Sazuna/UAT_keywords huggingface dataset:
Studying the Properties of Compressible Magnetohydrodynamic Turbulence Using Synchrotron Fluctuation Statistics. We study the observable properties of compressible magnetohydrodynamic (MHD) turbulence covering different turbulence regimes, based on synthetic synchrotron observations arising from 3D MHD numerical simulations. Using the synchrotron emissivity and intensity, we first explore how the cosmic-ray spectral indices affect the measurements of the turbulence properties by employing normalized correlation functions. We then study how the anisotropy of the synchrotron total and polarization intensities arising from the three fundamental MHD modes varies with the viewing angle, i.e., the angle between the mean magnetic field and the line of sight. We employ the ratio of the quadrupole moment to the monopole moment (QM) for this purpose. Our numerical results demonstrate that: (1) the two-point correlation function of synchrotron statistics for the arbitrary cosmic-ray spectral index is related to the special case of the magnetic field index γ = 2, in agreement with the analytical formulae provided by Lazarian &amp; Pogosyan; (2) the anisotropy of the synchrotron total and polarization intensities arising from the Alfvén and slow modes increases with the increase of the viewing angle, while that of fast mode remains almost unchanged with the viewing angle; and (3) the analytical formulae of the synchrotron intensities for studying turbulence can be applied to describe the statistics of the polarization intensities, and the QM can be successfully used to recover the turbulence anisotropy. This study validates the analytical approach of Lazarian &amp; Pogosyan and opens up a way of studying turbulence from observations.

Keywords: Interplanetary turbulence, Interstellar medium, Magnetohydrodynamics, Interstellar synchrotron emission
Very Metal-poor Stars in the Solar Vicinity: Age Determination. The ages of the oldest and most metal-poor stars in the Milky Way bear important information on the age of the universe and its standard model. We analyze a sample of 28 extremely metal-poor field stars in the solar vicinity culled from the literature and carefully determine their ages. To this aim, we critically make use of Gaia data to derive their distances and associated uncertainties. Particular attention has been paid to the estimate of the reddening and its effect on the derivation of stellar ages. We employed different reddenings and superimpose isochrones from different sources on the stars' color-magnitude diagram built up with different photometric systems. We highlight subtle metallicity effects when using the Johnson photometry for low-metallicity stars and finally adopt Gaia photometry. An automatic fitting method is devised to assign ages to each individual star taking into account the uncertainties in the input parameters. The mean age of the sample turns out to be 13.9 ± 0.5 Gyr using Padova isochrones, and 13.7 ± 0.4 Gyr using BASTI isochrones. We found also a group of very metal-poor stars ([Fe/H] = -2.7 to -2.0 dex) with relatively young ages, in the range 8-10 Gyr.

Keywords: Population II stars, Metallicity, Stellar ages
The Connection Between Galactic Outflows and the Escape of Ionizing Photons. We analyze spectra of a gravitationally lensed galaxy, known as the Sunburst Arc, that is leaking ionizing photons, also known as the Lyman continuum (LyC). Magnification from gravitational lensing permits the galaxy to be spatially resolved into one region that leaks ionizing photons and several that do not. Rest-frame UV and optical spectra from Magellan target 10 different regions along the lensed Arc, including six multiple images of the LyC leaking region and four regions that do not show LyC emission. The rest-frame optical spectra of the ionizing photon emitting regions reveal a blueshifted (ΔV = 27 km s-1) broad emission component (FWHM = 327 km s-1), comprising 55% of the total [O III] line flux, in addition to a narrow component (FWHM = 112 km s-1), suggesting the presence of strong highly ionized gas outflows. This is consistent with the high-velocity ionized outflow inferred from the rest-frame UV spectra. In contrast, the broad emission component is less prominent in the nonleaking regions, comprising ~26% of total [O III] line flux. The high-ionization absorption lines are prominent in both the leaker and the nonleaker, but the low-ionization absorption lines are very weak in the leaker, suggesting that the line-of-sight gas is highly ionized in the leaker. Analyses of stellar wind features reveal that the stellar population of the LyC leaking regions is considerably younger (~3 Myr) than that of the nonleaking regions (~12 Myr), emphasizing that stellar feedback from young stars may play an important role in ionizing photon escape.

Keywords: Reionization, High-redshift galaxies
ALMA Observations of the HD 110058 Debris Disk. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the young, gas-rich debris disk around HD 110058 at 0.″3-0.″6 resolution. The disk is detected in the 0.85 and 1.3 mm continuum, as well as the J = 2-1 and J = 3-2 transitions of 12CO and 13CO. The observations resolve the dust and gas distributions and reveal that this is the smallest debris disk around stars of similar luminosity observed by ALMA. The new ALMA data confirm the disk is very close to edge-on, as shown previously in scattered-light images. We use radiative transfer modeling to constrain the physical properties of dust and gas disks. The dust density peaks at around 31 au and has a smooth outer edge that extends out to ~70 au. Interestingly, the dust emission is marginally resolved along the minor axis, which indicates that it is vertically thick if truly close to edge-on with an aspect ratio between 0.13 and 0.28. We also find that the CO gas distribution is more compact than the dust (similar to the disk around 49 Ceti), which could be due to a low viscosity and a higher gas release rate at small radii. Using simulations of the gas evolution taking into account the CO photodissociation, shielding, and viscous evolution, we find that HD 110058's CO gas mass and distribution are consistent with a secondary origin scenario. Finally, we find that the gas densities may be high enough to cause the outward drift of small dust grains in the disk.

Keywords: Planetary system formation, Submillimeter astronomy, Debris disks
Millisecond Pulsars in Dense Star Clusters: Evolution, Scaling Relations, and the Galactic-center Gamma-Ray Excess. The number of millisecond pulsars (MSPs) observed in Milky Way globular clusters has increased explosively in recent years, but the underlying population is still uncertain due to observational biases. We use state-of-the-art N-body simulations to study the evolution of MSP populations in dense star clusters. These cluster models span a wide range in initial conditions, including different initial masses, metallicities, and virial radii, which nearly cover the full range of properties exhibited by the population of globular clusters in the Milky Way. We demonstrate how different initial cluster properties affect the number of MSPs, for which we provide scaling relations as a function of cluster age and mass. As an application, we use our formulae to estimate the number of MSPs delivered to the Galactic center from inspiralling globular clusters to probe the origin of the Galactic-center gamma-ray excess detected by Fermi. We predict about 400 MSPs in the Galactic center from disrupted globular clusters, which can potentially explain most of the observed gamma-ray excess.

Keywords: Galactic center, Pulsars, N-body simulations, Astronomical simulations, Star clusters
Multimessenger Picture of J1048+7143. We draw a multimessenger picture of J1048+7143, a flat-spectrum radio quasar known to show quasiperiodic oscillations in the γ-ray regime. We generate the adaptively binned Fermi Large Area Telescope light curve of this source above 168 MeV to find three major γ-ray flares of the source, such that each of the three flares consists of two sharp subflares. Based on radio interferometric imaging data taken with the Very Large Array, we find that the kiloparsec-scale jet is directed west, while our analysis of 8.6 GHz very long baseline interferometry data, mostly taken with the Very Long Baseline Array, revealed signatures of two parsec-scale jets, one pointing east, one pointing south. We suggest that the misalignment of the kiloparsec- and parsec-scale jets is a revealing signature of jet precession. We also analyze the 5 GHz total flux density curve of J1048+7143 taken with the Nanshan (Ur) and RATAN-600 single-dish radio telescopes and find two complete radio flares, lagging slightly behind the γ-ray flares. We model the timing of γ-ray flares as a signature of the spin-orbit precession in a supermassive black hole binary, and find that the binary could merge in the next ~60-80 yr. We show that both pulsar timing arrays and the planned Laser Interferometer Space Antenna lack sensitivity and frequency coverage to detect the hypothetical supermassive black hole binary in J1048+7143. We argue that the identification of sources similar to J1048+7143 plays a key role in revealing periodic high-energy sources in the distant universe. *Released xxxx 2022.

Keywords: Radio active galactic nuclei, Gamma-ray astronomy, Active galactic nuclei, High energy astrophysics
An Atmospheric Retrieval of the Brown Dwarf Gliese 229B. We present results from an atmospheric retrieval analysis of Gl 229B using the Brewster retrieval code. We find the best fit model to be cloud-free, consistent with the T dwarf retrieval work of Line et al.; Zalesky et al. and Gonzales et al. Fundamental parameters (mass, radius, log(L Bol /L Sun), log(g)) determined from our model agree within 1σ to SED-derived values, except for T eff where our retrieved T eff is approximately 100 K cooler than the evolutionary model-based SED value. We find a retrieved mass of ${50}_{-9}^{+12}$ M Jup, however, we also find that the observables of Gl 229B can be explained by a cloud-free model with a prior on mass at the dynamical value, 70 M Jup . We are able to constrain abundances for H2O, CO, CH4, NH3, Na and K and find a supersolar C/O ratio as compared to its primary, Gl 229A. We report an overall subsolar metallicity due to atmospheric oxygen depletion, but find a solar [C/H], which matches that of the primary. We find that this work contributes to a growing trend in retrieval-based studies, particularly for brown dwarfs, toward supersolar C/O ratios and discuss the implications of this result on formation mechanisms and internal physical processes, as well as model biases.

Keywords: M dwarf stars, Brown dwarfs, Fundamental parameters of stars, Companion stars, Atmospheric composition, T dwarfs
Discovery of One Neutron Star Candidate from Radial-velocity Monitoring. We report the discovery of one possible neutron star binary (P orb = 0.8666 days) by using LAMOST low-resolution spectroscopic data. The visible companion is a late A-type dwarf (T eff = 7900 ± 200 K; logg = 4.3 ± 0.2; M = 1.7 ± 0.1 M ⊙; R = 1.7 ± 0.2 R ⊙) at a distance of 1.11 ± 0.03 kpc. No double-lined feature can be seen from the Gran Telescopio Canarias/HORuS high-resolution spectra; thus the radial-velocity variation indicates an invisible object hiding in the binary. The system's optical light curves show clear ellipsoidal variability, suggesting that the visible companion is tidal distorted. By fitting the multiband light curves with the eclipsing light-curve (ELC) code and the Wilson-Devinney (WD) code, we constrain the mass of the invisible star to be 1.1-1.3 M ⊙. Spectral disentangling shows no additional component with optical absorption spectra, supporting the idea that the system contains one compact object. No X-ray or UV emission is detected in the ROSAT archive observations. Therefore, we suspect the invisible object is more likely a neutron star rather than a white dwarf. Our finding suggests the ability of LAMOST spectroscopic survey to discover X-ray-quiescent compact objects.

Keywords: Neutron stars, Ellipsoidal variable stars, Compact binary stars
Explicit Symplectic Methods in Black Hole Spacetimes. Many Hamiltonian problems in the solar system are separable into two analytically solvable parts, and thus serve as a great chance to develop and apply explicit symplectic integrators based on operator splitting and composing. However, such constructions are not in general available for curved spacetimes in general relativity and modified theories of gravity because these curved spacetimes correspond to nonseparable Hamiltonians without the two-part splits. Recently, several black hole spacetimes such as the Schwarzschild black hole were found to allow for the construction of explicit symplectic integrators, since their corresponding Hamiltonians are separable into more than two explicitly integrable pieces. Although some other curved spacetimes including the Kerr black hole do not have such multipart splits, their corresponding appropriate time-transformation Hamiltonians do. In fact, the key problem in obtaining symplectic analytically integrable decomposition algorithms is how to split these Hamiltonians or time-transformation Hamiltonians. Considering this idea, we develop explicit symplectic schemes in curved spacetimes. We introduce a class of spacetimes whose Hamiltonians are directly split into several explicitly integrable terms. For example, the Hamiltonian of a rotating black ring has a 13-part split. We also present two sets of spacetimes whose appropriate time-transformation Hamiltonians have the desirable splits. For instance, an eight-part split exists in a time-transformed Hamiltonian of a Kerr-Newman solution with a disformal parameter. In this way, the proposed symplectic splitting methods can be used widely for long-term integrations of orbits in most curved spacetimes we know of.

Keywords: Celestial mechanics, Computational methods, Computational astronomy, Achondrites
The Role of Magnetic Flux Rope in Ion Acceleration: MHD Simulations and Test-particle Tracing. Magnetic flux ropes (MFRs), playing a crucial role in particle energization and energy transport in the solar-terrestrial space, are helical structures produced by magnetic reconnection. It has been both theoretically predicted and observationally confirmed that MFRs and associated processes are inherently three-dimensional in space. Although such structures have been widely suggested as a favorable place for electron acceleration, whether large-scale MFRs can lead to ion acceleration has been rarely investigated. In this study, an MHD model is used to examine the evolution of large-scale MFRs in the magnetotail, and a test-particle simulation is further employed to study the associated ion energization. Results show that magnetic reconnections take place at multiple X-lines in the magnetotail current sheet, generating a twisted MFR with a scale of about 10 R  e  in azimuth. It propagates earthward following the tail reconnection but its east and west wings are significantly distorted azimuthally. Test-particle tracing reveals that ions (0.1-100 keV) can be trapped within the rope while being effectively accelerated. The rope therefore brings in energetic plasma sources into the inner magnetosphere as it transports earthward. These results demonstrate that the MFR is an important source carrier for the ring-current formation in the inner magnetosphere.

Keywords: Space plasmas, Interplanetary particle acceleration, Solar magnetic reconnection
A Direct Measurement of Galaxy Major and Minor Merger Rates and Stellar Mass Accretion Histories at Z &lt; 3 Using Galaxy Pairs in the REFINE Survey. We measure the role of major and minor mergers in forming the stellar masses of galaxies over redshifts 0 &lt; z &lt; 3 using a combination of ~3.25 deg2 of the deepest ground-based near-infrared imaging taken to date (Ultra Deep Survey, Ultra-VISTA, and VIDEO) as part of the collated REFINE survey. We measure the pair fraction and merger fractions for galaxy mergers of different mass ratios, and quantify the merger rate with newly measured timescales derived from the Illustris simulation as a function of redshift and merger mass ratio. For a M * &gt; 1011 M ☉ selection, we find that over 0 &lt; z &lt; 3 major mergers with mass ratios greater than 1:4 occur ${0.84}_{-0.2}^{+0.3}$ times on average, while minor mergers down to ratios of 1:10 occur on average ${1.43}_{-0.3}^{+0.5}$ times per galaxy. We also quantify the role of major and minor mergers in galaxy formation, whereby the increase in mass due to major mergers is ${93}_{-31}^{+49} \% $ while minor mergers account for an increase of ${29}_{-12}^{+17} \% $ using a M * &gt; 1011 M ☉ selection. We thus find that major mergers add more stellar mass to galaxies than minor mergers over this epoch. Overall, mergers will more than double the mass of massive galaxies over this epoch when selecting by stellar mass. We however find a lower increase in stellar mass when selecting by a constant number density. Finally, we compare our results to simulations, finding that minor mergers are overpredicted in Illustris and in semi-analytical models, suggesting a mismatch between observations and theory in this fundamental aspect of galaxy assembly.

Keywords: Galaxy evolution
The Closure Relations in Optical Afterglow of Gamma-Ray Bursts. Gamma-ray bursts (GRBs) are extremely high-energy events that can be observed at very high redshift. In addition to γ rays, they can emit in X-ray, optical, and sometimes radio wavelengths. Here, following the approach in Srinivasaragavan et al.; Dainotti et al.; and Dainotti et al., we consider 82 GRBs from Dainotti et al. that have been observed in optical wavelengths and fitted with a broken power law. We consider the relations between the spectral and temporal indices (closure relations; CRs) according to the synchrotron forward-shock model evolving in the constant-density interstellar medium (ISM; k = 0) and the stellar wind environment (k = 2) in both slow- and fast-cooling regimes, where the density profile is defined as n ∝ r -k . We find the $\nu \gt \max \{{\nu }_{{\rm{c}}},{\nu }_{{\rm{m}}}\}$ regime is most favored, where ν c and ν m are the cooling and characteristic frequencies, respectively. Finally, we test the 2D Dainotti correlation between the rest-frame end time of the plateau and the luminosity at that time on GRBs that fulfill the most-favored CRs. When we compare the intrinsic scatter σ  int  of those 2D correlations to the scatter presented in Dainotti et al., we see the scatters of our correlations generally agree with the previous values within 1σ, both before and after correction for selection bias. This new information has helped us to pinpoint subsamples of GRBs with features that could drive the GRB emission mechanism, and eventually allow for GRBs to be used as standard candles.

Keywords: Gamma-ray bursts
Clues to the Formation of Liller 1 from Modeling Its Complex Star Formation History. Liller 1 and Terzan 5 are two massive systems in the Milky Way bulge hosting populations characterized by significantly different ages (∆t &gt; 7-8 Gyr) and metallicities (∆[Fe/H] ~ 1 dex). Their origin is still strongly debated in the literature and all formation scenarios proposed so far require some level of fine-tuning. The detailed star formation histories of these systems may represent an important piece of information to assess their origin. Here we present the first attempt to perform such an analysis for Liller 1. The first key result we find is that Liller 1 has been forming stars over its entire lifetime. More specifically, three broad star formation episodes are clearly detected: (1) a dominant one, occurring some 12-13 Gyr ago with a tail extending for up to ~3 Gyr; (2) an intermediate burst, between 6 and 9 Gyr ago; and (3) a recent one, occurring between 1 and 3 Gyr ago. The old population contributes to about 70% of the total stellar mass, and the remaining fraction is almost equally split between the intermediate and young populations. If we take these results at face value, they would suggest that this system unlikely formed through the merger between an old globular cluster and a giant molecular cloud, as recently proposed. On the contrary, our findings provide further support to the idea that Liller 1 is the surviving relic of a massive primordial structure that contributed to the Galactic bulge formation, similarly to the giant clumps observed in star-forming high-redshift galaxies.

Keywords: Globular star clusters, Galactic bulge, Star formation, Photometry, Star clusters
Four Eccentric Mergers Increase the Evidence that LIGO-Virgo-KAGRA's Binary Black Holes Form Dynamically. The growing population of compact binary mergers detected with gravitational waves contains multiple events that are challenging to explain through isolated binary evolution. Such events have higher masses than are expected in isolated binaries, component spin tilt angles that are misaligned, and/or nonnegligible orbital eccentricities. We investigate the orbital eccentricities of 62 binary black hole candidates from the third gravitational-wave transient catalog of the LIGO-Virgo-KAGRA Collaboration with an aligned-spin, moderate-eccentricity waveform model. Within this framework, we find that at least four of these events show significant support for eccentricity e 10 ≥ 0.1 at a gravitational-wave frequency of 10 Hz (&gt;60% credibility, under a log-uniform eccentricity prior that spans the range 10-4 &lt; e 10 &lt; 0.2). Two of these events are new additions to the population: GW191109 and GW200208_22. If the four eccentric candidates are truly eccentric, our results suggest that densely populated star clusters may produce 100% of the observed mergers. However, it remains likely that other formation environments with higher yields of eccentric mergers-for example, active galactic nuclei-also contribute. We estimate that we will be able to confidently distinguish which formation channel dominates the eccentric merger rate after ≳80 detections of events with e 10 ≥ 0.05 at LIGO-Virgo sensitivity, with only ~5 detectably eccentric events required to distinguish formation channels with third-generation gravitational-wave detectors.

Keywords: Globular star clusters, Gravitational wave detectors, Bayesian statistics, Black holes, High energy astrophysics, Gravitational wave sources, Gravitational wave astronomy, Active galactic nuclei, Gravitational waves, Compact objects, Astrophysical black holes, Star clusters
Mildly Relativistic Perpendicular Multiple-ion GRB Shocks. Mildly relativistic perpendicular, collisionless multiple-ion gamma-ray burst shocks are analyzed using 2D3V particle-in-cell simulations. A characteristic feature of multiple-ion shocks is alternating maxima of the α particle and the proton densities, at least in the early downstream. Turbulence, shock-drift acceleration, and evidence of stochastic acceleration are observed. We performed simulations with both in-plane (B  y ) and out-of-plane (B  z ) magnetic fields, as well as in a perpendicular shock setup with φ = 45°, and saw multiple differences: while with B  z , the highest-energetic particles mostly gain energy at the beginning of the shock, with B  y , particles continue gaining energy and it does not appear that they have reached their final energy level. A larger magnetization σ leads to more high-energetic particles in our simulations. One important quantity for astronomers is the electron acceleration efficiency ϵ  e , which is measurable due to synchrotron radiation. This quantity hardly changes when changing the amount of α particles while keeping σ constant. It is, however, noteworthy that ϵ  e  strongly differs for in-plane and out-of-plane magnetic fields. When looking at the proton and α acceleration efficiency, ϵ  p  and ϵ  α , the energy of α particles always decreases when passing the shock into the downstream, whereas the energy of protons can increase if α particles account for the majority of the ions.

Keywords: Shocks, Gamma-ray bursts, Plasma astrophysics, Plasma jets