adsabs/SciX_UAT_keywords huggingface dataset:
Close Trans-Neptunian Object Passages as a Driver of the Origin and Evolution of Ultrawide Kuiper Belt Binaries

Within the dynamically cold low-inclination portion of the Classical Kuiper Belt, there exists a population of weakly bound binary systems with a number of unusual properties, most notable of which is their extremely wide orbital separations-beyond 7% of their Hill radii. The stability and evolution of these ultrawide Trans-Neptunian binaries (TNBs) have, in the past, been studied extensively under the assumption that the primary evolving mechanisms are interactions between the binary components and impacting Trans-Neptunian Objects (TNOs). Here, we instead study their evolution as driven by the gravitational perturbations of close passing but nonimpacting TNOs. By simulating these passages, we show that the aggregate effects of encounters over billions of years have a significant effect on Kuiper Belt binary evolution. Such processes can lead to tight binaries widening significantly over time, approaching and sometimes surpassing the separation of the widest known TNBs. We also find that the eccentricity and inclination distributions of observed ultrawide TNBs can be sampled from such widened binaries. While we are unable to produce enough wide binaries to explain their abundance, the orbital properties of ones we do produce are consistent with known wide binaries.

Keywords: trans-neptunian objects; kuiper belt
Observations of Waves and Structures by Frequency-Wavenumber Spectrum in Solar Wind Turbulence

A well-known shortcoming of single-spacecraft spectral analysis is that only the 1D wavenumber spectrum can be observed, assuming the characteristic wave propagation speed is much smaller than the solar wind flow speed. This limitation has motivated an extended debate about whether fluctuations observed in the solar wind are waves or structures. Multispacecraft analysis techniques can be used to calculate the wavevector independent of the observed frequency, thus allowing one to study the frequency-wavenumber spectrum of turbulence directly. The dispersion relation for waves can be identified, which distinguishes them from nonpropagating structures. We use magnetic field data from the four Magnetospheric Multiscale (MMS) spacecraft to measure the frequency-wavenumber spectrum of solar wind turbulence based on the k-filtering and phase differencing techniques. Both techniques have been used successfully in the past for the Earth's magnetosphere, although applications to solar wind turbulence have been limited. We conclude that the solar wind turbulence intervals observed by MMS show features of nonpropagating structures that are associated with frequencies close to zero in the plasma rest frame. However, there is no clear evidence of propagating Alfvén waves that have a nonzero rest-frame frequency. The lack of waves may be due to instrument noise and spacecraft separation. Our results support the idea of turbulence dominated by quasi-2D structures.

Keywords: solar wind; interplanetary turbulence
Time and Charge-sign Dependence of the Heliospheric Modulation of Cosmic Rays

Simultaneous and continuous observations of galactic cosmic-ray electrons (e-) and positrons (e+) from the PAMELA and AMS02 space experiments are most suitable for numerical modeling studies of the heliospheric modulation of these particles below 50 GeV. A well-established comprehensive three-dimensional modulation model is applied to compute full spectra for e- and e+ with the purpose of reproducing the observed ratio e+/e- for a period that covers the previous long and unusual deep solar minimum activity and the recent maximum activity phase, including the polarity reversal of the solar magnetic field. For this purpose, the very local interstellar spectra for these particles were established first. Our study is focused on how the main modulation processes, including particle drifts, and other parameters, such as the three major diffusion coefficients, evolved and how the corresponding charge-sign dependent modulation subsequently occurred. The end result of our effort is the detailed reproduction of e+/e- from 2006 to 2015, displaying both qualitative and quantitative agreement with the main observed features. Particularly, we determine how much particle drift is needed to explain the time dependence exhibited by the observed e+/e- during each solar activity phase, especially during the polarity reversal phase, when no well-defined magnetic polarity was found.

Keywords: galactic cosmic rays; particle astrophysics; heliosphere; solar activity
A Constraint on the Amount of Hydrogen from the CO Chemistry in Debris Disks

The faint CO gases in debris disks are easily dissolved into C by UV irradiation, while CO can be reformed via reactions with hydrogen. The abundance ratio of C/CO could thus be a probe of the amount of hydrogen in the debris disks. We conduct radiative transfer calculations with chemical reactions for debris disks. For a typical dust-to-gas mass ratio of debris disks, CO formation proceeds without the involvement of H2 because a small amount of dust grains makes H2 formation inefficient. We find that the CO to C number density ratio depends on a combination of n H Z 0.4 χ -1.1, where n H is the hydrogen nucleus number density, Z is the metallicity, and χ is the far-UV flux normalized by the Habing flux. Using an analytic formula for the CO number density, we give constraints on the amount of hydrogen and metallicity for debris disks. CO formation is accelerated by excited H2 when either the dust-to-gas mass ratio is increased or the energy barrier of chemisorption of hydrogen on the dust surface is decreased. This acceleration of CO formation occurs only when the shielding effects of CO are insignificant. In shielded regions, the CO fractions are almost independent of the parameters of dust grains.

Keywords: debris disks; astrochemistry; circumstellar matter; molecular physics; radiative transfer
Expected Gamma-Ray Burst Detection Rates and Redshift Distributions for the BlackCAT CubeSat Mission

We report the results of an extensive set of simulations exploring the sensitivity of the BlackCAT CubeSat to long-duration gamma-ray bursts (GRBs). BlackCAT is a NASA APRA-funded CubeSat mission for the detection and real-time subarcminute localization of high-redshift (z ≳ 3.5) GRBs. Thanks to their luminous and long-lived afterglow emissions, GRBs are uniquely valuable probes of high-redshift star-forming galaxies and the intergalactic medium. In addition, each detected GRB with a known redshift serves to localize a region of high-redshift star formation in three dimensions, enabling deep follow-on searches for host galaxies and associated local and large-scale structures. We explore two distinct models for the GRB redshift distribution and luminosity function, both consistent with Swift observations. We find that, for either model, BlackCAT is expected to detect a mean of 42 bursts per year on orbit, with 6.7% to 10% of these at z > 3.5. BlackCAT bursts will be localized to an r 90 ≲ 55″ precision and reported to the community within seconds. Due to the mission orbit and pointing scheme, bursts will be located in the night sky and well placed for deep multiwavelength follow-up observations. BlackCAT is on schedule to achieve launch readiness in 2025.

Keywords: gamma-ray bursts; star formation; x-ray telescopes; transient detection; high-redshift galaxies
Pair Cascades at the Edge of the Broad-line Region Shaping the Gamma-Ray Spectrum of 3C 279

The blazar 3C 279 emits a flux of gamma rays that is variable on timescales as short as the light-crossing time across the event horizon of its central black hole. It is commonly reported that the spectral energy distribution (SED) does not show signs of pair attenuation due to interactions of the gamma rays with ambient ultraviolet photons, concluding that the gamma rays must originate from substructures in the jet outside of the broad-line region (BLR). We address the spectral signature imprinted by atomic emission lines on the gamma-ray spectrum produced by an inverse-Compton pair cascade in the photon field of the BLR. We determine with high precision the gamma-ray SED of 3C 279 using Fermi Large Area Telescope data from MJD 58129-58150 and simulate the pair cascade spectrum for three different injection terms. Satisfactory fits to the observational data are obtained. The obtained SED shows features imprinted by pair production on atomic emission line photons due to optically thick radiation transport, but lacking further exponential attenuation expected if the emission region would lie buried deep within the BLR. The SED of 3C 279 is consistent with an inverse-Compton pair cascade spectrum without exponential external pair absorption. Our findings support the view that the gamma-ray emission in 3C 279 originates from the edge of the BLR.

Keywords: active galaxies; active galactic nuclei; blazars; flat-spectrum radio quasars; quasars; supermassive black holes; gamma-ray sources; gamma-rays; non-thermal radiation sources; relativistic jets; radiative processes
New Mass Estimates for Massive Binary Systems: A Probabilistic Approach Using Polarimetric Radiative Transfer

Understanding the evolution of massive binary stars requires accurate estimates of their masses. This understanding is critically important because massive star evolution can potentially lead to gravitational-wave sources such as binary black holes or neutron stars. For Wolf-Rayet (WR) stars with optically thick stellar winds, their masses can only be determined with accurate inclination angle estimates from binary systems which have spectroscopic $M\sin i$ measurements. Orbitally phased polarization signals can encode the inclination angle of binary systems, where the WR winds act as scattering regions. We investigated four Wolf-Rayet + O star binary systems, WR 42, WR 79, WR 127, and WR 153, with publicly available phased polarization data to estimate their masses. To avoid the biases present in analytic models of polarization while retaining computational expediency, we used a Monte Carlo radiative-transfer model accurately emulated by a neural network. We used the emulated model to investigate the posterior distribution of the parameters of our four systems. Our mass estimates calculated from the estimated inclination angles put strong constraints on existing mass estimates for three of the systems, and disagree with the existing mass estimates for WR 153. We recommend a concerted effort to obtain polarization observations that can be used to estimate the masses of WR binary systems and increase our understanding of their evolutionary paths.

Keywords: massive stars; binary stars; polarimetry; bayesian statistics; radiative transfer
Secular Gravitational Instability of Drifting Dust in Protoplanetary Disks: Formation of Dusty Rings without Significant Gas Substructures

Secular gravitational instability (GI) is one promising mechanism for creating annular substructures and planetesimals in protoplanetary disks. We perform numerical simulations of secular GI in a radially extended disk with inwardly drifting dust grains. The results show that, even in the presence of dust diffusion, dust rings form via secular GI while the dust grains are moving inward, and the dust surface density increases by a factor of 10. Once secular GI develops into a nonlinear regime, the total mass of the resultant rings can be a significant fraction of the dust disk mass. In this way, a large amount of drifting dust grains can be collected in the dusty rings and stored for planetesimal formation. In contrast to the emergence of remarkable dust substructures, secular GI does not create significant gas substructures. This result indicates that observations of a gas density profile near the disk midplane enable us to distinguish the mechanisms for creating the annular substructures in the observed disks. The resultant rings start decaying once they enter the inner region stable to secular GI. Because the ring-gap contrast smoothly decreases, it seems possible that the rings are observed even in the stable region. We also discuss the likely outcome of the nonlinear growth and indicate the possibility that a significantly developed region of secular GI may appear as a gap-like substructure in dust continuum emission as dust growth into larger solid bodies and planetesimal formation reduce the total emissivity.

Keywords: protoplanetary disks
Symmetric Periodic Orbits in the Dipole-segment Problem for Two Equal Masses

We consider a relatively simple model to represent some types of asteroids that are very elongated and with two protuberances on their end points. A conspicuous example of this type of body is asteroid 216-Kleopatra. To model such bodies, we consider a dipole segment, which consists of a massive segment with two spherical masses at the end point of the rod and which is rotating about its center of mass with uniform velocity. In particular, we restrict our study to the case in which both massive spheres are equal. For this problem, we obtain the potential, equilibria, and stability and compute the families of symmetric periodic orbits. We also discover asymptotic points in the family map, which represents heteroclinic orbits connecting different equilibria.

Keywords: small solar system bodies
ACCESS: Tentative Detection of H2O in the Ground-based Optical Transmission Spectrum of the Low-density Hot Saturn HATS-5b

We present a precise ground-based optical transmission spectrum of the hot Saturn HATS-5b (T eq = 1025 K), obtained as part of the ACCESS survey with the IMACS multi-object spectrograph mounted on the Magellan Baade Telescope. Our spectra cover the 0.5-0.9 μm region and are the product of five individual transits observed between 2014 and 2018. We introduce the usage of additional second-order light in our analyses, which allows us to extract an "extra" transit light curve, improving the overall precision of our combined transit spectrum. We find that the favored atmospheric model for this transmission spectrum is a solar-metallicity atmosphere with subsolar C/O, whose features are dominated by H2O and with a depleted abundance of Na and K. If confirmed, this would point to a "clear" atmosphere at the pressure levels probed by transmission spectroscopy for HATS-5b. Our best-fit atmospheric model predicts a rich near-IR spectrum, which makes this exoplanet an excellent target for future follow-up observations with the James Webb Space Telescope, both to confirm this H2O detection and to superbly constrain the atmosphere's parameters.

Keywords: exoplanet atmospheres; extrasolar gaseous giant planets; hot jupiters; exoplanets
Demographics of Neutron Stars in Young Massive and Open Clusters

Star clusters appear to be the ideal environment for the assembly of neutron star-neutron star (NS-NS) and black hole-neutron star (BH-NS) binaries. These binaries are among the most interesting astrophysical objects, being potential sources of gravitational waves (GWs) and gamma-ray bursts. We use for the first time high-precision N-body simulations of young massive and open clusters to study the origin and dynamical evolution of NSs, within clusters with different initial masses, metallicities, primordial binary fractions, and prescriptions for the compact object natal kicks at birth. We find that the radial profile of NSs is shaped by the BH content of the cluster, which partially quenches the NS segregation due to the BH-burning process. This leaves most of the NSs out of the densest cluster regions, where NS-NS and BH-NS binaries could potentially form. Due to a large velocity kick that they receive at birth, most of the NSs escape the host clusters, with the bulk of their retained population made up of NSs of ∼1.3 ${M}_{\odot }$ coming from the electron-capture supernova process. The details of the primordial binary fraction and pairing can smear out this trend. Finally, we find that a subset of our models produce NS-NS mergers, leading to a rate of ∼0.01-0.1 ${\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$ in the local universe, and compute an upper limit of ∼3 × 10-2-3 × 10-3 ${\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$ for the BH-NS merger rate. Our estimates are several orders of magnitude smaller than the current empirical merger rate from LIGO/Virgo, in agreement with the recent rate estimates for old globular clusters.

Keywords: astrophysical black holes; black holes; stellar mass black holes; neutron stars; star clusters; open star clusters; young star clusters; globular star clusters; gravitational wave astronomy; gravitational wave detectors; gravitational wave sources; gravitational waves
On the Evolution of Rotational Modulation Amplitude in Solar-mass Main-sequence Stars

We investigate the relation between rotation periods P rot and photometric modulation amplitudes R per for ≈4000 Sun-like main-sequence stars observed by Kepler, using P rot and R per from McQuillan et al., effective temperature T eff from LAMOST DR6, and parallax data from Gaia EDR3. As has been suggested in previous works, we find that P rot scaled by the convective turnover time τ c, or the Rossby number Ro, serves as a good predictor of R per: R per plateaus at around 1% in relative flux for 0.2 ≲ Ro/Ro⊙ ≲ 0.4, and decays steeply with increasing Ro for 0.4 ≲ Ro/Ro⊙ ≲ 0.8, where Ro⊙ denotes Ro of the Sun. In the latter regime we find ${\rm{d}}\,\mathrm{ln}\,{R}_{\mathrm{per}}/{\rm{d}}\,\mathrm{ln}\,\mathrm{Ro}$ ~ -4.5 to -2.5, although the value is sensitive to detection bias against weak modulation and may depend on other parameters including T eff and surface metallicity. The existing X-ray and Ca II H and K flux data also show transitions at Ro/Ro⊙ ~ 0.4, suggesting that all these transitions share the same physical origin. We also find that the rapid decrease of R per with increasing Ro causes rotational modulation of fainter Kepler stars with Ro/Ro⊙ ≳ 0.6 to be buried under the photometric noise. This effect sets the longest P rot detected in the McQuillan et al. sample as a function of T eff and obscures the signature of stalled spin down that has been proposed to set in around Ro/Ro⊙ ~ 1.

Keywords: light curves; starspots; stellar activity; stellar magnetic fields; stellar rotation
Modeling the Observed Distortion of Multiple (Ghost) CME Fronts in STEREO Heliospheric Imagers

In this work we have, for the first time, applied the interpretation of multiple "ghost-fronts" to two synthetic coronal mass ejections (CMEs) propagating within a structured solar wind using the Heliospheric Upwind eXtrapolation time (HUXt) solar wind model. The two CMEs occurred on 2012 June 13-14 showing multiple fronts in images from Solar Terrestrial Relations Observatory Heliospheric Imagers (HIs). The HUXt model is used to simulate the evolution of these CMEs across the inner heliosphere as they interacted with structured ambient solar wind. The simulations reveal that the evolution of CME shape is consistent with observations across a wide range of solar latitudes and that the manifestation of multiple "ghost-fronts" within HIs' field of view is consistent with the positions of the nose and flank of the same CME structure. This provides further confirmation that the angular separation of these features provides information on the longitudinal extent of a CME. For one of the CMEs considered in this study, both simulations and observations show that a concave shape develops within the outer CME front. We conclude that this distortion results from a latitudinal structure in the ambient solar wind speed. The work emphasizes that the shape of the CME cannot be assumed to remain a coherent geometrical shape during its propagation in the heliosphere. Our analysis demonstrates that the presence of "ghost" CME fronts can be used to infer the distortion of CMEs by ambient solar wind structure as a function of both latitude and longitude. This information has the potential to improve the forecasting of space weather events at Earth.

Keywords: heliosphere; solar coronal mass ejections; space weather
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Transmission Spectroscopy

Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (P orb) of 12.76 days. The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous P orb from TESS data. We confirmed the transit signal and P orb using ground-based photometry with MuSCAT2 and MuSCAT3, and validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host star is inactive, with an X-ray-to-bolometric luminosity ratio of . Joint analysis of the light curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R ⊕, a 3σ mass upper limit of 3.9 M ⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric (TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.

Keywords: exoplanet astronomy; exoplanet atmospheres; exoplanets; extrasolar rocky planets; space telescopes; transit photometry; radial velocity; astronomy data modeling; high resolution spectroscopy
HETDEX [O III] Emitters. I. A Spectroscopically Selected Low-redshift Population of Low-mass, Low-metallicity Galaxies

We assemble a sample of 17 low-metallicity (7.45 < log(O/H)+12 < 8.12) galaxies with z ≲ 0.1 found spectroscopically, without photometric preselection, in early data from the Hobby-Eberly Telescope Dark Energy Experiment. Star-forming galaxies that occupy the lowest-mass and lowest-metallicity end of the mass-metallicity relation tend to be undersampled in continuum-based surveys as their spectra are typically dominated by emission from newly forming stars. We search for galaxies with high [O III]λ5007/[O II]λ3727, implying highly ionized nebular emission often indicative of low-metallicity systems. With the Second Generation Low Resolution Spectrograph on the Hobby-Eberly Telescope we acquired follow-up spectra, with higher resolution and broader wavelength coverage, of each low-metallicity candidate in order to confirm the redshift, measure the Hα and [N II] line strengths, and, in many cases, obtain deeper spectra of the blue lines. We find our galaxies are consistent with the mass-metallicity relation of typical low-mass galaxies. However, galaxies in our sample tend to have similar specific star formation rates as the incredibly rare "blueberry" galaxies found by Yang et al. We illustrate the power of spectroscopic surveys for finding low-mass and low-metallicity galaxies and reveal that we find a sample of galaxies that are a hybrid between the properties of typical dwarf galaxies and the more extreme blueberry galaxies.

Keywords: emission line galaxies; galaxies; galaxy abundances; galaxy properties; star formation; galaxy evolution; spectroscopy; surveys; astronomical techniques; optical astronomy