Sazuna/UAT_keywords huggingface dataset:
Cloud Atlas: Variability in and out of the Water Band in the Planetary-mass HD 203030B Points to Cloud Sedimentation in Low-gravity L Dwarfs. We use the Wide Field Camera 3 on the Hubble Space Telescope to spectrophotometrically monitor the young L7.5 companion HD 203030B. Our time series reveal photometric variability at 1.27 and 1.39 μm on timescales compatible with rotation. We find a rotation period of {7.5}-0.5+0.6 hr: comparable to those observed in other brown dwarfs and planetary-mass companions younger than 300 Myr. We measure variability amplitudes of 1.1% ± 0.3% (1.27 μm) and 1.7% ± 0.4% (1.39 μm), and a phase lag of 56° ± 28° between the two light curves. We attribute the difference in photometric amplitudes and phases to a patchy cloud layer that is sinking below the level where water vapor becomes opaque. HD 203030B and the few other known variable young late-L dwarfs are unlike warmer (earlier-type and/or older) L dwarfs, for which variability is much less wavelength-dependent across the 1.1-1.7 μm region. We further suggest that a sinking of the top-most cloud deck below the level where water or carbon monoxide gas become opaque may also explain the often enhanced variability amplitudes of even earlier-type low-gravity L dwarfs. Because these condensate and gas opacity levels are already well-differentiated in T dwarfs, we do not expect the same variability amplitude enhancement in young versus old T dwarfs.

Keywords: Light curves, Brown dwarfs, Exoplanet atmospheres
Tidal-locking-induced Stellar Rotation Dichotomy in the Open Cluster NGC 2287?. Stars spend most of their lifetimes on the “main sequence” (MS) in the Hertzsprung-Russell diagram. The obvious double MSs seen in the equivalent color-magnitude diagrams characteristic of Milky Way open clusters (OCs) pose a fundamental challenge to our traditional understanding of star clusters as “single stellar populations.” The clear MS bifurcation of early-type stars with masses greater than ∼1.6 M ☉ is thought to result from a range in the stellar rotation rates. However, direct evidence connecting double MSs to stellar rotation properties has yet to emerge. Here, we show through analysis of the projected stellar rotational velocities (v sin i, where i represents the star’s inclination angle) that the well-separated double MS in the young, ∼200 Myr old Milky Way OC NGC 2287 is tightly correlated with a dichotomous distribution of stellar rotation rates. We discuss whether our observations may reflect the effects of tidal locking affecting a fraction of the cluster’s member stars in stellar binary systems. We show that the slow rotators could potentially be initially rapidly rotating stars that have been slowed down by tidal locking by a low-mass-ratio companion in a cluster containing a large fraction of short-period, low-mass-ratio binaries. This demonstrates that stellar rotation drives the split MSs in young, ⪅300 Myr old star clusters. However, special conditions, e.g., as regards the mass-ratio distribution, might be required for this scenario to hold.

Keywords: Open star clusters, Stellar rotation, Star clusters
The Astrochemical Impact of Cosmic Rays in Protoclusters. II. CI-to-H<SUB>2</SUB> and CO-to-H<SUB>2</SUB> Conversion Factors. We utilize a modified astrochemistry code that includes cosmic-ray (CR) attenuation in situ to quantify the impact of different CR models on the CO-to-H2 and CI-to-H2 conversion factors, X CO and X CI, respectively. We consider the impact of CRs accelerated by accretion shocks, and show that clouds with star formation efficiencies greater than 2% have X CO = (2.5 ± 1) × 1020 cm-2(K km s-1)-1, consistent with Milky Way observations. We find that changing the CR ionization rate from external sources from the canonical ζ ≈ 10-17 to ζ ≈ 10-16 s-1, which better represents observations in diffuse gas, reduces X CO by 0.2 dex for clusters with surface densities below 3 g cm-2. We show that embedded sources regulate X CO and decrease its variance across a wide range of surface densities and star formation efficiencies. Our models reproduce the trends of a decreased X CO in extreme CR environments. X CI has been proposed as an alternative to X CO due to its brightness at high redshifts. The inclusion of internal CR sources leads to 1.2 dex dispersion in X CI ranging from 2 × 1020 &lt; X CI &lt; 4 × 1021 cm-2 (K km s-1)-1. We show that X CI is highly sensitive to the underlying CR model.

Keywords: Stellar feedback, Molecular clouds, Photodissociation regions, Astrochemistry, Star formation, Cosmic rays
Synthetic Extreme-ultraviolet Emissions Modulated by Leaky Fast Sausage Modes in Solar Active Region Loops. We study the extreme-ultraviolet (EUV) emissions modulated by leaky fast sausage modes (FSMs) in solar active region (AR) loops and examine their observational signatures via spectrometers like the EUV imaging spectrometer (EIS). After computing fluid variables of leaky FSMs with magnetohydrodynamic (MHD) simulations, we forward-model the intensity and spectral properties of the Fe X 185 Å and Fe XII 195 Å lines by incorporating nonequilibrium ionization (NEI) in the computations of the relevant ionic fractions. The damping times derived from the intensity variations are then compared with the wave values, namely, the damping times directly found from our MHD simulations. Our results show that in the equilibrium ionization cases, the density variations and the intensity variations can be either in phase or in antiphase, depending on the loop temperature. NEI considerably impacts the intensity variations but has only marginal effects on the derived Doppler velocity or Doppler width. We find that the damping time derived from the intensity can largely reflect the wave damping time if the loop temperature is not drastically different from the nominal formation temperature of the corresponding emission line. These results are helpful for understanding the modulations to the EUV emissions by leaky FSMs and hence helpful for identifying FSMs in solar AR loops.

Keywords: Magnetohydrodynamics, Solar coronal waves, Solar corona, Solar extreme ultraviolet emission
Searches for Interstellar HCCSH and H<SUB>2</SUB>CCS. A longstanding problem in astrochemistry is the inability of many current models to account for missing sulfur content. Many relatively simple species that may be good candidates to sequester sulfur have not been measured experimentally at the high spectral resolution necessary to enable radioastronomical identification. On the basis of new laboratory data, we report searches for the rotational lines in the microwave, millimeter, and submillimeter regions of the sulfur-containing hydrocarbon HCCSH. This simple species would appear to be a promising candidate for detection in space owing to the large dipole moment along its b-inertial axis, and because the bimolecular reaction between two highly abundant astronomical fragments (CCH and SH radicals) may be rapid. An inspection of multiple line surveys from the centimeter to the far-infrared toward a range of sources from dark clouds to high-mass star-forming regions, however, resulted in nondetections. An analogous search for the lowest-energy isomer, {{{H}}}2{CCS}, is presented for comparison, and also resulted in nondetections. Typical upper limits on the abundance of both species relative to hydrogen are 10-9-10-10. We thus conclude that neither isomer is a major reservoir of interstellar sulfur in the range of environments studied. Both species may still be viable candidates for detection in other environments or at higher frequencies, providing laboratory frequencies are available.

Keywords: Interstellar molecules, Chemical abundances, Interstellar medium, Astrochemistry
The Optical Afterglow of GW170817: An Off-axis Structured Jet and Deep Constraints on a Globular Cluster Origin. We present a revised and complete optical afterglow light curve of the binary neutron star merger GW170817, enabled by deep Hubble Space Telescope (HST) F606W observations at ≈584 days post-merger, which provide a robust optical template. The light curve spans ≈110-362 days, and is fully consistent with emission from a relativistic structured jet viewed off-axis, as previously indicated by radio and X-ray data. Combined with contemporaneous radio and X-ray observations, we find no spectral evolution, with a weighted average spectral index of &lt; β &gt; =-0.583+/- 0.013, demonstrating that no synchrotron break frequencies evolve between the radio and X-ray bands over these timescales. We find that an extrapolation of the post-peak temporal slope of GW170817 to the luminosities of cosmological short gamma-ray bursts matches their observed jet break times, suggesting that their explosion properties are similar, and that the primary difference in GW170817 is viewing angle. Additionally, we place a deep limit on the luminosity and mass of an underlying globular cluster (GC) of L ≲ 6.7 × 103 L ⊙, or M ≲ 1.3 × 104 M ⊙, at least 4 standard deviations below the peak of the GC mass function of the host galaxy, NGC 4993. This limit provides a direct and strong constraint that GW170817 did not form and merge in a GC. As highlighted here, HST (and soon the James Webb Space Telescope) enables critical observations of the optical emission from neutron star merger jets and outflows.

Keywords: Neutron stars, Hubble Space Telescope, Gamma-ray bursts, Gravitational waves
The Origin of the X-Ray Emission in Two Well-aligned Extragalactic Jets: The Case for IC/CMB. Over the past two decades, the most commonly adopted explanation for high and hard X-ray emission in resolved quasar jets has been inverse-Compton upscattering of the cosmic microwave background (IC/CMB), which requires jets that remain highly relativistic on 10-1000 kpc scales. In more recent years various lines of observational evidence, including gamma-ray upper limits, have disfavored this explanation in favor of a synchrotron origin. While the IC/CMB model generally predicts a high level of gamma-ray emission, it has never been detected. Here we report the detection of a low-state Fermi/LAT gamma-ray spectrum associated with two jetted active galactic nuclei that is consistent with the predictions of the IC/CMB model for their X-ray emission. We have used archival multiwavelength observations to make precise predictions for the expected minimum flux in the GeV band, assuming that the X-ray emission from the kiloparsec-scale jet is entirely due to the IC/CMB process. In both sources—OJ 287 and PKS 1510-089—the minimum-detected gamma-ray flux level agrees with predictions. Both sources exhibit extreme superluminal proper motions relative to their jet power, which argues for the well-aligned jets required by the IC/CMB model. In the case of PKS 1510-089, it cannot be ruled out that the minimum gamma-ray flux level is due to a low state of the variable core that only matches the IC/CMB prediction by chance. Continued long-term monitoring with the Fermi/LAT could settle this issue by detecting a plateau signature in the recombined light curve that would clearly signal the presence of a nonvariable emission component.

Keywords: Radio loud quasars, BL Lacertae objects, Jets, High energy astrophysics
A Simple Phenomenological Emergent Dark Energy Model can Resolve the Hubble Tension. Motivated by the current status of cosmological observations and significant tensions in the estimated values of some key parameters assuming the standard ΛCDM model, we propose a simple but radical phenomenological emergent dark energy model where dark energy has no effective presence in the past and emerges at later times. Theoretically, in this phenomenological dark energy model with zero degrees of freedom (similar to a ΛCDM model), one can derive that the equation of state of dark energy increases from -\tfrac{2}{3{ln} 10}-1 in the past to -1 in the future. We show that by setting a hard-cut 2σ lower bound prior for H 0 associated with a 97.72% probability from recent local observations, this model can satisfy different combinations of cosmological observations at low and high redshifts (SNe Ia, baryon acoustic oscillation (BAO), Lyα BAO, and cosmic microwave background (CMB)) substantially better than the concordance ΛCDM model with {{Δ }}{χ }{bf}2∼ -41.08 and Δ DIC ∼ -35.38. If there are no substantial systematics in SN Ia, BAO, or Planck CMB data, and assuming the reliability of current local H 0 measurements, there is a very high probability that with more precise measurements of the Hubble constant our proposed phenomenological model rules out the cosmological constant with decisive statistical significance and is a strong alternative to explain the combination of different cosmological observations. This simple phenomenologically emergent dark energy model can guide theoretically motivated dark energy model building activities.

Keywords: Cosmological parameters, Observational cosmology, Hubble constant, Cosmological constant, Dark energy
A Fundamental Plane for Gamma-Ray Pulsars. We show that the γ-ray pulsar observables, i.e., their total γ-ray luminosity, {L}γ , spectral cutoff energy, {ɛ }cut}, stellar surface magnetic field, B ⋆, and spin-down power \dot{{ \mathcal E }}, obey a relation of the form {L}γ =f({ɛ }cut},{B}\star ,\dot{{ \mathcal E }}), which represents a 3D plane in their 4D logspace. Fitting the data of 88 pulsars of the second Fermi pulsar catalog, we show this relation to be {L}γ \propto {ɛ }cut}1.18+/- 0.24{B}\star 0.17+/- 0.05{\dot{{ \mathcal E }}}0.41+/- 0.08, a pulsar fundamental plane (FP). We show that the observed FP is remarkably close to the theoretical relation {L}γ \propto {ɛ }cut}4/3{B}\star 1/6{\dot{{ \mathcal E }}}5/12 obtained assuming that the pulsar γ-ray emission is due to curvature radiation by particles accelerated at the pulsar equatorial current sheet just outside the light cylinder. Interestingly, the FP seems incompatible with emission by synchrotron radiation. The corresponding scatter about the FP is ∼0.35 dex and can only partly be explained by the observational errors while the rest is probably due to the variation of the inclination and observer angles. We predict also that {ɛ }cut}\propto {\dot{{ \mathcal E }}}7/16 toward low \dot{{ \mathcal E }} for both young and millisecond pulsars implying that the observed death line of γ-ray pulsars is due to {ɛ }cut} dropping below the Fermi band. Our results provide a comprehensive interpretation of the observations of γ-ray pulsars, setting requirements for successful theoretical modeling.

Keywords: Akaike information criterion, Gamma-ray telescopes, Pulsars, Bayesian information criterion, Gamma-rays
A Gaia-Enceladus Analog in the EAGLE Simulation: Insights into the Early Evolution of the Milky Way. We identify a simulated Milky Way analog in the EAGLE suite of cosmological hydrodynamical simulations. This galaxy not only shares similar global properties as the Milky Way, but was specifically selected because its merger history resembles that currently known for the Milky Way. In particular we find that this Milky Way analog has experienced its last significant merger (with a stellar mass ratio ∼0.2) at z ∼ 1.2. We show that this merger affected both the dynamical properties of the stars present at the time, contributing to the formation of a thick disk, and also leading to a significant increase in the star formation rate of the host. This object is thus particularly suitable for understanding the early evolutionary history of the Milky Way. It is also an ideal candidate for re-simulation with much higher resolution, as this would allow addressing a plethora of interesting questions such as, for example, the specific distribution of dark matter near the Sun.

Keywords: Stellar kinematics, Galaxy mergers, Milky Way formation
Binary Mergers near a Supermassive Black Hole: Relativistic Effects in Triples. We study the general relativistic (GR) effects induced by a spinning supermassive black hole on the orbital and spin evolution of a merging black hole binary (BHB) in a hierarchical triple system. A sufficiently inclined outer orbit can excite Lidov-Kozai eccentricity oscillations in the BHB and induce its merger. These GR effects generate extra precessions on the BHB orbits and spins, significantly increasing the inclination window for mergers and producing a wide range of spin orientations when the BHB enters LIGO band. This “GR-enhanced” channel may play an important role in BHB mergers.

Keywords: Gravitation, Gravitational waves, Astrophysical processes, Gravitational wave sources
High-fidelity Imaging of the Inner AU Mic Debris Disk: Evidence of Differential Wind Sculpting?. We present new high-fidelity optical coronagraphic imagery of the inner ∼50 au of AU Mic’s edge-on debris disk using the BAR5 occulter of the Hubble Space Telescope Imaging Spectrograph (HST/STIS) obtained on 2018 July 26-27. This new imagery reveals that “feature A,” residing at a projected stellocentric separation of 14.2 au on the southeast side of the disk, exhibits an apparent “loop-like” morphology at the time of our observations. The loop has a projected width of 1.5 au and rises 2.3 au above the disk midplane. We also explored Transiting Exoplanet Survey Satellite photometric observations of AU Mic that are consistent with evidence of two starspot complexes in the system. The likely co-alignment of the stellar and disk rotational axes breaks degeneracies in detailed spot modeling, indicating that AU Mic’s projected magnetic field axis is offset from its rotational axis. We speculate that small grains in AU Mic’s disk could be sculpted by a time-dependent wind that is influenced by this offset magnetic field axis, analogous to co-rotating solar interaction regions that sculpt and influence the inner and outer regions of our own Heliosphere. Alternatively, if the observed spot modulation is indicative of a significant misalignment of the stellar and disk rotational axes, we suggest that the disk could still be sculpted by the differential equatorial versus polar wind that it sees with every stellar rotation.

Keywords: M dwarf stars, Starspots, Debris disks, Circumstellar disks
Dependence of 3D Self-correlation Level Contours on the Scales in the Inertial Range of Solar Wind Turbulence. The self-correlation level contours at the 1010 cm scale reveal a 3D isotropic feature in the slow solar wind and a quasi-anisotropic feature in the fast solar wind. However, the 1010 cm scale is approximately near the low-frequency break (outer scale of turbulence cascade), especially in the fast wind. How the self-correlation level contours behave with dependence on the scales in the inertial range of solar wind turbulence remains unknown. Here we present the 3D self-correlation function level contours and their dependence on the scales in the inertial range for the first time. We use data at 1 au from instruments on the Wind spacecraft in the period 2005-2018. We show the 3D isotropic self-correlation level contours of the magnetic field in the inertial range of both slow and fast solar wind turbulence. We also find that the self-correlation level contours of the velocity in the inertial range present 2D anisotropy with an elongation in the perpendicular direction and 2D isotropy in the plane perpendicular to the mean magnetic field. These results indicate differences between the magnetic field and the velocity, providing new clues to interpret the solar wind turbulence on the inertial scale.

Keywords: Interplanetary turbulence, Space plasmas, Solar wind, Luminous blue variable stars
Discovery of a Pulse-phase-transient Cyclotron Line in the X-Ray pulsar GRO J2058+42. We report the discovery of absorption features in the X-ray spectrum of the transient X-ray pulsar GRO J2058+42. The features are detected around ∼10, ∼20, and ∼30 keV in both NuSTAR observations carried out during the source type II outburst in spring 2019. The most intriguing property is that the deficit of photons around these energies is registered only in the narrow phase interval covering around 10% of the pulsar spin period. We interpret these absorption lines as a cyclotron resonant scattering line (fundamental) and two higher harmonics. The measured energy allow us to estimate the magnetic field strength of the neutron star as ∼1012 G.

Keywords: Neutron stars, X-ray binary stars, Binary pulsars
The Pivot Energy of Solar Energetic Particles Affecting the Martian Surface Radiation Environment. Space radiation is a major risk for humans, especially on long-duration missions to outer space, e.g., a manned mission to Mars. Galactic cosmic rays contribute a predictable radiation background; the main risk is due to the highly variable and currently unpredictable flux of solar energetic particles (SEPs). Such sporadic SEP events may induce acute health effects and are thus considered a critical mission risk for future human exploration of Mars. Therefore, it is of the utmost importance to study, model, and predict the surface radiation environment during such events. It is well known that the deep-space SEP differential energy spectrum at high energies is often given by a power law. We use a measurement-validated particle transport code to show that, for large SEP events with proton energy extending above ∼500 MeV with a power-law distribution, it is sufficient to measure the SEP flux at a pivot energy of ∼300 MeV above the Martian atmosphere to predict the dose rate on the Martian surface. In conjunction with a validation by in situ measurements from the Martian surface, this remarkable simplification and elegant quantification could enable instant predictions of the radiation environment on the surface of Mars upon the onset of large SEP events.

Keywords: Solar energetic particles, Space weather, Mars, Solar-planetary interactions, Particle physics, Cosmic rays
NuSTAR Discovery of Dead Quasar Engine in Arp 187. Recent active galactic nucleus (AGN) and quasar surveys have revealed a population showing rapid AGN luminosity variability by a factor of ∼10. Here we present the most drastic AGN luminosity decline by a factor of ≳103 constrained by a NuSTAR X-ray observation of the nearby galaxy Arp 187, which is a promising “dead” quasar whose current activity seems quiet but whose past activity of {L}bol}∼ {10}46 erg s-1 is still observable at a large scale by its light echo. The obtained upper bound of the X-ray luminosity is {log}({L}2-10{keV}/{erg} {{{s}}}-1)&lt; 41.2, corresponding to {log}({L}bol}/{erg} {{{s}}}-1)&lt; 42.5, indicating an inactive central engine. Even if a putative torus model with {N}{{H}}∼ 1.5× {10}24 cm-2 is assumed, the strong upper bound still holds with {log}({L}2-10{keV}/{erg} {{{s}}}-1)&lt; 41.8 or {log}({L}bol}/{erg} {{{s}}}-1)&lt; 43.1. Given the expected size of the narrow-line region, this luminosity decrease by a factor of ≳103 must have occurred within ≲104 yr. This extremely rapid luminosity/accretion shutdown is puzzling, and it requires one burst-like accretion mechanism producing a clear outer boundary for an accretion disk. We raise two possible scenarios realizing such an accretion mechanism: a mass accretion (1) by the tidal disruption of a molecular cloud and/or (2) by the gas depletion as a result of vigorous nuclear star formation after rapid mass inflow to the central engine.

Keywords: X-ray active galactic nuclei, Active galactic nuclei