adsabs/SciX_UAT_keywords huggingface dataset:
Optical Photometric Indicators of Galaxy Cluster Relaxation

The most dynamically relaxed clusters of galaxies play a special role in cosmological studies as well as astrophysical studies of the intracluster medium (ICM) and active galactic nucleus feedback. While high-spatial-resolution imaging of the morphology of the ICM has long been the gold standard for establishing a cluster's dynamical state, such data are not available from current or planned surveys, and thus require separate, pointed follow-up observations. With optical and/or near-IR photometric imaging, and red-sequence cluster finding results from those data, expected to be ubiquitously available for clusters discovered in upcoming optical and millimeter-wavelength surveys, it is worth asking how effectively photometric data alone can identify relaxed cluster candidates, before investing in, e.g., high-resolution X-ray observations. Here we assess the ability of several simple photometric measurements, based on the redMaPPer cluster finder run on Sloan Digital Sky Survey data, to reproduce X-ray classifications of dynamical state for an X-ray selected sample of massive clusters. We find that two simple metrics contrasting the bright central galaxy (BCG) to other cluster members can identify a complete sample of relaxed clusters with a purity of ∼40% in our data set. Including minimal ICM information in the form of a center position increases the purity to ∼60%. However, all three metrics depend critically on correctly identifying the BCG, which is presently a challenge for optical red-sequence cluster finders.

Keywords: galaxy clusters
Electron Acceleration Rate at Dipolarization Fronts

Although it has been shown that betatron and Fermi mechanisms contribute to electron acceleration at the dipolarization front (DF), the relative efficiency of these acceleration processes is unclear. In this paper, we directly calculate the electron adiabatic acceleration rate (the instantaneous acceleration) at DFs by using the data from the Magnetospheric Multiscale mission. We find that betatron acceleration dominates at the DF. Although the Fermi acceleration rate is smaller than the betatron acceleration rate, it is effective on a larger spatial scale than betatron acceleration, which is localized at the DF proper. The acceleration by the parallel electric field is negligible because it is far below the measurement uncertainties. The dependence of these acceleration rates on the DF normal, magnetic field, and thickness of the DF are analyzed. Our results provide important information for understanding the electron acceleration in the Earth's magnetotail.

Keywords: space plasmas
First Ultraviolet Outburst Detected from ASASSN-18eh Strengthens Its Interpretation as a Cataclysmic Variable

As part of the Transient UV Objects project, we have discovered a new outburst (at the beginning of 2020 October) of the candidate cataclysmic variable (CV) ASASSN-18eh using the UV/Optical Telescope aboard the Neil Gehrels Swift Observatory. During the outburst its brightness increased by about 6 mag in UV compared to its brightness in the quiescent state. The properties of this outburst are consistent with it being a dwarf nova, strongly supporting the CV nature of ASASSN-18eh.

Keywords: dwarf novae; cataclysmic variable stars; white dwarf stars; ultraviolet transient sources; ultraviolet photometry
The Greenland Telescope-Construction, Commissioning, and Operations in Pituffik

In 2018, the Greenland Telescope (GLT) started scientific observation in Greenland. Since then, we have completed several significant improvements and added new capabilities to the telescope system. This paper presents a full review of the GLT system, a summary of our observation activities since 2018, the lessons learned from the operations in the Arctic regions, and the prospect of the telescope.

Keywords: radio telescopes; submillimeter astronomy; astronomical instrumentation
QPOs in Compact Sources as a Nonlinear Hydrodynamical Resonance: Determining Spin of Compact Objects

The origin of wide varieties of quasiperiodic oscillations (QPOs) observed in compact sources is still not well established. Its frequencies range from millihertz to kilohertz spanning all compact objects. Are different QPOs, with different frequencies, originating from different physics? We propose that the emergence of QPOs is the result of nonlinear resonance of fundamental modes present in accretion disks forced by external modes including that of the spin of the underlying compact object. Depending on the properties of accreting flow, e.g., its velocity and gradient, resonances (and any mode-locking) take place at different frequencies, exhibiting low- to high-frequency QPOs. We explicitly demonstrate the origin of higher-frequency QPOs for black holes and neutron stars by a unified model and outline how the same physics could be responsible for producing lower-frequency QPOs. The model also predicts the spin of black holes, and constrains the radius of neutron stars and the mass of both.

Keywords: black hole physics; neutron stars; accretion; gravitation; hydrodynamics; stellar oscillations
Structure of Quark Star: A Comparative Analysis of Bayesian Inference and Neural Network Based Modeling

In this work, we compare two powerful parameter estimation methods, namely Bayesian inference and neural network based learning, to study the quark matter equation of state with constant speed of sound parameterization and the structure of the quark stars within the two-family scenario. We use the mass and radius estimations from several X-ray sources and also the mass and tidal deformability measurements from gravitational wave events to constrain the parameters of our model. The results found from the two methods are consistent. The predicted speed of sound is compatible with the conformal limit.

Keywords: nuclear astrophysics; neutron stars; bayesian statistics; neural networks
Discovery of Seven Volcanic Outbursts on Io from an Infrared Telescope Facility Observation Campaign, 2016-2022

This study analyzes near-infrared measurements of Io, Jupiter's moon, observed over 170 nights from 2016 to early 2022 using the NASA Infrared Telescope Facility (IRTF). During this period, seven new volcanic outbursts-the most energetic volcanic events on Io-were discovered and characterized, increasing the total number of observed outburst events from 18 to 25. We also present simplified criteria for the thermal detection of an outburst, requiring it to be both confined to a specific location of Io and above a threshold intensity in the Lp band (3.8 μm).

Keywords: volcanoes; lithosphere; infrared astronomical satellite; infrared observatories; infrared dark clouds; io
Confirmation of Iron Emission Lines and Nondetection of TiO on the Dayside of KELT-9b with MAROON-X

We present dayside thermal emission observations of the hottest exoplanet KELT-9b using the new MAROON-X spectrograph. We detect atomic lines in emission with a signal-to-noise ratio of 10 using cross-correlation with binary masks. The detection of emission lines confirms the presence of a thermal inversion in KELT-9b's atmosphere. We also use M-dwarf stellar masks to search for TiO, which has recently been invoked to explain the unusual Hubble Space Telescope WFC3 spectrum of the planet. We find that the KELT-9b atmosphere is inconsistent with the M-dwarf masks. Furthermore, we use an atmospheric retrieval approach to place an upper limit on the TiO volume mixing ratio of 10-8.5 (at 99% confidence). This upper limit is inconsistent with the models used to match the WFC3 data, which require at least an order of magnitude more TiO, thus suggesting the need for an alternate explanation of the space-based data. Our retrieval results also strongly prefer an inverted temperature profile and atomic/ion abundances largely consistent with the expectations for a solar composition gas in thermochemical equilibrium. The exception is the retrieved abundance of Fe+, which is about 1-2 orders of magnitude greater than predictions. These results highlight the growing power of high-resolution spectrographs on large ground-based telescopes to characterize exoplanet atmospheres when used in combination with new retrieval techniques.

Keywords: hot jupiters; exoplanet atmospheres
Dynamic Property and Magnetic Nonpotentiality of Two Types of Confined Solar Flares

We analyze 152 large confined flares (GOES class ≥ M1.0 and ≤ 45° from disk center) during 2010-2019, and classify them into two types according to the criterion taken from the work of Li et al. "Type I" flares are characterized by slipping motions of flare loops and ribbons and a stable filament underlying the flare loops. "Type II" flares are associated with the failed eruptions of the filaments, which can be explained by the classical 2D flare model. A total of 59 flares are "Type I" flares (about 40%) and 93 events are "Type II" flares (about 60%). There are significant differences in distributions of the total unsigned magnetic flux (ΦAR) of active regions (ARs) producing the two types of confined flares, with "Type I" confined flares from ARs with a larger ΦAR than "Type II." We calculate the mean shear angle ΨHFED within the core of an AR prior to the flare onset, and find that it is slightly smaller for "Type I" flares than that for "Type II" events. The relative nonpotentiality parameter ΨHFED/ΦAR has the best performance in distinguishing the two types of flares. About 73% of "Type I" confined flares have ΨHFED/ΦAR<1.0 × 10-21 degree Mx-1, and about 66% of "Type II" confined events have ΨHFED/ΦAR ≥ 1.0 × 10-21 degree Mx-1. We suggest that "Type I" confined flares cannot be explained by the standard flare model in 2D/3D, and the occurrence of multiple slipping magnetic reconnections within the complex magnetic systems probably leads to the observed flare.

Keywords: solar activity; solar active region magnetic fields; solar flares; solar filaments; solar coronal mass ejections
Eating Planets for Lunch and Dinner: Signatures of Planet Consumption by Evolving Stars

Exoplanets have been observed around stars at all stages of stellar evolution, in many cases orbiting in configurations that will eventually lead to the planets being engulfed or consumed by their host stars, such as hot Jupiters or ultrashort period planets. Furthermore, objects such as polluted white dwarfs provide strong evidence that the consumption of planets by stars is a common phenomenon. This consumption causes several significant changes in the stellar properties, such as changes to the stellar spin, luminosity, chemical composition, or mass-loss processes. Here, we explore this wide variety of effects for a comprehensive range of stellar and planetary masses and stages of stellar evolution, from the main sequence over red giants to white dwarfs. We determine that planet consumption can cause transient luminosity features that last on the order of centuries to millennia, and that the post-consumption stellar spins can often reach breakup speeds. Furthermore, stellar mass loss can be caused by this spin-up, as well as through surface grazing interactions, leading to to the formation of unusual planetary nebula shapes or collimated stellar gas ejections. Our results highlight several observable stellar features by which the presence or previous existence of a planet around a given star can be deduced. This will provide future observational campaigns with the tools to better constrain exoplanet demographics, as well as planetary formation and evolution histories.

Keywords: stellar evolution; stellar rotation; tidal interaction
Stellar Kinematics and Environment at z ∼ 0.8 in the LEGA-C Survey: Massive Slow Rotators Are Built First in Overdense Environments

In this Letter, we investigate the impact of environment on integrated and spatially resolved stellar kinematics of a sample of massive, quiescent galaxies at intermediate redshift (0.6 < z < 1.0). For this analysis, we combine photometric and spectroscopic parameters from the UltraVISTA and Large Early Galaxy Astrophysics Census surveys in the COSMOS field and environmental measurements. We analyze the trends with overdensity (1+δ) on the rotational support of quiescent galaxies and find no universal trends at either fixed mass or fixed stellar velocity dispersion. This is consistent with previous studies of the local universe; rotational support of massive galaxies depends primarily on stellar mass. We highlight two populations of massive galaxies ( $\mathrm{log}\,{M}_{\star }/{M}_{\odot }\geqslant 11$ ) that deviate from the average mass relation. First, the most massive galaxies in the most underdense regions ((1 + δ) ≤ 1) exhibit elevated rotational support. Similarly, at the highest masses ( $\mathrm{log}\,{M}_{\star }/{M}_{\odot }\geqslant 11.25$ ) the range in rotational support is significant in all but the densest regions. This corresponds to an increasing slow-rotator fraction such that only galaxies in the densest environments ((1 + δ) ≥ 3.5) are primarily (90% ± 10%) slow rotators. This effect is not seen at fixed velocity dispersion, suggesting minor merging as the driving mechanism: only in the densest regions have the most massive galaxies experienced significant minor merging, building stellar mass and diminishing rotation without significantly affecting the central stellar velocity dispersion. In the local universe, most massive galaxies are slow rotators, regardless of environment, suggesting minor merging occurs at later cosmic times (z ≲ 0.6) in all but the most dense environments.

Keywords: galaxy evolution; galaxy formation; quenched galaxies; galaxies
Accretion-induced Black Hole Spin-up Revised by Numerical General Relativistic MHD

We investigate the accretion-induced spin-up of the black hole via numerical simulations. Our method is based on general relativistic magnetohydrodynamics of the slowly rotating flows in the Kerr metric, where possibly transonic shock fronts may form. We account for the changing black hole mass and spin during accretion that enforces dynamical evolution of the spacetime metric. We first study nonmagnetized flows with shocks, and we also include magnetic field endowed in the gas. The aim of this study is to verify whether the high-mass black holes may be produced with large spins, even though at birth the collapsars might have contained slowly or moderately spinning cores. In this way, we put constraints on the content of angular momentum in the collapsing massive stars. Our studies are also showing that shock fronts and magnetic fields may halt accretion and limit the black hole spin-up in the exploding supernovae.

Keywords: bondi accretion; black hole physics; magnetohydrodynamics
Very Large Telescope MUSE Observations of the Bubble Nebula around NGC 1313 X-2 and Evidence for Additional Photoionization

The bubble nebula surrounding NGC 1313 X-2 is believed to be powered by high velocity winds from the central ultraluminous X-ray source (ULX) as a result of supercritical accretion. With the Multi-Unit Spectroscopic Explorer (MUSE) observation of the nebula, we find enhanced [O III] emission at locations spatially coincident with clusters of stars and the central X-ray source, suggesting that photoionization in addition to shock ionization plays an important role in powering the nebula. The X-ray luminosity of the ULX and the number of massive stars in the nebula region can account for the required ionizing luminosity derived with MAPPINGS V, which also confirms that pure shocks cannot explain the observed emission line ratios.

Keywords: ultraluminous x-ray sources; emission nebulae; superbubbles; accretion
The Molecular Gas in the NGC 6240 Merging Galaxy System at the Highest Spatial Resolution

We present the highest-resolution—15 pc (0"03)—ALMA 12CO(2-1) line emission and 1.3 mm continuum maps, tracers of the molecular gas and dust, respectively, in the nearby merging galaxy system NGC 6240, which hosts two supermassive black holes growing simultaneously. These observations provide an excellent spatial match to existing Hubble Space Telescope (HST) optical and near-infrared observations of this system. A significant molecular gas mass, ∼9 × 109 M⊙, is located between the two nuclei, forming a clumpy stream kinematically dominated by turbulence, rather than a smooth rotating disk, as previously assumed from lower-resolution data. Evidence for rotation is seen in the gas surrounding the southern nucleus but not in the northern one. Dynamical shells can be seen, likely associated with nuclear supernova remnants. We further detect the presence of significant high-velocity outflows, some of them reaching velocities >500 km s-1, affecting a significant fraction, ∼11%, of the molecular gas in the nuclear region. Inside the spheres of influence of the northern and southern supermassive black holes, we find molecular masses of 7.4 × 108 and 3.3 × 109 M⊙, respectively. We are thus directly imaging the reservoir of gas that can accrete onto each supermassive black hole. These new ALMA maps highlight the critical need for high-resolution observations of molecular gas in order to understand the feeding of supermassive black holes and its connection to galaxy evolution in the context of a major galaxy merger.

Keywords: galaxy mergers; galaxy interactions; active galaxies; agn host galaxies; active galactic nuclei; molecular gas
Most Planets Might Have More than 5 Myr of Time to Form

The lifetime of protoplanetary disks is a crucial parameter for planet formation research. Observations of disk fractions in star clusters imply median disk lifetimes of 1-3 Myr. This very short disk lifetime calls for planet formation to occur extremely rapidly. We show that young, distant clusters (≤5 Myr, >200 pc) often dominate these types of studies. Such clusters frequently suffer from limiting magnitudes leading to an over-representation of high-mass stars. As high-mass stars disperse their disks earlier, the derived disk lifetimes apply best to high-mass stars rather than low-mass stars. Including only nearby clusters (<200 pc) minimizes the effect of limiting magnitude. In this case, the median disk lifetime of low-mass stars is with 5-10 Myr, thus much longer than often claimed. The longer timescales provide planets ample time to form. How high-mass stars form planets so much faster than low-mass stars is the next grand challenge.

Keywords: planet formation; young star clusters; protoplanetary disks; exoplanets
Identification of the Nature of Electromagnetic Waves near the Proton-cyclotron Frequency in Solar-terrestrial Plasmas

Low-frequency (quasi-)monochromatic electromagnetic waves near the ion-cyclotron frequency always exhibit both left-hand (LH) and right-hand (RH) polarization in solar-terrestrial spacecraft observations. However, due to the Doppler frequency shift resulting from the bulk flow of charged particles, the nature of these waves in the plasma frame is still unclear. This paper proposes a useful method to directly identify the nature of the observed waves. Using three wave parameters including polarization, direction of the parallel Poynting flux, and correlation between perpendicular magnetic field and perpendicular ion/electron velocity, we could discriminate the wave mode (Alfvén/ion-cyclotron wave or fast-magnetosonic/whistler wave) and its propagation direction (along or against the magnetic field) in the plasma frame. Using Magnetospheric Multiscale spacecraft measurements, we analyze two wave events containing both LH- and RH-polarized low-frequency electromagnetic waves in the Earth's magnetosheath, and find that these waves correspond to counter-propagating Alfvén/ion-cyclotron waves in the plasma frame. Our method is helpful for studying low-frequency electromagnetic waves detected by satellites that have particle measurements with an adequate temporal resolution.

Keywords: planetary magnetospheres; solar wind; space plasmas; plasma physics
Grain Alignment and Rotational Disruption by Radiative Torques in Exoplanet Atmospheres

Dust clouds are ubiquitous in the atmospheres of hot Jupiters and affect their observable properties. The alignment of dust grains in the clouds and resulting dust polarization provide a promising way to study the magnetic fields of exoplanets. Moreover, the grain size distribution plays an important role in the physical and chemical processes in the atmospheres, which are rather uncertain. In this paper, we first study the grain alignment of dust grains in the atmospheres of hot Jupiters by radiative torques (RATs). We find that silicate grains can be aligned by RATs with the magnetic fields (B - RAT) due to the strong magnetic fields of hot Jupiters, but carbonaceous grains of diamagnetic material tend to be aligned with the radiation direction (k - RAT). At a low altitude of r < 2R p, where R p is the planet radius, only large grains can be aligned, but tiny grains of a ~ 0.01 μm can be aligned at a high altitude of r > 3R p. We then study the rotational disruption of dust grains by the RAT disruption (RAT-D) mechanism. We find that large grains can be disrupted by RAT-D into smaller sizes. Grains of high tensile strength are disrupted at an altitude of r > 3R p, but grains of low tensile strength can be disrupted at a lower altitude. We suggest that the disruption of large grains into smaller ones can facilitate dust clouds escaping to high altitudes due to lower gravity and may explain the presence of high-altitude clouds in hot Jupiters, as well as superpuff atmospheres.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; interplanetary dust; interplanetary magnetic fields
Blueshifted Fe II and Balmer Broad Emission lines in a Reddened Quasar

We present detailed analysis of the optical and near-infrared spectrum of the reddened radio-loud quasar F2M J154043.74+492323.9 with strong optical Fe II emission of ${R}_{4570}\equiv \tfrac{\mathrm{Fe}\,{\rm\small{II}}\lambda \lambda \,4434,4684}{{\rm{H}}\beta }=1.60\pm 0.14$ . It is found that the peaks of broad emission lines (BELs), including Hα, Hβ, and Hγ, and the peaks of individual Fe II BELs, are blueshifted as large as v ≈ 1500 km s-1 with respect to the systemic redshift determined by the low-ionization [O II] narrow emission line. BEL components at the systemic redshift are also significantly detected, though much weaker than the corresponding blueshifted components. Interestingly, the Mg II BEL also shows a similar double-peaked profile, yet with a weaker blueshifted component relative to the unshifted one. We interpret these exceptional BELs as originating from massive outflows, possibly with both densities and column densities much higher than those of the normal BEL region (BELR). Alternative scenarios, however, cannot be completely ruled out based on the data available, including a gravitationally bound binary of active supermassive black holes (SMBHs), each with an unattached BELR, or a recoiling SMBH caused by anisotropic gravitational radiation during the coalescence of the progenitor binary. Follow-up observations will be able to disentangle these scenarios, and to also provide valuable clues to understand the growth of SMBHs and the assembly of their host galaxies.

Keywords: active galaxies; radio loud quasars; double quasars; emission line galaxies