Sazuna/UAT_keywords huggingface dataset:
An Estimate of the Binary Star Fraction among Young Stars at the Galactic Center: Possible Evidence of a Radial Dependence. We present the first estimate of the intrinsic binary fraction of young stars across the central ≈0.4 pc surrounding the supermassive black hole (SMBH) at the Milky Way Galactic center (GC). This experiment searched for photometric variability in 102 spectroscopically confirmed young stars, using 119 nights of 10″ wide adaptive optics imaging observations taken at W. M. Keck Observatory over 16 yr in the $K^{\prime} $ -[2.1 μm] and H-[1.6 μm] bands. We photometrically detected three binary stars, all of which are situated more than 1″ (0.04 pc) from the SMBH and one of which, S2-36, is newly reported here with spectroscopic confirmation. All are contact binaries or have photometric variability originating from stellar irradiation. To convert the observed binary fraction into an estimate of the underlying binary fraction, we determined the experimental sensitivity through detailed light-curve simulations, incorporating photometric effects of eclipses, irradiation, and tidal distortion in binaries. The simulations assumed a population of young binaries, with stellar ages (4 Myr) and masses matched to the most probable values measured for the GC young star population, and underlying binary system parameters (periods, mass ratios, and eccentricities) similar to those of local massive stars. As might be expected, our experimental sensitivity decreases for eclipses narrower in phase. The detections and simulations imply that the young, massive stars in the GC have a stellar binary fraction ≥71% (68% confidence), or ≥42% (95% confidence). This inferred GC young star binary fraction is consistent with that typically seen in young stellar populations in the solar neighborhood. Furthermore, our measured binary fraction is significantly higher than that recently reported by Chu et al. based on radial velocity measurements for stars ≲1″ of the SMBH. Constrained with these two studies, the probability that the same underlying young star binary fraction extends across the entire region is &lt;1.4%. This tension provides support for a radial dependence of the binary star fraction, and therefore, for the dynamical predictions of binary merger and evaporation events close to the SMBH.

Keywords: Galactic center, Binary stars, Star formation, Eclipsing binary stars, Dynamical evolution
Irradiated Disks May Settle into Staircases. Much of a protoplanetary disk is thermally controlled by irradiation from the central star. Such a disk, long thought to have a smoothly flaring shape, is unstable due to the so-called irradiation instability. But what is the outcome of such an instability? In particular, is it possible that such a disk settles into a shape that is immune to the instability? We combine Athena++ with a simplified thermal treatment to show that passively heated disks settle into a staircase shape. Here, the disk is punctuated by bright rings and dark gaps, with the bright rings intercepting the lion's share of stellar illumination, and the dark gaps are hidden in their shadows. The optical surface of such a disk (the height at which starlight is absorbed) resembles a staircase. Although our simulations do not have realistic radiative transfer, we use the RADMC-3D code to show that this steady state is in good thermal equilibrium. It is possible that realistic disks reach such a state via ways not captured by our simulations. In contrast to our results here, two previous studies have claimed that irradiated disks stay smooth. We show here that they err on different issues. The staircase state, if confirmed by more sophisticated radiative hydrodynamic simulations, has a range of implications for disk evolution and planet formation.

Keywords: Protoplanetary disks, Radiative transfer, Circumstellar disks
Physical Properties of Molecular Clouds in the Overlap Region of the Merging Antennae Galaxies. As the closest major galaxy merger and home to thousands of super star clusters (SSCs), the Antennae Galaxies (NGC 4038 and NGC 4039) are an important location to study the molecular clouds at sites of vigorous star formation. We cataloged giant molecular clouds (GMCs) in the region where the two galaxies overlap using high-resolution (∼0.″1–10 pc) Atacama Large Millimeter/submillimeter Array observations of the 12CO(2‑1) and 13CO(2‑1) emission lines. Of the 72 individual GMCs identified in the overlap region, 17 are within uncertainties of having the necessary mass, pressure, and size needed to form SSCs. Of those 17 GMCs, only one has significant ionizing radiation, indicating that the birth environments are likely still intact in the 16 other GMCs. We compared the physical properties calculated from 12CO(2‑1) GMC data with observations of 10 other galaxies obtained using the same emission line and similar resolution. Compared to other sources in this sample, the GMCs from the Antennae, as well as in other starbursts and in the centers of galaxies, have the highest luminosities, surface densities, and turbulent pressures. The GMCs in starbursts and at the centers of galaxies also have large line widths, although the line widths in the Antennae are among the widest. These comparative results also indicate that the Antennae GMCs have the highest virial parameters despite their high densities.

Keywords: Starburst galaxies, Millimeter astronomy, Galaxy interactions, Molecular clouds, Star formation, Galaxy mergers, Interstellar medium
Intensive Swift and LCO Monitoring of PG 1302–102: Active Galactic Nucleus Disk Reverberation Mapping of a Supermassive Black Hole Binary Candidate. We present an intensive multiwavelength monitoring campaign of the quasar PG 1302‑102 with Swift and the Las Cumbres Observatory network telescopes. At z ∼ 0.3, it tests the limits of the reverberation mapping (RM) technique in probing the accretion disk around a supermassive black hole (SMBH) and extends the parameter space to high masses and high accretion rates. This is also the first time the RM technique has been applied to test disk structures predicted in the SMBH binary model that has been suggested for this source. PG 1302‑102 was observed at a ∼daily cadence for ∼9 months in 14 bands spanning from X-ray to UV and optical wavelengths, and it shows moderate to significant levels of variability correlated between wavelengths. We measure the interband time lags, which are consistent with a τ ∝ λ 4/3 relation as expected from standard disk reprocessing, albeit with large uncertainties. The disk size implied by the lag spectrum is consistent with the expected disk size for its black hole mass within uncertainties. While the source resembles other reverberation-mapped active galactic nuclei in many respects, and we do not find evidence supporting the prevalent hypothesis that it hosts an SMBH binary, we demonstrate the feasibility of studying SMBH binaries from this novel angle and suggest possibilities for the LSST Deep Drilling Fields.

Keywords: Supermassive black holes, Reverberation mapping, Active galactic nuclei
MIRI MRS Observations of β Pictoris. I. The Inner Dust, the Planet, and the Gas. We present JWST MIRI Medium Resolution Spectrograph (MRS) observations of the β Pictoris system. We detect an infrared excess from the central unresolved point source from 5 to 7.5 μm which is indicative of dust within the inner ∼7 au of the system. We perform point-spread function (PSF) subtraction on the MRS data cubes and detect a spatially resolved dust population emitting at 5 μm. This spatially resolved hot dust population is best explained if the dust grains are in the small grain limit (2πa ≪ λ). The combination of unresolved and resolved dust at 5 μm could suggest that dust grains are being produced in the inner few astronomical units of the system and are then radiatively driven outwards, where the particles could accrete onto the known planets in the system, β Pictoris b and c. We also report the detection of an emission line at 6.986 μm that we attribute to [Ar II]. We find that the [Ar II] emission is spatially resolved with JWST and appears to be aligned with the dust disk. Through PSF-subtraction techniques, we detect β Pictoris b at the 5σ level in our MRS data cubes and present the first mid-infrared spectrum of the planet from 5 to 7 μm. The planet's spectrum is consistent with having absorption from water vapor between 5 and 6.5 μm. We perform atmosphere model grid fitting of the spectra and photometry of β Pictoris b and find that the planet's atmosphere likely has a substellar C/O ratio.

Keywords: Debris disks, Circumstellar disks
Black Hole Activity Imprints on the Internal Plateau and the Subsequent Sharp Decay. A stellar-mass black hole (BH) or a millisecond magnetar is believed to be born as the central engine of gamma-ray bursts (GRBs). The presence of plateaus in the X-ray extended emission or afterglow of GRBs is widely accepted as an indicator of a magnetar central engine, particularly those with a sharp decay (faster than t ‑3), the so-called internal plateau. However, an alternative model, by taking the evolution of the magnetic flux at the BH horizon into account, suggests that an internal plateau can also arise from a jet powered by the Blandford–Znajek (BZ) mechanism (hereafter, a BZ jet). In this study, we propose that a precessional BZ jet would manifest a quasiperiodic oscillation (QPO) signature on the internal plateau and the subsequent sharp decay. Such lightcurves cannot be readily explained by the activity of a short-lived, supermassive magnetar, thus favoring a Kerr BH as the central engine. The X-ray afterglow of GRB 050904, comprising nine flares, is characterized by a QPO-modulated plateau and sharp decay, which can be well reproduced by a precessional BZ jet model. Therefore, one potential clue for distinguishing between these two engines lies in whether the QPO signature is present throughout the entire plateau and the subsequent sharp decay, as the magnetar scenario suggests a collapse at the end of the plateau.

Keywords: Stellar accretion disks, Black hole physics, Gamma-ray bursts, Relativistic jets
Modelling Time-dependent Convective Penetration in 1D Stellar Evolution. One-dimensional stellar evolution calculations produce uncertain predictions for quantities like the age, core mass, core compactness, and nucleosynthetic yields; a key source of uncertainty is the modeling of interfaces between regions that are convectively stable and those that are not. Theoretical and numerical work has demonstrated that there should be numerous processes adjacent to the convective boundary that induce chemical and angular momentum transport, as well as modify the thermal structure of the star. One such process is called convective penetration, wherein vigorous convection extends beyond the nominal convective boundary and alters both the composition and thermal structure. In this work, we incorporate the process of convective penetration in stellar evolution calculations using the stellar evolution software instrument MESA. We implement convective penetration according to the description presented by Anders et al. to to calculate a grid of models from the pre-main sequence to helium core depletion. The extent of the convective penetration zone is self-consistently calculated at each time step without introducing new free parameters. We find both a substantial penetration zone in all models with a convective core and observable differences to global stellar properties such as the luminosity and radius. We present how the predicted radial extent of the penetration zone scales with the total stellar mass, age, and metallicity of the star. We discuss our results in the context of existing numerical and observational studies.

Keywords: Stellar interiors, Stellar convective zones, Stellar structures, Stellar evolution
JWST Reveals a Luminous Infrared Source at the Position of the Failed Supernova Candidate N6946-BH1. N6946-BH1 (BH1) is the first plausible candidate for a failed supernova (SN), a peculiar event in which a massive star disappears without the expected bright SN, accompanied by collapse into a black hole (BH). Following a luminous outburst in 2009, the source experienced a significant decline in optical brightness, while maintaining a persistent IR presence. While it was proposed to be a potential failed SN, such behavior has been observed in SN impostor events in nearby galaxies. Here, we present late-time observations of BH1, taken 14 yr after disappearance, using JWST's NIRCam and MIRI instruments to probe a never before observed region of the object's spectral energy distribution (SED). We show for the first time that all previous observations of BH1 (pre- and postdisappearance) are actually a blend of at least three sources. In the near-infrared, BH1 is notably fainter than the progenitor but retains similar brightness to its state in 2017. In the mid-infrared the flux appears to have brightened compared to the inferred fluxes from the best-fitting progenitor model. The total luminosity of the source is between 13% and 25% that of the progenitor. We also show that the IR SED appears consistent with polycyclic aromatic hydrocarbon features that arise when dust is illuminated by near-ultraviolet radiation. At present, the interpretation of BH1 remains uncertain. The observations match expectations for a stellar merger, but theoretical ambiguity in the failed SN hypothesis makes it hard to dismiss.

Keywords: Massive stars, Black holes, Core-collapse supernovae, Stellar evolution
A Snapshot Survey of Nearby Supernovae with the Hubble Space Telescope. Over recent decades, robotic (or highly automated) searches for supernovae (SNe) have discovered several thousand events, many of them in quite nearby galaxies (distances &lt; 30 Mpc). Most of these SNe, including some of the best-studied events to date, were found before maximum brightness and have associated with them extensive follow-up photometry and spectroscopy. Some of these discoveries are so-called "SN impostors," thought to be superoutbursts of luminous blue variable stars, although possibly a new, weak class of massive-star explosions. We conducted a Snapshot program with the Hubble Space Telescope (HST) and obtained images of the sites of 31 SNe and four impostors, to acquire late-time photometry through two filters. The primary aim of this project was to reveal the origin of any lingering energy for each event, whether it is the result of radioactive decay or, in some cases, ongoing late-time interaction of the SN shock with preexisting circumstellar matter, or the presence of a light echo. Alternatively, lingering faint light at the SN position may arise from an underlying stellar population (e.g., a host star cluster, companion star, or a chance alignment). The results from this study complement and extend those from Snapshot programs by various investigators in previous HST cycles.

Keywords: Supernovae
Accretion Disk Size and Updated Time-delay Measurements in the Gravitationally Lensed Quasar SDSS J165043.44+425149.3. We analyze variability in 15-season optical lightcurves from the doubly imaged lensed quasar SDSS J165043.44+425149.3 (SDSS1650), comprising five seasons of monitoring data from the Maidanak Observatory (277 nights in total, including the two seasons of data previously presented in Vuissoz et al.), five seasons of overlapping data from the Mercator telescope (269 nights), and 12 seasons of monitoring data from the US Naval Observatory, Flagstaff Station at lower cadence (80 nights). We update the 2007 time-delay measurement for SDSS1650 with these new data, finding a time delay of ${\rm{\Delta }}{t}_{\mathrm{AB}}=-{55.1}_{-3.7}^{+4.0}$ days, with image A leading image B. We analyze the microlensing variability in these lightcurves using a Bayesian Monte Carlo technique to yield measurements of the size of the accretion disk at λ rest = 2420 Å, finding a half-light radius of log(r 1/2/cm) = ${16.19}_{-0.58}^{+0.38}$ assuming a 60° inclination angle. This result is unchanged if we model 30% flux contamination from the broad-line region. We use the width of the Mg II line in the existing Sloan Digital Sky Survey spectra to estimate the mass of this system's supermassive black hole, finding M BH = 2.47 × 109 M ⊙. We confirm that the accretion disk size in this system, whose black hole mass is on the very high end of the M BH scale, is fully consistent with the existing quasar accretion disk size–black hole mass relation.

Keywords: Quasar microlensing, Gravitational microlensing, Gravitational lensing, Quasars
Episodic Energy Release during the Main and Post-impulsive Phases of a Solar Flare. When and where the magnetic field energy is released and converted in eruptive solar flares remains an outstanding topic in solar physics. To shed light on this question, here we report multiwavelength observations of a C9.4-class eruptive limb flare that occurred on 2017 August 20. The flare, accompanied by a magnetic flux rope eruption and a white light coronal mass ejection, features three post-impulsive X-ray and microwave bursts immediately following its main impulsive phase. For each burst, both microwave and X-ray imaging suggest that the nonthermal electrons are located in the above-the-loop-top region. Interestingly, contrary to many other flares, the peak flux of the three post-impulsive microwave and X-ray bursts shows an increase for later bursts. Spectral analysis reveals that the sources have a hardening spectral index, suggesting a more efficient electron acceleration into the later post-impulsive bursts. We observe a positive correlation between the acceleration of the magnetic flux rope and the nonthermal energy release during the post-impulsive bursts in the same event. Intriguingly, different from some other eruptive events, this correlation does not hold for the main impulse phase of this event, which we interpret as energy release due to the tether-cutting reconnection before the primary flux rope acceleration occurs. In addition, using footpoint brightenings at conjugate flare ribbons, a weakening reconnection guide field is inferred, which may also contribute to the hardening of the nonthermal electrons during the post-impulsive phase.

Keywords: Solar flares, Solar magnetic reconnection, Solar radio emission, Non-thermal radiation sources, Solar coronal mass ejections, Solar filament eruptions
Global Impact of Emerging Internetwork Fields on the Low Solar Atmosphere. Small-scale, newly emerging internetwork (IN) magnetic fields are considered a viable source of energy and mass for the solar chromosphere and possibly the corona. Multiple studies show that single events of flux emergence can indeed locally heat the low solar atmosphere through interactions of the upward propagating magnetic loops and the preexisting ambient field lines. However, the global impact of the newly emerging IN fields on the solar atmosphere is still unknown. In this paper, we study the spatiotemporal evolution of IN bipolar flux features and analyze their impact on the energetics and dynamics of the quiet-Sun atmosphere. We use high-resolution, multiwavelength, coordinated observations obtained with the Interface Region Imaging Spectrograph, Hinode, and the Solar Dynamics Observatory to identify emerging IN magnetic fields and follow their evolution. Our observational results suggest that only the largest IN bipoles are capable of heating locally the low solar atmosphere, while the global contribution of these bipoles appears to be marginal. However, the total number of bipoles detected and their impact estimated in this work is limited by the sensitivity level, spatial resolution, and duration of our observations. To detect smaller and weaker IN fields that would maintain the basal flux, and examine their contribution to the chromospheric heating, we will need higher resolution, higher sensitivity, and longer time series obtained with current and next-generation ground- and space-based telescopes.

Keywords: Solar magnetic flux emergence, Solar photosphere, Solar magnetic fields, Solar transition region, Solar chromosphere
A Study of the Radio Spectrum of Mrk 421. We present the results of a spectral analysis using simultaneous multifrequency (22, 43, 86, and 129 GHz) very long baseline interferometry (VLBI) observations of the Korean VLBI Network on BL Lac object, Markarian 421. The data we used were obtained from 2013 January to 2018 June. The light curves showed several flux enhancements with global decreases. To separate the variable and quiescent components in the multifrequency light curves for milliarcsecond-scale emission regions, we assumed that the quiescent radiation comes from the emission regions radiating constant optically thin synchrotron emissions (i.e., a minimum flux density with an optically thin spectral index). The quiescent spectrum determined from the multifrequency light curves was subtracted from the total CLEAN flux density, yielding a variable component in the flux that produces the time-dependent spectrum. We found that the observed spectra were flat at 22–43 GHz, and relatively steep at 43–86 GHz, whereas the quiescent-corrected spectra are sometimes quite different from the observed spectra (e.g., sometimes inverted at 22–43 GHz). The quiescent-corrected spectral indices were much more variable than the observed spectral indices. This spectral investigation implies that the quiescent-spectrum correction can significantly affect the multifrequency spectral index of variable compact radio sources such as blazars. Therefore, the synchrotron self-absorption B-field strength (B SSA) can be significantly affected because B SSA is proportional to the fifth power of turnover frequency.

Keywords: BL Lacertae objects, Markarian galaxies, Blazars, Active galaxies, Relativistic jets
A Measurement of the Assembly of Milky Way Analogs at Redshifts 0.5 &lt; z &lt; 2 with Resolved Stellar Mass and Star Formation Rate Profiles. The resolved mass assembly of Milky Way–mass galaxies has been previously studied in simulations, the local Universe, and at higher redshifts using infrared (IR) light profiles. To better characterize the mass assembly of Milky Way analogs (MWAs), as well as their changes in star formation rate (SFR) and color gradients, we construct resolved stellar mass and SFR maps of MWA progenitors selected with abundance matching techniques up to z ∼2 using deep, multiwavelength imaging data from the Hubble Frontier Fields. Our results using stellar mass profiles agree well with previous studies that utilize IR light profiles, showing that the inner 2 kpc of the galaxies and the regions beyond 2 kpc exhibit similar rates of stellar mass growth. This indicates the progenitors of MWAs from z ∼ 2 to the present do not preferentially grow their bulges or their disks. The evolution of the SFR profiles indicates a greater decrease in SFR density in the inner regions versus the outer regions. Sérsic parameters indicate modest growth in the central regions at lower redshifts, perhaps indicating slight bulge growth. However, the Sérsic index does not rise above n ∼ 2 until z &lt; 0.5, meaning these galaxies are still disk-dominated systems. We find that the half-mass radii of the MWA progenitors increase between 1.5 &lt; z &lt; 2, but remain constant at later epochs (z &lt; 1.5). This implies mild bulge growth since z ∼ 2 in MWA progenitors, in line with previous MWA mass assembly studies.

Keywords: Milky Way evolution, High-redshift galaxies, Galaxy evolution, Galaxies