adsabs/SciX_UAT_keywords huggingface dataset:
DART Impact Ejecta Plume Evolution: Implications for Dimorphos

The NASA Double Asteroid Redirection Test (DART) spacecraft impacted the moon Dimorphos of the [65803] Didymos binary system and changed the binary orbit period, demonstrating asteroid deflection by a kinetic impact and indicating that more momentum was transferred to Dimorphos by escaping impact ejecta than was incident with DART. Images of the DART impact ejecta plume were obtained by the Light Italian cubesat for Imaging of Asteroids (LICIACube) in the first few minutes after the DART impact. The ejecta plume imaged by LICIACube 158 s after the DART impact prior to closest approach shows no evidence for plume clearing at low altitude. The ejecta plume imaged 175 s after the DART impact is optically thick up to projected altitudes of 200 m above the surface of Dimorphos. These observations are compared with models of the impact ejecta plume optical depth, structure, and evolution, which are developed from point-source scaling models fitted to numerical simulations of the DART impact into a rubble pile Dimorphos with different material strengths. The observations of the impact plume optical depth and the high momentum transfer from the DART impact are not consistent with impact and ejecta plume models assuming the Dimorphos cohesive strength to be as high as 5000 Pa. Models with 5 and 50 Pa Dimorphos cohesive strength provide the overall best consistency with plume opacity observations and high momentum transfer.

Keywords: asteroid satellites; asteroid surfaces; near-earth objects
Study of Double-mode RR Lyrae Stars in the Stripe 82 Region Using SDSS and ZTF

RRd stars are a subclass of RR Lyrae stars that pulsate simultaneously in the fundamental and the first-overtone radial modes. We report the analysis of 10 RRd stars discovered in the Sloan Digital Sky Survey (SDSS) Stripe 82 region of the Galactic halo using SDSS and Zwicky Transient Facility data. By combining the two data sets, we constructed ∼23 yr long lightcurves in gri bands, and conclude that out of 10, 9 were the classical RRd stars and 1 was the anomalous RRd star. We also observed the long-term variation, the Blazhko effect, in 3 classical RRd stars out of 10 stars, giving an incidence rate of 30%. The shortest Blazhko period observed was 226.4 ± 0.8 days and the longest was 2799 ± 75 days.

Keywords: rr lyrae variable stars; wide-field telescopes; blazhko effect; double-mode pulsation
Radiation Pressure Acting on the Neutral He Atoms in the Heliosphere

Interstellar neutral helium (ISN He) is an important source of information on the physical state of the local interstellar medium. Radiation pressure acting on the neutral helium atoms in the heliosphere has always been neglected; its effect has been considered insignificant compared to gravitational force. The most advanced numerical models of ISN He take into account more and more subtle effects; therefore, it is important to check if the effect of radiation pressure is still negligible. In this paper, we use the most up-to-date version of the Warsaw Test Particle Model (WTPM) to calculate the expected helium distribution in the heliosphere and simulate the flux of the ISN He observed by the Interstellar Boundary Explorer (IBEX) and in the future by the Interstellar Mapping and Acceleration Probe (IMAP). We compare results calculated with and without radiation pressure during low and high solar activity. The results show that in the analysis of IBEX-Lo observations, the radiation pressure acting on typical helium causes flux differences at a level of 1%-4% and is comparable to the observational errors. For the more sensitive IMAP-Lo instrument, there are some regions in the considered observation configurations where radiation pressure causes potentially statistically significant changes in the calculated fluxes. The effect can be up to 9% for the indirect beam and is likely to be higher than the estimated errors. Therefore, we claim that in the future analysis of the IMAP-Lo observations, radiation pressure acting on ISN He should be considered.

Keywords: heliosphere; solar extreme ultraviolet emission
The Distribution of Impactor Core Material During Large Impacts on Earth-like Planets

Large impacts onto young rocky planets may transform their compositions, creating highly reducing conditions at their surfaces and reintroducing highly siderophile metals to their mantles. Key to these processes is the availability of an impactor's chemically reduced core material (metallic iron). It is, therefore, important to constrain how much of an impactor's core remains accessible to a planet's mantle/surface, how much is sequestered to its core, and how much escapes. Here, we present 3D simulations of such impact scenarios using the shock physics code iSALE to determine the fate of impactor iron. iSALE's inclusion of material strength is vital in capturing the behavior of both solid and fluid components of the planet and thus characterizing iron sequestration to the core. We find that the mass fractions of impactor core material that accretes to the planet core (f core) or escapes (f esc) can be readily parameterized as a function of a modified specific impact energy, with ${f}_{\mathrm{core}}\gt {f}_{\mathrm{esc}}$ for a wide set of impacts. These results differ from previous works that do not incorporate material strength. Our work shows that large impacts can place substantial reducing impactor core material in the mantles of young rocky planets. Impact-generated reducing atmospheres may thus be common for such worlds. However, through escape and sequestration to a planet's core, large fractions of an impactor's core can be geochemically hidden from a planet's mantle. Consequently, geochemical estimates of late bombardments of planets based on mantle siderophile element abundances may be underestimates.

Keywords: impact phenomena; planetary science
Disentangling Magnetic Fields in NGC 6946 with Wide-band Polarimetry

We present λ13 cm polarization observations of the nearby spiral galaxy NGC 6946 with the Westerbork Synthesis Radio Telescope (WSRT) to examine the nearside halo magnetic fields. Despite λ13 cm exhibiting similar two-dimensional morphology as observed at longer (λ18–22 cm) or shorter (λ3 and λ6 cm) wavelengths, more complete frequency coverage will be required to explain the gap in polarization in the southwest quadrant of the galaxy. We fit models of the turbulent and coherent line-of-sight magnetic fields to the fractional degree of linearly polarized emission at λ3, λ6, λ13, λ18, and λ22 cm from observations taken with the WSRT, Karl G. Jansky Very Large Array, and Effelsberg telescopes. The results favor a multilayer turbulent magneto-ionized medium consistent with current observations of edge-on galaxies. We constrain the physical properties of the synchrotron-emitting thin and thick disks (scale heights of 300 pc and 1.4 kpc, respectively) along with the thermal thick disk and halo (scale heights of 1 and 5 kpc, respectively). Our preferred model indicates a clumpy and highly turbulent medium within 1 kpc of the midplane, and a diffuse extraplanar layer with a substantially lower degree of Faraday depolarization. In the halo, we estimate a regular magnetic field strength of 0.4–2.2 μG and that turbulence and a total magnetic field strength of ∼6 μG result in a Faraday dispersion of σ RM = 4–48 rad m‑2. This work is an example of how the advanced capabilities of modern radio telescopes are opening a new frontier for the study of cosmic magnetism.

Keywords: galaxy magnetic fields; radio continuum emission; radio astronomy; spiral galaxies; galaxies; magnetic fields; interstellar synchrotron emission; polarimetry; spectropolarimetry
Bright Stars from the Ancient Merger Gaia-Enceladus Visible with Binoculars

We present here a list of 25 bright stars (G < 8) that are possible members of Gaia-Enceladus, a system that merged with the Milky Way approximately 10 Gyr ago, and whose debris dominates the halo near the Sun. These stars were therefore born beyond the edges of the Milky Way and are visible with binoculars. We expect the list to be of interest for public outreach and amateur astronomers. These bright stars are also useful as standard stars for calibration and validation of analysis since very high-quality spectra can be obtained with reasonable amount of telescope time.

Keywords: stellar kinematics; chemical abundances; milky way stellar halo; galaxy accretion; amateur astronomy
Asteroid Collisions: Expected Visibility and Rate

Asteroid collisions are one of the main processes responsible for the evolution of bodies in the main belt. Using observations of the Dimorphos impact by the DART spacecraft, we estimate how asteroid collisions in the main belt may look in the first hours after the impact. If the DART event is representative of asteroid collisions with a ∼1 m sized impactor, then the light curves of these collisions will rise on timescales of about ≳100 s and will remain bright for about 1 hr. Next, the light curve will decay on a few hours' timescale to an intermediate luminosity level in which it will remain for several weeks, before slowly returning to its baseline magnitude. This estimate suffers from several uncertainties due to, e.g., the diversity of asteroid composition, their material strength, and spread in collision velocities. We estimate that the rate of collisions in the main belt with energy similar to or larger than the DART impact is of the order of 7000 yr‑1 (±1 dex). The large range is due to the uncertainty in the abundance of ∼1 m sized asteroids. We estimate the magnitude distribution of such events in the main belt, and we show that ∼6% of these events may peak at magnitudes brighter than 21. The detection of these events requires a survey with ≲1 hr cadence and may contribute to our understanding of the asteroids' size distribution, collisional physics, and dust production. With an adequate survey strategy, new survey telescopes may regularly detect asteroid collisions.

Keywords: asteroids
The Population Synthesis of Wolf–Rayet Stars Involving Binary Merger Channels

Wolf–Rayet (W-R) stars are very important massive stars. However, their origin and the observed binary fraction within the entire W-R population are still debated. We investigate some possible merger channels for the formation of W-R stars, including main sequence (MS)/Hertzsprung gap (HG) + MS, He + HG/giant branch (GB). We find that many products produced via binary merger can evolve into W-R stars, the MS/HG + MS merger channel can explain W-R stars with luminosities higher than ∼105.4 L ⊙, while the He + HG/GB merger channel can explain low-luminosity W-R stars in the range of 104.7 L ⊙ ∼ 105.5 L ⊙. In the population synthesis analysis of W-R stars, we assume an initial binary fraction (f ini,bin) of 50% and 100% for massive stars. We also assume that MS/HG + MS merger products are nonrotating or rapidly rotating (ω/ω crit = 0.8). In different cases, the calculated single fractions of W-R stars range from 22.2%–60.6% in the Milky Way (MW) and from 8.3%–70.9% in the Large Magellanic Cloud (LMC). The current observations fall within the range of our calculations. When the merger product of MS/HG + MS rotates rapidly, we estimate that there are approximately 1015–1396 W-R stars in the MW and 128–204 W-R stars in the LMC. Our model also roughly reproduces the observed single-peak luminosity distribution of W-R stars in the MW. However, the weak bimodal luminosity distribution observed in the LMC is not reproduced in our model. We assess that this may be due to the model underestimating the mass-loss rate in the LMC. In conclusion, we consider that the binary merger is a significant formation channel for W-R formation, and can explain the observed high fraction of the single W-R stars in the total population.

Keywords: wolf-rayet stars
A Search of TESS Full-frame Images for an Optical Counterpart of the Repeating FRB 20180916B

Recently, an association between an optical transient, AT2020hur, and a repeating fast radio burst, FRB 20180916b, has been suggested, based on a strong positional coincidence on the sky and the temporal coincidence with one of the fast radio burst's activity periods (~6 days duration every ~16 days). This suggestion is explored further and tested in this paper, utilizing full-frame images from the Transiting Exoplanet Survey Satellite (TESS) across three of its observing periods in 2019 and 2020 (Sectors 18, 24, and 25). The discovery observations of AT2020hur took place between Sectors 18 and 24, within 5 days of the commencement of Sector 24 observations. The TESS observations cover at least six activity periods for the FRB. Thus, the TESS data provide excellent temporal coverage close in time to the discovery of AT2020hur and at known times of FRB activity and radio detection. From the TESS data, no evidence is found for repeating optical transients with the suspected emission timescale of ⪆1000 s.

Keywords: radio transient sources
Atacama Cosmology Telescope: Dusty Star-forming Galaxies and Active Galactic Nuclei in the Equatorial Survey

We present a catalog of 510 radio-loud active galactic nuclei (AGNs, primarily blazars) and 287 dusty star-forming galaxies (DSFGs) detected by the Atacama Cosmology Telescope at $\gt 5\sigma $ significance in frequency bands centered on 148 GHz (2 mm), 218 GHz (1.4 mm), and 277 GHz (1.1 mm), from a 480 deg2 strip centered at R.A. 00h on the celestial equator with additional 360 deg2 shallower auxiliary fields at other longitudes. The combination of the deepest available 218 GHz wide-field imaging, our 277 GHz data, and multiband filtering results in the most sensitive wide-field millimeter-wave DSFG selection to date, with rms noise level referenced to 218 GHz reaching below 2 mJy. We have developed new techniques to remove Galactic contamination (including evidence for CO (2-1) line emission) from the extragalactic catalog, yielding a catalog of 321 Galactic sources in addition to the extragalactic catalog. We employ a new flux debiasing method that accounts for the heterogeneous sample selection in the presence of Galactic cuts. We present the spectral properties and source counts of the AGNs and DSFGs. The DSFG spectra depart from the Rayleigh-Jeans regime of an optically thin modified blackbody between 218 and 277 GHz, consistent with optically thick emission or an additional cold dust component. For AGNs with 148 and 218 GHz flux density >50 mJy, we estimate the interyear rms fractional deviation in flux density due to source variability to be 40% with a 0.98 interband correlation coefficient. We provide source counts for AGNs in the range of 8-2870 mJy and for DSFGs in the range of 8-90 mJy. Our DSFG counts probe both the brighter, lensed population and the fainter, unlensed population. At 277 GHz we report the first measurements of source counts at these flux densities, finding an excess above most model count predictions. Finally, we present 30 of the brightest DSFGs that were selected for multifrequency study as candidate high-z lensed systems.

Keywords: radio source catalogs; radio sources; radio source counts; extragalactic radio sources; galactic radio sources; cosmic microwave background radiation; blazars; submillimeter astronomy
Update of the Solar Lyα Profile Line Model

We present a modification of a model of solar cycle evolution of the solar Lyα line profile, along with a sensitivity study of interstellar neutral hydrogen to uncertainties in radiation pressure level. The line profile model, originally developed by Kowalska-Leszczynska et al., is parameterized by the composite solar Lyα flux, which recently was revised. We present modified parameters of the previously developed model of solar radiation pressure for neutral hydrogen and deuterium atoms in the heliosphere. The mathematical function used in the model, as well as the fitting procedure, remain unchanged. We show selected effects of the model modification on interstellar neutral H properties in the heliosphere, and we discuss the sensitivity of these quantities to uncertainties in the calibration of the composite Lyα series.

Keywords: heliosphere; solar spectral irradiance
SQuIGG ěc{L} E Survey: Massive z ∼ 0.6 Post-starburst Galaxies Exhibit Flat Age Gradients

We present Gemini Multi-Object Spectrograph (GMOS) integral field unit (IFU) observations of six massive (M⋆ ≥ 1011 M⊙) A-star dominated post-starburst galaxies at z ∼ 0.6. These galaxies are a subsample of the $\mathrm{SQuIGG}\vec{L}{\rm{E}}$ Survey, which selects intermediate-redshift post-starbursts from the Sloan Digital Sky Survey spectroscopic sample (DR14) with spectral shapes that indicate they have recently shut off their primary epoch of star formation. Using HδA absorption as a proxy for stellar age, we constrain five of the galaxies to have young (∼600 Myr) light-weighted ages at all radii and find that the sample on average has flat age gradients. We examine the spatial distribution of mass-weighted properties by fitting our profiles with a toy model including a young, centrally concentrated burst superimposed on an older, extended population. We find that galaxies with flat HδA profiles are inconsistent with formation via a central secondary starburst. This implies that the mechanism responsible for shutting off this dominant episode of star formation must have done so uniformly throughout the galaxy.

Keywords: galaxy evolution; galaxy formation
Revisiting the Dust Torus Size–Luminosity Relation Based on a Uniform Reverberation-mapping Analysis

We investigate the torus size–luminosity relation of Type 1 active galactic nuclei (AGNs) based on the reverberation-mapping analysis using the light curves of the optical continuum and the IR continuum obtained with the W1 and W2 bands of the Wide-field Infrared Survey Explorer survey. The final sample consists of 446 and 416 AGNs, respectively, for W1- and W2-band light curves, covering a large dynamic range of bolometric luminosity from 1043.4 to 1047.6 erg s‑1, which show reliable lag measurements based on our quality assessment analysis. After correcting for the accretion disk contamination in the observed IR flux, we constrain the torus size (R dust) and AGN bolometric luminosity (L bol) relationship with the best-fit slope of 0.39 (0.33) for the W1 (W2) band, which is shallower than expected from the dust radiation equilibrium model. By combining the previous K-band lag measurements, we find that the measured torus size depends on the observed wavelength of the dust radiation, as R dust,K : R dust,W1: R dust,W2 = 1.0:1.5:1.8 (R dust ∝ λ 0.80) at L bol = 1046 erg s‑1, confirming a stratified structure of the torus, where wavelength-dependent emissions originate from distinct regions of the torus. By investigating the deviation from the best-fit torus size–luminosity relation, we find a moderate correlation between the offset from the R dust–L bol relation and Eddington ratio. This suggests a possible influence of the Eddington ratio on the observed flattening of the R dust–L bol relationship.

Keywords: reverberation mapping; black holes; active galactic nuclei; quasars
Kronoseismology. VI. Reading the Recent History of Saturn's Gravity Field in Its Rings

Saturn's C ring contains multiple structures that appear to be density waves driven by time-variable anomalies in the planet's gravitational field. Semiempirical extensions of density wave theory enable the observed wave properties to be translated into information about how the pattern speeds and amplitudes of these gravitational anomalies have changed over time. Combining these theoretical tools with wavelet-based analyses of data obtained by the Visual and Infrared Mapping Spectrometer on board the Cassini spacecraft reveals a suite of structures in Saturn's gravity field with azimuthal wavenumber 3, rotation rates between 804° day-1 and 842° day-1, and local gravitational potential amplitudes between 30 and 150 cm2 s-2. Some of these anomalies are transient, appearing and disappearing over the course of a few Earth years, while others persist for decades. Most of these persistent patterns appear to have roughly constant pattern speeds, but there is at least one structure in the planet's gravitational field whose rotation rate steadily increased between 1970 and 2010. This gravitational field structure appears to induce two different asymmetries in the planet's gravity field, one with azimuthal wavenumber 3 that rotates at roughly 810° day-1 and another with azimuthal wavenumber 1 rotating three times faster. The atmospheric processes responsible for generating the latter pattern may involve solar tides.

Keywords: saturn; planetary rings; planetary atmospheres; planetary interior; wavelet analysis; stellar occultation; solar system gas giant planets; celestial mechanics
Efficiencies of Magnetic Field Amplification and Electron Acceleration in Young Supernova Remnants: Global Averages and Kepler's Supernova Remnant

Particle acceleration to suprathermal energies in strong astrophysical shock waves is a widespread phenomenon, generally explained by diffusive shock acceleration. Such shocks can also amplify the upstream magnetic field considerably beyond simple compression. The complex plasma physics processes involved are often parameterized by assuming that shocks put some fraction ϵe of their energy into fast particles and another fraction ϵB into the magnetic field. Modelers of shocks in supernovae, supernova remnants (SNRs), and gamma-ray bursters, among other locations, often assume typical values for these fractions, presumed to remain constant in time. However, it is rare that enough properties of a source are independently constrained that values of the epsilons can be inferred directly. SNRs can provide such circumstances. Here we summarize results from global fits to spatially integrated emission in six young SNRs, finding 10-4 ≲ ϵe ≲ 0.05 and 0.001 ≲ ϵB ≲ 0.1. These large variations might be put down to the differing ages and environments of these SNRs, so we conduct a detailed analysis of a single remnant, that of Kepler's supernova. Both epsilons can be determined at seven different locations around the shock, and we find even larger ranges for both epsilons, as well as for their ratio (thus independent of the shock energy itself). We conclude that unknown factors have a large influence on the efficiency of both processes. Shock obliquity, upstream neutral fraction, or other possibilities need to be explored, while calculations assuming fixed values of the epsilons should be regarded as provisional.

Keywords: shocks; supernova remnants; magnetic fields; cosmic rays
Initial Entropy and Potential Delayed Formation of the Directly Imaged Exoplanet AF Lep b

AF Lep b is a rare directly imaged exoplanet with properties consistent with core-accretion evolution models. Using its precise dynamical mass and spectroscopically inferred bolometric luminosity alongside the Spiegel & Burrows evolution models, I determined an initial entropy >8.7 k B /baryon at 3σ and an age of 12 ± 4 Myr for AF Lep b. Comparing this planet's age to the isochrone age (24 ± 3 Myr) of its host association, the β Pictoris moving group (BPMG), suggests AF Lep b formed 12 ± 5 Myr later than its host star. Alternatively, the BPMG's updated kinematic age ( ${16.3}_{-2.1}^{+3.4}$ Myr) implies that AF Lep b formed 5 ± 5 Myr after its host star's formation, aligning more closely with protoplanetary disk dispersal timescales. The sensitivities of our findings to the planet's mass and luminosity are discussed. AF Lep b uniquely facilitates the constraints of its initial entropy and formation epoch, paving the way for similar insights into forthcoming exoplanet discoveries.

Keywords: exoplanet formation; exoplanet evolution