Sazuna/UAT_keywords huggingface dataset:
Earth's Polar Night Boundary Layer as an Analog for Dark Side Inversions on Synchronously Rotating Terrestrial Exoplanets. A key factor in determining the potential habitability of synchronously rotating planets is the strength of the atmospheric boundary layer inversion between the dark side surface and the free atmosphere. Here we analyze data obtained from polar night measurements at the South Pole and Alert Canada, which are the closest analogs on Earth to conditions on the dark sides of synchronously rotating exoplanets without and with a maritime influence, respectively. On Earth, such inversions rarely exceed 30 K in strength, because of the effect of turbulent mixing induced by phenomena such as so-called "mesoscale slope winds," which have horizontal scales of 10-100 s of km, suggesting a similar constraint to near-surface dark side inversions. We discuss the sensitivity of inversion strength to factors such as orography and the global-scale circulation, and compare them to a simulation of the planet Proxima Centauri b. Our results demonstrate the importance of comparisons with Earth data in exoplanet research, and highlight the need for further studies of the exoplanet atmospheric collapse problem using mesoscale and eddy-resolving models.

Keywords: Land-atmosphere interactions, Exoplanet atmospheric composition , Exoplanets, Planetary boundary layers, Exoplanet atmospheric variability, Planetary atmospheres, Exoplanet surface variability, Exoplanet surface characteristics, Habitable planets, Exoplanet atmospheres, Atmospheric science
Evidence for Magnetar Precession in X-Ray Afterglows of Gamma-Ray Bursts. Many gamma-ray bursts are followed by periods of extended emission. At least in some cases, the burst afterglow may be powered by a rapidly rotating, highly magnetized neutron star, which spins down due to electromagnetic and gravitational-wave emission. Such a remnant is likely to strongly precess in the early stages of its life, which would lead to modulations in the X-ray luminosity as the triaxiality of the system evolves over time. Using a radiation profile appropriate for a precessing, oblique rotator, we find that Swift-XRT data of a long (080602) and a short (090510) burst matches the model with significantly higher accuracy (mean-square residuals dropping by ≳200% in the early stages of the extended emission) than for an orthogonal rotator. We interpret this as evidence for precession in newborn magnetars.

Keywords: Magnetars, Gamma-ray bursts, Magnetic fields, Stellar oscillations
A 1201 s Orbital Period Detached Binary: The First Double Helium Core White Dwarf LISA Verification Binary. We report the discovery of a 1201 s orbital period binary, the third shortest-period detached binary known. Sloan Digital Sky Survey J232230.20 + 050942.06 contains two He-core white dwarfs orbiting with a 27° inclination. Located 0.76 kpc from the Sun, the binary has an estimated Laser Interferometer Space Antenna (LISA) 4 yr signal-to-noise ratio of 40. J2322 + 0509 is the first He + He white dwarf LISA verification binary, a source class that is predicted to account for one-third of resolved LISA ultra-compact binary detections.

Keywords: White dwarf stars, Compact binary stars, Gravitational wave sources, Gravitational waves, DA stars, Compact objects, Detached binary stars, DC stars
The Low Earth Orbit Satellite Population and Impacts of the SpaceX Starlink Constellation. I discuss the current low Earth orbit artificial satellite population and show that the proposed "megaconstellation" of circa 12,000 Starlink Internet satellites would dominate the lower part of the Earth orbit, below 600 km, with a latitude-dependent areal number density of between 0.005 and 0.01 objects per square degree at airmass &lt;2. Such large, low-altitude satellites appear visually bright to ground observers, and the initial Starlinks are naked-eye objects. I model the expected number of illuminated satellites as a function of latitude, time of year, and time of night and summarize the range of possible consequences for ground-based astronomy. In winter at lower latitudes typical of major observatories, the satellites will not be illuminated for six hours in the middle of the night. However, at low elevations near twilight at intermediate latitudes (45°-55°, e.g., much of Europe) hundreds of satellites may be visible at once to naked-eye observers at dark sites.

Keywords: Ground-based astronomy, Artificial satellites, Astronomical site protection, Night sky brightness
High-resolution Spectroscopy of the GD-1 Stellar Stream Localizes the Perturber near the Orbital Plane of Sagittarius. The 100° long thin stellar stream in the Milky Way halo, GD-1, has an ensemble of features that may be due to dynamical interactions. Using high-resolution MMT/Hectochelle spectroscopy we show that a spur of GD-1-like stars outside of the main stream are kinematically and chemically consistent with the main stream. In the spur, as in the main stream, GD-1 has a low intrinsic radial velocity dispersion, σV_r ≲ 1 km s-1, is metal-poor, [Fe/H] ≈ -2.3, and has little intrinsic spread in the [Fe/H] and [α/Fe] abundances, which point to a common globular cluster progenitor. At a fixed location along the stream, the median radial velocity offset between the spur and the main stream is smaller than 0.5 km s-1, comparable to the measurement uncertainty. A flyby of a massive, compact object can change orbits of stars in a stellar stream and produce features like the spur observed in GD-1. In this scenario, the radial velocity of the GD-1 spur relative to the stream constrains the orbit of the perturber and its current on-sky position to ≈5000 deg2. The family of acceptable perturber orbits overlaps the stellar and dark-matter debris of the Sagittarius dwarf galaxy in present-day position and velocity. This suggests that GD-1 may have been perturbed by a globular cluster or an extremely compact dark-matter subhalo formerly associated with Sagittarius.

Keywords: High resolution spectroscopy, Milky Way dark matter halo, Tidal tails, Milky Way dynamics
Cometary Activity Discovered on a Distant Centaur: A Nonaqueous Sublimation Mechanism. Centaurs are minor planets thought to have originated in the outer solar system region known as the Kuiper Belt. Active Centaurs enigmatically display comet-like features (e.g., tails, comae) even though they orbit in the gas giant region where it is too cold for water to readily sublimate. Only 18 active Centaurs have been identified since 1927 and, consequently, the underlying activity mechanism(s) have remained largely unknown up to this point. Here we report the discovery of activity emanating from Centaur 2014 OG392, based on archival images we uncovered plus our own new observational evidence acquired with the Dark Energy Camera (Cerro Tololo Inter-American Observatory Blanco 4 m telescope), the Inamori-Magellan Areal Camera &amp; Spectrograph (Las Campanas Observatory 6.5 m Walter Baade Telescope), and the Large Monolithic Imager (Lowell Observatory 4.3 m Discovery Channel Telescope). We detect a coma as far as 400,000 km from 2014 OG392, and our novel analysis of sublimation processes and dynamical lifetime suggest carbon dioxide and/or ammonia are the most likely candidates for causing activity on this and other active Centaurs. We find 2014 OG392 is optically red, but CO2 and NH3 are spectrally neutral in this wavelength regime so the reddening agent is as yet unidentified.

Keywords: Comet tails, Centaur group, Comae, Astrochemistry
A Comparison of UV and Optical Metallicities in Star-forming Galaxies. Our ability to study the properties of the interstellar medium in the earliest galaxies will rely on emission-line diagnostics at rest-frame ultraviolet (UV) wavelengths. In this work, we identify metallicity-sensitive diagnostics using UV emission lines. We compare UV-derived metallicities with standard, well-established optical metallicities using a sample of galaxies with rest-frame UV and optical spectroscopy. We find that the He2-O3C3 diagnostic (He II λ1640 ${\rm{\mathring{\rm A} }}$ /C III] λ1906,1909 ${\rm{\mathring{\rm A} }}$ versus [O III] λ1666 ${\rm{\mathring{\rm A} }}$ /C III] λ1906,9 ${\rm{\mathring{\rm A} }}$ ) is a reliable metallicity tracer, particularly at low metallicity ( $12+{\mathrm{log}}_{10}({\rm{O}}/{\rm{H}})\leqslant 8$ ), where stellar contributions are minimal. We find that the Si3-O3C3 diagnostic ([Si III] λ1883 ${\rm{\mathring{\rm A} }}$ /C III] λ1906 ${\rm{\mathring{\rm A} }}$ versus [O III] λ1666 ${\rm{\mathring{\rm A} }}$ /C III] λ1906,9 ${\rm{\mathring{\rm A} }}$ ) is a reliable metallicity tracer, though with large scatter (0.2-0.3 dex), which we suggest is driven by variations in gas-phase abundances. We find that the C4-O3C3 diagnostic (C IV λ 1548,50 ${\rm{\mathring{\rm A} }}$ /[O III] λ 1666 ${\rm{\mathring{\rm A} }}$ versus [O III] λ 1666 ${\rm{\mathring{\rm A} }}$ /C III] λ 1906,9 ${\rm{\mathring{\rm A} }}$ ) correlates poorly with optically derived metallicities. We discuss possible explanations for these discrepant metallicity determinations, including the hardness of the ionizing spectrum, contribution from stellar wind emission, and non-solar-scaled gas-phase abundances. Finally, we provide two new UV oxygen abundance diagnostics, calculated from polynomial fits to the model grid surface in the He2-O3C3 and Si3-O3C3 diagrams.

Keywords: Massive stars, Emission line galaxies, Ultraviolet astronomy, Galaxy abundances, Metallicity
Gravitational-wave Radiation of Double Degenerates with Extremely Low-mass White Dwarf Companions. Double degenerate (DD) systems are supposed to be significant gravitational-wave (GW) sources for future space-based GW detectors, e.g., the Laser Interferometer Space Antenna (LISA). Recently, one type of DD system with extremely low-mass WD (ELM WD; ≲ 0.30 M⊙) companions was found in the ELM Survey. These companions have very short orbital periods and are therefore important sources for LISA detection. Further, due to the thick envelope of ELM WDs compared with massive WDs (e.g., CO WDs), they are much easier to find through the combination of electromagnetic (EM) and GW observations. In this paper, we first obtain the population of ELM WDs in DDs by considering the detailed evolutionary tracks of ELM WDs and then analyzing the GW radiation of these systems. We found that about 6 × 103 sources could be solely detected by LISA, including ∼2 × 103 chirping sources, and ∼13 (∼107) more sources are expected to be detected by both LISA and the ELM Survey (Gaia).

Keywords: Close binary stars, White dwarf stars, Gravitational waves
NuSTAR and Chandra Observations of the Galactic Center Nonthermal X-Ray Filament G0.13-0.11: A Pulsar-wind-nebula-driven Magnetic Filament. One of the most unique phenomena in the Galactic center region is the existence of numerous long and narrow filamentary structures within a few hundred parsecs of Sgr A⋆. While more than 100 radio filaments have been revealed by MeerKAT, only about two dozen X-ray filaments have been discovered so far. In this article, we report our analysis of deep Chandra and NuSTAR observations of a nonthermal X-ray filament, G0.13-0.11, which is located adjacent to the Radio Arc. Chandra revealed a unique morphology of G0.13-0.11, which is an elongated (0.1 pc in width and 3.2 pc in length) structure slightly bent toward the Radio Arc. A pulsar candidate (Γ ∼ 1.4) is detected in the middle of the filament, with a tail of diffuse nonthermal X-ray emission on one side of the filament. The filament is detected by NuSTAR up to 79 keV, with the hard X-ray centroid consistent with the pulsar candidate. We found that the X-ray intensity decays along the filament farther away from the pulsar candidate, dropping to half of its peak value 2.2 pc away. This system is most likely a pulsar wind nebula (PWN) interacting with the ambient interstellar magnetic field, where the filaments are kinetic jets from the PWN as recently proposed. The nature of this filament adds to the complex origin of X-ray filaments, which serve as powerful tools for probing local and global powerful particle accelerators in the Galactic center.

Keywords: Galactic center, Non-thermal radiation sources, Interstellar filaments
Building the Largest Spectroscopic Sample of Ultracompact Massive Galaxies with the Kilo Degree Survey. Ultracompact massive galaxies (UCMGs), I.e., galaxies with stellar masses ${M}_{\star }\gt 8\times {10}^{10}{M}_{\odot }$ and effective radii ${R}_{{\rm{e}}}\lt 1.5\,\mathrm{kpc}$ , are very rare systems, in particular at low and intermediate redshifts. Their origin as well as their number density across cosmic time are still under scrutiny, especially because of the paucity of spectroscopically confirmed samples. We have started a systematic census of UCMG candidates within the ESO Kilo Degree Survey, together with a large spectroscopic follow-up campaign to build the largest possible sample of confirmed UCMGs. This is the third paper of the series and the second based on the spectroscopic follow-up program. Here, we present photometrical and structural parameters of 33 new candidates at redshifts $0.15\lesssim z\lesssim 0.5$ and confirm 19 of them as UCMGs, based on their nominal spectroscopically inferred ${M}_{\star }$ and ${R}_{{\rm{e}}}$ . This corresponds to a success rate of $\sim 58 \% $ , nicely consistent with our previous findings. The addition of these 19 newly confirmed objects allows us to fully assess the systematics on the system selection - and to finally reduce the number density uncertainties. Moreover, putting together the results from our current and past observational campaigns and some literature data, we build the largest sample of UCMGs ever collected, comprising 92 spectroscopically confirmed objects at $0.1\lesssim z\lesssim 0.5$ . This number raises to 116, allowing for a 3σ tolerance on the ${M}_{\star }$ and ${R}_{{\rm{e}}}$ thresholds for the UCMG definition. For all these galaxies, we have estimated the velocity dispersion values at the effective radii, which have been used to derive a preliminary mass-velocity dispersion correlation.

Keywords: Galaxy formation, Galaxy kinematics, Galaxy mergers, Spectroscopy, Galaxy counts, Early-type galaxies
On the Number of Independent Parameters of Interstellar Extinction Curves. The number of independent parameters that ultraviolet interstellar extinction curves depend on has never been decisively clarified, yet the issue is critical for the comprehension and modeling of interstellar extinction observations. Cardelli, Clayton, &amp; Mathis (CCM89) concluded that normalized extinction curves rely on only one parameter, but E. Fitzpatrick and others consider this finding at most a first-order approximation favored by uncertainties in measurement. However, the multiparameter fits successively introduced by Fitzpatrick &amp; Massa were intended to give the best possible analytical representation of extinction curves, not to investigate their degrees of freedom. A deeper examination of these fits and of the CCM89 conclusion shows that they do not necessarily conflict. Fitzpatrick &amp; Massa's parameterization of extinction curves and the large database (nearly 600 directions) published by Krelowski &amp; Strobel are used in this paper to show that, within the precision allowed by the data, E(λ - V) correlates tightly with E(B - V) for all λ within the near-infrared to far-ultraviolet spectrum. This correlation confirms the relationships that led to the CCM89 fit and calls into question the reliability of today's interstellar dust models, which all need at least seven parameters (reddening included) to fit observed ultraviolet extinction curves.

Keywords: Interstellar dust extinction
Kinetic Simulations of Nonrelativistic Perpendicular Shocks of Young Supernova Remnants. III. Magnetic Reconnection. Fully kinetic two-dimensional particle-in-cell simulations are used to study electron acceleration at high-Mach-number nonrelativistic perpendicular shocks. Supernova remnant shocks are mediated by the Weibel instability, which is excited because of an interaction between shock-reflected and upstream ions. Nonlinear evolution of the Weibel instability leads to the formation of current sheets. At the turbulent shock ramp the current sheets decay through magnetic reconnection. The number of reconnection sites strongly depends on the ion-to-electron mass ratio and the Alfvénic Mach number of the simulated shock. Electron acceleration is observed at locations where magnetic reconnection operates. For the highest mass ratios almost all electrons are involved in magnetic reconnection, which makes the magnetic reconnection the dominant acceleration process for electrons at these shocks. We discuss the relevance of our results for 3D systems with realistic ion-to-electron mass ratio.

Keywords: Supernova remnants, Shocks, Interstellar medium, Space plasmas
Quasi-periodic Pulsation Detected in Lyα Emission During Solar Flares. We investigated the quasi-periodic pulsation (QPP) in Lyα, X-ray, and extreme-ultraviolet (EUV) emissions during two solar flares, I.e., an X-class (SOL2012-01-27T) and a C-class (SOL2016-02-08T). The full-disk Lyα and X-ray flux during these solar flares were recorded by the EUV Sensor and X-Ray Sensor on board the Geostationary Operational Environmental Satellite. The flare regions were located from the EUV images measured by the Atmospheric Imaging Assembly. The QPP could be identified as a series of regular and periodic peaks in the light curves, and its quasi-periodicity was determined from the global wavelet and Fourier power spectra. A quasi-periodicity at about 3 minutes is detected during the impulsive phase of the X-class flare, which could be explained as the acoustic wave in the chromosphere. Interestingly, a quasi-periodicity at roughly 1 minute is discovered during the entire evolutionary phases of solar flares, including the precursor, impulsive, and gradual phases. This is the first report of 1 minute QPP in the Lyα emission during solar flares, in particular during the flare precursor. It may be interpreted as a self-oscillatory regime of the magnetic reconnection, such as magnetic dripping.

Keywords: Solar flares, Solar ultraviolet emission, Solar x-ray emission, Solar oscillations, Solar chromosphere
Dark Matter Distribution of Four Low-z Clusters of Galaxies. We present here the weak gravitational lensing detection of four nearby galaxy clusters in the southern sky: A2029, A85, A1606, and A2457. The weak lensing detections of A1606 and A2457 are the first in the literature. This work capitalizes on the wide field of view of the Dark Energy Camera at the Cerro Tololo Inter-American Observatory, which we use to obtain deep, multiwavelength imaging of all targets. We publish maps of the clusters' projected mass distributions and obtain the M200 of their clusters through Navarro-Frenk-White profile fits to the 2D tangential ellipticity signal.

Keywords: Galaxy clusters, Abell clusters, Weak gravitational lensing
Magnetars from Neutron Star-White Dwarf Mergers: Application to Fast Radio Bursts. It is widely believed that magnetars could be born in core-collapse supernovae (SNe), binary neutron star (BNS) or binary white dwarf (BWD) mergers, or accretion-induced collapse (AIC) of white dwarfs. In this paper, we investigate whether magnetars could also be produced from neutron star-white dwarf (NSWD) mergers, motivated by FRB 180924-like fast radio bursts (FRBs) possibly from magnetars born in BNS/BWD/AIC channels suggested by Margalit et al. (2019). By a preliminary calculation, we find that NSWD mergers with unstable mass transfer could result in the NS acquiring an ultra-strong magnetic field via the dynamo mechanism due to differential rotation and convection or possibly via the magnetic flux conservation scenario of a fossil field. If NSWD mergers can indeed create magnetars, then such objects could produce at least a subset of FRB 180924-like FRBs within the framework of flaring magnetars, since the ejecta, local environments, and host galaxies of the final remnants from NSWD mergers resemble those of BNS/BWD/AIC channels. This NSWD channel is also able to well explain both the observational properties of FRB 180924-like and FRB 180916.J0158+65-like FRBs within a large range in local environments and host galaxies.

Keywords: Magnetars, Radio bursts, Gravitational waves
Constraining the Mass of the Emerging Galaxy Cluster SpARCS1049+56 at z = 1.71 with Infrared Weak Lensing. In the hierarchical structure formation model of the universe, galaxy clusters are assembled through a series of mergers. Accordingly, it is expected that galaxy clusters in the early universe are actively forming and dynamically young. Located at a high redshift of z = 1.71, SpARCS1049+56 offers a unique look into the galaxy cluster formation process. This cluster has been shown to be rich in cluster galaxies and to have intense star formation. Its high redshift pushes a weak-lensing analysis beyond the regime of the optical spectrum into that of the infrared. Equipped with deep Hubble Space Telescope Wide Field Camera 3 UVIS and IR observations, we present a weak-lensing characterization of SpARCS1049+56. As few IR weak-lensing studies have been performed, we discuss the details of point-spread function modeling and galaxy shape measurement for an IR weak-lensing procedure and the systematics that come with the territory. It will be critical to understand these systematics in future weak-lensing studies in the IR with the next-generation space telescopes such as the James Webb Space Telescope, Euclid, and WFIRST. Through a careful analysis, the mass distribution of this young galaxy cluster is mapped and the convergence peak is detected at a 3.3σ level. The weak-lensing mass of the cluster is estimated to be 3.5 ± 1.2 × 1014 M⊙ and is consistent with the mass derived from a mass-richness scaling relation. This mass is extreme for a cluster at such a high redshift and suggests that SpARCS1049+56 is rare in the standard ΛCDM universe.

Keywords: Weak gravitational lensing, Galaxy clusters, High-redshift galaxy clusters, Observational cosmology, Dark matter
Variability of Massive Stars in M31 from the Palomar Transient Factory. Using data from the (intermediate) Palomar Transient Factory (iPTF), we characterize the time variability of ≈500 massive stars in M31. Our sample is those stars that are spectrally typed by Massey and collaborators, including Luminous Blue Variables, Wolf-Rayets, and warm and cool supergiants. We use the high-cadence, long-baseline (≈5 yr) data from the iPTF survey, coupled with data-processing tools that model complex features in the light curves. We find widespread photometric (R-band) variability in the upper Hertzsprung Russell diagram (or CMD) with an increasing prevalence of variability with later spectral types. Red stars (V - I &gt; 1.5) exhibit larger amplitude fluctuations than their bluer counterparts. We extract a characteristic variability timescale, tch, via wavelet transformations that are sensitive to both continuous and localized fluctuations. Cool supergiants are characterized by longer timescales (&gt;100 days) than the hotter stars. The latter have typical timescales of tens of days but cover a wider range, from our resolution limit of a few days to longer than 100 days. Using a 60 night block of data straddling two nights with a cadence of around 2 minutes, we extracted tch in the range 0.1-10 days with amplitudes of a few percent for 13 stars. Though there is broad agreement between the observed variability characteristics in the different parts of the upper CMD with theoretical predictions, detailed comparison requires models with a more comprehensive treatment of the various physical processes operating in these stars, such as pulsation, subsurface convection, and the effect of binary companions.

Keywords: Surveys, Massive stars, Supergiant stars, Andromeda Galaxy, Catalogs