adsabs/SciX_UAT_keywords huggingface dataset:
Oscillating Strange Quark Matter Objects Excited in Stellar Systems

It is shown that strange quark matter (SQM) objects, stars, and planets, can very efficiently convert the mechanical energy into hadronic energy when they oscillate. This is because the mass density at the edge of SQM objects, ${\rho }_{0}=4.7\times {10}^{14}\,{\rm{g}}\,{\mathrm{cm}}^{-3}$ , is the critical density below which SQM is unstable with respect to decay into photons, hadrons, and leptons. We consider here radial oscillations of SQM objects that could be induced in stellar or planetary systems where tidal interactions are ubiquitous. Oscillations of $0.1 \% $ radius amplitude already result in $1\,\mathrm{keV}$ per unit baryon number excitation near the surface of SQM stars. The excitation energy is converted into electromagnetic energy in a short time of $1\,\mathrm{ms}$ , during a few oscillations. Higher amplitude oscillations result in faster energy release that could lead to fragmentation or dissolution of SQM stars. This would have significant consequences for hypothetical SQM star binaries and planetary systems of SQM planets with regard to gravitational wave emission.

Keywords: high energy astrophysics; stellar oscillations; compact objects; compact binary stars; gravitational wave sources; tidal distortion; relativistic stars
Flattening of Dark Matter Cusps during Mergers: Model of M31

We run high-resolution fully GPU N-body simulations to demonstrate that the dark matter (DM) distribution in M31 is well fitted by a core-like profile. Rich observational data especially on the giant stellar stream provides stringent constraints on the initial conditions of our simulations. We demonstrate that the accretion of a satellite on a highly eccentric orbit heats up the central parts of M31, causes an outward migration of DM particles, flattens the central cusp over more than a decade in scale, and generates a new model-independent DM profile that is well fitted by a core. Our results imply that core-like central profiles could be a common feature of massive galaxies that have been initially cuspy but have accreted satellites on nearly radial orbits.

Keywords: dark matter density; galaxy dynamics; galaxy mergers; andromeda galaxy
Spin-Orbit Alignment of the β Pictoris Planetary System

A crucial diagnostic that can tell us about processes involved in the formation and dynamical evolution of planetary systems is the angle between the rotation axis of a star and a planet's orbital angular momentum vector ("spin-orbit" alignment or "obliquity"). Here we present the first spin-orbit alignment measurement for a wide-separation exoplanetary system, namely on the directly imaged planet β Pictoris b. We use VLTI/GRAVITY spectro-interferometry with an astrometric accuracy of 1 μas (microarcsecond) in the Brγ photospheric absorption line to measure the photocenter displacement associated with the stellar rotation. Taking inclination constraints from astroseismology into account, we constrain the three-dimensional orientation of the stellar spin axis and find that β Pic b orbits its host star on a prograde orbit. The angular momentum vectors of the stellar photosphere, the planet, and the outer debris disk are well aligned with mutual inclinations ≤3° ± 5°, which indicates that β Pic b formed in a system without significant primordial misalignments. Our results demonstrate the potential of infrared interferometry to measure the spin-orbit alignment for wide-separation planetary systems, probing a highly complementary regime to the parameter space accessible with the Rossiter-McLaughlin effect. If the low obliquity is confirmed by measurements on a larger sample of wide-separation planets, it would lend support to theories that explain the obliquity in Hot Jupiter systems with dynamical scattering and the Kozai-Lidov mechanism.

Keywords: planetary system formation; stellar rotation; dynamical evolution; interferometers
Magnetar as Central Engine of Gamma-Ray Bursts: Quasi-universal Jet, Event Rate, and X-Ray Luminosity Function of Dipole Radiations

Early shallow-decaying X-ray afterglows of gamma-ray bursts (GRBs) may be attributed to the dipole radiations of newly born magnetars. Assuming that the GRB jets powered by magnetars are quasi-universal, we find that the jet structure can be parameterized as a uniform jet with a luminosity of $\mathrm{log}{L}_{{\rm{j}}}/\mathrm{erg}\ {{\rm{s}}}^{-1}={52.68}_{-0.33}^{+0.76}$ (1σ) and an opening angle ${\theta }_{{\rm{j}}}={2.10}_{-1.28}^{+1.90}$ (50% confidence level), surrounding by a power-law decay component with an index of $-{4.00}_{-0.37}^{+0.27}$ (1σ). The inferred local GRB rate is ρ = 9.6 Gpc-3 yr-1 by including both the typical GRBs and LL-GRBs as the same population. The typical viewing angle is 3.3°, and may be 20° ∼ 30° for LL-GRBs. The X-ray luminosity function of the dipole radiation wind can be empirically described by a broken power-law function with indices ${\beta }_{1}={0.78}_{-0.15}^{+0.16}$ and ${\beta }_{2}\gt 1.6$ broken at $\mathrm{log}{L}_{{\rm{b}},{\rm{w}}}/\mathrm{erg}\ {{\rm{s}}}^{-1}={48.51}_{-0.65}^{+0.53}$ . In the case where the wind outflow is collimated and coaxial with the GRB jet, we find that the wind structure is similar to the GRB jet, I.e., $\mathrm{log}{L}_{{\rm{c}},{\rm{w}}}/\mathrm{erg}\,{{\rm{s}}}^{-1}={48.38}_{-0.48}^{+0.30}$ , ${\theta }_{{\rm{c}},{\rm{w}}}={{2.65}^{o}}_{-{1.19}^{o}}^{+1.{73}^{o}}$ , and ${k}_{{\rm{w}}}={4.57}_{-0.75}^{+1.21}$ . The observed correlation between the prompt gamma-ray luminosity and X-ray luminosity of the wind may result from the viewing angle effect in such a jet-wind system. A discussion on surveys using the X-ray instruments on board the Einstein Probe mission in the soft X-ray band for the jet and wind emission is also presented.

Keywords: gamma-ray bursts; magnetars; relativistic jets; luminosity function
Solar Cycle and Seasonal Variability of Martian Ionospheric Irregularities from Mars Atmosphere and Volatile Evolution Observations

Spacecraft observations around Mars show that ionospheric irregularities occur frequently in the Martian ionosphere. In this study, Mars Atmosphere and Volatile Evolution data (the region is below ~200 km) during 2015 January to 2021 March were used to revisit the statistical characteristics of ionospheric irregularities and the comparison of irregularities in Martian years with higher or lower solar activity phase of solar cycle. Results show that the characteristics of the irregularities with a larger length scale associated with the magnetic field and solar zenith angle are similar to the previous studies. Moreover, our results show that the occurrence rate of irregularities exhibits dawn and dusk asymmetry, and the occurrence rate at dusk is higher than that at dawn. In addition, results demonstrate that the occurrence rate of irregularities is higher in Martian years with higher solar activity than Martian years with lower solar activity, which means that the solar cycle might play an important role in the formation of irregularity events. Further studies show that the solar zenith angle (SZA) and altitude at the maximum occurrence rate depend on the level of solar activity. The SZA and altitude of the maximum occurrence rate are smaller in the Martian year with higher solar activity than the lower. We also found that the rate of events is lower during the day than the terminator in the ionospheric dynamo region. By contrast, in the regions where both electrons and ions are magnetized, events have a higher rate during the day than the terminator. Furthermore, the seasonal variation of the irregularity events was also presented in this study. Results show that the occurrence rate in the dynamo region with 80° < SZA < 150° in MY34 and MY35 show an incremental trend from spring to winter, but this trend is not obvious in MY33.

Keywords: mars; plasma physics; solar-planetary interactions
Stellar Escape from Globular Clusters. II. Clusters May Eat Their Own Tails

We apply for the first time orbit-averaged Monte Carlo star cluster simulations to study tidal tail and stellar stream formation from globular clusters (GCs), assuming a circular orbit in a time-independent spherical Galactic potential. Treating energetically unbound bodies—potential escapers (PEs)—as collisionless enables this fast but spherically symmetric method to capture asymmetric extratidal phenomena with exquisite detail. Reproducing stream features such as epicyclic overdensities, we show how returning tidal tails can form after the stream fully circumnavigates the Galaxy, enhancing the stream's velocity dispersion by several kilometers per second in our ideal case. While a truly clumpy, asymmetric, and evolving Galactic potential would greatly diffuse such tails, they warrant scrutiny as potentially excellent constraints on the Galaxy's history and substructure. Reexamining the escape timescale Δt of PEs, we find new behavior related to chaotic scattering in the three-body problem; the Δt distribution features sharp plateaus corresponding to distinct locally smooth patches of the chaotic saddle separating the phase-space basins of escape. We study for the first time Δt in an evolving cluster, finding that for PEs with (low, high) Jacobi energy E J, flatter than for a static cluster ( ). Accounting for cluster mass loss and internal evolution lowers the median Δt from ∼10 Gyr to ≲100 Myr. We finally outline potential improvements to escape in the Monte Carlo method intended to enable the first large grids of tidal tail/stellar stream models from full GC simulations and detailed comparison to stream observations.

Keywords: globular star clusters; star clusters; stellar dynamics; n-body simulations; tidal disruption; stellar astronomy; tidal tails; stellar streams; three-body problem
NICER Observation of the Temporal and Spectral Evolution of Swift J1818.0-1607: A Missing Link between Magnetars and Rotation-powered Pulsars

We report on the hard X-ray burst and the first ∼100 days of NICER monitoring of the soft X-ray temporal and spectral evolution of the newly discovered magnetar Swift J1818.0-1607. The burst properties are typical of magnetars with a duration of T90 = 10 ± 4 ms and a temperature of kT = 8.4 ± 0.7 keV. The 2-8 keV pulse shows a broad, single-peak profile with a pulse fraction increasing with time from 30% to 43%. The NICER observations reveal strong timing noise with $\dot{\nu }$ varying erratically by a factor of 10, with an average long-term spin-down rate of $\dot{\nu }=(-2.48\pm 0.03)\times {10}^{-11}$ s-2, implying an equatorial surface magnetic field of 2.5 × 1014 G and a young characteristic age of ∼470 yr. We detect a large spin-up glitch at MJD 58928.56 followed by a candidate spin-down glitch at MJD 58934.81, with no accompanying flux enhancements. The persistent soft X-ray spectrum of Swift J1818.0-1607 can be modeled as an absorbed blackbody with a temperature of ∼1 keV. Its flux decayed by ∼60% while the modeled emitting area decreased by ∼30% over the NICER observing campaign. This decrease, coupled with the increase in the pulse fraction, points to a shrinking hot spot on the neutron star surface. Assuming a distance of 6.5 kpc, we measure a peak X-ray luminosity of 1.9 × 1035 erg s-1, lower than its spin-down luminosity of 7.2 × 1035 erg s-1. Its quiescent thermal luminosity is ≲1.7 × 1034 erg s-1, lower than those of canonical young magnetars. We conclude that Swift J1818.0-1607 is an important link between regular magnetars and high-magnetic-field, rotation-powered pulsars.

Keywords: pulsars; neutron stars; magnetars; x-ray stars
Investigating the Chemically Homogeneous Evolution Channel and Its Role in the Formation of the Enigmatic Binary Black Hole Progenitor Candidate HD 5980

Chemically homogeneous evolution (CHE) is a promising channel for forming massive binary black holes. The enigmatic, massive Wolf–Rayet binary HD 5980 A&B has been proposed to have formed through this channel. We investigate this claim by comparing its observed parameters with CHE models. Using MESA, we simulate grids of close massive binaries, then use a Bayesian approach to compare them with the stars' observed orbital period, masses, luminosities, and hydrogen surface abundances. The most probable models, given the observational data, have initial periods ∼3 days, widening to the present-day ∼20 days orbit as a result of mass loss—correspondingly, they have very high initial stellar masses (≳150 M ⊙). We explore variations in stellar-wind mass loss and internal mixing efficiency, and find that models assuming enhanced mass loss are greatly favored to explain HD 5980, while enhanced mixing is only slightly favored over our fiducial assumptions. Our most probable models slightly underpredict the hydrogen surface abundances. Regardless of its prior history, this system is a likely binary black hole progenitor. We model its further evolution under our fiducial and enhanced wind assumptions, finding that both stars produce black holes with masses ∼19–37 M ⊙. The projected final orbit is too wide to merge within a Hubble time through gravitational waves alone. However, the system is thought to be part of a 2+2 hierarchical multiple. We speculate that secular effects with the (possible) third and fourth companions may drive the system to promptly become a gravitational-wave source.

Keywords: stellar evolution; nonstandard evolution; massive stars; binary stars; gravitational wave sources; stellar mass black holes
Accreted or Not Accreted? The Fraction of Accreted Mass in Galaxies from the Magneticum Simulations and Observations

In the two-phase scenario of galaxy formation, a galaxy's stellar mass growth is first dominated by in-situ star formation, and subsequently by accretion. We analyze the radial distribution of the accreted stellar mass in ~500 galaxies from the (48 Mpc/h)3 box volume of the hydrodynamical cosmological simulation Magneticum, in a stellar-mass range of 1010 to 1012 M ⊙. We find that higher-mass galaxies have larger accreted fractions, as found in previous works, but predict generally higher accretion fractions for low-mass galaxies. Based on the 3D radial distribution of the accreted and in-situ components, we define six galaxy classes, from completely accretion to completely in-situ dominated, and measure the transition radii between in-situ and accretion-dominated regions for galaxies that reveal a transition. About 70% of our galaxies have one transition radius. However, about 10% of the galaxies are accretion dominated everywhere, and about 13% have two transition radii, with the center and the outskirts both being accretion dominated. We show that these classes are strongly correlated with the galaxy merger histories, especially with the cold gas fraction at the time of merging. We find high total in-situ (low accretion) fractions to be associated with smaller, lower-mass galaxies, lower central dark-matter fractions, and larger transition radii. Finally, we show that the dips in observed surface brightness profiles seen in many early-type galaxies do not correspond to the transition from in-situ to accretion-dominated regions, and that any inferred mass fractions are not indicative of the true accreted mass but contain information about the galaxies' dry-merger history.

Keywords: galaxy structure; galaxy formation; galaxy accretion; galaxy evolution
Decihertz Gravitational Waves from Double White Dwarf Merger Remnants

Close binaries of double white dwarfs (DWDs) inspiral and merge by emitting gravitational waves (GWs). Orbital motion of some of these binaries is expected to be observed at a low-frequency band by space-borne laser interferometric detectors of GWs. The merger remnant may suffer thermonuclear runaway and explode as SNe Ia if they are massive enough. As GW sources, the remnants have so far been scarcely studied. Here we propose a new mechanism of GW emission from DWD merger remnants that may be observed by planned GW detectors in a decihertz frequency band. A remnant is temporarily expected to have a high degree of differential rotation as a consequence of the merger process. It is then unstable to oscillation modes whose azimuthal pattern speed coincides with the stellar rotation. We solve the eigenvalue problem of differentially rotating remnants and identify unstable eigenmodes, which may be categorized to inertial modes. The estimate of characteristic strain of GWs shows that they may be detectable within the distance of the Virgo cluster by planned gravitational wave observatories targeting the decihertz band.

Keywords: white dwarf stars; close binary stars; gravitational wave sources
New Hard-TeV Extreme Blazars Detected with the MAGIC Telescopes

Extreme high-frequency-peaked BL Lac objects (EHBLs) are blazars that exhibit extremely energetic synchrotron emission. They also feature nonthermal gamma-ray emission whose peak lies in the very high-energy (VHE, E > 100 GeV) range, and in some sources exceeds 1 TeV: this is the case for hard-TeV EHBLs such as 1ES 0229+200. With the aim of increasing the EHBL population, 10 targets were observed with the MAGIC telescopes from 2010 to 2017, for a total of 265 hr of good-quality data. The data were complemented by coordinated Swift observations. The X-ray data analysis confirms that all but two sources are EHBLs. The sources show only a modest variability and a harder-when-brighter behavior, typical for this class of objects. At VHE gamma-rays, three new sources were detected and a hint of a signal was found for another new source. In each case, the intrinsic spectrum is compatible with the hypothesis of a hard-TeV nature of these EHBLs. The broadband spectral energy distributions (SEDs) of all sources are built and modeled in the framework of a single-zone, purely leptonic model. The VHE gamma-ray-detected sources were also interpreted with a spine-layer model and a proton synchrotron model. The three models provide a good description of the SEDs. However, the resulting parameters differ substantially in the three scenarios, in particular the magnetization parameter. This work presents the first mini catalog of VHE gamma-ray and multiwavelength observations of EHBLs.

Keywords: blazars; active galactic nuclei; relativistic jets; bl lacertae objects; x-ray active galactic nuclei; catalogs; non-thermal radiation sources; gamma-ray sources
The Roles of Flux Tube Entropy and Effective Gravity in the Inward Plasma Transport at Saturn

The inward plasma transport at the Saturnian magnetosphere is examined using the flux tube interchange stability formalism developed by Southwood & Kivelson. Seven events are selected. Three cases are considered: (1) the injected flux tube and ambient plasmas are nonisotropic, (2) the injected flux tube and ambient plasmas are isotropic, and (3) the injected flux tube plasma is isotropic, but the ambient plasma is nonisotropic. Case 1 may be relevant for fresh injections, while case 3 may be relevant for old injections. For cases 1 and 2, all but one event have negative stability conditions, suggesting that the flux tube should be moving inward. For case 3, the injections located at L > 11 have negative stability conditions, while four out of five of the injections at L < 9 have positive stability conditions. The positive stability condition for small L suggests that the injection may be near its equilibrium position and possibly oscillating thereabouts-hence the outward transport if the flux tube overshot the equilibrium position. The flux tube entropy plays an important role in braking the plasma inward transport. When the stability condition is positive, it is because the entropy term, which is positive, counters and dominates the effective gravity term, which is negative for all the events. The ambient plasma and drift-out from adjacent injections can affect the stability and the inward motion of the injected flux tube. The results have implications for inward plasma transport in the Jovian magnetosphere, as well as other fast-rotating planetary magnetospheres.

Keywords: saturn; planetary magnetospheres; space plasmas
Speckle Observations of TESS Exoplanet Host Stars. II. Stellar Companions at 1-1000 au and Implications for Small Planet Detection

We present high-angular-resolution imaging observations of 517 host stars of TESS exoplanet candidates using the 'Alopeke and Zorro speckle cameras at Gemini North and South. The sample consists mainly of bright F, G, K stars at distances of less than 500 pc. Our speckle observations span angular resolutions of ~20 mas out to 1"2, yielding spatial resolutions of <10-500 au for most stars, and our contrast limits can detect companion stars 5-9 mag fainter than the primary at optical wavelengths. We detect 102 close stellar companions and determine the separation, magnitude difference, mass ratio, and estimated orbital period for each system. Our observations of exoplanet host star binaries reveal that they have wider separations than field binaries, with a mean orbital semimajor axis near 100 au. Other imaging studies have suggested this dearth of very closely separated binaries in systems which host exoplanets, but incompleteness at small separations makes it difficult to disentangle unobserved companions from a true lack of companions. With our improved angular resolution and sensitivity, we confirm that this lack of close exoplanet host binaries is indeed real. We also search for a correlation between planetary orbital radii versus binary star separation; but, given the very short orbital periods of the TESS planets, we do not find any clear trend. We do note that in exoplanet systems containing binary host stars, there is an observational bias against detecting Earth-size planet transits due to transit depth dilution caused by the companion star.

Keywords: speckle interferometry; high angular resolution; exoplanets; binary stars
Coevolution of Brightest Cluster Galaxies and Their Host Clusters in IllustrisTNG

We use IllustrisTNG simulations to explore the dynamic scaling relation between massive clusters and their-central-brightest cluster galaxies (BCGs). The IllustrisTNG-300 simulation we use includes 280 massive clusters from the z = 0 snapshot with M 200 > 1014 M ⊙, enabling a robust statistical analysis. We derive the line-of-sight velocity dispersion of the stellar particles of the BCGs (σ *,BCG), analogous to the observed BCG stellar velocity dispersion. We also compute the subhalo velocity dispersion to measure the cluster velocity dispersion (σ cl). Both σ *,BCG and σ cl are proportional to the cluster halo mass, but the slopes differ slightly. Thus, like the observed relation, σ *,BCG/σ cl declines as a function of σ cl, but the scatter is large. We explore the redshift evolution of the σ *,BCG - σ cl scaling relation for z ≲ 1 in a way that can be compared directly with observations. The scaling relation has a similar slope at high redshift, but the scatter increases because of the large scatter in σ *,BCG. The simulations imply that high-redshift BCGs are dynamically more complex than their low-redshift counterparts.

Keywords: brightest cluster galaxies; galaxy clusters; magnetohydrodynamical simulations