Sazuna/UAT_keywords huggingface dataset:
The Sloan Digital Sky Survey Reverberation Mapping Project: Improving Lag Detection with an Extended Multiyear Baseline. We investigate the effects of extended multiyear light curves (9 yr photometry and 5 yr spectroscopy) on the detection of time lags between the continuum variability and broad-line response of quasars at z ≳ 1.5, and compare with the results using 4 yr photometry+spectroscopy presented in a companion paper. We demonstrate the benefits of the extended light curves in three cases: (1) lags that are too long to be detected by the shorter-duration data but can be detected with the extended data; (2) lags that are recovered by the extended light curves but are missed in the shorter-duration data due to insufficient light-curve quality; and (3) lags for different broad-line species in the same object. These examples demonstrate the importance of long-term monitoring for reverberation mapping to detect lags for luminous quasars at high redshift, and the expected performance of the final data set from the Sloan Digital Sky Survey Reverberation Mapping project that will have 11 yr photometric and 7 yr spectroscopic baselines.

Keywords: Supermassive black holes, Quasars, Surveys, Reverberation mapping, Astrophysical black holes
A Super-Earth and Sub-Neptune Transiting the Late-type M Dwarf LP 791-18. Planets occur most frequently around cool dwarfs, but only a handful of specific examples are known to orbit the latest-type M stars. Using TESS photometry, we report the discovery of two planets transiting the low-mass star called LP 791-18 (identified by TESS as TOI 736). This star has spectral type M6V, effective temperature 2960 K, and radius 0.17 R ☉, making it the third-coolest star known to host planets. The two planets straddle the radius gap seen for smaller exoplanets; they include a 1.1R ⊕ planet on a 0.95 day orbit and a 2.3R ⊕ planet on a 5 day orbit. Because the host star is small the decrease in light during these planets’ transits is fairly large (0.4% and 1.7%). This has allowed us to detect both planets’ transits from ground-based photometry, refining their radii and orbital ephemerides. In the future, radial velocity observations and transmission spectroscopy can both probe these planets’ bulk interior and atmospheric compositions, and additional photometric monitoring would be sensitive to even smaller transiting planets.

Keywords: High resolution spectroscopy, Exoplanet systems, Exoplanet astronomy, Low mass stars, Transit photometry
Energy Balance in Avalanche Models for Solar Flares. The distributions of solar flare energies and waiting times have not been described simultaneously by a single physical model, yet. In this research, we investigate whether recent avalanche models can describe the distributions for both the released energies and waiting times of flares in an active region. Flaring events are simulated using the modified Lu and Hamilton model and also the optimized model. Applying a probability balance equation approach, we study the statistics of the simulated flaring events and investigate the origin of the observed power law in the flare frequency-size distribution. The results indicate that the power law originates in the distribution of transition rates (the distribution of the probabilities of transitions between different energies) rather than the distribution of the energy of the active region. It is also observed that the waiting-time distribution of simulated flaring events follows a q-exponential function, which approximates a simple Poisson distribution.

Keywords: Solar active regions, Solar flares, Solar magnetic fields, Solar magnetic reconnection
The Changing Rotational Light-curve Amplitude of Varuna and Evidence for a Close-in Satellite. From CCD observations carried out with different telescopes, we present short-term photometric measurements of the large trans-Neptunian object Varuna in 10 epochs, spanning around 19 years. We observe that the amplitude of the rotational light curve has changed considerably during this period of time from 0.41 to 0.55 mag. In order to explain this variation, we constructed a model in which Varuna has a simple triaxial shape, assuming that the main effect comes from the change of the aspect angle as seen from Earth, due to Varuna’s orbital motion in the 19 year time span. The best fits to the data correspond to a family of solutions with axial ratios b/a between 0.56 and 0.60. This constrains the pole orientation in two different ranges of solutions presented here as maps. Apart from the remarkable variation of the amplitude, we have detected changes in the overall shape of the rotational light curve over shorter timescales. After the analysis of the periodogram of the residuals to a 6.343572 hr double-peaked rotational light-curve fit, we find a clear additional periodicity. We propose that these changes in the rotational light-curve shape are due to a large and close-in satellite whose rotation induces the additional periodicity. The peak-to-valley amplitude of this oscillation is in the order of 0.04 mag. We estimate that the satellite orbits Varuna with a period of 11.9819 hr (or 23.9638 hr), assuming that the satellite is tidally locked, at a distance of ∼1300 km (or ∼2000 km) from Varuna, outside the Roche limit.

Keywords: Observational astronomy, CCD photometry, Solar system formation, Optical observation, Small Solar System bodies, Trans-Neptunian objects
Effects of Anisotropic Viscosity on the Evolution of Active Galactic Nuclei Bubbles in Galaxy Clusters. The interaction between jets from active galactic nuclei (AGNs) and the intracluster medium (ICM) provides key constraints on the feeding and feedback of supermassive black holes. Much understanding about AGN feedback is gained from purely hydrodynamic models; however, whether such an approximation is adequate for the magnetized, weakly collisional ICM needs to be critically examined. For example, AGN-blown bubbles in hydrodynamic simulations are easily disrupted by fluid instabilities, making it difficult to explain the coherence of observed bubbles such as the northwest ghost bubble in Perseus. In order to investigate whether magnetic tension and viscosity in realistic conditions could preserve the bubble integrity, we performed the first Braginskii-magnetohydrodynamic simulations of jet-inflated bubbles in a medium with tangled magnetic field. We find that magnetic tension alone is insufficient to prevent bubble deformation due to large velocity shear at early stage of the evolution. Although unsuppressed anisotropic viscosity in tangled magnetic field can have similar effects as isotropic viscosity, when the pressure anisotropy is bounded by microscopic plasma instabilities, the level of viscosity is substantially limited, thereby failing to prevent bubble deformation as in the inviscid case. Our results suggest that Braginskii viscosity is unlikely to be the primary mechanism for suppressing the fluid instabilities for AGN bubbles, and it remains a challenging task to reproduce smooth and coherent bubbles as observed. Because the dynamical influence and heating of the ICM critically depend on the bubble morphology, our study highlights the fundamental role of “microphysics” on the macroscopic properties of AGN feedback processes.

Keywords: Active galactic nuclei, Intracluster medium, Plasma astrophysics, Magnetohydrodynamical simulations
The Impact of Metallicity Evolution of the Universe on the Maximum Mass of LIGO Binary Black Holes. We can be biased against observing massive black holes (BHs) merging in the local universe as the bounds on the maximum BH mass ({M}BH}\max ) depends on the assumptions regarding the metallicity evolution of the star-forming gas across the cosmic time. We investigate the bounds on the metallicity evolution, mass distribution, and delay times of the binary BH sources based on the 10 observed events by LIGO. We parametrize {M}BH}\max  to be a function of metallicity that itself is modeled to evolve with redshift in either a modest or rapid fashion. Rapid metallicity evolution models predict a stringent bound of {M}BH}\max ={44}-5+9{M}⊙ , while the bound on {M}BH}\max  in the models with modest metallicity evolution is {M}BH}\max ={52}-9+16{M}⊙ . Therefore, inferring {M}BH}\max  from GW data depends on the assumed metal enrichment history of the universe that is not severely constrained at the moment.

Keywords: Astronomy data analysis, Stellar mass black holes, Gravitational wave sources, Supernova remnants, Gravitational waves, Markov chain Monte Carlo, Metallicity
29P/Schwassmann-Wachmann 1, A Centaur in the Gateway to the Jupiter-family Comets. Jupiter-family comets (JFCs) are the evolutionary products of trans-Neptunian objects (TNOs) that evolve through the giant planet region as Centaurs and into the inner solar system. Through numerical orbital evolution calculations following a large number of TNO test particles that enter the Centaur population, we have identified a short-lived dynamical Gateway, a temporary low-eccentricity region exterior to Jupiter through which the majority of JFCs pass. We apply an observationally based size distribution function to the known Centaur population and obtain an estimated Gateway region population. We then apply an empirical fading law to the rate of incoming JFCs implied by the the Gateway region residence times. Our derived estimates are consistent with observed population numbers for the JFC and Gateway populations. Currently, the most notable occupant of the Gateway region is 29P/Schwassmann-Wachmann 1 (SW1), a highly active, regularly outbursting Centaur. SW1's present-day, very-low-eccentricity orbit was established after a 1975 Jupiter conjunction and will persist until a 2038 Jupiter conjunction doubles its eccentricity and pushes its semimajor axis out to its current aphelion. Subsequent evolution will likely drive SW1's orbit out of the Gateway region, perhaps becoming one of the largest JFCs in recorded history. The JFC Gateway region coincides with a heliocentric distance range where the activity of observed cometary bodies increases significantly. SW1's activity may be typical of the early evolutionary processing experienced by most JFCs. Thus, the Gateway region, and its most notable occupant SW1, are critical to both the dynamical and physical transition between Centaurs and JFCs.

Keywords: Centaur group, Kuiper belt, Orbits, Short period comets, Solar system, Trans-Neptunian objects
Merger Rate of Stellar Black Hole Binaries above the Pair-instability Mass Gap. In current stellar evolutionary models, the occurrence of pair-instability supernovae implies a lack of stellar black holes (BHs) with masses between about [60, 120] M⊙, resulting in the presence of an upper-mass gap in the BH mass distribution. In this Letter, we propose a simple approach to describe BHs beyond the pair-instability gap by convolving the initial mass function and star formation rate with the metallicity evolution across cosmic time. Under the ansatz that the underlying physics of binary formation does not change beyond the gap, we then construct the cosmic population of merging BH binaries. The detection rate of BH binaries with both mass components above the gap is found to range between ≃[0.4, 7] yr-1 for LIGO/Virgo at design sensitivity and [10, 460] yr-1 for third-generation ground-based detectors, considering the most pessimistic and optimistic scenarios. The Laser Interferometer Space Antenna (LISA) can individually detect these binaries up to thousands of years from coalescence. The number of events merging in less than four years, which enable multiband observation in sequence, is expected to be in the range [1, 20]. While ET will detect all these events, LIGO/Virgo is expected to detect ≲50% of them. Finally, we estimate that the gravitational-wave background from unresolved sources in the LISA band may in principle be detected with a signal-to-noise ratio between ≃2.5 and ≃80.

Keywords: Close binary stars, Black hole physics, Gravitational waves
Disintegrating Inbound Long-period Comet C/2019 J2. We present observations of the disintegrating long-period comet C/2019 J2 (Palomar), taken to determine the nature of the object and the cause of its demise. The data are consistent with the break-up of a sub-kilometer nucleus into a debris cloud of mass ∼109 kg, peaking on UT 2019 May 24 ± 12. This is ∼56 days before perihelion and at a heliocentric distance of ∼1.9 au. We consider potential mechanisms of disintegration. Tidal disruption is ruled out, because the comet has not passed within the Roche sphere of any planet. Impact disruption is implausible, because the comet orbit is highly inclined (inclination 105.°1) and disruption occurred far above the ecliptic, where asteroids are rare. The back pressure generated by sublimation (0.02-0.4 N m-2) is orders of magnitude smaller than the reported compressive strength (30-150 N m-2) of cometary material and, therefore, is of no importance. The depletion of volatiles by sublimation occurs too slowly to render the nucleus inactive on the timescale of infall. However, we find that the e-folding timescale for spin-up of the nucleus by the action of sublimation torques is shorter than the infall time, provided that the nucleus radius is r  n  &lt; 0.4 km. Thus, the disintegration of C/2019 J2 is tentatively interpreted as the rotational disruption of a sub-kilometer nucleus caused by outgassing torques.

Keywords: Long period comets, Small Solar System bodies, Oort cloud objects
Spectropolarimetry of the Solar Mg II h and k Lines. We report on spectropolarimetric observations across the Mg II h and k lines at 2800 Å made by the Ultraviolet Spectrometer and Polarimeter on board the Solar Maximum Mission satellite. Our analysis confirms the strong linear polarization in the wings of both lines observed near the limb, as previously reported, but also demonstrates the presence of a negatively (i.e., radially oriented) polarized signal between the two lines. We find evidence for fluctuations of the polarization pattern over a broad spectral range, resulting in some depolarization with respect to the pure scattering case when observed at very low spatial and temporal resolutions. This is consistent with recent theoretical modeling that predicts this to be the result of redistribution effects, quantum interference between the atomic levels of the upper term, and magneto-optical effects. A first attempt at a quantitative exploitation of these signals for the diagnosis of magnetic fields in the chromosphere is attempted. In active regions, we present observations of circular polarization dominated by the Zeeman effect. We are able to constrain the magnetic field strength in the upper active chromosphere using an analysis based on the magnetograph formula, as justified by theoretical modeling. We inferred a significantly strong magnetic field (∼500 G) at the 2.5σ level on an exceptionally active, flaring region.

Keywords: Solar magnetic fields, Solar chromosphere, Spectropolarimetry, Solar ultraviolet emission
Radial Dependence of the Proto-globular Cluster Contribution to the Milky Way Formation. Recent interpretation of the color-magnitude diagrams of the Milky Way (MW) bulge has suggested that the observed double red-clump feature can be a natural consequence of He-enhanced stellar populations in the MW bulge. This implies that globular clusters (GCs), where the He-enhanced second-generation (SG) stars can be efficiently created, are the most likely candidate contributors of He-rich stars to the MW bulge. We extend this idea to the Galactic inner halo and investigate the fraction of the SG stars as a function of the Galactocentric distance. We use bluer blue horizontal branch (bBHB) stars, which are assumed to have originated from He-rich SG populations, as proxies of SG stars, and find that the fraction of bBHB stars increases with decreasing Galactocentric distance. Simulations of the GC evolution in the MW tidal field qualitatively support the observed trend of bBHB enhancement in the inner halo. In these simulations, the increasing tidal force with decreasing Galactocentric distance leads to stripping of stars not only from the outskirts but also from the central regions of GCs, where SG stars are more abundant. We discuss the implication and prospect of our findings concerning the formation history of the bulge and inner halo of the MW.

Keywords: Globular star clusters, Horizontal branch stars, Stellar abundances, Computational methods, Milky Way stellar halo, Stellar evolution
Dragonfly Imaging of the Galaxy NGC 5907: A Different View of the Iconic Stellar Stream. In 2008 it was reported that the stellar stream of the edge-on spiral NGC 5907 loops twice around the galaxy, enveloping it in a giant corkscrew-like structure. Here we present imaging of this iconic object with the Dragonfly Telephoto Array, reaching a 1σ surface brightness level of μ  g  = 30.3 mag arcsec-2 on spatial scales of 1‧ (the approximate width of the stream). We find a qualitatively different morphology from that reported in the 2008 study. The Dragonfly data do not show two loops but a single curved stream with a total length of 45‧ (220 kpc). The surface brightness of the stream ranges from μ  g  ≈ 27.6 mag arcsec-2 to μ  g  ≈ 28.8 mag arcsec-2, and it extends significantly beyond the region where tidal features had previously been detected. We find a density enhancement near the luminosity-weighted midpoint of the stream which we identify as the likely remnant of a nearly disrupted progenitor galaxy. A restricted N-body simulation provides a qualitative match to the detected features. In terms of its spatial extent and stellar mass the stream is similar to Sagittarius, and our results demonstrate the efficacy of low surface brightness-optimized telescopes for obtaining maps of such large streams outside the Local Group. The census of these rare, relatively high mass events complements the census of common, low-mass ones that is provided by studies of streams in the Milky Way halo.

Keywords: Tidal disruption, Dwarf galaxies, Low surface brightness galaxies
Off the Baryonic Tully-Fisher Relation: A Population of Baryon-dominated Ultra-diffuse Galaxies. We study the gas kinematics traced by the 21 cm emission of a sample of six H I-rich low surface brightness galaxies classified as ultra-diffuse galaxies (UDGs). Using the 3D kinematic modeling code 3DBarolo we derive robust circular velocities, revealing a startling feature: H I-rich UDGs are clear outliers from the baryonic Tully-Fisher relation, with circular velocities much lower than galaxies with similar baryonic mass. Notably, the baryon fraction of our UDG sample is consistent with the cosmological value: these UDGs are compatible with having no “missing baryons” within their virial radii. Moreover, the gravitational potential provided by the baryons is sufficient to account for the amplitude of the rotation curve out to the outermost measured point, contrary to other galaxies with similar circular velocities. We speculate that any formation scenario for these objects will require very inefficient feedback and a broad diversity in their inner dark matter content.

Keywords: Galaxy formation, Dwarf galaxies, Galaxy dynamics, Galaxy kinematics, Galaxy evolution, Galaxy rotation curves, Dark matter, Low surface brightness galaxies
Discovery of a Red Supergiant Donor Star in SN2010da/NGC 300 ULX-1. SN2010da/NGC 300 ULX-1 was first detected as a supernova impostor in 2010 May and was recently discovered to be a pulsating ultraluminous X-ray source. In this Letter, we present Very Large Telescope/X-shooter spectra of this source obtained in 2018 October, covering the wavelength range 350-2300 nm. The J- and H-bands clearly show the presence of a red supergiant (RSG) donor star that is best matched by a MARCS stellar atmosphere with T eff = 3650-3900 K and log(L bol/L ☉) = 4.25 ± 0.10, which yields a stellar radius R = 310 ± 70R ☉. To fit the full spectrum, two additional components are required: a blue excess that can be fitted either by a hot blackbody (T ≳ 20,000 K) or a power law (spectral index α ≈ 4) and is likely due to X-ray emission reprocessed in the outer accretion disk or the donor star; and a red excess that is well fitted by a blackbody with a temperature of ∼1100 K, and is likely due to warm dust in the vicinity of SN2010da. The presence of an RSG in this system implies an orbital period of at least 0.8-2.1 yr, assuming Roche-lobe overflow. Given the large donor-to-compact object mass ratio, orbital modulations of the radial velocity of the RSG are likely undetectable. However, the radial velocity amplitude of the neutron star is large enough (up to 40-60 km s-1) to potentially be measured in the future, unless the system is viewed at a very unfavorable inclination.

Keywords: Late-type supergiant stars, Neutron stars, High mass x-ray binary stars
Precursor Wave Amplification by Ion-Electron Coupling through Wakefield in Relativistic Shocks. We investigated electromagnetic precursor wave emission in relativistic shocks by using two-dimensional particle-in-cell simulations. We found that the wave amplitude is significantly enhanced by a positive feedback process associated with ion-electron coupling through the wakefields for high magnetization. The wakefields collapse during the nonlinear process of the parametric decay instability in the near-upstream region, where nonthermal electrons and ions are generated. The intense coherent emission and the particle acceleration may operate in high-energy astrophysical objects.

Keywords: Cosmic rays, Shocks, High energy astrophysics, Plasma physics
Revisiting the Strongest Martian X-Ray Halo Observed by XMM-Newton on 2003 November 19-21. On 2003 November 20-21, when the most intense geomagnetic storm during solar cycle 23 was observed at Earth, XMM-Newton recorded the strongest Martian X-ray halo hitherto. The strongest Martian X-ray halo has been suggested to be caused by the unusual solar wind, but no direct evidence has been given in previous studies. Here, we examined the Mars Global Surveyor (MGS) observations and found unambiguous evidence of unusual solar wind impact during that XMM-Newton observation: the whole induced magnetosphere of Mars was highly compressed. By comparing the solar wind dynamic pressure estimated at Mars from MGS observation and that predicted by different solar wind propagation models, it is further supported that the interplanetary condition during the XMM-Newton observation is not related to the quiet solar wind, but to solar wind disturbances with enhanced dynamic pressure, which is probably related to the interplanetary coronal mass ejection observed at Earth on 2003 November 20. A solar energetic particle event also impacted Mars during the XMM-Newton observation and lasted for several days. Its impact on the production of the X-ray emission from Mars may be worth investigating in the future.

Keywords: X-ray astronomy, Exosphere, Mars, Planetary atmospheres, Solar coronal mass ejections