adsabs/SciX_UAT_keywords huggingface dataset:
Testing Cosmic-Ray Propagation Scenarios with AMS-02 and Voyager Data

AMS-02 on board the International Space Station provides precise measurements of cosmic rays (CR) near Earth, while Voyager measures CRs in the local interstellar medium, beyond the effects of solar modulation. Based on these data, we test and revise various CR propagation scenarios under standard assumptions: pure diffusion, diffusion with convection, diffusion with reacceleration, and diffusion with reacceleration and convection. We report on the scenarios' performance against CR measurements, aiming to limit the number of model parameters as much as possible. For each scenario, we find parameters that are able to reproduce Voyager and AMS-02 data for the entire energy band for all the CR species tested. Above several GV, we observe a similar injection spectral index for He and C, with He harder than H. Some scenarios previously disfavored are now reconsidered. For example, contrary to usual assumptions, we find that the pure diffusion scenario does not need an upturn in the diffusion coefficient at low energy, while it needs the same number of low-energy breaks in the injection spectrum as diffusive-reacceleration scenarios. We show that scenarios differ in modeled spectra of one order of magnitude for positrons at ∼1 GeV and of a factor of 2 for antiprotons at several GV. The force-field approximation describes well the AMS-02 and Voyager spectra analyzed, except antiprotons. We confirm the ∼10 GeV excess in the antiproton spectrum for all scenarios. Also, for all scenarios, the resulting modulation should be stronger for positrons than for nuclei, with reacceleration models requiring much larger modulation.

Keywords: galactic cosmic rays
Probable Detection of Water Ice in the Coma of the Inbound Long-period Comet C/2017 K2 (PanSTARRS)

We present near-infrared reflectance spectra from 0.7 to 2.5 μm taken 2021 April 30 at the NASA Infrared Telescope Facility that show strong evidence for water ice within the coma of comet C/2017 K2 (PanSTARRS) at a heliocentric distance of RH = 6.488 au. This object has likely been active since ~35 au inbound and this provides a key piece of information to interpreting these early observations, understanding its dust properties, and assessing its overall volatile inventory and release mechanisms. A preliminary spectral model is best-fit with a volume fraction of ice of ~14% assuming that the refractory and volatile materials are mixed intimately. More sophisticated modeling and a deeper analysis of these data will be presented in a manuscript to be submitted later this year.

Keywords: comets
Cosmic Reionization On Computers: The Galaxy-Halo Connection between 5 ≤ z ≤ 10

We explore the connection between the stellar component of galaxies and their host halos during the epoch of reionization (5 ≤ z ≤ 10) using the CROC (Cosmic Reionization on Computers) simulations. We compare simulated galaxies with observations and find that CROC underpredicts the abundance of luminous galaxies when compared to observed UV luminosity functions, and analogously the most massive galaxies when compared to observed stellar mass functions. We can trace the deficit of star formation to high redshifts, where the slope of the star formation rate to stellar mass relation is consistent with observations, but the normalization is systematically low. This results in a star formation rate density and stellar mass density that are systematically offset from observations. However, the less luminous or lower stellar mass objects have luminosities and stellar masses that agree fairly well with observational data. We explore the stellar-to-halo mass ratio (SHMR), a key quantity that is difficult to measure at high redshifts and that models do not consistently predict. In CROC, the SHMR decreases with redshift, a trend opposite to some abundance-matching studies. These discrepancies uncover where future effort should be focused in order to improve the fidelity of modeling cosmic reionization. We also compare the CROC galaxy bias with observational measurements using Lyman-break galaxy samples, finding reasonable consistency.

Keywords: galaxies; reionization; hydrodynamical simulations
The Longest Delay: A 14.5 yr Campaign to Determine the Third Time Delay in the Lensing Cluster SDSS J1004+4112

We present new light curves for the four bright images of the five image cluster-lensed quasar gravitational lens system SDSS J1004+4112. The light curves span 14.5 yr and allow the measurement of the time delay between the trailing bright quasar image D and the leading image C. When we fit all four light curves simultaneously and combine the models using the Bayesian information criterion, we find a time delay of Δt DC = 2458.47 ± 1.02 days (6.73 yr), the longest ever measured for a gravitational lens. For the other two independent time delays we obtain Δt BC = 782.20 ± 0.43 days (2.14 yr) and Δt AC = 825.23 ± 0.46 days (2.26 yr), in agreement with previous results. The information criterion is needed to weight the results for light curve models with different polynomial orders for the intrinsic variability and the effects of differential microlensing. The results using the Akaike information criterion are slightly different, but, in practice, the absolute delay errors are all dominated by the ~4% cosmic variance in the delays rather than the statistical or systematic measurement uncertainties. Despite the lens being a cluster, the quasar images show slow differential variability due to microlensing at the level of a few tenths of a magnitude.

Keywords: gravitational lensing; strong gravitational lensing; galaxy clusters; quasars; photometry; light curves
The Origin of Massive Stars: The Inertial-inflow Model

We address the problem of the origin of massive stars, namely the origin, path, and timescale of the mass flows that create them. Based on extensive numerical simulations, we propose a scenario where massive stars are assembled by large-scale, converging, inertial flows that naturally occur in supersonic turbulence. We refer to this scenario of massive-star formation as the inertial-inflow model. This model stems directly from the idea that the mass distribution of stars is primarily the result of turbulent fragmentation. Under this hypothesis, the statistical properties of turbulence determine the formation timescale and mass of prestellar cores, posing definite constraints on the formation mechanism of massive stars. We quantify such constraints by analyzing a simulation of supernova-driven turbulence in a 250 pc region of the interstellar medium, describing the formation of hundreds of massive stars over a time of approximately 30 Myr. Due to the large size of our statistical sample, we can say with full confidence that massive stars in general do not form from the collapse of massive cores nor from competitive accretion, as both models are incompatible with the numerical results. We also compute synthetic continuum observables in the Herschel and ALMA bands. We find that, depending on the distance of the observed regions, estimates of core mass based on commonly used methods may exceed the actual core masses by up to two orders of magnitude and that there is essentially no correlation between estimated and real core masses.

Keywords: interstellar medium; protostars; interstellar dynamics; magnetohydrodynamics; star formation
Wobbling Jets in Common Envelope Evolution

We find that the convective motion in the envelopes of red supergiant (RSG) stars supplies a non-negligible stochastic angular momentum to the mass that a secondary star accretes in a common envelope evolution (CEE), such that jets that the secondary star launches wobble. The orbital motion of the secondary star in a CEE and the density gradient in the envelope impose a nonzero angular momentum to the accreted mass with a constant direction parallel to the orbital angular momentum. From one-dimensional stellar evolution simulations with the numerical code MESA we find that the stochastic convection motion in the envelope of RSG stars adds a stochastic angular momentum component with an amplitude that is about 0.1-1 times that of the constant component due to the orbital motion. We mimic a CEE of the RSG star by removing envelope mass at a high rate and by depositing energy into its envelope. The stochastic angular momentum implies that the accretion disk around the secondary star (which we do not simulate), and therefore the jets that it launches, wobble with angles of up to tens of degrees with respect to the orbital angular momentum axis. This wobbling makes it harder for jets to break out from the envelope and can shape small bubbles in the ejecta that compress filaments that appear as arcs in the ejected nebula, i.e., in planetary nebulae when the giant is an asymptotic giant branch star.

Keywords: stellar jets; common envelope evolution; common envelope binary stars; red supergiant stars
Quantifying the Toroidal Flux of Preexisting Flux Ropes of Coronal Mass Ejections

In past decades, much progress has been achieved in understanding the origin and evolution of coronal mass ejections (CMEs). In situ observations of the counterparts of CMEs, especially magnetic clouds (MCs) near the Earth, have provided measurements of the structure and total flux of CME flux ropes. However, it has been difficult to measure these properties in an erupting CME flux rope, in particular in a preexisting flux rope. In this work, we propose a model to estimate the toroidal flux of a preexisting flux rope by subtracting the flux contributed by magnetic reconnection during the eruption from the flux measured in the MC. The flux contributed by the reconnection is derived from geometric properties of two-ribbon flares based on a quasi-2D reconnection model. We then apply the model to four CME/flare events and find that the ratio of toroidal flux in the preexisting flux rope to that in the associated MC lies in the range 0.40-0.88. This indicates that the toroidal flux of the preexisting flux rope makes an important contribution to that of the CME flux rope and is usually at least as large as the flux arising from the eruption process for the selected events.

Keywords: solar corona; solar coronal mass ejections; solar flares
Energy Transfer Across the Magnetopause Under Radial IMF Conditions

A global MHD model is used to study the energy transfer from solar wind to magnetosphere through magnetopause under radial interplanetary magnetic fields (IMFs). We use the streamline method to determine the smooth surface of the magnetopause by searching the inner boundary of the solar-wind streamline and discuss the roles of magnetic reconnection and viscous interaction under radial IMFs, which we compare with cases of north-south IMFs. We find that (1) the energy transfer across the magnetopause is asymmetric between the northern and southern hemispheres due to different reconnection locations, particularly for electromagnetic energy; (2) for sunward IMF, the most significant area of the net input of mechanical energy occurs on the day side and near-Earth magnetotail, and the electromagnetic energy input in the northern hemisphere is much larger than in the southern hemisphere on the night side; (3) the mechanical and electromagnetic energy-transfer distribution in the northern (southern) hemisphere for earthward IMF is the same as that in the southern (northern) hemisphere for sunward IMF; (4) the electromagnetic energy input for radial IMF is two times larger than for northward IMF, but three times smaller than for southward IMF, the viscous effect is smaller than for northward IMF but comparable to that for southward IMF, the rate of energy transfer is 2.22% for radial IMF, which is lower than 4.95% for southward IMF, but higher than 1.7% for northward IMF; and (5) the Akasofu-type energy-coupling formula, ϵ, is not suitable for the solar-wind events dominated by IMF Bx.

Keywords: planetary magnetospheres; magnetohydrodynamical simulations
A New Mechanism for Maunder-like Solar Minima: Phase Synchronization Dynamics in a Simple Nonlinear Oscillator of Magnetohydrodynamic Rossby Waves

The long-term solar cycle variability and Grand solar minima remain open questions from a theoretical point of view. Recently, a growing basis of evidence points out to the role of the magnetic Rossby waves in the solar cycle. Here we present a simple deterministic model, based on a low-order spectral representation of the barotropic quasi-geostrophic-magnetohydrodynamic equations for the Solar tachocline. This model supports the idea of the long-term behavior of the solar activity as a result of nonlinear interaction of magnetic Rossby modes. Solutions show that Rossby waves undergo irregular switches between periods of high activity and periods of suppressed activity, resembling the Maunder minimum. Low-energy states in the model are associated with the synchronization of the dynamical phases of the waves. These irregular transitions in the amplitudes of the waves are reminiscent of the observed time series of the solar activity. This suggests that Maunder-like states arise from chaotic transitions between regimes with different degrees of organization in the system.

Keywords: solar cycle; maunder minimum; sunspot cycle; magnetohydrodynamics; alfven waves; solar magnetic fields
The Impact of Bayesian Hyperpriors on the Population-level Eccentricity Distribution of Imaged Planets

Orbital eccentricities directly trace the formation mechanisms and dynamical histories of substellar companions. Here, we study the effect of hyperpriors on the population-level eccentricity distributions inferred for the sample of directly imaged substellar companions (brown dwarfs and cold Jupiters) from hierarchical Bayesian modeling (HBM). We find that the choice of hyperprior can have a significant impact on the population-level eccentricity distribution inferred for imaged companions, an effect that becomes more important as the sample size and orbital coverage decrease to values that mirror the existing sample. We reanalyze the current observational sample of imaged giant planets in the 5-100 au range from Bowler et al. and find that the underlying eccentricity distribution implied by the imaged planet sample is broadly consistent with the eccentricity distribution for close-in exoplanets detected using radial velocities. Furthermore, our analysis supports the conclusion from that study that long-period giant planets and brown dwarf eccentricity distributions differ by showing that it is robust to the choice of hyperprior. We release our HBM and forward-modeling code in an open-source Python package, ePop!, and make it freely available to the community.

Keywords: extrasolar gaseous giant planets
Thermodynamic Evolution of Solar Flare Supra-arcade Downflows

Solar flares are rapid energy release phenomena that appear as bright ribbons in the chromosphere and high temperature loops in the corona, respectively. Supra-arcade Downflows (SADs) are plasma voids that first come out above the flare loops and then move quickly toward the flare loop top during the decay phase of the flare. In our work, we study 20 SADs appearing in three flares. By differential emission measure (DEM) analysis, we calculate the DEM weighted average temperature and emission measure of the front region and the main body of SADs. It is found that the temperatures of the SAD front and body tend to increase during the course of SADs flowing downwards. The relationship between the pressure and temperature fits well with the adiabatic equation for both the SAD front and body, suggesting that the heating of SADs is mainly caused by adiabatic compression. Moreover, we also estimate the velocities of SADs via the Fourier Local Correlation Tracking method and find that increase of the temperature of the SAD front presents a correlation with the decrease of the SAD kinetic energy, while the SAD body does not, implying that the viscous process may also heat the SAD front in spite of a limited role.

Keywords: solar flares; solar magnetic reconnection; solar coronal heating
Dependence of X CO on Metallicity, Intensity, and Spatial Scale in a Self-regulated Interstellar Medium

We study the CO(1-0)-to-H2 conversion factor (X CO) and the line ratio of CO(2-1)-to-CO(1-0) (R 21) across a wide range of metallicity (0.1 ≤ Z/Z ⊙ ≤ 3) in high-resolution (~0.2 pc) hydrodynamical simulations of a self-regulated multiphase interstellar medium. We construct synthetic CO emission maps via radiative transfer and systematically vary the observational beam size to quantify the scale dependence. We find that the kpc-scale X CO can be overestimated at low Z if assuming steady-state chemistry or assuming that the star-forming gas is H2 dominated. On parsec scales, X CO varies by orders of magnitude from place to place, primarily driven by the transition from atomic carbon to CO. The parsec-scale X CO drops to the Milky Way value of $2\times {10}^{20}\ {\mathrm{cm}}^{-2}\,{\left({\rm{K}}\,\mathrm{km}\,{{\rm{s}}}^{-1}\right)}^{-1}$ once dust shielding becomes effective, independent of Z. The CO lines become increasingly optically thin at lower Z, leading to a higher R 21. Most cloud area is filled by diffuse gas with high X CO and low R 21, while most CO emission originates from dense gas with low X CO and high R 21. Adopting a constant X CO strongly over- (under-)estimates H2 in dense (diffuse) gas. The line intensity negatively (positively) correlates with X CO (R 21) as it is a proxy of column density (volume density). On large scales, X CO and R 21 are dictated by beam averaging, and they are naturally biased toward values in dense gas. Our predicted X CO is a multivariate function of Z, line intensity, and beam size, which can be used to more accurately infer the H2 mass.

Keywords: interstellar medium; astrochemistry; hydrodynamical simulations
Dispersion Characteristics of the Multi-mode Fiber-fed VIPA Spectrograph

A high-resolution ( ${ \mathcal R }\gt {10}^{5}$ ), multi-mode fiber-fed spectrograph on large telescopes with a reasonable size is desirable in astronomy. In this work, the dispersion characteristics of a multi-mode fiber-fed Virtually Imaged Phased Array (VIPA) spectrograph are studied theoretically and experimentally. A VIPA spectrograph, fed by multi-mode optical fibers with the operating wavelength at 750 ~ 770 nm, is designed and built in our laboratory. After calibration with a homemade Yb:fiber ring laser frequency comb (with a repetition frequency of 808 MHz), the measured spectral resolution fed by multi-mode fibers with core diameters $\varnothing =10$ , 25, 50, and 105 μm is comparable with that of the single-mode fiber, i.e., ${ \mathcal R }=7.62\times {10}^{5}\sim 8.97\times {10}^{5}$ , with equivalent transmission efficiencies. This verifies experimentally that the spectral resolution is much less affected by the core diameters of the input fibers when compared with that of échelle spectrographs. It is also found that the diffraction envelope of the VIPA spectrograph relies on the coherence of light sources and the width of the point-spread function is inversely proportional to the spatial position on the detector. Since the VIPA spectrograph has no imaging process in the main dispersion direction, the spectral resolution is insensitive to the width of the input slit or the fiber diameter. This makes the VIPA spectrograph a promising instrument to attain an ultra-high spectral resolution ( ${ \mathcal R }\gt 3\times {10}^{5}$ ) on very large telescopes.

Keywords: high resolution spectroscopy; astronomical methods; astronomical instrumentation; astronomical techniques
K-shell X-Ray Emission from Lithium-like Nitrogen N V

We present laboratory measurements of n = 3 → n = 1 N V X-ray emission lines situated near 26 Å. The lines are excited by electron-impact collisions and are shown to reach a combined intensity of about a fifth of the combined strong N V 1s2s2p 2 P 1/2,3/2 → 1s 22s 2 S 1/2 resonance lines, commonly labeled q and r, at 29.4 Å. In addition, we present new experimental data for the wavelength of the blended q and r lines at 29.4 Å, as well as for that of the blended inner-shell-excited N V lines u and v at 30.0 Å. All of these collisional N V lines need to be included in astrophysical emission models in order to properly account for flux from N V in the soft X-ray region. The measured wavelengths provide benchmarks for testing atomic structure calculations and excellent agreement is found with our calculations using the many-body perturbation theory method. We provide a complete listing of the N V energy levels with valence electrons in the n = 2, 3, and 4 shells calculated with this approach. The experimental and theoretical data, thus, provide accurate rest-frame wavelengths needed for velocity determinations based on high-resolution absorption features in spectra of warm absorbers in active galactic nuclei and other astrophysical objects.

Keywords: atomic spectroscopy; active galactic nuclei; x-ray astronomy; line positions
Rotation of a Stealth CME on 2012 October 5 Observed in the Inner Heliosphere

Coronal mass ejections (CMEs) are subject to changes in their direction of propagation, tilt, and other properties. This is because CMEs interact with the ambient solar wind and other large-scale magnetic field structures. In this work, we report on the observations of the 2012 October 5 stealth CME using coronagraphic and heliospheric images. We find clear evidence of a continuous rotation of the CME, i.e., an increase in the tilt angle, estimated using the graduated cylindrical shell (GCS) reconstruction at different heliocentric distances, up to 58 R ⊙. We find a further increase in the tilt at L1 estimated from the toroidal and cylindrical flux rope fitting on the in situ observations of interplanetary magnetic field (IMF) and solar wind parameters. This study highlights the importance of observations of Heliospheric Imager (HI), on board the Solar Terrestrial Relations Observatory. In particular, the GCS reconstruction of CMEs in the HI field of view promises to bridge the gap between the near-Sun and in situ observations at the L1. The changes in the CME tilt have significant implications for the space weather impact of stealth CMEs.

Keywords: solar coronal mass ejections; heliosphere
An Optically Thin View of the Solar Chromosphere from Observations of the O I 1355 Å Spectral Line

The O I 1355 Å spectral line is one of the only optically thin lines that are both routinely observed and thought to be formed in the chromosphere. We present an analysis of a variety of observations of this line with the Interface Region Imaging Spectrograph (IRIS), and compare it with other IRIS diagnostics as well as diagnostics of the photospheric magnetic field. We utilize special deep exposure modes on IRIS and provide an overview of the statistical properties of this spectral line for several different regions on the Sun. We analyze the spatiotemporal variations of the line intensity and find that it is often significantly enhanced when and where magnetic flux of opposite polarities cancel. Significant emission occurs in association with chromospheric spicules. Because of the optically thin nature of the O I line, the nonthermal broadening can provide insight into unresolved small-scale motions. We find that the nonthermal broadening is modest, with typical values of 5-10 km s-1, and shows some center-to-limb variation, with a modest increase toward the limb. The dependence with the height of the intensity and line broadening off-limb is compatible with the line broadening being dominated by the superposition of Alfvén waves on different structures. The nonthermal broadening shows a modest but significant enhancement above locations that are in between photospheric magnetic flux concentrations in plage, i.e., where the magnetic field is likely to be more inclined with respect to the line of sight. Our measurements provide strict constraints on future theoretical models of the chromosphere.

Keywords: solar chromosphere; solar transition region; solar magnetic fields