adsabs/SciX_UAT_keywords huggingface dataset:
Dynamics of Descending Knots in a Solar Prominence and Their Possible Contributions to the Heating of the Local Corona

The knots in solar prominences are often observed to fall with nearly constant velocity, but the associated physical mechanism is currently not well understood. In this Letter, we present a prominence observed by the New Vacuum Solar Telescope in Hα wavelength. Knots that rose within the prominence appear to have been preferentially located at higher altitude, whereas those that fell were found throughout the entire prominence structure. The descending speed of the knots near the solar surface was higher than that far away from the solar surface. We noted that the knots near the solar surface may run along a set of coronal loops observed from the Atmospheric Imaging Assembly. Elsewhere, the majority of knots are interpreted to have descended across more horizontal magnetic fields with a nearly constant speed. This lack of acceleration indicates that the liberated gravitational potential energy may not manifest as an increase in kinetic energy. Assuming instead that the descending knots were capable of exciting Alfvén waves that could then dissipate within the local corona, the gravitational potential energy of the knots may have been converted into thermal energy. Assuming a perfectly elastic system, we therefore estimate that the gravitational energy loss rate of these observed knots amounts to ≈1/2000 of that required to heat the entire quiet Sun, increasing to 1/320 when considering possibly further downward motions of the knots having disappeared in the Hα observations. This result suggests such a mechanism may contribute to the heating of the corona local to these prominences.

Keywords: the sun; solar prominences; solar chromosphere; solar coronal heating; solar corona; solar filaments; solar magnetic fields; solar physics
Seventeen 2 Micron All Sky Survey (2MASS) Hypervelocity Stars (HVS) from Gaia DR3

As part of an ongoing search for hypervelocity stars I found seventeen two micron all sky survey sources with Gaia G magnitudes less than 16.0 and radial velocities less than -600 km s-1. All these stars are brighter in the K band when compared with their V and G magnitudes. Ten of these (including three carbon stars) are long period variable stars of Mira type. One is a relatively nearby high proper motion star and one is a very high galactic latitude chemically peculiar metal-poor star. It may be a galactic halo star. One star is a Kepler red giant, two stars may be cluster members and two are in the star-forming region (probably YSOs). It is not clear how these stars acquired such high radial velocities. Further study of these seventeen stars is needed.

Keywords: hypervelocity stars
Revisiting Dynamical Friction: The Role of Global Modes and Local Wakes

The orbital decay of a perturber within a larger system plays a key role in the dynamics of many astrophysical systems-from nuclear star clusters or globular clusters in galaxies, to massive black holes in galactic nuclei, to dwarf galaxy satellites within the dark matter halos of more massive galaxies. For many decades, there have been various attempts to determine the underlying physics and timescales of the drag mechanism, ranging from the local dynamical friction approach to descriptions based on the back-reaction of global modes induced in the background system. We present ultra-high-resolution N-body simulations of massive satellites orbiting a Milky Way-like galaxy (with > 108 particles), that appear to capture both the local "wake" and the global "mode" induced in the primary halo. We address directly the mechanism of orbital decay from the combined action of local and global perturbations and specifically analyze where the bulk of the torque originates.

Keywords: dark matter; galaxies; dwarf galaxies; galaxy interactions; galaxy dynamics; galaxy kinematics; dynamical friction
High-z Dusty Star-forming Galaxies: A Top-heavy Initial Mass Function?

Recent estimates point to abundances of z > 4 submillimeter galaxies far above model predictions. The matter is still debated. According to some analyses the excess may be substantially lower than initially thought and perhaps accounted for by flux boosting and source blending. However, there is no general agreement on this conclusion. An excess of z > 6 dusty galaxies has also been reported albeit with poor statistics. On the other hand, evidence of a top-heavy initial mass function (IMF) in high-z starburst galaxies has been reported in the past decades. This would translate into a higher submillimeter luminosity of dusty galaxies at fixed star formation rate, I.e., into a higher abundance of bright high-z submillimeter galaxies than expected for a universal Chabrier IMF. Exploiting our physical model for high-z protospheroidal galaxies, we find that part of the excess can be understood in terms of an IMF somewhat top-heavier than Chabrier. Such an IMF is consistent with that recently proposed to account for the low 13C/18O abundance ratio in four dusty starburst galaxies at z = 2-3. However, extreme top-heavy IMFs are inconsistent with the submillimeter counts at z > 4.

Keywords: initial mass function; galaxy evolution; high-redshift galaxies; submillimeter astronomy
Missing Giants: Predictions on Dust-obscured Galaxy Stellar Mass Assembly Throughout Cosmic Time

Due to their extremely dust-obscured nature, much uncertainty still exists surrounding the stellar mass growth and content in dusty, star-forming galaxies (DSFGs) at z > 1. In this work, we present a numerical model built using empirical data on DSFGs to estimate their stellar mass contributions across the first ~10 Gyr of cosmic time. We generate a dust-obscured stellar mass function that extends beyond the mass limit of star-forming stellar mass functions in the literature, and predict that massive DSFGs constitute as much as 50%-100% of all star-forming galaxies with M ≥1011 M ⊙ at z > 1. We predict the number density of massive DSFGs and find general agreement with observations, although more data is needed to narrow wide observational uncertainties. We forward-model mock massive DSFGs to their quiescent descendants and find remarkable agreement with observations from the literature demonstrating that, to first order, massive DSFGs are a sufficient ancestral population to describe the prevalence of massive quiescent galaxies at z > 1. We predict that massive DSFGs and their descendants contribute as much as 25%-60% to the cosmic stellar mass density during the peak of cosmic star formation, and predict an intense epoch of population growth during the ~1 Gyr from z = 6 to 3 during which the majority of the most massive galaxies at high-z grow and then quench. Future studies seeking to understand massive galaxy growth and evolution in the early universe should strategize synergies with data from the latest observatories (e.g., JWST and the Atacama Large Millimeter/submillimeter Array) to better include the heavily dust-obscured galaxy population.

Keywords: galaxy evolution; luminous infrared galaxies; high-redshift galaxies
JWST Spectroscopy of SN H0pe: Classification and Time Delays of a Triply Imaged Type Ia Supernova at z = 1.78

SN H0pe is a triply imaged supernova (SN) at redshift z = 1.78 discovered using the James Webb Space Telescope. In order to classify the SN spectroscopically and measure the relative time delays of its three images (designated A, B, and C), we acquired NIRSpec follow-up spectroscopy spanning 0.6–5 μm. From the high signal-to-noise spectra of the two bright images B and C, we first classify the SN, whose spectra most closely match those of SN 1994D and SN 2013dy, as a Type Ia SN. We identify prominent blueshifted absorption features corresponding to Si II λ6355 and Ca II H λ3970 and K λ3935. We next measure the absolute phases of the three images from our spectra, which allow us to constrain their relative time delays. The absolute phases of the three images, determined by fitting the three spectra to Hsiao07 SN templates, are days, days, and days for the brightest to faintest images. These correspond to relative time delays between Image A and Image B and between Image B and Image C of days and days, respectively. The SALT3-NIR model yields phases and time delays consistent with these values. After unblinding, we additionally explored the effect of using Hsiao07 template spectra for simulations through 80 days instead of 60 days past maximum, and found a small (11.5 and 1.0 days, respectively) yet statistically insignificant (∼0.25σ and ∼0.1σ) effect on the inferred image delays.

Keywords: type ia supernovae; gravitational lensing; strong gravitational lensing; rich galaxy clusters; spectroscopy; james webb space telescope; hubble constant
On the Correct Use of Gravity-darkening Coefficients in the JKTEBOP Eclipsing-binary Code

Users of the JKTEBOP code to solve the light curves of eclipsing binaries often confuse the gravity darkening coefficients, y(λ), with the bolometric gravity darkening exponents, β. JKTEBOP requires the wavelength-dependent coefficients. I show that the numerical values of y(λ) and β can be rather different, leading to potential biases in the solution if the wrong quantities are used.

Keywords: eclipsing binary stars; light curves
pynucastro: A Python Library for Nuclear Astrophysics

We describe pynucastro 2.0, an open-source library for interactively creating and exploring astrophysical nuclear reaction networks. We demonstrate new methods for approximating rates and use detailed balance to create reverse rates, show how to build networks and determine whether they are appropriate for a particular science application, and discuss the changes made to the library over the past few years. Finally, we demonstrate the validity of the networks produced and share how we use pynucastro networks in simulation codes.

Keywords: nuclear astrophysics; nucleosynthesis; nuclear fusion; astrophysical processes; reaction rates; astronomy software; computational astronomy
Evidence for Radial Expansion at the Core of the Orion Complex with Gaia EDR3

We present a phase-space study of two stellar groups located at the core of the Orion Complex: Briceño-1 and Orion Belt Population-near (OBP-near). We identify the groups with the unsupervised clustering algorithm, Shared Nearest Neighbor (SNN), which previously identified 12 new stellar substructures in the Orion Complex. For each of the two groups, we derive the 3D space motions of individual stars using Gaia EDR3 proper motions supplemented by radial velocities from Gaia DR2, APOGEE-2, and GALAH DR3. We present evidence for radial expansion of the two groups from a common center. Unlike previous work, our study suggests that evidence of stellar group expansion is confined only to OBP-near and Briceño-1, whereas the rest of the groups in the complex show more complicated motions. Interestingly, the stars in the two groups lie at the center of a dust shell, as revealed via an extant 3D dust map. The exact mechanism that produces such coherent motions remains unclear, while the observed radial expansion and dust shell suggest that massive stellar feedback could have influenced the star formation history of these groups.

Keywords: stellar feedback; stellar associations; stellar ages; stellar dynamics
Deep Learning Based Solar Flare Forecasting Model. II. Influence of Image Resolution

Due to the accumulation of solar observational data and the development of data-driven algorithms, deep learning methods are widely applied to build a solar flare forecasting model. Most of the works focus on how to design or select proper deep networks for the forecasting task. Nevertheless, the influence of image resolution on the learning based solar flare forecasting model has not been analyzed and discussed. In this Paper, we investigate the influence of the resolution of magnetograms on the accuracy of solar flare forecasting. We study the active regions by the Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) magnetograms from 2010 to 2019. Then, we downsample them to get a database containing active regions with several resolutions. Afterwards, three deep neural networks (i) AlexNet, (ii) ResNet-18, and (iii) SqueezeNet are implemented to evaluate the performance of solar flare forecasting compared to different resolutions of magnetogram. In experiments, we first did comparative experiments on our own simulated HMI database with different resolutions. Then we conducted experiments on two selected actual overlapping databases, Hinode-HMI and Michelson Doppler Imager-HMI, to reconfirm our conclusions. The experiment results show that all the selected deep learning networks are insensitive to the resolution to a certain extent. We visualized the regions of interest of the network from an interpretable perspective and found that the deep learning network pays more attention to the global features extracted from active regions that are not sensitive to local information in magnetograms.

Keywords: solar physics; solar activity; convolutional neural networks
An XMM-Newton X-Ray View of Supernova Remnant W49B: Revisiting Its Recombining Plasmas and Progenitor Type

We present a comprehensive X-ray spectroscopy and imaging study of supernova remnant W49B using archival XMM-Newton observations. The overionization state of the shocked ejecta in W49B is clearly indicated by the radiative recombination continua of Si XIV, S XV, and Fe XXV, combined with the Lyα lines of Ca and Fe. The line flux images of W49B indicate high emission measures of the central bar-like region for almost all of the emission lines, while the equivalent width maps reveal a stratified structure for the metal abundance distributions. The global spectrum of W49B is well reproduced by a model containing one collisional ionization equilibrium (CIE) plasma component and two recombining plasma (RP) components. The CIE plasma represents the shocked interstellar medium, which dominates the X-ray emitting volume in W49B with a mass ∼450 ${M}_{\odot }$ . The two RP components with a total mass ∼4.6 ${M}_{\odot }$ are both dominated by the ejecta material, but characterized by different electron temperatures (∼1.60 and ∼0.64 keV). The recombination ages of the RP components are estimated as ∼6000 yr and ∼3400 yr, respectively. We then reveal the possibility of a thermal conduction origin for the high-temperature RP in W49B by calculating the conduction timescale. The metal abundance ratios of the ejecta in W49B are roughly consistent with a core-collapse explosion model with a ≲15 ${M}_{\odot }$ progenitor, except for a rather high Mn/Fe. A Type Ia origin can explain the Mn abundance, while it predicts much higher ejecta masses than observed values for all of the metal species considered in our analysis.

Keywords: supernova remnants; interstellar medium; x-ray astronomy
Rotational Spectra of Vibrationally Excited AlO and TiO in Oxygen-rich Stars

Rotational transitions in vibrationally excited AlO and TiO—two possible precursors of dust—were observed in the 300 GHz range (1 mm wavelength) toward the oxygen-rich asymptotic giant branch (AGB) stars R Dor and IK Tau with ALMA, and vibrationally excited AlO was observed toward the red supergiant VY CMa with the SMA. The J = 11 → 10 transition of TiO in the v = 1 and 2 levels and the N = 9 → 8 transition in the v = 2 level of AlO were identified toward R Dor, the J = 11 → 10 line of TiO was identified in the v = 1 level toward IK Tau, and two transitions in the v = 1 and 2 levels of AlO were identified toward VY CMa. The newly derived high vibrational temperature of TiO and AlO in R Dor of 1800 ± 200 K and prior measurements of the angular extent confirm that the majority of the emission is from a region within ≲2R⋆ of the central star. A full radiative transfer analysis of AlO in R Dor yielded a fractional abundance of ∼3% of the solar abundance of Al. From a similar analysis of TiO a fractional abundance of ∼78% of the solar abundance of Ti was found. The observations provide indirect evidence that TiO is present in a rotating disk close to the star. Further observations in the ground and excited vibrational levels are needed to determine whether AlO, TiO, and TiO2 are seeds of the Al2O3 dust in R Dor, and perhaps in the gravitationally bound dust shells in other AGB stars with low mass-loss rates.

Keywords: asymptotic giant branch stars; circumstellar matter; submillimeter astronomy; spectral line identification
PopSyCLE: A New Population Synthesis Code for Compact Object Microlensing Events

We present a new Milky Way microlensing simulation code, dubbed PopSyCLE (Population Synthesis for Compact object Lensing Events). PopSyCLE is the first resolved microlensing simulation to include a compact object distribution derived from numerical supernova explosion models and both astrometric and photometric microlensing effects. We demonstrate the capabilities of PopSyCLE by investigating the optimal way to find black holes (BHs) with microlensing. Candidate BHs have typically been selected from wide-field photometric microlensing surveys, such as OGLE, by selecting events with long Einstein crossing times (tE > 120 days). These events can be selected at closest approach and monitored astrometrically in order to constrain the mass of each lens; PopSyCLE predicts a BH detection rate of ∼40% for such a program. We find that the detection rate can be enhanced to ∼85% by selecting events with both tE > 120 days and a microlensing parallax of πE < 0.08. Unfortunately, such a selection criterion cannot be applied during the event, as πE requires both pre- and post-peak photometry. However, historical microlensing events from photometric surveys can be revisited using this new selection criterion in order to statistically constrain the abundance of BHs in the Milky Way. The future Wide Field Infrared Survey Telescope (WFIRST) microlensing survey provides both precise photometry and astrometry and will yield individual masses of ${ \mathcal O }(100\mbox{--}1000)$ BHs, which is at least an order of magnitude more than is possible with individual candidate follow-up with current facilities. The resulting sample of BH masses from WFIRST will begin to constrain the shape of the BH present-day mass function, BH multiplicity, and BH kick velocity distributions.

Keywords: gravitational microlensing; stellar mass black holes; stellar remnants
If Dark Matter is Fuzzy, the First Stars Form in Massive Pancakes

Fuzzy dark matter (FDM) is a proposed modification for the standard cold dark matter (CDM) model motivated by small-scale discrepancies in low-mass galaxies. Composed of ultralight (mass ~ 1022 eV) axions with kiloparsec-scale de Broglie wavelengths, this is one of a class of candidates that predicts that the first collapsed objects form in relatively massive dark matter halos. This implies that the formation history of the first stars and galaxies would be very different, potentially placing strong constraints on such models. Here we numerically simulate the formation of the first stars in an FDM cosmology, following the collapse in a representative volume all the way down to primordial protostar formation including a primordial nonequilibrium chemical network and cooling for the first time. We find two novel results: first, the large-scale collapse results in a very thin and flat gas "pancake"; second, despite the very different cosmology, this pancake fragments until it forms protostellar objects indistinguishable from those in CDM. Combined, these results indicate that the first generation of stars in this model are also likely to be massive and, because of the sheet morphology, do not self-regulate, resulting in a massive Population III starburst. We estimate the total number of first stars forming in this extended structure to be 104 over 20 Myr using a simple model to account for the ionizing feedback from the stars, and should be observable with the James Webb Space Telescope. These predictions provide a potential smoking gun signature of FDM and similar dark matter candidates.

Keywords: population iii stars; dark matter; cosmology; galaxy formation
Multimessenger Implications of Sub-PeV Diffuse Galactic Gamma-Ray Emission

The diffuse Galactic gamma-ray flux between 0.1 and 1 PeV has recently been measured by the Tibet ASγ Collaboration. The flux and spectrum are consistent with the decay of neutral pions from hadronuclear interactions between Galactic cosmic rays and the interstellar medium (ISM). We derive the flux of the Galactic diffuse neutrino emission from the same interaction process that produces the gamma rays. Our calculation accounts for the effect of gamma-ray attenuation inside the Milky Way and uncertainties due to the spectrum and distribution of cosmic rays, gas density, and infrared emission of the ISM. We find that the contribution from the Galactic plane (GP) to the all-sky neutrino flux is ≲5%-10% around 100 TeV. The Galactic and extragalactic neutrino intensities are comparable in the GP region. Our results are consistent with the upper limit reported by the IceCube and ANTARES Collaborations, and predict that next-generation neutrino experiments may observe the Galactic component. We also show that the Tibet ASγ data imply either an additional component in the cosmic-ray nucleon spectrum or contribution from discrete sources, including PeVatrons such as superbubbles and hypernova remnants, and PeV electron accelerators. Future multimessenger observations between 1 TeV and 1 PeV are crucial to decomposing the origin of sub-PeV gamma-rays.

Keywords: galactic cosmic rays; neutrino astronomy; high-energy cosmic radiation
Design and Operation of the ATLAS Transient Science Server

The Asteroid Terrestrial impact Last Alert System (ATLAS) system consists of two 0.5 m Schmidt telescopes with cameras covering 29 square degrees at plate scale of 1.86 arcsec per pixel. Working in tandem, the telescopes routinely survey the whole sky visible from Hawaii (above $\delta \gt -50^\circ $ ) every two nights, exposing four times per night, typically reaching $o\lt 19$ magnitude per exposure when the moon is illuminated and $c\lt 19.5$ magnitude per exposure in dark skies. Construction is underway of two further units to be sited in Chile and South Africa which will result in an all-sky daily cadence from 2021. Initially designed for detecting potentially hazardous near earth objects, the ATLAS data enable a range of astrophysical time domain science. To extract transients from the data stream requires a computing system to process the data, assimilate detections in time and space and associate them with known astrophysical sources. Here we describe the hardware and software infrastructure to produce a stream of clean, real, astrophysical transients in real time. This involves machine learning and boosted decision tree algorithms to identify extragalactic and Galactic transients. Typically we detect 10-15 supernova candidates per night which we immediately announce publicly. The ATLAS discoveries not only enable rapid follow-up of interesting sources but will provide complete statistical samples within the local volume of 100 Mpc. A simple comparison of the detected supernova rate within 100 Mpc, with no corrections for completeness, is already significantly higher (factor 1.5 to 2) than the current accepted rates.

Keywords: asteroids; surveys; variable stars; supernovae
The Behavior of HgMn Stars in the Far UV-Paper 17: HD 35548A

The analysis of high resolution spectra of the HgMn star HD 35548A recorded by the SWP camera on board the International Ultraviolet Explorer reveals no variations of the far-ultraviolet flux of this star over about 21 hr in 1981. The resonance lines of Ga II and Ga III, characteristic of classical HgMn stars, are salient features in the mean SWP spectrum of HD 35548A. The TESS lightcurve of the system HD 35548A and HD 35548B has an asymetric structure with a steep descent to the minimum and a slower rise to next maximum. The period, measured between two successive maxima, is close to 6.07 ± 0.09 days which could be the orbital and rotational period due to synchronization with the companion of HD 35548A.

Keywords: chemically peculiar stars; mercury-manganese stars