adsabs/SciX_UAT_keywords huggingface dataset:
Two Views of the Radius Gap and the Role of Light Curve Fitting

Recently, several groups have resolved a gap that bifurcates planets between the size of Earth and Neptune into two populations. The location and depth of this feature is an important signature of the physical processes that form and sculpt planets. In particular, planets residing in the radius gap are valuable probes of these processes as they may be undergoing the final stages of envelope loss. Here, we discuss two views of the radius gap by Fulton & Petigura (F18) and Van Eylen et al. (V18). In V18, the gap is wider and more devoid of planets. This is due, in part, to V18's more precise measurements of planet radius ${R}_{{\rm{p}}}$ . Thanks to Gaia, uncertainties in stellar radii ${R}_{\star }$ are no longer the limiting uncertainties in determining ${R}_{{\rm{p}}}$ for the majority of Kepler planets; instead, errors in ${R}_{{\rm{p}}}$ / ${R}_{\star }$ dominate. V18's analysis incorporated short-cadence photometry along with constraints on mean stellar density that enabled more accurate determinations of ${R}_{{\rm{p}}}$ / ${R}_{\star }$ . In the F18 analysis, less accurate ${R}_{{\rm{p}}}$ / ${R}_{\star }$ blurs the boundary the radius gap. The differences in ${R}_{{\rm{p}}}$ / ${R}_{\star }$ are largest at high impact parameter ( $b\gtrsim 0.8$ ) and often exceed 10%. This motivates excluding high-b planets from demographic studies, but identifying such planets from long-cadence photometry alone is challenging. We show that transit duration can serve as an effective proxy, and we leverage this information to enhance the contrast between the super-Earth and sub-Neptune populations.

Keywords: exoplanet detection methods; transit photometry; exoplanet catalogs; exoplanet formation; planet hosting stars; exoplanets; super earths; mini neptunes
Warm Molecular Gas in the Central Parsecs of the Buried Nucleus of NGC 4418 Traced with the Fundamental CO Rovibrational Absorptions

We investigated the inner buried nucleus of a nearby luminous infrared galaxy, NGC 4418, using high-resolution spectroscopy of fundamental carbon monoxide (CO) rovibrational absorptions around 4.67 μm for the first time. This method allowed us to examine the physical and kinematical properties in the hot inner region of this nucleus. We detected a series of both very deep (partly saturated) 12CO and moderately deep (optically thin) 13CO absorption lines and inferred a large column density (N H2 = (5 ± 3) × 1023 cm-2 in front of the 5 μm photosphere) of warm (T ex ≃ 170 K) molecular gas by assuming an isothermal plane-parallel slab illuminated by a compact background mid-infrared-emitting source. We modeled that the warm CO absorber almost covers the central heating source and that it is an inner layer around the 5 μm photosphere (at r = several parsecs) of a compact shroud of gas and dust (d ~ 100 pc). The width of the absorption lines (110 km s-1) and their small deviation from the systemic velocity (<10 km s-1) are consistent with a warm and turbulent layer with little bulk motion in the radial direction.

Keywords: luminous infrared galaxies; infrared spectroscopy
The Behavior of Bp He-weak Stars in the far-UV-Paper VIII: HD 131120

The analysis of four spectra of the B8 He-weak star HD 131120 recorded by the SWP camera on board the International Ultraviolet Explorer reveals low amplitude variations of the far-ultraviolet spectral energy distribution shortwards of 1500 Å over about half its rotational period in 1984. Silicon must be distributed in a non uniform manner over the surface of HD 131120 so as to modulate the FUV flux over the rotational period. This confirms the results of earlier investigations based on phase resolved high resolution optical spectra.

Keywords: chemically peculiar stars; helium-weak stars
A Simulation Study of Ultra-relativistic Jets. III. Particle Acceleration in FR-II Jets

We study the acceleration of ultra-high-energy cosmic rays (UHECRs) in Class II Fanaroff-Riley (FR-II) radio galaxies by performing Monte Carlo simulations for the transport, scattering, and energy change of CR particles injected into time-evolving jet flows that are realized through relativistic hydrodynamic simulations. Toward that end, we adopt physically motivated models for the magnetic field and particle scattering. By identifying the primary acceleration process among diffusive shock acceleration (DSA), turbulent shear acceleration (TSA), and relativistic shear acceleration (RSA), we find that CRs of E ≲ 1 EeV gain energy mainly through DSA in the jet‑spine flow and backflow containing many shocks and turbulence. After they attain E ≳ a few exaelectronvolts, CRs are energized mostly via RSA at the jet-backflow interface, reaching energies well above 1020 eV. TSA makes a relatively minor contribution. The time-asymptotic energy spectrum of escaping particles is primarily governed by the jet power, shifting to higher energies at more powerful jets. The UHECR spectrum fits well to a double power-law form, whose break energy, E break, corresponds to the size-limited maximum energy. It is close to $d{ \mathcal N }/{dE}\propto {E}^{-0.5}$ below E break, while it follows $d{ \mathcal N }/{dE}\propto {E}^{-2.6}$ above E break, decreasing more gradually than the exponential. The power-law slope of the high-energy end is determined by energy boosts via non-gradual shear acceleration across the jet-backflow interface and confinement by an elongated cocoon. We conclude that giant radio galaxies could be major contributors to the observed UHECRs.

Keywords: relativistic fluid dynamics; relativistic jets; radio galaxies; hydrodynamical simulations; ultra-high-energy cosmic radiation
Astrometric Apparent Motion of High-redshift Radio Sources

Radio-loud quasars at high redshift (z ≥ 4) are rare objects in the universe and rarely observed with Very Long Baseline Interferometry (VLBI). But some of them have flux density sufficiently high for monitoring of their apparent position. The instability of the astrometric positions could be linked to the astrophysical process in the jetted active galactic nuclei in the early universe. Regular observations of the high-redshift quasars are used for estimating their apparent proper motion over several years. We have undertaken regular VLBI observations of several high-redshift quasars at 2.3 GHz (S band) and 8.4 GHz (X band) with a network of five radio telescopes: 40 m Yebes (Spain), 25 m Sheshan (China), and three 32 m telescopes of the Quasar VLBI Network (Russia)-Svetloe, Zelenchukskaya, and Badary. Additional facilities joined this network occasionally. The sources have also been observed in three sessions with the European VLBI Network in 2018-2019 and one Long Baseline Array experiment in 2018. In addition, several experiments conducted with the Very Long Baseline Array in 2017-2018 were used to improve the time sampling and the statistics. Based on these 37 astrometric VLBI experiments between 2017 and 2021, we estimated the apparent proper motions of four quasars: 0901+697, 1428+422, 1508+572, and 2101+600.

Keywords: quasars
The Determination of the Rotational State and Interior Structure of Venus with VERITAS

Understanding the processes that led Venus to its current state and will drive its future evolution is a major objective of the next generation of orbiters. In this work we analyze the retrieval of the spin vector, the tidal response, and the moment of inertia of Venus with VERITAS, a NASA Discovery-class mission. By simulating a systematic joint analysis of Doppler tracking data and tie points provided by the onboard synthetic aperture radar, we show that VERITAS will provide accuracies (3σ) in the estimates of the tidal Love number k2 to 4.6 × 10-4, its tidal phase lag to 0°05, and the moment of inertia factor to 9.8 × 10-4 (0.3% of the expected value). Applying these results to recent models of the Venus interior, we show that VERITAS will provide much-improved constraints on the interior structure of the planet.

Keywords: venus; solar system terrestrial planets; orbit determination; planetary interior; planetary structure; remote sensing; planetary science
Illuminating the Dark Side of Cosmic Star Formation. II. A Second Date with RS-NIRdark Galaxies in COSMOS

About 12 billion years ago, the Universe was first experiencing light again after the dark ages, and galaxies filled the environment with stars, metals, and dust. How efficient was this process? How fast did these primordial galaxies form stars and dust? We can answer these questions by tracing the star formation rate density (SFRD) back to its widely unknown high-redshift tail, traditionally observed in the near-infrared (NIR), optical, and UV bands. Thus, objects with a large amount of dust were missing. We aim to fill this knowledge gap by studying radio-selected NIR-dark (RS-NIRdark) sources, i.e., sources not having a counterpart at UV-to-NIR wavelengths. We widen the sample of Talia et al. from 197 to 272 objects in the Cosmic Evolution Survey (COSMOS) field, including also photometrically contaminated sources, which were previously excluded. Another important step forward consists in the visual inspection of each source in the bands from u* to MIPS 24 μm. According to their "environment" in the different bands, we are able to highlight different cases of study and calibrate an appropriate photometric procedure for the objects affected by confusion issues. We estimate that the contribution of RS-NIRdark sources to the cosmic SFRD at 3 < z < 5 is ~10%-25% of that based on UV-selected galaxies.

Keywords: extragalactic radio sources; galaxy formation; galaxy evolution; high-redshift galaxies; star formation
Single-hemisphere Dynamos in M-dwarf Stars

M-dwarf stars below a certain mass are convective from their cores to their photospheres. These fully convective objects are extremely numerous, very magnetically active, and the likely hosts of many exoplanets. Here we study, for the first time, dynamo action in simulations of stratified, rotating, fully convective M-dwarf stars. Importantly, we use new techniques to capture the correct full ball geometry down to the center of the star. We find surprising dynamo states in these systems, with the global-scale mean fields confined strongly to a single hemisphere, in contrast to prior stellar dynamo solutions. These hemispheric-dynamo stars are likely to have profoundly different interactions with their surroundings, with important implications for exoplanet habitability and stellar spindown.

Keywords: m dwarf stars; stellar magnetic fields; magnetohydrodynamical simulations; astrophysical fluid dynamics
Hidden Companions to Intermediate-mass Stars. XV. Discovery of a 1.2M ⊙, 8.4 au Companion to the δ Scuti star HIP 41375 = 2 Hydrae

2 Hydrae is a nearby M Aa = 1.66M ⊙ δ Scuti star with strong astrometric evidence for a close companion in addition to its known M B = 0.20M ⊙ M dwarf companion at 530 au. Here we report on a VLTI/GRAVITY near-infrared interferometric observation that reveals the close companion to be a M Ab = 1.18M ⊙ star at a projected separation ρ = 168 mas ↔ 8.4 au. This triple system is a potential progenitor for a double white dwarf binary under the dynamical influence of an outer M dwarf companion with a low enough hierarchy for potentially interesting dynamical effects. *Based on observations collected at the European Southern Observatory, Chile, Program ID 110.241W.001.

Keywords: multiple stars; a stars; delta scuti variable stars; optical interferometry
The Hydrodynamic Evolution of Binary Black Holes Embedded within the Vertically Stratified Disks of Active Galactic Nuclei

Stellar-mass black holes can become embedded within the disks of active galactic nuclei (AGNs). Afterwards, their interactions are mediated by their gaseous surroundings. Here, we study the evolution of stellar-mass binary black holes (BBHs) embedded within AGN disks using three-dimensional hydrodynamic simulations and analytic methods, focusing on environments where the AGN disk scale height H is ≳ the BBH sphere of influence. We model the local surroundings of the embedded BBHs using a wind tunnel formalism and characterize different accretion regimes based on the local properties of the disk. We develop prescriptions for accretion and drag for embedded BBHs. Using these prescriptions with AGN disk models that can represent the Toomre-unstable outer regions of AGN disks, we study the long-term evolution of BBHs as they migrate through the disk. We find that BBHs typically merge within ≲1-30 Myr, increasing their mass significantly in the process, allowing BBHs to enter (or cross) the pair-instability supernova mass gap. The BBH accretion rate often exceeds the Eddington limit, sometimes by several orders of magnitude. Many embedded BBHs will merge before migrating significantly in the disk. We also discuss possible electromagnetic signatures during and following the inspiral, finding that it is generally unlikely for the bolometric luminosity of the BBH to exceed the AGN luminosity.

Keywords: black holes; astrophysical black holes; active galactic nuclei; binary stars; hydrodynamics; hydrodynamical simulations
GWSkyNet-Multi: A Machine-learning Multiclass Classifier for LIGO-Virgo Public Alerts

Compact object mergers which produce both detectable gravitational waves and electromagnetic (EM) emission can provide valuable insights into the neutron star equation of state, the tension in the Hubble constant, and the origin of the r-process elements. However, EM follow-up of gravitational wave sources is complicated by false-positive detections, and the transient nature of the associated EM emission. GWSkyNet-Multi is a machine learning model that attempts facilitate EM follow-up by providing real-time predictions of the source of a gravitational wave detection. The model uses information from Open Public Alerts (OPAs) released by LIGO-Virgo within minutes of a gravitational wave detection. GWSkyNet was introduced in Cabero et al. as a binary classifier and uses the OPA skymaps to classify sources as either astrophysical or as glitches. In this paper, we introduce GWSkyNet-Multi, an extension of GWSkyNet which further distinguishes sources as binary black hole mergers, mergers involving a neutron star, or non-astrophysical glitches. GWSkyNet-Multi is a sequence of three one-versus-all classifiers trained using a class-balanced and physically motivated source mass distribution. Training on this data set, we obtain test set accuracies of 93.7% for binary black hole-versus-all, 94.4% for neutron star-versus-all, and 95.1% for glitch-versus-all. We obtain an overall accuracy of 93.4% using a hierarchical classification scheme. Furthermore, we correctly identify 36 of the 40 gravitational wave detections from the first half of LIGO-Virgo's third observing run (O3a) and present predictions for O3b sources. As gravitational wave detections increase in number and frequency, GWSkyNet-Multi will be a powerful tool for prioritizing successful EM follow-up.

Keywords: gravitational wave astronomy; gravitational wave sources
New Observations of Solar Wind 1/f Turbulence Spectrum from Parker Solar Probe

The trace magnetic power spectrum in the solar wind is known to be characterized by a double power law at scales much larger than the proton gyro-radius, with flatter spectral exponents close to -1 found at the lower frequencies below an inertial range with indices closer to [-1.5, -1.67]. The origin of the 1/f range is still under debate. In this study, we selected 109 magnetically incompressible solar wind intervals (δ∣ B ∣/∣ B ∣ ≪ 1) from Parker Solar Probe encounters 1-13 that display such double power laws, with the aim of understanding the statistics and radial evolution of the low-frequency power spectral exponents from Alfvén point up to 0.3 au. New observations from closer to the Sun show that in the low-frequency range solar wind, turbulence can display spectra much shallower than 1/f, evolving asymptotically to 1/f as advection time increases, indicating a dynamic origin for the 1/f range formation. We discuss the implications of this result on the Matteini et al. conjecture for the 1/f origin as well as example spectra displaying a triple power law consistent with the model proposed by Chandran et al., supporting the dynamic role of parametric decay in the young solar wind. Our results provide new constraints on the origin of the 1/f spectrum and further show the possibility of the coexistence of multiple formation mechanisms.

Keywords: solar wind; interplanetary turbulence; magnetohydrodynamics; space plasmas; heliosphere; alfven waves
Constraining the Neutrino Mass with the Drifting Coefficient of the Field Cluster Mass Function

A new diagnostics to break the degeneracy between the total neutrino mass (Mν) and the primordial power spectrum amplitude (σ8) using the drifting coefficient of the field cluster mass function is presented. Analyzing the data from the Cosmological Massive Neutrino Simulations, we first determine the numerical mass functions of the field clusters at various redshifts. Then, we compare the numerical results with the analytical model characterized by a single parameter called the drifting coefficient, which measures the drifts of the collapse density threshold, δc, from the Einstein-de Sitter spherical value, δsc, at a given mass scale. It is found that the analytic model for the field cluster mass function is found to work excellently even in the presence of massive neutrinos, and that its drifting coefficient evolves differently in the cosmologies with different values of Mν. At low redshifts (z ≲ 0.3) the more massive neutrinos drift δc further from δsc, while the opposite trend is found at higher redshifts (z ≳ 0.3). Speculating that this distinct redshift-dependent effect of massive neutrinos on the drifting coefficient of the field cluster mass function might help break the σ8-Mν degeneracy, we also show that the sensitivity of this new diagnostics to Mν is high enough to discriminate the case of Mν = 0.1 eV from that of massless neutrinos.

Keywords: large-scale structure of the universe; cosmological parameters from large-scale structure
Onset of Particle Acceleration during the Prompt Phase in Gamma-Ray Bursts as Revealed by Synchrotron Emission in GRB 160821A

The physical processes of gamma-ray emission and particle acceleration during the prompt phase in gamma-ray bursts (GRBs) are still unsettled. In order to perform unambiguous physical modeling of observations, a clear identification of the emission mechanism is needed. An instance of a clear identification is the synchrotron emission during the very strong flare in GRB 160821A, which occurred during the prompt phase at 135 s. Here we show that the distribution of the radiating electrons in this flare is initially very narrow but later develops a power-law tail of accelerated electrons. We thus identify for the first time the onset of particle acceleration in a GRB jet. The flare is consistent with a late energy release from the central engine causing an external shock as it encounters a preexisting ring nebula of a progenitor Wolf-Rayet star. Relativistic forward and reverse shocks develop, leading to two distinct emission zones with similar properties. The particle acceleration only occurs in the forward shock, moving into the dense nebula matter. Here, the magnetization also decreases below the critical value, which allows for Fermi acceleration to operate. Using this fact, we find a bulk Lorentz factor of 420 ≲ Γ ≲ 770 and an emission radius of R ~ 1018 cm, indicating a tenuous gas of the immediate circumburst surroundings. The observation of the onset of particle acceleration thus gives new and independent constraints on the properties of the flow as well as on theories of particle acceleration in collisionless astrophysical shocks.

Keywords: gamma-ray bursts
Cloudy Atmospheres on Directly Imaged Exoplanets: The Need for Accurate Particulate Representation in Photopolarimetric Simulations

Missions like the upcoming Roman Space Telescope and its follow-on missions, Habitable Exoplanet Observatory (HabEx) and the Large UV/Optical/IR Surveyor (LUVOIR), will provide direct imaging observations of stellar light reflected by exoplanets with successively closer orbits. The synergistic use of ground-based polarimeters like Gemini Planet Imager and Very Large Telescope/Spectro-Polarimetric High-contrast Exoplanet Research instrument (SPHERE) would allow us to characterize cloudy exoplanet atmospheres using spectropolarimetric direct imaging. We present an extension of our semianalytic 3D radiative transfer modeling framework for brown dwarfs to include stellar light reflected by exoplanets with cloudy atmospheres. Using Mie theory to compute scattering by cloud and haze consisting of spherical particles, we show that the currently widespread use of approximations like the scalar Two-Term Henyey-Greenstein or the vector Henyey-Greenstein Rayleigh (HGR) composite result in a blurring of the phase-dependent features of exoplanet lightcurves, causing a 10%-39% loss of sensitivity to atmospheric parameters in an average measurement for signal-to-noise ratios (S/Ns) between 5 and 500. The HGR approximation creates the misleading impression that clouds are as polarizing as Rayleigh scatterers, regardless of their droplet size. This not only causes significant errors in the scientific interpretation of polarimetric measurements, but also results in a negligible sensitivity of HGR simulations to polarization measurements at the S/Ns considered, whereas Mie simulations show a 10%-30% gain in parametric sensitivity through the addition of polarimetry.

Keywords: earth's clouds; atmospheric composition; exoplanet atmospheric composition; direct imaging; polarimetry
Misaligned Twin Molecular Outflows from the Class 0 Protostellar Binary System VLA 1623A Unveiled by ALMA

We present the results of ALMA observations toward the low-mass Class 0 binary system VLA 1623Aab in the Ophiuchus molecular cloud in 12CO, 13CO, and C18O(2-1) lines. Our 12CO (J = 2-1) data reveal that the VLA 1623 outflow consists of twin spatially overlapped outflows/jets. The redshifted northwestern jet exhibits three cycles of wiggle with a spatial period of 1360 ± 10 au, corresponding to a time period of 180 yr. The wiggle-like structure is also found in the position-velocity (PV) diagram, showing an amplitude in the velocity of about 0.9 km s-1. Both the period and velocity amplitude of the wiggle are roughly consistent with those expected from the binary parameters, i.e., the orbital period (460 ± 20 yr) and the Keplerian velocity (2.2 km s-1). Our 13CO and C18O images show a dense gas nature in the two centimeter/millimeter sources, VLA 1623B and W, and its relation to the outflows, and strongly support the previous interpretation that both are shocked cloudlets. The driving sources of the twin molecular outflows are, therefore, likely to be the VLA 1623Aab binary. The outflow axes of the two molecular outflows are estimated to be inclined by 70° to each other across the plane of sky, implying that protostellar disks are also misaligned by $70^\circ $ . Such nature together with a small binary separation of 34 au in one of the youngest protobinary systems seems difficult to explain by disk fragmentation in quiescent environments. Other effects such as turbulence probably play roles.

Keywords: star formation; molecular clouds; stellar jets; interstellar molecules