adsabs/SciX_UAT_keywords huggingface dataset:
Spiral-arm Substructures in the Asymmetrical Dust Rings of the Circumstellar Disk MWC 758

Asymmetrical features in disks provide indirect evidence of embedded objects, such as planets. Observed with the Atacama Large Millimeter/submillimeter Array (ALMA), the circumstellar disk in MWC 758 traced with thermal dust continuum emission at wavelengths of 0.9 mm with an angular resolution up to 0"1 (15 au) exhibits an asymmetrical dust ring with additional features. In order to analyze the structures azimuthally and radially, we split the dust ring into small segments in azimuth. For each segment, we fit two-Gaussian functions to the radial intensity profile. The obtained best-fit parameters as a function of azimuth are analyzed. Three spiral-like arm structures are identified. When fitting the 0.9 mm features with the spiral density wave theory using the WKB approximation, two sets of disk aspect ratios are found: one solution gives relatively low values (∼0.03) while the other solution is at the upper bound of the free parameter (∼0.2). The planet locations suggested by the upper-bound result are similar to the ones determined by Benisty et al. for the NIR polarized intensity image. Comparing the reported spiral-like structures with the higher angular resolution (0"04) ALMA image in Dong et al., we identify different structures in the west of the disk due to differences in the adopted analysis methods and the respective resolutions of the images.

Keywords: protoplanetary disks; circumstellar disks; planet formation
An X-Ray View of Two Infrared Dark Clouds G034.43+00.24 and G035.39-00.33

We present a high spatial resolution Chandra X-ray study of two infrared dark clouds (IRDCs), G034.43+00.24 and G035.39-00.33, which are expected to be in the early phases of star cluster formation. We detect 112 and 209 valid X-ray point sources toward G034.43+00.24 and G035.39-00.33, respectively. We cross-match the X-ray point sources with the Two Micron All Sky Survey (2MASS), Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE), and Wide-field Infrared Survey Explorer (WISE) catalogs and find 53% and 59% of the X-ray sources in G034.43+00.24 and in G035.39-00.33 have corresponding infrared counterparts, respectively. These sources are probable members of young massive clusters in formation, and using stellar isochrones we estimate that a population of 1-2 Myr old, intermediate- to high-mass young stellar objects (YSOs) exist in both IRDCs. Two and 10 Class II counterparts to X-ray sources were identified in G034.43+00.24 and in G035.39-00.33, respectively, which are located in or near dark filaments. The X-ray luminosity function (XLF) of G035.39-00.33 implies that the total mass consists of up to ∼1700M⊙ of stars, using the XLF of the well-studied Orion Nebula Cluster as a calibrator. This corresponds to a star formation efficiency of at most 5%, indicating the system is still very much gas dominated and in an early stage of the star formation process. The population of G034.43+00.24 is less well determined due to the lower sensitivity of its observations.

Keywords: star formation; infrared dark clouds; x-ray stars
TESS Spots a Hot Jupiter with an Inner Transiting Neptune

Hot Jupiters are rarely accompanied by other planets within a factor of a few in orbital distance. Previously, only two such systems have been found. Here, we report the discovery of a third system using data from the Transiting Exoplanet Survey Satellite (TESS). The host star, TOI-1130, is an eleventh magnitude K-dwarf in Gaia G-band. It has two transiting planets: a Neptune-sized planet (3.65 ± 0.10 R\oplus) with a 4.1 days period, and a hot Jupiter (1.50-0.22+0.27 RJ) with an 8.4 days period. Precise radial-velocity observations show that the mass of the hot Jupiter is 0.974-0.044+0.043 MJ. For the inner Neptune, the data provide only an upper limit on the mass of 0.17 MJ (3σ). Nevertheless, we are confident that the inner planet is real, based on follow-up ground-based photometry and adaptive-optics imaging that rule out other plausible sources of the TESS transit signal. The unusual planetary architecture of and the brightness of the host star make TOI-1130 a good test case for planet formation theories, and an attractive target for future spectroscopic observations.

Keywords: exoplanet astronomy; extrasolar gaseous giant planets; extrasolar rocky planets; exoplanets; hot jupiters
Turbulent Magnetic Diffusivity β Effect in a Magnetically Forced System

We have studied the large-scale dynamo forced with helical magnetic energy. Compared to the kinetic forcing process, the magnetic process is not clearly observed nor intuitive. However, it may represent the actual B field amplification in the stellar corona, accretion disk, plasma lab, or other magnetically dominated systems where the strong kinetic effect does not exist. The interaction between the magnetic field and the plasma is essentially nonlinear. However, when the plasma system is driven by helical energy, whether kinetic or magnetic, the nonlinear process can be linearized with pseudotensors a, β and the large-scale magnetic field $\overline{{\boldsymbol{B}}}$ . Conventionally, the α effect is thought to be the main dynamo effect converting kinetic energy into magnetic energy and transferring it to the large-scale regime. In contrast, β effect has been thought to diffuse magnetic energy. However, these conclusions are not based on the exact definition of α and β. In this paper, instead of the analytic definition of α and β, we derive a semi-analytic equation and apply it to the simulation data. The half analytic and numerical result shows that the averaged α effect is not so important in amplifying the $\overline{{\boldsymbol{B}}}$ field. Rather, it is the negative β effect combined with the Laplacian (∇2 → -k 2) that plays a key role in the dynamo process. Further, the negative magnetic diffusivity accounts for the attenuation of the plasma kinetic energy ${\overline{E}}_{V}$ in large scales. We discuss this process using the theoretical method and the intuitive field structure model.

Keywords: solar dynamo; magnetohydrodynamics; magnetic fields; plasma astrophysics
Where Are the Water Worlds? Identifying Exo-water-worlds Using Models of Planet Formation and Atmospheric Evolution

Planet formation models suggest that the small exoplanets that migrate from beyond the snowline of the protoplanetary disk likely contain water-ice-rich cores (∼50% by mass), also known as water worlds. While the observed radius valley of the Kepler planets is well explained by the atmospheric dichotomy of the rocky planets, precise measurements of the mass and radius of the transiting planets hint at the existence of these water worlds. However, observations cannot confirm the core compositions of those planets, owing to the degeneracy between the density of a bare water-ice-rich planet and the bulk density of a rocky planet with a thin atmosphere. We combine different formation models from the Genesis library with atmospheric escape models, such as photoevaporation and impact stripping, to simulate planetary systems consistent with the observed radius valley. We then explore the possibility of water worlds being present in the currently observed sample by comparing them with simulated planets in the mass–radius–orbital period space. We find that the migration models suggest ≳10% and ≳20% of the bare planets, i.e., planets without primordial H/He atmospheres, to be water-ice-rich around G- and M-type host stars, respectively, consistent with the mass–radius distributions of the observed planets. However, most of the water worlds are predicted to be outside a period of 10 days. A unique identification of water worlds through radial velocity and transmission spectroscopy is likely to be more successful when targeting such planets with longer orbital periods.

Keywords: exoplanet formation; exoplanet migration; exoplanet atmospheric structure; exoplanet catalogs; exoplanet atmospheric evolution; exoplanet systems; radial velocity; ocean planets
The ALMA REBELS Survey: The Cosmic H I Gas Mass Density in Galaxies at z ≈ 7

The neutral atomic gas content of individual galaxies at large cosmological distances has until recently been difficult to measure due to the weakness of the hyperfine H I 21 cm transition. Here we estimate the H I gas mass of a sample of main-sequence star-forming galaxies at z ~ 6.5-7.8 surveyed for [C II] 158 μm emission as part of the Reionization Era Bright Emission Line Survey (REBELS), using a recent calibration of the [C II]-to-H I conversion factor. We find that the H I gas mass excess in galaxies increases as a function of redshift, with an average of M HI /M ⋆ ≈ 10, corresponding to H I gas mass fractions of f HI = M HI /(M ⋆ + M HI ) = 90%, at z ≈ 7. Based on the [C II] 158 μm luminosity function (LF) derived from the same sample of galaxies, we further place constraints on the cosmic H I gas mass density in galaxies (ρ HI ) at this redshift, which we measure to be ${\rho }_{{\rm{H}}{\rm\small{I}}}={7.1}_{-3.0}^{+6.4}\times {10}^{6}\,{M}_{\odot }\,{\mathrm{Mpc}}^{-3}$ . This estimate is substantially lower by a factor of ≈10 than that inferred from an extrapolation of damped Lyα absorber (DLA) measurements and largely depends on the exact [C II] LF adopted. However, we find this decrease in ρ HI to be consistent with recent simulations and argue that this apparent discrepancy is likely a consequence of the DLA sight lines predominantly probing the substantial fraction of H I gas in high-z galactic halos, whereas [C II] traces the H I in the ISM associated with star formation. We make predictions for this buildup of neutral gas in galaxies as a function of redshift, showing that at z ≳ 5, only ≈10% of the cosmic H I gas content is confined in galaxies and associated with the star-forming ISM.

Keywords: high-redshift galaxies; galaxy evolution; interstellar medium
Dense Molecular Gas Properties of the Central Kiloparsec of Nearby Ultraluminous Infrared Galaxies Constrained by ALMA Three Transition-line Observations

We report the results of Atacama Large Millimeter/submillimeter Array (ALMA) 1-2 kpc resolution, three rotational transition-line (J = 2-1, J = 3-2, and J = 4-3) observations of multiple dense molecular gas tracers (HCN, HCO+, and HNC) for 10 nearby (ultra)luminous infrared galaxies ((U)LIRGs). Following the matching of beam sizes to 1-2 kpc for each (U)LIRG, the high-J-to-low-J transition-line flux ratios of each molecule and the emission-line flux ratios of different molecules at each J transition are derived. We conduct RADEX non-LTE model calculations and find that, under a wide range of gas density and kinetic temperature, the observed HCN-to-HCO+ flux ratios in the overall (U)LIRGs are naturally reproduced with enhanced HCN abundance compared to HCO+. Thereafter, molecular gas properties are constrained primarily through the use of HCN and HCO+ data and the adoption of fiducial values for the HCO+ column density and HCN-to-HCO+ abundance ratio. We quantitatively confirm the following: (i) molecular gas at the (U)LIRGs' nuclei is dense (≳103-4 cm-3) and warm (≳100 K), (ii) the molecular gas density and temperature in nine ULIRGs' nuclei are significantly higher than those of one LIRG's nucleus, (iii) molecular gas in starburst-dominated sources tends to be less dense and cooler than ULIRGs with luminous AGN signatures. For six selected sources, we also apply a Bayesian approach by freeing all parameters and support the above main results. Our ALMA 1-2 kpc resolution, multiple transition-line data of multiple molecules are a very powerful tool for scrutinizing the properties of molecular gas concentrated around luminous energy sources in nearby (U)LIRGs' nuclei.

Keywords: ultraluminous infrared galaxies; luminous infrared galaxies; active galactic nuclei; supermassive black holes; galaxy mergers; starburst galaxies; molecular spectroscopy; molecular gas; millimeter astronomy; submillimeter astronomy; radio interferometry; active galaxies
A Data-driven Approach to X-Ray Spectral Fitting: Quasi-deconvolution

X-ray spectral fitting of astronomical sources requires convolving the intrinsic spectrum or model with the instrumental response. Standard forward modeling techniques have proven success in recovering the underlying physical parameters in moderate to high signal-to-noise regimes; however, they struggle to achieve the same level of accuracy in low signal-to-noise regimes. Additionally, the use of machine learning techniques on X-ray spectra requires access to the intrinsic spectrum. Therefore, the measured spectrum must be effectively deconvolved from the instrumental response. In this note, we explore numerical methods for inverting the matrix equation describing X-ray spectral convolution. We demonstrate that traditional methods are insufficient to recover the intrinsic X-ray spectrum and argue that a novel approach is required.

Keywords: x-ray astronomy; computational astronomy; astronomical methods
The Extreme Space Weather Event in 1903 October/November: An Outburst from the Quiet Sun

While the Sun is generally more eruptive during its maximum and declining phases, observational evidence shows certain cases of powerful solar eruptions during the quiet phase of solar activity. Occurring in the weak Solar Cycle 14 just after its minimum, the extreme space weather event in 1903 October-November is one of these cases. Here, we reconstruct the time series of geomagnetic activity based on contemporary observational records. With the mid-latitude magnetograms, the 1903 magnetic storm is thought to be caused by a fast coronal mass ejection (≈1500 km s-1) and is regarded as a superstorm with an estimated minimum of the equivalent disturbance storm time index (Dst') of ≈-531 nT. The reconstructed time series has been compared with the equatorward extension of auroral oval (≈44°1 in invariant latitude) and the time series of telegraphic disturbances. This case study shows that potential threats posed by extreme space weather events exist even during weak solar cycles or near their minima.

Keywords: solar coronal mass ejections; sunspots; solar flares; solar-terrestrial interactions; solar storm; geomagnetic fields
Probing the Evolutionary History of Comets: An Investigation of the Hypervolatiles CO, CH4, and C2H6 in the Jupiter-family Comet 21P/Giacobini-Zinner

Understanding the cosmogonic record encoded in the parent volatiles stored in cometary nuclei requires investigating whether evolution (thermal or otherwise) has modified the composition of short-period comets during successive perihelion passages. As the most volatile molecules systematically observed in comets, the abundances of CO, CH4, and C2H6 in short-period comets may serve to elucidate the interplay between natal conditions and post-formative evolution in setting present-day composition, yet secure measurements of CO and CH4 in Jupiter-family comets (JFCs) are especially sparse. The highly favorable 2018 apparition of JFC 21P/Giacobini-Zinner enabled a sensitive search for these “hypervolatiles” in a prototypical carbon-chain depleted comet. We observed 21P/Giacobini-Zinner with the iSHELL spectrograph at the NASA Infrared Telescope Facility on four pre-perihelion dates, two dates near-perihelion, and one post-perihelion date. We obtained detections of CO, CH4, and C2H6 simultaneously with H2O on multiple dates. We present rotational temperatures, production rates, and mixing ratios. Combined with previous work, our results may indicate that the hypervolatile coma composition of 21P/Giacobini-Zinner was variable across apparitions as well as within a particular perihelion passage, yet the spread in these measurements is a relatively small fraction of the variation in each molecule from comet to comet. We discuss the implications of our measured hypervolatile content of 21P/Giacobini-Zinner for the evolution of JFCs, and place our results in the context of findings from the Rosetta mission and ground-based studies of comets.

Keywords: molecular spectroscopy; high resolution spectroscopy; near infrared astronomy
On the Magnetic Field Properties of Protostellar Envelopes in Orion

We present 870 μm polarimetric observations toward 61 protostars in the Orion molecular clouds with ∼400 au (1″) resolution using the Atacama Large Millimeter/submillimeter Array. We successfully detect dust polarization and outflow emission in 56 protostars; in 16 of them the polarization is likely produced by self-scattering. Self-scattering signatures are seen in several Class 0 sources, suggesting that grain growth appears to be significant in disks at earlier protostellar phases. For the rest of the protostars, the dust polarization traces the magnetic field, whose morphology can be approximately classified into three categories: standard-hourglass, rotated-hourglass (with its axis perpendicular to outflow), and spiral-like morphology. A total of 40.0% (±3.0%) of the protostars exhibit a mean magnetic field direction approximately perpendicular to the outflow on several × 102–103 au scales. However, in the remaining sample, this relative orientation appears to be random, probably due to the complex set of morphologies observed. Furthermore, we classify the protostars into three types based on the C17O (3–2) velocity envelope's gradient: perpendicular to outflow, nonperpendicular to outflow, and unresolved gradient (≲1.0 km s‑1 arcsec‑1). In protostars with a velocity gradient perpendicular to outflow, the magnetic field lines are preferentially perpendicular to outflow, with most of them exhibiting a rotated hourglass morphology, suggesting that the magnetic field has been overwhelmed by gravity and angular momentum. Spiral-like magnetic fields are associated with envelopes having large velocity gradients, indicating that the rotation motions are strong enough to twist the field lines. All of the protostars with a standard-hourglass field morphology show no significant velocity gradient due to the strong magnetic braking.

Keywords: star formation; magnetic fields; protostars
Gamma-Rays from Kilonovae and the Cosmic Gamma-Ray Background

The recent detection of the gravitational-wave event GW170817, produced by the coalescence of two neutron stars, and of its optical-infrared counterpart, powered by the radioactive decay of r-process elements, has opened a new window onto gamma-ray astronomy: the direct detection of photons coming from such decays. Here, we calculate the contribution of kilonovae to the diffuse gamma-ray background in the MeV range, using recent results on the spectra of the gamma-rays emitted in individual events, and we compare it with that from other sources. We find that the contribution from kilonovae is not dominant in such an energy range, but within current uncertainties, and its addition to other sources might help to fit the observational data.

Keywords: gamma-ray astronomy; gamma-ray transient sources; nucleosynthesis; r-process
Structural and Dynamical Analysis of 0.1 pc Cores and Filaments in the 30 Doradus-10 Giant Molecular Cloud

High-resolution (<0.1 pc) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 30Dor-10 molecular cloud 15 pc north of R136 are presented. The 12CO 2-1 emission morphology contains clumps near the locations of known mid-IR massive protostars, as well as a series of parsec-long filaments oriented almost directly toward R136. There is elevated kinetic energy (line widths at a given size scale) in 30Dor-10 compared to other Large Magellanic Cloud and Galactic star formation regions, consistent with large-scale energy injection to the region. Analysis of the cloud substructures is performed by segmenting emission into disjoint approximately round “cores” using clumpfind, by considering the hierarchical structures defined by isointensity contours using dendrograms, and by segmenting into disjoint long thin “filaments” using Filfinder. Identified filaments have widths ∼0.1 pc. The inferred balance between gravity and kinematic motions depends on the segmentation method: entire objects identified with clumpfind are consistent with freefall collapse or virial equilibrium with moderate external pressure, whereas many dendrogram-identified parts of hierarchical structures have higher mass surface densities ΣLTE than if gravitational and kinetic energies were in balance. Filaments have line masses that vary widely compared to the critical line mass calculated assuming thermal and nonthermal support. Velocity gradients in the region do not show any strong evidence for accretion of mass along filaments. The upper end of the “core” mass distribution is consistent with a power law with the same slope as the stellar initial mass function.

Keywords: large magellanic cloud; interstellar medium; star formation; stellar feedback; molecular clouds
New Methanol Maser Transitions and Maser Variability Identified from an Accretion Burst Source G358.93-0.03

The high-mass young stellar object G358.93-0.03 underwent an accretion burst during the period from 2019 January to June. Given its extraordinary conditions, a number of new maser transitions may have been naturally excited during the burst stage. Searching for new maser lines and monitoring maser variability associated with the accretion burst event are important for understanding the complex conditions of the massive star formation toward G358.93-0.03. In this work, using the Shanghai 65 m Tianma Radio Telescope, we continuously monitored the multiple maser (including methanol and water) transitions toward G358.93-0.03 during the burst in the period from 2019 March 14 to May 20. There were 23 CH3OH maser transitions and one H2O maser transition detected from the monitoring. Nearly all the detected maser transitions toward this source have dramatic variations in their intensities within a short period of ~2 months. Eight new methanol transitions from G358.93-0.03 were identified to be masering in our observations based on their spectral profile, line width, intensity, and the rotation diagram. During the monitoring, the gas temperature of the clouds in the case of saturated masers can show a significant decline, indicating that the maser clouds were going through a cooling process, possibly associated with the propagation of a heat wave induced by the accretion burst. Some of the maser transitions were even detected with the second flares in 2019 April, which may be associated with the process of the heat-wave propagation induced by the same accretion burst acting on different maser positions.

Keywords: interstellar masers; star formation; massive stars; accretion; young stellar objects