adsabs/SciX_UAT_keywords huggingface dataset:
Bayesian Inference of the Symmetry Energy of Superdense Neutron-rich Matter from Future Radius Measurements of Massive Neutron Stars

Using as references the posterior probability distribution functions of the equation of state (EOS) parameters inferred from the radii of canonical neutron stars (NSs) reported by the LIGO/VIRGO and NICER Collaborations based on their observations of GW170817 and PSR J0030+0451, we investigate how future radius measurements of more massive NSs will improve our current knowledge about the EOS of superdense neutron-rich nuclear matter, especially its symmetry energy term. Within the Bayesian statistical approach using an explicitly isospin-dependent parametric EOS for the core of NSs, we infer the EOS parameters of superdense neutron-rich nuclear matter from three sets of imagined mass-radius correlation data representing typical predictions by various nuclear many-body theories, that is, the radius stays the same, decreases, or increases with increasing NS mass within ±15% between 1.4 and 2.0 M⊙. The corresponding NS average density increases quickly or slowly or slightly decreases as the NS mass increases from 1.4 to 2.0 M⊙. While the EOSs of symmetric nuclear matter (SNM) inferred from the three data sets are approximately the same, the corresponding symmetry energies above about twice the saturation density of nuclear matter are very different, indicating that the radii of massive NSs carry important information about the high-density behavior of nuclear symmetry energy with little influence from the remaining uncertainties of the SNM EOS at suprasaturation densities.

Keywords: neutron stars
A Comparative Study of Machine-learning Methods for X-Ray Binary Classification

X-ray binaries (XRBs) consist of a compact object that accretes material from an orbiting secondary star. The most secure method we have for determining if the compact object is a black hole is to determine its mass: This is limited to bright objects and requires substantial time-intensive spectroscopic monitoring. With new X-ray sources being discovered with different X-ray observatories, developing efficient, robust means to classify compact objects becomes increasingly important. We compare three machine-learning classification methods (Bayesian Gaussian Processes (BGPs), K-Nearest Neighbors (KNN), Support Vector Machines) for determining whether the compact objects are neutron stars or black holes (BHs) in XRB systems. Each machine-learning method uses spatial patterns that exist between systems of the same type in 3D color-color-intensity diagrams. We used lightcurves extracted using 6 yr of data with MAXI/GSC for 44 representative sources. We find that all three methods are highly accurate in distinguishing pulsing from nonpulsing neutron stars (NPNS) with 95% of NPNS and 100% of pulsars accurately predicted. All three methods have high accuracy in distinguishing BHs from pulsars (92%) but continue to confuse BHs with a subclass of NPNS, called bursters, with KNN doing the best at only 50% accuracy for predicting BHs. The precision of all three methods is high, providing equivalent results over 5-10 independent runs. In future work, we will suggest a fourth dimension be incorporated to mitigate the confusion of BHs with bursters. This work paves the way toward more robust methods to efficiently distinguish BHs, NPNS, and pulsars.

Keywords: x-ray binary stars; black holes; pulsars; neutron stars; astrostatistics; bayesian statistics
Effects of the Central Mass Concentration on Bar Formation in Disk Galaxies

While bars are common in disk galaxies, their formation conditions are not well understood. We use N-body simulations to study the formation and evolution of a bar in isolated galaxies consisting of a stellar disk, a classical bulge, and a dark halo. We consider 24 galaxy models that are similar to the Milky Way but differ in the mass and compactness of the classical bulge and halo concentration. We find that the bar formation requires ${({Q}_{T,\min }/1.2)}^{2}+{(\mathrm{CMC}/0.05)}^{2}\lesssim 1$ , where ${Q}_{T,\min }$ and CMC refer to the minimum value of the Toomre stability parameter and the central mass concentration, respectively. Bars tend to be stronger and longer, and to rotate more slowly, in galaxies with a less massive and less compact bulge and halo. All bars formed in our models correspond to slow bars. A model with the bulge mass of ~10%-20% of the disk under a concentrated halo produces a bar similar to that of the Milky Way. We discuss our findings in relation to other bar formation criteria suggested by previous studies.

Keywords: disk galaxies; milky way galaxy; galaxy bulges; galaxy disks; barred spiral galaxies; galaxy bars
GN-z11 in Context: Possible Signatures of Globular Cluster Precursors at Redshift 10

The first JWST spectroscopy of the luminous galaxy GN-z11 simultaneously established its redshift at z = 10.6 and revealed a rest-ultraviolet spectrum dominated by signatures of highly ionized nitrogen, which has so far defied clear interpretation. We present a reappraisal of this spectrum in the context of both detailed nebular modeling and nearby metal-poor reference galaxies. The N IV] emission enables the first nebular density measurement in an apparently predominantly star-forming galaxy at z > 10, revealing evidence for extremely high densities n e ≳ 105 cm‑3. With a suite of photoionization models, we establish that regardless of the ionization mechanism and accounting for depletion and this density enhancement, gas substantially enriched in nitrogen ([N/O] = +0.52 assuming the nebular emission is dominated by star formation) is required to reproduce the observed lines. We compare the GN-z11 spectrum to local UV databases and highlight a unique nearby galaxy, Mrk 996, where a high concentration of Wolf–Rayet stars and their CNO-processed ejecta produce a UV spectrum remarkably similar in some respects to that of GN-z11 and the Sunburst Arc. Collating this evidence in the context of Galactic stellar abundances, we suggest that the peculiar nitrogenic features prominent in GN-z11 may be a unique signature of intense and densely clustered star formation in the evolutionary chain of the present-day globular clusters, consistent with in situ early enrichment with nuclear-processed stellar ejecta on a massive scale. Combined with insight from local galaxies, these and future JWST data open a powerful new window into the physical conditions of star formation and chemical enrichment at the highest redshifts.

Keywords: high-redshift galaxies; blue compact dwarf galaxies; galaxy abundances; globular star clusters
Nonparametric Model for the Equations of State of a Neutron Star from Deep Neural Network

It is of great interest to understand the equation of state (EOS) of the neutron star, whose core includes highly dense matter. However, there are large uncertainties in the theoretical predictions for the EOS of a neutron star. It is useful to develop a new framework, which is flexible enough to consider the systematic error in theoretical predictions and to use them as a best guess at the same time. We employ a deep neural network to perform a nonparametric fit of the EOS of a neutron star using currently available data. In this framework, the Gaussian process is applied to represent the EOSs and the training set data required to close physical solutions. Our model is constructed under the assumption that the true EOS of a neutron star is a perturbation of the relativistic mean-field model prediction. We fit the EOSs of neutron star using two different example data sets, which can satisfy the latest constraints from the massive neutron stars, NICER, and the gravitational wave of the binary neutron stars. Given our assumptions, we find that a maximum neutron star mass is ${2.38}_{-0.13}^{+0.15}{M}_{\odot }$ or ${2.41}_{-0.14}^{+0.15}{M}_{\odot }$ at the 95% confidence level from two different example data sets. It implies that the 1.4M ⊙ radius is ${12.31}_{-0.31}^{+0.29}$ or ${12.30}_{-0.37}^{+0.35}$ km. These results are consistent with results from previous studies using similar priors. It has demonstrated the recovery of the EOS of NS using a nonparametric model.

Keywords: neutron stars; neural networks; nuclear physics
COSMOS-Web: An Overview of the JWST Cosmic Origins Survey

We present the survey design, implementation, and outlook for COSMOS-Web, a 255 hr treasury program conducted by the James Webb Space Telescope in its first cycle of observations. COSMOS-Web is a contiguous 0.54 deg2 NIRCam imaging survey in four filters (F115W, F150W, F277W, and F444W) that will reach 5σ point-source depths ranging ~27.5-28.2 mag. In parallel, we will obtain 0.19 deg2 of MIRI imaging in one filter (F770W) reaching 5σ point-source depths of ~25.3-26.0 mag. COSMOS-Web will build on the rich heritage of multiwavelength observations and data products available in the COSMOS field. The design of COSMOS-Web is motivated by three primary science goals: (1) to discover thousands of galaxies in the Epoch of Reionization (6 ≲ z ≲ 11) and map reionization's spatial distribution, environments, and drivers on scales sufficiently large to mitigate cosmic variance, (2) to identify hundreds of rare quiescent galaxies at z > 4 and place constraints on the formation of the universe's most-massive galaxies (M ⋆ > 1010 M ⊙), and (3) directly measure the evolution of the stellar-mass-to-halo-mass relation using weak gravitational lensing out to z ~ 2.5 and measure its variance with galaxies' star formation histories and morphologies. In addition, we anticipate COSMOS-Web's legacy value to reach far beyond these scientific goals, touching many other areas of astrophysics, such as the identification of the first direct collapse black hole candidates, ultracool subdwarf stars in the Galactic halo, and possibly the identification of z > 10 pair-instability supernovae. In this paper we provide an overview of the survey's key measurements, specifications, goals, and prospects for new discovery.

Keywords: sky surveys; large-scale structure of the universe; galaxy evolution; reionization; weak gravitational lensing
The Third Data Release of the KODIAQ Survey

We present and make publicly available the third data release (DR3) of the Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ) survey. KODIAQ DR3 consists of a fully reduced sample of 727 quasars at 0.1 < zem < 6.4 observed with the Echellette Sepctrograph and Imager at moderate resolution (4000 ≤ R ≤ 10,000). DR3 contains 872 spectra available in flux calibrated form, representing a sum total exposure time of ∼2.8 megaseconds. These coadded spectra arise from a total of 2753 individual exposures of quasars taken from the Keck Observatory Archive (KOA) in raw form and uniformly processed using a data reduction package made available through the XIDL distribution. DR3 is publicly available to the community, housed as a higher level science product at the KOA and in the igmspec database.

Keywords: lyman limit systems; quasars; damped lyman-alpha systems; intergalactic medium; circumgalactic medium; double quasars
An 8.56 keV Absorption Line in the Hyperluminous X-Ray Source in NGC 4045: Ultrafast Outflow or Cyclotron Line?

We report on the discovery of an absorption line at $E={8.56}_{-0.11}^{+0.05}$ keV detected with a significance of >3.3σ in the NuSTAR and XMM-Newton spectra of a newly discovered hyperluminous X-ray source (L X > 1041 erg s-1) in the galaxy NGC 4045 at a distance of 32 Mpc. The source was first discovered serendipitously in a Swift/XRT observation of the galaxy, and Swift monitoring reveals a highly variable source changing by over an order of magnitude from maximum to minimum. The origin of the absorption line appears likely to be from highly ionized iron with a blueshift of 0.19c, indicating an ultrafast outflow. However, the large equivalent width of the line ( $\mathrm{EW}=-{0.22}_{-0.09}^{+0.08}$ keV) paired with the lack of other absorption lines detected is difficult to reconcile with models. An alternative explanation is that the line is due to a cyclotron resonance scattering feature produced by the interaction of X-ray photons with the powerful magnetic field of a neutron star.

Keywords: ultraluminous x-ray sources; x-ray sources; x-ray transient sources; neutron stars; black holes
Source and Propagation of a Streamer Blowout Coronal Mass Ejection Observed by the Parker Solar Probe

In the first orbit of the Parker Solar Probe (PSP), in situ thermal plasma and magnetic field measurements were collected as close as 35 RSun from the Sun, an environment that had not been previously explored. During the first orbit of PSP, the spacecraft flew through a streamer blowout coronal mass ejection (SBO-CME) on 2018 November 11 at 23:50 UT as it exited the science encounter. The SBO-CME on November 11 was directed away from the Earth and was not visible by L1 or Earth-based telescopes due to this geometric configuration. However, PSP and the STEREO-A spacecraft were able to make observations of this slow (V ≈ 380 km s-1) SBO-CME. Using the PSP data, STEREO-A images, and Wang-Sheeley-Arge model, the source region of the CME is found to be a helmet streamer formed between the northern polar coronal hole and a mid-latitude coronal hole. Using the YGUAZU-A model, the propagation of the CME is traced from the source at the Sun to PSP. This model predicts the travel time of the flux rope to the PSP spacecraft as 30 hr, which is within 0.33 hr of the actual measured arrival time. The in situ Solar Wind Electrons Alphas and Protons data were examined to determine that no shock was associated with this SBO-CME. Modeling of the SBO-CME shows that no shock was present at PSP; however, at other positions along the SBO-CME front, a shock could have formed. The geometry of the event requires in situ and remote sensing observations to characterize the SBO-CME and further understand its role in space weather.

Keywords: space weather; solar coronal mass ejections
Peter Pan Disks: Long-lived Accretion Disks Around Young M Stars

WISEA J080822.18-644357.3, an M star in the Carina association, exhibits extreme infrared excess and accretion activity at an age greater than the expected accretion disk lifetime. We consider J0808 as the prototypical example of a class of M star accretion disks at ages ≳20 Myr, which we call "Peter Pan" disks, because they apparently refuse to grow up. We present four new Peter Pan disk candidates identified via the Disk Detective citizen science project, coupled with Gaia astrometry. We find that WISEA J044634.16-262756.1 and WISEA J094900.65-713803.1 both exhibit significant infrared excess after accounting for nearby stars within the Two Micron All Sky Survey (2MASS) beams. The J0446 system has >95% likelihood of Columba membership. The J0949 system shows >95% likelihood of Carina membership. We present new Gemini Multi-Object Spectrograph optical spectra of all four objects, showing possible accretion signatures on all four stars. We present ground-based and TESS light curves of J0808 and 2MASS J0501-4337, including a large flare and aperiodic dipping activity on J0808, and strong periodicity on J0501. We find Paβ and Brγ emission indicating ongoing accretion in near-IR spectroscopy of J0808. Using observed characteristics of these systems, we discuss mechanisms that lead to accretion disks at ages ≳20 Myr, and find that these objects most plausibly represent long-lived CO-poor primordial disks, or "hybrid" disks, exhibiting both debris and primordial-disk features. The question remains: why have gas-rich disks persisted so long around these particular stars?

Keywords: m dwarf stars; circumstellar disks; stellar accretion disks; protoplanetary disks; exoplanet formation; stellar activity
The Near-Sun Dust Environment: Initial Observations from Parker Solar Probe

The Parker Solar Probe (PSP) spacecraft has flown into the densest, previously unexplored, innermost region of our solar system's zodiacal cloud. While PSP does not have a dedicated dust detector, multiple instruments on the spacecraft are sensitive to the effects of meteoroid bombardment. Here, we discuss measurements taken during PSP's second orbit and compare them to models of the zodiacal cloud's dust distribution. Comparing the radial impact rate trends and the timing and location of a dust impact to an energetic particle detector, we find the impactor population to be consistent with dust grains on hyperbolic orbits escaping the solar system. Assuming PSP's impact environment is dominated by hyperbolic impactors, the total quantity of dust ejected from our solar system is estimated to be 0.5-10 tons/s. We expect PSP will encounter an increasingly intense impactor environment as its perihelion distance and semimajor axis are decreased.

Keywords: meteoroids; interplanetary dust
Between Local Interstellar Magnetic and Dynamic Pressure Balance of Heliospheric Boundaries Measured with the IBEX Ribbon-A New Paradigm

The Interstellar Boundary Explorer (IBEX) mission discovered a global structure observed in energetic neutral atoms (ENA) emissions-the IBEX "ribbon." We study the ribbon spatially retained by Alfvén waves. The IBEX ribbon width is used to derive Alfvén speeds in the modified local interstellar medium (LISM), which, averaged across the ribbon, is vA = 42.7 ± 3.0 km s-1. The increase of Alfvén speeds from polar regions to near the nose yields the compression ratio from the pristine LISM into the modified LISM as a function of angle from the ENA pressure maximum in the globally distributed flux. Averaged across the ribbon, the average compression ratio is rc = 1.63 ± 0.22. The compression ratios and Alfvén speeds across the ribbon provide for extrapolations into the pristine LISM, resulting in an average LISM Alfvén speed, vA-LISM = 31.7 ± 3.3 km s-1. With the LISM flow speed of uLISM = 25.82 ± 0.33 km s-1 derived from previous IBEX studies, we find that the ratio of the ram flow energy density to the magnetic energy density in the LISM is ${u}_{\mathrm{LISM}}^{2}/{v}_{{\rm{A}}-\mathrm{LISM}}^{2}=0.66\pm 0.14$ . This indicates that the heliosphere is between the extremes of dynamic and magnetic pressure balance. The complex and time-varying structure of the heliosphere is strongly influenced both by interactions with the interstellar magnetic field and the interstellar flow, representing a new paradigm that will be explored as we connect IBEX observations with those made in the future by the Interstellar Mapping and Acceleration Probe (IMAP).

Keywords: heliosphere; interstellar medium
Inferring Coupling Strengths of Mixed-mode Oscillations in Red Giant Stars Using Deep Learning

Asteroseismology is a powerful tool that may be applied to shed light on stellar interiors and stellar evolution. Mixed modes, behaving like acoustic waves in the envelope and buoyancy modes in the core, are remarkable because they allow for probing the radiative cores and evanescent zones of red giant stars. Here, we have developed a neural network that can accurately infer the coupling strength, a parameter related to the size of the evanescent zone, of solar-like stars in ~5 ms. In comparison with existing methods, we found that only ~43% of inferences were in agreement with a difference less than 0.03 in a sample of ~1700 Kepler red giants. To understand the origin of these differences, we analyzed a few of these stars using independent techniques such as the Monte Carlo Markov Chain method and echelle diagrams. Through our analysis, we discovered that these alternate techniques are supportive of the neural-net inferences. We also demonstrate that the network can be used to yield estimates of coupling strength and period spacing in stars with structural discontinuities. Our findings suggest that the rate of decline in the coupling strength in the red giant branch is greater than previously believed. These results are in closer agreement with calculations of stellar-evolution models than prior estimates, further underscoring the remarkable success of stellar evolution theory and computation. Additionally, we show that the uncertainty in measuring period spacing increases rapidly with diminishing coupling strength.

Keywords: asteroseismology; red giant branch; neural networks; red giant clump
Possible Periodic Dips in the Pulsating Ultraluminous X-Ray Source M51 ULX-7

We report the discovery of possible periodic X-ray dips in a pulsating ultraluminous X-ray source, M51 ULX-7, with archival Chandra observations. With ∼20 days of monitoring in the superorbital descending state, we discovered three dips with separations of ∼2 and ∼8 days via the Bayesian block technique. A phase-dispersion minimization and a ${\chi }^{2}$ test suggest that the dip is likely recurrent with a period of ∼2 days, consistent with the orbital period of M51 ULX-7. We interpret the dip as an obscuring of the emission from the pulsar by the vertical structure on the stream-disk interaction region or the atmosphere of the companion star. Both interpretations suggest the viewing angle to be ∼60°. Given that the magnetic field of M51 ULX-7 is moderately high, B ∼ 1013 G, a low geometric beaming with $b\gtrsim 1/2$ is sufficient to explain the observed flux and the presence of dips. Obscuration of the stellar wind remains an alternative possible origin and further monitoring of the dips will be required.

Keywords: neutron stars; x-ray binary stars; x-ray sources
Influence of Neptune's Migration Parameters on the Inclination Distribution of Kuiper Belt Objects (KBOs)

Nesvorný suggested that Neptune's early migration must have been slow (one e-fold τ ≳ 10 Myr) to explain the wide inclination distribution of dynamically hot populations in the Kuiper Belt. Volk & Malhotra reported that the median inclination of implanted KBOs, iM, depends on Neptune's orbital inclination during migration. They did not find any simple relationship between iM and τ for 5 ≤ τ ≤ 50 Myr (very short migration timescales τ < 5 Myr can be ruled out; e.g., Figure 2 in Nesvorný). Here we briefly explain—a full account of our research will be published elsewhere—how these seemingly contradictory findings can be reconciled.

Keywords: kuiper belt
A BL Lacertae Object at a Cosmic Age of 800 Myr

We report the discovery of the BL Lacertae object FIRST J233153.20+112952.11 at redshift >6 using near-infrared spectroscopy and broadband observations in the infrared, submillimeter, and radio wavelengths. The detection of the continuum break at ~0.92 μm in the near-infrared spectrum of FIRST J233153.20+112952.11 provides an approximate redshift of 6.57, corresponding to an age of the universe of ~800 Myr. The rest-frame UV/optical spectrum of FIRST J233153.20+112952.11 shows no emission lines detected with equivalent width >1.5 Å. The nondetection of the C IV λ1549 broad emission line constrains the luminosity of the accretion disk to be ≲1045 erg s-1, which corresponds to the radiatively inefficient accretion regime of BL Lacertae objects. The spectral index of the rest-frame UV/optical continuum, α ν,opt = 1.43 ± 0.23, is consistent with the expected spectral index of the synchrotron emission spectrum of the relativistic jet. The flat radio continuum (α ν,r ≈ 0) in a rest-frame frequency interval of 7-23 GHz is similar to that of the typical BL Lacertae objects and also consistent with originating from the synchrotron jet emission. The rest-frame UV/optical and radio fluxes of FIRST J233153.20+112952.11 show significant (15%-40%) variations. The shortest recorded rest-frame timescale of these variations is ~8 days. Assuming the local scaling relation between the radio luminosity and black hole mass, the 5 GHz radio luminosity of FIRST J233153.20+112952.11, 1.6 × 1033 erg s-1 Hz-1, suggests a billion solar mass central supermassive black hole.

Keywords: galaxies; galaxy evolution; high-redshift galaxies; active galaxies; active galactic nuclei; blazars; bl lacertae objects; radio jets; supermassive black holes; observational astronomy