adsabs/SciX_UAT_keywords huggingface dataset:
Intermittency in the Expanding Solar Wind: Observations from Parker Solar Probe (0.16 au), Helios 1 (0.3-1 au), and Voyager 1 (1-10 au)

We examine statistics of magnetic-field vector components to explore how intermittency evolves from near-Sun plasma to radial distances as large as 10 au. Statistics entering the analysis include autocorrelation, magnetic structure functions of the order of n (SF n ), and scale-dependent kurtosis (SDK), each grouped in ranges of heliocentric distance. The Goddard Space Flight Center Space Physics Data Facility provides magnetic-field measurements for resolutions of 6.8 ms for Parker Solar Probe, 6 s for Helios, and 1.92 s for Voyager 1. We compute SF2 to determine the scales encompassing the inertial range and examine SDK to investigate the degree of non-Gaussianity. Autocorrelations are used to resolve correlation scales. Correlation lengths and ion inertial lengths provide an estimate of effective Reynolds number (Re). Variation in Re allows us to examine for the first time the relationship between SDK and Re in an interplanetary plasma. A conclusion from this observed relationship is that regions with lower Re at a fixed physical scale have on average lower kurtosis, implying less intermittent behavior. Kolmogorov refined similarity hypothesis is applied to magnetic SF n and kurtosis to calculate intermittency parameters and fractal scaling in the inertial range. A refined Voyager 1 magnetic-field data set is generated.

Keywords: solar wind; interplanetary magnetic fields; space plasmas; interplanetary turbulence; interplanetary physics
Explosive Nucleosynthesis in Near-Chandrasekhar Mass White Dwarf Models for Type Iax Supernovae: Dependence on Model Parameters

The recently observed diversity of Type Ia supernovae (SNe Ia) has motivated us to conduct the theoretical modeling of SNe Ia for a wide parameter range. In particular, the origin of Type Iax supernovae (SNe Iax) has been obscure. Following our earlier work on the parameter dependence of SN Ia models, we focus on SNe Iax in the present study. For a model of SNe Iax, we adopt the currently leading model of pure turbulent deflagration of near-Chandrasekhar mass C+O white dwarfs (WDs). We carry out two-dimensional hydrodynamical simulations of the propagation of the deflagration wave, which leaves a small WD remnant behind and ejects nucleosynthesis materials. We show how the explosion properties, such as nucleosynthesis and explosion energy, depend on the model parameters, such as central densities and compositions of the WDs (including the hybrid WDs), turbulent flame prescription, and initial flame geometry. We extract the associated observables in our models and compare with the recently discovered low-mass WDs with unusual surface abundance patterns and the abundance patterns of some SN remnants. We provide the nucleosynthesis yield tables for applications to stellar archeology and galactic chemical evolution. Our results are compared with the representative models in the literature.

Keywords: explosive nucleosynthesis; type ia supernovae; hydrodynamical simulations; white dwarf stars; supernova remnants
A Lack of Variability between Repeated Spitzer Phase Curves of WASP-43b

Though the global atmospheres of hot Jupiters have been extensively studied using phase curve observations, the level of time variability in these data is not well constrained. To investigate possible time variability in a planetary phase curve, we observed two full-orbit phase curves of the hot Jupiter WASP-43b at 4.5 μm using the Spitzer Space Telescope, and reanalyzed a previous 4.5 μm phase curve from Stevenson et al. We find no significant time variability between these three phase curves, which span timescales of weeks to years. The three observations are best fit by a single phase curve with an eclipse depth of 3907 ± 85 ppm, a dayside-integrated brightness temperature of 1479 ± 13 K, a nightside integrated brightness temperature of 755 ± 46 K, and an eastward-shifted peak of 10.°4 ± 1.°8. To model our observations, we performed 3D general circulation model simulations of WASP-43b with simple cloud models of various vertical extents. In comparing these simulations to our observations, we find that WASP-43b likely has a cloudy nightside that transitions to a relatively cloud-free dayside. We estimate that any change in WASP-43b's vertical cloud thickness of more than three pressure scale heights is inconsistent with our observed upper limit on variation. These observations, therefore, indicate that WASP-43b's clouds are stable in their vertical and spatial extent over timescales up to several years. These results strongly suggest that atmospheric properties derived from previous, single Spitzer phase curve observations of hot Jupiters likely show us the equilibrium properties of these atmospheres.

Keywords: exoplanets; hot jupiters; exoplanet atmospheres; exoplanet atmospheric variability; observational astronomy
A Six-planet Resonance Chain in K2-138?

The K2-138 system hosts six planets and presents an interesting case study due to its distinctive dynamical structure. Its five inner planets are near a chain of 3/2 two-body mean-motion resonances, while the outermost body (planet g) is significantly detached, having a mean-motion ratio of n f/n g ~ 3.3 with its closest neighbor. We show that the orbit of m g is actually consistent with the first-order three-planet resonance (3P-MMR) characterized by the relation 2n e - 4n f + 3n g = 0 and is the first time a pure first-order 3P-MMR has been found in a multiplanet system and tied to its current dynamical structure. Adequate values for the masses allow one to trace the dynamical history of the system from an initial capture in a six-planet chain (with n f/n g in a 3/1 resonance) up to its current configuration due to tidal interactions over the age of the star. The increase in resonance offset with semimajor axis, as well as its large value for n f/n g, can be explained by the slopes of the pure three-planet resonances in the mean-motion ratio plane. The triplets slide outward over these curves when the innermost pair is pulled apart by tidal effects, in a pantograph-like manner. The capture into the 3P-MMR is found to be surprisingly robust given similar masses for m g and m f, and it is possible that the same effect may also be found in other compact planetary systems.

Keywords: exoplanets; orbital resonances
Metastable Helium Absorptions with 3D Hydrodynamics and Self-consistent Photochemistry. I. WASP-69b, Dimensionality, X-Ray and UV Flux Level, Spectral Types, and Flares

The metastable helium (He*) lines near 10830 Å are ideal probes of atmospheric erosion-a common phenomenon of close-in exoplanet evolution. A handful of exoplanet observations yielded well-resolved He* absorption features in transits, yet they were mostly analyzed with 1D isothermal models prescribing mass-loss rates. This work devises 3D hydrodynamics coevolved with ray-tracing radiative transfer and nonequilibrium thermochemistry. Starting from the observed stellar/planetary properties with reasonable assumptions about the host's high-energy irradiation, we predict from first principles the mass-loss rate, the temperature and ionization profiles, and 3D outflow kinematics. Our simulations well reproduce the observed He* line profiles and light curves of WASP-69b. We further investigate the dependence of He* observables on simulation conditions and host radiation. The key findings are as follows: (1) Simulations reveal a photoevaporative outflow (~0.55 M⊕ Gyr-1 ≃ 1011 g s-1) for WASP-69b without a prominent comet-like tail, consistent with the symmetric transit shape. (2) 3D simulations are mandatory for hydrodynamic features, including Coriolis force, advection, and kinematic line broadening. (3) EUV (>13.6 eV) photons dominate photoevaporative outflows and populate He* via recombination; FUV is also detrimental by destroying He*; X-ray plays a secondary role. (4) K stars hit the sweet spot of EUV/far-UV balance for He* line observation, while G and M stars are also worthy targets. (5) Stellar flares create characteristic responses in the He* line profiles.

Keywords: exoplanet atmospheres; exoplanet evolution; exoplanet astronomy; hydrodynamical simulations; astronomical simulations; hydrodynamics; astrochemistry
Vetting the "Lobster" Diagram: Searching for Unseen Companions in Wide Binaries Using NASA Space Exoplanet Missions

Over the past decade, the number of known wide-binary systems has expanded exponentially, thanks to the release of data from the Gaia Mission. Some of these wide-binary systems are actually higher-order multiples, where one of the components is an unresolved binary itself. One way to search for these systems is by identifying the overluminous components in the systems. In this study, we examine 4947 K+K wide-binary pairs from the SUPERWIDE catalog, and quantify the relative colors and luminosities of the components to find evidence for additional unresolved companions. The method is best illustrated in a graph that we call the "Lobster" diagram. To confirm that the identified overluminous components are close binary systems, we cross-match our wide binaries with the TESS, K2, and Kepler archives, and search for signs of eclipses and fast stellar rotation modulation in the light curves. We find that 78.9% ± 20.7% of the wide binaries that contain an eclipsing system are identified as overluminous in the "Lobster" diagram, and that 73.5% ± 12.4% of the wide binaries that contain a component showing fast rotation (P < 5 days) also show an overluminous component. From these results, we calculate a revised lower limit on the higher-order multiplicity fraction for K+K wide binaries of 40.0% ± 1.6%. We also examine the higher-order multiplicity fraction as a function of projected physical separation and metallicity. The fraction is unusually constant as a function of projected physical separation, while we see no statistically significant evidence that the fraction varies with metallicity.

Keywords: multiple stars; eclipsing binary stars; visual binary stars; low mass stars; stellar rotation
Estimators of Bolometric Luminosity and Black Hole Mass with Mid-infrared Continuum Luminosities for Dust-obscured Quasars: Prevalence of Dust-obscured SDSS Quasars

We present bolometric luminosity (L bol) and black hole (BH) mass (M BH) estimators based on mid-infrared (MIR) continuum luminosity (hereafter, L MIR) that are measured from infrared (IR) photometric data. The L MIR-based estimators are relatively immune from dust extinction effects, hence they can be used for dust-obscured quasars. To derive the L bol and M BH estimators, we use unobscured quasars selected from the Sloan Digital Sky Survey (SDSS) quasar catalog, which have wide ranges of L bol (1044.62-1046.16 erg s-1) and M BH (107.14-109.69 M ⊙). We find empirical relations between (i) continuum luminosity at 5100 Å (hereafter, L5100) and L MIR; (ii) L bol and L MIR. Using these relations, we derive the L MIR-based L bol and M BH estimators. We find that our estimators allow the determination of L bol and M BH at an accuracy of ~0.2 dex against the fiducial estimates based on the optical properties of the unobscured quasars. We apply the L MIR-based estimators to SDSS quasars at z ≲ 0.5 including obscured ones. The ratios of L bol from the L MIR-based estimators to those from the optical luminosity-based estimators become larger with the amount of the dust extinction, and a non-negligible fraction (~15%) of the SDSS quasars exhibits ratios greater than 1.5. This result suggests that dust extinction can significantly affect physical parameter derivations even for SDSS quasars, and that dust extinction needs to be carefully taken into account when deriving quasar properties.

Keywords: supermassive black holes; quasars; active galactic nuclei; infrared astronomy; galaxy evolution
Solar-cycle and Latitude Variations in the Internetwork Magnetism

The importance of the quiet-Sun magnetism is that it is always there to a greater or lesser extent, being a constant provider of energy, independently of the solar cycle phase. The open questions about the quiet-Sun magnetism include those related to its origin. Most people claim that the local dynamo action is the mechanism that causes it. This fact would imply that the quiet-Sun magnetism is nearly the same at any location over the solar surface and at any time. Many works claim that the quiet Sun does not have any variation at all, although a few of them raise doubt on this claim and find mild evidence of a cyclic variation in the the quiet-Sun magnetism. In this work, we detect clear variations in the internetwork magnetism both with latitude and solar cycle. In terms of latitude, we find an increase in the averaged magnetic fields toward the solar poles. We also find long-term variations in the averaged magnetic field at the disk center and solar poles, and both variations are almost anticorrelated. These findings do not support the idea that the local dynamo action is the unique factory of the quiet-Sun magnetism.

Keywords: quiet sun; solar cycle; solar dynamo; solar magnetic fields; solar physics
The Effect of Thermal Pressure on Collisionless Magnetic Reconnection Rate

Modeling collisionless magnetic reconnection rate is an outstanding challenge in basic plasma physics research. While the seemingly universal rate of an order ${ \mathcal O }(0.1)$ is often reported in the low-β regime, it is not clear how reconnection rate scales with a higher plasma β. Due to the complexity of the pressure tensor, the available reconnection rate model is limited to the low plasma-β regime, where the thermal pressure is arguably negligible. However, the thermal pressure effect becomes important when $\beta \gtrsim { \mathcal O }(1)$ . Using first-principle kinetic simulations, we show that both the reconnection rate and outflow speed drop as β gets larger. A simple analytical framework is derived to take account of the self-generated pressure anisotropy and pressure gradient in the force balance around the diffusion region, explaining the varying trend of key quantities and reconnection rates in these simulations with different β. The predicted scaling of the normalized reconnection rate is $\simeq { \mathcal O }(0.1/\sqrt{{\beta }_{i0}})$ in the high-β limit, where βi0 is the ion β of the inflow plasma.

Keywords: plasma astrophysics; plasma physics; heliosphere; intergalactic medium; galactic center
Spacetime Tomography Using the Event Horizon Telescope

We have now entered a new era of high-resolution imaging astronomy with the beginning of the Event Horizon Telescope (EHT). The EHT can resolve the dynamics of matter in the immediate vicinity around black holes at and below the horizon scale. One of the candidate black holes, Sagittarius A*, flares 1-4 times a day depending on the wavelength. A possible interpretation of these flares could be hotspots generated through magnetic-reconnection events in the accretion flow. In this paper, we construct a semi-analytical model for hotspots that includes the effects of shearing as a spot moves along the accretion flow. We then explore the ability of the EHT to recover these hotspots. Even including significant systematic uncertainties, such as thermal noise, diffractive scattering, and background emission due to an accretion disk, we were able to recover the hotspots and spacetime structure to sub-percent precision. Moreover, by observing multiple flaring events we show how the EHT could be used to tomographically map spacetime. This provides new avenues for testing relativistic fluid dynamics and general relativity near the event horizon of supermassive black holes.

Keywords: gravitation; general relativity; black hole physics; accretion; galactic center; radiative transfer
TESS Detection of Rotation in the A1V Star α Lacertae

The A1V star α Lacertae was observed by TESS in 2019 September and October. The short-cadence photometry reveals periodic variation at the 24.6 ppm level. The 0.708 day variation is consistent with rotational modulation seen in main sequence A stars, and implies an equatorial rotation velocity of 153 km s-1. With prior spectroscopic measurement of the rotational broadening of 128 km s-1, this indicates an inclination of the rotation axis of 57°. The first harmonic of this period is present in the data, along with a two non-commensurate periods of 0.763 and 0.257 day, suggesting spot modulation with different periods, perhaps indicating differential rotation with latitude. Follow-up spectroscopy and photometry of this bright (V = 3.77) star can place valuable constraints on differential rotation and spot formation and evolution in A stars.

Keywords: a stars; stellar rotation; starspots
Understanding the Duration of Solar and Stellar Flares at Various Wavelengths

Recent irradiance measurements from numerous heliophysics and astrophysics missions including Solar Dynamics Observatory (SDO), GOES, Kepler, TESS, Chandra, the X-ray Multi-Mirror Mission, and NICER have provided critical input into understanding the physics of the most powerful transient events on the Sun and magnetically active stars:solar and stellar flares. The light curves of flare events from the Sun and stars show remarkably similar shapes, typically with a sharp rise and protracted decay phase. The duration of solar and stellar flares has been found to be correlated with the intensity of the event in some wavelengths, such as white light, but not in other wavelengths, such as soft X-rays, but it is not evident why this is the case. In this study, we use a radiative hydrodynamics code to examine factors affecting the duration of flare emission at various wavelengths. The duration of a light curve depends on the temperature of the plasma, the height in the atmosphere at which the emission forms, and the relative importance of cooling due to radiation, thermal conduction, and enthalpy flux. We find that there is a clear distinction between emission that forms low in the atmosphere and responds directly to heating, and emission that forms in the corona, indirectly responding to heating-induced chromospheric evaporation, a facet of the Neupert effect. We discuss the implications of our results for a wide range of flare energies.

Keywords: stellar flares; solar flares; solar coronal loops
Additions to the Spectrum of Fe IX in the 110-200 Å Region

The spectrum of eight-times ionized iron, Fe IX, was studied in the 110-200 Å region. A low inductance vacuum spark and a 3 m grazing incidence spectrograph were used for the excitation and recording of the spectrum. Previous analyses of Fe IX have been greatly extended and partly revised. The number of known lines in the 3p 53d-3p 54f and 3p 53d-3p 43d 2 transition arrays is extended to 25 and 81, respectively. Most of the identifications of the Fe IX lines from the 3p 53d-3p 43d 2 transition array in the solar spectrum have been confirmed and several new identifications are suggested.

Keywords: atomic spectroscopy; spectroscopy; line intensities; solar extreme ultraviolet emission; solar atmosphere
Numerical Testing of Mirror Diffusion of Cosmic Rays

The tension between recent observations and theories on cosmic-ray (CR) diffusion necessitates exploration of new CR diffusion mechanisms. We perform the first numerical study on the mirror diffusion of CRs that is recently proposed by Lazarian & Xu. We demonstrate that the perpendicular superdiffusion of turbulent magnetic fields and magnetic mirroring that naturally arise in magnetohydrodynamic (MHD) turbulence are the two essential physical ingredients for the mirror diffusion to happen. In supersonic, subsonic, and incompressible MHD turbulence, with the pitch angles of CRs repeatedly crossing 90° due to the mirror reflection, we find that the mirror diffusion strongly enhances the confinement of CRs, and their pitch-angle-dependent parallel mean free path can be much smaller than the injection scale of turbulence. With the stochastic change of pitch angles due to gyroresonant scattering, CRs stochastically undergo slow mirror diffusion at relatively large pitch angles and fast scattering diffusion at smaller pitch angles, resulting in a Lévy-flight-like propagation.

Keywords: magnetohydrodynamics; cosmic rays
Heavy Positive Ion Groups in Titan's Ionosphere from Cassini Plasma Spectrometer IBS Observations

Titan's ionosphere contains a plethora of hydrocarbons and nitrile cations and anions as measured by the Ion Neutral Mass Spectrometer and Cassini Plasma Spectrometer (CAPS) on board the Cassini spacecraft. Data from the CAPS Ion Beam Spectrometer (IBS) sensor have been examined for five close encounters of Titan during 2009. The high relative velocity of Cassini with respect to the cold ions in Titan's ionosphere allows CAPS IBS to function as a mass spectrometer. Positive ion masses between 170 and 310 u/q are examined with ion mass groups identified between 170 and 275 u/q containing between 14 and 21 heavy (carbon/nitrogen/oxygen) atoms. These groups are the heaviest positive ion groups reported so far from the available in situ ion data at Titan. The ion group peaks are found to be consistent with masses associated with polycyclic aromatic compounds (PAC), including polycyclic aromatic hydrocarbon (PAH) and nitrogen-bearing polycyclic aromatic molecular ions. The ion group peak identifications are compared with previously proposed neutral PAHs and are found to be at similar masses, supporting a PAH interpretation. The spacing between the ion group peaks is also investigated, finding a spacing of 12 or 13 u/q indicating the addition of C or CH. Lastly, the occurrence of several ion groups is seen to vary across the five flybys studied, possibly relating to the varying solar radiation conditions observed across the flybys. These findings further the understanding between the low-mass ions and the high-mass negative ions, as well as with aerosol formation in Titan's atmosphere.

Keywords: planetary atmospheres; planetary science; saturnian satellites
Change of Spectral Properties of Magnetic Field Fluctuations across Different Types of Interplanetary Shocks

The interaction between interplanetary (IP) shocks and the solar wind has been studied in the past for the understanding of energy dissipation mechanisms within collisionless plasmas. Compared to the study of fast shocks, other types of IP shocks, including slow mode shocks (i.e., fast forward, fast reverse, slow forward, and slow reverse shocks) remained largely unnoticed. We analyze magnetic field fluctuations observed by the Wind spacecraft from 1995 to 2021 upstream and downstream of the IP shocks using a continuous wavelet transform. The evolution of spectral indices in the ion inertial and transition ranges and the changes in distributions of characteristic ion length scales with respect to the spectral break and proton beta are presented. We found that spectral indices in both inertial and transition ranges and the characteristic length scale distributions are statistically conserved across three types of IP shocks, suggesting that mechanisms associated with the energy dissipation are unaffected by the shocks. The results obtained for the transition range of fast reverse shocks show a larger difference between upstream and downstream plasmas and this will be further studied.

Keywords: interplanetary shocks; solar wind; interplanetary turbulence