 may also be due to accretion in an AGN disk.

Keywords: gravitational waves; astrophysical black holes; neutron stars
Using the Baryonic Tully-Fisher Relation to Measure Ho

We explore the use of the baryonic Tully-Fisher relation (bTFR) as a new distance indicator. Advances in near-IR imaging and stellar population models, plus precise rotation curves, have reduced the scatter in the bTFR such that distance is the dominant source of uncertainty. Using 50 galaxies with accurate distances from Cepheids or the tip magnitude of the red giant branch, we calibrate the bTFR on a scale independent of Ho. We then apply this calibrated bTFR to 95 independent galaxies from the SPARC sample, using CosmicFlows-3 velocities, to deduce the local value of Ho. We find Ho = 75.1 ± 2.3 (stat) ±1.5 (sys) km s-1 Mpc-1.

Keywords: cosmology; hubble constant
The Emergence of the X-Ray Luminosity/Cluster Richness Relation for Radio Galaxies

The idea that mergers are more likely in dense groups or clusters coupled with the assumption that such events lead to cold gas flows onto black holes suggests a direct relationship between the radiative efficiency of an active galactic nucleus and environmental richness. Observations, however, increasingly challenge this and other basic expectations. Mounting evidence, for example, shows an inverse trend between near-Eddington accreting objects and environmental richness. Broken down by radio galaxy subgroup, recent work has explored connections between low excitation radio galaxies with Fanaroff-Riley II jet morphology (FR II LERGs) and other radio galaxies. We make contact with that work by adding a discussion of the recently discovered FR0 radio galaxies and show how to fit them in a picture in which FRII LERGs are not initial or final phases in the lifetime of a radio galaxy, but de facto transition states. We describe how to understand the observed X-ray luminosity/cluster richness relation as a fundamental correlation to the nature of the jet-disk connection.

Keywords: radio galaxies
Fully Kinetic Shearing-box Simulations of Magnetorotational Turbulence in 2D and 3D. I. Pair Plasmas

The magnetorotational instability (MRI) is a fundamental mechanism determining the macroscopic dynamics of astrophysical accretion disks. In collisionless accretion flows around supermassive black holes, MRI-driven plasma turbulence cascading to microscopic (i.e., kinetic) scales can result in enhanced angular-momentum transport and redistribution, nonthermal particle acceleration, and a two-temperature state where electrons and ions are heated unequally. However, this microscopic physics cannot be captured with standard magnetohydrodynamic (MHD) approaches typically employed to study the MRI. In this work, we explore the nonlinear development of MRI turbulence in a pair plasma, employing fully kinetic particle-in-cell (PIC) simulations in two and three dimensions. First, we thoroughly study the axisymmetric MRI with 2D simulations, explaining how and why the 2D geometry produces results that differ substantially from 3D MHD expectations. We then perform the largest (to date) 3D simulations, for which we employ a novel shearing-box approach, demonstrating that 3D PIC models can reproduce the mesoscale (i.e., MHD) MRI dynamics in sufficiently large runs. With our fully kinetic simulations, we are able to describe the nonthermal particle acceleration and angular-momentum transport driven by the collisionless MRI. Since these microscopic processes ultimately lead to the emission of potentially measurable radiation in accreting plasmas, our work is of prime importance to understand current and future observations from first principles, beyond the limitations imposed by fluid (MHD) models. While in this first study we focus on pair plasmas for simplicity, our results represent an essential step toward designing more realistic electron-ion simulations, on which we will focus in future work.

Keywords: plasma astrophysics; accretion; plasma physics
Enhanced Acceleration and Escape of Hydrogen Pickup Ions Upstream from Mars by Interplanetary Shocks

The pickup process of newly ionized hydrogen (H) from the Martian extended exosphere represents an important H+ escape channel on Mars. It is generally believed that interplanetary (IP) shocks can accelerate the pickup ions and, in turn, affect the pickup process. However, the underlying processes inherent to the acceleration are not yet fully understood. Here, we concentrate on the dynamic processes involved in acceleration arising from IP shock compression. We examine two typical IP shock events characterized by a sudden increase in the average energy of upstream H+ pickup ions across the shock. The H+ pickup ions continuously enter the field of view of Supra-Thermal And Thermal Ion Composition or Solar Wind Ion Analyzer on board the Mars Atmosphere and Volatile EvolutioN spacecraft in a narrow angular range. Moreover, they correspond to a similar part of their respective ring distributions in velocity space. By comparing measured and theoretical H+ pickup ion energies, we attribute the more energetic H+ pickup ions to the enhanced convection electric field acceleration caused by the shock compression. An increase in the guiding center drift speed across the shock implies a higher escape rate of the H+ pickup ions. Furthermore, the pitch-angle scattering could facilitate the escape of the higher energy H+ pickup ions from Mars. The results may shed light on the understanding of the energization and escape of planetary pickup ions in the solar system.

Keywords: mars; pickup ions; interplanetary shocks
Citizen ASAS-SN: Citizen Science with The All-Sky Automated Survey for SuperNovae (ASAS-SN)

We present "Citizen ASAS-SN," a citizen science project hosted on the Zooniverse platform which utilizes data from the All-Sky Automated Survey for SuperNovae (ASAS-SN). Volunteers are presented with ASAS-SN g-band light curves of variable star candidates. The classification workflow allows volunteers to classify these sources into major variable groups, while also allowing for the identification of unique variable stars for additional follow-up.

Keywords: variable stars; light curves; stellar classification
Origins of Chiral Life in Interstellar Molecular Clouds

The exploring of galactic chemical composition across the the Milky Way, and specifically across the solar neighborhood, provides insights into the chemical evolution of the universe. Since the formation of the first stars some hundred million years after the big bang (BB), heavier elements are synthesized in different stellar production processes at the expense of lighter elements. When the relative abundances of the life-forming elements evaluated for the Last Universal Common Ancestor (LUCA) are compared with the solar neighborhood stellar abundances, a striking similarity occurs. In this study, we tested the hypothesis that in some particular regions and at some particular time, the abundance curve of the first living matter and the universe coincided. Indeed, the best agreement between the two curves was obtained for (4 ± 1)× 109 yr after the BB, indicating the time of the origin of life. All organisms evolved on the Earth independently of place and time are leading to the LUCA and involve chiral molecules such as L amino acids and D sugars in fundamental life processes. The growing evidence from carbonaceous meteorites analysis shows an excess of L-type amino acids and D-type sugars, suggesting that the increase in L-type or D-type molecular chirality is the process that takes place in planetary and stellar forming systems, thus the life emerging from interstellar molecular clouds (IMCs) had to be chiral. Here we propose the spin-polarized proton-proton scattering as a potential physical process that takes place in IMCs environments and could lead to enrichment of L-type amino acids and D-type sugars.

Keywords: interstellar dust; astrobiology; galactic cosmic rays
Constraints on the Evolution of the Ionizing Background and Ionizing Photon Mean Free Path at the End of Reionization

The variations in Lyα forest opacity observed at z > 5.3 between lines of sight to different background quasars are too strong to be caused by fluctuations in the density field alone. The leading hypothesis for the cause of this excess variance is a late, ongoing reionization process at redshifts below six. Another model proposes strong ionizing background fluctuations coupled to a short, spatially varying mean free path of ionizing photons, without explicitly invoking incomplete reionization. With recent observations suggesting a short mean free path at z ∼ 6, and a dramatic improvement in z > 5 Lyα forest data quality, we revisit this latter possibility. Here, we apply the likelihood-free inference technique of approximate Bayesian computation (ABC) to jointly constrain the hydrogen photoionization rate ΓHI and the mean free path of ionizing photons λ mfp from the effective optical depth distributions at z = 5.0–6.1 from XQR-30. We find that the observations are well-described by fluctuating mean free path models with average mean free paths that are consistent with the steep trend implied by independent measurements at z ∼ 5–6, with a concomitant rapid evolution of the photoionization rate.

Keywords: intergalactic medium; reionization
HELIOS-K 2.0 Opacity Calculator and Open-source Opacity Database for Exoplanetary Atmospheres

Computing and using opacities is a key part of modeling and interpreting data of exoplanetary atmospheres. Since the underlying spectroscopic line lists are constantly expanding and currently include up to ∼1010-1011 transition lines, the opacity calculator codes need to become more powerful. Here we present major upgrades to the HELIOS-K GPU-accelerated opacity calculator and describe the necessary steps to process large line lists within a reasonable amount of time. Besides performance improvements, we include more capabilities and present a toolbox for handling different atomic and molecular data sets, from downloading and preprocessing the data to performing the opacity calculations in a user-friendly way. HELIOS-K supports line lists from ExoMol, HITRAN, HITEMP, NIST, Kurucz, and VALD3. By matching the resolution of 0.1 cm-1 and cutting length of 25 cm-1 used by the ExoCross code for timing performance (251 s excluding data read-in time), HELIOS-K can process the ExoMol BT2 water line list in 12.5 s. Using a resolution of 0.01 cm-1, it takes 45 s, equivalent to about 107 lines s-1. As a wavenumber resolution of 0.01 cm-1 suffices for most exoplanetary atmosphere spectroscopic calculations, we adopt this resolution in calculating opacity functions for several hundred atomic and molecular species and make them freely available on the open-access DACE database. For the opacity calculations of the database, we use a cutting length of 100 cm-1 for molecules and no cutting length for atoms. Our opacities are available for downloading from https://dace.unige.ch/opacityDatabase and may be visualized using https://dace.unige.ch/opacity.

Keywords: exoplanet atmospheres
When Gas Dynamics Decouples from Galactic Rotation: Characterizing ISM Circulation in Disk Galaxies

In galactic disks, galactic rotation sets the bulk motion of gas, and its energy and momentum can be transferred toward small scales. Additionally, in the interstellar medium, random and noncircular motions arise from stellar feedback, cloud-cloud interactions, and instabilities, among other processes. Our aim is to comprehend to what extent small-scale gas dynamics is decoupled from galactic rotation. We study the relative contributions of galactic rotation and local noncircular motions to the circulation of gas, Γ, a macroscopic measure of local rotation, defined as the line integral of the velocity field around a closed path. We measure the circulation distribution as a function of spatial scale in a set of simulated disk galaxies and model the velocity field as the sum of galactic rotation and a Gaussian random field. The random field is parameterized by a broken power law in Fourier space, with a break at the scale λc. We define the spatial scale λeq at which galactic rotation and noncircular motions contribute equally to Γ. For our simulated galaxies, the gas dynamics at the scale of molecular clouds is usually dominated by noncircular motions, but in the center of galactic disks galactic rotation is still relevant. Our model shows that the transfer of rotation from large scales breaks at the scale λc, and this transition is necessary to reproduce the circulation distribution. We find that λeq, and therefore the structure of the gas velocity field, is set by the local conditions of gravitational stability and stellar feedback.

Keywords: hydrodynamical simulations; hydrodynamics; astronomical simulations; astrophysical fluid dynamics; galaxy dynamics; interstellar dynamics; galaxy rotation; astrostatistics strategies; posterior distribution
The Feasibility of Directly Imaging Nearby Cold Jovian Planets with MIRI/JWST

The upcoming launch of the James Webb Space Telescope (JWST) will dramatically increase our understanding of exoplanets, particularly through direct imaging. Microlensing and radial velocity surveys indicate that some M dwarfs host long-period giant planets. Some of these planets will likely be just a few parsecs away and a few astronomical units from their host stars, a parameter space that cannot be probed by existing high-contrast imagers. We studied whether the coronagraphs on the Mid-infrared Instrument on JWST can detect Jovian-type planets around nearby M dwarfs. For a sample of 27 very nearby M dwarfs, we simulated a sample of Saturn-Jupiter-mass planets with three atmospheric configurations and three orbital separations, observed in three different filters. We found that the f1550c 15.5 μm filter is best suited for detecting Jupiter-like planets. Jupiter-like planets with patchy cloud cover, 2 au from their star, are detectable at 15.5 μm around 14 stars in our sample, while Jupiters with clearer atmospheres are detectable around all stars in the sample. Saturns were most detectable at 10.65 and 11.4 μm (f1065c and f1140c filters), but only with cloud-free atmospheres and within 3 pc (six stars). Surveying all 27 stars would take <170 hr of JWST integration time, or just a few hours for a shorter survey of the most favorable targets. There is one potentially detectable known planet in our sample: GJ 832 b. Observations aimed at detecting this planet should occur in 2024-2026, when the planet is maximally separated from the star.

Keywords: direct imaging; m stars; solar neighborhood; extrasolar gaseous giant planets; exoplanets; infrared astronomy
Chandra Observations of the Newly Discovered Magnetar Swift J1818.0-1607

Swift J1818.0-1607 is a new radio-loud magnetar discovered by the Swift Burst Alert Telescope on 2020 March 12. It has a magnetic field B ∼ 2.5 × 1014 G, spin-down luminosity $\dot{E}$ ∼ 7.2 × 1035 erg s-1, and characteristic age τc ∼ 470 yr. Here we report on the Chandra observations of Swift J1818.0-1607, which allowed for a high-resolution imaging and spectroscopic study of the magnetar and its environment. The 1-10 keV spectrum of the magnetar is best described by a single blackbody model with a temperature of 1.2 ± 0.1 keV and an unabsorbed flux of 1.9-0.3+0.4 × 10-11 erg cm-2 s-1. This implies an X-ray luminosity of 9.6-1.5+2.0×1034 d6.52 erg s-1 and efficiency of ${L}_{{\rm{X}}}/\dot{E}$ ∼ 0.13 d6.52 at a distance of 6.5 kpc. The Chandra image also shows faint diffuse emission out to $\geqslant 10^{\prime\prime} $ from the magnetar, with its spectrum adequately described by a power law with a photon index of 2.0 ± 0.5 and a luminosity of ∼8.1 × 1033 ${d}_{6.5}^{2}$ erg s-1. The extended emission is likely dominated by a dust-scattering halo and future observations of the source in quiescence will reveal any underlying compact wind nebula. We conclude that Swift J1818.0-1607 is a transient source showing properties between high-B pulsars and magnetars, and could be powered at least partly by its high spin-down, similar to rotation-powered pulsars.

Keywords: high energy astrophysics
Observations of Heating along Intermittent Structures in the Inner Heliosphere from PSP Data

The solar wind proton temperature at 1 au has been found to be correlated with small-scale intermittent magnetic structures, I.e., regions with enhanced temperature are associated with coherent structures, such as current sheets. Using Parker Solar Probe data from the first encounter, we study this association using measurements of the radial proton temperature, employing the partial variance of increments (PVI) technique to identify intermittent magnetic structures. We observe that the probability density functions of high PVI events have higher median temperatures than those with lower PVI. The regions in space where PVI peaks were also locations that had enhanced temperatures when compared with similar regions, suggesting a heating mechanism in the young solar wind that is associated with intermittency developed by a nonlinear turbulent cascade in the immediate vicinity.

Keywords: solar wind; heliosphere; solar coronal heating
Estimations of Elemental Abundances during Solar Flares Observed in Soft X-Rays by the MinXSS-1 CubeSat Mission

Solar flares are complex phenomena emitting all types of electromagnetic radiation and accelerating particles on timescales of minutes, converting magnetic energy to thermal, radiative, and kinetic energy through magnetic reconnections. As a result, local plasma can be heated to temperatures in excess of 20 MK. During the soft X-ray (SXR) solar flare peak, the elemental abundance of low first ionization potential elements are typically observed to be depleted from coronal values. We explored the abundance variations using disk-integrated solar spectra from the Miniature X-ray Solar Spectrometer CubeSat-1 (MinXSS-1). MinXSS-1 is sensitive to the 1-12 keV energy range with an effective 0.25 keV FWHM resolution at 5.9 keV. During the year-long mission of MinXSS-1, between 2016 May and 2017 May, 21 flares with intermittent data downlinks were observed ranging from C to M class. We examine the time evolution of temperature, volume emission measure, and elemental abundances of Fe, Ca, Si, S, and Ar with CHIANTI spectral models near the peak SXR emission times observed in the MinXSS-1 data. We determined the average absolute abundance of A(Fe) = 7.81, A(Ca) = 6.84, A(S) = 7.28, A(Si) = 7.90, and A(Ar) = 6.56. These abundances are depleted from coronal values during the SXR peak compared to nonflaring times. The elemental abundance values that are depleted from their coronal values are consistent with the process of chromospheric evaporation, in which the lower atmospheric plasma fills the coronal loops.

Keywords: solar x-ray flares; solar flare spectra; solar abundances
Time-resolved Hubble Space Telescope Wide Field Camera 3 Spectrophotometry Reveals Inefficient Day-to-night Heat Redistribution in the Highly Irradiated Brown Dwarf SDSS 1557B

Brown dwarfs (BDs) in ultra-short-period orbits around white dwarfs (WDs) offer a unique opportunity to study the properties of tidally locked, fast-rotating (1–3 hr), and highly irradiated atmospheres. Here we present phase-resolved spectrophotometry of the WD–BD binary SDSS 1557, which is the fifth WD–BD binary in our six-object sample. Using the Hubble Space Telescope Wide Field Camera 3 Near-infrared G141 instrument, the 1.1–1.7 μm phase curves show rotational modulations with semiamplitudes of 10.5% ± 0.1%. We observe a wavelength-dependent amplitude, with longer wavelengths producing larger amplitudes, while no wavelength-dependent phase shifts were identified. The phase-resolved extracted BD spectra exhibit steep slopes and are nearly featureless. A simple radiative energy redistribution atmospheric model re-creates the hemisphere-integrated brightness temperatures at three distinct phases and finds evidence for weak redistribution efficiency. Our model also predicts a higher inclination than previously published. We find that SDSS 1557B, the second most irradiated BD in our sample, is likely dominated by clouds on the nightside, whereas the featureless dayside spectrum is likely dominated by H‑ opacity and a temperature inversion, much like the other highly irradiated BD EPIC 2122B.

Keywords: brown dwarfs; exoplanet atmospheres; white dwarf stars; hot jupiters
OSIRIS-APEX: An OSIRIS-REx Extended Mission to Asteroid Apophis

The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft mission characterized and collected a sample from asteroid (101955) Bennu. After the OSIRIS-REx Sample Return Capsule released to Earth's surface in 2023 September, the spacecraft diverted into a new orbit that encounters asteroid (99942) Apophis in 2029, enabling a second mission with the same unique capabilities: OSIRIS-Apophis Explorer (APEX). On 2029 April 13, the 340 m diameter Apophis will draw within ~32,000 km of Earth's surface, less than 1/10 the lunar distance. Apophis will be the largest object to approach Earth this closely in recorded history. This rare planetary encounter will alter Apophis's orbit, will subject it to tidal forces that change its spin state, and may seismically disturb its surface. APEX will distantly observe Apophis during the Earth encounter and capture its evolution in real time, revealing the consequences of an asteroid undergoing tidal disturbance by a major planet. Beginning in 2029 July, the spacecraft's instrument suite will begin providing high-resolution data of this "stony" asteroid-advancing knowledge of these objects and their connection to meteorites. Near the mission's end, APEX will use its thrusters to excavate regolith, a technique demonstrated at Bennu. Observations before, during, and after excavation will provide insight into the subsurface and material properties of stony asteroids. Furthermore, Apophis's material and structure have critical implications for planetary defense.

Keywords: asteroid dynamics; asteroid surfaces; near-earth objects; close encounters; space observatories