adsabs/SciX_UAT_keywords huggingface dataset:
Discovery of Correlated Evolution in Solar Noise Storm Source Parameters: Insights on Magnetic Field Dynamics during a Microflare

A solar type-I noise storm is produced by accelerated particle beams generated at active regions undergoing magnetic field restructuring. Their intensity varies by orders of magnitude within subsecond and sub-MHz scales. But the morphological evolution of these sources is not studied at these scales due to the lack of required imaging cadence and fidelity in meterwave bands. Using data from the Murchison Widefield Array, this work explores the coevolution of size, sky-orientation, and intensity of a noise storm source associated with a weak microflare. This work presents the discovery of two correlated modes of evolution in the source parameters: a sausage like "S" mode where the source intensity and size show an anticorrelated evolution; and a torsional like "T" mode where the source size and sky-orientation show a correlated evolution. A flare mediated mode conversion is observed from "T" to "S" for the first time in these sources. These results support the idea of build up of magnetic stress energy in braided active region loops, which later become unstable causing flares and particle acceleration until they relax to a minimally braided state. The discovered mode conversion can be a future diagnostic for such events.

Keywords: alfven waves; solar flares; solar radio flares; solar active region magnetic fields; solar active regions; solar coronal heating; solar radio emission; solar x-ray flares; solar extreme ultraviolet emission; solar coronal transients; solar oscillations; solar magnetic reconnection
The Axisymmetric Streaming Instability Revisited

We examine the accuracy of the terminal velocity approximation and clarify a number of misunderstandings regarding the streaming instability in protoplanetary disks under axisymmetric geometry. In the limit of small Stokes number, St ≪ 1, we derive a prediction for the growth rate of the secular modes, which is accurate to the leading order of St and applies to arbitrary dust-to-gas ratio, $\bar{\epsilon }$ . Unlike the claim by a recent study, we show that the secular modes are always unstable. We clarify that the terminal velocity approximation is compatible with the resonant drag instability in the dust-poor limit, $\bar{\epsilon }\ll 1$ , and the predicted growth rate for the resonant modes by the approximation is analytically derived and numerically tested. We find that the terminal velocity approximation is accurate to the leading order of ${\bar{\epsilon }}^{-1}$ in the dust-rich limit with $\bar{\epsilon }\gg 1$ . However, the approximation is not accurate to the leading order of St and may lead to inaccurate predictions, especially for $\bar{\epsilon }\sim 1$ . We show that, besides dust trapping in local pressure maxima, the only process that causes dust clustering under the terminal velocity approximation, there are additional mechanisms of dust clustering that may contribute to the growth rate. The phase differences between the pressure and density perturbations in both Eulerian and Lagrangian frames are also studied for a better physical understanding of the streaming instability.

Keywords: planet formation; planetesimals
Brighter-fatter Effect in Near-infrared Detectors—III. Fourier-domain Treatment of Flat Field Correlations and Application to WFIRST

Weak gravitational lensing has emerged as a leading probe of the growth of cosmic structure. However, the shear signal is very small and accurate measurement depends critically on our ability to understand how non-ideal instrumental effects affect astronomical images. The Wide-Field Infrared Survey Telescope (WFIRST) will fly a focal plane containing 18 Teledyne H4RG-10 near-infrared detector arrays, which present different instrument calibration challenges from previous weak lensing observations. Previous work [Paper I: Hirata & Choi, PASP, 132, 014501 (2020); and Paper II: Choi & Hirata, PASP, 132, 014502 (2020)] has shown that correlation functions of flat field images, including cross-correlations between different time slices that are enabled by the non-destructive read capability of the infrared detectors, are effective tools for disentangling linear and nonlinear inter-pixel capacitance (IPC) and the brighter-fatter effect (BFE). Here we present a Fourier-domain treatment of the flat field correlations, which allows us to expand the previous formalism to all orders in IPC, BFE, and classical nonlinearity. We show that biases in simulated flat field analyses in Paper I are greatly reduced through the use of this formalism. We then apply this updated formalism to flat field data from three WFIRST flight candidate detectors, and explore the robustness to variations in the analysis. We find that the BFE is present in all three detectors, and that its contribution to the flat field correlations dominates over the nonlinear IPC, in accordance with the results from Paper II on a development detector. The magnitude of the BFE is such that the effective area of a pixel is increased by (3.54 ± 0.03) × 10-7 for every electron deposited in a neighboring pixel (sensor chip assembly [SCA] 20829, statistical error, not IPC-deconvolved). We compare IPC maps from flat field autocorrelation measurements to those obtained from the single pixel reset method and find a median difference of 0.113% for SCA 20829. After further diagnosis of this difference, we ascribe it largely to an additional source of cross-talk, the vertical trailing pixel effect, and recommend further work to develop a model for this effect. These results represent a significant step toward calibration of the non-ideal effects in WFIRST detectors.

Keywords: astronomical instrumentation
Statistical Survey of Reservoir Phenomenon in Energetic Proton Events Observed by Multiple Spacecraft

In this work, reservoir phenomenon in the decay phase of gradual solar energetic particle (SEP) events are investigated with two Helios and the IMP 8 spacecraft from 1976 January to 1980 March and two STEREO and the SOHO spacecraft from 2010 January to 2014 September. Using these data, 62 reservoir events of solar energetic protons were identified, and the effects of perpendicular diffusion and magnetic mirroring on the formation of the reservoir phenomenon have been studied. We find that the reservoir events could be observed in almost all longitudes in the ecliptic at 1 au; thus, the perpendicular diffusion in interplanetary space is an important mechanism to explain the uniform distribution of SEPs. Furthermore, in the 1976 April 30 event, the effects of magnetic mirroring associated with an interplanetary coronal mass ejection were observed during the reservoir phenomenon. Therefore, the effects of magnetic mirroring could also help to form the reservoir phenomenon. This study could improve the understanding of the propagation of SEPs in interplanetary space.

Keywords: solar energetic particles; solar particle emission; interplanetary particle acceleration; solar coronal mass ejections; solar flares
Comprehensive Laboratory Measurements Resolving the LMM Dielectronic Recombination Satellite Lines in Ne-like Fe xvii Ions

We investigated experimentally and theoretically dielectronic recombination (DR) populating doubly excited configurations $3l3l^{\prime}$ (LMM) in Fe xvii, the strongest channel for soft X-ray line formation in this ubiquitous species. We used two different electron beam ion traps and two complementary measurement schemes for preparing the Fe xvii samples and evaluating their purity, observing negligible contamination effects. This allowed us to diagnose the electron density in both EBITs. We compared our experimental resonant energies and strengths with those of previous independent work at a storage ring as well as those of configuration interaction, multiconfiguration Dirac-Fock calculations, and many-body perturbation theory. This last approach showed outstanding predictive power in the comparison with the combined independent experimental results. From these we also inferred DR rate coefficients, unveiling discrepancies from those compiled in the OPEN-ADAS and AtomDB databases.

Keywords: laboratory astrophysics; atomic physics; experimental techniques; theoretical techniques; spectral line lists; dielectronic recombination; atomic data benchmarking
Observation of the A Carinid Meteor Shower 2020 Unexpected Outburst

We present observations of the sudden outburst of the A Carinid meteor shower recorded with the Southern Argentina Agile MEteor Radar Orbital System (SAAMER-OS) near the south toroidal sporadic region. The outburst peaked between 21 UT and 22 UT on 2020 October 14 and lasted 7 days (199° ≤ λ⊙ ≤ 205°), with a mean Sun-centered geocentric ecliptic radiant of λg - λ⊙ = 271°04, βg = -76°4, and a geocentric speed of 33.3 km s-1. Assuming a mass index value of s = 2.0, we compute a peak 24 hr average flux of 0.029 meteoroids km-2 hr-1 to a limit of 9th magnitude, which is equivalent to a zenithal hourly rate (ZHR) of 5.7 and comparable to other established showers with similar mass indices. By further estimating the peak fluxes for other typical mass index values, we find that the outburst likely never exceeded a maximum ZHR of ∼44, well below the activity of other strong showers. The mean orbital elements resemble those of a short-period object, a = 3.5 ± 0.1 au, q ≃ 1 au, e = 0.72 ± 0.02, i = 55°8 ± 0°3, ω = 1° ± 173°, and Ω = 21°7, and are similar to those derived for two previous shower outbursts observed with SAAMER-OS at high southern ecliptic latitudes. Using the $D^{\prime} $ criterion did not reveal a parent object associated with this shower in the known object catalogs.

Keywords: meteor showers; meteors; radar astronomy
Characterizing the Directionality of Gravitational Wave Emission from Matter Motions within Core-collapse Supernovae

We analyze the directional dependence of the gravitational wave (GW) emission from 15 3D neutrino radiation hydrodynamic simulations of core-collapse supernovae (CCSNe). Using spin weighted spherical harmonics, we develop a new analytic technique to quantify the evolution of the distribution of GW emission over all angles. We construct a physics-informed toy model that can be used to approximate GW distributions for general ellipsoid-like systems, and use it to provide closed form expressions for the distribution of GWs for different CCSN phases. Using these toy models, we approximate the protoneutron star (PNS) dynamics during multiple CCSN stages and obtain similar GW distributions to simulation outputs. When considering all viewing angles, we apply this new technique to quantify the evolution of preferred directions of GW emission. For nonrotating cases, this dominant viewing angle drifts isotropically throughout the supernova, set by the dynamical timescale of the PNS. For rotating cases, during core bounce and the following tens of milliseconds, the strongest GW signal is observed along the equator. During the accretion phase, comparable-if not stronger-GW amplitudes are generated along the axis of rotation, which can be enhanced by the low T/∣W∣ instability. We show two dominant factors influencing the directionality of GW emission are the degree of initial rotation and explosion morphology. Lastly, looking forward, we note the sensitive interplay between GW detector site and supernova orientation, along with its effect on detecting individual polarization modes.

Keywords: core-collapse supernovae; gravitational waves; general relativity; astronomical simulations; high energy astrophysics
Time Variability of Nonthermal X-Ray Stripes in Tycho's Supernova Remnant with Chandra

Analyzing Chandra data of Tycho's supernova remnant (SNR) taken in 2000, 2003, 2007, 2009, and 2015, we search for time-variable features of synchrotron X-rays in the southwestern part of the SNR, where stripe structures of hard X-ray emission were previously found. By comparing X-ray images obtained at each epoch, we discover a knot-like structure in the northernmost part of the stripe region became brighter particularly in 2015. We also find a bright filamentary structure gradually became fainter and narrower as it moves outward. Our spectral analysis reveals that not only the nonthermal X-ray flux but also the photon indices of the knot-like structure change from year to year. During the period from 2000 to 2015, the small knot shows a brightening of ∼70% and hardening of ΔΓ ∼ 0.45. The time variability can be explained if the magnetic field is amplified to $\sim 100\,\mu {\rm{G}}$ and/or if magnetic turbulence significantly changes with time.

Keywords: supernova remnants; interstellar medium; x-ray sources; cosmic ray sources; galactic cosmic rays; magnetic fields
The MASSIVE Survey. XVI. The Stellar Initial Mass Function in the Center of MASSIVE Early-type Galaxies

The stellar initial mass function (IMF) is a fundamental property in the measurement of stellar masses and galaxy star formation histories. In this work, we focus on the most massive galaxies in the nearby universe $\mathrm{log}({M}_{\star }/\,{M}_{\odot })\gt 11.2$ . We obtain high-quality Magellan/LDSS-3 long-slit spectroscopy with a wide wavelength coverage of 0.4-1.01 μm for 41 early-type galaxies (ETGs) in the MASSIVE survey and derive high signal-to-noise spectra within an aperture of R e/8. Using detailed stellar synthesis models, we constrain the elemental abundances and stellar IMF of each galaxy through full spectral modeling. All the ETGs in our sample have an IMF that is steeper than a Milky Way (Kroupa) IMF. The best-fit IMF mismatch parameter, α IMF = (M/L)/(M/L)MW, ranges from 1.1 to 3.1, with an average of <α IMF> = 1.84, suggesting that on average, the IMF is more bottom heavy than Salpeter. Comparing the estimated stellar masses with the dynamical masses, we find that most galaxies have stellar masses that are smaller than their dynamical masses within the 1σ uncertainty. We complement our sample with lower-mass galaxies from the literature and confirm that $\mathrm{log}({\alpha }_{\mathrm{IMF}})$ is positively correlated with $\mathrm{log}(\sigma )$ , $\mathrm{log}({M}_{\star })$ , and $\mathrm{log}({M}_{\mathrm{dyn}})$ . From the combined sample, we show that the IMF in the centers of more massive ETGs is more bottom heavy. In addition, we find that $\mathrm{log}({\alpha }_{\mathrm{IMF}})$ is positively correlated with both [Mg/Fe] and the estimated total metallicity [Z/H]. We find suggestive evidence that the effective stellar surface density ΣKroupa might be responsible for the variation of α IMF. We conclude that σ, [Mg/Fe], and [Z/H] are the primary drivers of the global stellar IMF variation.

Keywords: initial mass function; galaxy evolution; galaxy formation; galaxy properties; galaxy stellar content
Deep Narrowband Photometry of the M101 Group: Strong-line Abundances of 720 H II Regions

We present deep, narrowband imaging of the nearby spiral galaxy M101 and its satellites to analyze the oxygen abundances of their H II regions. Using Case Western Reserve University's Burrell Schmidt telescope, we add to the narrowband data set of the M101 Group, consisting of Hα, Hβ, and [O III] emission lines and the blue [O II] λ3727 emission line for the first time. This allows for complete spatial coverage of the oxygen abundance of the entire M101 Group. We used the strong-line ratio R 23 to estimate oxygen abundances for the H II regions in our sample, utilizing three different calibration techniques to provide a baseline estimate of the oxygen abundances. This results in ~650 H II regions for M101, 10 H II regions for NGC 5477, and ~60 H II regions for NGC 5474, the largest sample for this Group to date. M101 shows a strong abundance gradient, while the satellite galaxies present little or no gradient. There is some evidence for a flattening of the gradient in M101 beyond R ~ 14 kpc. Additionally, M101 shows signs of azimuthal abundance variations to the west and southwest. The radial and azimuthal abundance variations in M101 are likely explained by an interaction it had with its most massive satellite, NGC 5474, ~300 Myr ago combined with internal dynamical effects such as corotation.

Keywords: chemical abundances; galaxy abundances; narrow band photometry; interacting galaxies; galaxy dynamics
A Lower Limit on the Mass of Our Galaxy from the H3 Survey

The timing argument provides a lower limit on the mass of the Milky Way. Using a sample of 32 stars at R > 60 kpc drawn from the H3 Spectroscopic Survey and mock catalogs created from published numerical simulations, we find that M200 > 0.91 × 1012 M⊙ with 90% confidence. We recommend using this limit to refine the allowed prior mass range in more complex and sophisticated statistical treatments of Milky Way dynamics. The use of such a prior would have significantly reduced many previously published uncertainty ranges. Our analysis suggests that the most likely value of M200 is ≈1.5 × 1012 M⊙, but establishing this as the Milky Way mass requires a larger sample of outer halo stars and a more complete analysis of the inner halo stars in H3. The imminent growth in the sample of outer halo stars due to ongoing and planned surveys will make this possible.

Keywords: milky way galaxy; milky way dark matter halo; milky way stellar halo
The Chromosphere Underneath a Coronal Bright Point

Coronal bright points (CBPs) are sets of small-scale coronal loops, connecting opposite magnetic polarities, primarily characterized by their enhanced extreme-ultraviolet (EUV) and X-ray emission. Being ubiquitous, they are thought to play an important role in heating the solar corona. We aim at characterizing the barely explored chromosphere underneath CBPs, focusing on the related spicular activity and on the effects of small-scale magnetic flux emergence on CBPs. We used high-resolution observations of a CBP in Hβ and Fe I 617.3 nm from the Swedish 1 m Solar Telescope in coordination with the Solar Dynamics Observatory. This work presents the first high-resolution observation of spicules imaged in Hβ. The spicules were automatically detected using advanced image processing techniques, which were applied to the Dopplergrams derived from Hβ. Here we report their abundant occurrence close to the CBP "footpoints" and find that the orientation of such spicules is aligned along the EUV loops, indicating that they constitute a fundamental part of the whole CBP magnetic structure. Spatiotemporal analysis across multiple channels indicates that there are coronal propagating disturbances associated with the studied spicules, producing transient EUV intensity variations of the individual CBP loops. Two small-scale flux emergence episodes appearing below the CBP were analyzed, one of them leading to quiet-Sun Ellerman bombs and enhancing the nearby spicular activity. This paper presents unique evidence of the tight coupling between the lower and upper atmosphere of a CBP, thus helping to unravel the dynamic phenomena underneath CBPs and their impact on the latter.

Keywords: solar coronal heating; solar spicules; solar chromosphere; solar corona; solar magnetic flux emergence; computational methods
Small-amplitude Compressible Magnetohydrodynamic Turbulence Modulated by Collisionless Damping in Earth's Magnetosheath: Observation Matches Theory

Plasma turbulence is a ubiquitous dynamical process that transfers energy across many spatial and temporal scales and affects energetic particle transport. Recent advances in the understanding of compressible magnetohydrodynamic (MHD) turbulence demonstrate the important role of damping in shaping energy distributions on small scales, yet its observational evidence is still lacking. This study provides the first observational evidence of substantial collisionless damping (CD) modulation on the small-amplitude compressible MHD turbulence cascade in Earth's magnetosheath using four Cluster spacecraft. Based on an improved compressible MHD decomposition algorithm, turbulence is decomposed into three eigenmodes: incompressible Alfvén modes and compressible slow and fast (magnetosonic) modes. Our observations demonstrate that CD enhances the anisotropy of compressible MHD modes because CD has a strong dependence on wave propagation angle. The wavenumber distributions of slow modes are mainly stretched perpendicular to the background magnetic field ( B 0) and weakly modulated by CD. In contrast, fast modes are subjected to a more significant CD modulation. Fast modes exhibit a weak, scale-independent anisotropy above the CD truncation scale. Below the CD truncation scale, the anisotropy of fast modes enhances as wavenumbers increase. As a result, fast-mode fractions in the total energy of compressible modes decrease with the increase of perpendicular wavenumber (to B 0) or wave propagation angle. Our findings reveal how the turbulence cascade is shaped by CD and its consequences for anisotropies in the space environment.

Keywords: interplanetary turbulence; interplanetary physics; space plasmas; plasma astrophysics; magnetohydrodynamics
Precision Orbital Dynamics from Interstellar Scintillation Arcs for PSR J0437-4715

Intensity scintillations of radio pulsars are known to originate from interference between waves scattered by the electron density irregularities of interstellar plasma, often leading to parabolic arcs in the two-dimensional power spectrum of the recorded dynamic spectrum. The degree of arc curvature depends on the distance to the scattering plasma and its transverse velocity with respect to the line of sight. We report the observation of annual and orbital variations in the curvature of scintillation arcs over a period of 16 yr for the bright millisecond pulsar, PSR J0437-4715. These variations are the signature of the relative transverse motions of Earth, the pulsar, and the scattering medium, which we model to obtain precise measurements of parameters of the pulsar's binary orbit and the scattering medium itself. We observe two clear scintillation arcs in most of our >5000 observations, and we show that they originate from scattering by thin screens located at distances D1 = 89.8 ± 0.4 pc and D2 = 124 ± 3 pc from Earth. The best-fit scattering model we derive for the brightest arc yields the pulsar's orbital inclination angle, i = 137°1 ± 0°3, and longitude of ascending node, Ω = 206°3 ± 0°4. Using scintillation arcs for precise astrometry and orbital dynamics can be superior to modeling variations in the diffractive scintillation timescale, because the arc curvature is independent of variations in the level of turbulence of interstellar plasma. This technique can be used in combination with pulsar timing to determine the full three-dimensional orbital geometries of binary pulsars and provides parameters essential for testing theories of gravity and constraining neutron star masses.

Keywords: pulsars; millisecond pulsars; interstellar medium; interstellar plasma; binary pulsars; radio pulsars; interstellar scintillation; radio astronomy; orbital motion; astrometry; orbits; orbit determination
The Mass-Temperature Relation for B and Early A Stars Based on International Ultraviolet Explorer Spectra of Detached Eclipsing Binaries

Ultraviolet spectra were taken of 25 detached eclipsing binaries (DEBs) with spectral types O, B, and early A with the International Ultraviolet Explorer satellite in the 1150-1900 Å region. The spectra were compared with BOSZ model atmospheres. The composite spectra of the DEBs were modeled by a combination of models representing the hot and cool components, and the temperatures of the hottest components of the systems were determined. From these temperatures a direct mass-temperature relation was obtained for stars close to the main sequence with solar metallicity for B and early A stars: log M/M ⊙ = -5.90 ± 0.27 + (1.56 ± 0.07) × log T. This relation allows a mass to be inferred for comparable stars from an ultraviolet spectrum. The five chemically peculiar Am stars in the sample have larger radii than normal A stars of the same mass.

Keywords: fundamental parameters of stars