Sazuna/UAT_keywords huggingface dataset:
The Observability of Vortex-driven Spiral Arms in Protoplanetary Disks: Basic Spiral Properties. Some circumstellar disks are observed to show prominent spiral arms in infrared scattered light or (sub-)millimeter dust continuum. The spirals might be formed from self-gravity, shadows, or planet-disk interactions. Recently, it was hypothesized that massive vortices can drive spiral arms in protoplanetary disks in a way analogous to planets. In this paper, we study the basic properties of vortex-driven spirals by the Rossby Wave Instability in 2D hydrodynamics simulations. We study how the surface density contrast, the number, and the shape of vortex-driven spirals depend on the properties of the vortex. We also compare vortex-driven spirals with those induced by planets. The surface density contrast of vortex-driven spirals in our simulations are comparable to those driven by a sub-thermal mass planet, typically a few to a few tens of Earth masses. In addition, different from the latter, the former is not sensitive to the mass of the vortex. Vortex-driven spiral arms are not expected to be detectable in current scattered light observations, and the prominent spirals observed in scattered light in a few protoplanetary disks, such as SAO 206462 (HD 135344B), MWC 758, and LkHα 330, are unlikely to be induced by the candidate vortices in them.

Keywords: Hydrodynamical simulations, Planet formation, Protoplanetary disks, Hydrodynamics
The Habitability of GJ 357D: Possible Climate and Observability. The GJ 357 system harbors three planets orbiting a bright, nearby M2.5V star at 9.44 pc. The innermost planet, GJ 357b (TOI-562.01), is a hot transiting Earth-sized planet with Earth-like density, which receives about 12 times the irradiation Earth receives from the Sun, and was detected using data from TESS. Radial velocities discovered two more planets in the system at 9.12 (GJ 357 c) and 55.6 days (GJ 357 d), with minimum masses of 3.59 ± 0.50 and 6.1 ± 1 Earth masses, and an irradiation of 4.4 and 0.38 Earth’s irradiation, respectively. GJ 357 d receives slightly less stellar irradiation than Mars does in our own solar system, which puts it in the Habitable Zone (HZ) for its host star. GJ 357 d could not have been detected with TESS and whether it transits remains an open question. Here we model possible conditions within which GJ357 d could sustain surface habitability and present planetary models as well as synthetic transmission, reflection, and emission spectra for a range of models for GJ 357 d from water worlds to Earth-like models. With Earth-analog outgassing rates, GJ 357 d would be a frozen rocky world; however, with an increased CO2 level, as would be expected if a geological cycles regulates CO2 concentration like on Earth, the planet models show temperate surface conditions. If we can detect a transit of GJ 357 d, it would become the closest transiting, potentially habitable planet in the solar neighborhood. Even if GJ 357 d does not transit, the brightness of its star makes this planet, in the HZ of a close-by M star, a prime target for observations with Extremely Large telescopes as well as future space missions.

Keywords: Exoplanet astronomy, Habitable zone, Exoplanet atmospheres, Planet hosting stars
A Future Percent-level Measurement of the Hubble Expansion at Redshift 0.8 with Advanced LIGO. Simultaneous measurements of distance and redshift can be used to constrain the expansion history of the universe and associated cosmological parameters. Merging binary black hole (BBH) systems are standard sirens—their gravitational waveform provides direct information about the luminosity distance to the source. There is, however, a perfect degeneracy between the source masses and redshift; some nongravitational information is necessary to break the degeneracy and determine the redshift of the source. Here we suggest that the pair instability supernova (PISN) process, thought to be the source of the observed upper limit on the black hole mass in merging BBH systems at ∼ 45 {M}⊙ , imprints a mass scale in the population of BBH mergers and permits a measurement of the redshift-luminosity-distance relation with these sources. We simulate five years of BBH detections in the Advanced LIGO and Virgo detectors with a realistic BBH merger rate, mass distribution with smooth PISN cutoff, and measurement uncertainty. We show that after one year of operation at design sensitivity the BBH population can constrain H(z) to 6.1 % at a pivot redshift z≃ 0.8. After five years the constraint improves to 2.9 % . If the PISN cutoff is sharp, the uncertainty is smaller by about a factor of two. This measurement relies only on general relativity and the presence of a mass scale that is approximately fixed or calibrated across cosmic time; it is independent of any distance ladder. Observations by future “third-generation” gravitational wave detectors, which can see BBH mergers throughout the universe, would permit subpercent cosmographical measurements to z ≳ 4 within one month of observation.

Keywords: Hubble constant, Distance measure, Gravitational wave astronomy
Discovery of an Mg II Changing-look Active Galactic Nucleus and Its Implications for a Unification Sequence of Changing-look Active Galactic Nuclei. Changing look (CL) is a rare phenomenon of active galactic nuclei (AGNs) that exhibit emerging or disappearing broad lines accompanied by continuum variations on astrophysically short timescales (≲1 yr to a few decades). While previous studies have found Balmer-line (broad Hα and/or Hβ) CL AGNs, the broad Mg II line is persistent even in dim states. No unambiguous Mg II CL AGN has been reported to date. We perform a systematic search of Mg II CL AGNs using multi-epoch spectra of a special population of Mg II-emitters (characterized by strong broad Mg II emission with little evidence for AGNs from other normal indicators such as broad Hα and Hβ or blue power-law continua) from the Sloan Digital Sky Survey Data Release 14. We present the discovery of the first unambiguous case of a Mg II CL AGN, SDSS J152533.60+292012.1 (at redshift z = 0.449), which is turning off within rest-frame 286 days. The dramatic diminishing of Mg II equivalent width (from 110 ± 26 Å to being consistent with zero), together with little optical continuum variation (ΔV max-min = 0.17 ± 0.05 mag) coevally over ∼10 yr, rules out dust extinction or a tidal disruption event. Combined with previously known Hβ CL AGNs, we construct a sequence that represents different temporal stages of CL AGNs. This CL sequence is best explained by the photoionization model of Guo et al. In addition, we present two candidate turn-on Mg II CL AGNs and a sample of 361 Mg II-emitters for future Mg II CL AGN searches.

Keywords: Black hole physics, Active galaxies, Active galactic nuclei
The Complete Evolution of a Neutron-star Binary through a Common Envelope Phase Using 1D Hydrodynamic Simulations. Over 40 years of research suggests that the common envelope phase, in which an evolved star engulfs its companion upon expansion, is the critical evolutionary stage forming short-period, compact-object binary systems, such as coalescing double compact objects, X-ray binaries, and cataclysmic variables. In this work, we adapt the one-dimensional hydrodynamic stellar evolution code, MESA, to model the inspiral of a 1.4 M ⊙ neutron star (NS) inside the envelope of a 12 M ⊙ red supergiant star. We self-consistently calculate the drag force experienced by the NS and the back-reaction onto the expanding envelope as the NS spirals in. Nearly all of the hydrogen envelope escapes, expanding to large radii (∼102 au) where it forms an optically thick envelope with temperatures low enough that dust formation occurs. We simulate the NS orbit until only 0.8 M ⊙ of the hydrogen envelope remains around the giant star’s core. Our results suggest that the inspiral will continue until another ≈0.3 M ⊙ are removed, at which point the remaining envelope will retract. Upon separation, a phase of dynamically stable mass transfer onto the NS accretor is likely to ensue, which may be observable as an ultraluminous X-ray source. The resulting binary, comprised of a detached 2.6 M ⊙ helium star and an NS with a separation of 3.3-5.7 R ⊙, is expected to evolve into a merging double neutron-star, analogous to those recently detected by LIGO/Virgo. For our chosen combination of binary parameters, our estimated final separation (including the phase of stable mass transfer) suggests a very high α CE-equivalent efficiency of ≈5.

Keywords: X-ray binary stars, Binary stars, Close binary stars, Massive stars, Compact binary stars, High mass x-ray binary stars, Interacting binary stars, Gravitational wave sources, Gravitational wave astronomy, Compact objects, Low-mass x-ray binary stars, Binary pulsars
Runaway Young Stars near the Orion Nebula. The star-forming region of the Orion Nebula (ONC) is ideal to study the stellar dynamics of young stars in a clustered environment. Using Gaia DR2 we search for pre-main sequence stars with unusually high proper motions that may be representative of a dynamical ejection from unstable young triple systems or other close three-body encounters. We identify 26 candidate stars that are likely to have had such an encounter in the last 1 Myr. Nine of these stars could be traced back to the densest central-most region of the ONC, the Trapezium, while five others have likely interactions with other OB-type stars in the cluster. Seven stars originate from other nearby populations within the Orion Complex that coincidentally scattered toward the ONC. A definitive point of origin cannot be identified for the remaining sources. These observations shed light on the frequency of the ejection events in young clusters.

Keywords: Young massive clusters, Stellar dynamics, Pre-main sequence stars, Three-body problem, Proper motions
Subkiloparsec Imaging of Lyα Emission in a Low-mass, Highly Ionized, Gravitationally Lensed Galaxy at z = 1.84. Low-mass, low-metallicity galaxies at low to moderate (z ≲ 3) redshifts offer the best opportunity for detailed examination of the interplay between massive stars, ionizing radiation and gas in sources similar to those that likely reionized the universe. We present new narrowband Hubble Space Telescope observations of {Ly}α emission and the adjacent ultraviolet (UV) continuum in the low-mass (M ⋆ = 2 × 108 {M}⊙ ), low-metallicity (Z ∼ 1/20 Z⊙), and highly ionized gravitationally lensed galaxy SL2S J02176-0513 at z = 1.844. The galaxy has strong {Ly}α emission with photometric equivalent width {W}Lyα }phot}=218+/- 12 \mathringA , at odds with the {Ly}α escape fraction of 10%. However, the spectroscopic {Ly}α profile suggests the presence of broad absorption underlying the emission, and the total equivalent width is consistent with the escape fraction once this underlying absorption is included. The {Ly}α emission is more spatially extended than the UV continuum, and the 0.″14 spatial resolution of HST coupled with the magnification of gravitational lensing enables us to examine the distribution of {Ly}α and the UV continuum on subkiloparsec scales. We find that the peaks of the {Ly}α emission and the UV continuum are offset by 650 pc, and there is no {Ly}α emission arising from the region with the strongest UV light. Our combined spectroscopic and imaging data imply a significant range in neutral hydrogen column density across the object. These observations offer indirect support for a model in which ionizing radiation escapes from galaxies through channels with low column density of neutral gas. Based on observations with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. Support for program number 14632 was provided through a grant from the STScI under NASA contract NAS5-26555.

Keywords: Lyman-alpha galaxies, Reionization, Dwarf galaxies
Exploring the Mid-infrared SEDs of Six AGN Dusty Torus Models. I. Synthetic Spectra. At distances from the active galaxy nucleus where the ambient temperature falls below ∼1500-1800 K, dust is able to survive. It is thus possible to have a large dusty structure present that surrounds the active galaxy nucleus. This is the first of two papers aiming at comparing six dusty torus models with available spectral energy distributions, namely, Fritz et al., Nenkova et al., Hönig &amp; Kishimoto, Siebenmorgen et al., Stalevski et al., and Hönig &amp; Kishimoto. In this first paper we use synthetic spectra to explore the discrimination between these models and under which circumstances they allow us to restrict the torus parameters, while our second paper analyzes the best model to describe the mid-infrared spectroscopic data. We have produced synthetic spectra from current instruments GTC/CanariCam and Spitzer/IRS and future James Webb Space Telescope (JWST)/MIRI and JWST/NIRSpec instruments. We find that for a reasonable brightness (F 12 μm &gt; 100 mJy) we can actually distinguish among models except for the two pairs of parent models. We show that these models can be distinguished based on the continuum slopes and the strength of the silicate features. Moreover, their parameters can be constrained within 15% of error, irrespective of the instrument used, for all the models except Hönig &amp; Kishimoto. However, the parameter estimates are ruined when more than 50% of circumnuclear contributors are included. Therefore, future high spatial resolution spectra such as those expected from JWST will provide enough coverage and spatial resolution to tackle this topic.

Keywords: Dust continuum emission, Active galactic nuclei, Infrared galaxies
Exploring the Mid-infrared SEDs of Six AGN Dusty Torus Models. II. The Data. This is the second in a series of papers devoted to exploring a set of six dusty models of active galactic nuclei (AGN) with available spectral energy distributions. These models are the smooth torus by Fritz et al., the clumpy torus by Nenkova et al., the clumpy torus by Hönig &amp; Kishimoto, the two-phase torus by Siebenmorgen et al., the two-phase torus by Stalevski et al., and the wind model by Hönig &amp; Kishimoto. The first paper explores discrimination among models and the parameter restriction using synthetic spectra. Here we perform spectral fitting of a sample of 110 AGN drawn from the Swift/BAT survey with Spitzer/IRS spectroscopic data. The aim is to explore which is the model that describes better the data and the resulting parameters. The clumpy wind-disk model by Hönig &amp; Kishimoto provides good fits for ∼50% of the sample, and the clumpy torus model by Nenkova et al. is good at describing ∼30% of the objects. The wind-disk model by Hönig &amp; Kishimoto is better for reproducing the mid-infrared spectra of type 1 Seyferts (with 60% of the type 1 Seyferts well reproduced by this model compared to the 10% well represented by the clumpy torus model by Nenkova et al.), while type 2 Seyferts are equally fitted by both models (roughly 40% of the type 2 Seyferts). Large residuals are found irrespective of the model used, indicating that the AGN dust continuum emission is more complex than predicted by the models or that the parameter space is not well sampled. We found that all the resulting parameters for our AGN sample are roughly constrained to 10%-20% of the parameter space. Contrary to what is generally assumed, the derived outer radius of the torus is smaller (reaching up to a factor of ∼5 smaller for 10 pc tori) for the smooth torus by Fritz et al. and the two-phase torus by Stalevski et al. than the one derived from the clumpy torus by Nenkova et al. Covering factors and line-of-sight viewing angles strongly depend on the model used. The total dust mass is the most robust derived quantity, giving equivalent results for four of these models.

Keywords: Infrared astronomy, Dust continuum emission, Active galactic nuclei
A Fresh Look at Narrow-angle Tail Radio Galaxy Dynamics, Evolution, and Emissions. We present a 3D magnetohydrodynamic study of narrow-angle tail (NAT) radio galaxy (RG) dynamics, including passive cosmic ray electrons. We follow the evolution of a bipolar-jet RG in a persistent crosswind through hundreds of Myr. We confirm traditional jet-bending models, while noting that our NAT exhibits a transitional morphology reminiscent of wide-angle radio tails. Once deflected, jets remain internally stable, but are intermittently disrupted by external disturbances induced by the NAT dynamics itself. The disruptions enhance jet and tail magnetic fields. Disrupted jet plasma is heterogeneously mixed with denser wind plasma, yielding patchy, filamentary tails that grow longer at a rate exceeding the wind speed. Such fast tail extension could, for example, allow NAT tails to overtake extraneous intracluster medium (ICM) features, such as shocks and shear layers downwind of where the tails first form. Those events, in turn, could generate enhanced radio emissions within the ICM features themselves that do not follow the geometrical extension of the tails past the encounter. Analysis of synthetic radio observations reveals an extended time period once the NAT has developed in which it displays a nearly steady-state morphology with integrated fluxes that are roughly constant, along with a self-similar, curved integrated spectrum. In an appendix, we outline a simple analytic jet trajectory formalism with one adjustable parameter, using it to illustrate explicit trajectories that extend the classic bending model to arbitrary jet-wind orientations.

Keywords: Intracluster medium, Tailed radio galaxies, Galaxy jets, Magnetohydrodynamical simulations
Curvature-induced Polarization and Spectral Index Behavior for PKS 1502+106. A comprehensive study of multifrequency correlations can shed light on the nature of variation for blazars. In this work, we collect the long-term radio, optical, and γ-ray light curves of PKS 1502+106. After performing the localized cross-correlation function analysis, we find that correlations between radio and γ-ray or V band are beyond the 3σ significance level. The lag of the γ-ray relative to 15 GHz is -{60}-10+5 days, translating to a distance of {3.18}-0.27+0.50 parsec (pc) between them. Within uncertainties, the locations of the γ-ray and optical emitting regions are roughly the same, and are away from the jet base within 1.2 pc. The derived magnetic field in optical and γ-ray emitting regions is about 0.36 G. The logarithm of γ-ray flux is significantly linearly correlated with that of V-band fluxes, which can be explained by the synchrotron self-Compton process, the external Compton processes, or the combination of them. We find a significant linear correlation in the plot of {log}\prod (polarization degree) versus {log}ν {F}ν  at V band, and use the empirical relation Π ∼ sin n  θ‧ (θ‧ is the observing angle in the comoving frame blob) to explain it. The behaviors of color index (generally redder when brighter at the active state) and γ-ray spectral index (softer when brighter) could be well explained by the twisted jet model. These findings suggest that the curvature effect (mainly due to the change of the viewing angle) is dominant in the variation phenomena of fluxes, spectral indices, and polarization degrees for PKS 1502+106.

Keywords: Radio jets, Gamma-ray sources, Blazars, Relativistic jets, Active galactic nuclei
Can an Unobserved Concentration of Magnetic Flux Above the Poles of the Sun Resolve the Open Flux Problem?. Global models of the extended solar corona, driven by observed photospheric magnetic fields, generally cannot reproduce the amplitude of the measured interplanetary magnetic field at 1 au (or elsewhere in the heliosphere), often underestimating it by a factor of two or more. Some modelers have attempted to resolve this “open flux” problem by adjusting what they believe to be errors in the estimates of the photospheric field values. Others have simply multiplied interplanetary estimates by some correction factor to match 1 au values. Here, we investigate whether this “missing” flux can be explained by a source of largely unobserved, concentrated bundles of flux in the photosphere at latitudes too high to be adequately resolved by ground-based observatories or Earth-based spacecraft. Using potential field source-surface and magnetohydrodynamic models, we demonstrate that this additional polar flux can (at least partially) resolve the open flux problem, without generating any new observational discrepancies. For example, we show that model solutions without this additional flux systematically produce streams lying at higher hello-latitudes than is inferred from observations. More importantly, adding this polar flux to the models does not substantially change the location or size of computed coronal holes. The upcoming joint ESA/NASA Solar Orbiter mission may be able to support or refute this idea.

Keywords: Solar photosphere, Interplanetary magnetic fields, Solar coronal holes, Solar coronal streamers, Magnetohydrodynamical simulations
Multiwavelength Period-Luminosity and Period-Luminosity-Color Relations at Maximum Light for Mira Variables in the Magellanic Clouds. We present Period-Luminosity and Period-Luminosity-Color relations at maximum light for Mira variables in the Magellanic Clouds using time-series data from the Optical Gravitational Lensing Experiment (OGLE-III) and Gaia data release 2. The maximum-light relations exhibit a scatter typically up to ∼30% smaller than their mean-light counterparts. The apparent magnitudes of oxygen-rich Miras at maximum light display significantly smaller cycle-to-cycle variations than at minimum light. High-precision photometric data for Kepler Mira candidates also exhibit stable magnitude variations at the brightest epochs, while their multi-epoch spectra display strong Balmer emission lines and weak molecular absorption at maximum light. The stability of maximum-light magnitudes for Miras possibly occurs due to the decrease in the sensitivity to molecular bands at their warmest phase. At near-infrared wavelengths, the period-luminosity relations (PLRs) of Miras display similar dispersion at mean and maximum light with limited time-series data in the Magellanic Clouds. A kink in the oxygen-rich Mira PLRs is found at 300 days in the VI-bands, which shifts to longer periods (∼350 days) at near-infrared wavelengths. Oxygen-rich Mira PLRs at maximum light provide a relative distance modulus, Δμ = 0.48 ± 0.08 mag, between the Magellanic Clouds with a smaller statistical uncertainty than the mean-light relations. The maximum-light properties of Miras can be very useful for stellar atmosphere modeling and distance scale studies provided their stability and the universality can be established in other stellar environments in the era of extremely large telescopes.

Keywords: Mira variable stars, Magellanic Clouds, Long period variable stars, Pulsating variable stars