adsabs/SciX_UAT_keywords huggingface dataset:
Toward an Accurate Description of an Accretion-induced Collapse and the Associated Ejected Mass

We revisit the accretion-induced collapse (AIC) process, in which a white dwarf collapses into a neutron star. We are motivated by the persistent radio source associated with the fast radio burst FRB 121102, which was explained by Waxman as a weak stellar explosion with a small (∼10-5 M⊙) mildly relativistic mass ejection that may be consistent with AIC. Additionally, the interaction of the relatively low ejected mass with a pre-collapse wind might be related to fast optical transients. The AIC is simulated with a one-dimensional, Lagrangian, Newtonian hydrodynamic code. We put an emphasis on accurately treating the equation of state and the nuclear burning, which is required for any study that attempts to accurately simulate AIC. We leave subjects such as neutrino physics and general relativity corrections for future work. Using an existing initial profile and our own initial profiles, we find that the ejected mass is ∼10-2 to 10-1 M⊙ over a wide range of parameters, and we construct a simple model to explain our results.

Keywords: hydrodynamics; hydrodynamical simulations; neutron stars; white dwarf stars; radio transient sources
Molecular Bubble and Outflow in S Mon Revealed by Multiband Data Sets

We identify a molecular bubble, and study the star formation and its feedback in the S Mon region, using multiple molecular lines, young stellar objects (YSOs), and infrared data. We revisit the distance to S Mon, ∼722 ± 9 pc, using Gaia Data Release 3 parallaxes of the associated Class II YSOs. The bubble may be mainly driven by a massive binary system (namely 15 Mon), the primary of which is an O7V-type star. An outflow is detected in the shell of the bubble, suggesting ongoing star formation activities in the vicinity of the bubble. The total wind energy of the massive binary star is 3 orders of magnitude higher than the sum of the observed turbulent energy in the molecular gas and the kinetic energy of the bubble, indicating that stellar winds help to maintain the turbulence in the S Mon region and drive the bubble. We conclude that the stellar winds of massive stars have an impact on their surrounding environment.

Keywords: young stellar objects; interstellar molecules; stellar wind bubbles
Magnetization of Relativistic Current-carrying Jets with Radial Velocity Shear

Astrophysical jets, launched from the immediate vicinity of accreting black holes, carry away large amounts of power in a form of bulk kinetic energy of jet particles and electromagnetic flux. Here we consider a simple analytical model for relativistic jets at larger distances from their launching sites, assuming a cylindrical axisymmetric geometry with a radial velocity shear, and purely toroidal magnetic field. We argue that as long as the jet plasma is in magnetohydrostatic equilibrium, such outflows tend to be particle dominated, i.e., the ratio of the electromagnetic to particle energy flux, integrated over the jet cross-sectional area, is typically below unity, σ < 1. At the same time, for particular magnetic and radial velocity profiles, magnetic pressure may still dominate over particle pressure for certain ranges of the jet radius, i.e., the local jet plasma parameter β pl < 1, and this may be relevant in the context of particle acceleration and production of high-energy emission in such systems. The jet magnetization parameter can be elevated up to the modest values of $\sigma \lesssim { \mathcal O }(10)$ only in the case of extreme gradients or discontinuities in the gaseous pressure, and a significantly suppressed velocity shear. Such configurations, which consist of a narrow, unmagnetized jet spine surrounded by an extended, force-free layer, may require an additional poloidal field component to stabilize them against current-driven oscillations, but even this will not substantially elevate their σ parameter.

Keywords: jets; plasma jets; magnetohydrodynamics
UMaMI: A New Frontiers-style Mission Concept to Explore the Uranian System

With the public and scientific community's growing interest in ocean worlds, the icy moons of Uranus offer an ideal opportunity to explore a native ice giant satellite system. Although it is uncertain whether any of the Uranian moons currently host subsurface oceans, there is tantalizing evidence-including geologically young surface features and volatiles that are not stable-that this could be the case, making these objects possible ocean worlds in their own right. Determining whether subsurface oceans are present in the interiors of these moons would increase our understanding of the conditions under which subsurface oceans are formed and maintained over the history of the solar system. The presence and stability of a subsurface ocean in the interiors of any icy body is key to identifying its potential as a habitable environment. In this work, we describe a midsize (New Frontiers class) mission concept: the Uranian Magnetosphere and Moons Investigator. The magnetosphere and moons are tightly coupled parts of the Uranian system, complementary to study, and best analyzed together in order to investigate the Uranian moons as potential ocean worlds. Additionally, this mission concept includes study of Uranus's unique rings and magnetosphere-solar wind interaction. With a future, more detailed trade study, there also could be opportunities for studies of Uranus itself.

Keywords: uranian satellites; uranus; planetary science
Nearby SNR: A Possible Common Origin of Multi-messenger Anomalies in the Spectra, Ratios, and Anisotropy of Cosmic Rays

Multi-messenger anomalies, including spectral hardening or excess of nuclei, leptons, ratios of $\bar{p}/p$ and B/C, and anisotropic reversal, have been observed in past years. The AMS-02 experiment also revealed different spectral breaks for positrons and electrons at 284 GeV and beyond tera electron volts, respectively. It is natural to ask whether all those anomalies originate from one unified physical scenario. In this work, the spatially dependent propagation (SDP) with a nearby supernova remnant (SNR) source is adopted to reproduce the abovementioned anomalies. There possibly exists a dense molecular cloud (DMC) around SNRs and the secondary particles can be produced by pp collision or fragmentation between the accelerated primary cosmic rays and DMC. As a result, the spectral hardening for primary and secondary particles and ratios of B/C and $\bar{p}/p$ can be well reproduced. Due to the energy loss at the source age of 330 kyr, the characteristic spectral break-off for a primary electron is at about 1 TeV as hinted at by the measurements. The secondary positrons and electrons from charged pion take up 5% of energy from their mother particles, so the positron spectrum has a break-off at ~250 GeV. Therefore, the different spectral breaks for positrons and electrons together with other anomalies can be fulfilled in this unified physical scenario. More interesting is that we also obtain the featured structures as spectral break-offs at 5 TeV for secondary particles of Li, Be, and B, which can be used to verify our model. We hope that those tagged structures can be observed by the new generation of spaceborne experiment HERD in the future.

Keywords: cosmic ray sources; secondary cosmic rays; cosmic anisotropy; supernova remnants
Point-source Contribution to the Diffuse X-Ray Background below 1 keV and Its Effect on Our Understanding of the Circumgalactic Medium

We studied the spectral signature of different components of the diffuse X-ray background (DXB), including Local Hot Bubble, solar wind charge exchange, galactic halo, and typically unresolved point sources (galaxies and active galactic nuclei), in the direction of the Chandra Deep Field South using the 4 Ms XMM-Newton survey and Chandra 4 Ms Source Catalog. In this paper, we present our results showing how the different components contribute to the DXB below 1 keV. In particular, we have found that ~6% of the emission at $\tfrac{3}{4}$ keV (all-sky average value ≈3 × 10-3 cm-6 pc), which is typically associated with galactic halo (GH) and circumgalactic medium (CGM), is, in fact, due to emission from typically unresolved galaxies. We will discuss the effect that this has on our understanding of GH and CGM and to our understanding of the missing CGM baryons.

Keywords: diffuse x-ray background; galaxies; milky way stellar halo
Nearby SN-associated GRB 190829A: Environment, Jet Structure, and VHE Gamma-Ray Afterglows

We present a self-consistent paradigm to interpret the striking features of nearby low-luminosity GRB 190829A. Its prompt gamma-ray lightcurve has two separated pulses. We propose that the interaction of the hard prompt gamma-ray photons ( ${E}_{p}={624}_{-303}^{+2432}$ keV) of its initial pulse with the dusty medium (AV = 2.33) not only results in the second soft gamma-ray pulse (Ep ~ 12 keV) but also makes a pre-accelerated e± -rich medium shell via the γγ annihilation. In this paradigm, we show that the observed radio, optical, and X-ray afterglow lightcurves are well-fitted with the forward shock model. Its jet is almost isotropic (θj > 1.0 rad) with a Lorentz factor of ~35, and the electron density of the e± -rich medium shell is ~15 cm-3, which is about seven times higher than the electron density of its normal surrounding medium. The GRB ejecta catches up with and propagates into the e± -rich medium shell at a region of R = (4.07-6.46) × 1016 cm. This results in a bright afterglow bump at ~103 seconds after the GRB trigger. The predicted very high energy (VHE) gamma-ray emission from the synchrotron self-Compton process agrees with the H.E.S.S. observation. The derived broadband spectral energy distribution shows that GRB 190829A like nearby GRBs would be promising targets of the VHE gamma-ray telescopes, such as H.E.S.S., MAGIC, and CTA (Cerenkov Telescope Arrays).

Keywords: gamma-ray bursts
In the Trenches of the Solar-Stellar Connection. VII. Wilson-Bappu 2022

The Wilson-Bappu effect (WBE) is a remarkable correlation between the width of the chromospheric emission core of the Ca II 3934 Å K line and stellar absolute visual magnitude over an astonishing range, from diminutive red dwarfs to bloated yellow supergiants. The WBE signifies a deep connection between the nonclassical, mechanically heated chromosphere and fundamental stellar properties. The present study considers the parallel WBE in the analogous Mg II k line at 2796 Å, utilizing near-ultraviolet spectra from Hubble Space Telescope (HST), and stellar parameters mainly derived from Gaia. The final sample is 300 stars (301 including the Sun). The high cosmic abundance of magnesium allowed Mg II k emissions to be recovered in the warmer F-types, at the edge of convection and chromospheric activity, and in low-activity Sunlike dwarfs-situations in which Ca II K might be too weak to measure. Nevertheless, the derived slope of the Mg II WBE was similar to previous reports based on the K line; as well as other Mg II efforts with smaller samples of pre-HST spectra. Further, a decomposition of the Mg II WBE in temperature, gravity, activity, and metallicity yielded similar results to previous Ca II work, but with the greater clarity afforded by the large, diverse HST sample. Parametric dependences of the k-line WBE match, tolerably well, predictions based on the "ionization-valve" theory of chromospheric structure. In the end, the WBE is not merely an astrophysical curiosity, but rather informs the question of how chromospheres-arguably the central bastion of nonclassical heating-have come to be.

Keywords: stellar spectral lines; stellar radii; stellar masses; stellar luminosities; stellar effective temperatures; stellar activity; solar activity; stellar chromospheres
A New Study on a Type Iax Stellar Remnant and its Probable Association with SN 1181

We report observations and modeling of the stellar remnant and presumed double-degenerate merger of Type Iax supernova Pa 30, which is the probable remnant of SN 1181 AD. It is the only known bound stellar SN remnant and the only star with Wolf-Rayet features that is neither a planetary nebula central star nor a massive Population I progenitor. We model the unique emission-line spectrum with broad, strong O VI and O VIII lines as a fast stellar wind and shocked, hot gas. Non-LTE wind modeling indicates a mass-loss rate of ~10-6 M ⊙ yr-1 and a terminal velocity of ~15,000 km s-1, consistent with earlier results. O VIII lines indicate shocked gas temperatures of T ≃ 4 MK. We derive a magnetic field upper limit of B < 2.5 MG, below earlier suggestions. The luminosity indicates a remnant mass of 1.0-1.65 M ⊙ with ejecta mass 0.15 ± 0.05 M ⊙. Archival photometry suggests the stellar remnant has dimmed by ~0.5 mag over 100 yr. A low Ne/O < 0.15 argues against an O-Ne white dwarf in the merger. A cold dust shell is only the second detection of dust in an SN Iax and the first of cold dust. Our ejecta mass and kinetic energy estimates of the remnant are consistent with Type Iax extragalactic sources.

Keywords: supernova remnants; type ia supernovae; white dwarf stars; stellar mergers
TYCHO: Realistically Simulating Exoplanets within Stellar Clusters. I. Improving the Monte Carlo Approach

To fully understand the diverse population of exoplanets, we must study their early lives within open clusters, the birthplace of most stars with masses >0.5M⊙ (including those currently in the field). Indeed, when we observe planets within clustered environments, we notice highly eccentric and odd systems that suggest the importance of dynamical pathways created by interactions with additional bodies (as in the case of HD 285507b). However, it has proven difficult to investigate these effects, as many current numerical solvers for the multi-scale N-body problem are simplified and limited in scope. To remedy this, we aim to create a physically complete computational solution to explore the role of stellar close encounters and interplanetary interactions in producing the observed exoplanet populations for both open cluster stars and field stars. We present a new code, TYCHO, which employs a variety of different computational techniques, including multiple N-body integration methods, close encounter handling, modified Monte Carlo scattering experiments, and a variety of empirically informed initial conditions. We discuss the methodology in detail, and its implementation within the AMUSE software framework. Approximately 1% of our systems are promptly disrupted by star-star encounters contributing to the rogue planets occurrence rate. Additionally, we find that close encounters which that perturb long-period planets lead to 38.3% of solar-system-like planetary systems becoming long-term unstable.

Keywords: exoplanet dynamics; computational methods; open star clusters; exoplanet systems; interstellar dynamics
Big Bang Nucleosynthesis with f(R) Gravity Scalarons and Astrophysical Consequences

f(R) gravity is one of the serious alternatives of general relativity with a large range of astronomical consequences. In this work, we study Big Bang nucleosynthesis (BBN) in f(R) gravity theory. We consider a modification to gravity due to the existence of primordial black holes (PBHs) in the radiation era that introduce additional degrees of freedom known as scalarons. We calculate the light element abundances by using the BBN code PArthENoPE. It is found that for a range of scalaron mass (2.2 ‑ 3.5) × 104 eV, the abundance of lithium is lowered by 3‑4 times the value predicted by general relativistic BBN, which is a level desired to address the cosmological lithium problem. For the above scalaron mass range, the helium abundance is within the observed bound. However, the deuterium abundance is found to be increased by 3‑6 times the observed primordial abundance. It calls for a high efficiency of stellar formation and evolution processes for the destruction of primordial deuterium, which is suggested as possible in scalaron gravity. A novel relation between scalaron mass and black hole mass has been used to show that the above scalaron mass range corresponds to PBHs of subplanetary mass (∼1019 g) serving as one of the potential candidates of nonbaryonic dark matter. We infer Big Bang equivalence of power-law f(R) gravity with PBHs that are detectable with upcoming gravitational wave detectors.

Keywords: big bang nucleosynthesis; cosmology; dark energy; gravitation
Atmospheric Metallicity and C/O of HD 189733 b from High-resolution Spectroscopy

We present high-resolution K-band emission spectra of the quintessential hot Jupiter HD 189733 b from the Keck Planet Imager and Characterizer. Using a Bayesian retrieval framework, we fit the dayside pressure-temperature profile, orbital kinematics, mass-mixing ratios of H2O, CO, CH4, NH3, HCN, and H2S, and the 13CO/12CO ratio. We measure mass fractions of ${\mathrm{logH}}_{2}{\rm{O}}=-{2.0}_{-0.4}^{+0.4}$ and $\mathrm{logCO}=-{2.2}_{-0.5}^{+0.5}$ , and place upper limits on the remaining species. Notably, we find logCH4 < -4.5 at 99% confidence, despite its anticipated presence at the equilibrium temperature of HD 189733 b assuming local thermal equilibrium. We make a tentative (~3σ) detection of 13CO, and the retrieved posteriors suggest a 12C/13C ratio similar to or substantially less than the local interstellar value. The possible 13C enrichment would be consistent with accretion of fractionated material in ices or in the protoplanetary disk midplane. The retrieved abundances correspond to a substantially substellar atmospheric C/O = 0.3 ± 0.1, while the carbon and oxygen abundances are stellar to slightly superstellar, consistent with core-accretion models which predict an inverse correlation between C/O and metallicity. The specific combination of low C/O and high metallicity suggests significant accretion of solid material may have occurred late in the formation process of HD 189733 b.

Keywords: hot jupiters; exoplanets; high resolution spectroscopy; exoplanet atmospheric composition; exoplanet atmospheres
Mitigating Bias in CMB B-modes from Foreground Cleaning Using a Moment Expansion

One of the primary challenges facing upcoming cosmic microwave background (CMB) polarization experiments aiming to measure the inflationary B-mode signal is the removal of polarized foregrounds. The thermal dust foreground is often modeled as a single modified blackbody; however, overly simplistic foreground models can bias measurements of the tensor-to-scalar ratio r. As CMB polarization experiments become increasingly sensitive, thermal dust emission models must account for greater complexity in the dust foreground while making minimal assumptions about the underlying distribution of dust properties within a beam. We use Planck dust temperature data to estimate the typical variation in dust properties along the line of sight and examine the impact of these variations on the bias in r if a single modified blackbody model is assumed. We then assess the ability of the moment method to capture the effects of spatial averaging and to reduce bias in the tensor-to-scalar ratio for different possible toy models of dust emission. We find that the expected bias due to temperature variations along the line of sight is significant compared to the target sensitivities of future CMB experiments, and that the use of the moment method could reduce bias as well as shed light into the distribution of dust physical parameters.

Keywords: cosmic microwave background radiation; interstellar dust
New Parameters for Star Cluster Dynamics: The Role of Clusters' Initial Conditions

We recently introduced three new parameters that describe the shape of the normalized cumulative radial distribution (nCRD) of the innermost stars in globular clusters (GCs) and trace the clusters' dynamical evolution. Here, we extend our previous investigations to the case of a large set of Monte Carlo simulations of GCs, started from a broad range of initial conditions. All the models are analyzed at the same age of 13 Gyr when they have reached different evolutionary phases. The sample of models is well representative of the structural properties of the observed population of Galactic GCs. We confirm that the three nCRD parameters are powerful tools to distinguish systems in the early stages of dynamical evolution from those that have already experienced core collapse. They might also help disentangle clusters hosting a low-mass intermediate-mass black hole of a few hundred solar masses from cases with large concentrations of dark remnants in their centers. With respect to other dynamical indicators, the nCRD parameters offer the advantage of being fully empirical and easier to measure from observational data.

Keywords: star clusters; globular star clusters; dynamical evolution
Formation of the Mg II h and k Polarization Profiles in a Solar Plage Model and Their Suitability to Infer Magnetic Fields

The Mg II h and k lines are among the strongest in the near-ultraviolet solar spectrum and their line core originates in the upper chromosphere, just below the transition region. Consequently, they have become one of the main targets for investigating the magnetism of the upper solar atmosphere. The recent Chromospheric Layer Spectropolarimeter (CLASP2) mission obtained unprecedented spectropolarimetric data on these lines in an active region plage, which have already been used to infer the longitudinal component of the magnetic field by applying the weak-field approximation. In this paper, we aim at improving our understanding of the diagnostic capabilities of these lines by studying the emergent Stokes profiles resulting from radiative transfer calculations in a radiative magnetohydrodynamic time-dependent model representative of a solar plage. To this end, we create a synthetic observation with temporal and spatial resolutions similar to those of CLASP2. We find strong asymmetries in the synthetic profiles of circular polarization, which considerably complicate the application of the weak-field approximation. We demonstrate that the selective application of the weak-field approximation to fit different spectral regions in the profile allows us to retrieve information about the longitudinal component of the magnetic field in different regions of the model atmosphere, even when the circular polarization profiles are not antisymmetric and are formed in the presence of strong velocity and magnetic field gradients.

Keywords: spectropolarimetry; solar chromosphere; solar magnetic fields; solar transition region
Pre-maximum Evolution of the Classical Nova YZ Reticuli

The pre-maximum evolution of a nova is the last frontier in studying such objects. YZ Reticuli 2020 is the only nova whose X-ray flash was detected. The X-ray flash occurs immediately after the onset of thermonuclear runaway, so its physical properties impose severe constraints on the nova model. We discuss what we can learn from the early phase observations.

Keywords: classical novae; cataclysmic variable stars; high energy astrophysics; x-ray astronomy; white dwarf stars