adsabs/SciX_UAT_keywords huggingface dataset:
A 4 Gyr M-dwarf Gyrochrone from CFHT/MegaPrime Monitoring of the Open Cluster M67

We present stellar rotation periods for late K- and early M-dwarf members of the 4 Gyr old open cluster M67 as calibrators for gyrochronology and tests of stellar spin-down models. Using Gaia EDR3 astrometry for cluster membership and Pan-STARRS (PS1) photometry for binary identification, we build this set of rotation periods from a campaign of monitoring M67 with the Canada-France-Hawaii Telescope's MegaPrime wide-field imager. We identify 1807 members of M67, of which 294 are candidate single members with significant rotation period detections. Moreover, we fit a polynomial to the period versus color-derived effective temperature sequence observed in our data. We find that the rotation of very cool dwarfs can be explained by simple solid-body spin-down between 2.7 and 4 Gyr. We compare this rotational sequence to the predictions of gyrochronological models and find that the best match is Skumanich-like spin-down, P rot ∝ t 0.62, applied to the sequence of Ruprecht 147. This suggests that, for spectral types K7-M0 with near-solar metallicity, once a star resumes spinning down, a simple Skumanich-like relation is sufficient to describe their rotation evolution, at least through the age of M67. Additionally, for stars in the range M1-M3, our data show that spin-down must have resumed prior to the age of M67, in conflict with the predictions of the latest spin-down models.

Keywords: open star clusters; stellar evolution; stellar ages; stellar rotation
The Initial Mass Function of Low-mass Stars and Brown Dwarfs in the W3 Complex

We have used archival infrared images obtained with the Wide Field Camera 3 on board the Hubble Space Telescope to constrain the initial mass function of low-mass stars and brown dwarfs in the W3 star-forming region. The images cover 438 arcmin2, which encompasses the entire complex, and were taken in the filters F110W, F139M, and F160W. We have estimated extinctions for individual sources in these data from their colors and have dereddened their photometry accordingly. By comparing an area of the images that contains the richest concentration of previously identified W3 members to an area that has few members and is dominated by background stars, we have estimated the luminosity function for members of W3 with masses of 0.03-0.4 M⊙. That luminosity function closely resembles data in typical nearby star-forming regions that have much smaller stellar populations than W3 ( ≲ 500 versus several thousand objects). Thus, we do not find evidence of significant variations in the initial mass function of low-mass stars and brown dwarfs with star-forming conditions, which is consistent with recent studies of other distant massive star-forming regions.

Keywords: brown dwarfs; initial mass function; hubble space telescope
Mid-term Periodicity of Coronal Mass Ejections during the Time Interval 1996–2022

Coronal mass ejections (CMEs) exhibit a wide range of quasiperiodic variations and are crucial for our understanding of the cyclical evolution of large-scale magnetic fields. However, the mid-term periodicities of different types of CMEs associated with different processes at the source location need to be clearly understood. Based on the CDAW catalog released by the Large Angle and Spectroscopic Coronagraph mission on the Solar and Heliospheric Observatory, we investigated the period of CMEs based on the speeds and accelerations using the continuous wavelet transformation method. Our results revealed that the distribution of CMEs over time is quite distinctly different for different speeds, and there are Rieger-type periods and quasi-biennial oscillations of the CMEs. The two types of periodic signals show significant differences in solar cycles 23 and 24. Furthermore, the periodicity patterns for the northern hemisphere differ from those in the southern hemisphere. The potential mechanisms and explanations of the results are also discussed.

Keywords: solar coronal mass ejections; solar-terrestrial interactions; solar magnetic fields
Pre-eruption Splitting of the Double-decker Structure in a Solar Filament

Solar filaments often erupt partially. Although how they split remains elusive, the splitting process has the potential of revealing the filament structure and eruption mechanism. Here we investigate the pre-eruption splitting of an apparently single filament and its subsequent partial eruption on 2012 September 27. The evolution is characterized by three stages with distinct dynamics. During the quasi-static stage, the splitting proceeds gradually for about 1.5 hr, with the upper branch rising at a few kilometers per second and displaying swirling motions about its axis. During the precursor stage that lasts for about 10 minutes, the upper branch rises at tens of kilometers per second, with a pair of conjugated dimming regions starting to develop at its footpoints; with the swirling motions turning chaotic, the axis of the upper branch whips southward, which drives an arc-shaped extreme-ultraviolet front propagating in a similar direction. During the eruption stage, the upper branch erupts with the onset of a C3.7-class two-ribbon flare, while the lower branch remains stable. Judging from the well-separated footpoints of the upper branch from those of the lower one, we suggest that the pre-eruption filament processes a double-decker structure composed of two distinct flux bundles, whose formation is associated with gradual magnetic flux cancellations and converging photospheric flows around the polarity inversion line.

Keywords: solar filament eruptions; solar active region magnetic fields; solar flares; solar filaments
The Regulation of the Solar Wind Electron Heat Flux by Wave–Particle Interactions

The solar wind electrons carry a significant heat flux into the heliosphere. The weakly collisional state of the solar wind implicates collisionless processes as the primary factor that constrains nonthermal features of the velocity distribution function (VDF), including the heat flux. Previous observational work suggests that the electron VDF sometimes becomes unstable to the whistler wave, but reliance on model VDFs (e.g., drifting bi-Maxwellians) has proven insufficient for an exact description of the behavior of the solar wind electrons—in particular, the regulation of the heat flux. The characterization of these processes requires methods to obtain fine details of the VDF and quantification of the impact of kinetic processes on the VDF. We employ measurements of the electron VDF by Solar Orbiter's Solar Wind Analyser and of the magnetic field by the Radio and Plasma Waves instrument to study an unstable solar wind electron configuration. Through a Hermite–Laguerre expansion of the VDF, we implement a low-pass filter in velocity space to remove velocity space noise and obtain a VDF suitable for analysis. With our method, we directly measure the instability growth rate and the rate of change of the electron heat flux through wave–particle interactions.

Keywords: space plasmas; solar wind
Does the HCN/CO Ratio Trace the Star-forming Fraction of Gas? I. A Comparison with Analytical Models of Star Formation

We use archival ALMA observations of the HCN and CO J = 1-0 transitions, in addition to the radio continuum at 93 GHz, to assess the relation between dense gas, star formation, and gas dynamics in 10 nearby (ultra)luminous IR galaxies (U)LIRGs and late-type galaxy centers. We frame our results in the context of turbulent and gravoturbulent models of star formation to assess whether the HCN/CO ratio tracks the gravitationally bound star-forming gas in molecular clouds (f grav) at subkiloparsec scales in nearby galaxies. We confirm that the HCN/CO ratio is a tracer of gas above n SF ≈ 104.5 cm-3, but the subkiloparsec variations in HCN/CO do not universally track f grav. We find strong evidence for the use of varying star formation density-threshold models, which are able to reproduce trends observed in t dep and ϵ ff that fixed-threshold models do not reproduce. Composite lognormal and power-law models outperform pure lognormal models in reproducing the observed trends, even when a fixed power-law slope is used. The ability of the composite models to better reproduce the star formation properties of the gas provides additional indirect evidence that the star formation efficiency per freefall time is proportional to the fraction of gravitationally bound gas.

Keywords: star formation; galaxies; molecular gas; galaxy mergers; starburst galaxies; ultraluminous infrared galaxies; luminous infrared galaxies; barred spiral galaxies
Maps of Solar Wind Plasma Precipitation onto Mercury's Surface: A Geographical Perspective

Mercury is the closest planet to the Sun, possesses a weak intrinsic magnetic field, and has only a very tenuous atmosphere (exosphere). These three conditions result in a direct coupling between the plasma emitted from the Sun (namely, the solar wind) and Mercury's surface. The planet's magnetic field leads to a nontrivial pattern of plasma precipitation onto the surface that is expected to contribute to the alteration of the regolith over geological timescales. The goal of this work is to study the solar wind plasma precipitation onto the surface of Mercury from a geographical perspective, as opposed to the local time-of-day approach of previous precipitation modeling studies. We employ solar wind precipitation maps for protons and electrons from two fully kinetic numerical simulations of Mercury's plasma environment. These maps are then integrated over two full Mercury orbits (176 Earth days). We found that the plasma precipitation pattern at the surface is most strongly affected by the upstream solar wind conditions, particularly the interplanetary magnetic field direction, and less by Mercury's 3:2 spin-orbit resonance. We also found that Mercury's magnetic field is able to shield the surface from roughly 90% of the incoming solar wind flux. At the surface, protons have a broad energy distribution from below 500 eV to more than 1.5 keV, while electrons are mostly found in the range 0.1-10 keV. These results will help to better constrain space weathering and exosphere source processes at Mercury, as well as interpret observations by the ongoing ESA/JAXA BepiColombo mission.

Keywords: mercury (planet); space weather; space plasmas; regolith; planetary science; planetary surfaces; solar wind; planetary geology; interplanetary magnetic fields; magnetic fields
Collisional Shaping of Nuclear Star Cluster Density Profiles

A supermassive black hole surrounded by a dense, nuclear star cluster resides at the center of many galaxies. In this dense environment, high-velocity collisions frequently occur between stars. About 10% of the stars within the Milky Way's nuclear star cluster collide with other stars before evolving off the main sequence. Collisions preferentially affect tightly bound stars, which orbit most quickly and pass through regions of the highest stellar density. Over time, collisions therefore shape the bulk properties of the nuclear star cluster. We examine the effect of collisions on the cluster's stellar density profile. We show that collisions produce a turning point in the density profile, which can be determined analytically. Varying the initial density profile and collision model, we characterize the evolution of the stellar density profile over 10 Gyr. We find that old, initially cuspy populations exhibit a break around 0.1 pc in their density profile, while shallow density profiles retain their initial shape outside of 0.01 pc. The initial density profile is always preserved outside of a few tenths of a parsec irrespective of initial conditions. We generalize this model to an arbitrary galactic nucleus and show that the location of the collisional break can be simply estimated from the nuclear properties. Lastly, we comment on the implications of collisions for the luminosity and color of stars in the collisionally shaped inner cluster.

Keywords: stellar dynamics; galactic center; star clusters; stellar mergers
unTimely: a Full-sky, Time-domain unWISE Catalog

We present the unTimely Catalog, a deep time-domain catalog of detections based on Wide-field Infrared Survey Explorer (WISE) and NEOWISE observations spanning the 2010 through 2020 time period. Detections are extracted from "time-resolved unWISE coadds," which stack together each biannual sky pass of WISE imaging to create a set of ~16 all-sky maps (per band), each much deeper and cleaner than individual WISE exposures. unTimely incorporates the W1 (3.4 μm) and W2 (4.6 μm) channels, meaning that our data set effectively consists of ~32 full-sky unWISE catalogs. We run the crowdsource crowded-field point-source photometry pipeline (Schlafly et al. 2018) on each epochal coadd independently, with low detection thresholds: S/N = 4.0 (2.5) in W1 (W2). In total, we tabulate and publicly release 23.5 billion (19.9 billion) detections at W1 (W2). unTimely is ~1.3 mag deeper than the WISE/NEOWISE Single Exposure Source Tables near the ecliptic, with further enhanced depth toward higher ecliptic latitudes. The unTimely Catalog is primarily designed to enable novel searches for faint, fast-moving objects, such as Y dwarfs and/or late-type (T/Y) subdwarfs in the Milky Way's thick disk or halo. unTimely will also facilitate other time-domain science applications, such as all-sky studies of quasar variability at mid-infrared wavelengths over a decade-long time baseline.

Keywords: catalogs; infrared astronomy; time domain astronomy; transient detection; variable stars
Orbital Evolution of Gas-driven Inspirals with Extreme Mass Ratios: Retrograde Eccentric Orbits

Using two-dimensional simulations, we compute the torque and rate of work (power) on a low-mass gravitational body, with softening length Rsoft, embedded in a gaseous disk when its orbit is eccentric and retrograde with respect to the disk. We explore orbital eccentricities e between 0 and 0.6. We find that the power has its maximum at e ≃ 0.25(h/0.05)2/3, where h is the aspect ratio of the disk. We show that the power and the torque converge to the values predicted in the local (nonresonant) approximation of the dynamical friction (DF) when Rsoft tends to zero. For retrograde inspirals with mass ratios ≲5 × 10-4 embedded in disks with h ≥ 0.025, our simulations suggest that (I) the rate of inspiral barely depends on the orbital eccentricity and (II) the local approximation provides the value of this inspiral rate within a factor of 1.5. The implications of the results for the orbital evolution of extreme mass ratio inspirals are discussed.

Keywords: gravitational interaction; active galactic nuclei; compact objects; galaxy accretion disks; tidal interaction; dynamical friction; supermassive black holes; hydrodynamical simulations
Intermittency and Ion Temperature-Anisotropy Instabilities: Simulation and Magnetosheath Observation

Weakly collisional space plasmas are rarely in local thermal equilibrium and often exhibit non-Maxwellian electron and ion velocity distributions that lead to the growth of microinstabilities—that is, enhanced electric and magnetic fields at relatively short wavelengths. These instabilities play an active role in the evolution of space plasmas, as does ubiquitous broadband turbulence induced by turbulent structures. This study compares certain properties of a 2.5-dimensional particle-in-cell (PIC) simulation for the forward cascade of Alfvénic turbulence in a collisionless plasma against the same properties of turbulence observed by the Magnetospheric Multiscale Mission spacecraft in the terrestrial magnetosheath. The PIC simulation is of decaying turbulence that develops both coherent structures and anisotropic ion velocity distributions with the potential to drive kinetic scale instabilities. The uniform background magnetic field points perpendicular to the plane of the simulation. Growth rates are computed from linear theory using the ion temperature anisotropies and ion beta values for both the simulation and the observations. Both the simulation and the observations show that strong anisotropies and growth rates occur highly intermittently in the plasma, and the simulation further shows that such anisotropies preferentially occur near current sheets. This suggests that, though microinstabilities may affect the plasma globally, they act locally and develop in response to extreme temperature anisotropies generated by turbulent structures. Further studies will be necessary to understand why there is an apparent correlation between linear instability theory and strongly intermittent turbulence.

Keywords: space plasmas; magnetohydrodynamical simulations
Fast Radio Burst Counterparts and Their Implications for the Central Engine

While the radiation mechanism of fast radio bursts (FRBs) is unknown, coherent curvature radiation and synchrotron maser are promising candidates. We find that both radiation mechanisms work for a neutron star (NS) central engine with B ≳ 1012 G, while for a synchrotron maser, the central engine can also be an accreting black hole (BH) with B ≳ 1012 G and a white dwarf (WD) with B ∼ 108 - 109 G. We study the electromagnetic counterparts associated with such central engines, I.e., nebulae for repeating FRBs and afterglows for nonrepeating FRBs. In general, the energy spectrum and flux density of the counterpart depend strongly on its size and total injected energy. We apply the calculation to the nebula of FRB 121102 and find that the persistent radio counterpart requires the average energy injection rate into the nebula to be between 2.7 × 1039 erg s-1 and 1.5 × 1044 erg s-1, and the minimum injected energy to be 6.0 × 1047 erg in around 7 yr. Consequently, we find that for FRB 121102 and its nebula: (1) WD and accretion BH central engines are disfavored; (2) a rotation-powered NS central engine works when 1.2 × 1012 G ≲ B ≲ 7.8 × 1014 G with initial period P < 180 ms, but the radio emission must be more efficient than that in typical giant pulses of radio pulsars; and (3) a magnetic-powered NS central engine works when its internal magnetic field B ≳ 1016 G. We also find that the radio-emitting electrons in the nebula could produce a significant rotation measure (RM), but cannot account for the entire observed RM of FRB 121102.

Keywords: radio transient sources; non-thermal radiation sources; magnetars
Evaluation of Automated Fermi GBM Localizations of Gamma-Ray Bursts

The capability of the Fermi Gamma-ray Burst Monitor (GBM) to localize gamma-ray bursts (GRBs) is evaluated for two different automated algorithms: the GBM Team's RoboBA algorithm and the independently developed BALROG algorithm. Through a systematic study utilizing over 500 GRBs with known locations from instruments like Swift and the Fermi Large Area Telescope, we directly compare the effectiveness of, and accurately estimate the systematic uncertainty for, both algorithms. We show that simple adjustments to the GBM Team's RoboBA, in operation since early 2016, yield significant improvement in the systematic uncertainty, removing the long tail identified in the systematic, and improve the overall accuracy. The systematic uncertainty for the updated RoboBA localizations is 1°8 for 52% of GRBs and 4°1 for the remaining 48%. Both from public reporting by BALROG and our systematic study, we find the systematic uncertainty of 1°-2° quoted in circulars for bright GRBs is an underestimate of the true magnitude of the systematic, which we find to be 2°7 for 74% of GRBs and 33° for the remaining 26%. We show that, once the systematic uncertainty is considered, the RoboBA 90% localization confidence regions can be more than an order of magnitude smaller in area than those produced by BALROG.

Keywords: gamma-ray bursts; astronomy data analysis
Can the Solar p-modes Contribute to the High-frequency Transverse Oscillations of Spicules?

Lateral motions of spicules serve as vital indicators of transverse waves in the solar atmosphere, and their study is crucial for understanding the wave-heating process of the corona. Recent observations have focused on high-frequency transverse waves (periods < 100 s), which have the potential to transport sufficient energy for coronal heating. These high-frequency spicule oscillations are distinct from granular motions, which have much longer timescales of 5-10 minutes. Instead, it is proposed that they are generated through the mode conversion from high-frequency longitudinal waves that arise from a shock-steepening process. Therefore, these oscillations may not solely be produced by the horizontal buffeting motions of granulation but also by the leakage of p-mode oscillations. To investigate the contribution of p-modes, our study employs a two-dimensional magneto-convection simulation spanning from the upper convection zone to the corona. During the course of the simulation, we introduce a p-mode-like driver at the bottom boundary. We reveal a notable increase in the mean velocity amplitude of the transverse oscillations in spicules, ranging from 10%-30%, and attribute this to the energy transfer from longitudinal to transverse waves. This effect results in an enhancement of the estimated energy flux by 30%-80%.

Keywords: solar spicules; solar oscillations; solar chromosphere; solar coronal heating; radiative magnetohydrodynamics
Titania's Heat Fluxes Revealed by Messina Chasmata

Messina Chasmata is a relatively young tectonic structure on Titania based on cross-cutting relationships, although an absolute age has not been estimated. We investigated lithospheric flexure bounding Messina and found that the terrain along both rims reflects Titania's thermal properties. We estimate Titania's heat fluxes to have been 5-12 mW m-2 in this region, assuming that the lithosphere is composed of pure H2O ice without porosity. These estimates are lower if lithospheric porosity and/or NH3-H2O are also present. If Messina is ancient, forming as a result of freeze expansion, then the reflected heat fluxes are consistent with radiogenic heating. However, if Messina is instead young, then an additional heat source is required. In this scenario, perhaps tidal heating associated with the past three-body resonance shared between Titania, Ariel, and Umbriel generated this heat. However, this scenario is unlikely because the amount of tidal heating produced on Titania would have been minimal. Titania's heat fluxes are notably lower than estimates for Miranda or Ariel, and future work is needed to investigate Umbriel and Oberon to gain a fuller understanding of Uranian moon thermal and orbital histories. Additionally, further constraints on Titania's more ancient heat fluxes could be obtained by investigating relatively older features, such as some viscously relaxed impact craters.

Keywords: natural satellite surfaces; planetary science; tectonics; natural satellites (solar system); uranian satellites