adsabs/SciX_UAT_keywords huggingface dataset:
Thermally Unstable Cooling Stimulated by Uplift: The Spoiler Clusters

Chandra X-ray observations are analyzed for five galaxy clusters whose atmospheric cooling times, entropy parameters, and ratios of cooling time to freefall time within the central galaxies lie below 1 Gyr, below 30 keV cm2, and between 20 ≲ min(tcool/tff) ≲ 50, respectively. These thermodynamic properties are commonly associated with molecular clouds, bright Hα emission, and star formation in central galaxies. However, all have Hα luminosities below 1040 erg s-1 in the ACCEPT database. Star formation and molecular gas are absent at the levels seen in other central galaxies with similar atmospheric properties. Only RBS 0533 may host a radio/X-ray bubble, which are commonly observed in cooling atmospheres. Signatures of uplifted, high-metallicity atmospheric gas are absent. Their atmospheres are apparently thermodynamically stable despite the absence of strong nuclear feedback. We suggest that extended filaments of nebular emission and associate molecular clouds are absent at appreciable levels because their central radio sources have failed to lift low-entropy atmospheric gas to an altitude where the ratio of the cooling time to the freefall time falls below unity and the gas becomes thermally unstable.

Keywords: brightest cluster galaxies; intracluster medium; x-ray astronomy; active galactic nuclei; galaxy clusters
Successive Coronal Mass Ejections Associated with Weak Solar Energetic Particle Events

The scenario of twin coronal mass ejections (CMEs), i.e., a fast and wide primary CME (priCME) preceded by preceding CMEs (preCMEs), has been found to be favorable to a more efficient particle acceleration in large solar energetic particle (SEP) events. Here we study 19 events during 2007-2014 associated with twin-CME eruptions but without large SEP observations at the L1 point. We combine remote-sensing and in situ observations from multiple spacecraft to investigate the role of magnetic connectivity in SEP detection and the CME information in three-dimensional (3D) space. We study one-on-one correlations of the priCME 3D speed, flare intensity, suprathermal backgrounds, and height of CME-CME interaction with the SEP intensity. Among these, the priCME speed is found to correlate with the SEP peak intensity at the highest level. We use the projection correlation method to analyze the correlations between combinations of these multiple independent factors and the SEP peak intensity. We find that the only combination of two or more parameters that has a higher correlation with the SEP peak intensity than the CME speed is the CME speed combined with the propagation direction. This further supports the dominant role of the priCME in controlling the SEP enhancements and emphasizes the consideration of the latitudinal effect. Overall, the magnetic connectivity in longitude as well as latitude and the relatively lower priCME speed may explain the existence of the twin-CME SEP-poor events. The role of the barrier effect of preCME(s) is discussed for an event on 2013 October 28.

Keywords: solar energetic particles; solar coronal mass ejections
A Coupled Guiding Center-Boris Particle Pusher for Magnetized Plasmas in Compact-object Magnetospheres

We present a novel numerical scheme for simulating the motion of relativistic charged particles in magnetospheres of compact objects, typically filled with highly magnetized collisionless plasmas. The new algorithm is based on a dynamic switch between the full system of equations of motion and a guiding-center approximation. The switch between the two formulations is based on the magnetization of the plasma particles, such that the dynamics are accurately captured by the guiding-center motion even when the gyrofrequency is underresolved by the time step. For particles with a large gyroradius, due to acceleration in, e.g., reconnecting current sheets, the algorithm adaptively switches to solve the full equations of motion instead. The new scheme is directly compatible with standard particle-in-cell codes, and is readily applicable in curved spacetimes via a dedicated covariant formulation. We test the performance of the coupled algorithm by evolving charged particles in electromagnetic configurations of reconnecting current sheets in magnetized plasma, obtained from special- and general-relativistic particle-in-cell simulations. The new coupled pusher is capable of producing highly accurate particle trajectories even when the time step is many orders of magnitude larger than the gyroperiod, substantially reducing the restrictions of the temporal resolution.

Keywords: compact objects; neutron stars; space plasmas; plasma physics
Broadband Linear Polarization in the Region of the Open Star Cluster NGC 1817

Multiband linear polarimetric observations of 125 stars in the region of the cluster NGC 1817 have been carried out intending to study properties of interstellar dust and grains in that direction. The polarization is found to be wavelength-dependent, being maximum in the V band with an average value of 0.95%. The foreground interstellar dust grains appear to be the main source of linear polarization of starlight toward the direction of NGC 1817. The average value of the position angle in the V band of 119°2 is found to be less than the direction of the Galactic parallel in the region, indicating that the dust grains in the direction are probably not yet relaxed. Spatial distribution of dust appears to be more diverse in the coronal region than the core region of the cluster. The maximum value of the degree of polarization is estimated to be 0.93% for members of the cluster using the Serkowski relation. The average value of wavelength corresponding to the maximum polarization of 0.54 ± 0.02 μm indicates that the size distribution of dust grains in the line of sight is similar to that of the general interstellar medium. Several variable stars in the cluster were also observed polarimetrically and pulsating variables appear to have a slightly lower value of polarization from other nonvariable member stars of the cluster. There are indications of the existence of dust layers in front of those clusters which are located close to galactic plane while for clusters located away from galactic plane no major dust layers are observed.

Keywords: starlight polarization; polarimeters; open star clusters; interstellar dust; interstellar dust extinction; interstellar medium
Exploring the Lower Mass Gap and Unequal Mass Regime in Compact Binary Evolution

On 2019 August 14, the LIGO and Virgo detectors observed GW190814, a gravitational-wave signal originating from the merger of a $\simeq \,23\,{M}_{\odot }$ black hole (BH) with a $\simeq \,2.6\,{M}_{\odot }$ compact object. GW190814's compact-binary source is atypical both in its highly asymmetric masses and in its lower-mass component lying between the heaviest known neutron star (NS) and lightest known BH in a compact-object binary. If formed through isolated binary evolution, the mass of the secondary is indicative of its mass at birth. We examine the formation of such systems through isolated binary evolution across a suite of assumptions encapsulating many physical uncertainties in massive-star binary evolution. We update how mass loss is implemented for the neutronization process during the collapse of the proto-compact object to eliminate artificial gaps in the mass spectrum at the transition between NSs and BHs. We find it challenging for population modeling to match the empirical rate of GW190814-like systems while simultaneously being consistent with the rates of other compact binary populations inferred from gravitational-wave observations. Nonetheless, the formation of GW190814-like systems at any measurable rate requires a supernova engine model that acts on longer timescales such that the proto-compact object can undergo substantial accretion immediately prior to explosion, hinting that if GW190814 is the result of massive-star binary evolution, the mass gap between NSs and BHs may be narrower or nonexistent.

Keywords: gravitational waves; gravitational wave sources; neutron stars; stellar mass black holes; astrophysical black holes; supernovae; core-collapse supernovae; stellar evolutionary models
Photospheric and Chromospheric Magnetic Field Evolution during the X1.6 Flare in Active Region NOAA 12192

We report on observations acquired by the Interferometric Bidimensional Spectropolarimeter (IBIS) during SOL2014-10-22T14:02, an X1.6 flare that occurred in active region NOAA 12192, taken in the Fe I 617.30 nm and Ca II 854.2 nm line profiles. We analyze polarization signatures in the Stokes profiles of the two lines across one of the flare ribbons. Focusing our attention on the chromospheric signals and using the weak-field approximation (WFA), we study the temporal variation of the line-of-sight (LOS) magnetic field. We find variations of the magnetic field or the opacity along the flare ribbon, in most cases within the first 3 minutes of the observation just after the flare peak, during the tail of the flare impulsive phase. This result was validated by the STiC inversion of the pixels used for the WFA analysis. The analysis of the photospheric magnetic field shows that in this layer, the LOS magnetic field does not show the same changes observed in the chromosphere in the selected pixels, nor clear evidence of changes along the polarity inversion line around a magnetic polarity intrusion. In this respect, we also find that the temporal observing window is not suitable for assessing the presence of stepwise changes. The nonlinear force-free field extrapolations, together with the analysis of the ribbons' isophotes obtained from Interface Region Imaging Spectrograph data, suggest that the region corresponding to the magnetic intrusion observed by IBIS is characterized by a complex magnetic connectivity and is almost cospatial with the area affected by the initial energy release.

Keywords: active solar chromosphere; spectropolarimetry; solar flares; high angular resolution; solar magnetic fields
A Sudden Period of High Activity from Repeating Fast Radio Burst 20201124A

The repeating FRB 20201124A was first discovered by CHIME/FRB in November of 2020, after which it was seen to repeat a few times over several months. It entered a period of high activity in April of 2021, at which time several observatories recorded tens to hundreds more bursts from the source. These follow-up observations enabled precise localization and host-galaxy identification. In this paper, we report on the CHIME/FRB-detected bursts from FRB 20201124A, including their best-fit morphologies, fluences, and arrival times. The large exposure time of the CHIME/FRB telescope toward the location of this source allows us to constrain its rates of activity. We analyze the repetition rates over different spans of time, constraining the rate prior to discovery to <3.4 day-1 (at 3σ), and demonstrate a significant change in the event rate following initial detection. Lastly, we perform a maximum-likelihood estimation of a power-law luminosity function, finding a best-fit index α = -4.6 ± 1.3 ± 0.6, with a break at a fluence threshold of ${F}_{\min }\sim 16.6$ Jy ms, consistent with the fluence completeness limit of the observations. This index is consistent within uncertainties with those of other repeating FRBs for which it has been determined.

Keywords: radio bursts; radio transient sources
Modeling Binary Asteroids: Integrating Orbital and Rotational Motion for Physical Property Inversion

The field of space science places significant emphasis on deep space exploration, with a particular focus on asteroids as a potential hazard to humanity. Inverting their physical characteristics from photometric observations is essential for uncovering their origins and evolution. This article attempts to present a solution to the challenging task of estimating the physical properties of binary asteroids, which are common in near-Earth asteroids larger than 200 meters. A novel model for binary asteroids is proposed, which integrates orbital and rotational motions to simulate brightness variations based on two Cellinoid shapes. The model combines the projection and occultation effects of the shapes to generate the simulated brightness. The inversion of determining physical properties is optimized based on the Levenberg-Marquardt algorithm through a simulation process involving several parameter corrections. Finally, the performance of the proposed model is demonstrated through numerical experiments and applications to two real binary asteroids, namely, asteroid (317) Roxane and asteroid (624) Hektor. The derived results are nearly identical to those from other publications, which confirms that the proposed model provides reliable and accurate estimations of the physical properties of binary asteroids. Additionally, this method has a potential application in supporting the development of effective strategies for the Double Asteroid Redirection Test (DART) project, the first planetary defense experiment in space undertaken by humans.

Keywords: solar system; asteroids
ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP). II. Survey Overview: A First Look at 1.3 mm Continuum Maps and Molecular Outflows

Planck Galactic Cold Clumps (PGCCs) are considered to be the ideal targets to probe the early phases of star formation. We have conducted a survey of 72 young dense cores inside PGCCs in the Orion complex with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm (band 6) using three different configurations (resolutions ∼0"35, 1"0, and 7"0) to statistically investigate their evolutionary stages and substructures. We have obtained images of the 1.3 mm continuum and molecular line emission (12CO, and SiO) at an angular resolution of ∼0"35 (∼140 au) with the combined arrays. We find 70 substructures within 48 detected dense cores with median dust mass ∼0.093 M⊙ and deconvolved size ∼0"27. Dense substructures are clearly detected within the central 1000 au of four candidate prestellar cores. The sizes and masses of the substructures in continuum emission are found to be significantly reduced with protostellar evolution from Class 0 to Class I. We also study the evolutionary change in the outflow characteristics through the course of protostellar mass accretion. A total of 37 sources exhibit CO outflows, and 20 (>50%) show high-velocity jets in SiO. The CO velocity extents (ΔVs) span from 4 to 110 km s-1 with outflow cavity opening angle width at 400 au ranging from [Θobs]400 ∼ 0"6-3"9, which corresponds to 33°4-125°7. For the majority of the outflow sources, the ΔVs show a positive correlation with [Θobs]400, suggesting that as protostars undergo gravitational collapse, the cavity opening of a protostellar outflow widens and the protostars possibly generate more energetic outflows.

Keywords: star formation; star forming regions; early stellar evolution; protostars; low mass stars; stellar jets; stellar winds; astrochemistry; stellar abundances; spectral energy distribution; dense interstellar clouds; interstellar medium
Cosmological Vlasov-Poisson Simulations of Structure Formation with Relic Neutrinos: Nonlinear Clustering and the Neutrino Mass

We present the results of cosmological simulations of large-scale structure formation with massive neutrinos. The phase-space distribution of the cosmic relic neutrinos is followed, for the first time, by directly integrating the six-dimensional Vlasov-Poisson equations. Our novel approach allows us to represent free streaming and clustering of neutrinos, and their gravitational interaction with cold dark matter accurately. We thus obtain solutions for the collisionless dynamics independent of conventional N-body methods. We perform a suite of hybrid N-body/Vlasov simulations with varying the neutrino mass, and systematically examine the dynamical effects of massive neutrinos on large-scale structure formation. Our simulations show characteristic large-scale clustering of the neutrinos and their coherent streaming motions relative to dark matter. The effective local neutrino "temperature" around massive galaxy clusters varies by several percent with respect to the cosmic mean; the neutrinos in clusters can be hotter or colder depending on the neutrino mass. We study a number of statistics of the large-scale structure and of dark matter halos in comparison with those obtained by N-body simulations and/or by perturbation theory. Our simulations mark an important milestone in numerical cosmology, and pave a new way to study cosmic structure formation with massive neutrinos.

Keywords: cosmological neutrinos; neutrino masses; cosmological parameters from large-scale structure; large-scale structure of the universe
First In Situ Measurements of Electron Density and Temperature from Quasi-thermal Noise Spectroscopy with Parker Solar Probe/FIELDS

Heat transport in the solar corona and wind is still a major unsolved astrophysical problem. Because of the key role played by electrons, the electron density and temperature(s) are important prerequisites for understanding these plasmas. We present such in situ measurements along the two first solar encounters of the Parker Solar Probe, between 0.5 and 0.17 au from the Sun, revealing different states of the emerging solar wind near the solar activity minimum. These preliminary results are obtained from a simplified analysis of the plasma quasi-thermal noise (QTN) spectrum measured by the Radio Frequency Spectrometer (FIELDS). The local electron density is deduced from the tracking of the plasma line, which enables accurate measurements, independent of calibrations and spacecraft perturbations, whereas the temperatures of the thermal and suprathermal components of the velocity distribution, as well as the average kinetic temperature, are deduced from the shape of the plasma line. The temperature of the weakly collisional thermal population, similar for both encounters, decreases with the distance as R -0.74, which is much slower than adiabatic. In contrast, the temperature of the nearly collisionless suprathermal population exhibits a virtually flat radial variation. The 7 s resolution of the density measurements enables us to deduce the low-frequency spectrum of compressive fluctuations around perihelion, varying as f -1.4. This is the first time that QTN spectroscopy is implemented with an electric antenna length not exceeding the plasma Debye length. As PSP will approach the Sun, the decrease in the Debye length is expected to considerably improve the accuracy of the temperature measurements.

Keywords: solar wind; space probes; plasma astrophysics; space plasmas; radio spectroscopy; space vehicle instruments
Searching for Molecular Outflows with Support Vector Machines: The Dark Cloud Complex in Cygnus

We present a survey of molecular outflows across the dark cloud complex in the Cygnus region, based on a 46.75 deg2 field of CO isotopologue data from the Milky Way Imaging Scroll Painting survey. A supervised machine-learning algorithm, the support vector machine, is introduced to accelerate our visual assessment of outflow features in the data cube of 12CO and 13CO J = 1-0 emission. A total of 130 outflow candidates are identified, 77 of which show bipolar structures and 118 are new detections. Spatially, these outflows are located inside dense molecular clouds, and some of them are found in clusters or in elongated linear structures tracing the underlying gas filament morphology. Along the line of sight, 97, 31, and 2 candidates reside in the Local, Perseus, and Outer Arms, respectively. Young stellar objects as outflow drivers are found near most outflows, while 36 candidates show no associated source. The clusters of outflows that we detect are inhomogeneous in their properties; nevertheless, we show that the outflows cannot inject turbulent energy on cloud scales. Instead, at best, they are restricted to affecting the so-called "clump" and "core" scales, and only on short (∼0.3 Myr) estimated timescales. Combined with outflow samples in the literature, our work shows a tight outflow mass-size correlation.

Keywords: stellar jets; astronomical object identification; molecular clouds
A 3D Framework to Explore the Propagation Effects in Stars Exhibiting Electron Cyclotron Maser Emission

Recently, coherent radio emission has been discovered from a number of hot magnetic stars, via the process of electron cyclotron maser emission (ECME). This emission, observed in the form of highly circularly polarized pulses, has interesting properties that contain information about the host star. One of the important properties of ECME is the frequency dependence of the pulse arrival time. This has been attributed to the propagation effect by Trigilio et al. and could explain the sequence observed for CU Vir qualitatively. However, no quantitative treatment exists for this phenomenon despite it being a promising tool to estimate the density in the stellar magnetosphere. Additionally, the effect of propagation through the magnetosphere on ECME has been thought to be limited to giving rise to a particular sequence of arrival of pulses, and in some cases producing the upper cutoff frequency for ECME. Here, we present a framework to deal with the propagation effect by considering continuous refraction in the inner magnetosphere of the star. This framework is capable of incorporating any type of density distribution, and in principle any type of magnetic field, though we limit ourselves to a dipolar magnetic field for this work. We show by simulation that for stars with high obliquity, the propagation effect can influence not only the sequence of arrival of pulses drastically, but also the pulse shapes, and the observability of a pulse from a particular magnetosphere.

Keywords: early-type variable stars; magnetic stars; astronomical simulations; astrophysical masers
ELM of ELM-WD: An Extremely-low-mass Hot Star Discovered in LAMOST Survey

The extremely-low-mass white dwarfs (ELM WDs) and pre-ELM WDs are helium-core white dwarfs with mass <~ 0.3M ⊙. Evolution simulations show that a lower mass limit for ELM WDs exists at ≈0.14M ⊙ and no ELM WD is proposed by observation to be less massive than that. Here we report the discovery of a binary system, LAMOST J224040.77-020732.8 (J2240 in short), which consists of a very low-mass hot star and a compact companion. Multiepoch spectroscopy shows an orbital period P orb = 0.219658 ± 0.000002 days and a radial-velocity semiamplitude K1 = 318.5 ± 3.3 km s-1, which gives the mass function of 0.74M ⊙, indicating the companion is a compact star. The F-type low-resolution spectra illustrate no emission features, and the temperature (~7400 K) is consistent with that from spectral energy distribution fitting and multicolor light-curve solution. The optical light curves, in ZTF g, r, and i bands and the Catalina V band, show ellipsoidal variability with amplitudes of ~30%, suggesting that the visible component is heavily tidally distorted. Combining the distance from Gaia survey, the ZTF light curves are modeled with Wilson-Devinney code and the result shows that the mass of the visible component is $M1={0.085}_{-0.024}^{+0.036}{M}_{\odot }$ , and the mass of the invisible component is $M2={0.98}_{-0.09}^{+0.16}{M}_{\odot }$ . The radius of the visible component is $R1={0.29}_{-0.03}^{+0.04}{R}_{\odot }$ . The inclination angle is approximately between 60° and 90°. The observations indicate the system is most likely a pre-ELM WD + WD/NS binary, and the mass of pre-ELM is possibly lower than the 0.14M ⊙ theoretical limit.

Keywords: white dwarf stars; close binary stars