adsabs/SciX_UAT_keywords huggingface dataset:
Variation of the Interplanetary Shocks in the Inner Heliosphere

Observations of the solar wind plasma and interplanetary magnetic field in the ecliptic plane by the Voyager 1 and 2 spacecraft are utilized to study the variation of the interplanetary shocks (with magnetosonic Mach number >1) encountered in the inner heliosphere, between ~1 and ~15 au from the Sun. The overwhelming majority (~76%) of the shocks are fast forward (FF) moving at an average shock speed (Vsh) of ~458 km s-1 away from the Sun, and only ~24% are fast reverse (FR) shocks with an average Vsh of ~323 km s-1 toward the Sun. About ~89% of the shocks are quasi-perpendicular with an average shock angle (θBn) of ~72° relative to the ambient magnetic field, and only ~11% are quasi-parallel with an average θBn of ~32°. While the interplanetary coronal mass ejections are the major (~89%) driver of the FF shocks, a significant part (~41%) of the FR shocks are associated with the corotating interaction regions. The shock occurrence rate, with a peak at the heliocentric distance (Rh) of ~5 au, exhibits a clear decrease with the increasing Rh. While the shock strength and propagation angle do not exhibit any systematic change with Rh, Vsh increases with the increasing Rh at a rate of ~11 km s-1 au-1.

Keywords: interplanetary shocks; solar coronal mass ejections; corotating streams; interplanetary magnetic fields; solar wind
Transverse Oscillation of Prominence and Filament Induced by an Extreme-ultraviolet Wave from the Far Side of the Sun

In this paper, we report our multi-angle observations of the transverse oscillation of a prominence and a filament induced by an EUV wave originating from the far side of the Sun on 2014 September 1. The prominence oscillation was simultaneously observed by both the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory spacecraft and the Extreme-UltraViolet Imager on board the Behind Solar Terrestrial Relations Observatory spacecraft. The speed of the shock traveling in interplanetary space exceeds that of the EUV wave, and the coronal dimming area experiences minimal growth. This indicates that the shock wave is driven by the CME, while the EUV wave freely propagates after the lateral motion of the CME flanks has stopped. The observed oscillation direction of the prominence, determined through three-dimensional reconstruction, further supports this point. Moreover, detailed investigation of the oscillations in the prominence and filament induced by the EUV wave reveals initial amplitudes of 16.08 and 2.15 Mm, periods of 1769 and 1863 s, damping timescales of 2640 and 1259 s, and damping ratios of 1.49 and 0.68, respectively. The radial component of the magnetic field, as derived from the prominence and filament oscillation measurements, was estimated to be 5.4 and 4.1 G, respectively. In turn, utilizing the onset times of both the prominence and filament oscillation, the average speeds of the EUV wave are determined to be 498 and 451 km s‑1, respectively.

Keywords: solar flares; solar coronal mass ejections; solar prominences
Low-amplitude Solar-like Oscillations in the K5 V Star ϵ Indi A

We have detected solar-like oscillations in the mid-K-dwarf ϵ Indi A, making it the coolest dwarf to have measured oscillations. The star is noteworthy for harboring a pair of brown dwarf companions and a Jupiter-type planet. We observed ϵ Indi A during two radial velocity campaigns, using the high-resolution spectrographs HARPS (2011) and UVES (2021). Weighting the time series, we computed the power spectra and established the detection of solar-like oscillations with a power excess located at 5265 ± 110 μHz—the highest frequency solar-like oscillations so far measured in any star. The measurement of the center of the power excess allows us to compute a stellar mass of 0.782 ± 0.023 M ⊙ based on scaling relations and a known radius from interferometry. We also determine the amplitude of the peak power and note that there is a slight difference between the two observing campaigns, indicating a varying activity level. Overall, this work confirms that low-amplitude solar-like oscillations can be detected in mid-K-type stars in radial velocity measurements obtained with high-precision spectrographs.

Keywords: asteroseismology; radial velocity; k dwarf stars
Transient Formation of C2 and CN in the Near-maximum Phase of Nova Cas 2020(=V1391 Cas)

Nova Cas 2020 was a second example of a classical nova forming both C2 and CN molecules during its near-maximum phase. The formation C2 and CN is indicative of the carbon-rich (C/O > 1) gas envelope of the nova. Our low-resolution spectroscopic observations in the optical from UT 2020 July 31 to August 19 revealed the appearance and the disappearance of the molecular absorption bands of C2 and CN in Nova Cas 2020. These molecules were present during ∼3 days only. Based on analysis of the C2 Swan band profiles, C2 (and probably CN also) formed at ∼5000 K in the nova envelope (see ∼8000 K for typical novae at their visual brightness maxima). Spectral evolution and the formation conditions of the molecules are similar to those of V2676 Oph, which is the first example of a C2/CN-forming nova. We predict that a late-phase grain formation episode similar to that seen in V2676 Oph will occur in Nova Cas 2020.

Keywords: classical novae; slow novae; dq herculis stars
Automated Driving for Global Nonpotential Simulations of the Solar Corona

We describe a new automated technique for active region emergence in coronal magnetic field models, based on the inversion of the electric field locally from a single line-of-sight magnetogram for each region. The technique preserves the arbitrary shapes of magnetic field distribution associated with individual active regions and incorporates emerging magnetic helicity (twist) in a parametrized manner through a noninductive electric field component. We test the technique with global magnetofrictional simulations of the coronal magnetic field during Solar Cycle 24 Maximum from 2011 June 1 to 2011 December 31. The active regions are determined in a fully automated and objective way using Spaceweather HMI Active Region Patch (SHARP) data. Our primary aim is to constrain two free parameters in the emergence algorithm: the duration of emergence and the twist parameter for each individual active region. While the duration has a limited effect on the resulting coronal magnetic field, changing the sign and amplitude of the twist parameters profoundly influences the amount of nonpotentiality generated in the global coronal magnetic field. We explore the possibility of constraining both the magnitude and sign of the twist parameter using estimates of the current helicity derived from vector magnetograms and supplied in the SHARP metadata for each region. Using the observed sign of twist for each region reduces the overall nonpotentiality in the corona, highlighting the importance of scatter in the emerging active region helicities.

Keywords: solar magnetic fields; solar surface; solar atmosphere; active solar corona
The Quest for the Missing Dust. II. Two Orders of Magnitude of Evolution in the Dust-to-gas Ratio Resolved within Local Group Galaxies

We explore evolution in the dust-to-gas ratio with density within four well-resolved Local Group galaxies-the LMC, SMC, M31, and M33. We do this using new Herschel maps, which restore extended emission that was missed by previous Herschel reductions. Combining this sensitivity to diffuse dust emission with excellent physical resolution allows us to probe the dust-to-gas ratio across 2.5 orders of magnitude in interstellar medium (ISM) surface density. We find a significant increase in the dust-to-gas ratio with density, with the dust-to-gas ratio varying within each galaxy by up to a factor 22.4, as density changes. We explore several possible reasons for this, and our favored explanation is that it is being driven by dust grain growth in denser regions of the ISM. We find that the evolution of the dust-to-gas ratio with ISM surface density is very similar between M31 and M33, despite their large differences in mass, metallicity, and star formation rate; conversely, we find M33 and the LMC to have very different dust-to-gas evolution profiles, despite their close similarity in those properties. Our dust-to-gas ratios address previous disagreement between UV- and far-IR-based dust-to-gas estimates for the Magellanic Clouds, removing the disagreement for the LMC, and considerably reducing it for the SMC-with our new dust-to-gas measurements being factors of 2.4 and 2.0 greater than the previous far-IR estimates, respectively. We also observe that the dust-to-gas ratio appears to fall at the highest densities for the LMC, M31, and M33; this is unlikely to be an actual physical phenomenon, and we posit that it may be due to a combined effect of dark gas, and changing dust mass opacity.

Keywords: dwarf galaxies; local group; interstellar dust; far infrared astronomy; submillimeter astronomy
Correction to the Photometric Colors of Gaia Early Data Release 3

In this work, we use the spectroscopy-based stellar color regression method with ∼0.7 million common stars between LAMOST DR7 and Gaia EDR3 to acquire color corrections in G - GRP and GBP - GRP. A sub-millimagnitude precision is achieved. Our results demonstrate that improvements in the calibration process of the EDR3 have removed the color term in GBP - GRP and eliminated the discontinuity caused by the changes of instrument configurations to a great extent. However, modest systematic trends with G magnitude are still detected. The corresponding color correction terms as a function of G are provided for 9.5 mag < G < 17.5 mag and compared with other determinations. We conclude that the corrections given in this work are particularly suited for cases where the color-color investigations are required, while for color-magnitude investigations other corrections may be better owing to systematics with reddening. Possible applications of our results are discussed.

Keywords: stellar photometry; astronomy data analysis; fundamental parameters of stars
Phase Separation in Ultramassive White Dwarfs

Ultramassive white dwarfs are extreme endpoints of stellar evolution. Recent findings, such as a missing multi-Gyr cooling delay for a number of ultramassive white dwarfs and a white dwarf with a quasi-Chandrasekhar mass, motivate a better understanding of their evolution. A key process still subject to important uncertainties is the crystallization of their dense cores, which are generally assumed to be constituted of 16O, 20Ne, and a mixture of several trace elements (most notably 23Na and 24Mg). In this work, we use our recently developed Clapeyron integration technique to compute accurate phase diagrams of three-component mixtures relevant to the modeling of O/Ne ultramassive white dwarfs. We show that, unlike the phase separation of 22Ne impurities in C/O cores, the phase separation of 23Na impurities in O/Ne white dwarfs cannot lead to the enrichment of their cores in 23Na via a distillation process. This severely limits the prospect of transporting large quantities of 23Na toward the center of the star, as needed in the white dwarf core-collapse mechanism recently proposed by Caiazzo et al. We also show that despite representing ≈10% of the ionic mixture, 23Na and 24Mg impurities only have a negligible impact on the O/Ne phase diagram, and the two-component O/Ne phase diagram can be safely used in white dwarf evolution codes. We provide analytic fits to our high-accuracy O/Ne phase diagram for implementation in white dwarf models.

Keywords: degenerate matter; plasma physics; stellar evolution; stellar interiors; white dwarf stars
ALMA Observations of Young Eruptive Stars: Continuum Disk Sizes and Molecular Outflows

We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations of four young, eruptive star-disk systems at 0"4 resolution: two FUors (V582 Aur and V900 Mon), one EXor (UZ Tau E), and one source with an ambiguous FU/EXor classification (GM Cha). The disks around GM Cha, V900 Mon, and UZ Tau E are resolved. These observations increase the sample of FU/EXors observed at subarcsecond resolution by 15%. The disk sizes and masses of FU/EXors objects observed by ALMA so far suggest that FUor disks are more massive than Class 0/I disks in Orion and Class II disks in Lupus of similar size. EXor disks in contrast do not seem to be distinguishable from these two populations. We reach similar conclusions when comparing the FU/EXor sample to the Class I and Class II disks in Ophiuchus. FUor disks around binaries are host to more compact disks than those in single-star systems, similar to noneruptive young disks. We detect a wide-angle outflow around GM Cha in 12CO emission, wider than typical Class I objects and more similar to those found around some FUor objects. We use radiative transfer models to fit the continuum and line data of the well-studied disk around UZ Tau E. The line data are well described by a Keplerian disk, with no evidence of outflow activity (similar to other EXors). The detection of wide-angle outflows in FUors but not in EXors support the current picture in which FUors are more likely to represent an accretion burst in the protostellar phase (Class I), while EXors are smaller accretion events in the protoplanetary (Class II) phase.

Keywords: protoplanetary disks; star formation; stellar accretion disks
The Population III Origin of GW190521

We explore the possibility that the recently detected black hole binary (BHB) merger event GW190521 originates from the first generation of massive, metal-free, so-called Population III (Pop III) stars. Based on improved binary statistics derived from N-body simulations of Pop III star clusters, we calculate the merger rate densities of Pop III BHBs similar to GW190521, in two evolution channels: classical binary stellar evolution and dynamical hardening in high-redshift nuclear star clusters. Both channels can explain the observed rate density. However, the latter is favored by better agreement with observation and less restrictions on uncertain parameters. Our analysis also indicates that given the distinct features of the two channels, future observation of BHB mergers similar to GW190521 with third-generation gravitational wave detectors will greatly improve our knowledge of the evolution of Pop III BHBs, especially for their dynamics during cosmic structure formation.

Keywords: gravitational wave astronomy; population iii stars; early universe
The NANOGrav 15 yr Data Set: Observations and Timing of 68 Millisecond Pulsars

We present observations and timing analyses of 68 millisecond pulsars (MSPs) comprising the 15 yr data set of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). NANOGrav is a pulsar timing array (PTA) experiment that is sensitive to low-frequency gravitational waves (GWs). This is NANOGrav's fifth public data release, including both "narrowband" and "wideband" time-of-arrival (TOA) measurements and corresponding pulsar timing models. We have added 21 MSPs and extended our timing baselines by 3 yr, now spanning nearly 16 yr for some of our sources. The data were collected using the Arecibo Observatory, the Green Bank Telescope, and the Very Large Array between frequencies of 327 MHz and 3 GHz, with most sources observed approximately monthly. A number of notable methodological and procedural changes were made compared to our previous data sets. These improve the overall quality of the TOA data set and are part of the transition to new pulsar timing and PTA analysis software packages. For the first time, our data products are accompanied by a full suite of software to reproduce data reduction, analysis, and results. Our timing models include a variety of newly detected astrometric and binary pulsar parameters, including several significant improvements to pulsar mass constraints. We find that the time series of 23 pulsars contain detectable levels of red noise, 10 of which are new measurements. In this data set, we find evidence for a stochastic GW background.

Keywords: millisecond pulsars; pulsar timing method; time series analysis; pulsars; gravitational waves
The Role of Parametric Instabilities in Turbulence Generation and Proton Heating: Hybrid Simulations of Parallel-propagating Alfvén Waves

Large-amplitude Alfvén waves tend to be unstable to parametric instabilities that result in a decay process of the initial wave into different daughter waves depending upon the amplitude of the fluctuations and the plasma beta. The propagation angle with respect to the mean magnetic field of the daughter waves plays an important role in determining the type of decay. In this paper, we revisit this problem by means of multidimensional hybrid simulations. In particular, we study the decay and the subsequent nonlinear evolution of large-amplitude Alfvén waves by investigating the saturation mechanism of the instability and its final nonlinear state reached for different wave amplitudes and plasma beta conditions. As opposed to one-dimensional simulations where the Decay instability is suppressed for increasing plasma beta values, we find that the decay process in multidimensions persists at large values of the plasma beta via the filamentation/magnetosonic decay instabilities. In general, the decay process acts as a trigger both to develop a perpendicular turbulent cascade and to enhance mean field-aligned wave-particle interactions. We find indeed that the saturated state is characterized by a turbulent plasma displaying a field-aligned beam at the Alfvén speed and increased temperatures that we ascribe to the Landau resonance and pitch-angle scattering in phase space.

Keywords: solar wind; interplanetary particle acceleration; interplanetary turbulence; alfven waves; space plasmas
Tidal Inflation Reconciles Low-density Sub-Saturns with Core Accretion

While the solar system contains no planets between the sizes of Uranus and Saturn, our current exoplanet census includes several dozen such planets with well-measured masses and radii. These sub-Saturns exhibit a diversity of bulk densities, ranging from ∼0.1 to 3 g cm-3. When modeled simply as hydrogen/helium envelopes atop rocky cores, this diversity in densities translates to a diversity in planetary envelope fractions, fenv = Menv/Mp, ranging from ∼10% to ∼50%. Planets with fenv ≈ 50% pose a challenge to traditional models of giant planet formation by core-nucleated accretion, which predict the onset of runaway gas accretion when Menv ∼ Mcore. Here, we show that many of these apparent fenv ≈ 50% planets are less envelope-rich than they seem, after accounting for tidal heating. We present a new framework for modeling sub-Saturn interiors that incorporates envelope inflation due to tides, which are driven by the observed nonzero eccentricities, as well as potential obliquities. Consequently, when we apply our models to known sub-Saturns, we infer lower fenv than tides-free estimates. We present a case study of K2-19 b, a moderately eccentric sub-Saturn. Neglecting tides, K2-19 b appears to have fenv ≈ 50%, poised precariously near the runaway threshold; by including tides, however, we find fenv ≈ 10%, resolving the tension. Through a systematic analysis of 4-8 R⊕ planets, we find that most (but not all) of the similarly envelope-rich planets have more modest envelopes of fenv ≈ 10%-20%. Thus, many sub-Saturns may be understood as sub-Neptunes that have undergone significant radius inflation, rather than a separate class of objects. Tidally induced radius inflation likely plays an important role in other size classes of planets including ultra-low-density Jupiter-size planets like WASP-107 b.

Keywords: exoplanet structure; extrasolar gaseous giant planets; exoplanet atmospheres; exoplanet tides; exoplanets
The Population of Small Near-Earth Objects: Composition, Source Regions, and Rotational Properties

The study of small (<300 m) near-Earth objects (NEOs) is important because they are more closely related than larger objects to the precursors of meteorites that fall on Earth. Collisions of these bodies with Earth are also more frequent. Although such collisions cannot produce massive extinction events, they can still produce significant local damage. Here we present the results of a photometric and spectroscopic survey of small NEOs that include near-infrared spectra of 84 objects with a mean diameter of 126 m and photometric data of 59 objects with a mean diameter of 87 m. We found that S-complex asteroids are the most abundant among the NEOs, comprising ∼66% of the sample. Most asteroids in the S-complex were found to have compositions consistent with LL-chondrites. Our study revealed the existence of NEOs with spectral characteristics similar to those in the S-complex but that could be hidden within the C- or X-complex due to their weak absorption bands. We suggest that the presence of metal or shock darkening could be responsible for the attenuation of the absorption bands. These objects have been grouped into a new subclass within the S-complex called Sx-types. The dynamical modeling showed that 83% of the NEOs escaped from the ν 6 resonance, 16% from the 3:1, and just 1% from the 5:2 resonance. Lightcurves and rotational periods were derived from the photometric data. No clear trend between the axis ratio and the absolute magnitude or rotational period of the NEOs was found.

Keywords: asteroids; near-earth objects; spectroscopy; photometry
Coincident Sunyaev-Zel'dovich and Gamma-Ray Signals from Cluster Virial Shocks

Virial shocks around galaxy clusters are expected to show a cutoff in the thermal Sunyaev-Zel'dovich (SZ) signal, coincident with a leptonic ring. However, until now, leptonic virial signals have only been reported in Coma and in stacked Fermi Large Area Telescope (LAT) clusters, and an SZ virial shock signal reported only in A2319. We point out that a few clusters—presently Coma, A2319, and A2142—already show a significant ( $3.1\sigma -14\sigma $ ) sharp drop in the Planck y parameter near the virial radius, coincident with a (2.2σ-3.9σ) LAT γ-ray excess. These signatures are naturally interpreted as tracers of the virial shocks of these clusters, at joint medium to high confidence levels. The electron acceleration rates inferred from the γ-rays are consistent with previous measurements. The combined signal, along with galaxy count data, allows a separate measurement of the ∼0.5% (with a factor of ∼2 uncertainty) acceleration efficiency and of the accretion rate. Lower limits on order of a few are imposed on the shock Mach numbers.

Keywords: shocks; galaxy clusters; gamma-rays; sunyaev-zeldovich effect