adsabs/SciX_UAT_keywords huggingface dataset:
Excitation Sources of Oscillations in Solar Coronal Loops: A Multi-wavelength Analysis

An investigation into the excitation sources of oscillations detected in a coronal loop structure is carried out using the images obtained with Interface Region Imaging Spectrometer (IRIS) and the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory (SDO). A loop structure in the active region AR 11967 on 2014 January 28, oscillating in the vicinity of a strong eruption and an M3.6 class flare site, is clearly noticeable in SDO/AIA 171 Å images. We study in detail, the oscillations with detected periods between 4 and 13 minutes and their connection in IRIS SJI 1330 Å and SDO/AIA 1700 Å images; both of these wavelengths sample the lower parts of the solar atmosphere. The simultaneous presence of many oscillations in the region of interest in all three wavelength passbands suggest that these oscillations were excited in the lower-chromosphere-photosphere plasma connected to the loop structure and then propagated at higher heights. We further investigate the Doppler velocity measurements from the spectrograph snapshots in IRIS C II 1336 Å, Si IV 1403 Å and Mg II k 2796 Å. These show signatures of upflows in the vicinity of the loop structure's endpoints estimated from 171 Å images. We suggest that some of the oscillations observed in AIA 171 Å have been triggered by plasma ejections and perturbations seen in the lower layers of the solar atmosphere. Based on the estimated phase speeds, the oscillations are likely to be slow magnetoacoustic in nature.

Keywords: solar physics; solar atmosphere; solar corona
Thaddäus Derfflinger's Sunspot Observations during 1802-1824: A Primary Reference to Understand the Dalton Minimum

As we are heading toward the next solar cycle, presumably with a relatively small amplitude, it is of significant interest to reconstruct and describe the past secular minima on the basis of actual observations at the time. The Dalton Minimum is often considered one of the secular minima captured in the coverage of telescopic observations. Nevertheless, the reconstructions of the sunspot group number vary significantly, and the existing butterfly diagrams have a large data gap during the period. This is partially because most long-term observations at that time have remained unexplored in historical archives. Therefore, to improve our understanding on the Dalton Minimum, we have located two series of Thaddäus Derfflinger's observational records spanning 1802-1824 (a summary manuscript and logbooks), as well as his Brander's 5.5 feet azimuthal quadrant preserved in the Kremsmünster Observatory. We have revised the existing Derfflinger's sunspot group number with Waldmeier classification, and eliminated all the existing "spotless days" to remove contaminations from solar elevation observations. We have reconstructed the butterfly diagram on the basis of his observations and illustrated sunspot distributions in both solar hemispheres. Our article aims to revise the trend of Derfflinger's sunspot group number and to bridge a data gap of the existing butterfly diagrams around the Dalton Minimum. Our results confirm that the Dalton Minimum is significantly different from the Maunder Minimum, both in terms of cycle amplitudes and sunspot distributions. Therefore, the Dalton Minimum is more likely a secular minimum in the long-term solar activity, while further investigations for the observations at that time are required.

Keywords: solar magnetic fields; sunspot cycle; solar cycle; sunspots; solar-terrestrial interactions; stellar activity; astronomy databases
Coadded Spectroscopic Stellar Parameters and Abundances from the LAMOST Low Resolution Survey

I combine duplicate spectroscopic stellar parameter estimates in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release 6 Low Resolution Spectral Survey A, F, G, and K Type stellar parameter catalog. Combining repeat measurements results in a factor of two improvement in the precision of the spectroscopic stellar parameter estimates. Moreover, this trivializes the process of performing coordinate-based cross-matching with other catalogs. Similarly, I combine duplicate stellar abundance estimates for the Xiang et al. catalog which was produced using LAMOST Data Release 5 Low Resolution Spectral Survey data. These data have numerous applications in stellar, galactic, and exoplanet astronomy. The catalogs I produce are available as machine-readable tables at https://doi.org/10.7281/T1/QISGRU.

Keywords: stellar abundances; stellar astronomy; fundamental parameters of stars; sky surveys; stellar properties; astronomy data analysis
The Effect of Superpositions on the Planetary Nebula Luminosity Function

Planetary nebula (PN) surveys in systems beyond ~10 Mpc often find high-excitation, point-like sources with [O III] λ5007 fluxes greater than the apparent bright-end cutoff of the planetary nebula luminosity function (PNLF). Here we identify PN superpositions as one likely cause for the phenomenon and describe the proper procedures for deriving PNLF distances when object blends are a possibility. We apply our technique to two objects: a model Virgo-distance elliptical galaxy observed through a narrowband interference filter, and the Fornax lenticular galaxy NGC 1380 surveyed with the MUSE integral-field unit spectrograph. Our analyses show that even when the most likely distance to a galaxy is unaffected by the possible presence of PN superpositions, the resultant value will still be biased toward too small a distance due to the asymmetrical nature of the error bars. We discuss the future of the PNLF in an era where current ground-based instrumentation can push the technique to distances beyond ~35 Mpc.

Keywords: galaxy distances; planetary nebulae; astrostatistics techniques
The R-Process Alliance: Abundance Universality among Some Elements at and between the First and Second R-Process Peaks

We present new observational benchmarks of rapid neutron-capture process (r-process) nucleosynthesis for elements at and between the first (A ~ 80) and second (A ~ 130) peaks. Our analysis is based on archival ultraviolet and optical spectroscopy of eight metal-poor stars with Se (Z = 34) or Te (Z = 52) detections, whose r-process enhancement varies by more than a factor of 30 (-0.22 ≤ [Eu/Fe] ≤ +1.32). We calculate ratios among the abundances of Se, Sr through Mo (38 ≤ Z ≤ 42), and Te. These benchmarks may offer a new empirical alternative to the predicted solar system r-process residual pattern. The Te abundances in these stars correlate more closely with the lighter r-process elements than the heavier ones, contradicting and superseding previous findings. The small star-to-star dispersion among the abundances of Se, Sr, Y, Zr, Nb, Mo, and Te (≤0.13 dex, or 26%) matches that observed among the abundances of the lanthanides and third r-process-peak elements. The concept of r-process universality that is recognized among the lanthanide and third-peak elements in r-process-enhanced stars may also apply to Se, Sr, Y, Zr, Nb, Mo, and Te, provided the overall abundances of the lighter r-process elements are scaled independently of the heavier ones. The abundance behavior of the elements Ru through Sn (44 ≤ Z ≤ 50) requires further study. Our results suggest that at least one relatively common source in the early Universe produced a consistent abundance pattern among some elements spanning the first and second r-process peaks. * Based on archival observations made with the NASA/ESA Hubble Space Telescope (program GO-7348, program GO-8342, program GO-9455, program GO-14161, and program GO-14672) and observations collected from the Keck Observatory Archive (program U25H).

Keywords: nucleosynthesis; r-process; stellar abundances; ultraviolet astronomy
Persistent Emission Properties of SGR J1935+2154 during Its 2020 Active Episode

We present detailed spectral and temporal characteristics of the persistent X-ray emission of SGR J1935+2154 based on our XMM-Newton and Chandra observations taken in the aftermath of its 2020 April burst storm, during which hundreds of energetic X-ray bursts were emitted, including one associated with an extraordinary fast radio burst. We clearly detect the pulsed X-ray emission in the XMM-Newton data. An average spin-down rate of 1.6 × 10-11 s s-1 is obtained using our spin period measurement combined with three earlier values reported from the same active episode. Our investigations of the XMM-Newton and Chandra spectra with a variety of phenomenological and physically motivated models concluded that the magnetic field topology of SGR J1935+2154 is most likely highly nondipolar. The spectral models indicate that surface field strengths in somewhat localized regions substantially exceed the polar value of 4.4 × 1014 G inferred from a spin-down torque associated with a rotating magnetic dipole.

Keywords: magnetars; neutron stars; soft gamma-ray repeaters
Galactic Cosmic-Ray Background Deduction Method Based on Empirical Mode Decomposition

The inversion of the relative content and spatial distribution characteristics of radioactive elements on the lunar surface, as inferred from gamma-ray spectrometer data, holds substantial importance for forecasting lunar surface compositions. During the inversion process of gamma-ray spectrometer data, galactic cosmic rays (GCRs) have engendered disruptive "stripe noise" in the distribution map of radioactive elements. This phenomenon significantly hampers the interpretation of data and the extraction of lunar surface information. The proposed approach adeptly separates the influence of GCR from the counting rate distribution map of the lunar surface by employing the empirical mode decomposition method. It achieves the deduction of GCR background from the Chang'e-2 gamma-ray spectrometer data with precision. Compared to conventional GCR background deduction methods employed by predecessors, this model does not need to process a large amount of original data repeatedly. Moreover, it achieves an accurate deduction of the GCR background without intricate formulaic derivations. The procedural simplicity and reduced time investment make this approach significantly superior. * Released in 2024.

Keywords: gamma-rays; galactic cosmic rays
Measuring the Ellipticity of M87* Images

The Event Horizon Telescope (EHT) images of the supermassive black hole at the center of the galaxy M87 provided the first image of the accretion environment on horizon scales. General relativity (GR) predicts that the image of the shadow should be nearly circular given the inclination angle of the black hole M87*. A robust detection of ellipticity in image reconstructions of M87* could signal new gravitational physics on horizon scales. Here we analyze whether the imaging parameters used in EHT analyses are sensitive to ring ellipticity, and measure the constraints on the ellipticity of M87*. We find that the top set is unable to recover ellipticity. Even for simple geometric models, the true ellipticity is biased low, preferring circular rings. Therefore, to place a constraint on the ellipticity of M87*, we measure the ellipticity of 550 synthetic data sets produced from GRMHD simulations. We find that images with intrinsic axis ratios of 2:1 are consistent with the ellipticity seen from EHT image reconstructions.

Keywords: black hole physics; submillimeter astronomy; astronomy data analysis; astronomy image processing
Identifying Lensed Quasars and Measuring Their Time Delays from Unresolved Light Curves

Identifying multiply imaged quasars is challenging owing to their low density in the sky and the limited angular resolution of wide-field surveys. We show that multiply imaged quasars can be identified using unresolved light curves, without assuming a light-curve template or any prior information. After describing our method, we show, using simulations, that it can attain high precision and recall when we consider high-quality data with negligible noise well below the variability of the light curves. As the noise level increases to that of the Zwicky Transient Facility telescope, we find that precision can remain close to 100% while recall drops to ~60%. We also consider some examples from Time Delay Challenge 1 and demonstrate that the time delays can be accurately recovered from the joint light-curve data in realistic observational scenarios. We further demonstrate our method by applying it to publicly available COSMOGRAIL data of the observed lensed quasar SDSS J1226-0006. We identify the system as a lensed quasar based on the unresolved light curve and estimate a time delay in good agreement with the one measured by COSMOGRAIL using the individual image light curves. The technique shows great potential to identify lensed quasars in wide-field imaging surveys, especially the soon-to-be-commissioned Vera Rubin Observatory.

Keywords: time series analysis
Filamentary Dust Polarization and the Morphology of Neutral Hydrogen Structures

Filamentary structures in neutral hydrogen (H I) emission are well aligned with the interstellar magnetic field, so H I emission morphology can be used to construct templates that strongly correlate with measurements of polarized thermal dust emission. We explore how the quantification of filament morphology affects this correlation. We introduce a new implementation of the Rolling Hough Transform (RHT) using spherical harmonic convolutions, which enables efficient quantification of filamentary structure on the sphere. We use this Spherical RHT algorithm along with a Hessian-based method to construct H I-based polarization templates. We discuss improvements to each algorithm relative to similar implementations in the literature and compare their outputs. By exploring the parameter space of filament morphologies with the Spherical RHT, we find that the most informative H I structures for modeling the magnetic field structure are the thinnest resolved filaments. For this reason, we find a ~10% enhancement in the B-mode correlation with polarized dust emission with higher-resolution H I observations. We demonstrate that certain interstellar morphologies can produce parity-violating signatures, i.e., nonzero TB and EB, even under the assumption that filaments are locally aligned with the magnetic field. Finally, we demonstrate that B modes from interstellar dust filaments are mostly affected by the topology of the filaments with respect to one another and their relative polarized intensities, whereas E modes are mostly sensitive to the shapes of individual filaments.

Keywords: interstellar dust; interstellar filaments; milky way magnetic fields; neutral hydrogen clouds; cosmic microwave background radiation; algorithms; interstellar magnetic fields; interstellar medium; interstellar atomic gas; interstellar phases; galaxy magnetic fields; magnetic fields
Constraining the Physical Properties of Stellar Coronal Mass Ejections with Coronal Dimming: Application to Far-ultraviolet Data of ϵ Eridani

Coronal mass ejections (CMEs) are a prominent contributor to solar system space weather and might have impacted the Sun's early angular momentum evolution. A signal diagnostic of CMEs on the Sun is coronal dimming: a drop in coronal emission, tied to the mass of the CME, that is the direct result of removing emitting plasma from the corona. We present the results of a coronal dimming analysis of Fe XII 1349 Å and Fe XXI 1354 Å emission from ϵ Eridani (ϵ Eri), a young K2 dwarf, with archival far-ultraviolet observations by the Hubble Space Telescope's Cosmic Origins Spectrograph. Following a flare in 2015 February, ϵ Eri's Fe XXI emission declined by 81 ± 5%. Although enticing, a scant 3.8 minutes of preflare observations allows for the possibility that the Fe XXI decline was the decay of an earlier, unseen flare. Dimming nondetections following each of three prominent flares constrain the possible mass of ejected Fe XII-emitting (1 MK) plasma to less than a few × 1015 g. This implies that CMEs ejecting this much or more 1 MK plasma occur less than a few times per day on ϵ Eri. On the Sun, 1015 g CMEs occur once every few days. For ϵ Eri, the mass-loss rate due to CME-ejected 1 MK plasma could be < 0.6 ${\dot{M}}_{\odot }$ , well below the star's estimated 30 ${\dot{M}}_{\odot }$ mass-loss rate (wind + CMEs). The order-of-magnitude formalism we developed for these mass estimates can be broadly applied to coronal dimming observations of any star.

Keywords: stellar coronal mass ejections; solar coronal mass ejections; space weather; ultraviolet astronomy; stellar mass loss
Ejected Particles after Impact Splash on Mars: Aggregates and Aerodynamics

Our earlier laboratory measurements showed that low-velocity sand impacts release fine <5 μm dust from a Martian simulant soil. This dust will become airborne in the Martian atmosphere. Here, we extend this study by measuring aerodynamic properties of ejecta and characterizing deviations from the behavior of spherical, monolithic grains. We observe the settling of particles emitted as part of an impact splash. The sizes (20 to 280 μm) and sedimentation velocities (0.1 to 0.8 m s-1) of the particles are deduced from high-speed videos while the particles sediment under low ambient pressure of about 1 mbar. The particles regularly settle slower than expected, down to a factor of about 0.3. Using optical microscopy, the shape of the captured particles is characterized by simple axis ratios (longest/smallest), which show that the vast majority of particles are irregular but typically not too elongated, with axis ratios below 2 on average. Electron microscopy further reveals that the particles are typically porous aggregates, which is the most likely reason for the reduction of the sedimentation velocity. Due to the reduced bulk density, aggregates up to 10 μm in diameter should regularly be a part of the dust in the Martian atmosphere.

Keywords: mars; planetary atmospheres
Rotational Modulation of Spectroscopic Zeeman Signatures in Low-mass Stars

Accurate tracers of the stellar magnetic field and rotation are cornerstones for the study of M dwarfs and for reliable detection and characterization of their exoplanetary companions. Such measurements are particularly challenging for old, slowly rotating, fully convective M dwarfs. To explore the use of new activity and rotation tracers, we examined multiyear near-infrared (NIR) spectroscopic monitoring of two such stars-GJ 699 (Barnard's Star) and Teegarden's Star-carried out with the Habitable-zone Planet Finder spectrograph. We detected periodic variations in absorption line widths across the stellar spectrum, with higher amplitudes toward longer wavelengths. We also detected similar variations in the strength and width of the 12435.67 Å neutral potassium (K I) line, a known tracer of the photospheric magnetic field. Attributing these variations to rotational modulation, we confirm the known 145 ± 15 day rotation period of GJ 699, and measure the rotation period of Teegarden's Star to be 99.6 ± 1.4 days. Based on simulations of the K I line and the wavelength dependence of the line-width signal, we argue that the observed signals are consistent with varying photospheric magnetic fields and the associated Zeeman effect. These results highlight the value of detailed line profile measurements in the NIR for diagnosing stellar magnetic field variability. Such measurements may be pivotal for disentangling activity and exoplanet-related signals in spectroscopic monitoring of old, low-mass stars.

Keywords: stellar rotation; m dwarf stars; stellar activity; stellar spectral lines; near infrared astronomy
Laboratory Study of Rate Coefficients for H2:H2 Inelastic Collisions between 295 and 20 K

A laboratory study of state-to-state rate coefficients (STS rates) for H2:H2 inelastic collisions in the V = 0 state is reported. The study, which spans the 295-20 K thermal range, is based on the use of a kinetic master equation. It describes the time-space evolution of populations of H2 rotational levels as induced by inelastic collisions. It is applied here to a supersonic jet of natural H2. This medium bears a large amount of relevant data that allows for the establishment of best values and confidence margins for the dominant STS rates of H2:H2 inelastic collisions on an experimental basis. The primary experimental data derived from the supersonic jet are the local number density, the populations of the H2 rotational levels, and their gradients along the jet by means of high-sensitivity Raman spectroscopy with superb space resolution. First, two sets of theoretical STS rates from the literature have been tested against the experiment. The set that shows a better agreement with the experiment has then been scaled to derive an improved set of experiment-scaled STS rates (ES rates). They allow the reproduction of more than 50 experimental population gradient data within a standard deviation <1.4% along the 295-20 K thermal range. The estimated uncertainty for the ES rates ranges from ≈3% near 300 K to ≈6% near 20 K. ES rates and uncertainties for H2:H2 ground-state inelastic collisions between 300 and 20 K are presented in machine-readable format. Other (incomplete) sets of theoretical rates from the literature are discussed.

Keywords: astronomy databases; laboratory astrophysics; molecular spectroscopy
Orbital Stability and Secular Dynamics of the Proxima Centauri Planetary System

The two innermost planets of the Proxima Centauri system are separated by just 0.02 au, inducing strong gravitational interactions between them. We assess this interaction by leveraging fast orbital stability indicators and find that orbital stability is very likely if the initial eccentricities of planets b and d are less than ∼0.2, but cannot confirm stability at larger values. We find that stability is not strongly affected by the true masses of the planets or by the distant planet c. However, mutual inclinations between 95° and 142° often result in unstable motion. We further explore the long-term evolution of the orbits in these stable regions of parameter space and find that circularization can take over 5 Gyr. This tidal evolution could support surface energy fluxes in excess of 1 W m‑2 for over 1 Gyr, possibly affecting planet b's habitability.

Keywords: astrobiology; exoplanet dynamics; n-body simulations
The Role of Sulfate in Cation Exchange Reactions: Applications to Clay-Brine Interactions on Mars

Phyllosilicates on Mars record a complex history of aqueous activity, including at Gale crater and Meridiani Planum, where stratigraphic differences in clay mineralogy have been recorded in outcrops that also contain calcium sulfate minerals. Thus, characterizing associations between phyllosilicates and calcium sulfates may provide constraints that are useful for constraining the geochemical environments that formed these outcrops. Previous studies have documented calcium sulfate precipitation as a result of clay-salt-atmospheric H2O interactions, but the compositions of brines throughout Mars' history would have depended on the volume of water available on the Martian surface. Variations in brine composition influence the type and extent of reactions between the brines and the minerals that they come in contact with. To better understand how clay-brine interactions affected near-surface mineral assemblages on Mars, we performed two sets of experiments. The first set of experiments examined the effect of differing total brine concentrations and the second set explored variations in Na+ and SO4 2- concentrations independently. The results of this study show that gypsum readily forms due to cation exchange between montmorillonite and Na2SO4 brines of any concentration, but only near-saturated MgSO4 brines produced gypsum, and these also produced higher quantities of epsomite. Additionally, we found that the amount of gypsum produced from clay-Na2SO4 brine reactions is more strongly influenced by SO4 2- than Na+ or Cl- concentrations. Understanding how rapidly gypsum forms as a product of clay-brine interactions, as well as the influence of SO4 2- on cation exchange, will aid interpretations of sediments and environments that are observed on Mars.

Keywords: mars