adsabs/SciX_UAT_keywords huggingface dataset:
Comparison of Electron Capture Rates in the N = 50 Region using 1D Simulations of Core-collapse Supernovae

Recent studies have highlighted the sensitivity of core-collapse supernovae (CCSNe) models to electron-capture (EC) rates on neutron-rich nuclei near the N = 50 closed-shell region. In this work, we perform a large suite of one-dimensional CCSN simulations for 200 stellar progenitors using recently updated EC rates in this region. For comparison, we repeat the simulations using two previous implementations of EC rates: a microphysical library with parametrized N = 50 rates (LMP), and an older independent-particle approximation (IPA). We follow the simulations through shock revival up to several seconds post-bounce, and show that the EC rates produce a consistent imprint on CCSN properties, often surpassing the role of the progenitor itself. Notable impacts include the timescale of core collapse, the electron fraction and mass of the inner core at bounce, the accretion rate through the shock, the success or failure of revival, and the properties of the central compact remnant. We also compare the observable neutrino signal of the neutronization burst in a DUNE-like detector, and find consistent impacts on the counts and mean energies. Overall, the updated rates result in properties that are intermediate between LMP and IPA, and yet slightly more favorable to explosion than both.

Keywords: core-collapse supernovae; supernova neutrinos; neutrino astronomy; reaction rates
Evolution of Accretion Modes between Spectral States Inferred from Spectral and Timing Analysis of Cygnus X-1 with Insight-HXMT Observations

We execute a detailed spectral-timing study of Cygnus X-1 in the low/hard, intermediate, and high/soft states with observations from the Hard X-ray Modulation Telescope. The broadband energy spectra fit well with the "truncated disk model": the inner boundary of the accretion disk stays within ~10 R g and moves inward as the source softens. Through studying the power density spectrum, rms, and Fourier frequency component resolved spectroscopy, we find that the X-ray variations are generated in two different regions for each state. We discover that the major contribution to the X-ray variation is from the hot corona rather than the accretion disk. We suggest a scenario with different coronal geometry for each state based on the truncated disk geometry in which the corona envelops the disk to form a sandwich geometry in the low/hard state, and then gradually moves away from the disk in a direction perpendicular to the disk until it forms a jet-like geometry in the high/soft state.

Keywords: high mass x-ray binary stars
Heating of Heavy Ions in Low-beta Compressible Turbulence

Enhancement of minor ions such as 3He and heavy ions in flare-associated solar energetic particle (SEP) events remains one of the major puzzles in heliophysics. In this work, we use 3D hybrid simulations (kinetic protons and fluid electrons) to investigate particle energization in a turbulent low-beta environment similar to solar flares. It is shown that in this regime the injected large-amplitude Alfvén waves develop into compressible and anisotropic turbulence, which efficiently heats thermal ions of different species. We find that temperature increase of heavy ions is inversely proportional to the charge-to-mass ratio, which is consistent with observations of impulsive SEP events. Further analysis reveals that ions are energized by interacting with nearly perpendicular magnetosonic waves near a proton inertial scale.

Keywords: solar energetic particles; n-body simulations; interplanetary turbulence; alfven waves; space plasmas
A CO-to-H2 Ratio of ≈10-5 toward the Herbig Ae Star HK Ori

Measurements of gas mass in protoplanetary gas disks form the basis for estimating the conditions of planet formation. Among the most important constraints derived from disk diagnostics are the abundances of gas-phase species critical for understanding disk chemistry. Toward this end, we present direct line-of-sight measurements of H2 and CO, employing UV absorption spectroscopy from Hubble Space Telescope Cosmic Origins Spectrograph to characterize disk composition, molecular excitation temperatures, and spatial distribution in the circumstellar material around the Herbig Ae stars HK Ori and T Ori. We observe strong CO (N(CO) = 1015.5 cm-2; Trot(CO) = 19 K) and H2 (N(H2) = 1020.34 cm-2; Trot(H2) = 141 K) absorption toward HK Ori with a CO/H2 ratio of (≡N(CO)/N(H2)) = ${1.3}_{-0.7}^{+1.6}$ <!-- --> × 10-5. These measurements place direct empirical constraints on the CO-to-H2 conversion factor in the disk around a Herbig Ae star for the first time, although there is uncertainty concerning the exact viewing geometry of the disk. The spectra of T Ori show CO (N(CO) = 1014.9 cm-2; Trot(CO) = 124 K) absorption. Interestingly, we do not detect any H2 absorption toward this star (N(H2) < 1015.9 cm-2). We discuss a potential scenario for the detection of CO without H2, which deserves further investigation. The low abundance ratio measured around HK Ori suggests significant depletion of CO in the circumstellar gas, which conforms with the handful of other recent CO abundance measurements in protoplanetary disks.

Keywords: circumstellar disks; ultraviolet astronomy; star formation
The Effects of Rotation, Metallicity, and Magnetic Field on the Islands of Failed Supernovae

Failed supernovae (FSN) are a possible channel for the formation of heavy stellar-mass black holes (M BH > ~30 M ⊙). However, the effects of metallicity, rotation, and magnetic field on the islands of explodabilty of massive stars are not clear. Here, we simulate the stellar structure and evolution in the mass range between 6 and 55 M ⊙ with different initial rotational velocities, metallicities, and magnetic fields from zero-age main sequence (ZAMS) to pre-collapse. We find that the rapid rotating stars can remain lower 12C mass fraction at the time of C ignition, which allows the transition, from convective carbon burning to radiative burning, to occur at lower M ZAMS than those from stars without rotation. However, the rapid rotation is unfavorable for FSN occurring but is conducive to long gamma-ray bursts (lGRBs) because it results in the specific angular momentum in the CO core being greater than the last stable orbit at core collapse. The increasing metallicity does not affect FSN islands, but high metallicity inhibits rotational mixing and is unfavorable for producing lGRBs. A magnetic field can constrain the mass-loss rate even for rapid rotating stars, resulting in higher mass at pre-collapse. The magnetic braking triggered by the magnetic field can reduce the rotation velocity for high-metallicity models, which decreases the specific angular momentum in the CO core and is favorable for FSN occurring. We suggest that the heavy-mass black holes detected by LIGO may originate from rapidly rotating massive stars with strong magnetic fields, rather than those with very low metallicity.

Keywords: stellar evolution; stellar rotation; massive stars; magnetic fields
Revisiting the Sun's Strong Differential Rotation along Radial Lines

Current state-of-the-art models of the solar convection zone consist of solutions to the Navier-Stokes equations in rotating, 3D spherical shells. Such models are highly sensitive to the choice of boundary conditions. Here we present two suites of simulations differing only in their outer thermal boundary condition, which is either one of fixed entropy (FE) or fixed flux (FF; corresponding to a fixed gradient in the entropy). We find that the resulting differential rotation is markedly different between the two sets. The FF simulations have strong differential rotation contrast and isocontours tilted along radial lines (in good agreement with the Sun's interior rotation revealed by helioseismology), whereas the FE simulations have weaker contrast and contours tilted in the opposite sense. We examine in detail the force balances in our models and find that the poleward transport of heat by Busse columns drives a thermal wind responsible for the different rotation profiles. We conclude that the Sun's strong differential rotation along radial lines may result from the solar emissivity being invariant with latitude (which is similar to the FF condition in our models) and the poleward transport of heat by Busse columns. In future work on convection in the solar context, we strongly advise modelers to use an FF outer boundary condition.

Keywords: solar differential rotation; solar convective zone; astrophysical fluid dynamics; hydrodynamical simulations; stellar convective zones; stellar rotation; von zeipel theorem
Evolution of Electron Acceleration by Corotating Interaction Region Shocks at 1 au

We present the first observations of in situ electron acceleration at corotating interaction region (CIR) shocks near 1 au, utilizing measurements from Wind and Magnetospheric Multiscale (MMS) mission in the interplanetary medium. As the forward (reverse) shock of the 2018 January CIR (the 2020 February CIR) moves from Wind at [206, 92, ‑7]R E ([257, 25, 3]R E ) to MMS1 at [24, 2, 7]R E ([25, 3, 0.5]R E ), the shock's thickness becomes 8 (3) times thinner, but the convective electric field E drift gets weaker (stronger) along the shock; both the upstream and shocked suprathermal electrons exhibit a flatter flux energy spectrum, while the electron shock acceleration becomes less (more) significant. For the shocked suprathermal electrons with significant flux enhancement, the flux ratio across the shock appears to peak in the direction perpendicular to the magnetic field. Therefore, the CIR shock acceleration of solar wind suprathermal electrons at 1 au exhibits an efficiency increasing with the E drift strength. These results also suggest that such acceleration through the interplanetary medium can contribute to the formation of solar wind suprathermal electrons.

Keywords: interplanetary particle acceleration; interplanetary shocks; corotating streams
Modeling CO Line Profiles in Shocks of W28 and IC 443

Molecular emission arising from the interactions of supernova remnant (SNR) shock waves and molecular clouds provide a tool for studying the dispersion and compression that might kick-start star formation as well as understanding cosmic-ray production. Purely rotational CO emission created by magnetohydrodynamic shock in the SNR-molecular cloud interaction is an effective shock tracer, particularly for slow-moving, continuous shocks into cold inner clumps of the molecular cloud. In this work, we present a new theoretical radiative transfer framework for predicting the line profile of CO with the Paris-Durham 1D shock model. We generated line profile predictions for CO emission produced by slow, magnetized C shocks into gas of density ~104 cm-3 with shock speeds of 35 and 50 km s-1. The numerical framework to reproduce the CO line profile utilizes the large velocity gradient (LVG) approximation and the omission of optically thick plane-parallel slabs. With this framework, we generated predictions for various CO spectroscopic observations up to J = 16 in SNRs W28 and IC 443, obtained with SOFIA, IRAM-30 m, APEX, and KPNO. We found that CO line profile prediction offers constraints on the shock velocity and pre-shock density independent of the absolute line brightness and requires fewer CO lines than diagnostics using a rotational excitation diagram.

Keywords: supernova remnants; interstellar medium; magnetohydrodynamics; radiative transfer
Contribution of Neutrino-dominated Accretion Flows to the Cosmic MeV Neutrino Background

Neutrino-dominated accretion flows (NDAFs) are one of the important MeV neutrino sources and significantly contribute to the cosmic diffuse neutrino background. In this paper, we investigate the spectrum of the diffuse NDAF neutrino background (DNNB) by fully considering the effects of the progenitor properties and initial explosion energies based on core-collapse supernova (CCSN) simulations, and estimate the detectable event rate by the Super-Kamiokande detector. We find that the predicted background neutrino flux is mainly determined by the typical CCSN initial explosion energy and progenitor metallicity. For the optimistic cases, in which the typical initial explosion energy is low, the diffuse flux of the DNNB is comparable to the diffuse supernova neutrino background, which might be detected by upcoming larger neutrino detectors, such as Hyper-Kamiokande, the Jiangmen Underground Neutrino Observatory, and the Deep Underground Neutrino Experiment. Moreover, the strong outflows from NDAFs could dramatically decrease their contribution to the neutrino background.

Keywords: accretion; black holes; core-collapse supernovae; massive stars; neutrino astronomy
TeV Emission of Galactic Plane Sources with HAWC and H.E.S.S.

The High Altitude Water Cherenkov (HAWC) observatory and the High Energy Stereoscopic System (H.E.S.S.) are two leading instruments in the ground-based very-high-energy γ-ray domain. HAWC employs the water Cherenkov detection (WCD) technique, while H.E.S.S. is an array of Imaging Atmospheric Cherenkov Telescopes (IACTs). The two facilities therefore differ in multiple aspects, including their observation strategy, the size of their field of view, and their angular resolution, leading to different analysis approaches. Until now, it has been unclear if the results of observations by both types of instruments are consistent: several of the recently discovered HAWC sources have been followed up by IACTs, resulting in a confirmed detection only in a minority of cases. With this paper, we go further and try to resolve the tensions between previous results by performing a new analysis of the H.E.S.S. Galactic plane survey data, applying an analysis technique comparable between H.E.S.S. and HAWC. Events above 1 TeV are selected for both data sets, the point-spread function of H.E.S.S. is broadened to approach that of HAWC, and a similar background estimation method is used. This is the first detailed comparison of the Galactic plane observed by both instruments. H.E.S.S. can confirm the γ-ray emission of four HAWC sources among seven previously undetected by IACTs, while the three others have measured fluxes below the sensitivity of the H.E.S.S. data set. Remaining differences in the overall γ-ray flux can be explained by the systematic uncertainties. Therefore, we confirm a consistent view of the γ-ray sky between WCD and IACT techniques.

Keywords: high energy astrophysics
The MESAS Project: ALMA Observations of the F-type Stars γ Lep, γ Vir A, and γ Vir B

The spectrum of stars in the submillimeter to centimeter wavelength range remains poorly constrained due to a lack of data for most spectral types. An accurate characterization of stellar emission in this regime is needed to test stellar atmosphere models, and is also essential for revealing emission associated with unresolved circumstellar debris. We present Atacama Large Millimeter/submillimeter Array observations of the three nearby, main-sequence, debris-poor, F-type stars γ Lep, γ Vir A, and γ Vir B at 0.87 and 1.29 mm. We use these data to constrain semiempirical atmospheric models. We discuss the atmospheric structure of these stars, explore potential short-term variability, and the potential impact on debris disk studies. These results are part of an ongoing campaign to obtain long wavelength observations of debris-poor stars, entitled Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths.

Keywords: debris disks; stellar atmospheres; submillimeter astronomy; millimeter astronomy; radio continuum emission
Multiple Rings and Asymmetric Structures in the Disk of SR 21

Crescent-like asymmetric dust structures discovered in protoplanetary disks indicate dust aggregations. Thus, researching these structures helps us understand the planet formation process. Here we analyze ALMA data of the protoplanetary disk around the T-Tauri star SR 21, which has asymmetric structures that were detected in previous submillimeter observations. Imaged at ALMA Band 6 (1.3 mm) with a spatial resolution of about 0.″04, the disk is found to consist of two rings and three asymmetric structures, with two of the asymmetric structures being in the same ring. Compared to the Band 6 image, the Band 3 (2.7 mm) image also shows the three asymmetric structures, but with some clumps. The elongated asymmetric structures in the outer ring could be due to the interactions of a growing planet. Based on fitting the Band 3 and Band 6 dust continuum data, two branches of solutions for the maximum dust size in the disk are suggested: one is larger than 1 mm, and the other is smaller than 300 μm. High-resolution continuum observations at longer wavelengths as well as polarization observations can help break the degeneracy. We also suggest that the prominent spiral previously identified in VLT/SPHERE observations south of the star at 0.″25 may be the scattered-light counterpart of the inner arc, and the structure is a dust-trapping vortex in nature. The discovered features in SR 21 make it a good target for studying the evolution of asymmetric structures and planet formation.

Keywords: protoplanetary disks; planet formation
The Effect of Metallicity on the Formation of Massive Black Holes through Stellar Collisions in Young Massive Star Clusters

Dynamical interactions facilitated by the high densities in massive star clusters can lead to large numbers of stellar collisions and unique stellar evolution pathways not possible for stars evolving in isolation. Using N-body cluster models, we study the role of stellar collisions in the formation of massive black holes, specifically studying the effect of stellar metallicity on this process. We show that at high metallicity (up to solar), the number of massive black holes formed may be reduced by up to a factor of ten compared to low-metallicity clusters. We also examine the role of collisions in the production of pair-instability supernovae and predict event rates of these transients in the local universe.

Keywords: astrophysical black holes; globular star clusters; young star clusters; supernovae
Early Evolution of Spin Direction in Dark Matter Halos and the Effect of the Surrounding Large-scale Tidal Field

It is usually assumed that the angular momentum (AM) of dark matter halos arises during the linear stages of structure formation, as a consequence of the coupling between the proto-haloes' shape and the tidal field produced by their surrounding density perturbations. This approach, known as linear tidal torque theory (TTT), has been shown to make fairly good predictions about the mean evolution of both the AM amplitude and orientation up to approximately the time when the proto-haloes collapse. After this point, proto-haloes are increasingly affected by nonlinear processes that are not taken into account by the model. However, it has been seen in numerical simulations that, even at very early stages, the AM of proto-haloes is systematically reoriented toward perpendicularity with respect to the forming cosmic filaments, in contradiction with the fixed direction expected from the TTT. In this work we present a novel analytical approach that introduces an anisotropic scaling factor to the standard TTT equations, which allows the AM orientation to change in time, even during the linear regime. The amplitude and direction of this shift depend on the large scale tidal field around the forming proto-haloes. Our results significantly improve the predictions for the AM direction up to the time of protohalo collapse and, in some cases, even further in time. *Thesis work conducted at Facultad de Matemática, Astronomía, Física y Computación, Universidad Nacional de Córdoba, Córdoba, Argentina. † PhD Thesis directed by Manuel Merchán; PhD Degree awarded 2023 July 31.

Keywords: large-scale structure of the universe; galaxy dark matter halos; intergalactic filaments; galaxy formation
The Surface Abundances of 17 Com B: A Test for Self-consistent Evolutionary Models

Elemental abundances are derived for 17 Com B for 16 elements. They reinforce the Am status of this star. We show that the measured abundances are properly reproduced by stellar models including atomic diffusion and a parametrized turbulent diffusion coefficient. This parameterization agrees with that used in previous studies of Am stars.

Keywords: chemically peculiar stars; chemical abundances; stellar evolution; stellar evolutionary models
Shock Cooling and Possible Precursor Emission in the Early Light Curve of the Type II SN 2023ixf

We present the densely sampled early light curve of the Type II supernova (SN) 2023ixf, first observed within hours of explosion in the nearby Pinwheel Galaxy (Messier 101; 6.7 Mpc). Comparing these data to recently updated models of shock-cooling emission, we find that the progenitor likely had a radius of 410 ± 10 R ⊙. Our estimate is model dependent but consistent with a red supergiant. These models provide a good fit to the data starting about 1 day after the explosion, despite the fact that the classification spectrum shows signatures of circumstellar material around SN 2023ixf during that time. Photometry during the first day after the explosion, provided almost entirely by amateur astronomers, does not agree with the shock-cooling models or a simple power-law rise fit to data after 1 day. We consider the possible causes of this discrepancy, including precursor activity from the progenitor star, circumstellar interaction, and emission from the shock before or after it breaks out of the stellar surface. The very low luminosity (-11 mag > M > -14 mag) and short duration of the initial excess lead us to prefer a scenario related to prolonged emission from the SN shock traveling through the progenitor system.

Keywords: circumstellar matter; core-collapse supernovae; red supergiant stars; stellar mass loss; supernovae; type ii supernovae
SN 2019ein: New Insights into the Similarities and Diversity among High-velocity Type Ia Supernovae

We present optical observations of the Type Ia supernova (SN) 2019ein, starting two days after the estimated explosion date. The spectra and light curves show that SN 2019ein belongs to a high-velocity (HV) and broad-line group with a relatively rapid decline in the light curves (Δm15(B) = 1.36 ± 0.02 mag) and a short rise time (15.37 ± 0.55 days). The Si II λ6355 velocity, associated with a photospheric component but not with a detached high-velocity feature, reached ∼20,000 km s-1 12 days before the B-band maximum. The line velocity, however, decreased very rapidly and smoothly toward maximum light, to ∼13,000 km s-1, which is relatively low among HV SNe. This indicates that the speed of the spectral evolution of HV SNe Ia is correlated with not only the velocity at maximum light, but also the light-curve decline rate, as is the case for normal-velocity (NV) SNe Ia. Spectral synthesis modeling shows that the outermost layer at >17,000 km s-1 is well described by an O-Ne-C burning layer extending to at least 25,000 km s-1, and there is no unburnt carbon below 30,000 km s-1; these properties are largely consistent with the delayed detonation scenario and are shared with the prototypical HV SN 2002bo despite the large difference in Δm15(B). This structure is strikingly different from that derived for the well-studied NV SN 2011fe. We suggest that the relation between the mass of 56Ni (or Δm15) and the extent of the O-Ne-C burning layer provides an important constraint on the explosion mechanism(s) of HV and NV SNe.

Keywords: type ia supernovae; supernovae