Sazuna/UAT_keywords huggingface dataset:
Constraining Hadron-quark Phase Transition Parameters within the Quark-mean-field Model Using Multimessenger Observations of Neutron Stars. We extend the quark mean-field (QMF) model for nuclear matter and study the possible presence of quark matter inside the cores of neutron stars. A sharp first-order hadron-quark phase transition is implemented combining the QMF for the hadronic phase with "constant-speed-of-sound" parameterization for the high-density quark phase. The interplay of the nuclear symmetry energy slope parameter, L, and the dimensionless phase transition parameters (the transition density ntrans/n0, the transition strength Δɛ/ɛtrans, and the sound speed squared in quark matter ${c}_{\mathrm{QM}}^{2}$ ) are then systematically explored for the hybrid star properties, especially the maximum mass Mmax and the radius and the tidal deformability of a typical 1.4 M⊙ star. We show the strong correlation between the symmetry energy slope L and the typical stellar radius R1.4, similar to that previously found for neutron stars without a phase transition. With the inclusion of phase transition, we obtain robust limits on the maximum mass (Mmax &lt; 3.6 M⊙) and the radius of 1.4 M⊙ stars (R1.4 ≳ 9.6 km), and we find that a phase transition that is too weak (Δɛ/ɛtrans ≲ 0.2) taking place at low densities ≲1.3-1.5 n0 is strongly disfavored. We also demonstrate that future measurements of the radius and tidal deformability of ∼1.4 M⊙ stars, as well as the mass measurement of very massive pulsars, can help reveal the presence and amount of quark matter in compact objects.

Keywords: Neutron stars, Neutron star cores
Precision Orbital Dynamics from Interstellar Scintillation Arcs for PSR J0437-4715. Intensity scintillations of radio pulsars are known to originate from interference between waves scattered by the electron density irregularities of interstellar plasma, often leading to parabolic arcs in the two-dimensional power spectrum of the recorded dynamic spectrum. The degree of arc curvature depends on the distance to the scattering plasma and its transverse velocity with respect to the line of sight. We report the observation of annual and orbital variations in the curvature of scintillation arcs over a period of 16 yr for the bright millisecond pulsar, PSR J0437-4715. These variations are the signature of the relative transverse motions of Earth, the pulsar, and the scattering medium, which we model to obtain precise measurements of parameters of the pulsar's binary orbit and the scattering medium itself. We observe two clear scintillation arcs in most of our &gt;5000 observations, and we show that they originate from scattering by thin screens located at distances D1 = 89.8 ± 0.4 pc and D2 = 124 ± 3 pc from Earth. The best-fit scattering model we derive for the brightest arc yields the pulsar's orbital inclination angle, i = 137°1 ± 0°3, and longitude of ascending node, Ω = 206°3 ± 0°4. Using scintillation arcs for precise astrometry and orbital dynamics can be superior to modeling variations in the diffractive scintillation timescale, because the arc curvature is independent of variations in the level of turbulence of interstellar plasma. This technique can be used in combination with pulsar timing to determine the full three-dimensional orbital geometries of binary pulsars and provides parameters essential for testing theories of gravity and constraining neutron star masses.

Keywords: Orbital motion, Millisecond pulsars, Orbits, Orbit determination, Interstellar plasma, Pulsars, Astrometry, Interstellar medium, Interstellar scintillation, Radio astronomy, Binary pulsars, Radio pulsars
Background Parameter Effects on Linear-Nonlinear Chorus Wave Growth in the Planetary Magnetosphere. We investigate the effects of the background dipole magnetic field and cold electron number density on the linear and nonlinear growth of whistler-mode chorus waves for a region of relatively small anisotropy (AT) in Saturn's inner magnetosphere. The linear and nonlinear features of wave growth rate and associated frequency at L = 6 are presented in detail. Although a large anisotropy is generally in favor of linear and nonlinear wave growth, the nonlinear wave growth for a small anisotropy can still be generated. All cases show a small threshold for wave amplitudes ${\tilde{B}}_{\mathrm{th}}$ , which compromises the requirement to trigger the nonlinear wave growth, but the comparisons also clearly indicate the important transition process from the linear phase to the nonlinear phase. After checking the variation of the calculation time steps depending on the chosen electron number density Nc and background magnetic field Bc, respectively, a large Nc can promote the nonlinear wave growth, but a large Bc works against it. Our results present how these parameters really affect the generations of linear and nonlinear wave growth quantitatively. This could be significant to further understand the monumental importance of whistler-mode chorus waves and the corresponding wave-particle interactions in the planetary magnetosphere.

Keywords: Space plasmas, Planetary magnetospheres
Free-form Lens Model and Mass Estimation of the High-redshift Galaxy Cluster ACT-CL J0102-4915, "El Gordo". We examine the massive colliding cluster El Gordo, one of the most massive clusters at high redshift. We use a free-form lensing reconstruction method that avoids making assumptions about the mass distribution. We use data from the RELICS program and identify new multiply lensed system candidates. The new set of constraints and free-form method provide a new independent mass estimate of this intriguing colliding cluster. Our results are found to be consistent with earlier parametric models, indirectly confirming the assumptions made in earlier work. By fitting a double gNFW profile to the lens model and extrapolating to the virial radius, we infer a total mass for the cluster of ${M}_{200c}=({1.08}_{-0.12}^{+0.65})\times {10}^{15}$ M ${}_{\odot }$ . We estimate the uncertainty in the mass due to errors in the photometric redshifts and discuss the uncertainty in the inferred virial mass due to the extrapolation from the lens model. We also find in our lens map a mass overdensity corresponding to the large cometary tail of hot gas, reinforcing its interpretation as a large tidal feature predicted by hydrodynamical simulations that mimic El Gordo. Finally, we discuss the observed relation between the plasma and the mass map, finding that the peak in the projected mass map may be associated with a large concentration of colder gas exhibiting possible star formation. El Gordo is one of the first clusters that will be observed with JWST, which is expected to unveil new high-redshift lensed galaxies around this interesting cluster and provide a more accurate estimation of its mass.

Keywords: Rich galaxy clusters, Gravitational lensing, Dark matter, High-redshift galaxy clusters
Investigating the Effect of Galaxy Interactions on the Enhancement of Active Galactic Nuclei at 0.5 &lt; z &lt; 3.0. Galaxy interactions and mergers are thought to play an important role in the evolution of galaxies. Studies in the nearby universe show a higher fraction of active galactic nuclei (AGNs) in interacting and merging galaxies than in their isolated counterparts, indicating that such interactions are important contributors to black hole growth. To investigate the evolution of this role at higher redshifts, we have compiled the largest known sample of major spectroscopic galaxy pairs (2381 with ∆V &lt; 5000 km s-1) at 0.5 &lt; z &lt; 3.0 from observations in the COSMOS and CANDELS surveys. We identify X-ray and IR AGNs among this kinematic pair sample, a visually identified sample of mergers and interactions, and a mass-, redshift-, and environment-matched control sample for each in order to calculate AGN fractions and the level of AGN enhancement as a function of relative velocity, redshift, and X-ray luminosity. While we see a slight increase in AGN fraction with decreasing projected separation, overall, we find no significant enhancement relative to the control sample at any separation. In the closest projected separation bin (&lt; 25 kpc, ∆V &lt; 1000 km s-1), we find enhancements of a factor of ${0.94}_{-0.16}^{+0.21}$ and ${1.00}_{-0.31}^{+0.58}$ for X-ray and IR-selected AGNs, respectively. While we conclude that galaxy interactions do not significantly enhance AGN activity on average over 0.5 &lt; z &lt; 3.0 at these separations, given the errors and the small sample size at the closest projected separations, our results would be consistent with the presence of low-level AGN enhancement.

Keywords: Galaxy interactions, Galaxy pairs, Active galactic nuclei, Galaxy mergers, Extragalactic astronomy, Interacting galaxies, High-redshift galaxies
Pre-main-sequence Stars in Taurus: Comparison of Magnetic and Nonmagnetic Model Fits to the Low-mass Stars. Stellar associations should be co-eval, but some associations exhibit apparently discrepant ages: M stars appear younger than FG stars. Among M stars in the Upper Sco association (age ≈ 11 Myr), magnetic effects have been shown to slow down evolution of the lowest mass stars, thereby alleviating the age discrepancy. A recent study of pre-main-sequence (PMS) stars in the much younger Taurus star-forming region (SFR) suggest that an age discrepancy may also exist there. Our goal is to compare two approaches to magnetic/nonmagnetic modeling of the Taurus stars. In one approach, Simon et al. concluded that an age discrepancy exists, but it can be resolved by magnetic models if one imposes an "equipartition condition" on the photospheric field of each star. In this paper, we examine an independent sample of seven Taurus PMS stars reported by Rizzuto et al. Our approach to modeling magneto-convection imposes no condition on the photospheric field strength. We find that nonmagnetic isochrones can successfully fit the stars in the Rizzuto et al. sample with ages 1.6-2.4 Myr, without the need to invoke magnetic effects. An upper limit on the vertical field strength on the surfaces of the Rizzuto stars is found to be ∼300 G for the low-mass secondaries of FF Tau and HP Tau/G2 and ∼100 G for the other, more massive stars. The Taurus SFR is so large (extending over many square degrees in the sky) that magnetic conditions may plausibly differ from star to star.

Keywords: Magnetic stars, Stellar convective zones, Stellar evolutionary models, Stellar magnetic fields, Pre-main sequence stars
Statistical Signatures of Nanoflare Activity. II. A Nanoflare Explanation for Periodic Brightenings in Flare Stars Observed by NGTS. Several studies have documented periodic and quasi-periodic signals from the time series of dMe flare stars and other stellar sources. Such periodic signals, observed within quiescent phases (i.e., devoid of larger-scale microflare or flare activity), range in a period from 1 to 1000 s and hence have been tentatively linked to ubiquitous p-mode oscillations generated in the convective layers of the star. As such, most interpretations for the observed periodicities have been framed in terms of magnetohydrodynamic wave behavior. However, we propose that a series of continuous nanoflares, based upon a power-law distribution, can provide a similar periodic signal in the associated time series. Adapting previous statistical analyses of solar nanoflare signals, we find the first statistical evidence for stellar nanoflare signals embedded within the noise envelope of M-type stellar lightcurves. Employing data collected by the Next Generation Transit Survey (NGTS), we find evidence for stellar nanoflare activity demonstrating a flaring power-law index of 3.25 ± 0.20, alongside a decay timescale of 200 ± 100 s. We also find that synthetic time series, consistent with the observations of dMe flare star lightcurves, are capable of producing quasi-periodic signals in the same frequency range as p-mode signals, despite being purely composed of impulsive signatures. Phenomena traditionally considered a consequence of wave behavior may be described by a number of high-frequency but discrete nanoflare energy events. This new physical interpretation presents a novel diagnostic capability, by linking observed periodic signals to given nanoflare model conditions.

Keywords: Computational methods, Stellar flares, Optical flares, Flare stars
Rotational Spectra of Vibrationally Excited AlO and TiO in Oxygen-rich Stars. Rotational transitions in vibrationally excited AlO and TiO—two possible precursors of dust—were observed in the 300 GHz range (1 mm wavelength) toward the oxygen-rich asymptotic giant branch (AGB) stars R Dor and IK Tau with ALMA, and vibrationally excited AlO was observed toward the red supergiant VY CMa with the SMA. The J = 11 → 10 transition of TiO in the v = 1 and 2 levels and the N = 9 → 8 transition in the v = 2 level of AlO were identified toward R Dor, the J = 11 → 10 line of TiO was identified in the v = 1 level toward IK Tau, and two transitions in the v = 1 and 2 levels of AlO were identified toward VY CMa. The newly derived high vibrational temperature of TiO and AlO in R Dor of 1800 ± 200 K and prior measurements of the angular extent confirm that the majority of the emission is from a region within ≲2R⋆ of the central star. A full radiative transfer analysis of AlO in R Dor yielded a fractional abundance of ∼3% of the solar abundance of Al. From a similar analysis of TiO a fractional abundance of ∼78% of the solar abundance of Ti was found. The observations provide indirect evidence that TiO is present in a rotating disk close to the star. Further observations in the ground and excited vibrational levels are needed to determine whether AlO, TiO, and TiO2 are seeds of the Al2O3 dust in R Dor, and perhaps in the gravitationally bound dust shells in other AGB stars with low mass-loss rates.

Keywords: Submillimeter astronomy, Circumstellar matter, Asymptotic giant branch stars, Spectral line identification
The Infrared Medium-deep Survey. VIII. Quasar Luminosity Function at z ∼ 5. Faint z ∼ 5 quasars with M1450 ∼ -23 mag are known to be potentially important contributors to the ultraviolet ionizing background in the postreionization era. However, their number density has not been well determined, making it difficult to assess their role in the early ionization of the intergalactic medium (IGM). In this work, we present the updated results of our z ∼ 5 quasar survey using the Infrared Medium-deep Survey (IMS), a near-infrared imaging survey covering an area of 85 deg2. From our spectroscopic observations with the Gemini Multi-Object Spectrograph on the Gemini-South 8 m telescope, we discovered eight new quasars at z ∼ 5 with -26.1 ≤ M1450 ≤ -23.3. Combining our IMS faint quasars (M1450 &gt; -27 mag) with the brighter Sloan Digital Sky Survey quasars (M1450 &lt; -27 mag), we derive the z ∼ 5 quasar luminosity function (QLF) without any fixed parameters down to the magnitude limit of M1450 = -23 mag. We find that the faint-end slope of the QLF is very flat ( $\alpha =-{1.2}_{-0.6}^{+1.4}$ ), with a characteristic luminosity of ${M}_{1450}^{* }=-{25.8}_{-1.1}^{+1.4}$ mag. The number density of z ∼ 5 quasars from the QLF gives an ionizing emissivity at 912 Å of ∊912 = (3.7-7.1) × 1023 erg s-1 Hz-1 Mpc-3 and an ionizing photon density of ${\dot{n}}_{\mathrm{ion}}=(3.0\mbox{--}5.7)\,\times {10}^{49}$ Mpc-3 s-1. These results imply that quasars are responsible for only 10%-20% (up to 50% even in the extreme case) of the photons required to completely ionize the IGM at z ∼ 5, disfavoring the idea that quasars alone could have ionized the IGM at z ∼ 5.

Keywords: Observational astronomy, Early universe, Sky surveys, Quasars, Active galactic nuclei, Reionization
Hubble Space Telescope Astrometry of the Metal-poor Visual Binary μ Cassiopeiae: Dynamical Masses, Helium Content, and Age. μ Cassiopeiae is a nearby, high-velocity, metal-poor ([Fe/H] = -0.81) visual binary. We have used high-resolution imaging with the Hubble Space Telescope (HST), obtained over nearly two decades, to determine the period (21.568 yr) and precise orbital elements. Combining these with published ground- and space-based astrometry, we determined dynamical masses for both components of μ Cas: 0.7440 ± 0.0122 M⊙ for the G5 V primary and 0.1728 ± 0.0035 M⊙ for its faint dM companion. We detect no significant perturbations in the HST astrometry owing to a third body in the system. The primary aim of our program was to determine, with the aid of stellar models, the helium content and age of the metal-deficient primary star, μ Cas A. Although we now have a precise mass, there remain uncertainties about other parameters, including its effective temperature. Moreover, a reexamination of archival interferometric observations leads to a suspicion that the angular diameter was overestimated by a few percent. In the absolute magnitude versus color plane, μ Cas A lies slightly cooler and more luminous than the main sequence of the globular cluster 47 Tucanae; this may imply that the star has a lower helium content, and/or is older, and/or has a higher metallicity, than the cluster. Our best estimates for the helium content and age of μ Cas A are Y = 0.255 ± 0.014 and 12.7 ± 2.7 Gyr—making μ Cas possibly the oldest star in the sky visible to the naked eye. Improved measurements of the absolute parallax of the system, the effective temperature of μ Cas A, and its angular diameter would provide tighter constraints. * Based on observations with the NASA/ESA Hubble Space Telescope obtained at Space Telescope Science Institute, operated by Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Keywords: Binary stars, Stellar evolutionary models, Space astrometry, Stellar masses, Visual binary stars
On Socially Distant Neighbors: Using Binaries to Constrain the Density of Objects in the Galactic Center. Stars often reside in binary configurations. The nuclear star cluster surrounding the supermassive black hole (SMBH) in the Galactic Center (GC) is expected to include a binary population. In this dense environment, a binary frequently encounters and interacts with neighboring stars. These interactions vary from small perturbations to violent collisions. In the former case, weak gravitational interactions unbind a soft binary over the evaporation timescale, which depends on the binary properties as well as the density of surrounding objects and velocity dispersion. Similarly, collisions can also unbind a binary, and the collision rate depends on the density. Thus, the detection of a binary with known properties can constrain the density profile in the GC with implications for the number of compact objects, which are otherwise challenging to detect. We estimate the density necessary to unbind a binary within its lifetime for an orbit of arbitrary eccentricity about the SMBH. We find that the eccentricity has a minimal impact on the density constraint. In this proof of concept, we demonstrate that this procedure can probe the density in the GC using hypothetical young and old binaries as examples. Similarly, a known density profile provides constraints on the binary orbital separation. Our results highlight the need to consider multiple dynamical processes in tandem. In certain cases, often closer to the SMBH, the collision timescale rather than the evaporation timescale gives the more stringent density constraint, while other binaries farther from the SMBH provide unreliable density constraints because they migrate inward due to mass segregation.

Keywords: Galactic center, Binary stars, Stellar dynamics
The Galaxy "Missing Dark Matter" NGC 1052-DF4 is Undergoing Tidal Disruption. The existence of long-lived galaxies lacking dark matter represents a challenge to our understanding of how galaxies form. Here, we present evidence that explains the lack of dark matter in one such galaxy: NGC 1052-DF4. Deep optical imaging of the system has detected tidal tails in this object caused by its interaction with its neighboring galaxy NGC 1035. As stars are more centrally concentrated than dark matter, tidal stripping will remove a significant percentage of dark matter before affecting the stars of the galaxy. Only $\sim 7 \% $ of the stellar mass of the galaxy is in the tidal tails, suggesting that the stars of NGC 1052-DF4 are only now starting to be affected by the interaction, while the percentage of remaining dark matter is $\lesssim 1 \% $ . This naturally explains the low content of dark matter inferred for this galaxy and reconciles these types of galaxies with our current models of galaxy formation.

Keywords: Galaxy formation, Galaxy interactions, Dark matter
Element Abundances in the Unshocked Ejecta of Cassiopeia A. We analyze and model the infrared spectrum of the Cassiopeia A supernova remnant with the aim of determining the masses of various elements in the unshocked ejecta. In this way, we complement the survey of the X-ray-emitting ejecta to provide a complete census of the elemental composition of the Cas A ejecta. We calculate photoionization-recombination equilibria to determine the ionization balance of various elements in the ejecta as a function of density using the X-ray and UV emission from the forward and reverse shocks as the ionizing radiation. With the assumption that all emission lines are principally excited at the ejecta density that maximizes their emission, we can convert observed line intensities into element masses. We find that the majority of the ∼3 M⊙ ejecta have already been through the reverse shock and are seen today in X-rays. A minority, ∼0.47 ± 0.05 M⊙, with uncertainties quoted here coming from the data fitting procedure only, are still expanding inside the reverse shock and emitting in the infrared. This component is comprised mainly of O, Si, and S, with no Fe readily detectable. Incorporating uncertainties estimated to come from our modeling, we quote $0.47{\pm }_{0.24}^{0.47}$ M⊙. We speculate that up to a further 0.07 M⊙ of Fe may be present in diffuse gas in the inner ejecta, depending on the Fe charge state.

Keywords: Core-collapse supernovae, High energy astrophysics, Plasma astrophysics, Chemical abundances, Supernova remnants, Shocks
Kink Oscillations in Solar Coronal Loops with Elliptical Cross Sections. I. The Linear Regime. The cross sections of solar coronal loops are suggested to be rarely circular. We examine linear kink oscillations in straight, density-enhanced, magnetic cylinders with elliptical cross sections by solving the three-dimensional magnetohydrodynamic equations from an initial-value-problem perspective. Motivated by relevant eigenmode analyses, we distinguish between two independent polarizations, one along the major axis (the M-modes) and the other along the minor one (the m-modes). We find that, as happens for coronal loops with circular cross sections, the apparent damping of the transverse displacement of the loop axis is accompanied by the accumulation of transverse Alfvénic motions and the consequent development of small scales therein, suggesting the robustness of the concepts of resonant absorption and phase mixing. In addition, two stages can in general be told apart in the temporal evolution of the loop displacement: a Gaussian time dependence precedes an exponential one. For the two examined density ratios between loops and their surroundings, the periods of the M-modes (m-modes) tend to increase (decrease) with the major-to-minor-half-axis ratio, and the damping times in the exponential stage for the M-modes tend to exceed their m-mode counterparts. This is true for the two transverse profiles we examine. However, the relative magnitudes of the damping times in the exponential stage for different polarizations depend on the specification of the transverse profile or the density contrast. The applications of our numerical findings are discussed in the context of coronal seismology.

Keywords: Magnetohydrodynamics, Solar coronal waves, Solar corona