Sazuna/UAT_keywords huggingface dataset:
Turbulence Regulates the Rate of Planetesimal Formation via Gravitational Collapse. We study how the interaction between the streaming instability (SI) and intrinsic gas-phase turbulence affects planetesimal formation via gravitational collapse in protoplanetary disks. Turbulence impedes the formation of particle clumps by acting as an effective turbulent diffusivity, but it can also promote planetesimal formation by concentrating solids, for example, in zonal flows. We quantify the effect of turbulent diffusivity using numerical simulations of the SI in small local domains, forced with velocity perturbations that establish approximately Kolmogorov-like turbulence. We find that planetesimal formation is suppressed by turbulence once velocity fluctuations exceed $\langle \delta {v}^{2}\rangle $ ≃ (10-3.5-10-3) ${c}_{s}^{2}$ . Turbulence whose strength is just below the threshold reduces the rate at which solids are bound into clumps. Our results suggest that the well-established turbulent thickening of the midplane solid layer is the primary mechanism by which turbulence influences planetesimal formation and that planetesimal formation requires a midplane solid-to-gas ratio ɛ ≳ 0.5. We also quantify the initial planetesimal mass function using a new clump-tracking method to determine each planetesimal mass shortly after collapse. For models in which planetesimals form, we show that the mass function is well described by a broken power law, whose parameters are robust to the inclusion and strength of imposed turbulence. Turbulence in protoplanetary disks is likely to substantially exceed the threshold for planetesimal formation at radii where temperatures T ≳ 103 K lead to thermal ionization. Planetesimal formation may therefore be unviable in the inner disk out to 2-3 times the dust sublimation radius.

Keywords: Stellar accretion disks, Protoplanetary disks, Planet formation, Planetesimals
AGILE and Konus-Wind Observations of GRB 190114C: The Remarkable Prompt and Early Afterglow Phases. GRB 190114C represents a breakthrough for the physics of gamma-ray bursts (GRBs), being the first GRB with delayed emission above 300 GeV, as reported by MAGIC. We present in this paper the sub-MeV/MeV data of the prompt and early afterglow emissions of GRB 190114C, as detected by AGILE and Konus-Wind, in the 20 keV-100 MeV energy range. The first stages of the burst exhibit multiple emission components, associated with an interesting spectral evolution. The first 2 s of the prompt emission can be described by a single "Band-like" spectral component. The successive 4 s show the presence of an additional high-energy spectral component, which quickly evolves into a "hard-flat" component of the νFν spectrum, extending up to 10-100 MeV and likely produced by inverse Compton radiation, whose onset and evolution are clearly shown in our data. After this phase, the νFν spectrum evolves into a "V shape," showing the persistence and spectral hardening of the additional high-energy component in substantial agreement with Fermi and Swift results. We also analyze the first ∼200 s of the early afterglow that show a reflaring episode near T0 + 15 s. We identify a new, so-far-unnoticed flux temporal break near T0 + 100 s, which is detected in hard X-rays by both Konus-Wind and INTEGRAL/SPI-ACS. We find this break incompatible with the commonly assumed adiabatic evolution of a fireball in a constant-density medium. We interpret this break as a consequence of radiative evolution of the early afterglow from a fireball expanding in a wind-like circumburst medium.

Keywords: Gamma-ray astronomy, Gamma-ray bursts, Gamma-ray transient sources
Can Large-scale Migration Explain the Giant Planet Occurrence Rate?. The giant planet occurrence rate rises with orbital period out to at least ∼300 days. Large-scale planetary migration through the disk has long been suspected to be the origin of this feature, as the timescale of standard Type I migration in a standard solar nebula is longer farther from the star. These calculations also find that typical Jupiter-bearing cores shuttle toward the disk inner edge on timescales orders of magnitude shorter than the gas disk lifetime. The presence of gas giants at myriad distances requires mechanisms to slow large-scale migration. We revisit the migration paradigm by building model occurrence rates to compare to the observations, computing simultaneously the migration of cores, their mass growth by gas accretion, and their gap opening. We show explicitly that the former two processes occur in tandem. Radial transport of planets can slow down significantly once deep gaps are carved out by their interaction with disk gas. Disks are more easily perturbed closer to the star, so accounting for gap opening flattens the final orbital period distribution. To recover the observed rise in occurrence rate, gas giants need to be more massive farther out, which is naturally achieved if their envelopes are dust-free. We find that only a narrow region of parameter space can recover the observed giant planet occurrence rate in orbital period, but not simultaneously the mass distribution of low-eccentricity giant planets. This challenges disk migration as the dominant origin channel of hot and warm Jupiters. Future efforts in characterizing the unbiased mass distribution will place stronger constraints on predictions from migration theory.

Keywords: Exoplanet dynamics, Exoplanet formation, Extrasolar gaseous giant planets
Unveiling the Intrinsic Alignment of Galaxies with Self-calibration and DECaLS DR3 Data. Galaxy intrinsic alignment (IA) is a source of both systematic contamination of cosmic shear measurement and its cosmological applications and valuable information on the large-scale structure of the universe and galaxy formation. The self-calibration (SC) method was designed to separate IA from cosmic shear, free of IA modeling. It was first successfully applied to the KiDS450 and KV450 data. We improve the SC method in several aspects and apply it to the DECaLS DR3 shear + photo-z catalog and significantly improve the IA detection to ∼14σ. We find a strong dependence of IA on galaxy color, with strong IA signal (∼17.6σ) for red galaxies, while the IA signal for blue galaxies is consistent with zero. The detected IAs for red galaxies are in reasonable agreement with the nonlinear tidal alignment model, and the inferred IA amplitude increases with redshift. Our measurements rule out the constant IA amplitude assumption at ∼3.9σ for the red sample. We address the systematics in the SC method carefully and perform several sanity checks. We discuss various caveats, such as redshift/shear calibrations and possible improvements in the measurement, theory, and parameter fitting that will be addressed in future works.

Keywords: Weak gravitational lensing, Galaxy formation, Large-scale structure of the universe, Astrostatistics techniques, Galaxy physics, Two-point correlation function
Temperature Structure of the Pipe Nebula Studied by the Intensity Anomaly of the OH 18 cm Transition. We present observations of the four hyperfine structure components of the OH 18 cm transition (1612, 1665, 1667, and 1720 MHz) toward a filamentary dark cloud, the Pipe nebula, with the Green Bank Telescope. A statistical equilibrium analysis is applied to the spectra, and the kinetic temperature of a diffuse molecular gas surrounding dense cores is determined accurately; the derived temperature ranges from 40 to 75 K. From this result, we assess the heating effect on the filamentary structure of the nebula's "stem" region due to UV photons from a nearby star θ-Ophiuchi and a possible filament-filament collision in the interface of the "stem" and "bowl" regions. In the stem region, the gas kinetic temperature is found to be almost independent of the apparent distance from θ-Ophiuchi: the UV-heating effect by the star is not visible. On the other hand, the gas kinetic temperature is raised, as high as ∼75 K, at the interface of the two filamentary structures. This result provides us with additional support for the filament-filament collision scenario in the Pipe nebula.

Keywords: Interstellar molecules, Molecular clouds
Remarkable Migration of the Solar System from the Innermost Galactic Disk; a Wander, a Wobble, and a Climate Catastrophe on the Earth. Recent knowledge of Galactic dynamics suggests that stars radially move on the disk when they encounter transient spiral arms that are naturally generated during the process of disk formation. We argue that the large movement of the solar system from the innermost disk over its lifetime is inferred from an elemental abundance pattern of the Sun to those of solar twins within the Galactic chemical evolutionary framework. The implied metal-rich environment at the Sun's birthplace and its formation time are supported by measured silicon isotopic ratios in presolar silicon carbide grains. We perform numerical simulations of the dynamical evolution of disk stars in a Milky Way-like galaxy to identify the lifetime trajectory of the solar system. We find that a solar system born in the proximity of the Galactic bulge could travel to the current locus by the effect of radial migration induced by several major encounters with spiral arms. The frequent feature we identify is the repeated passages of stars inside the same spiral arm owing to the wobble of stars traveling in and out of the spiral arms. We predict that such episodes are evidenced in the Earth's geological history as snowball Earth and that their occurrence times are within our predictions. In particular, the stellar motion that vertically oscillates during passages through spiral arms occasionally leads to a split into two discrete passage episodes with an interval of several tens of megayears, implying two relevant snowball Earth events that occurred in rapid succession (∼720 and 650 million years ago).

Keywords: Galaxy chemical evolution, Earth atmosphere, Stellar motion, Stellar abundances, Galaxy dynamics, Solar abundances, Spiral arms, Milky Way disk
Detection of 2-4 GHz Continuum Emission from ɛ Eridani. The nearby star ɛ Eridani has been a frequent target of radio surveys for stellar emission and extraterrestrial intelligence. Using deep 2-4 GHz observations with the Very Large Array, we have uncovered a 29 μJy compact, steady continuum radio source coincident with ɛ Eridani to within 0"06 (≲2σ; 0.2 au at the distance of the star). Combining our data with previous high-frequency continuum detections of ɛ Eridani, our observations reveal a spectral turnover at 6 GHz. We ascribe the 2-6 GHz emission to optically thick, thermal gyroresonance radiation from the stellar corona, with thermal free-free opacity likely becoming relevant at frequencies below 1 GHz. The steep spectral index (α ≃ 2) of the 2-6 GHz spectrum strongly disfavors its interpretation as stellar-wind-associated thermal bremsstrahlung (α ≃ 0.6). Attributing the entire observed 2-4 GHz flux density to thermal free-free wind emission, we thus derive a stringent upper limit of 3 × 10-11 M⊙ yr-1 on the mass-loss rate from ɛ Eridani. Finally, we report the nondetection of flares in our data above a 5σ threshold of 95 μJy. Together with the optical nondetection of the most recent stellar maximum expected in 2019, our observations postulate a likely evolution of the internal dynamo of ɛ Eridani.

Keywords: Radio continuum emission, K stars, Stellar coronae, Stellar atmospheres
NGC 7538 IRS1—an O Star Driving an Ionized Jet and Giant N-S Outflow. NGC 7538 IRS 1 is a very young embedded O star driving an ionized jet and accreting mass with an accretion rate &gt;10-4 ${M}_{\odot }$ yr-1, which is quenching the hypercompact H II region. We use SOFIA GREAT data, Herschel PACS and SPIRE archive data, SOFIA FORCAST archive data, Onsala 20 m and CARMA data, and JCMT archive data to determine the properties of the O star and its outflow. IRS 1 appears to be a single O star with a bolometric luminosity &gt;1 × 105 ${L}_{\odot }$ , i.e., spectral type O7 or earlier. We find that IRS 1 drives a large molecular outflow with the blueshifted northern outflow lobe extending to ∼280″ or 3.6 pc from IRS 1. Near IRS 1 the outflow is well aligned with the ionized jet. The dynamical timescale of the outflow is ∼1.3 × 105 yr. The total outflow mass is ∼130 ${M}_{\odot }$ . We determine a mass outflow rate of 1.0 × 10-3 ${M}_{\odot }$ yr-1, roughly consistent with the observed mass accretion rate. We observe strong high-velocity [C II] emission in the outflow, confirming that strong UV radiation from IRS 1 escapes into the outflow lobes and is ionizing the gas. Many O stars may form like low-mass stars, but with a higher accretion rate and in a denser environment. As long as the accretion stays high enough to quench the H II region, the star will continue to grow. When the accretion rate drops, the H II region will rapidly start to expand.

Keywords: Compact H II region, Radio jets, O stars, Giant molecular clouds, Star formation, Stellar accretion, Stellar accretion disks
When Do Stalled Stars Resume Spinning Down? Advancing Gyrochronology with Ruprecht 147. Recent measurements of rotation periods ( ${P}_{\mathrm{rot}}$ ) in the benchmark open clusters Praesepe (670 Myr), NGC 6811 (1 Gyr), and NGC 752 (1.4 Gyr) demonstrate that, after converging onto a tight sequence of slowly rotating stars in mass-period space, stars temporarily stop spinning down. These data also show that the duration of this epoch of stalled spin-down increases toward lower masses. To determine when stalled stars resume spinning down, we use data from the K2 mission and the Palomar Transient Factory to measure ${P}_{\mathrm{rot}}$ for 58 dwarf members of the 2.7 Gyr old cluster Ruprecht 147, 39 of which satisfy our criteria designed to remove short-period or near-equal-mass binaries. Combined with the Kepler ${P}_{\mathrm{rot}}$ data for the approximately coeval cluster NGC 6819 (30 stars with M⋆ &gt; 0.85 ${M}_{\odot }$ ), our new measurements more than double the number of ≍2.5 Gyr benchmark rotators and extend this sample down to ≍0.55 ${M}_{\odot }$ . The slowly rotating sequence for this joint sample appears relatively flat (22 ± 2 days) compared to sequences for younger clusters. This sequence also intersects the Kepler intermediate-period gap, demonstrating that this gap was not created by a lull in star formation. We calculate the time at which stars resume spinning down and find that 0.55 ${M}_{\odot }$ stars remain stalled for at least 1.3 Gyr. To accurately age-date low-mass stars in the field, gyrochronology formulae must be modified to account for this stalling timescale. Empirically tuning a core-envelope coupling model with open cluster data can account for most of the apparent stalling effect. However, alternative explanations, e.g., a temporary reduction in the magnetic braking torque, cannot yet be ruled out.

Keywords: Open star clusters, Stellar rotation, Stellar ages, Stellar evolution
Scaling Laws for Dynamic Solar Loops. The scaling laws that relate the peak temperature TM and volumetric heating rate EH to the pressure P and length L for static coronal loops were established over 40 yr ago; they have proved to be of immense value in a wide range of studies. Here we extend these scaling laws to dynamic loops, where enthalpy flux becomes important to the energy balance, and study impulsive heating/filling characterized by upward enthalpy flows. We show that for collision-dominated thermal conduction, the functional dependencies of the scaling laws are the same as for the static case, when the radiative losses scale as T-1/2, but with a different constant of proportionality that depends on the Mach number M of the flow. The dependence on the Mach number is such that the scaling laws for low to moderate Mach number flows are almost indistinguishable from the static case. When thermal conduction is limited by turbulent processes, however, the much weaker dependence of the scattering mean free path (and hence thermal conduction coefficient) on temperature leads to a limiting Mach number for return enthalpy fluxes driven by thermal conduction between the corona and chromosphere.

Keywords: Solar coronal loops, Solar corona
Limiting Spectral Resolution of a Reflection Grating Made via Electron-beam Lithography. Gratings enable dispersive spectroscopy from the X-ray to the optical, and feature prominently in proposed flagships and SmallSats alike. The exacting performance requirements of these future missions necessitate assessing whether the present state-of-the-art in grating manufacture will limit spectrometer performance. In this work, we manufacture a 1.5 mm thick, 1000 nm period (1000 gr mm-1) flat grating using electron-beam lithography (EBL), a promising lithographic technique for patterning gratings for future astronomical observatories. We assess the limiting spectral resolution of this grating by interferometrically measuring the diffracted wavefronts produced in ± first order. Our measurements show this grating has a performance of at least R ∼ 14,600, and that our assessment is bounded by the error of our interferometric measurement. The impact of EBL stitching error on grating performance is quantified, and a path to measuring the period error of customized, curved gratings is presented.

Keywords: Spectrometers, Astronomical instrumentation, Astronomical optics
The M Supergiant High-mass X-Ray Binary 4U 1954+31. The X-ray binary 4U 1954+31 has been classified as a low-mass X-ray binary containing an M giant and a neutron star (NS). It has also been included in the rare class of X-ray symbiotic binaries. The Gaia parallax, infrared colors, spectral type, abundances, and orbital properties of the M star demonstrate that the cool star in this system is not a low-mass giant but a high-mass M supergiant. Thus, 4U 1954+31 is a high-mass X-ray binary (HMXB) containing a late-type supergiant. It is the only known binary system of this type. The mass of the M I is ${9}_{-2}^{+6}$ M⊙ giving an age of this system in the range 12-50 Myr with the NS no more than 43 Myr old. The spin period of the NS is one of the longest known, 5 hr. The existence of M I plus NS binary systems is in accord with stellar evolution theory, with this system a more evolved member of the HMXB population.

Keywords: Late-type supergiant stars, Stellar abundances, X-ray binary stars, Late stellar evolution
Texas Spectroscopic Search for Lyα Emission at the End of Reionization. III. The Lyα Equivalent-width Distribution and Ionized Structures at z &gt; 7. Lyα emission from galaxies can be utilized to characterize the ionization state in the intergalactic medium (IGM). We report our search for Lyα emission at z &gt; 7 using a comprehensive Keck/MOSFIRE near-infrared spectroscopic data set, as part of the Texas Spectroscopic Search for Lyα Emission at the End of Reionization Survey. We analyze data from 10 nights of MOSFIRE observations which together target 72 high-z candidate galaxies in the GOODS-N field, all with deep exposure times of 4.5-19 hr. Utilizing an improved automated emission-line search, we report 10 Lyα emission lines detected (&gt;4σ) at z &gt; 7, significantly increasing the spectroscopically confirmed sample. Our sample includes large equivalent-width (EW) Lyα emitters (&gt;50 Å), and additional tentative Lyα emission lines detected at 3σ-4σ from five additional galaxies. We constrain the Lyα EW distribution at z ∼ 7.6, finding a significant drop from z ≲ 6, suggesting an increasing fraction of neutral hydrogen (H I) in the IGM in this epoch. We estimate the Lyα transmission through the IGM (=EWz ∼ 7.6/EW ${}_{z\sim 2\mbox{--}6}$ ) and infer an IGM H I fraction (XHI) of ${49}_{-19}^{+19}{\rm{ \% }}$ at z ∼ 7.6, which is lower in modest tension (&gt;1σ) with recent measurements at z ∼ 7.6. The spatial distribution of the detected Lyα emitters implies the presence of a potential highly ionized region at z ∼ 7.55, which hosts four Lyα emitters within a ∼40 cMpc spatial separation. The prominence of this ionized region in our data set could explain our lower inferred value of XHI, though our analysis is also sensitive to the chosen reference Lyα EW distribution values and reionization models.

Keywords: Early universe, Galaxy formation, Galaxy distances, Lyman-alpha galaxies, Galaxy evolution, Intergalactic medium, Extragalactic astronomy, Reionization, High-redshift galaxies, Galaxies
The Ultimately Large Telescope: What Kind of Facility Do We Need to Detect Population III Stars?. The launch of the James Webb Space Telescope (JWST) will open up a new window for observations at the highest redshifts, reaching out to $z\approx 15$ . However, even with this new facility, the first stars will remain out of reach, as they are born in small minihalos with luminosities too faint to be detected even by the longest exposure times. In this paper, we investigate the basic properties of the Ultimately Large Telescope, a facility that can detect Population III star formation regions at high redshift. Observations will take place in the near-infrared and therefore a Moon-based facility is proposed. An instrument needs to reach magnitudes as faint as 39 magAB, corresponding to a primary mirror size of about 100 m in diameter. Assuming JWST NIRCam filters, we estimate that Population III sources will have unique signatures in a color-color space and can be identified unambiguously.

Keywords: Early universe, Population III stars, Infrared telescopes
The First Extensive Spectroscopic Study of Young Stars in the North America and Pelican Nebulae. We present a spectroscopic survey of over 3400 potential members in the North America and Pelican Nebulae (NAP) using several low-resolution (R ≈ 1300-2000) spectrographs: Palomar/Norris, WIYN/Hydra, Keck/DEep Imaging Multi-Object Spectrograph (DEIMOS), and the Multiple Mirror Telescope (MMT)/Hectospec. We identify 580 young stars as likely members of the NAP region based on criteria involving infrared excess, Li I 6708 Å absorption, X-ray emission, parallax, and proper motions. The spectral types of individual spectra are derived by fitting them with templates that are either empirical spectra of pre-main-sequence stars or model atmospheres. The templates are artificially veiled, and a best-fit combination of spectral type and veiling parameter is derived for each star. We use the spectral types with archival photometry to derive V-band extinction and stellar luminosity. From the Hertzsprung-Russell diagram, the median age of the young stars is about 1 Myr, with a luminosity dispersion of ∼0.3-0.4 dex. We investigate the photometric variability of the spectroscopic member sample using Zwicky Transient Facility data and conclude that photometric variability, while present, does not significantly contribute to the luminosity dispersion. While larger than the formal errors, the luminosity dispersion is smaller than if veiling were not taken into account in our spectral typing process. The measured ages of the stellar kinematic groups, combined with the inferred ages for embedded stellar populations revealed by Spitzer, suggest a sequential history of star formation in the NAP region.

Keywords: Star forming regions, Pre-main sequence stars, Star formation, Protoplanetary disks, Stellar accretion disks, Stellar spectral types, Stellar associations