Sazuna/UAT_keywords huggingface dataset:
Physical Characterization of the 2017 December Outburst of the Centaur 174P/Echeclus. The Centaurs are the small solar system bodies intermediate between the active inner solar system Jupiter family comets and their inactive progenitors in the trans-Neptunian region. Among the fraction of Centaurs which show comet-like activity, 174P/Echeclus is best known for its massive 2005 outburst in which a large apparently active fragment was ejected above the escape velocity from the primary nucleus. We present visible imaging and near-infrared spectroscopy of Echeclus during the first week after its 2017 December outburst taken at the Faulkes North and South Telescopes and the NASA IRTF, the largest outburst since 2005. The coma was seen to be highly asymmetric. A secondary peak was seen in the near-infrared 2D spectra, which is strongly hinted at in the visible images, moving hyperbolically with respect to the nucleus. The retrieved reflectance spectrum of Echelcus is consistent with the unobscured nucleus but becomes bluer when a wider extraction aperture is used. We find that Echeclus’s coma is best explained as dominated by large blue dust grains, which agrees with previous work. We also conducted a high-resolution orbital integration of Echeclus’s recent evolution and found no large orbital changes that could drive its modern evolution. We interpret the second peak in the visible and near-infrared data sets as a large cloud of larger-than-dust debris ejected at the time of outburst. If Echeclus is typical of the Centaurs, there may be several debris ejection or fragmentation events per year on other Centaurs that are going unnoticed.

Keywords: Centaur group, Orbits, Orbital evolution, Spectroscopy, Comets
New Insights into Interstellar Object 1I/2017 U1 (‘Oumuamua) from SOHO/STEREO Nondetections. Object 1I/2017 U1 (‘Oumuamua) is the first interstellar small body ever discovered in the solar system. By the time of discovery, it had already passed perihelion. To investigate the behavior of ‘Oumuamua around perihelion, we searched for it in Solar and Heliospheric Observatory (SOHO) and Solar TErrestrial RElations Observatory (STEREO) images from early 2017 September (preperihelion), but did not detect it. The nondetection of ‘Oumuamua by STEREO renders more stringent constraints on its physical properties thanks to the extreme forward-scattering observing geometry. Assuming a geometric albedo of p  V  = 0.1, the effective scattering cross-section of any dust coma was ≲ ≤ft(2.1+/- 0.2\right)× {10}4 m2. Assuming that it behaved like a typical solar system comet, this would correspond to a total mass of ≲20 ± 2 kg and a water production rate of ≲(6.1 ± 0.5) × 1025 s-1 at a heliocentric distance of r H = 0.375 au. If scaled to post-discovery r H, the water production rate would be smaller than any of the previously reported upper limits by at least an order of magnitude. To exhibit the reported nongravitational motion with our default assumptions requires a nucleus bulk density ≲40 kg m-3 higher bulk densities are possible for other assumptions. Alternatively, we show that thermal fracturing could have plausibly removed an inert surface layer between these observations and discovery, thus initiating activity after ‘Oumuamua left the field of view of STEREO.

Keywords: Near-Earth objects, Astronomy data analysis, Interstellar objects, Comets
Avocado: Photometric Classification of Astronomical Transients with Gaussian Process Augmentation. Upcoming astronomical surveys such as the Large Synoptic Survey Telescope (LSST) will rely on photometric classification to identify the majority of the transients and variables that they discover. We present a set of techniques for photometric classification that can be applied even when the training set of spectroscopically confirmed objects is heavily biased toward bright, low-redshift objects. Using Gaussian process regression to model arbitrary light curves in all bands simultaneously, we “augment” the training set by generating new versions of the original light curves covering a range of redshifts and observing conditions. We train a boosted decision tree classifier on features extracted from the augmented light curves, and we show how such a classifier can be designed to produce classifications that are independent of the redshift distributions of objects in the training sample. Our classification algorithm was the best-performing among the 1094 models considered in the blinded phase of the Photometric LSST Astronomical Time-Series Classification Challenge, scoring 0.468 on the organizers’ logarithmic-loss metric with flat weights for all object classes in the training set, and achieving an AUC of 0.957 for classification of SNe Ia. Our results suggest that spectroscopic campaigns used for training photometric classifiers should focus on typing large numbers of well-observed, intermediate-redshift transients, instead of attempting to type a sample of transients that is directly representative of the full data set being classified. All of the algorithms described in this paper are implemented in the avocado software package (https://www.github.com/kboone/avocado).

Keywords: Supernovae, Variable stars, Transient sources, Classification
Improved Analysis of Clarke Exobelt Detectability. We analyze the potential transit light curve effects due to a Clarke belt of satellites around an exoplanet. Building on code and analysis from Korpela et al., we refine the transit analysis of Socas-Navarro by incorporating limb-darkening and taking an observer-centered approach to examining residuals. These considerations make Clarke exobelt detectability more difficult than previous estimates. We also consider practical dynamical issues for exobelts, confirming that synchronously orbiting belts are dynamically unstable around planets in the habitable zones of M stars, and determining the maximum quasi-stable belt size in these situations. Using simulations for both G and M stars, we conclude that to have an even marginally detectable impact on transit light curves, exobelts must be substantially denser than previous estimates. We also estimate collision rates for the required satellite densities assuming random orbits, and find that they would present significant monitoring and guidance challenges. If detectable belts exist, they would require some (possibly high) degree of ordering to avoid collisions, and must be actively maintained or they will dissipate on relatively short astronomical timescales. We conclude that detectable exobelts are likely to be rare, and have extremely low prospects for detection by transit monitoring from both current and upcoming missions.

Keywords: Exoplanet astronomy, Astrobiology, Exoplanets
Analysis of HST WFPC2 Observations of Centaur 29P/Schwassmann-Wachmann 1 while in Outburst to Place Constraints on the Nucleus’ Rotation State. We present analysis of Hubble Space Telescope observations of Centaur 29P/Schwassmann-Wachmann 1 (SW1) while in outburst to characterize the outburst coma and place constraints on the nucleus’ spin state. The observations consist of Wide Field and Planetary Camera 2 (WFPC2) images from Cycle 5, GO-5829 acquired on UT 1996 March 11.3 and 12.1, which serendipitously imaged the Centaur shortly after a major outburst. A multi-component coma was detected consisting of an expanding outburst dust coma with complex morphology possessing an east-west asymmetry and north-south symmetry contained within 5″ (∼19,000 km) of the nucleus, the residual dust shell of an earlier UT 1996 February outburst, and a nearly circular coma with underlying quiescent activity level detectable to ∼70″ (∼267,000 km) away from the nucleus. Photometry of the calibrated WFPC2 images resulted in an equivalent R-band magnitude of 12.86 ± 0.02 for a measured 5″ radius aperture and an estimated (2.79 ± 0.05) × 108 kg for the lower limit of dust material emitted during the outburst. No appreciable evolution of morphological features, indicating signatures of nuclear rotation, was detected between the two imaging epochs. The observations were modeled using a 3D Monte Carlo coma model to place constraints on the nucleus’ rotation state. Modeling indicated that the morphology is representative of a non-isotropic ejection of dust emitted during a single outburst event with a duration of the order of hours from a single source region corresponding to ∼1% of the surface area. A spin period with lower limit of the order of days is suggested to reproduce the coma morphology seen in the observations.

Keywords: Centaur group, Small Solar System bodies, Solar system, Trans-Neptunian objects, Comets
Optical Reddening, Integrated H I Optical Depth, and Total Hydrogen Column Density. Despite the vastly different angular scales on which they are measured, the integrated λ21 cm H I optical depth measured interferometrically, {{{\Upsilon }}}{{H}{{I}}}, is a good proxy for the optical reddening derived from IR dust emission, with {{{\Upsilon }}}{{H}{{I}}} ∝ E(B-V)1.10 for 0.04 mag ≲ E(B-V) ≲ 4 mag. For E(B-V) ≲ 0.04 mag or {{{\Upsilon }}}{{H}{{I}}} &lt; 0.7 {km} {{{s}}}-1, less-absorbent warm and ionized gases assert themselves and τ(H I) is a less reliable tracer of E(B-V). The {{{\Upsilon }}}{{H}{{I}}}-E(B-V) relationship can be inverted to give a broken power-law relationship between the total hydrogen column density N(H) and {{{\Upsilon }}}{{H}{{I}}} such that knowledge of {{{\Upsilon }}}{{H}{{I}}} alone predicts N(H) with an accuracy of a factor of 1.5 (±0.18 dex) across two orders of magnitude variation of {{{\Upsilon }}}{{H}{{I}}}. The {{{\Upsilon }}}{{H}{{I}}}-N(H) relation is invariant under a linear rescaling of the reddening measure used in the analysis and does not depend on knowing properties of the H I such as the spin temperature.

Keywords: Interstellar line absorption, Interstellar dust extinction, Interstellar atomic gas, Diffuse interstellar clouds
Graze-and-merge Collisions under External Perturbers. Graze-and-merge collisions are common multi-step mergers occurring in low-velocity, off-axis impacts between similar-sized planetary bodies. The first impact happens at somewhat faster than the mutual escape velocity; for typical impact angles this does not result in immediate accretion, but the smaller body is slowed down so that it loops back around and collides again, ultimately accreting. The scenario changes in the presence of a third major body, i.e., planets accreting around a star, or satellites around a planet. We find that when the loop-back orbit remains inside roughly one third of the Hill radius from the target, then the overall process is not strongly affected. As the loop-back orbit increases in radius, the return velocity and angle of the second collision become increasingly random, with no record of the first collision’s orientation. When the loop-back orbit gets to about three quarters of the Hill radius, the path of smaller body is disturbed up to the point that it will usually escape the target.

Keywords: Planet formation, Natural satellite formation
Hot Hydrogen Climates Near the Inner Edge of the Habitable Zone. Young terrestrial planets can capture or outgas hydrogen-rich atmospheres with tens to hundreds of bars of H2, which persist for 100 Myr or longer. Although the earliest habitable conditions on Earth and terrestrial exoplanets could thus arise while the atmosphere is still dominated by H2, the climatic effects of H2 remain poorly understood. Previous work showed that H2 induces strong greenhouse warming at the outer edge of the habitable zone. Here we use a 1D radiative-convective model to show that H2 also leads to strong warming near the inner edge of the habitable zone. Unlike H2's greenhouse warming at the outer edge, however, its effect near the inner edge is driven by thermodynamics: H2's large thermal scale height allows the atmosphere to store more water vapor than either a pure H2O atmosphere or an atmosphere with a heavy background gas, such as N2 or CO2, thereby amplifying the greenhouse effect of H2O. Using idealized gray calculations, we then present a general argument for how different background gases affect the inner edge of the habitable zone. H2 stands out for its ability to induce novel “soufflé” climates, which further support its warming effect. Our results show that if the earliest conditions on a planet near the inner edge of the habitable zone were H2-rich, they were likely also hot: 1 bar of H2 is sufficient to raise surface temperatures above 340 K, and 50 bar of H2 are sufficient to raise surface temperatures above 450 K.

Keywords: Exoplanet atmospheric composition , Earth atmosphere, Planetary atmospheres, Exoplanet evolution, Green valley galaxies, Astrobiology, Habitable zone
Most Black Holes Are Born Very Slowly Rotating. The age of gravitational-wave astronomy has begun, and black hole (BH) mergers detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) are providing novel constraints on massive star evolution. A major uncertainty in stellar theory is the angular momentum (AM) transport within the star that determines its core rotation rate and the resulting BH’s spin. Internal rotation rates of low-mass stars measured from asteroseismology prove that AM transport is efficient, suggesting that massive stellar cores may rotate slower than prior expectations. We investigate AM transport via the magnetic Tayler instability, which can largely explain the rotation rates of low-mass stars and white dwarfs. Implementing an updated AM transport prescription into models of high-mass stars, we compute the spins of their BH remnants. We predict that BHs born from single stars rotate very slowly, with a ∼ 10-2, regardless of initial rotation rate, possibly explaining the low χ eff of most BH binaries detected by LIGO thus far. A limited set of binary models suggests slow rotation for many binary scenarios as well, although homogeneous evolution and tidal spin-up of post-common-envelope helium stars can create moderate or high BH spins. We make predictions for the values of χ eff in future LIGO events, and we discuss implications for engine-powered transients.

Keywords: Magnetohydrodynamics, Massive stars, Stellar evolutionary models, Stellar mass black holes, Rotating black holes, Stellar rotation, Astrophysical fluid dynamics, Solar evolution
Single-spacecraft Identification of Flux Tubes and Current Sheets in the Solar Wind. A novel technique is presented for describing and visualizing the local topology of the magnetic field using single-spacecraft data in the solar wind. The approach merges two established techniques: the Grad-Shafranov (GS) reconstruction method, which provides a plausible regional two-dimensional magnetic field surrounding the spacecraft trajectory, and the Partial Variance of Increments (PVI) technique that identifies coherent magnetic structures, such as current sheets. When applied to one month of Wind magnetic field data at 1 minute resolution, we find that the quasi-two-dimensional turbulence emerges as a sea of magnetic islands and current sheets. Statistical analysis confirms that current sheets associated with high values of PVI are mostly located between and within the GS magnetic islands, corresponding to X points and internal boundaries. The method shows great promise for visualizing and analyzing single-spacecraft data from missions such as Parker Solar Probe and Solar Orbiter, as well as 1 au Space Weather monitors such as ACE, Wind, and IMAP.

Keywords: Interplanetary turbulence, Solar wind, Magnetic fields, Astronomical location
Constraining the Solar System's Debris Disk with In Situ New Horizons Measurements from the Edgeworth-Kuiper Belt. The solar system currently possesses two remnant debris disks leftover from the planetary formation era in the form of the asteroid belt and the Edgeworth-Kuiper Belt (EKB). Similar to other stellar systems, these debris disks continually generate submillimeter-sized dust grains through processes such as mutual collisions, interstellar dust grain bombardment, and sublimation/sputtering of larger grains. Here, we use recent in situ measurements by the New Horizons Student Dust Counter and an interplanetary dust dynamics model to constrain the overall structure and magnitude of the solar system’s debris disk, including the disk mass, optical depth, and surface brightness in both scattered light and thermal emission. We find that ∼99% of the solar system’s dust disk mass (grains with diameter &lt;1 mm) is contained within EKB and Oort Cloud cometary grains outside of 30 au, with the remaining ∼1% mass in the form of Jupiter-family cometary dust within 5 au. The total disk mass is estimated to be ∼8 × 10-7 M ⊕ with a total fractional luminosity of ∼5 × 10-7, confirming our solar system as a relatively dust-poor system compared to debris disks around similar-aged FGK stars. Finally, we estimate that Kuiper Belt Object collisional events such as that which created the Haumea family could transiently increase the current surface brightness of our debris disk by a factor of only ∼6, far less than median brightnesses seen in other nearby disks. This further supports the idea that the EKB has been largely depleted of its primordial mass relative to other stellar systems by instabilities triggered by planetary migration.

Keywords: Interplanetary dust, Debris disks, Kuiper belt
Compact Object Binary Mergers Driven By Cluster Tides: A New Channel for LIGO/Virgo Gravitational-wave Events. The detections of gravitational waves (GWs) produced in mergers of binary black holes (BHs) and neutron stars (NSs) by LIGO/Virgo have stimulated interest in the origin of the progenitor binaries. Dense stellar systems—globular and nuclear star clusters—are natural sites of compact object binary formation and evolution toward merger. Here we explore a new channel for the production of binary mergers in clusters, in which the tidal field of the cluster secularly drives the binary to high eccentricity (even in the absence of a central massive BH) until GW emission becomes important. We employ the recently developed secular theory of cluster tide-driven binary evolution to compute present day merger rates for BH-BH, NS-BH, and NS-NS binaries, varying cluster potential and central concentration of the binary population (but ignoring cluster evolution and stellar flybys for now). Unlike other mechanisms, this new dynamical channel can produce a significant number of mergers out to cluster-centric distances of several parsecs. For NS-NS binaries we find merger rates in the range of 0.01-0.07 Gpc-3 yr-1 from globular clusters and 0.1-0.2 Gpc-3 yr-1 from cusped nuclear clusters. For NS-BH and BH-BH binaries we find small merger rates from globular clusters, but a rate of 0.1-0.2 Gpc-3 yr-1 from cusped nuclear clusters, contributing to the observed LIGO/Virgo rate at the level of several percent. Therefore, cluster tide-driven mergers constitute a new channel that can be further explored with current and future GW detectors.

Keywords: Globular star clusters, Astrodynamics, Relativistic binary stars, Compact binary stars, Gravitational wave sources, Celestial mechanics, LIGO, Star clusters
Smoothing of MHD Shocks in Mode Conversion. Shock waves are simulated passing through the Alfvén-acoustic equipartition layer in a stratified isothermal magneto-atmosphere. The recent ray-theoretic calculations of Núñez predicted smoothing of the shock through this layer, causing both the fast and slow components to emerge as continuous waves. However, it is found that the partial mode conversion expected from linear theory for oblique incidence of the shock on the magnetic field is accompanied by a smoothing of the slow shock only, while the fast shock persists. Explanations are presented based on magnetohydrodynamic mode conversion and shock theory.

Keywords: Stellar chromospheres, Solar oscillations, Shocks, Solar chromosphere, Stellar atmospheres, Magnetohydrodynamical simulations
Reconnection Front Associated with Asymmetric Magnetic Reconnection: Particle-in-cell Simulations. Reconnection front (RF) has frequently been observed in the magnetotail and is well known as the dipolarization front in the near-Earth tail. Whether the RF exists in reconnection with distinct plasma/field properties across the reconnecting current sheet (i.e., asymmetric reconnection) is unknown yet. In this Letter, we use 2.5D particle-in-cell simulations to investigate the properties of RF in asymmetric reconnection and compare to RFs in symmetric reconnection. We find that RF is a robust structure in asymmetric reconnection. Its moving speed and thickness are smaller than those in symmetric reconnection. Its properties, such as the current density, electromagnetic field structure, are examined. Some features of RF in asymmetric reconnection are drastically different than those in symmetric reconnection. These results are of great help for studying RF in plasma environments with asymmetric reconnection, such as Earth’s magnetopause.

Keywords: Planetary boundary layers, Solar magnetic reconnection, Astronomical simulations
Searches after Gravitational Waves Using ARizona Observatories (SAGUARO): System Overview and First Results from Advanced LIGO/Virgo’s Third Observing Run. We present Searches After Gravitational-waves Using ARizona Observatories (SAGUARO), a comprehensive effort dedicated to the discovery and characterization of optical counterparts to gravitational-wave (GW) events. SAGUARO utilizes ground-based facilities ranging from 1.5 to 10 m in diameter, located primarily in the Northern Hemisphere. We provide an overview of SAGUARO’s telescopic resources, its pipeline for transient detection, and its database for candidate visualization. We describe SAGUARO’s discovery component, which utilizes the 5 deg2 field of view optical imager on the Mt. Lemmon 1.5 m telescope, reaching limits of ≈21.3 AB mag while rapidly tiling large areas. We also describe the follow-up component of SAGUARO, used for rapid vetting and monitoring of optical candidates. With the onset of Advanced LIGO/Virgo’s third observing run, we present results from the first three SAGUARO searches following the GW events S190408an, S190425z and S190426c, which serve as a valuable proof-of-concept of SAGUARO. We triggered and searched 15, 60, and 60 deg2 respectively, 17.6, 1.4, and 41.8 hr after the initial GW alerts. We covered 7.8%, 3.0%, and 5.1% of the total probability within the GW event localizations, reaching 3σ limits of 19.8, 21.3, and 20.8 AB mag, respectively. Although no viable counterparts associated with these events were found, we recovered six known transients and ruled out five potential candidates. We also present Large Binocular Telescope spectroscopy of PS19eq/SN2019ebq, a promising kilonova candidate that was later determined to be a supernova. With the ability to tile large areas and conduct detailed follow-up, SAGUARO represents a significant addition to GW counterpart searches.

Keywords: Gravitational wave astronomy, Transient detection, Ground-based astronomy
The Role of Upper Hybrid Waves in the Magnetotail Reconnection Electron Diffusion Region. Plasma waves are believed to play an important role during magnetic reconnection. However, the specific role of upper hybrid (UH) waves in the electron diffusion region (EDR) remains elusive, owing to the absence of high-resolution measurements. We analyze one EDR event in the magnetotail on 2017 July 11 observed by the Magnetospheric Multiscale (MMS) mission. To the best of our knowledge, this is the first time that intense UH waves have been observed in the EDR by MMS. The agyrotropic crescent-shaped electron distributions could result in the observed UH waves. Concomitant with the observations of UH waves, the agyrotropy parameter \sqrt{Q} of the electrons decreases, implying that the UH waves could effectively scatter the electrons in the EDR. The good accordance of positive energy conversion ({\boldsymbol{J}}\cdot {\boldsymbol{E}}\prime &gt; 0, likely dissipation) and the observed UH waves indicates that UH waves may contribute to the energy conversion from the magnetic fields to the plasma particles during magnetic reconnection.

Keywords: Solar magnetic reconnection, Plasma physics, Plasma astrophysics, Earth (planet), Magnetic fields