adsabs/SciX_UAT_keywords huggingface dataset:
The Formation of Intermediate-mass Black Holes in Galactic Nuclei

Most stellar evolution models predict that black holes (BHs) should not exist above approximately 50-70 M ⊙, the lower limit of the pair-instability mass gap. However, recent LIGO/Virgo detections indicate the existence of BHs with masses at and above this threshold. We suggest that massive BHs, including intermediate-mass BHs (IMBHs), can form in galactic nuclei through collisions between stellar-mass BHs and the surrounding main-sequence stars. Considering dynamical processes such as collisions, mass segregation, and relaxation, we find that this channel can be quite efficient, forming IMBHs as massive as 104 M ⊙. This upper limit assumes that (1) the BHs accrete a substantial fraction of the stellar mass captured during each collision and (2) that the rate at which new stars are introduced into the region near the SMBH is high enough to offset depletion by stellar disruptions and star-star collisions. We discuss deviations from these key assumptions in the text. Our results suggest that BHs in the pair-instability mass gap and IMBHs may be ubiquitous in galactic centers. This formation channel has implications for observations. Collisions between stars and BHs can produce electromagnetic signatures, for example, from X-ray binaries and tidal disruption events. Additionally, formed through this channel, both BHs in the mass gap and IMBHs can merge with the SMBHs at the center of a galactic nucleus through gravitational waves. These gravitational-wave events are extreme- and intermediate-mass ratio inspirals.

Keywords: astrophysical black holes; intermediate-mass black holes; stellar mass black holes; stellar dynamics
Fizzy Super-Earths: Impacts of Magma Composition on the Bulk Density and Structure of Lava Worlds

Lava worlds are a potential emerging population of Super-Earths that are on close-in orbits around their host stars, with likely partially molten mantles. To date, few studies have addressed the impact of magma on the observed properties of a planet. At ambient conditions, magma is less dense than solid rock; however, it is also more compressible with increasing pressure. Therefore, it is unclear how large-scale magma oceans affect planet observables, such as bulk density. We update ExoPlex, a thermodynamically self-consistent planet interior software, to include anhydrous, hydrous (2.2 wt% H2O), and carbonated magmas (5.2 wt% CO2). We find that Earth-like planets with magma oceans larger than ~1.5 R ⊕ and ~3.2 M ⊕ are modestly denser than an equivalent-mass solid planet. From our model, three classes of mantle structures emerge for magma ocean planets: (1) a mantle magma ocean, (2) a surface magma ocean, and (3) one consisting of a surface magma ocean, a solid rock layer, and a basal magma ocean. The class of planets in which a basal magma ocean is present may sequester dissolved volatiles on billion-year timescales, in which a 4 M ⊕ mass planet can trap more than 130 times the mass of water than in Earth's present-day oceans and 1000 times the carbon in the Earth's surface and crust.

Keywords: exoplanet astronomy
A QPO in Mkn 421 from Archival RXTE Data

We report a 325(-7, +8) day quasi-periodic oscillation (QPO) in the X-ray emission of the blazar Mkn 421 based on data obtained with the Rossi X-ray Timing Explorer satellite. The QPO is seen prominently in the ASM data (at least 15 cycles) due to the fact that it has had near-continuous sampling for more than a decade. The PCA data, where the sampling is not uniform and shows many large gaps, provide supporting evidence at lower significance. The QPOs are an important observable in accretion disks, can be modulated by various orbital timescales, and may be generated by a number of mechanisms. They have been studied extensively in X-ray binaries and should be present in active galactic nuclei (AGN) if they are governed by a common set of physical principles. In jetted sources, QPOs can probe jet-disk interactions or helical oscillations. This QPO has previously been claimed intermittently in X-ray, radio, and gamma-ray data, but the continuous, 15 yr extent (1996-2011) of the ASM observations (in which Mkn 421 is the brightest AGN observed) provides a unique window. The QPO appears to be present for nearly the entire extent of the ASM observations. We explore various physical origins and modulating mechanisms, particularly interpretations of the QPO as a result of disk-jet interactions, due to either an accretion disk limit cycle, jet instabilities, or helical motions. Limit cycle oscillations would not interact with either Keplerian or Lense-Thirring modulated oscillations; however, those associated with jet instabilities or helical motions in the jet would likely be modulated by Lense-Thirring precession.

Keywords: active galactic nuclei; blazars; bl lacertae objects; galaxy accretion disks; x-ray astronomy
Modeling Long-term Variability in Stellar-compact Object Binary Systems for Mass Determinations

This work models the effects of gravitational lensing, Doppler boosting, and ellipsoidal variations on eccentric eclipsing binary-system light curves. This is accomplished using a Newtonian orbital-motion code that simulates the orbital velocities and separation of the binary components as a function of time. Improving on previous literature, we examine the effects of orbital eccentricity and period, as well as stellar limb darkening on the expected light curves. Whether lensing, Doppler boosting, or ellipsoidal variation is dominant in the light curves is a function of the separation between the binary components; thus, the combination of all three effects allows for a unique mass-determination method that greatly expands the parameter space for the discovery of compact objects. This suggests the exciting possibility of revealing a large population of nonaccreting compact objects in galactic binary systems. At the same time, the model can be used on systems exhibiting any subset of these effects. In a case study, we fit our model to optical data from the ellipsoidal variable binary system Cygnus X-1, and we compare our determinations with those previously found by different modeling techniques.

Keywords: black hole physics; compact binary stars; ellipsoidal variable stars; gravitational microlensing
Thresholds for Particle Clumping by the Streaming Instability

The streaming instability (SI) is a mechanism to aerodynamically concentrate solids in protoplanetary disks and trigger the formation of planetesimals. The SI produces strong particle clumping if the ratio of solid to gas surface density-an effective metallicity-exceeds a critical value. This critical value depends on particle sizes and disk conditions such as radial drift-inducing pressure gradients and levels of turbulence. To quantify these thresholds, we perform a suite of vertically stratified SI simulations over a range of dust sizes and metallicities. We find a critical metallicity as low as 0.4% for the optimum particle sizes and standard radial pressure gradients (normalized value of Π = 0.05). This subsolar metallicity is lower than previous results, due to improved numerical methods and computational effort. We discover a sharp increase in the critical metallicity for small solids, when the dimensionless stopping time (Stokes number) is ≤0.01. We provide simple fits to the size-dependent SI clumping threshold, including generalizations to different disk models and levels of turbulence. We also find that linear, unstratified SI growth rates are a surprisingly poor predictor of particle clumping in nonlinear, stratified simulations, especially when the finite resolution of simulations is considered. Our results widen the parameter space for the SI to trigger planetesimal formation.

Keywords: planet formation; protoplanetary disks; planetesimals; hydrodynamics; hydrodynamical simulations; gas-to-dust ratio
Frequencies of Warm Debris Disks Based on Point Source Catalogs of Spitzer, WISE, and Gaia

More than a thousand warm debris disks have been detected as infrared excess at mid-infrared wavelengths, and their frequencies have been obtained for various spectral types of stars. However, the dependence of the frequencies on spectral type is still debated because the number of stars with significant and detectable infrared excess is limited. Herein, we present the largest systematic search for infrared excess using data from Gaia, WISE, and Spitzer. We identified 373, 485, and 255-reliable infrared excesses in the mid-infrared archival data at wavelengths of 12, 22, and 24 μm for WISE/W3, W4, and Spitzer/MIPS ch1, respectively. Although we confirmed that more massive stars tend to show higher frequencies of debris disks, these disk frequencies are relatively flat for both low- and intermediate-mass stars, with a jump at 7000 K for all three wavelengths. Assuming that bright, warm debris disks have lifetimes of a few to several hundred million years, the disk frequency can be understood as the ratio between the timescale and the upper limits of the sample ages. We also found that intermediate-mass stars with infrared excess tend to be bluer and fainter along the evolutionary track than those without, implying that massive stars hosting debris disks are relatively young, with an isochronal age of approximately 500 Myr. These tendencies are reasonably explained by a standard scenario in which debris disks are likely to be produced by collisions of planetesimals in the early stages of stellar evolution, such as the Late Heavy Bombardment.

Keywords: debris disks; infrared excess; spectral energy distribution; catalogs; main sequence stars; space observatories; gaia
Magnetohydrodynamic Simulation of Multiple Coronal Mass Ejections: An Effect of "Pre-events"

Coronal mass ejections (CMEs) are a major source of solar wind disturbances that affect the space plasma and magnetic field environment along their propagation path. Accurate prediction of the arrival of a CME at Earth or any point in the heliosphere is still a daunting task. In this study we explore an often overlooked factor-the effects of "pre-events" that can alter the propagation of a CME due to a preceding CME. A data-driven magnetohydrodynamic numerical model is used to simulate the propagation of multiple CMEs and their driven shocks that occurred in 2012 July. The simulation results are validated with in situ solar wind plasma and magnetic field measurements at 1 au, testing the appropriateness of our simulation results for interpreting the CME/shock evolution. By comparing the simulation results with and without preceding CMEs, we find that the trailing CME can be accelerated by the "wake" of a preceding CME. A detailed analysis suggests that the acceleration is caused partially by an increase in the background solar wind and partially by the so-called "snowplow" effect, with the latter being the major contributor for the 2012 July event.

Keywords: interplanetary shocks; solar coronal mass ejections; magnetohydrodynamical simulations; solar coronal mass ejection shocks
Double Trouble: Two Transits of the Super-Earth GJ 1132 b Observed with JWST NIRSpec G395H

The search for rocky planet atmospheres with JWST has focused on planets transiting M dwarfs. Such planets have favorable planet-to-star size ratios, enhancing the amplitude of atmospheric features. Since the expected signal strength of atmospheric features is similar to the single-transit performance of JWST, multiple observations are required to confirm any detection. Here, we present two transit observations of the rocky planet GJ 1132 b with JWST NIRSpec G395H, covering 2.8-5.2 μm. Previous Hubble Space Telescope WFC3 observations of GJ 1132 b were inconclusive, with evidence reported for either an atmosphere or a featureless spectrum based on analyses of the same data set. Our JWST data exhibit substantial differences between the two visits. One transit is consistent with either an H2O-dominated atmosphere containing ~1% CH4 and trace N2O ( ${\chi }_{\nu }^{2}=1.13$ ) or stellar contamination from unocculted starspots ( ${\chi }_{\nu }^{2}=1.36$ ). However, the second transit is consistent with a featureless spectrum. Neither visit is consistent with a previous report of HCN. Atmospheric variability is unlikely to explain the scale of the observed differences between the visits. Similarly, our out-of-transit stellar spectra show no evidence of changing stellar inhomogeneity between the two visits-observed 8 days apart, only 6.5% of the stellar rotation rate. We further find no evidence of differing instrumental systematic effects between visits. The most plausible explanation is an unlucky random noise draw leading to two significantly discrepant transmission spectra. Our results highlight the importance of multivisit repeatability with JWST prior to claiming atmospheric detections for these small, enigmatic planets.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; transmission spectroscopy; astronomy data reduction; planetary atmospheres; stellar atmospheres; starspots; super earths; infrared spectroscopy; extrasolar rocky planets
A Comparison of Star-formation Histories Derived from UniverseMachine and LEGA-C at 0.6 < z < 1

In this work, we compare star formation histories of massive (10.5 $\lt \,\mathrm{log}({M}_{* }/{M}_{\odot })\,\lt $ 12) galaxies in the UniverseMachine model to those measured from the Large Early Galaxy Astrophysics Census (LEGA-C) at 0.6 < z < 1. Following the LEGA-C study, we investigate how 50% (t 50) and 90% (t 90) formation timescales depend on total stellar mass. We find good agreement between the observed and model timescales for the star-forming population Δ t SF ≲ 1 Gyr across the full mass range. In contrast, the observed age-mass correlation is weaker for the quiescent population compared to UniverseMachine models (Δt Q ≲ 2 Gyr), especially at the high-mass end. This indicates continued star formation or additional processes in the most massive quiescent galaxies, a behavior not accounted for in the UniverseMachine model.

Keywords: extragalactic astronomy; theoretical models; surveys; galaxy evolution; astronomy data modeling; astronomy data analysis; galaxy dark matter halos
Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions

The protagonists of the last great phase transition of the universe - cosmic reionization - remain elusive. Faint star-forming galaxies are leading candidates because they are found to be numerous and may have significant ionizing photon escape fractions (fesc). Here we update this picture via an empirical model that successfully predicts latest observations (e.g., the rapid drop in star-formation density (ρSFR at z > 8). We generate an ionizing spectrum for each galaxy in our model and constrain fesc by leveraging latest measurements of the reionization timeline (e.g., Lyα damping of quasars and galaxies at z > 7). Assuming a constant fesc across all sources at z > 6, we find MUV < -13.5 galaxies need fesc = 0.21-0.04+0.06 to complete reionization. The inferred Intergalactic Medium neutral fraction is [0.9, 0.5, 0.1] at z=[8.2,6.8,6.2] ± 0.2 - that is, the bulk of reionization transpires rapidly in 300 Myr, driven by the z > 8 ρSFR and favored by high neutral fractions (∼60%-90%) measured at z ∼ 7-8. Inspired by the emergent sample of Lyman Continuum (LyC) leakers spanning z ∼ 0-6.6 that overwhelmingly displays higher-than-average star-formation surface density (ΣSFR), we propose a physically motivated model relating fesc to ΣSFR and find fesc ∝ ΣSFR0.4±0.1. Since ΣSFR falls by ∼2.5 dex between z = 8 and z = 0, our model explains the humble upper limits on fesc at lower redshifts and its required evolution to fesc ∼ 0.2 at z > 6. Within this model, strikingly, <5% of galaxies with MUV < -18 and log(M⋆/M⊙) > 8 (the "oligarchs") account for ≳80% of the reionization budget - a stark departure from the canonical "democratic" reionization led by copious faint sources. In fact, faint sources (MUV > -16) must be relegated to a limited role in order to ensure high neutral fractions at z = 7-8. Shallow faint-end slopes of the UV luminosity function (αUV > -2) and/or fesc distributions skewed toward massive galaxies produce the required late and rapid reionization. We predict that LyC leakers like COLA1 (z = 6.6, fesc ∼ 30%, MUV = -21.5) will become increasingly common toward z ∼ 6 and that the drivers of reionization do not lie hidden across the faint end of the luminosity function but are already known to us.

Keywords: reionization; early universe; observational cosmology; intergalactic medium; galaxy evolution; extragalactic astronomy; cool intergalactic medium; lyman-alpha galaxies
Supervirial Temperature or Neon Overabundance? Suzaku Observations of the Milky Way Circumgalactic Medium

We analyzed Suzaku and Chandra observations of the soft diffuse X-ray background toward four sight lines with the goal of characterizing the X-ray emission from the Milky Way circumgalactic medium (CGM). We identified two thermal components of the CGM, one at a uniform temperature of kT = 0.176 ± 0.008 keV and the other at temperatures in the range kT = 0.65-0.90 keV. The uniform lower-temperature component is consistent with the Galaxy's virial temperature (∼106 K). The temperatures of the hotter components are similar to that recently discovered (∼107 K) in the sight line to blazar 1ES 1553+113, passing close to the Fermi bubble. Alternatively, the spectra can be described by just one lower-temperature component with supersolar neon abundance, once again similar to that found in the 1ES 1553+113 sight line. The additional hot component or the overabundance of Ne is required at a significance of >4σ, but we cannot distinguish between the two possibilities. These results show that the supervirial temperature gas or an enhanced Ne abundance in the warm-hot gas in the CGM is widespread, and these are not necessarily related to the Fermi bubble.

Keywords: circumgalactic medium
Is It Possible to Measure the Lense-Thirring Orbital Shifts of the Short-period S Star S4716 Orbiting Sgr A*?

The maximal values of the general relativistic Lense-Thirring (LT) orbital shifts ΔI LT, ΔΩLT, and Δω LT of the inclination I, the longitude of the ascending node Ω, and the perinigricon ω, respectively, of the recently discovered star S4716, which has the shortest orbital period $\left({P}_{{\rm{b}}}=4.02\,\mathrm{yr}\right)$ of all the S stars that orbit the supermassive black hole (SMBH) in Sgr A*, are of the order of ≃5-16 arcseconds per revolution $\left({}^{{\prime\prime} }\,{\mathrm{rev}}^{-1}\right)$ . Given the current error σ ω = 0.°02 in determining ω, which is the most accurate orbital parameter of S4716 among all those affected by the SMBH's gravitomagnetic field through its angular momentum J •, about 48 yr would be needed to reduce σ ω to ≃10% of the cumulative LT perinigricon shift over the same time span. Measuring ΔI LT and ΔΩLT to the same level of accuracy would take much longer. Instead, after just 16 yr, a percent measurement of the larger gravitoelectric (GE) Schwarzschild-like perinigricon shift Δω GE, which depends only on the SMBH's mass M •, would be possible. On the other hand, the uncertainties in the physical and orbital parameters entering Δω GE would cause a huge systematic bias of Δω LT itself. The SMBH's quadrupole mass moment ${Q}_{2}^{\bullet }$ induces orbital shifts as little as ≃0.01-0.05″ rev-1.

Keywords: kerr black holes; orbital elements; general relativity
Research on Autofocus Recognition of the LAMOST Fiber View Camera System Under Front and Back Illumination

In the closed-loop detection system of the LAMOST, the lens of the fiber view camera system must focus the end of the optical fiber to accurately acquire the fiber position. It is difficult to evaluate the fibers image with a very small proportion of the image with the traditional autofocus algorithm, whether it is recognition of the front illuminated by the fiber ceramic ferrules, or the light-emitting spot of the fibers in the black background, that is, the recognition of the back illumination of the fibers. In this paper, we propose an autofocus determination method for the LAMOST closed-loop control under front and back illumination conditions. Under the condition of front illumination, to greatly reduce the calculation time, the system first pre-recognizes the focusing target through the Faster R-CNN and then uses an optimized contrast algorithm to evaluate the image definition of the corrected focusing target ROI. Then, the algorithm is compared with Tenengrad gradient and Laplacian gradient calculations using the Sobel operator and Laplacian operator in OpenCV. The results show that this method takes only one-ninth of the time required by the other methods to obtain the same accuracy. Under the condition of back illumination, we use the average number and average brightness of spot pixels as the evaluation basis of image sharpness. This method can complete the evaluation of image sharpness in the process of spot recognition and provide initial data for the subsequent detection for closed-loop control. The focus accuracy of the camera is of great significance for thousand-fiber metrology, which will have an important influence on the accuracy of astronomical observations. These focusing methods not only play an important role in the closed-loop control of the LAMOST but also apply to the focusing of closed-loop detection systems of other multi-target optical fiber spectral astronomical telescopes.

Keywords: astronomical instrumentation; astronomical techniques
Plasmoid-fed Prominence Formation (PF2) During Flux Rope Eruption

We report a new, plasmoid-fed scenario for the formation of an eruptive prominence (PF2), involving reconnection and condensation. We use grid-adaptive resistive two-and-a-half-dimensional magnetohydrodynamic simulations in a chromosphere-to-corona setup to resolve this plasmoid-fed scenario. We study a preexisting flux rope (FR) in the low corona that suddenly erupts due to catastrophe, which also drives a fast shock above the erupting FR. A current sheet (CS) forms underneath the erupting FR, with chromospheric matter squeezed into it. The plasmoid instability occurs and multiple magnetic islands appear in the CS once the Lundquist number reaches ~3.5 × 104. The remnant chromospheric matter in the CS is then transferred to the FR by these newly formed magnetic islands. The dense and cool mass transported by the islands accumulates in the bottom of the FR, thereby forming a prominence during the eruption phase. More coronal plasma continuously condenses into the prominence due to the thermal instability as the FR rises. Due to the fine structure brought in by the PF2 process, the model naturally forms filament threads, aligned above the polarity inversion line. Synthetic views at our resolution of 15 km show many details that may be verified in future high-resolution observations.

Keywords: solar prominences; solar flares; solar magnetic reconnection; magnetohydrodynamics; solar coronal mass ejections