adsabs/SciX_UAT_keywords huggingface dataset:
Ejecta–Circumstellar Medium Interaction in High-density Environment Contribution to Kilonova Emission: Application to GRB 191019A

The nearby long-duration GRB 191019A recently detected by Swift lacks an associated supernova and belongs to a host galaxy with little star formation activity, suggesting that the origin of this burst is the result of a merger of two compact objects with dynamical interactions in a high-density medium of an active galactic nucleus. Given the potential motivation of this event, and given that it occurs in such a high-density environment, the ejecta–circumstellar medium (CSM) interaction cannot be ignored as possibly contributing to the kilonova emission. Here, we theoretically calculate the kilonova emission by considering the contribution of the ejecta–CSM interaction in a high-density environment. We find that the contribution to the kilonova emission from the ejecta–CSM interaction will dominate at a later time, and a smaller ejecta mass will have a stronger kilonova emission from the ejecta–CSM interaction. Moreover, we try to apply it to GRB 191019A, but we find that it is difficult to identify the possible kilonova emission from the observations, due to the contribution of the bright host galaxy. On the other hand, less injected mass (less than M ej = 2 × 10‑5 M ⊙) will be required if one can detect the kilonova emission associated with a GRB 191019A–like event in the future. The r-process-powered and spin energy contributions from the magnetar are also discussed.

Keywords: gamma-ray bursts
Cosmic Spin and Mass Evolution of Black Holes and Its Impact

We build an evolution model of the central black hole that depends on the processes of gas accretion, the capture of stars, mergers, and electromagnetic torque. In the case of gas accretion in the presence of cooling sources, the flow is momentum driven, after which the black hole reaches a saturated mass; subsequently, it grows only by stellar capture and mergers. We model the evolution of the mass and spin with the initial seed mass and spin in ΛCDM cosmology. For stellar capture, we have assumed a power-law density profile for the stellar cusp in a framework of relativistic loss cone theory that includes the effects of black hole spin, Carter's constant, loss cone angular momentum, and capture radius. Based on this, the predicted capture rates of 10-5 to 10-6 yr-1 are closer to the observed range. We have considered the merger activity to be effective for z ≲ 4, and we self-consistently include the Blandford-Znajek torque. We calculate these effects on the black hole growth individually and in combination, for deriving the evolution. Before saturation, accretion dominates the black hole growth (∼95% of the final mass), and subsequently stellar capture and mergers take over with roughly equal contributions. The simulations of the evolution of the M•-σ relation using these effects are consistent with available observations. We run our model backward in time and retrodict the parameters at formation. Our model will provide useful inputs for building demographics of the black holes and in formation scenarios involving stellar capture.

Keywords: black hole physics; accretion; stellar dynamics; cosmological evolution; galaxy nuclei
PHANGS-JWST First Results: Measuring Polycyclic Aromatic Hydrocarbon Properties across the Multiphase Interstellar Medium

Ratios of polycyclic aromatic hydrocarbon (PAH) vibrational bands are a promising tool for measuring the properties of the PAH population and their effect on star formation. The photometric bands of the MIRI and NIRCam instruments on JWST provide the opportunity to measure PAH emission features across entire galaxy disks at unprecedented resolution and sensitivity. Here we present the first results of this analysis in a sample of three nearby galaxies: NGC 628, NGC 1365, and NGC 7496. Based on the variations observed in the 3.3, 7.7, and 11.3 μm features, we infer changes to the average PAH size and ionization state across the different galaxy environments. High values of F335MPAH/F1130W and low values of F1130W/F770W are measured in H II regions in all three galaxies. This suggests that these regions are populated by hotter PAHs, and/or that the PAH ionization fraction is larger. We see additional evidence of heating and/or changes in PAH size in regions with higher molecular gas content as well as increased ionization in regions with higher Hα intensity.

Keywords: dust physics; interstellar dust; polycyclic aromatic hydrocarbons
Evolution of the Local Spiral Structure Revealed by OB-type Stars in Gaia DR3

The structure and evolution of the spiral arms of the Milky Way have long been an important yet controversial issue. The wide age range of OB-type stars, coupled with the large amount of high-precision astrometric data provided by Gaia DR3, presents us with an opportunity to explore this issue. After constructing overdensity maps and examining the variations of overdensities with Galactocentric distance along the Galactic azimuth, we compare the spiral structures traced by B3–B5, B6–B7, B8, and B9 stars with those of young O–B2 stars in the vicinity of the Sun. We find that as the ages of the OB tracer stars increase, the Perseus Arm traced by them gradually shifts toward the anti-Galactic center direction, and the pitch angle of the Carina Arm gradually decreases. These results will help us to understand better the evolutionary properties of nearby spiral arms.

Keywords: galaxy structure; galaxy evolution; galaxy stellar content; solar neighborhood
Curved Jet Motion. I. Orbiting and Precessing Jets

Astrophysical jets are often observed as bent or curved structures. We also know that the different jet sources may be binary in nature, which may lead to a regular, periodic motion of the jet nozzle, an orbital motion, or precession. Here we present the results of 2D (M)HD simulations in order to investigate how a precessing or orbiting jet nozzle affects the propagation of a high-speed jet. We have performed a parameter study of systems with different precession angles, different orbital periods or separations, and different magnetic field strengths. We find that these kinds of nozzles lead to curved jet propagation, which is determined by the main parameters that define the jet nozzle. We find C-shaped jets from orbiting nozzles and S-shaped jets from precessing nozzles. Over a long time and long distances, the initially curved jet motion bores a broad channel into the ambient gas that is filled with high-speed jet material whose lateral motion is damped, however. A strong (longitudinal) magnetic field can damp the jet curvature that is enforced by either precession or orbital motion of the jet sources. We have investigated the force balance across the jet and ambient medium and found that the lateral magnetic pressure and gas pressure gradients are almost balanced, but that a lack of gas pressure on the concave side of the curvature is leading to the lateral motion. Magnetic tension does not play a significant role. Our results are obtained in code units, but we provide scaling relations such that our results may be applied to young stars, microquasars, symbiotic stars, or active galactic nuclei.

Keywords: interstellar medium
A Murchison Widefield Array Search for Transmissions from the 4M Spacecraft, On Board the Chang'e 5-T1 Booster, Prior to its Predicted Collision with the Moon

Using the Murchison Widefield Array we searched for, and did not detect, 145.980 MHz transmissions from the 4M spacecraft attached to the Chang'e 5-T1 rocket booster. This object was predicted to collide with the Moon on 2022 March 4. We observed for a ten minutes period on 2022 March 1, achieving noise levels of ~4 Jy in a 10 kHz bandwidth. The expected signal level of a nominally operational transmitter would be ~7500 Jy. Thus, we conclude that the transmitter was inactive (or operating at less than 5 mW) in the days before the predicted impact with the Moon, which is reasonable given that the nominal mission life of 4M was approximately 8 days in late 2014. A detection would have allowed 4M and its host booster to be tracked to near the point of collision, which was not possible using optical telescopes due to the event occurring in daytime.

Keywords: the moon
Occultation of a Large Star by the Large Plutino (28978) Ixion on 2020 October 13 UTC

We observed the occultation of the star Gaia DR2 4056440205544338944 by (28978) Ixion. The event was observed from two Lowell Observatory sites, using the 4.3 m Lowell Discovery Telescope (LDT), near Happy Jack, AZ, USA, and a 0.32 m telescope co-mounted with the Titan Monitoring telescope on Lowell's Mars Hill campus in Flagstaff, AZ. The LDT chord, at 44.86 s, was roughly 30% longer than the longest predicted possible chord. Under the assumption of a spherical body, Ixion's fitted diameter D = 709.6 ± 0.2 km. The LDT light-curve profile was used to place an upper limit on the surface pressure P < 2 μbar on any possible atmosphere of Ixion. At the distance of Ixion, the occulted star had a fitted projected diameter of 19.25 ± 0.3 km assuming uniform disk illumination, giving a stellar angular diameter of 0.675 ± 0.010 mas. Using the Gaia EDR3 parallax of 0.565 mas, the stellar radius is ${130}_{-17}^{+20}\,{R}_{\odot }$ <!-- --> . The measured size is consistent with prior spectral classification of this star as a reddened mid-M giant. This is one of only a modest number of M5 III stars to have a directly measured diameter, and is more distant than most.

Keywords: asteroid occultation; stellar occultation; trans-neptunian objects; high angular resolution
Construction of Explicit Symplectic Integrators in General Relativity. IV. Kerr Black Holes

In previous papers, explicit symplectic integrators were designed for nonrotating black holes, such as a Schwarzschild black hole. However, they fail to work in the Kerr spacetime because not all variables can be separable, or not all splitting parts have analytical solutions as explicit functions of proper time. To cope with this difficulty, we introduce a time transformation function to the Hamiltonian of Kerr geometry so as to obtain a time-transformed Hamiltonian consisting of five splitting parts, whose analytical solutions are explicit functions of the new coordinate time. The chosen time transformation function can cause time steps to be adaptive, but it is mainly used to implement the desired splitting of the time-transformed Hamiltonian. In this manner, new explicit symplectic algorithms are easily available. Unlike Runge-Kutta integrators, the newly proposed algorithms exhibit good long-term behavior in the conservation of Hamiltonian quantities when appropriate fixed coordinate time steps are considered. They are better than same-order implicit and explicit mixed symplectic algorithms and extended phase-space explicit symplectic-like methods in computational efficiency. The proposed idea on the construction of explicit symplectic integrators is suitable for not only the Kerr metric but also many other relativistic problems, such as a Kerr black hole immersed in a magnetic field, a Kerr-Newman black hole with an external magnetic field, axially symmetric core-shell systems, and five-dimensional black ring metrics.

Keywords: black hole physics; computational methods; computational astronomy
Conservation of Total Wave Action in the Expanding Solar Wind

The conservation of wave action in moving plasmas has been well known for over half a century. However, wave action is not conserved when multiple wave modes propagate and coexist close to the degeneration condition (where the sound speed equals the Alfvén speed, i.e., plasma β ~ 1). Here, we show that the violation of conservation is due to wave mode conversion, and that the total wave action summed over the interacting modes is still conserved. Though the result is general, we focus on MHD waves and identify three distinctive mode-conversion mechanisms, i.e., degeneracy, linear mode conversion, and resonance, and provide an intuitive physical picture for the mode-conversion processes. We use one-dimensional MHD simulations with the Expanding Box Model to simulate the nonlinear evolution of monochromatic MHD waves in the expanding solar wind. The simulation results validate the theory; total wave action therefore remains an interesting diagnostic for studies of waves and turbulence in the solar wind.

Keywords: magnetohydrodynamics; solar wind; plasma astrophysics; space plasmas
Li-rich Giants Identified from LAMOST DR8 Low-resolution Survey

A small fraction of giants possess photospheric lithium (Li) abundance higher than the value predicted by the standard stellar evolution models, and the detailed mechanisms of Li enhancement are complicated and lack a definite conclusion. In order to better understand the Li enhancement behaviors, a large and homogeneous Li-rich giant sample is needed. In this study, we designed a modified convolutional neural network model called Coord-DenseNet to determine the A(Li) of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) low-resolution survey (LRS) giant spectra. The precision is good on the test set: MAE = 0.15 dex, and σ = 0.21 dex. We used this model to predict the Li abundance of more than 900,000 LAMOST DR8 LRS giant spectra and identified 7768 Li-rich giants with Li abundances ranging from 2.0 to 5.4 dex, accounting for about 1.02% of all giants. We compared the Li abundance estimated by our work with those derived from high-resolution spectra. We found that the consistency was good if the overall deviation of 0.27 dex between them was not considered. The analysis shows that the difference is mainly due to the high A(Li) from the medium-resolution spectra in the training set. This sample of Li-rich giants dramatically expands the existing sample size of Li-rich giants and provides us with more samples to further study the formation and evolution of Li-rich giants.

Keywords: chemical abundances; stellar abundances; chemically peculiar giant stars; chemical enrichment; stellar evolution
Can Cold Jupiters Sculpt the Edge-of-the-multis?

Compact systems of multiple close-in super-Earths/sub-Neptunes (compact multis) are a ubiquitous outcome of planet formation. It was recently discovered that the outer edges of compact multis are located at smaller orbital periods than expected from geometric and detection biases alone, suggesting some truncation or transition in the outer architectures. Here we test whether this edge-of-the-multis might be explained in any part by distant giant planets in the outer regions (≳1 au) of the systems. We investigate the dynamical stability of observed compact multis in the presence of hypothetical giant (≳0.5 M Jup) perturbing planets. We identify what parameters would be required for hypothetical perturbing planets if they were responsible for dynamically sculpting the outer edges of compact multis. Edge-sculpting perturbers are generally in the range of P ~ 100-500 days for the average compact multi, with most between P ~ 200 and 300 days. Given the relatively close separation, we explore the detectability of the hypothetical edge-sculpting perturbing planets, finding that they would be readily detectable in transit and radial velocity data. We compare to observational constraints and find it unlikely that dynamical sculpting from distant giant planets contributes significantly to the edge-of-the-multis. However, this conclusion could be strengthened in future work by a more thorough analysis of the detection yields of the perturbing planets.

Keywords: exoplanet dynamics; exoplanet astronomy; exoplanet formation; exoplanet systems; exoplanets; extrasolar gaseous planets; exoplanet detection methods; exoplanet evolution; planetary dynamics; planetary system evolution
The Carbon-to-oxygen Ratio in Cool Brown Dwarfs and Giant Exoplanets. I. The Benchmark Late-T Dwarfs GJ 570D, HD 3651B, and Ross 458C

Measurements of the C/O ratio in brown dwarfs are lacking, in part due to past models adopting solar C/O only. We have expanded the ATMO 2020 atmosphere model grid to include nonsolar metallicities and C/O ratios in the T dwarf regime. We change the C/O ratio by altering either the carbon or oxygen elemental abundances, and we find that nonsolar abundances of these elements can be distinguished based on the shapes of the H and K bands. We compare these new models with medium-resolution (R ≈ 1700), near-infrared (0.8–2.4 μm) Gemini Near-Infrared Spectrograph (GNIRS) spectra of three benchmark late-T dwarfs, GJ 570D, HD 3651B, and Ross 458C. We find solar C/O ratios and best-fitting parameters (T eff, $\mathrm{log}(g)$ , Z) broadly consistent with other analyses in the literature based on low-resolution (R ∼ 100) data. The model-data discrepancies in the near-infrared spectra are consistent across all three objects. These discrepancies are alleviated when fitting the Y, J, H, and K bands individually, but the resulting best-fit parameters are inconsistent and disagree with the results from the full spectrum. By examining the model atmosphere properties we find this is due to the interplay of gravity and metallicity on H2–H2 collisionally induced absorption. We therefore conclude that there are no significant issues with the molecular opacity tables used in the models at this spectral resolution. Instead, deficiencies are more likely to lie in the model assumptions regarding the thermal structures. Finally, we find a discrepancy between the GNIRS, SpeX, and other near-infrared spectra in the literature of Ross 458C, indicating potential spectroscopic variability.

Keywords: brown dwarfs; t dwarfs; spectroscopy; near infrared astronomy; exoplanet atmospheres
Neutrinos and Asteroseismology of Stars over the Helium Flash

The helium flash, occurring in stars of 0.6-2.0 M ⊙ at the end of the red giant branch, is not observable via optical means due to the energy of the process being used to lift the core out of degeneracy. Neutrinos, which are linked to the ignition of reactions triggered during the flash and serve as the only cooling process in the inert core, can help characterize changes in internal structure. In this work, we create 18 stellar models across three mass and six metallicity values, chosen in the context of the stellar abundance problem, to compare the evolutionary path up to and probe the helium flash by conducting a detailed study of neutrino emission throughout this crucial phase of stellar evolution. We demonstrate how thermal neutrino emissions could have an imprint on global asteroseismic parameters and use them as an additional tool to infer the impact of compositional changes. We find that a precision of 0.3 μHz in the determination of Δν is enough to distinguish between between the two most prominent solar composition models and confirm that asteroseismic observation can be enough to classify a star as undergoing the process of helium subflashes. We also predict nuclear neutrino emission fluxes and their evolution for all relevant sources.

Keywords: asteroseismology; neutrino astronomy; red giant tip; stellar abundances
A Multi-instrument Study of the 2018 Hard-state-only Outburst of H1743-322

Distinct changes of the spectral and variability properties observed in black hole transients during a bright outburst deliver insight into the evolution of the accretion flow and accretion geometry. We investigated NICER and Swift monitoring observations of H 1743-322 during its 2018 outburst as well as NuSTAR and XMM-Newton data. The observed hardness ratios, rms amplitudes, and properties of quasiperiodic oscillations indicate that H 1743-322 showed another hard-state-only, or so-called "failed", outburst. The energy spectra obtained from NuSTAR and XMM-Newton data confirm the hard-state nature and give photon indices of ~1.7, typically found in the hard state of H 1743-322. The NICER monitoring observations allow us to follow the evolution of covariance ratios during a hard-state-only outburst of H 1743-322 for the first time. We confirm that the presence of flat covariance ratios at low energies is established early in the outburst and find that this shape is maintained throughout the outburst.

Keywords: stellar mass black holes; low-mass x-ray binary stars; close binary stars; transient sources; time series analysis
Constraining the Mass of the Emerging Galaxy Cluster SpARCS1049+56 at z = 1.71 with Infrared Weak Lensing

In the hierarchical structure formation model of the universe, galaxy clusters are assembled through a series of mergers. Accordingly, it is expected that galaxy clusters in the early universe are actively forming and dynamically young. Located at a high redshift of z = 1.71, SpARCS1049+56 offers a unique look into the galaxy cluster formation process. This cluster has been shown to be rich in cluster galaxies and to have intense star formation. Its high redshift pushes a weak-lensing analysis beyond the regime of the optical spectrum into that of the infrared. Equipped with deep Hubble Space Telescope Wide Field Camera 3 UVIS and IR observations, we present a weak-lensing characterization of SpARCS1049+56. As few IR weak-lensing studies have been performed, we discuss the details of point-spread function modeling and galaxy shape measurement for an IR weak-lensing procedure and the systematics that come with the territory. It will be critical to understand these systematics in future weak-lensing studies in the IR with the next-generation space telescopes such as the James Webb Space Telescope, Euclid, and WFIRST. Through a careful analysis, the mass distribution of this young galaxy cluster is mapped and the convergence peak is detected at a 3.3σ level. The weak-lensing mass of the cluster is estimated to be 3.5 ± 1.2 × 1014 M⊙ and is consistent with the mass derived from a mass-richness scaling relation. This mass is extreme for a cluster at such a high redshift and suggests that SpARCS1049+56 is rare in the standard ΛCDM universe.

Keywords: weak gravitational lensing; observational cosmology; dark matter; galaxy clusters; high-redshift galaxy clusters
Hard X-Ray Observations of the Hydrogen-poor Superluminous Supernova SN 2018hti with NuSTAR

Some hydrogen-poor superluminous supernovae are likely powered by a magnetar central engine, making their luminosity larger than common supernovae. Although a significant amount of X-ray flux is expected from the spin-down of the magnetar, direct observational evidence is still to be found, giving rise to the "missing energy" problem. Here we present NuSTAR observations of nearby SN 2018hti 2.4 yr (rest frame) after its optical peak. We expect that, by this time, the ejecta have become optically thin for photons more energetic than ~15 keV. No flux is detected at the position of the supernova down to F 10-30 keV = 9.0 × 10-14 erg cm-2 s-1, or an upper limit of 7.9 × 1041 erg s-1 at a distance of 271 Mpc. This constrains the fraction of bolometric luminosity from the putative spinning down magnetar to be f X ≲ 36% in the 10-30 keV range in a conservative case, f X ≲ 11% in an optimistic case.

Keywords: transient sources; supernovae; x-ray transient sources
The Photodissociation and Ionization Fronts in M17-SW Localized with FIFI-LS on Board SOFIA

To understand star formation rates, studying feedback mechanisms that regulate star formation is necessary. The radiation emitted by nascent massive stars play a significant role in feedback by photodissociating and ionizing their parental molecular clouds. To gain a detailed picture of the physical processes, we mapped the photodissociation region (PDR) M17-SW in several fine-structure and high-J CO lines with FIFI-LS, the far-infrared imaging spectrometer aboard SOFIA. An analysis of the CO and [O I]146 μm line intensities, combined with the far-infrared intensity, allows us to create a density and UV intensity map using a one-dimensional model. The density map reveals a sudden change in the gas density crossing the PDR. The strengths and limits of the model and the locations of the ionization and photodissociation front of the edge-on PDR are discussed.

Keywords: molecular clouds; infrared spectroscopy; photodissociation regions; far infrared astronomy