adsabs/SciX_UAT_keywords huggingface dataset:
The Challenge of Ruling Out Inflation via the Primordial Graviton Background

Recent debates around the testability of the inflationary paradigm raise the question of how to model-independently discriminate it from competing scenarios. We argue that a detection of the cosmic graviton background (CGB), the relic radiation from gravitons decoupling around Planck time, would rule out the inflationary paradigm, as realistic inflationary models would dilute the CGB to an unobservable level. The CGB contribution to the effective number of relativistic species, ΔN eff,g ≈ 0.054, is well within the reach of next-generation cosmological probes. We argue that detecting the high-frequency stochastic gravitational wave background associated to the CGB will be challenging but potentially feasible. We briefly discuss expectations within alternatives to inflation, focusing on bouncing cosmologies and emergent scenarios.

Keywords: cosmic inflation; gravitational waves; cosmology; observational cosmology; alternatives to cosmic inflation
A Potential Site for Wide-orbit Giant Planet Formation in the IM Lup Disk

The radial transport, or drift, of dust has taken a critical role in giant planet formation theory. However, it has been challenging to identify dust drift pileups in the hard-to-observe inner disk. We find that the IM Lup disk shows evidence that it has been shaped by an episode of dust drift. Using radiative transfer and dust dynamical modeling we study the radial and vertical dust distribution. We find that high dust drift rates exceeding 110 M ⊕ Myr-1 are necessary to explain both the dust and CO observations. Furthermore, the bulk of the large dust present in the inner 20 au needs to be vertically extended, implying high turbulence (α z ≳ 10-3) and small grains (0.2-1 mm). We suggest that this increased level of particle stirring is consistent with the inner dust-rich disk undergoing turbulence triggered by the vertical shear instability. The conditions in the IM Lup disk imply that giant planet formation through pebble accretion is only effective outside of 20 au. If such an early, high-turbulence inner region is a natural consequence of high dust drift rates, then this has major implications for understanding the formation regions of giant planets including Jupiter and Saturn.

Keywords: protoplanetary disks; exoplanet formation
Asteroseismic Investigation on KIC 10526294 to Probe Convective Core Overshoot Mixing

In the overshoot mixing model with an exponentially decreasing diffusion coefficient, the initial value of the diffusion coefficient plays a crucial role. According to the turbulent convective mixing model, the characteristic length of convection in the convection zone differs from that in the overshoot region, resulting in a rapid decrease of the diffusion coefficient near the convective boundary. To investigate this quick decrease, we conducted an asteroseismic study on the intermediate-mass slowly pulsating B-type star KIC 10526294. We generated stellar models with varied input parameters, including the overshoot parameters, and compared the resulting stellar oscillation periods with observations. To mitigate the potential issue arising from large steps in the stellar parameters and stellar age, we employed a comprehensive interpolation scheme for the stellar oscillatory frequencies, considering all stellar parameters and stellar age. Our analysis revealed that the quick decreasing of the diffusion coefficient has discernible effects on the stellar oscillations, and a quick decrease with 4 orders of magnitude shows the best oscillatory frequencies compared with the observations. This provides weak evidence in support of the prediction made by the turbulent convective mixing model. Furthermore, we examined the residuals of the oscillation periods and discovered a potential association between abundance anomalies in the buoyancy frequency profile and the oscillation-like patterns observed in the residuals.

Keywords: asteroseismology; stellar interiors; stellar inner cores; stellar convective zones
Optical Transients Found by MASTER during the Observation of LIGO/VIRGO S200219ac Gravitational-wave Event

We present the results of MASTER Global Robotic Net optical observations of the region within the LIGO/Virgo S200219ac error-box, triggered during the O3 run. We observed 1124 square degrees inside the 3σ error box during a half month. We present the identified optical transients found during this study, which are not related to gravitational waves, and briefly discuss the MASTER observation strategy.

Keywords: transient detection; gravitational wave astronomy; sky surveys; ligo; automatic patrol telescopes
A Red Giants' Toy Story. II. Understanding the Red-giant Branch Bump

The Red-Giant Branch Bump (RGBB) is one of the most noteworthy features in the red-giant luminosity function of stellar clusters. It is caused by the passage of the hydrogen-burning shell through the composition discontinuity left at the point of the deepest penetration by the convective envelope. When crossing the discontinuity the usual trend in increasing luminosity reverses for a short time before it increases again, causing a zig-zag in the evolutionary track. In spite of its apparent simplicity the actual physical reason behind the decrease in luminosity is not well understood and several different explanations have been offered. Here we use a recently proposed simple toy model for the structure of low-mass RGs, together with previous results, to show beyond reasonable doubt that the change in luminosity at the RGBB can be traced to the change in the mean molecular weight of the layers on top of the burning shell. And that these changes happen on a nuclear timescale. The change in the effective mean molecular weight, as the burning shell approaches the discontinuity, causes a drop in the temperature of the burning shell which is attenuated by the consequent feedback contraction of the layers immediately below the burning shell. Our work shows that, when applied correctly, including the feedback on the structure of the core together with the increase in the mass of the core, shell-source homology relations do a great quantitative job in explaining the properties of full evolutionary models at the RGBB.

Keywords: stellar structures; red giant stars; stellar interiors; red giant branch; red giant bump
Understanding Sun-as-a-Star Variability of Solar Balmer Lines

Precise, high-cadence, long-term records of stellar spectral variability at different temporal scales lead to better understanding of a wide variety of phenomena including stellar atmospheres and dynamos, convective motions, and rotational periods. Here, we investigate the variability of solar Balmer lines (Hα, β, γ, δ) observed by space-borne radiometers (OSIRIS, SCIAMACHY, OMI, and GOME-2), combining these precise, long-term observations with high-resolution data from the ground-based NSO/ISS spectrograph. We relate the detected variability to the appearance of magnetic features on the solar disk. We find that on solar-rotational timescales (about 1 month), the Balmer line activity indices (defined as line-core to line-wing ratios) closely follow variations in the total solar irradiance (which is predominantly photospheric), thus frequently (specifically, during passages of sunspot groups) deviating from behavior of activity indices that track chromospheric activity levels. On longer timescales, the correlation with chromospheric indices increases, with periods of low correlation or even anticorrelation found at intermediate timescales. Comparison of these observations with estimates from semiempirical irradiance reconstructions helps quantify the contributions of different magnetic and quiet features. We conclude that both the lower sensitivity to network and in part the higher sensitivity to filaments and prominences, may result in complex, time-dependent relationships between Balmer and other chromospheric indices observed for the Sun and solar-like stars. The fact that core and wings contribute in a similar manner to the variability, and current knowledge of Balmer-lines formation in stellar atmospheres, supports the notion that Balmer line core-to-wing ratio indices behave more like photospheric rather than chromospheric indices.

Keywords: solar activity; solar cycle; solar electromagnetic emission; solar faculae; solar filaments; solar radiation; solar spectral irradiance; sunspot cycle; spectral index
Identifying Physical Structures in Our Galaxy with Gaussian Mixture Models: An Unsupervised Machine Learning Technique

We explore the potential of the Gaussian mixture model (GMM), an unsupervised machine-learning method, to identify coherent physical structures in the interstellar medium. The implementation we present can be used on any kind of spatially and spectrally resolved data set. We provide a step-by-step guide to use these models on different sources and data sets. Following the guide, we run the models on NGC 1977, RCW 120, and RCW 49 using the [C II] 158 μm mapping observations from the SOFIA telescope. We find that the models identified six, four, and five velocity coherent physical structures in NGC 1977, RCW 120, and RCW 49, respectively, which are validated by analyzing the observed spectra toward these structures and by comparison to earlier findings. In this work we demonstrate that GMM is a powerful tool that can better automate the process of spatial and spectral analysis to interpret mapping observations.

Keywords: star forming regions; gaussian mixture model
Saturation Level of Turbulence in Collapsing Gas Clouds

We investigate the physical mechanism that determines the saturation level of the turbulence in collapsing gas clouds. We perform a suite of high-resolution numerical simulations that follow the collapse of turbulent gas clouds, with various effective polytropic exponents γ eff, initial Mach numbers ${{ \mathcal M }}_{0}$ , and initial turbulent seeds. Equating the energy injection rate from gravitational contraction and the dissipation rate of the turbulence, we obtain an analytic expression for the saturation level of the turbulence, and compare it with the numerical results. Consequently, the numerical results are well described by the analytic model, given that the turbulent driving scale in collapsing gas clouds is one-third the Jeans length of the collapsing core. These results indicate that the strength of the turbulence at first-core formations in the early universe/the present-day star formation process can be estimated solely by γ eff.

Keywords: population iii stars; population i stars; early universe; hydrodynamics; collapsing clouds; gravitational collapse
Advanced Γ Method for Small-scale Vortex Detection in the Solar Atmosphere

Ubiquitous vortical structures are considered to act as a natural source of various solar plasma phenomena, for example, a wide range of magnetohydrodynamic waves and jet excitations. This work aims to develop an advanced vortex detection algorithm based on the Γ method and using a separable convolution kernel technique. This method is applied to detect and analyze the photospheric vortices in 3D realistic magnetoconvection numerical and observational data. We present the advanced Γ method (AGM), and our results indicate that the AGM performs with better accuracy in comparison with the original Γ method. The AGM allows us to identify small- and large-scale vortices with no vortex interposition and without requiring the changing of the threshold. In this way, the nondetection issue is mostly prevented. It was found that the Γ method failed to identify the large and longer-lived vortices, which were detected by the AGM. The size of the detected vortical structures tends to vary over time, with most vortices shrinking toward their end. The vorticity at the center is also not constant, presenting a sharp decay as the vortex ceases to exist. Due to its capability of identifying vortices with minimum nondetection, the vortex properties-such as lifetime, geometry, and dynamics-are better captured by the AGM than by the Γ method. In this era of new high-resolution observation, the AGM can be used as a precise technique for identifying and performing statistical analysis of solar atmospheric vortices.

Keywords: solar atmosphere; solar atmospheric motions
A Study of Broad Emission Line and Doppler Factor Estimation for Fermi Blazars

In this work, we obtained a sample of 979 Fermi blazars with broad emission lines, including 701 objects collected from published works and 278 objects developed in this work. For the 278 objects, we made a crossmatch from three catalogs, the Fermi Large Area Telescope Fourth Source Catalog (4FGL), the Sloan Digital Sky Survey, and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, and calculated the broad-line region (BLR) luminosity. Then, we estimated the Doppler factor and studied the correlations between the BLR luminosities and the γ-ray luminosities, the synchrotron peak frequency (ν p ), and Doppler factor (δ) for the whole sample. Our analyses and discussions came to the following main conclusions: For the 278 blazars, their BLR luminosity (log L BLR) ranges from 40.44 to 45.45 erg s‑1, with a mean value of 43.39 erg s‑1. The Doppler factor ranges from δ = 0.45 to δ = 88.52, with a mean value of 12.99 for the 979 Fermi blazars, which is consistent with the results in the literature. Both the BLR luminosity and the Doppler factor exhibit positive correlations with the γ-ray luminosity. The BLR luminosity is anticorrelated with synchrotron peak frequency, implying a Compton cooling. A line of $\mathrm{log}{L}_{\mathrm{BLR}}=1.58\mathrm{log}{\nu }_{p}-19.46$ separating BL Lacertae objects and flat-spectrum radio quasars was obtained in the diagram of $\mathrm{log}{\text{}}{L}_{\mathrm{BLR}}$ against $\mathrm{log}{\nu }_{p}$ using a machine-learning method. Based on the analysis of the equivalent width and the Doppler factors, we proposed five changing-look blazar candidates.

Keywords: blazars; active galactic nuclei; high energy astrophysics; jets
Magnetohydrodynamics with Post-Newtonian Corrections

Using the fully nonlinear and exact perturbation formulation with magnetohydrodynamics (MHD) in the Minkowski background, we derive first-order, post-Newtonian (1PN) equations without imposing the slicing (temporal gauge) condition. The 1PN-MHD formulation is complementary to our recently presented fully relativistic MHD combined with 0PN gravity available only in the maximal slicing. We present the 1PN-MHD equations in two gauge conditions previously used in the literature and provide gauge transformation relations between different gauges. We derive the PN effects on MHD waves in a static homogeneous medium.

Keywords: plasma astrophysics; relativity; magnetohydrodynamics; astrophysical fluid dynamics
Comprehensive Analysis of the Neutrino Process in Core-collapsing Supernovae

We investigate the neutrino flavor change effects due to neutrino self-interaction and shock wave propagation, as well as the matter effects on the neutrino process in core-collapsing supernovae (CCSNe). For the hydrodynamics, we use two models: a simple thermal bomb model and a specified hydrodynamics model for SN1987A. For the presupernova model, we take an updated model, adjusted to explain SN1987A, which employs recent developments in the (n, γ) reaction rates for nuclei near the stability line (A ~ 100). As for the neutrino luminosity, we adopt two different models: equivalent neutrino luminosity and nonequivalent luminosity models. The latter is taken from a synthetic analysis of CCSN simulation data, which quantitatively presented the results obtained by various neutrino transport models. Relevant neutrino-induced reaction rates are calculated using a shell model for light nuclei and a quasiparticle random phase approximation model for heavy nuclei. For each model, we present abundances of the light nuclei (7Li, 7Be, 11B, and 11C) and the heavy nuclei (92Nb, 98Tc, 138La, and 180Ta) produced by the neutrino process. The light nuclei abundances turn out to be sensitive to the Mikheyev-Smirnov-Wolfenstein (MSW) region around O-Ne-Mg layer while the heavy nuclei are mainly produced prior to the MSW region. Through detailed analyses, we find that neutrino self-interaction becomes a key ingredient, in addition to the MSW effect, for understanding the neutrino process and the relevant nuclear abundances. The normal mass hierarchy is shown to be more compatible with the meteorite data. The main nuclear reactions for each nucleus are also investigated in detail.

Keywords: supernova neutrinos; neutrino oscillations; explosive nucleosynthesis; neutrino masses; core-collapse supernovae
The Fourth Fermi-GBM Gamma-Ray Burst Catalog: A Decade of Data

We present the fourth in a series of catalogs of gamma-ray bursts (GRBs) observed with Fermi's Gamma-ray Burst Monitor (Fermi-GBM). It extends the six year catalog by four more years, now covering the 10 year time period from trigger enabling on 2008 July 12 to 2018 July 11. During this time period GBM triggered almost twice a day on transient events, 2356 of which we identified as cosmic GRBs. Additional trigger events were due to solar flare events, magnetar burst activities, and terrestrial gamma-ray flashes. The intention of the GBM GRB catalog series is to provide updated information to the community on the most important observables of the GBM-detected GRBs. For each GRB the location and main characteristics of the prompt emission, the duration, peak flux, and fluence are derived. The latter two quantities are calculated for the 50-300 keV energy band, where the maximum energy release of GRBs in the instrument reference system is observed and also for a broader energy band from 10-1000 keV, exploiting the full energy range of GBM's low-energy detectors. Furthermore, information is given on the settings of the triggering criteria and exceptional operational conditions during years 7 to 10 in the mission. This fourth catalog is an official product of the Fermi-GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.

Keywords: catalogs; gamma-ray bursts
M-dwarf Eclipsing Binaries with Flare Activity

The physical properties of 12 eclipsing binaries of M-type dwarfs with superflare activity are characterized by combining the ground-based spectroscopic measurements and the photometric light curves obtained by the Kepler Space Telescope. All of these binary systems have Algol-type orbital configurations. The primary components are mostly of the early M-type dwarfs (M0-M3). Even though the occurrence rate of large flares with energy >1034 erg of the EBs is less than the hyperflaring M dwarfs, the corresponding cumulative flare frequency is in general about a factor of 10 higher than the single M dwarfs with flare activity. This might be the consequence of magnetic interaction between the primary and secondary component of individual binaries. The slow rotators are not as active as the fast rotators, some of which display a possible eclipsing effect in their flare activity.

Keywords: stellar flares
Radio Emission of Pulsars. II. Coherence Catalyzed by Cerenkov-unstable Shear Alfvén Waves

This paper explores small-scale departures from force-free electrodynamics around a rotating neutron star, extending our treatment of resistive instability in a quantizing magnetic field. A secondary, Cerenkov instability is identified: relativistic particles flowing through thin current sheets excite propagating charge perturbations that are localized near the sheets. Growth is rapid at wavenumbers below the inverse ambient skin depth k p,ex. Small-scale Alfvénic wavepackets are promising sources of coherent curvature radiation. When the group Lorentz factor ${\gamma }_{\mathrm{gr}}\lesssim {({k}_{p,\mathrm{ex}}{R}_{c})}^{1/3}\sim 100$ , where R c is the magnetic curvature radius, a fraction ~10-3-10-2 of the particle kinetic energy is radiated into the extraordinary mode at a peak frequency ~10-2 ck p,ex. Consistency with observations requires a high pair multiplicity (~103-5) in the pulsar magnetosphere. Neither the primary, slow resistive instability nor the secondary, Alfvénic instability depend directly on the presence of magnetospheric gaps, and may activate where the mean current is fully supplied by outward drift of the corotation charge. The resistive mode is overstable and grows at a rate comparable to the stellar spin frequency; the model directly accommodates strong pulse-to-pulse radio flux variations and coordinated subpulse drift. Alfvén mode growth can track the local plasma conditions, allowing for lower-frequency emission from the outer magnetosphere. Beamed radio emission from charged packets with γ gr ~ 50-100 also varies on submillisecond timescales. The modes identified here will be excited inside the magnetosphere of a magnetar, and may mediate Taylor relaxation of the magnetic twist.

Keywords: plasma physics; radio pulsars; magnetars; magnetic fields; compact radiation sources
The Regulated NiCu Cycles with the New 57Cu(p,γ)58Zn Reaction Rate and Its Influence on Type I X-Ray Bursts: the GS 1826-24 Clocked Burster

During the X-ray bursts of GS 1826-24, a "clocked burster", the nuclear reaction flow that surges through the rapid-proton capture process path has to pass through the NiCu cycles before reaching the ZnGa cycles that moderate further hydrogen burning in the region above the germanium and selenium isotopes. The 57Cu(p,γ)58Zn reaction that occurs in the NiCu cycles plays an important role in influencing the burst light curves found by Cyburt et al. We deduce the 57Cu(p,γ)58Zn reaction rate based on the experimentally determined important nuclear structure information, isobaric-multiplet-mass equation, and large-scale shell-model calculations. Based on the isobaric-multiplet-mass equation, we propose a possible order of ${1}_{1}^{+}$ - and ${2}_{3}^{+}$ -dominant resonance states and constrain the resonance energy of the ${1}_{2}^{+}$ state. The latter reduces the contribution of the ${1}_{2}^{+}$ -dominant resonance state. The new reaction rate is up to a factor of 4 lower than the Forstner et al. rate recommended by JINA REACLIB v2.2 at the temperature regime sensitive to clocked bursts of GS 1826-24. Using the simulation from the one-dimensional implicit hydrodynamic code KEPLER to model the thermonuclear X-ray bursts of the GS 1826-24 clocked burster, we find that the new 57Cu(p,γ)58Zn reaction rate, coupled with the latest 56Ni(p,γ)57Cu and 55Ni(p,γ)56Cu reaction rates, redistributes the reaction flow in the NiCu cycles and strongly influences the burst ash composition, whereas the 59Cu(p,α)56Ni and 59Cu(p,γ)60Zn reactions suppress the influence of the 57Cu(p,γ)58Zn reaction and diminish the impact of nuclear reaction flow that bypasses the important 56Ni waiting point induced by the 55Ni(p,γ)56Cu reaction on the burst light curve.

Keywords: nucleosynthesis; explosive nucleosynthesis; nuclear astrophysics; neutron stars; nuclear abundances; x-ray bursts; computational methods; nuclear physics