adsabs/SciX_UAT_keywords huggingface dataset:
Crustal Failure as a Tool to Probe Hybrid Stars

It is currently unknown if neutron stars (NSs) are composed of nucleons only or are hybrid stars, i.e., in addition to nucleonic crusts and outer cores, they also possess quark cores. Quantum chromodynamics allows for such a possibility, but accurate calculations relevant for compact stars are still elusive. Here we investigate some crust-breaking aspects of hybrid stars. We show that the crust-breaking frequency and maximum fiducial ellipticity are sensitive to the quark-hadron density jump and equation of state stiffness. Remarkably, the crust-breaking frequency related to static tides scales linearly with the mass of the star (for a given companion mass), and its slope encompasses information about the microphysics of the star. However, for precise crust-breaking frequency predictions, relativistic corrections to Kepler's third law and the Newtonian tidal field should not be ignored. When a liquid quark core touches an elastic hadronic phase (the result of a significant energy density jump), the maximum ellipticity can increase by around an order of magnitude when compared to a liquid quark core touching a liquid hadronic phase. That is relevant because it would increase the odds of detecting continuous gravitational waves from NSs. Our order-of-magnitude analysis also suggests that a given upper limit to the ellipticity (crust-breaking frequency) could have representatives in stars with either small or intermediate (large) energy density jumps. Therefore, when upper limits to the ellipticity for isolated stars are better constrained or electromagnetic radiation (e.g., gamma-ray precursors) is detected along with gravitational waves in inspiraling binary systems, they may help constrain some aspects of phase transitions in NSs.

Keywords: neutron stars; general relativity; asteroseismology
Simulations of the Early Postbounce Phase of Core-collapse Supernovae in Three-dimensional Space with Full Boltzmann Neutrino Transport

We report on the core-collapse supernova simulation we conducted for a 11.2M⊙ progenitor model in three-dimensional space up to 20 ms after bounce, using a radiation-hydrodynamics code with full Boltzmann neutrino transport. We solve the six-dimensional Boltzmann equations for three neutrino species and the three-dimensional compressible Euler equations with Furusawa and Togashi's nuclear equation of state. We focus on the prompt convection at ∼10 ms after bounce and investigate how neutrinos are transported in the convective matter. We apply a new analysis based on the eigenvalues and eigenvectors of the Eddington tensor and make a comparison between the Boltzmann transport results and the M1 closure approximation in the transition regime between the optically thick and thin limits. We visualize the eigenvalues and eigenvectors using an ellipsoid, in which each principal axis is parallel to one of the eigenvectors and has a length proportional to the corresponding eigenvalue. This approach enables us to understand the difference between the Eddington tensor derived directly from the Boltzmann simulation and the one given by the M1 prescription from a new perspective. We find that the longest principal axis of the ellipsoid is almost always nearly parallel to the energy flux in the M1 closure approximation, whereas in the Boltzmann simulation it becomes perpendicular in some transition regions, where the mean free path is ∼0.1 times the radius. In three spatial dimensions, the convective motions make it difficult to predict where this happens and to possibly improve the closure relation there.

Keywords: core-collapse supernovae
Timing and Spectral Analysis of HMXB 4U 1700-37 Observed with Insight-HXMT

We report timing and spectral studies of the high-mass X-ray binary 4U 1700-37 using Insight-HXMT observations carried out in 2020 during its out-of-eclipse state. We found significant variations in flux on a timescale of kilo-seconds, while the hardness (count rate ratio between 10–30 keV and 2–10 keV) remains relatively stable. No evident pulsations were found over a frequency range of 10‑3–2000 Hz. During the spectral analysis, for the first time, we took the configuration of different Insight-HXMT detectors' orientations into account, which allows us to obtain reliable results even if stable contamination exists in the field of view. We found that the spectrum could be well described by some phenomenological models that are commonly used in accreting pulsars (e.g., a power law with a high energy cutoff) in the energy range of 2–100 keV. We found hints of cyclotron absorption features around ∼16 keV or/and ∼50 keV.

Keywords: high mass x-ray binary stars
An Unbiased Method of Measuring the Ratio of Two Data Sets

In certain cases of astronomical data analysis, the meaningful physical quantity to extract is the ratio R between two data sets. Examples include the lensing ratio, the interloper rate in spectroscopic redshift samples, and the decay rate of gravitational potential and E G to test gravity. However, simply taking the ratio of the two data sets is biased, since it renders (even statistical) errors in the denominator into systematic errors in R. Furthermore, it is not optimal in minimizing statistical errors of R. Based on Bayesian analysis and the usual assumption of Gaussian error in the data, we derive an analytical expression of the posterior probability density function P(R). This result enables fast and unbiased R measurement, with minimal statistical errors. Furthermore, it relies on no underlying model other than the proportionality relation between the two data sets. Even more generally, it applies to cases where the proportionality relation holds for the underlying physics/statistics instead of the two data sets directly. It also applies to the case of multiple ratios (R → R = (R 1, R 2, ⋯ )). We take the lensing ratio as an example to demonstrate our method. We take lenses as DESI imaging survey galaxies, and sources as DECaLS cosmic shear and Planck cosmic microwave background (CMB) lensing. We restrict the analysis to the ratio between CMB lensing and cosmic shear. The resulting P(R) values, for multiple lens-shear pairs, are all nearly Gaussian. The signal-to-noise ratio of measured R ranges from 4.9 to 8.4. We perform several tests to verify the robustness of the above result.

Keywords: weak gravitational lensing; large-scale structure of the universe; astrostatistics; observational cosmology; cosmic microwave background radiation
Disk Structure around the Class I Protostar L1489 IRS Revealed by ALMA: A Warped-disk System

We have observed the Class I protostar L1489 IRS with the Atacama Millimeter/submillimeter Array (ALMA) in Band 6. The C18O J = 2-1 line emission shows flattened and non-axisymmetric structures in the same direction as its velocity gradient due to rotation. We discovered that the C18O emission shows dips at a radius of ∼200-300 au while the 1.3 mm continuum emission extends smoothly up to r ∼ 400 au. At the radius of the C18O dips, the rotational axis of the outer portion appears to be tilted by ∼15° from that of the inner component. Both the inner and outer components with respect to the C18O dips exhibit the r-0.5 Keplerian rotation profiles until r ∼ 600 au. These results not only indicate that a Keplerian disk extends up to ∼600 au but also that the disk is warped. We constructed a three-dimensional warped-disk model rotating at the Keplerian velocity, and demonstrated that the warped-disk model reproduces main observed features in the velocity channel maps and the PV diagrams. Such a warped-disk system can form by mass accretion from a misaligned envelope. We also discuss a possible disk evolution scenario based on comparisons of disk radii and masses between Class I and Class II sources.

Keywords: young stellar objects; protostars; protoplanetary disks; star formation; circumstellar disks
Results of Polarimetric Observations of Near-Earth Asteroid 433 Eros

Near-Earth asteroids are of great importance for science. We present the results of polarimetric observations of near-Earth asteroid 433 Eros. Previous polarimetric observations of this asteroid did not cover a range of phase angles less than 9°. We were able to measure the degree of linear polarization of asteroid 433 Eros at a phase angle ≈4.°8. The data obtained made it possible to determine the parameters of the negative branch of the degree of linear polarization of this asteroid, such as the magnitude and position of the polarization minimum in four spectral ranges.

Keywords: asteroids; polarimetry
Environmental Dependence of Type Ia Supernovae in Low-redshift Galaxy Clusters

We present an analysis of 102 Type Ia supernovae (SNe Ia) in nearby (z < 0.1), x-ray-selected galaxy clusters. This is the largest such sample to date and is based on archival data primarily from ZTF and ATLAS. We divide our SNe Ia into an inner cluster sample projected within r 500 of the cluster center and an outer cluster sample projected between r 500 and 2 r 500. We compare these to field samples of SNe Ia at similar redshifts in both quiescent and star-forming host galaxies. Based on SALT3 fits to the light curves, we find that the inner cluster SNe Ia have a higher fraction of fast-evolving objects (SALT3 x 1 < ‑1) than the outer cluster or field quiescent samples. This implies an intrinsically different population of SNe Ia occurs in inner cluster environments, beyond known correlations based on host galaxy alone. Our cluster samples show a strongly bimodal x 1 distribution with a fast-evolving component that dominates the inner cluster objects (≳75%) but is just a small fraction of SNe Ia in field star-forming galaxies (≲10%). We do not see strong evidence for variations in the color (SALT3 c) distributions among the samples and find only minor differences in SN Ia standardization parameters and Hubble residuals. We suggest that the age of the stellar population drives the observed distributions, with the oldest populations nearly exclusively producing fast-evolving SNe Ia.

Keywords: type ia supernovae; light curves; galaxy clusters; field galaxies; cosmological parameters
The Impact of Black Hole Formation on Population-averaged Supernova Yields

The landscape of black hole (BH) formation-in which massive stars explode as core-collapse supernovae (CCSN) and which implode into BHs-profoundly affects the initial-mass-function (IMF)-averaged nucleosynthetic yields of a stellar population. Building on the work of Sukhbold et al., we compute IMF-averaged yields at solar metallicity for a wide range of assumptions, including neutrino-driven engine models with extensive BH formation, models with a simple mass threshold for BH formation, and a model in which all stars from 8 to 120 M⊙ explode. For plausible choices, the overall yields of α-elements span a factor of 3, but changes in relative yields are more subtle, typically 0.05-0.2 dex. To constrain the overall level of BH formation, ratios of C and N to O or Mg are promising diagnostics. To distinguish complex, theoretically motivated landscapes from simple mass thresholds, abundance ratios involving Mn or Ni are promising because of their sensitivity to the core structure of the CCSN progenitors. We confirm previous findings of a substantial (factor 2.5-4) discrepancy between predicted O/Mg yield ratios and observationally inferred values, implying that models either overproduce O or underproduce Mg. No landscape choice achieves across-the-board agreement with observed abundance ratios; the discrepancies offer empirical clues to aspects of massive star evolution or explosion physics still missing from the models. We find qualitatively similar results using the massive star yields of Limongi & Chieffi. We provide tables of IMF-integrated yields for several landscape scenarios, and more flexible user-designed models can be implemented through the publicly available Versatile Integrator for Chemical Evolution (VICE; https://pypi.org/project/vice/).

Keywords: core-collapse supernovae; nucleosynthesis; stellar nucleosynthesis; abundance ratios; stellar abundances; stellar mass black holes
Parker Solar Probe Observations of High Plasma β Solar Wind from the Streamer Belt

In general, slow solar wind from the streamer belt forms a high plasma β equatorial plasma sheet around the heliospheric current sheet (HCS) crossing, namely, the heliospheric plasma sheet (HPS). Current Parker Solar Probe (PSP) observations show that the HCS crossings near the Sun could be full or partial current sheet (PCS) crossings, and they share some common features but also have different properties. In this work, using the PSP observations from encounters 4–10, we identify streamer belt solar wind from enhancements in plasma β, and we further use electron pitch angle distributions to separate it into HPS solar wind around the full HCS crossings and PCS solar wind in the vicinity of PCS crossings. Based on our analysis, we find that the PCS solar wind has different characteristics as compared with HPS solar wind: (a) the PCS solar wind could be non-pressure-balanced structures rather than magnetic holes, and the total pressure enhancement mainly results from the less reduced magnetic pressure; (b) some of the PCS solar wind is mirror-unstable; and (c) the PCS solar wind is dominated by very low helium abundance but varied alpha–proton differential speed. We suggest that the PCS solar wind could originate from coronal loops deep inside the streamer belt, and it is pristine solar wind that still actively interacts with ambient solar wind; thus, it is valuable for further investigations of the heating and acceleration of slow solar wind.

Keywords: slow solar wind; interplanetary magnetic fields; space plasmas
Reheating after an Inflationary Universe from a Perfect Fluid and Its Comparison with Observational Data

We present the reheating constraints on an inflationary universe induced by perfect fluid models. Starting with the descriptions for the observables of the scalar field inflationary models in the reconstructed methods, we outline the procedure of perfect fluid inflationary models through these methods to calculate the inflationary observables and reheating. We show that the reheating e-folds number Nre and the reheating final temperature Tre are bound depending on the finite range of reasonable values of ${\omega }_{{re}}$ . By restricting the equation-of-state parameter in the reheating stage, $-\tfrac{1}{3}\lt {\omega }_{{re}}\lt 1$ , more stringent constraints can be derived for the model's parameter space of perfect fluid. These constraints correspond to viable values of the scalar spectral index ns and tensor-to-scalar ratio r, released by Planck2018 observational data.

Keywords: cosmic inflation; observational cosmology
Extending the Z2n and H Statistics to Generic Pulsed Profiles

The search for astronomical pulsed signals within noisy data in the radio band is usually performed through an initial Fourier analysis to find "candidate" frequencies and then refined through the folding of the time series using trial frequencies close to the candidate. In order to establish the significance of the pulsed profiles found at these trial frequencies, pulsed profiles are evaluated with a χ2 test to establish how much they depart from a null hypothesis where the signal is consistent with a flat distribution of noisy measurements. In high-energy astronomy, the χ2 statistic has widely been replaced by the ${Z}_{n}^{2}$ statistic and H-test, as they are more sensitive to extra information, such as the harmonic content of the pulsed profile. The ${Z}_{n}^{2}$ statistic and H-test were originally developed for use with "event data" composed of arrival times of single photons, leaving it unclear how these methods could be used in radio astronomy. In this paper, we present a version of the ${Z}_{n}^{2}$ statistic and H-test for pulse profiles with Gaussian uncertainties appropriate for radio or even optical pulse profiles. We show how these statistical indicators provide better sensitivity to low-significance pulsar candidates with respect to the usual χ2 method and a straightforward way to discriminate between pulse profile shapes. Moreover, they provide an additional tool for radio frequency interference rejection.

Keywords: astrostatistics tools; pulsars; period search
Revealing the Galaxy-Halo Connection through Machine Learning

Understanding the connections between galaxy stellar mass, star formation rate, and dark matter halo mass represents a key goal of the theory of galaxy formation. Cosmological simulations that include hydrodynamics, physical treatments of star formation, feedback from supernovae, and the radiative transfer of ionizing photons can capture the processes relevant for establishing these connections. The complexity of these physics can prove difficult to disentangle and obfuscate how mass-dependent trends in the galaxy population originate. Here, we train a machine-learning method called Explainable Boosting Machines (EBMs) to infer how the stellar mass and star formation rate of nearly 6 million galaxies simulated by the Cosmic Reionization on Computers project depend on the physical properties of halo mass, the peak circular velocity of the galaxy during its formation history v peak, cosmic environment, and redshift. The resulting EBM models reveal the relative importance of these properties in setting galaxy stellar mass and star formation rate, with v peak providing the most dominant contribution. Environmental properties provide substantial improvements for modeling the stellar mass and star formation rate in only ≲10% of the simulated galaxies. We also provide alternative formulations of EBM models that enable low-resolution simulations, which cannot track the interior structure of dark matter halos, to predict the stellar mass and star formation rate of galaxies computed by high-resolution simulations with detailed baryonic physics.

Keywords: galaxy formation; galaxy dark matter halos; large-scale structure of the universe; n-body simulations
The Formation of Carbonaceous Material in the Early Solar Nebula: The Role of Metal Dusting

For many years it has been suggested that the carbonaceous material found in association with Fe/Ni metal and metal carbides in primitive bodies is linked to the Fischer-Tropsch reaction. This is especially true with chondritic-porous interplanetary dust particles, which are considered to have a cometary origin and are among some of the most primitive and least processed materials available for study. Another phenomenon which occurs under the same carburizing conditions as the Fischer-Tropsch reaction is called metal dusting and could be a possible pathway to forming some of the carbonaceous material found in primitive bodies. Metal dusting is a catastrophic corrosion of metal under these carburizing conditions that results in a porous mixture of carbonaceous material, metal, and metal carbides. In the case of pure iron, type I metal dusting results in the formation of a metastable iron carbide, typically cementite, Fe3C. While metal dusting has been studied industrially for over 50 years, it does not appear to have been applied to the formation of carbonaceous material in astrophysical settings. In this work, the general mechanism of metal dusting on iron is described and a thermodynamic analysis of the dusting phenomena applied to solar nebula conditions. Rate measurements are made with pure iron samples over the temperature range from 400°C to 950°C. In addition, the products from experimental runs at 500°C and 600°C are studied by transmission electron microscopy. Results show that iron carbide particles are formed with carbonaceous material consisting of poorly graphitized carbon.

Keywords: interplanetary dust; meteorite composition; reaction catalysts; carbonaceous grains
Developing an Automated Detection, Tracking, and Analysis Method for Solar Filaments Observed by CHASE via Machine Learning

Studies on the dynamics of solar filaments have significant implications for understanding their formation, evolution, and eruption, which are of great importance for space weather warning and forecasting. The Hα Imaging Spectrograph (HIS) on board the recently launched Chinese Hα Solar Explorer (CHASE) can provide full-disk solar Hα spectroscopic observations, which bring us an opportunity to systematically explore and analyze the plasma dynamics of filaments. The dramatically increased observation data require automated processing and analysis, which are impossible if dealt with manually. In this paper, we utilize the U-Net model to identify filaments and implement the Channel and Spatial Reliability Tracking algorithm for automated filament tracking. In addition, we use the cloud model to invert the line-of-sight velocity of filaments and employ the graph theory algorithm to extract the filament spine, which can advance our understanding of the dynamics of filaments. The favorable test performance confirms the validity of our method, which will be implemented in the following statistical analyses of filament features and dynamics of CHASE/HIS observations.

Keywords: solar filaments; astronomy image processing; convolutional neural networks
Chandra's Insights into SN 2023ixf

We report Chandra-ACIS observations of supernova (SN) 2023ixf in M101 on day 13 and 86 since the explosion. The X-rays in both epochs are characterized by high-temperature plasma from the forward shocked region as a result of circumstellar interaction. We are able to constrain the absorption column density at both Chandra epochs, which is much larger than that due to the Galactic and host absorption column, and we attribute it to absorption by the circumstellar matter in the immediate vicinity of SN 2023ixf. Combining our column density measurements with the published measurement on day 4, we show that the column density declines as t ‑2 between day 4 to day 13 and then evolves as t ‑1. The unabsorbed 0.3–10 keV luminosity evolves as t ‑1 during the Chandra epochs. On the Chandra first epoch observation, when the SN was 13 days old, we detect the Fe Kα fluorescent line at 6.4 keV indicating presence of cold material in the vicinity of the supernova. The line is absent on day 86, consistent with the decreased column density by a factor of 7 between the two epochs. Our analysis indicates that during 10–1.5 yr before explosion, the progenitor was evolving with a constant mass-loss rate of 5.6 × 10‑4 M ⊙ yr‑1.

Keywords: circumstellar matter; supernovae; stellar mass loss; x-ray transient sources