adsabs/SciX_UAT_keywords huggingface dataset:
Comprehensive Analysis of Magnetospheric Gaps around Kerr Black Holes Using 1D GRPIC Simulations

Spark gaps are likely the source of plasma in active black hole (BH) magnetospheres. In this paper, we present results of 1D general relativistic particle-in-cell simulations of a starved BH magnetosphere with a realistic treatment of inverse-Compton scattering and pair production, for a broad range of conditions, run times longer than in previous studies, and different setups. We find that following the initial discharge, the system undergoes gradual evolution over prolonged time until either restoring the vacuum state or reaching a state of quasiperiodic oscillations, depending on the spectral shape and luminosity of the ambient radiation field. The oscillations occur near the null charge surface in cases where the global magnetospheric current is in the direction defined by the product of the asymptotic Goldreich-Julian charge density and the radial velocity, while they occur near the boundary of the simulation box when it is the opposite direction (return current). Their amplitude and the resultant luminosity of TeV photons emitted from the gap depend sensitively on the conditions; for the cases studied here the ratio of TeV luminosity to the Blandford-Znajek power ranges from 10-5 to 10-2, suggesting that strong flares may be generated by moderate changes in disk emission. We also examined the dependence of the solution on the initial number of particles per cell (PPC) and found convergence for PPC of about 50 for the cases examined. At lower PPC values the pair multiplicity is found to be artificially high, affecting the solution considerably.

Keywords: black hole physics; high energy astrophysics; plasma astrophysics; non-thermal radiation sources
Photoevaporation of Minihalos During Cosmic Reionization: Primordial and Metal-enriched Halos

The density distribution of the intergalactic medium is an uncertain but highly important issue in the study of cosmic reionization. It is expected that there are abundant gas clouds hosted by low-mass "minihalos" in the early universe, which act as photon sinks until being photoevaporated by the emerging ultraviolet background (UVB) radiation. We perform a suite of radiation-hydrodynamic simulations to study the photoevaporation of minihalos. Our simulations follow hydrodynamics, nonequilibrium chemistry, and the associated cooling processes in a self-consistent manner. We conduct a parametric study by considering a wide range of gas metallicities (0 Z⊙ ≤ Z ≤ 10-3 Z⊙), halo mass (103 M⊙ ≤ M ≤ 108 M⊙), UVB intensity (0.01 ≤ J21 ≤ 1), and turn-on redshift of ionizing sources (10 ≤ zIN ≤ 20). We show that small halos are evaporated in a few tens of millions of years, whereas larger mass halos survive 10 times longer. The gas mass evolution of a minihalo can be characterized by a scaling parameter that is given by a combination of the halo mass, background radiation intensity, and redshift. Efficient radiative cooling in metal-enriched halos induces fast condensation of the gas to form a dense, self-shielded core. The cold, dense core can become gravitationally unstable in halos with high metallicities. Early metal enrichment may allow star formation in minihalos during cosmic reionization.

Keywords: hydrodynamical simulations; metallicity; star formation; chemical enrichment; reionization
Polar Circumtriple Planets and Disks Can Only Form Close to a Triple Star

Observations of protoplanetary disks around binary and triple star systems suggest that misalignments between the orbital plane of the stars and the disks are common. Motivated by recent observations of polar circumbinary disks, we explore the possibility of polar circumtriple disks and therefore polar circumtriple planets that could form in such a disk. With n-body simulations and analytic methods, we find that the inclusion of a third star, and the associated apsidal precession, significantly reduces the radial range of polar orbits so that circumtriple polar disks and planets can only be found close to the stellar system. Outside of a critical radius that is typically in the range of 3-10 times the outer binary separation, depending upon the binary parameters, the orbits behave the same as they do around a circular orbit binary. For some observed systems that have shorter-period inner binaries, the critical radius is considerably larger. If polar circumtriple planets can form, we suggest that it is likely that they form in a disk that was subject to breaking.

Keywords: exoplanet dynamics; celestial mechanics; trinary stars; protoplanetary disks
A Possible Tidal Disruption Event Candidate in the Black Hole Binary System of OJ 287

The BL Lacertae OJ 287 is a supermassive black hole binary system with complex physics of its irregular flares. During 2016 October-2017 April, a surprising outburst in the X-ray, UV, and optical bands was detected, while no variability was seen in the γ-ray light curve. During the outburst, the X-ray light curves were dominated by the soft X-rays, whose peak in luminosity was ~1046 erg s-1-more than 10 times higher than the mean level before the outburst-and a "softer-when-brighter" phenomenon was exhibited. These above phenomena have been reported by some previous works. The hardness ratio showed negligible evolution with flare time and soft X-ray luminosity. Critically, the luminosity of the soft X-rays decayed following a power law of t-5/3, which occurs in most tidal disruption events (TDEs), and a similar trend can be seen in the UV and optical bands during the soft X-ray declining period. Helium and oxygen narrow emission lines are strengthened prominently in the optical spectra of postoutburst epochs, that could be attributed to the surrounding gas caused by TDE. We discuss three possible origins of the event, including the jet's precession, the aftereffects of the black hole-disk impaction, and the TDE. Our results show that the TDE is the more likely scenario to explain the outburst.

Keywords: tidal disruption; supermassive black holes; black hole physics; blazars; x-ray bursts; accretion
The Lazy Giants: APOGEE Abundances Reveal Low Star Formation Efficiencies in the Magellanic Clouds

We report the first APOGEE metallicities and α-element abundances measured for 3600 red giant stars spanning a large radial range of both the Large (LMC) and Small Magellanic Clouds, the largest Milky Way (MW) dwarf galaxies. Our sample is an order of magnitude larger than that of previous studies and extends to much larger radial distances. These are the first results presented that make use of the newly installed southern APOGEE instrument on the du Pont telescope at Las Campanas Observatory. Our unbiased sample of the LMC spans a large range in metallicity, from [Fe/H] = -0.2 to very metal-poor stars with [Fe/H] ≈ -2.5, the most metal-poor Magellanic Cloud (MC) stars detected to date. The LMC [α/Fe]-[Fe/H] distribution is very flat over a large metallicity range but rises by ∼0.1 dex at -1.0 < [Fe/H] ≲ -0.5. We interpret this as a sign of the known recent increase in MC star formation activity and are able to reproduce the pattern with a chemical evolution model that includes a recent "starburst." At the metal-poor end, we capture the increase of [α/Fe] with decreasing [Fe/H] and constrain the "α-knee" to [Fe/H] ≲ -2.2 in both MCs, implying a low star formation efficiency of ∼0.01 Gyr-1. The MC knees are more metal-poor than those of less massive MW dwarf galaxies such as Fornax, Sculptor, or Sagittarius. One possible interpretation is that the MCs formed in a lower-density environment than the MW, a hypothesis that is consistent with the paradigm that the MCs fell into the MW's gravitational potential only recently.

Keywords: magellanic clouds; galaxy abundances; local group; surveys; star formation
KIC 9845907: A δ Scuti Star with the First Overtone as the Dominant Frequency and with Many Equidistant Structures in Its Spectrum

In this paper, we present an analysis of the pulsating behavior of Kepler target KIC 9845907. Using the data from Kepler, we detected 85 significant frequencies, including the first overtone f 1 = 17.597 day-1 as the dominant frequency, the non-radial independent frequency f 3 = 31.428 day-1 (ℓ = 1), as well as two modulation terms f m1 = 0.065 day-1 and f m2 = 1.693 day-1. We found fourteen pairs of triplet structures with f m1 or f m2, four pairs of which can further form quintuplet structures. We note these are the most intriguing features discovered in this study and they were recognized for the first time in δ Scuti stars. We discussed several possible explanations, i.e., beating, the Blazhko effect, combination mode hypothesis, nonlinear mode coupling, large separation, and stellar rotational splitting for these equidistant structures. Our asteroseismic models indicate this modulation with f m1 might be related to the rotational splitting. The study of more δ Scuti stars with triplet and/or quintuplet structures using high-precision space photometry would be helpful to further explore its origin.

Keywords: delta scuti variable stars; stellar oscillations
Inferences About the Magnetic Field Structure of a CME with Both In Situ and Faraday Rotation Constraints

On 2012 August 2, two coronal mass ejections (CMEs; CME-1 and CME-2) erupted from the west limb of the Sun as viewed from Earth, and were observed in images from the white-light coronagraphs on the SOlar and Heliospheric Observatory and Solar TErrestrial RElations Observatory (STEREO) spacecraft. These events were also observed by the Very Large Array (VLA), which was monitoring the Sun at radio wavelengths, allowing time-dependent Faraday rotation observations to be made of both events. We use the white-light imaging and radio data to model the 3D field geometry of both CMEs, assuming a magnetic flux rope geometry. For CME-2, we also consider 1 au in situ field measurements in the analysis, as this CME hits STEREO-A on August 6, making this the first CME with observational constraints from stereoscopic coronal imaging, radio Faraday rotation, and in situ plasma measurements combined. The imaging and in situ observations of CME-2 provide two clear predictions for the radio data: VLA should observe positive rotation measures (RMs) when the radio line of sight first encounters the CME, and the sign should reverse to negative within two hours. The initial positive RMs are in fact observed. The expected sign reversal is not, but the VLA data unfortunately end too soon to be sure of the significance of this discrepancy. We interpret an RM increase prior to the expected occultation time of the CME as a signature of a sheath region of deflected field ahead of the CME itself.

Keywords: solar coronal mass ejections; interplanetary medium
Observing Planetesimal Formation under Streaming Instability in the Rings of HD 163296

We introduce a new technique to determine the gas turbulence and surface density in bright disk rings, under the assumption that dust growth is limited by turbulent fragmentation at the ring center. We benchmark this prescription in HD 163296, showing that our measurements are consistent with available turbulence upper limits and agree with independent estimates of the gas surface density within a factor of 2. We combine our results with literature measurements of the dust surface density and grain size to determine the dust-to-gas ratio and Stokes number in the 67 and 100 au rings. Our estimates suggest that particle clumping is taking place under the effect of streaming instability (SI) in the 100 au ring. Even though in the presence of external isotropic turbulence this process might be hindered, we provide evidence that turbulence is nonisotropic in both rings and likely originates from mechanisms (such as ambipolar diffusion) that could ease particle clumping under SI. Finally, we determine the mass accretion rate under the assumption that the disk is in steady state and turbulence regulates angular momentum transport. Our results are in tension with spectroscopic measurements and suggest that other mechanisms might be responsible for accretion, in qualitative agreement with the detection of a magnetocentrifugal wind in this system. Applying our method to larger samples can be used to statistically assess if SI is a viable mechanism to form planetesimals in bright rings.

Keywords: co line emission; dust continuum emission; gas-to-dust ratio; planet formation; planetary cores; planetesimals; protoplanetary disks; submillimeter astronomy
The Lyman Continuum Escape Survey: Connecting Time-dependent [O III] and [O II] Line Emission with Lyman Continuum Escape Fraction in Simulations of Galaxy Formation

Escaping Lyman continuum photons from galaxies likely reionized the intergalactic medium at redshifts z ≳ 6. However, the Lyman continuum is not directly observable at these redshifts and secondary indicators of Lyman continuum escape must be used to estimate the budget of ionizing photons. Observationally, at redshifts z ∼ 2-3 where the Lyman continuum is observationally accessible, surveys have established that many objects that show appreciable Lyman continuum escape fractions fesc also show enhanced [O III]/[O II] (O32) emission line ratios. Here, we use radiative transfer analyses of cosmological zoom-in simulations of galaxy formation to study the physical connection between fesc and O32. Like the observations, we find that the largest fesc values occur at elevated O32 ∼ 3-10 and that the combination of high fesc and low O32 is extremely rare. While high fesc and O32 often are observable concurrently, the timescales of the physical origin for the processes are very different. Large O32 values fluctuate on short (∼1 Myr) timescales during the Wolf-Rayet-powered phase after the formation of star clusters, while channels of low absorption are established over tens of megayears by collections of supernovae. We find that while there is no direct causal relation between fesc and O32, high fesc most often occurs after continuous input from star formation-related feedback events that have corresponding excursions to large O32 emission. These calculations are in agreement with interpretations of observations that large fesc tends to occur when O32 is large, but large O32 does not necessarily imply efficient Lyman continuum escape.

Keywords: emission nebulae; radiative transfer simulations; galaxy formation; interstellar line emission; star forming regions; high-redshift galaxies; high time resolution astrophysics
CO Observations of Early-mid Stage Major Mergers in the MaNGA Survey

We present a study of the molecular gas in early-mid stage major mergers, with a sample of 43 major-merger galaxy pairs selected from the Mapping Nearby Galaxies at Apache Point Observatory survey and a control sample of 195 isolated galaxies selected from the xCOLD GASS survey. Adopting kinematic asymmetry as a new effective indicator to describe the merger stage, we aim to study the role of molecular gas in the merger-induced star formation enhancement along the merger sequence of galaxy pairs. We obtain the molecular gas properties from CO observations with the James Clerk Maxwell Telescope, Institut de Radioastronomie Milimetrique 30 m telescope, and the MaNGA-ARO Survey of CO Targets survey. Using these data, we investigate the differences in molecular gas fraction ( ), star formation rate (SFR), star formation efficiency (SFE), molecular-to-atomic gas ratio ( /M H I ), total gas fraction (f gas), and the SFE of total gas (SFEgas) between the pair and control samples. In the full pair sample, our results suggest the of paired galaxies is significantly enhanced, while the SFE is comparable to that of isolated galaxies. We detect significantly increased and /M H I in paired galaxies at the pericenter stage, indicating an accelerated transition from atomic gas to molecular gas due to interactions. Our results indicate that the elevation of plays a major role in the enhancement of global SFR in paired galaxies at the pericenter stage, while the contribution of enhanced SFE in specific regions requires further explorations through spatially resolved observations of a larger sample spanning a wide range of merger stages.

Keywords: galaxy pairs; galaxy mergers; molecular gas; star formation
Constraints on the Frequency and Mass Content of r-process Events Derived from Turbulent Mixing in Galactic Disks

Metal-poor stars in the Milky Way (MW) halo display large star-to-star dispersion in their r-process abundance relative to lighter elements. This suggests a chemically diverse and unmixed interstellar medium (ISM) in the early universe. This study aims to help shed light on the impact of turbulent mixing, driven by core-collapse supernovae (cc-SNe), on the r-process abundance dispersal in galactic disks. To this end, we conduct a series of simulations of small-scale galaxy patches which resolve metal-mixing mechanisms at parsec scales. Our setup includes cc-SNe feedback and enrichment from r-process sources. We find that the relative rate of the r-process events to cc-SNe is directly imprinted on the shape of the r-process distribution in the ISM with more frequent events causing more centrally peaked distributions. We consider also the fraction of metals that is lost on galactic winds and find that cc-SNe are able to efficiently launch highly enriched winds, especially in smaller galaxy models. This result suggests that smaller systems, e.g., dwarf galaxies, may require higher levels of enrichment in order to achieve similar mean r-process abundances as MW-like progenitors systems. Finally, we are able to place novel constraints on the production rate of r-process elements in the MW, $6\times {10}^{-7}{M}_{\odot }\,{\mathrm{yr}}^{-1}\lesssim {\dot{m}}_{\mathrm{rp}}\ll 4.7\times {10}^{-4}{M}_{\odot }\,{\mathrm{yr}}^{-1}$ , imposed by accurately reproducing the mean and dispersion of [Eu/Fe] in metal-poor stars. Our results are consistent with independent estimates from alternate methods and constitute a significant reduction in the permitted parameter space.

Keywords: r-process; stellar feedback; metallicity; interstellar medium; galactic winds; milky way galaxy physics; chemical abundances
iPTF 16asu Revisited: A Rapidly Evolving Superluminous Broad-lined Ic Supernova?

In this paper, we fit the spectral energy distributions of iPTF 16asu, which has so far been classified as a luminous rapidly evolving broad-lined Ic supernova (SN Ic-BL), and reconstruct its postpeak bolometric light curve. We find that the luminosity of the postpeak bolometric light curve of iPTF 16asu is about 3 times that of the pseudobolometric light curve derived in the literature, and the extrapolated peak luminosity exceeds ~1044 erg s-1, which is higher than the threshold of superluminous supernovae (SLSNe). We then use the 56Ni model and the magnetar plus 56Ni model to fit the multiband light curves of iPTF 16asu, and construct the theoretical bolometric light curve using the best-fitting theoretical multiband light curves. We find that the magnetar plus 56Ni model can account for the photometry of iPTF 16asu, and the peak luminosity of its theoretical bolometric light curve is ~1.06 × 1044 erg s-1. We suggest that iPTF 16asu and similar SNe (e.g., SN 2018gep) constitute the class of rapidly evolving SLSNe Ic-BL.

Keywords: type ic supernovae; magnetars; spectral energy distribution
The "Canonical" White Dwarf Cooling Sequence of M5

Recently, slowly cooling white dwarfs (WDs) are a new class of WD that have been identified in two globular clusters (namely M13 and NGC 6752), showing a horizontal branch (HB) morphology with an extended blue tail. The cooling rate of these WDs is reduced by stable thermonuclear hydrogen burning in their residual envelope, and they are thought to originate by stars that populate the blue tail of the HB and then skip the asymptotic giant branch phase. Consistently, no evidence of such kind of WDs has been found in M3, a similar cluster with no blue extension of the HB. To further explore this phenomenon, we took advantage of deep photometric data acquired with the Hubble Space Telescope in the near-ultraviolet and investigated the bright portion of the WD cooling sequence in M5, another Galactic globular cluster with HB morphology similar to M3. The normalized WD luminosity function derived in M5 was found to be impressively similar to that observed in M3, in agreement with the fact that the stellar mass distribution along the HB of these two systems is almost identical. The comparison with theoretical predictions is consistent with the fact that the cooling sequence in this cluster is populated by canonical (fast cooling) WDs. Thus, the results presented in this paper provide further support to the scenario proposing a direct causal connection between the slow cooling WD phenomenon and the horizontal branch morphology of the host stellar cluster.

Keywords: globular star clusters; white dwarf stars; luminosity function; hst photometry; ultraviolet photometry; hertzsprung russell diagram
Daniel Mögling's Sunspot Observations in 1626-1629: A Manuscript Reference for the Solar Activity before the Maunder Minimum

The sunspots have been observed since 1610, and their group numbers have been used for evaluating the amplitude of solar activity. Daniel Mögling recorded his sunspot observations for more than 100 days in 1626-1629 and formed a significant data set of sunspot records before the Maunder Minimum. Here we have analyzed his original manuscripts in the Universitäts- und Landesbibliothek Darmstadt to review Mögling's personal profile and observational instruments and derived the number and positions of the recorded sunspot groups. In his manuscript, we have identified 134 days with an exact sunspot group number and 3 days of additional descriptions. Our analyses have completely revised the observational dates and group numbers, added 19 days of hitherto overlooked observations, and removed 8 days of misinterpreted observations. We have also revisited the sunspot observations of Schickard and Hortensius and revised their data. These results have been compared with the contemporary observations. Moreover, we have derived the sunspot positions from his sunspot drawings and located them at 2°-23° in heliographic latitude in both solar hemispheres. Contextualized with contemporary observations, these results indicate their temporal migration to lower heliographic latitudes and emphasize their location in the declining phase of solar cycle -12 in the 1620s. Mögling's observations were probably conducted using a pinhole and camera obscura, which likely made him underestimate the sunspot group number by ≥33%-52%. This underestimation should be noted upon comparison with modern data sets.

Keywords: sunspot cycle; sunspot groups; sunspot number; solar cycle; history of astronomy; solar-terrestrial interactions; maunder minimum