adsabs/SciX_UAT_keywords huggingface dataset:
Rapid Formation of Gas-giant Planets via Collisional Coagulation from Dust Grains to Planetary Cores

Gas-giant planets, such as Jupiter, Saturn, and massive exoplanets, were formed via the gas accretion onto the solid cores, each with a mass of roughly 10 Earth masses. However, rapid radial migration due to disk-planet interaction prevents the formation of such massive cores via planetesimal accretion. Comparably rapid core growth via pebble accretion requires very massive protoplanetary disks because most pebbles fall into the central star. Although planetesimal formation, planetary migration, and gas-giant core formation have been studied with a lot of effort, the full evolution path from dust to planets is still uncertain. Here we report the result of full simulations for collisional evolution from dust to planets in a whole disk. Dust growth with realistic porosity allows the formation of icy planetesimals in the inner disk (≲10 au), while pebbles formed in the outer disk drift to the inner disk and there grow to planetesimals. The growth of those pebbles to planetesimals suppresses their radial drift and supplies small planetesimals sustainably in the vicinity of cores. This enables rapid formation of sufficiently massive planetary cores within 0.2-0.4 million years, prior to the planetary migration. Our models shows the first gas giants form at 2-7 au in rather common protoplanetary disks, in agreement with the exoplanet and solar systems.

Keywords: planet formation; protoplanetary disks; planetary system formation; solar system formation
TESS-Keck Survey. XIV. Two Giant Exoplanets from the Distant Giants Survey

We present the Distant Giants Survey, a three-year radial velocity campaign to measure P(DG∣CS), the conditional occurrence of distant giant planets (DG; M p ~ 0.3-13 M J, P > 1 yr) in systems hosting a close-in small planet (CS; R p < 10 R ⊕). For the past two years, we have monitored 47 Sun-like stars hosting small transiting planets detected by TESS. We present the selection criteria used to assemble our sample and report the discovery of two distant giant planets, TOI-1669 b and TOI-1694 c. For TOI-1669 b we find that $M\sin i=0.573\pm 0.074\,\,{M}_{{\rm{J}}}$ , P = 502 ± 16 days, and e < 0.27, while for TOI-1694 c, $M\sin i=1.05\pm 0.05\,\,{M}_{{\rm{J}}}$ , P = 389.2 ± 3.9 days, and e = 0.18 ± 0.05. We also confirmed the 3.8 days transiting planet TOI-1694 b by measuring a true mass of M = 26.1 ± 2.2 M ⊕. At the end of the Distant Giants Survey, we will incorporate TOI-1669 b and TOI-1694 c into our calculation of P(DG∣CS), a crucial statistic for understanding the relationship between outer giants and small inner companions.

Keywords: radial velocity; extrasolar gaseous giant planets; exoplanet detection methods; transits
A New 6-15 GHz Solar Radio Observation System

In this study, we have developed a centimeter-band solar radio telescope covering the 6-15 GHz frequency band. The radio telescope has the outstanding advantages of a large instantaneous sampling bandwidth and wide frequency coverage. As a new solar radio telescope, its time resolution reaches a very high level of 0.26 ms at a frequency resolution of 3 MHz, which is very conducive to observing the fine structure of radio burst signals. In terms of the structure design, the system employs a 3 m diameter parabolic antenna to receive solar radio signals. The antenna has high gain and good directivity, and the pointing accuracy reaches 0.°02, which ensures the ability to accurately track the Sun in real time. In the analog signal processing module, the combination of radio frequency direct acquisition and down conversion is used to reduce the interference caused by multiple spectrum shifts. Regarding the digital receiver, a digital receiving module with high sampling rate and acquisition resolution is used for data acquisition and processing, which ensures that the observation system can obtain observation data with high time and frequency resolutions and real-time data processing. During the trial operation of the system, solar radio bursts have been observed many times, and these observations have been supported by similar international observation equipment. According to a data comparison, the data obtained by our observation system are more precise. At present, equipment calibration methods are being improved and constructed to obtain more accurate observation data.

Keywords: solar radio telescopes; flux calibration
A First Spectroscopic Measurement of the Magnetic-field Strength for an Active Region of the Solar Corona

For all involved in astronomy, the importance of monitoring and determining astrophysical magnetic-field strengths is clear. It is also a well-known fact that the corona magnetic fields play an important part in the origin of solar flares and the variations of space weather. However, after many years of solar corona studies, there is still no direct and continuous way to measure and monitor the solar magnetic-field strength. We present here a scheme that allows such a measurement, based on a careful study of an exotic class of atomic transitions, known as magnetic induced transitions, in Fe9+. In this contribution we present a first application of this methodology and determine a value of the coronal field strength using the spectroscopic data from Hinode.

Keywords: active sun; the sun; solar magnetic fields; solar corona; spectroscopy; atomic spectroscopy; astronomical techniques
New Grids of Pure-hydrogen White Dwarf NLTE Model Atmospheres and the HST/STIS Flux Calibration

Nonlocal thermodynamic equilibrium (NLTE) calculations of hot white dwarf (WD) model atmospheres are the cornerstone of modern flux calibrations for the Hubble Space Telescope and for the CALSPEC database. These theoretical spectral energy distributions (SEDs) provide the relative flux versus wavelength, and only the absolute flux level remains to be set by reconciling the measured absolute flux of Vega in the visible with the Midcourse Space Experiment values for Sirius in the mid-IR. The most recent SEDs calculated by the TLUSTY and TMAP NLTE model atmosphere codes for the primary WDs G191-B2B, GD 153, and GD 71 show improved agreement to 1% from 1500 Å to 30 μm, in comparison to the previous 1% consistency only from 2000 Å to 5 μm. These new NLTE models of hot WDs now provide consistent flux standards from the far UV to the mid-IR.

Keywords: astronomical instrumentation; white dwarf stars
Fluorine Abundances in Local Stellar Populations

We present the first fluorine measurements in 12 normal K giants belonging to the Galactic thin and thick disks using spectra obtained with the Phoenix infrared spectrometer on the 2.1 m telescope at Kitt Peak. Abundances are determined from the (1‑0) R9 2.3358 μm feature of the molecule HF. Additionally, sodium abundances are derived in 25 giants in the thin disk, thick disk, and halo using the Na I line at 2.3379 μm. We report fluorine abundances for thin and thick disk stars in the metallicity range ‑0.7 < [Fe/H] < 0. We add two abundance measurements for stars with [Fe/H] < 0.5 dex, which are at a critical metallicity range to constrain models. We find a larger dispersion in fluorine abundances than sodium abundances despite both species having similar overall uncertainties due to atmospheric parameters, suggesting this dispersion is real and not observational. The dispersion is slightly larger in the thick disk than the thin. The thin and thick disk average [F/Fe] for our sample of stars combined with the literature differ by 0.03 dex. The observations are compared to available chemical evolution models.

Keywords: stellar abundances; late-type stars; galactic abundances
A New Method Linking the Solar Wind Speed to the Coronal Magnetic Field

The release and acceleration of the solar wind is still an outstanding question. There are several aspects related to this phenomenon that still need to be investigated, and one of these is the identification of the region within the inner corona where the larger fraction of acceleration occurs. To address this matter, it is necessary to have reliable measurements of the solar wind speed between 1 and 10 solar radii (R ⊙). Moreover, in order to describe the coronal plasma behavior, it is important to consider its interaction with the magnetic field. Within this context, our intent is to investigate a method to combine measurements of the solar wind with the extrapolated magnetic field in the corona to derive how the solar wind velocity evolves along the magnetic field lines, aiming at better understanding the sources, origins, and acceleration of the solar wind. To this purpose, we used outflow speed measurements of the coronal plasma derived by applying the Doppler dimming technique, as well as the global magnetic field configuration derived from the measured photospheric magnetic field by using the Wang-Sheeley-Arge model. These two sets of data are then combined for heliocentric distances between 2.6 and 5 R ⊙. This paper presents the proposed method and the results obtained over two different Carrington rotations (CR 1923 and CR 1924), demonstrating the applicability of the method and the capability to link measured solar wind velocity to the extrapolated coronal magnetic field in order to derive the velocity profile.

Keywords: solar wind; solar magnetic fields; solar corona
Systematic KMTNet Planetary Anomaly Search. I. OGLE-2019-BLG-1053Lb, a Buried Terrestrial Planet

In order to exhume the buried signatures of "missing planetary caustics" in Korea Microlensing Telescope Network (KMTNet) data, we conducted a systematic anomaly search of the residuals from point-source point-lens fits, based on a modified version of the KMTNet EventFinder algorithm. This search revealed the lowest-mass-ratio planetary caustic to date in the microlensing event OGLE-2019-BLG-1053, for which the planetary signal had not been noticed before. The planetary system has a planet-host mass ratio of q = (1.25 ± 0.13) × 10-5. A Bayesian analysis yielded estimates of the mass of the host star, ${M}_{\mathrm{host}}={0.61}_{-0.24}^{+0.29}\,{M}_{\odot }$ , the mass of its planet, ${M}_{\mathrm{planet}}={2.48}_{-0.98}^{+1.19}\,{M}_{\oplus }$ , the projected planet-host separation, ${a}_{\perp }={3.4}_{-0.5}^{+0.5}$ au, and the lens distance, ${D}_{{\rm{L}}}={6.8}_{-0.9}^{+0.6}$ kpc. The discovery of this very-low-mass-ratio planet illustrates the utility of our method and opens a new window for a large and homogeneous sample to study the microlensing planet-host mass ratio function down to q ~ 10-5.

Keywords: exoplanet detection methods; gravitational microlensing exoplanet detection
Detection of Diffuse γ-Ray Emission toward a Massive Star-forming Region Hosting Wolf-Rayet Stars

Isotopic and elemental abundances seen in Galactic cosmic rays (GCRs) imply that ~20% of the cosmic-ray (CR) nuclei are probably synthesized by massive Wolf-Rayet (W-R) stars. Massive star clusters hosting W-R- and OB-type stars have been proposed as potential GCR accelerators for decades, in particular via diffusive shock acceleration at wind termination shocks. Here we report the analysis of Fermi Large Area Telescope data toward the direction of Masgomas-6a, a young massive star cluster candidate hosting two W-R stars. We detect an extended γ-ray source with a test statistic = 183 in the vicinity of Masgomas-6a, spatially coincident with two unassociated Fermi 4FGL sources. We also present the CO observational results of molecular clouds in this region, using the data from the Milky Way Imaging Scroll Painting project. The γ-ray emission intensity correlates well with the distribution of molecular gas at the distance of Masgomas-6a, indicating that these γ-rays may be produced by CRs accelerated by massive stars in Masgomas-6a. At the distance of 3.9 kpc of Masgomas-6a, the luminosity of the extended source is (1.81 ± 0.02) × 1035 erg s-1. With a kinetic luminosity of ~1037 erg s-1 in the stellar winds, the W-R stars are capable of powering the γ-ray emission via neutral pion decay resulted from CR proton-proton interactions. The size of the GeV source and the energetic requirement suggests a CR diffusion coefficient smaller than that in the Galactic interstellar medium, indicating a strong suppression of CR diffusion in the molecular cloud.

Keywords: young massive clusters; wolf-rayet stars; molecular clouds; gamma-ray sources
The Polar Precursor Method for Solar Cycle Prediction: Comparison of Predictors and Their Temporal Range

The polar precursor method is widely considered to be the most robust physically motivated method to predict the amplitude of an upcoming solar cycle. It uses indicators of the magnetic field concentrated near the poles around the sunspot minimum. Here, we present an extensive analysis of the performance of various such predictors, based on both observational data (Wilcox Solar Observatory (WSO) magnetograms, Mount Wilson Observatory polar faculae counts, and Pulkovo A(t) index) and outputs (polar cap magnetic flux and global dipole moment) of various existing flux transport dynamo models. We calculate Pearson correlation coefficients (r) of the predictors with the next cycle amplitude as a function of time measured from several solar cycle landmarks: setting r = 0.8 as a lower limit for acceptable predictions, we find that observations and models alike indicate that the earliest time when the polar predictor can be safely used is 4 yr after the polar field reversal. This is typically 2-3 yr before the solar minimum and about 7 yr before the predicted maximum, considerably extending the usual temporal scope of the polar precursor method. Reevaluating the predictors another 3 yr later, at the time of the solar minimum, further increases the correlation level to r ≳ 0.9. As an illustration of the result, we determine the predicted amplitude of Cycle 25 based on the value of the WSO polar field at the now official minimum date of 2019 December as 126 ± 3. A forecast based on the value in early 2017, 4 yr after the polar reversal would have only differed from this final prediction by 3.1 ± 14.7%.

Keywords: solar cycle; solar dynamo; solar magnetic fields; sunspot cycle
Nonthermal X-Rays from Pulsation-driven Shocks in Cepheids

Rapid X-ray phase-dependent flux enhancement in the archetype classical Cepheid star δ Cep was observed by XMM-Newton and Chandra. We jointly analyze thermal and nonthermal components of the time-resolved X-ray spectra prior to, during, and after the enhancement. A comparison of the timescales of shock particle acceleration and energy losses is consistent with the scenario of a pulsation-driven shock wave traveling into the stellar corona and accelerating electrons to ~GeV energies, and with Inverse Compton (IC) emission from the UV stellar background leading to the observed X-ray enhancement. The index of the nonthermal IC photon spectrum, assumed to be a simple power law in the [1-8] keV energy range, radially integrated within the shell [3-10] stellar radii, is consistent with an enhanced X-ray spectrum powered by shock-accelerated electrons. An unlikely ~100-fold amplification via turbulent dynamo of the magnetic field at the shock propagating through density inhomogeneities in the stellar corona is required for the synchrotron emission to dominate over the IC; the lack of time correlation between radio synchrotron and stellar pulsation contributes to make synchrotron as an unlikely emission mechanism for the flux enhancement. Although current observations cannot rule out a high-flux two-temperature thermal spectrum with a negligible nonthermal component, this event might confirm for the first time the association of Cepheids pulsation with shock-accelerated GeV electrons.

Keywords: cepheid variable stars; shocks; x-ray transient sources
Central Black Hole Mass in the Distant Tidal Disruption Event Candidate of Swift J2058.4+0516

In this article, the central black hole (BH) mass in the distant tidal disruption event (TDE) of Swift J2058.4+0516, the second candidate of relativistic jet birth related to a TDE, is estimated. Swift J2058.4+0516 has quite different BH masses estimated through different indirect methods in the literature. Therefore, it is necessary and interesting to determine the central BH mass in Swift J2058.4+0516 by another independent method. Here, based on the theoretical TDE model applied to describe the long-term time-dependent X-ray variabilities of Swift J2058.4+0516, the central BH mass can be well determined to be around ${1.05}_{-0.29}^{+0.39}\times {10}^{5}{M}_{\odot }$ , after considering the suggested intrinsic beaming effects from such relativistic jets tightly related to TDEs. Moreover, Swift J2058.4+0516 is a unique object in the space of BH masses versus energy transfer efficiencies of the reported TDE candidates, providing interesting clues to detect and/or anticipate candidates of relativistic TDEs that cause the birth of relativistic jets.

Keywords: active galactic nuclei; active galaxies; tidal disruption; supermassive black holes
The First Instrumentally Documented Fall of an Iron Meteorite: Orbit and Possible Origin

A bright fireball observed on 2020 November 7, over Scandinavia, produced the first iron meteorite with a well-determined pre-atmospheric trajectory. We calculated the orbit of this meteoroid and found that it demonstrates no close affinity with the orbit of any known asteroid. We found that the meteoroid (or its parent body) most probably entered the near-Earth orbit from the main asteroid belt via either ν 6 secular resonance with Saturn (89%) or 3:1 mean-motion resonance with Jupiter (11%). The long YORP timescale of the meteoroid suggests that it could have been produced in the main asteroid belt and survived the journey to the near-Earth orbit.

Keywords: iron meteorites; meteorites; meteoroids; meteors; fireballs; asteroids; celestial mechanics; astronomical simulations
370 New Eclipsing Binary Candidates from TESS Sectors 1-26

We present 370 candidate eclipsing binaries (EBs), identified from ~510,000 short cadence TESS light curves. Our statistical criteria identify 5105 light curves with features consistent with eclipses (~1% of the initial sample). After visual confirmation of the light curves, we have a final sample of 2288 EB candidates. Among these, we find 370 sources that were not included in the catalog recently published by Prša et al. We publish our full sample of 370 new EB candidates, and statistical features used for their identification, reported per observation sector.

Keywords: eclipsing binary stars
Effects of Turbulence in the Circumnuclear Disk

A circumnuclear disk (CND) of molecular gas occupies the central few parsecs of the Galactic Center. It is likely subject to turbulent disruptions from violent events in its surrounding environment, but the effect of such perturbations has not yet been investigated in detail. Here we perform 3D, N-body/smoothed particle hydrodynamic simulations with an adapted general turbulence driving method to investigate the CND's structural evolution, in particular its reaction to varied scales of injected turbulence. We find that, because of shear flow in the disk, transient arcs of gas (streams) naturally arise when turbulence is driven on large scales (up to ~4 pc), as might occur when a supernova blast wave encounters the CND. Because energetic events arise naturally and often in the central parsecs of our Galaxy, this result suggests that the transient structures that characterize the CND do not imply that the CND itself is a transient structure. We also note that features similar to the density concentrations, or clumps, detailed in the literature emerge when we account for the observed orientation of the disk and for the spatial resolution of observations. As such, clumps could be an artifact of observational limitations.

Keywords: galaxy circumnuclear disk; interstellar medium; galactic center
Isotope Exchange Reaction of OH- Anion with HD at Temperatures from 15 K up to 300 K: Ion Trap Study

This paper presents the results of an experimental study of the reaction of OH- anions with HD molecules leading to the formation of OD- anions. The study's main goal was to obtain the temperature dependence of the reaction rate coefficient and determine the reaction's enthalpy. This study was carried out at astrophysically relevant temperatures from 15 to 300 K. The reaction was studied using a temperature-variable cryogenic linear 22-pole radio-frequency ion trap. The rotational temperature of the OH- anions in the ion trap was characterized by near-threshold photodetachment spectroscopy. At 15 K, the measured reaction rate coefficient is 5 × 10-10 cm3 s-1. With increasing temperature, the reaction rate coefficient decreases monotonically to 5 × 10-11 cm3 s-1 at 300 K. Comparing with the previously determined rate coefficient of the reverse reaction of OD- anions with H2, we obtained the temperature dependence of the equilibrium constant. The enthalpy and entropy of the title reaction were determined in the studied temperature range as ΔH = (-23.9 ± 0.7 ± 2.6sys) meV and ΔS = (-8.5 ± 1.2 ± 1.4sys) J mol-1 K-1, respectively.

Keywords: astrochemistry; interstellar molecules; isotopic abundances; laboratory astrophysics; reaction rates
Understanding the Angular Momentum Evolution of T Tauri and Herbig Ae/Be Stars

We investigate a sample of six Herbig Ae/Be stars belonging to the Orion OB1 association, as well as 73 low-mass objects, members of the σ Orionis cluster, in order to explore the angular momentum evolution at early stages of evolution, and its possible connection with main-sequence Ap/Bp magnetic stars. Using FIES and HECTOCHELLE spectra, we obtain projected rotational velocities through two independent methods. Individual masses, radii, and ages are computed using evolutionary models, distance, and cluster extinction. Under the assumption that similar physical processes operate in both T Tauri and Herbig Ae/Be stars, we construct snapshots of the protostar's rotation against mass during the first 10 Myr with the aid of a rotational model that includes a variable disk lifetime, changes in the stellar moment of inertia, a dipolar magnetic field with variable strength, and angular momentum loss through stellar winds powered by accretion. We use these snapshots, as well as the rotational data, to infer a plausible scenario for the angular momentum evolution. We find that magnetic field strengths of a few kilo-Gauss at 3 Myr are required to match the rotational velocities of both groups of stars. Models with masses between 2 M⊙ and 3 M⊙ display larger angular momentum values by a factor of ~3, in comparison to stars of similar spectral types on the main sequence. Even though some quantitative estimates on this dramatic decrease with age for Ap/Bp magnetic main-sequence stars are presented, the results obtained for the angular momentum evolution do not explain their low rotation rates.

Keywords: stellar rotation; stellar properties; young stellar objects; t tauri stars; herbig ae/be stars; protostars; pre-main sequence stars; stellar accretion disks; interstellar magnetic fields