adsabs/SciX_UAT_keywords huggingface dataset:
New Insights into Variations in Enceladus Plume Particle Launch Velocities from Cassini-VIMS Spectral Data

Enceladus's plume consists mainly of a mixture of water vapor and solid ice particles that may originate from a subsurface ocean. The physical processes underlying Enceladus's plume particle dynamics are still being debated, and quantifying the particles' size distribution and launch velocities can help constrain these processes. Cassini's Visual and Infrared Mapping Spectrometer observed the Enceladus plume over a wavelength range of 0.9-5.0 μm for a significant fraction of Enceladus's orbital period on three dates in the summer of 2017. We find that the relative brightness of the plume on these different dates varies with wavelength, implying that the particle size distribution in the plume changes over time. These observations also enable us to study how the particles' launch velocities vary with time and observed wavelength. We find that the typical launch velocity of particles remains between 140 and 148 m s-1 at wavelengths between 1.2 and 3.7 μm. This may not be consistent with prior models where particles are only accelerated by interactions with the vent walls and gas and could imply that mutual particle collisions close to the vent are more important than previously recognized.

Keywords: enceladus; dust physics; volcanism; infrared spectroscopy
H- and Dissociation in Ultra-hot Jupiters: A Retrieval Case Study of WASP-18b

Atmospheres of a number of ultra-hot Jupiters (UHJs) with temperatures ≳2000 K have been observed recently. Many of these planets show largely featureless thermal spectra in the near-infrared observed with the HST WFC3 spectrograph (1.1-1.7 μm) even though this spectral range contains strong H2O opacity. Recent works have proposed the possibility of H- opacity masking the H2O feature and/or thermal dissociation of H2O causing its apparent depletion at the high temperatures of UHJs. In this work, we test these hypotheses using observations of the exoplanet WASP-18b as a case study. We report detailed atmospheric retrievals of the planet using the HyDRA retrieval code, extended to include the effects of H- opacity and thermal dissociation. We report constraints on the H2O, CO, and H- abundances as well as the pressure-temperature profile of the dayside atmosphere for retrievals with and without H-/dissociation for each data set. We find that the H2O and H- abundances are relatively unconstrained given the featureless WFC3 spectra. We do not conclusively detect H- in the planet, contrary to previous studies that used equilibrium models to infer its presence. The constraint on the CO abundance depends on the combination of WFC3 and Spitzer data, ranging from solar to super-solar CO values. We additionally see signs of a thermal inversion from two of the data sets. Our study demonstrates the potential of atmospheric retrievals of UHJs, including the effects of H- and thermal dissociation of molecules.

Keywords: exoplanet atmospheres; spectroscopy; radiative transfer; hot jupiters; exoplanets
Improving Cosmological Constraints by Inferring the Formation Channel of Extreme-mass-ratio Inspirals

Extreme-mass-ratio inspirals (EMRIs) could be detected by space-borne gravitational-wave (GW) detectors, such as the Laser Interferometer Space Antenna (LISA), TianQin, and Taiji. Localizing EMRIs by GW detectors can help us select candidate host galaxies, which can be used to infer the cosmic expansion history. In this paper, we demonstrate that the localization information can also be used to infer the formation channel of EMRIs, and can hence allow us to extract more precisely the redshift probability distributions. By conducting mock observations of the EMRIs that can be detected by TianQin and LISA, as well as the galaxies that can be provided by the future Chinese Space Station Telescope, we find that TianQin can constrain the Hubble–Lemaître constant H 0 to a precision of ∼3%–8% and the dark energy equation-of-state parameter w 0 to ∼10%–40%. The TianQin+LISA network, by increasing the localization accuracy, can improve the precisions of H 0 and w 0 to ∼0.4%–7% and ∼4%–20%, respectively. Then, considering an illustrative case in which all EMRIs originate in active galactic nuclei (AGNs), and combining the mock EMRI observation with a mock AGN catalog, we show that TianQin can recognize the EMRI–AGN correlation with ∼1300 detections. The TianQin+LISA network can reduce this required number to ∼30. Additionally, we propose a statistical method to directly estimate the fraction of EMRIs produced in AGNs, f agn, and show that observationally deriving this value could significantly improve the constraints on the cosmological parameters. These results demonstrate the potentials of using EMRIs as well as galaxy and AGN surveys to improve the constraints on cosmological parameters and the formation channel of EMRIs.

Keywords: gravitational waves; black holes; sky surveys; hubble constant; bayesian statistics; poisson distribution
The Effect of Flow on the Resonance Absorption of Slow MHD Waves in Magnetic Flux Tubes

In this paper, we study kink and sausage oscillations in the presence of longitudinal background flow. We study the resonance absorption of kink and sausage modes in the slow continuum, under magnetic pore conditions, in the presence of flow. We determine the dispersion relation, and solve it numerically to find the frequencies and damping rates of the slow kink and sausage surface modes. We also obtain an analytical solution for the damping rate of the slow surface mode in the long wavelength limit. We show that in the presence of plasma flow, resonance absorption can result in strong damping for forward waves, and can be considered as an efficient mechanism to justify the extremely rapid damping of slow surface sausage waves observed in magnetic pores. Moreover, the plasma flow reduces the efficiency of resonance absorption to damp backward waves. With respect to pore conditions, resonance instability is avoided in our model.

Keywords: solar physics; solar photosphere; solar atmosphere
Linemake: An Atomic and Molecular Line List Generator

In this research note, we present linemake, an open-source atomic and molecular line list generator. Rather than a replacement for a number of well-established atomic and molecular spectral databases, linemake aims to be a lightweight, easy-to-use tool to generate formatted and curated lists suitable for spectral synthesis work. We encourage users of linemake to understand the sources of their transition data and cite them as appropriate in published work. We provide the code, line database, and an extensive list of literature references in a GitHub repository (https://github.com/vmplacco/linemake), which will be updated regularly as new data become available.

Keywords: spectroscopy; atomic physics; laboratory astrophysics; molecular physics; spectral line lists
Toward a Better Understanding of Cosmic Chronometers: A New Measurement of H(z) at z 0.7

We analyze the stellar ages obtained from a combination of Lick indices in Borghi et al. for 140 massive and passive galaxies selected in the LEGA-C survey at 0.6 < z < 0.9. From their median age-redshift relation, we derive a new direct measurement of H(z) without any cosmological model assumption using the cosmic chronometer approach. We thoroughly study the main systematics involved in this analysis: the choice of the Lick indices combination, the binning method, the assumed stellar population model, and the adopted star formation history; these effects are included in the total error budget. We obtain H(z = 0.75) = 98.8 ± 33.6 km s-1 Mpc-1. In parallel, we also propose a simple framework based on a cosmological model to describe the age-redshift relations in the context of galaxy downsizing. This allows us to derive constraints on the Hubble constant H 0 and the typical galaxy formation time. This new H(z) measurement, whose accuracy is currently limited by the scarcity of the sample analyzed, paves the road for the joint study of the stellar populations of individual passive galaxies and the expansion history of the universe in light of future spectroscopic surveys.

Keywords: observational cosmology; galaxy ages; cosmological evolution; hubble constant
Chemodynamical Signatures of Bar Resonances in the Galactic Disk: Current Data and Future Prospects

The Galactic disk exhibits complex chemical and dynamical substructure thought to be induced by the bar, spiral arms, and satellites. Here, we explore the chemical signatures of bar resonances in action and velocity space, and characterize the differences between the signatures of corotation (CR) and higher-order resonances using test particle simulations. Thanks to recent surveys, we now have large data sets containing metallicities and kinematics of stars outside the solar neighborhood. We compare the simulations to the observational data from Gaia EDR3 and LAMOST DR5 and find weak evidence for a slow bar with the "hat" moving group (250 km s-1 ≲ v ϕ ≲ 270 km s-1) associated with its outer Lindblad resonance and "Hercules" (170 km s-1 ≲ v ϕ ≲ 195 km s-1) with CR. While constraints from current data are limited by their spatial footprint, stars closer in azimuth than the Sun to the bar's minor axis show much stronger signatures of the bar's outer Lindblad and CR resonances in test particle simulations. Future data sets with greater azimuthal coverage, including the final Gaia data release, will allow reliable chemodynamical identification of bar resonances.

Keywords: milky way dynamics; orbital resonances; metallicity
The Detection of Hot Molecular Cores in the Small Magellanic Cloud

We report the first detection of hot molecular cores in the Small Magellanic Cloud (SMC), a nearby dwarf galaxy with 0.2 solar metallicity. We observed two high-mass young stellar objects in the SMC with the Atacama Large Millimeter/submillimeter Array and detected emission lines of CO, HCO+, H13CO+, SiO, H2CO, CH3OH, SO, and SO2. Compact hot-core regions are traced by SO2, whose spatial extent is about 0.1 pc, and the gas temperature is higher than 100 K based on the rotation diagram analysis. In contrast, CH3OH, a classical hot-core tracer, is dominated by extended (~0.2-0.3 pc) components in both sources, and the gas temperature is estimated to be ${39}_{-6}^{+8}$ K for one source. Protostellar outflows are also detected from both sources as high-velocity components of CO. The metallicity-scaled abundances of SO2 in hot cores are comparable among the SMC, Large Magellanic Cloud (LMC), and Galactic sources, suggesting that the chemical reactions leading to SO2 formation would be regulated by elemental abundances. On the other hand, CH3OH shows a large abundance variation within SMC and LMC hot cores. The diversity in the initial condition of star formation (e.g., degree of shielding, local radiation field strength) may lead to the large abundance variation of organic molecules in hot cores. This work, in conjunction with previous hot-core studies in the LMC and outer/inner Galaxy, suggests that the formation of a hot core would be a common phenomenon during high-mass star formation across the metallicity range of 0.2-1 Z⊙. High-excitation SO2 lines will be a useful hot-core tracer in the low-metallicity environments of the SMC and LMC.

Keywords: astrochemistry; interstellar molecules; protostars; magellanic clouds; complex organic molecules; radio astronomy; stellar jets; small magellanic cloud; metallicity
New Insights into the Structure of Open Clusters in the Gaia Era

With the help of Gaia data, it is noted that in addition to the core components, there are low-density outer halo components in the extended region of open clusters. In order to study the extended structure beyond the core radius of the cluster (~10 pc), based on Gaia Early Data Release 3, taking up to 50 pc as the searching radius, we use the pyUPMASK algorithm to redetermine the member stars of the open cluster within 1-2 kpc. We obtain the member stars of 256 open clusters, especially those located in the outer halo region of open clusters. Furthermore, we find that the radial density profile in the outer region for most open clusters deviates from the Kings profile. In order to better describe the internal and external structural characteristics of open clusters, we propose a two-component model: a core component with a King model distribution and an outer halo component with a logarithmic Gaussian distribution, and then suggest using four radii (r c , r t , r o , r e ) for describing the structure and distribution profile of star clusters, where r t and r e represent the boundaries of the core component and outer halo component, respectively. Finally, we provide a catalog of 256 clusters with structural parameters. In addition, our study shows the sizes of these radii are statistically linearly related, which indicates that the inner and outer regions of the cluster are interrelated and follow similar evolutionary processes. Further, we show that the structure of two components can be used to better trace the cluster evolution properties at different stages.

Keywords: open star clusters
Black Hole Mergers Driven by a Captured Low-mass Companion

Increased eccentricity of a black hole binary leads to reduced merger times. With n-body simulations and analytic approximations including the effects of general relativity (GR), we show that even a low-mass companion orbiting a black hole binary can cause significant eccentricity oscillations of the binary as a result of the Kozai-Lidov mechanism. A companion with a mass as low as about 1% of the binary mass can drive the binary eccentricity up to ≳0.8, while a mass of a few percent can drive eccentricities greater than 0.98. For low-mass companions, this mechanism requires the companion to be on an orbit that is closer to retrograde than to prograde to the binary orbit, and this may occur through capture of the third body. The effects of GR limit the radial range for the companion for which this mechanism works for the closest binaries. The merger timescale may be reduced by several orders of magnitude for a captured companion mass of only a few percent of the binary mass.

Keywords: stellar dynamics; black holes
An Ancient Massive Quiescent Galaxy Found in a Gas-rich z 3 Group

Deep Atacama Large Millimeter/submillimeter Array and Hubble Space Telescope observations reveal the presence of a quenched massive galaxy within the z = 2.91 galaxy group RO-1001. With a mass-weighted stellar age of 1.6 ± 0.4 Gyr this galaxy is one of the oldest known at z ~ 3, implying that most of its 1011 M⊙ of stars were rapidly formed at z > 6-8. This is a unique example of the predominantly passive evolution of a galaxy over at least 3 < z < 6 following its high-redshift quenching and a smoking-gun event pointing to the early imprint of an age-environment relation. At the same time, being in a dense group environment with extensive cold gas reservoirs as betrayed by a giant Lyα halo, the existence of this galaxy demonstrates that gas accretion shutdown is not necessary for quenching and its maintenance.

Keywords: high-redshift galaxies; galaxy evolution; galaxy groups
Extremely Long Convergence Times in a 3D GCM Simulation of the Sub-Neptune Gliese 1214b

We present gray gas general circulation model (GCM) simulations of the tidally locked mini-Neptune GJ 1214b. On timescales of 1000-10,000 Earth days, our results are comparable to previous studies of the same planet, in the sense that they all exhibit two off-equatorial eastward jets. Over much longer integration times (50,000-250,000 Earth days) we find a significantly different circulation and observational features. The zonal-mean flow transitions from two off-equatorial jets to a single wide equatorial jet that has higher velocity and extends deeper. The hot spot location also shifts eastward over the integration time. Our results imply a convergence time far longer than the typical integration time used in previous studies. We demonstrate that this long convergence time is related to the long radiative timescale of the deep atmosphere and can be understood through a series of simple arguments. Our results indicate that particular attention must be paid to model convergence time in exoplanet GCM simulations, and that other results on the circulation of tidally locked exoplanets with thick atmospheres may need to be revisited.

Keywords: exoplanet atmospheres; planetary atmospheres; mini neptunes; hot neptunes; hot jupiters; extrasolar gaseous giant planets; exoplanets; atmospheric circulation
The NASA Ames PAH IR Spectroscopic Database: The Laboratory Spectra

The astronomical emission features, formerly known as the unidentified infrared bands, are now commonly ascribed to polycyclic aromatic hydrocarbons (PAHs). The laboratory experiments and computational modeling performed at NASA Ames Research Center generated a collection of PAH IR spectra that have been used to test and refine the PAH model. These data have been assembled into the NASA Ames PAH IR Spectroscopic Database (PAHdb). PAHdb's library of computed spectra, currently at version 3.20, contains data on more than 4000 species and the library of laboratory-measured spectra, currently at version 3.00, contains data on 84 species. The spectra can be perused and are available for download at www.astrochemistry.org/pahdb/. This paper introduces the library of laboratory-measured spectra. Although it has been part of PAHdb since its inception, the library of laboratory-measured spectra lacked a proper description in the literature. Here, the experimental methods used to obtain the data are described in detail, an overview of the contents of the experimental library is given, and specific tools developed to analyze and interpret astronomical spectra with the laboratory data are discussed. In addition, updates to the website, documentation and software tools since our last reporting are presented. Software tools to work with the spectroscopic libraries are being developed actively and are available at GitHub. Lastly, a comprehensive demonstration showing how the laboratory-measured data can be applied to explore absorption features in observations toward embedded sources is presented. This demonstration suggests that PAHs very likely contribute to interstellar absorption spectra associated with dense clouds and underscores the need for further IR spectroscopic studies of PAHs trapped in water ice.

Keywords: polycyclic aromatic hydrocarbons; astrochemistry; interstellar dust; astronomy databases; astronomy data analysis; laboratory astrophysics; experimental techniques
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
An Extension of the Athena++ Framework for Fully Conservative Self-gravitating Hydrodynamics

Numerical simulations of self-gravitating flows evolve a momentum equation and an energy equation that account for accelerations and gravitational energy releases due to a time-dependent gravitational potential. In this work, we implement a fully conservative numerical algorithm for self-gravitating flows, using source terms, in the astrophysical magnetohydrodynamics framework Athena++. We demonstrate that properly evaluated source terms are conservative when they are equivalent to the divergence of a corresponding "gravity flux" (i.e., a gravitational stress tensor or a gravitational energy flux). We provide test problems that demonstrate several advantages of the source-term-based algorithm, including second-order convergence and round-off error total momentum and total energy conservation. The fully conservative scheme suppresses anomalous accelerations that arise when applying a common numerical discretization of the gravitational stress tensor that does not guarantee curl-free gravity.

Keywords: hydrodynamics; gravitation; computational methods
How Flat Can a Planetary System Get? I. The Case of TRAPPIST-1

The seven planets orbiting TRAPPIST-1 in a compact near-resonant chain offer a unique case to study in planet formation theory. We demonstrate in this paper that the remarkable flatness of the system, exceeding that of any other known planetary system, is an important constraint on the mass of the gaseous disk in which it formed and attained its current configuration. We use three-dimensional hydrodynamic simulations of the gas and planets to study specific formation models. In particular, we report simulations motivated by the model proposed by Ormel et al.—in this model, the dispersal of the gas disk pushes the planets from an initial resonant chain into their present configuration. We find that a disk with the mass used in this model is consistent with the flatness of the TRAPPIST-1 system, but a more massive disk is not, with the transition occurring between 15 and 50 times the mass of the Ormel et al. disk. This upper limit on mass rules out certain models of the formation of the system, namely in situ formation and disk migration on long timescales.

Keywords: exoplanet formation; protoplanetary disks; planetary-disk interactions
Protoneutron Star Convection Simulated with a New General Relativistic Boltzmann Neutrino Radiation Hydrodynamics Code

We investigate protoneutron star (PNS) convection using our newly developed general relativistic Boltzmann neutrino radiation hydrodynamics code. This is a pilot study for more comprehensive investigations later. As such, we take a snapshot of a PNS at 2.3 s after bounce from a 1D PNS cooling calculation and run our simulation for ~160 ms in 2D under axisymmetry. The original PNS cooling calculation neglected convection entirely and the initial conditions were linearly unstable to convection. We find in our 2D simulation that convection is instigated there indeed and expands inward after being full-fledged. The convection then settled to a quasi-steady state after ~100 ms, being sustained by the negative Y e gradient, which is in turn maintained by neutrino emissions. It enhances the luminosities and mean energies of all species of neutrinos compared to 1D. Taking advantage of the Boltzmann solver, we analyse the possible occurrence of neutrino fast flavor conversion (FFC). We found that FFC is likely to occur in regions where Y e is lower, and that the growth rate can be as high as ~10-1 cm-1.

Keywords: neutron stars; core-collapse supernovae; supernova neutrinos; radiative transfer simulations; neutrino oscillations