Sazuna/UAT_keywords huggingface dataset:
Pulsar Timing Signatures of Circumbinary Asteroid Belts. The gravitational pull of a large number of asteroids perturbs a pulsar's motion to a degree that is detectable through precision timing of millisecond pulsars. The result is a low-frequency, correlated noise process, similar in form to the red timing noise known to affect canonical pulsars, or to the signal expected from a stochastic gravitational-wave background. Motivated by the observed fact that many millisecond pulsars are in binary systems, we describe the ways in which the presence of a binary companion to the pulsar would affect the signal produced by an asteroid belt. The primary effect of the companion is to destabilize the shortest-period orbits, cutting off the high-frequency component of the signal from the asteroid belt. We also discuss the implications of asteroid belts for gravitational-wave search efforts. Compared to the signal from a stochastic gravitational-wave background, asteroid-belt noise has a similar frequency and amplitude, and is similarly independent of radio frequency, but is not correlated between different pulsars, which should allow the two kinds of signal to be distinguished.

Keywords: Asteroids, Millisecond pulsars, Pulsars, Gravitational interaction, Binary pulsars
Modeling of the Effects of Stellar Feedback during Star Cluster Formation Using a Hybrid Gas and N-Body Method. Understanding the formation of stellar clusters requires following the interplay between gas and newly formed stars accurately. We therefore couple the magnetohydrodynamics code FLASH to the N-body code ph4 and the stellar evolution code SeBa using the Astrophysical Multipurpose Software Environment (AMUSE) to model stellar dynamics, evolution, and collisional N-body dynamics and the formation of binary and higher-order multiple systems, while implementing stellar feedback in the form of radiation, stellar winds, and supernovae in FLASH. We here describe the algorithms used for each of these processes. We denote this integrated package Torch. We then use this novel numerical method to simulate the formation and early evolution of several examples of open clusters of ∼1000 stars formed from clouds with a mass range of 103 M⊙ to 105 M⊙. Analyzing the effects of stellar feedback on the gas and stars of the natal clusters, we find that in these examples, the stellar clusters are resilient to disruption, even in the presence of intense feedback. This can even slightly increase the amount of dense, Jeans unstable gas by sweeping up shells; thus, a stellar wind strong enough to trap its own H II region shows modest triggering of star formation. Our clusters are born moderately mass segregated, an effect enhanced by feedback, and retained after the ejection of their natal gas, in agreement with observations.

Keywords: Star forming regions, Molecular clouds, Stellar dynamics, Computational methods, Star formation, H II regions, N-body simulations, Collapsing clouds
The Electron Acoustic Wave and Its Role in Solar Flaring Loops Heating. From soft X-ray emission, the solar flare temperatures are from several MK to dozens of times MK, which are higher than the preflare coronal temperatures. A combination of several heating mechanisms may contribute to the heating problem in solar flare loops. In this paper, we propose an important mechanism of solar flaring loops heating, in which the excited electron acoustic wave (EAW) by flare-accelerated fast electron beams can lead to electron heating via collisionless Landau damping effect produced by wave-particle resonant interaction. Taking account of the return-current effect of fast electron beams, by use of numerical and analytic solutions, the plasma wave instability driven by fast electron beams is investigated in typical solar flare loop plasma parameters. The results show that the EAW is the strongest unstable wave mode rather than other wave modes. The dissipation of EAW via collisionless Landau damping and its application to solar flaring loops heating are discussed in detail.

Keywords: Solar coronal waves, Solar flares, Plasma astrophysics
What Is the Role of Stellar Radiative Feedback in Setting the Stellar Mass Spectrum?. In spite of decades of theoretical efforts, the physical origin of the stellar initial mass function (IMF) is still debated. Particularly crucial is the question of what sets the peak of the distribution. To investigate this issue, we perform high-resolution numerical simulations with radiative feedback exploring, in particular, the role of the stellar and accretion luminosities. We also perform simulations with a simple effective equation of state (EOS), and we investigate 1000 solar-mass clumps having, respectively, 0.1 and 0.4 pc of initial radii. We found that most runs, both with radiative transfer or an EOS, present similar mass spectra with a peak broadly located around 0.3-0.5 M⊙ and a power-law-like mass distribution at higher masses. However, when accretion luminosity is accounted for, the resulting mass spectrum of the most compact clump tends to be moderately top-heavy. The effect remains limited for the less compact one, which overall remains colder. Our results support the idea that rather than the radiative stellar feedback, this is the transition from the isothermal to the adiabatic regime, which occurs at a gas density of about 1010 cm-3, that is responsible for setting the peak of the IMF. This stems from (i) the fact that extremely compact clumps for which the accretion luminosity has a significant influence are very rare and (ii) the luminosity problem, which indicates that the effective accretion luminosity is likely weaker than expected.

Keywords: Hydrodynamical simulations, Initial mass function, Stellar feedback, Star formation, Radiative transfer, Stellar accretion, Collapsing clouds
On the Walén Relation for Alfvénic Fluctuations in Interplanetary Space. In interplanetary space, the majority of the Alfvénic fluctuations cannot satisfy the Walén relation even though plasma and magnetic field fluctuations are correlated very well. Finding a proper de Hoffman-Teller (HT) wave frame velocity is thus important for characterizing the Alfvénic fluctuations. Recognizing that the Alfvénic fluctuations emanating from different sizes of solar wind streams have their own HT frames, we propose a new scheme called the wave frame with varying velocity (WFVV) method by considering the local averaged HT frame to find a time-varying profile of HT frame velocity. We apply this WFVV method to two Alfvénic events on 2002 October 14 and 17. Unlike the three other schemes discussed in this study, the WFVV method is preferable because it can provide the HT frame variation in more detail, particularly for the large solar wind changes associated with directional discontinuities observed in the October 14 event. For such Alfvénic structures, a time-dependent HT frame derived from the WFVV method, rather than a constant HT frame, produces a better result of the Walén test together with a smaller convection electric field. The difference of estimated HT frame velocities among different schemes was as large as 30 km s-1 for these two events. In addition, we noted that the degree of Alfvénicity tends to decrease with an increasing variance of HT frame velocity, suggesting that a constant HT frame will also give good results for cases of a small variance of HT frame velocity.

Keywords: Space plasmas, Magnetohydrodynamics, Solar wind, Alfven waves, Interplanetary magnetic fields
Discovery of a Young Stellar Snake with Two Dissolving Cores in the Solar Neighborhood. We report the discovery of a young (only 30-40 Myr) snake-like structure (dubbed a stellar snake) in the solar neighborhood from Gaia DR2. The average distance of this structure is about 310 pc from us. Both the length and width are over 200 pc, but the thickness is only about 80 pc. The snake has one tail and two dissolving cores, which can be clearly distinguished in the 6D phase space. The whole structure includes thousands of members with a total mass of larger than 2000 M⊙ in a uniform population. The population is so young that it cannot be well explained with the classical theory of tidal tails. We therefore suspect that the snake is hierarchically primordial, rather than the result of dynamically tidal stripping, even if the snake is probably expanding. The coherent 5D phase information and the ages suggest that the snake was probably born in the same environment as the filamentary structure of Beccari et al. If so, the snake could extend the sky region of the Vela OB2 association by a factor of ∼2 and supplement the census of its coeval structures. This finding is useful to understanding the history of the formation and evolution of the Vela OB2 complex. The age of the snake well matches with that of the Gould Belt. In the sky region of our interest, we detect one new open cluster, which is named Tian 1 in this work.

Keywords: Stellar kinematics, Gould Belt, Stellar dynamics, OB associations, Solar neighborhood, Young stellar objects, Pre-main sequence stars, Tidal tails, Proper motions, Open star clusters, Filamentary nebulae, Stellar associations
Exploiting Network Topology for Accelerated Bayesian Inference of Grain Surface Reaction Networks. In the study of grain-surface chemistry in the interstellar medium, there exists much uncertainty regarding the reaction mechanisms with few constraints on the abundances of grain-surface molecules. Bayesian inference can be performed to determine the likely reaction rates. In this work, we consider methods for reducing the computational expense of performing Bayesian inference on a reaction network by looking at the geometry of the network. Two methods of exploiting the topology of the reaction network are presented. One involves reducing a reaction network to just the reaction chains with constraints on them. After this, new constraints are added to the reaction network and it is shown that one can separate this new reaction network into subnetworks. The fact that networks can be separated into subnetworks is particularly important for the reaction networks of interstellar complex-organic molecules, whose surface reaction networks may have hundreds of reactions. Both methods allow the maximum-posterior reaction rate to be recovered with minimal bias.

Keywords: Interstellar abundances, Reaction rates, Astrochemistry, Dark interstellar clouds, Astrostatistics strategies
Exploring the Mass Segregation Effect of X-Ray Sources in Globular Clusters. IV. Evidence of Black Hole Burning in ω Centauri. Using X-ray sources as sensitive probes of stellar dynamical interactions in globular clusters (GCs), we study the mass segregation and binary burning processes in ω Cen. We show that the mass segregation of X-ray sources is quenched in ω Cen, while the X-ray source abundance of ω Cen is much smaller than other GCs, and the binary hardness ratio (defined as ${L}_{{\rm{X}}}/({L}_{K}{f}_{b})$ , with fb being the binary fraction, ${L}_{{\rm{X}}}$ and LK being the cumulative X-ray and K-band luminosity of GCs, respectively) of ω Cen is located far below the ${L}_{{\rm{X}}}/({L}_{K}{f}_{b})\mbox{--}{\sigma }_{c}$ correlation line of the dynamically normal GCs. This evidence suggests that the binary burning processes are highly suppressed in ω Cen, and other heating mechanisms, very likely a black hole subsystem (BHS), are essential in the dynamical evolution of ω Cen. Through the black hole burning processes (i.e., dynamical hardening of the BH binaries), the BHS is dominating the energy production of ω Cen, which also makes ω Cen a promising factory of gravitational-wave sources in the Galaxy.

Keywords: Globular star clusters, Intermediate-mass black holes, X-ray binary stars, Binary stars, Stellar mass black holes, Gravitational wave sources, Stellar dynamics
Small-scale Flux Emergence, Coronal Hole Heating, and Flux-tube Expansion: A Hybrid Solar Wind Model. Extreme-ultraviolet images from the Solar Dynamics Observatory often show loop-like fine structure to be present where no minority-polarity flux is visible in magnetograms, suggesting that the rate of ephemeral region (ER) emergence inside "unipolar" regions has been underestimated. Assuming that this rate is the same inside coronal holes as in the quiet Sun, we show that interchange reconnection between ERs and open field lines gives rise to a solar wind energy flux that exceeds 105 erg cm-2 s-1 and that scales as the field strength at the coronal base, consistent with observations. In addition to providing ohmic heating in the low corona, these reconnection events may be a source of Alfvén waves with periods ranging from the granular timescale of ∼10 minutes to the supergranular/plume timescale of many hours, with some of the longer-period waves being reflected and dissipated in the outer corona. The asymptotic wind speed depends on the radial distribution of the heating, which is largely controlled by the rate of flux-tube expansion. Along the rapidly diverging flux tubes associated with slow wind, heating is concentrated well inside the sonic point (1) because the outward conductive heat-flux density and thus the outer coronal temperatures are reduced, and (2) because the net wave energy flux is dissipated at a rate proportional to the local Alfvén speed. In this "hybrid" solar wind model, reconnection heats the lower corona and drives the mass flux, whereas waves impart energy and momentum to the outflow at greater distances.

Keywords: Slow solar wind, Solar magnetic flux emergence, Solar magnetic reconnection, Heliosphere, Fast solar wind, Solar wind, Solar coronal heating, Alfven waves, Solar corona, Solar magnetic fields, Solar coronal holes, Solar coronal plumes
Radio Activity of Supermassive Black Holes with Extremely High Accretion Rates. Radio emission from the high- and super-Eddington accreting active galactic nuclei (AGNs) has various origins: a persistent jet, the magnetized corona, and the wind-like outflows. It is still unclear which is the leading mechanism responsible for the observed radio emission and how the radio emission is related to other characteristic parameters such as the Eddington ratio and black hole mass. In this paper, we present the 5 GHz Very Large Array (VLA) observational results of a sample of 25 extremely high Eddington accreting supermassive black holes (EESBHs, the Eddington ratio λEdd close to or above 1) in narrow-line Seyfert 1 galaxies, among which 22 sources are detected. Most of the EESBHs show a compact radio structure from a few hundred parsecs to 1 kpc scale. We estimated the lowest star formation rate surface density required for producing the observed radio emission and found that it is higher than the largest value previously detected in circumnuclear starburst galaxies, implying that the radio emission is from the AGN activity. Along with a comparison sample, we find an overall inverse ${ \mathcal R }$ -λEdd correlation ranging from sub- to super-Eddington ratios. The high-Eddington and mildly super-Eddington AGNs (-0.5 &lt; log ${\lambda }_{\mathrm{Edd}}\lt 0.6$ ) have a radio-to-X-ray luminosity ratio LR/LX ∼ 10-5-10-4 and a steep radio spectrum, supporting that the radio emission is from transient ejecta (outflows) of corona; however, the jet contribution cannot be entirely ruled out. Our highly super-Eddington sources (log ${\lambda }_{\mathrm{Edd}}\gtrsim 0.6$ ) have a flatter radio spectrum, along with its low radio luminosity: ${L}_{{\rm{R}}}/{L}_{{\rm{X}}}\sim {10}^{-5}$ ; their radio emission is likely dominated by a magnetized corona, and a radiation-pressure-caused jet is also proposed in this paper.

Keywords: Supermassive black holes, Active galactic nuclei, Active galaxies, Jets
Heavy-element Abundances in P-rich Stars: A New Site for the s-process?. The recently discovered phosphorus-rich stars pose a challenge to stellar evolution and nucleosynthesis theory, as none of the existing models can explain their extremely peculiar chemical abundances pattern. Apart from the large phosphorus enhancement, such stars also show enhancement in other light (O, Mg, Si, and Al) and heavy (e.g., Ce) elements. We have obtained high-resolution optical spectra of two optically bright phosphorus-rich stars (including a new P-rich star), for which we have determined a larger number of elemental abundances (from C to Pb). We confirm the unusual light-element abundance pattern with very large enhancements of Mg, Si, Al, and P, and possibly some Cu enhancement, but the spectrum of the new P-rich star are the only ones to reveal some C(+N) enhancement. When compared to other appropriate metal-poor and neutron-capture enhanced stars, the two P-rich stars show heavy-element overabundances similar to low neutron density s-process nucleosynthesis, with high first-peak (Sr, Y, and Zr) and second-peak (Ba, La, Ce, and Nd) element enhancements (even some Pb enhancement in one star) and a negative [Rb/Sr] ratio. However, this s-process is distinct from the one occurring in asymptotic giant branch (AGB) stars. The notable distinctions encompass larger [Ba/La] and lower Eu and Pb than their AGB counterparts. Our observations should guide stellar nucleosynthesis theoreticians and observers to identify the P-rich star progenitor, which represents a new site for s-process nucleosynthesis, with important implications for the chemical evolution of our Galaxy.

Keywords: S-process, Stellar abundances, Population II stars, Stellar nucleosynthesis, Chemically peculiar stars
The Kinematic Evolution of Erupting Structures in Confined Solar Flares. In this Letter, we study the kinematic properties of ascending hot blobs associated with confined flares. Taking advantage of high-cadence extreme-ultraviolet images provided by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we find that for the 26 events selected here, the hot blobs are first impulsively accelerated outward, but then quickly slow down to motionlessness. Their velocity evolution is basically synchronous with the temporal variation of the Geostationary Operational Environmental Satellite soft X-ray flux of the associated flares, except that the velocity peak precedes the soft X-ray peak by minutes. Moreover, the duration of the acceleration phase of the erupting blobs is moderately correlated with that of the flare rise phase. For nine of the 26 cases, the erupting blobs even appear minutes prior to the onset of the associated flares. Our results show that a fraction of confined flares also involve the eruption of a magnetic flux rope, which sometimes is formed and heated prior to the flare onset. We suggest that the initiation and development of these confined flares are similar to that of eruptive ones, and the main difference may lie in the background field constraint, which is stronger for the former than for the latter.

Keywords: Solar activity, Solar coronal mass ejections, Solar flares, Solar corona
Kozai Migration Naturally Explains the White Dwarf Planet WD1856 b. The Jovian-sized object WD 1856 b transits a white dwarf (WD) in a compact 1.4 day orbit. Unlikely to have endured stellar evolution in its current orbit, WD 1856 b is thought to have migrated from much wider separations. Because the WD is old, and a member of a well-characterized hierarchical multiple, the well-known Kozai mechanism provides an effective migration channel for WD 1856 b. The tidal dissipation that makes this mechanism possible is sensitive to the mass of WD 1856 b, which remains unconstrained by observations. Moreover, the lack of tides in the star allows us to directly connect the current semimajor axis to the pre-migration one, from which we can infer the initial conditions of the system. By further requiring that planets must survive all previous phases of stellar evolution before migrating, we are able to constrain the main-sequence semimajor axis of WD 1856 b to have been ∼2.5 au, and its mass to be ≃0.7-3MJ. These mass limits put WD 1856 b firmly within the planet category. Furthermore, our inferred values imply that WD 1856 b was born a typical gas giant. We further estimate the occurrence rate of Kozai-migrated planets around WDs to be ${ \mathcal O }({10}^{-3}-{10}^{-4})$ , suggesting that WD 1856 b is the only one in the TESS sample, but implying ${ \mathcal O }({10}^{2})$ future detections by the LSST survey. In a sense, WD 1856 b was an ordinary Jovian planet that underwent an extraordinary dynamical history.

Keywords: Exoplanet dynamics, Multiple stars, Binary stars, White dwarf stars, Exoplanet evolution
Survivor Bias: Divergent Fates of the Solar System's Ejected versus Persisting Planetesimals. The orbital architecture of the solar system is thought to have been sculpted by a dynamical instability among the giant planets. During the instability a primordial outer disk of planetesimals was destabilized and ended up on planet-crossing orbits. Most planetesimals were ejected into interstellar space, but a fraction were trapped on stable orbits in the Kuiper Belt and Oort cloud. We use a suite of N-body simulations to map out the diversity of planetesimals' dynamical pathways. We focus on two processes: tidal disruption from very close encounters with a giant planet, and loss of surface volatiles from repeated passages close to the Sun. We show that the rate of tidal disruption is more than a factor of 2 higher for ejected planetesimals than for surviving objects in the Kuiper Belt or Oort cloud. Ejected planetesimals are preferentially disrupted by Jupiter and surviving ones by Neptune. Given that the gas giants contracted significantly as they cooled but the ice giants did not, taking into account the thermal evolution of the giant planets decreases the disruption rate of ejected planetesimals. The frequency of volatile loss and extinction is far higher for ejected planetesimals than for surviving ones and is not affected by the giant planets' contraction. Even if all interstellar objects were ejected from solar system-like systems, our analysis suggests that their physical properties should be more diverse than those of solar system small bodies as a result of their divergent dynamical histories. This is consistent with the characteristics of the two currently known interstellar objects.

Keywords: Comets, Solar system formation, Comet volatiles , Tidal disruption
Double-peaked Pulse Profile of FRB 200428: Synchrotron Maser Emission from Magnetized Shocks Encountering a Density Jump. Very recently a fast radio burst (FRB) 200428 associated with a strong X-ray burst from the Galactic magnetar SGR 1935+2154 was detected; this provides direct evidence supporting the magnetar progenitor models of FRBs. Assuming that the FRB radiation mechanism is synchrotron maser emission from magnetized shocks, we develop a specific scenario by introducing a density-jump structure of upstream medium, thus making the double-peaked character of FRB 200428 a natural outcome. The luminosity and emission frequency of two pulses can be well explained in this scenario. Furthermore, we find that the synchrotron emission of shock-accelerated electrons is in the X-ray band, and therefore can be responsible for at least a portion of observed X-ray fluence. With the proper upgrade, in the future this density-jump scenario could be applied to FRBs with multiple peaks.

Keywords: Neutron stars, Magnetars, Radio transient sources