adsabs/SciX_UAT_keywords huggingface dataset:
On the Relation between Kappa Distribution Functions and the Plasma Beta Parameter in the Earth's Magnetosphere: THEMIS Observations

The Earth's magnetosphere represents a natural plasma laboratory that allows us to study the behavior of particle distribution functions in the absence of Coulomb collisions, typically described by the kappa distributions. We have investigated the properties of these functions for ions and electrons in different magnetospheric regions, thereby making it possible to reveal the κ-parameters for a wide range of plasma beta (β) values (from 10-3 to 102). This was done using simultaneous ion and electron measurements from the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft spanning the years 2008-2018. It was found that for a fixed plasma β, the κ-index and core energy (Ec) of the distribution can be modeled by the power law $\kappa ={{AE}}_{c}^{\gamma }$ <!-- --> for both species, and the relation between β, κ, and Ec is much more complex than earlier reported: both A and γ exhibit systematic dependencies with β. Our results indicate that β ∼ 0.1-0.3 is a range where the plasma is more dynamic, since it is influenced by both the magnetic field and temperature fluctuations, which suggests that the transition between magnetically and kinetically dominated plasmas occurs at these values of β. For β > 1, both A and γ take nearly constant values, a feature that is especially notable for the electrons and might be related to their demagnetization. The relation between β, κ, and Ec that we present is an important result that can be used by theoretical models in the future.

Keywords: interplanetary medium; planetary magnetospheres; plasma astrophysics; plasma physics; space plasmas; magnetohydrodynamics
Bayesian Inference of Dense Matter Equation of State within Relativistic Mean Field Models Using Astrophysical Measurements

We present a Bayesian analysis to constrain the equation of state of dense nucleonic matter by exploiting the available data from symmetric nuclear matter at saturation, observations of compact X-ray sources, and the gravitational wave event GW170817. For the first time, such an analysis is performed by using a class of models, the relativistic mean field models, that allow one to consistently construct an equation of state in a wide range of densities, isospin asymmetries, and temperatures. The selected class of models contains five nuclear physics empirical parameters at saturation for which we construct the joint posterior distributions. By exploring different types of priors, we find that the equations of state with the largest evidence are the ones featuring a strong reduction of the effective mass of the nucleons in dense matter, which can be interpreted as an indication of a phase transition to a chiral symmetry restored phase. Those equations of state, in turn, predict R1.4 ∼ 12 km. Finally, we present a preliminary investigation of the effect of including Λ hyperons, showing that they appear in stars more massive than about 1.6 M⊙ and lead to radii larger than about R1.4 ∼ 14 km. Within the model explored here, the formation of such particles provides poor agreement with the constraints from GW170817.

Keywords: bayesian statistics; neutron stars; nuclear astrophysics; neutron star cores
The Merging of a Coronal Dimming and the Southern Polar Coronal Hole

We report on the merging between the southern polar coronal hole and an adjacent coronal dimming induced by a coronal mass ejection on 2022 March 18, resulting in the merged region persisting for at least 72 hr. We use remote sensing data from multiple co-observing spacecraft to understand the physical processes during this merging event. The evolution of the merger is examined using Extreme-UltraViolet (EUV) images obtained from the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory and Extreme Ultraviolet Imager, which is on board the Solar Orbiter spacecraft. The plasma dynamics are quantified using spectroscopic data obtained from the EUV Imaging Spectrometer on board Hinode. The photospheric magnetograms from the Helioseismic and Magnetic Imager are used to derive the magnetic field properties. To our knowledge, this work is the first spectroscopical analysis of the merging of two open-field structures. We find that the coronal hole and the coronal dimming become indistinguishable after the merging. The upflow speeds inside the coronal dimming become more similar to that of a coronal hole, with a mixture of plasma upflows and downflows observable after the merging. The brightening of the bright points and the appearance of coronal jets inside the merged region further imply ongoing reconnection processes. We propose that component reconnection between the coronal hole and coronal dimming fields plays an important role during this merging event because the footpoint switching resulting from the reconnection allows the coronal dimming to intrude onto the boundary of the southern polar coronal hole.

Keywords: solar corona; solar coronal mass ejections; solar coronal holes; solar magnetic reconnection; ultraviolet spectroscopy; solar extreme ultraviolet emission; solar magnetic fields; solar physics; solar coronal transients; stellar coronal dimming
Corrected SFD: A More Accurate Galactic Dust Map with Minimal Extragalactic Contamination

The widely used Milky Way dust-reddening map, the Schlegel-Finkbeiner-Davis (SFD) map, was found to contain extragalactic large-scale structure (LSS) imprints. Such contamination is inherent in maps based on infrared emission, which pick up not only Galactic dust but also the cosmic infrared background (CIB). When SFD is used for extinction correction, overcorrection occurs in a spatially correlated and redshift-dependent manner, which could impact precision cosmology using galaxy clustering, lensing, and Type Ia supernova distances. Similarly, LSS imprints in other Galactic templates can affect intensity mapping and cosmic microwave background experiments. This paper presents a generic way to remove LSS traces in Galactic maps and applies it to SFD. First, we measure descriptive summary statistics of the CIB in SFD by cross-correlating the map with spectroscopic galaxies and quasars in the Sloan Digital Sky Survey tomographically as functions of redshift and angular scale. To reconstruct the LSS on the map level, however, additional information on the phases is needed. We build a large set of 180 overcomplete, full-sky basis template maps from the density fields of over 600 million galaxies in the Wide-field Infrared Survey Explorer and find a linear combination that reproduces all of the high-dimensional tomographic two-point statistics of the CIB in SFD. After subtracting this reconstructed LSS/CIB field, the end product is a full-sky Galactic dust-reddening map that supersedes SFD, carrying all Galactic features therein, with maximally suppressed CIB. We release this new dust map dubbed CSFD-the corrected SFD-at https://idv.sinica.edu.tw/ykchiang/CSFD.html and NASA's LAMBDA archive.

Keywords: interstellar dust extinction; large-scale structure of the universe; clustering
Discovery of Year-scale Time Variability from Thermal X-Ray Emission in Tycho's Supernova Remnant

Mechanisms of particle heating are crucial to understanding the shock physics in supernova remnants (SNRs). However, there has been little information on time variabilities of thermalized particles so far. Here, we present a discovery of a gradually brightening thermal X-ray emission found in the Chandra data of Tycho's SNR obtained during 2000-2015. The emission exhibits a knot-like feature (Knot1) with a diameter of ≃0.04 pc located in the northwestern limb, where we also find localized Hα filaments in an optical image taken with the Hubble Space Telescope in 2008. The model with the solar abundance reproduces the spectra of Knot1, suggesting that Knot1 originates from the interstellar medium; this is the first detection of thermal X-ray emission from swept-up gas found in Tycho's SNR. Our spectral analysis indicates that the electron temperature of Knot1 has increased from ~0.30 to ~0.69 keV within the period between 2000 and 2015. These results lead us to ascribe the time-variable emission to a small dense clump recently heated by the forward shock at the location of Knot1. The electron-to-proton temperature ratio immediately downstream of the shock (β 0 ≡ T e /T p ) is constrained to be m e /m p ≤ β 0 ≤ 0.15 to reproduce the data, indicating the collisionless electron heating with efficiency is consistent with previous Hα observations of Tycho and other SNRs with high shock velocities.

Keywords: supernova remnants; x-ray sources; interstellar medium; interstellar thermal emission; plasma astrophysics
Detection of PAH Absorption and Determination of the Mid-infrared Diffuse Interstellar Extinction Curve from the Sight Line toward Cyg OB2-12

The sight line toward the luminous blue hypergiant Cyg OB2-12 is widely used to study interstellar dust on account of its large extinction (AV ≃ 10 mag) and the fact that this extinction appears to be dominated by dust typical of the diffuse interstellar medium. We present a new analysis of archival Infrared Space Observatory Short Wavelength Spectrometer and Spitzer IRS observations of Cyg OB2-12 using a model of the emission from the star and its stellar wind to determine the total extinction Aλ from 2.4 to 37 μm. In addition to the prominent 9.7 and 18 μm silicate features, we robustly detect absorption features associated with polycyclic aromatic hydrocarbons, including the first identification of the 7.7 μm feature in absorption. The 3.3 μm aromatic feature is found to be much broader in absorption than is typically seen in emission. The 3.4 and 6.85 μm aliphatic hydrocarbon features are observed with relative strengths that are consistent with observations of these features on sight lines toward the Galactic center. We identify and characterize more than 60 spectral lines in this wavelength range, which may be useful in constraining models of the star and its stellar wind. Based on this analysis, we present an extinction curve ${A}_{\lambda }/{A}_{2.2\mu {\rm{m}}}$ that extrapolates smoothly to determinations of the mean Galactic extinction curve at shorter wavelengths and to dust opacities inferred from emission at longer wavelengths, providing a new constraint on models of interstellar dust in the mid-infrared.

Keywords: interstellar dust; carbonaceous grains; polycyclic aromatic hydrocarbons; silicate grains; stellar winds; interstellar dust extinction
Nucleosynthesis of Binary-stripped Stars

The cosmic origin of the elements, the fundamental chemical building blocks of the universe, is still uncertain. Binary interactions play a key role in the evolution of many massive stars, yet their impact on chemical yields is poorly understood. Using the MESA stellar evolution code, we predict the chemical yields ejected in wind mass loss and the supernovae of single and binary-stripped stars. We do this with a large 162-isotope nuclear network at solar metallicity. We find that binary-stripped stars are more effective producers of the elements than single stars, due to their increased mass loss and an increased chance to eject their envelopes during a supernova. This increased production by binaries varies across the periodic table, with F and K being more significantly produced by binary-stripped stars than single stars. We find that the 12C/13C could be used as an indicator of the conservativeness of mass transfer, as 13C is preferentially ejected during mass transfer while 12C is preferentially ejected during wind mass loss. We identify a number of gamma-ray-emitting radioactive isotopes that may be used to help constrain progenitor and explosion models of core-collapse supernovae with next-generation gamma-ray detectors. For single stars we find that 44V and 52Mn are strong probes of the explosion model, while for binary-stripped stars it is 48Cr. Our findings highlight that binary-stripped stars are not equivalent to two single stars and that detailed stellar modeling is needed to predict their final nucleosynthetic yields.

Keywords: binary stars; nucleosynthesis; explosive nucleosynthesis; core-collapse supernovae; massive stars
A Physically Motivated Framework to Compare Pair Fractions of Isolated Low- and High-mass Galaxies across Cosmic Time

Low-mass galaxy pair fractions are understudied, and it is unclear whether low-mass pair fractions evolve in the same way as more massive systems over cosmic time. In the era of JWST, Roman, and Rubin, selecting galaxy pairs in a self-consistent way will be critical to connect observed pair fractions to cosmological merger rates across all mass scales and redshifts. Utilizing the Illustris TNG100 simulation, we create a sample of physically associated low-mass (108 < M * < 5 × 109 M ⊙) and high-mass (5 × 109 < M * < 1011 M ⊙) pairs between z = 0 and 4.2. The low-mass pair fraction increases from z = 0 to 2.5, while the high-mass pair fraction peaks at z = 0 and is constant or slightly decreasing at z > 1. At z = 0 the low-mass major (1:4 mass ratio) pair fraction is 4× lower than high-mass pairs, consistent with findings for cosmological merger rates. We show that separation limits that vary with the mass and redshift of the system, such as scaling by the virial radius of the host halo (r sep < 1R vir), are critical for recovering pair fraction differences between low-mass and high-mass systems. Alternatively, static physical separation limits applied equivalently to all galaxy pairs do not recover the differences between low- and high-mass pair fractions, even up to separations of 300 kpc. Finally, we place isolated mass analogs of Local Group galaxy pairs, i.e., Milky Way (MW)–M31, MW–LMC, LMC–SMC, in a cosmological context, showing that isolated analogs of LMC–SMC-mass pairs and low-separation (<50 kpc) MW–LMC-mass pairs are 2–3× more common at z ≳ 2–3.

Keywords: galaxy pairs; interacting galaxies; galaxy evolution; local group
Intercycle and Intracycle Variation of Halo CME Rate Obtained from SOHO/LASCO Observations

We report on the properties of halo coronal mass ejections (HCMEs) in solar cycles 23 and 24. We compare the HCME properties between the corresponding phases (rise, maximum, and declining) in cycles 23 and 24 and compare those between the whole cycles. Despite the significant decline in the sunspot number (SSN) in cycle 24, which dropped by 46% with respect to cycle 23, the abundance of HCMEs is similar in the two cycles. The HCME rate per SSN is 44% higher in cycle 24. In the maximum phase, cycle 24 rate normalized to SSN increased by 127%, while the SSN dropped by 43%. The source longitudes of cycle 24 HCMEs are more uniformly distributed than those in cycle 23. We found that the average sky-plane speed in cycle 23 is ∼16% higher than that in cycle 24. The size distributions of the associated flares between the two cycles and the corresponding phases are similar. The average speed at a central meridian distance (CMD) ≥ 600 for cycle 23 is ∼28% higher than that of cycle 24. We discuss the unusual bump in HCME activity in the declining phase of cycle 23 as being due to exceptional active regions that produced many CMEs during 2003 October-2005 October. The differing HCME properties in the two cycles can be attributed to the anomalous expansion of cycle 24 CMEs. Considering the HCMEs in the rise, maximum, and declining phases, we find that the maximum phase shows the highest contrast between the two cycles.

Keywords: solar coronal mass ejections; active sun; solar cycle; sunspots; solar flares; solar x-ray flares; heliosphere
Ghostly Galaxies: Accretion-dominated Stellar Systems in Low-mass Dark Matter Halos

Wide-area deep imaging surveys have discovered large numbers of extremely low surface brightness (LSB) dwarf galaxies, which challenge galaxy formation theory and, potentially, offer new constraints on the nature of dark matter. Here we discuss one as-yet-unexplored formation mechanism that may account for a fraction of LSB dwarfs. We call this the "ghost galaxy" scenario. In this scenario, inefficient radiative cooling prevents star formation in the "main branch" of the merger tree of a low-mass dark matter halo, such that almost all its stellar mass is acquired through mergers with less massive (but nevertheless star-forming) progenitors. Present-day systems formed in this way would be "ghostly" isolated stellar halos with no central galaxy. We use merger trees based on the extended Press-Schechter formalism and the Copernicus Complexio cosmological N-body simulation to demonstrate that mass assembly histories of this kind can occur for low-mass halos in ΛCDM, but they are rare. They are most probable in isolated halos of present-day mass ~4 × 109 M ⊙, occurring for ~5% of all halos of that mass under standard assumptions about the timing and effect of cosmic reionization. The stellar masses of star-forming progenitors in these systems are highly uncertain; abundance-matching arguments imply a bimodal present-day mass function having a brighter population (median M ⋆ ~ 3 × 106 M ⊙) consistent with the tail of the observed luminosity function of ultradiffuse galaxies. This suggests that observable analogs of these systems may await discovery. We find that a stronger ionizing background (globally or locally) produces brighter and more extended ghost galaxies.

Keywords: dwarf galaxies; reionization; cold dark matter
Prospects for Characterizing the Haziest Sub-Neptune Exoplanets with High-resolution Spectroscopy

Observations to characterize planets larger than Earth but smaller than Neptune have led to largely inconclusive interpretations at low spectral resolution due to hazes or clouds that obscure molecular features in their spectra. However, here we show that high-resolution spectroscopy (R ∼ 25,000-100,000) enables one to probe the regions in these atmospheres above the clouds where the cores of the strongest spectral lines are formed. We present models of transmission spectra for a suite of GJ 1214b-like planets with thick photochemical hazes covering 1-5 μm at a range of resolutions relevant to current and future ground-based spectrographs. Furthermore, we compare the utility of the cross-correlation function that is typically used with a more formal likelihood-based approach, finding that only the likelihood-based method is sensitive to the presence of haze opacity. We calculate the signal-to-noise ratio (S/N) of these spectra, including telluric contamination, Required to robustly detect a host of molecules such as CO, CO2, H2O, and CH4 and photochemical products like HCN as a function of wavelength range and spectral resolution. Spectra in the M band require the lowest S/Nres to detect multiple molecules simultaneously. CH4 is only observable for the coolest models (Teff = 412 K) and only in the L band. We quantitatively assess how these requirements compare to what is achievable with current and future instruments, demonstrating that characterization of small cool worlds with ground-based high-resolution spectroscopy is well within reach.

Keywords: exoplanets; exoplanet atmospheres
Electron Densities in the Solar Corona Measured Simultaneously in the Extreme Ultraviolet and Infrared

Accurate measurements of electron density are critical for determination of the plasma properties in the solar corona. We compare the electron densities diagnosed from Fe XIII lines observed by the Extreme-Ultraviolet Imaging Spectrometer (EIS) onboard the Hinode mission with the near-infrared (NIR) measurements provided by the ground-based Coronal Multichannel Polarimeter (CoMP). To do that, the emissivity-ratio method based on all available observed lines of Fe XIII is used for both EIS and CoMP. The EIS diagnostics is further supplemented by the results from Fe XII lines. We find excellent agreement, within 10%, between the electron densities measured from both extreme-ultraviolet and NIR lines. In the five regions selected for detailed analysis, we obtain electron densities of log(Ne [cm-3]) = 8.2-8.6. Where available, the background subtraction has a significant impact on the diagnostics, especially on the NIR lines, where the loop contributes less than a quarter of the intensity measured along the line of sight. For the NIR lines, we find that the line center intensities are not affected by stray light within the instrument, and recommend using these for density diagnostics. The measurements of the Fe XIII NIR lines represent a viable method for density diagnostics using ground-based instrumentation.

Keywords: solar corona; solar coronal loops; solar electromagnetic emission; solar extreme ultraviolet emission; solar instruments; infrared astronomy
Effect of Vegetation on the Temperatures of TRAPPIST-1 Planets

TRAPPIST-1 is an ultracool dwarf hosting a system consisting of seven planets. While orbital properties, radii, and masses of the planets are nowadays well constrained, one of the fascinating open issues is the possibility that an environment hospitable to life could develop on some of these planets. Here, we use a simple formulation of an energy balance model that includes vegetation coverage to investigate the possibility of life affecting the climate of the planets in the TRAPPIST-1 system. Results confirm that planet TRAPPIST-1e has the best chance to be a habitable world and indicate that vegetation coverage significantly affects the resulting temperatures and habitability properties. The influence of vegetation has been evaluated in different scenarios characterized by different vegetation types, land-sea distributions and levels of greenhouse effect. While changes in vegetation type produce small changes, about 0.1%, in the habitable surface fraction, different land-sea distributions, by also affecting the vegetation growth, produce different temperature distributions. Finally, at latitudes where vegetation grows, the lowering of local albedo still represents a relevant contribution in settling the planetary temperature profiles even when levels of greenhouse effect higher than the Earth-like case are considered.

Keywords: astrobiology; exoplanets; exoplanet systems; habitable planets; computational methods; extrasolar rocky planets; ocean planets; exoplanet surfaces
A Lithium Depletion Age for the Carina Association

The dispersed remnants of stellar nurseries, stellar associations, provide unparalleled samples of coeval stars critical for studies of stellar and planetary formation and evolution. The Carina Stellar Association is one of the closest stellar associations to Earth, and yet measurements of its age have varied from 13 to 45 Myr. We aim to update the age of Carina using the lithium depletion boundary (LDB) method. We obtain new measurements of the Li 6708 Å absorption feature in likely members using optical spectra from the Goodman High Throughput Spectrograph on SOAR and NRES on LCO. We detect the depletion boundary at M K ≃ 6.8 (M5). This age is consistent within uncertainties across six different models, including those that account for magnetic fields and spots. We also estimate the age through analysis of the group's overall variability, and by comparing the association members' color-magnitude diagram to stellar evolutionary models using a Gaussian Mixture Model, recovering ages consistent with the LDB. Combining these age measures we obtain an age for the Carina association of ${41}_{-5}^{+3}$ Myr. The resulting age agrees with the older end of previous age measurements and is consistent with the lithium depletion age for the neighboring Tucana-Horologium moving group.

Keywords: m dwarf stars; stellar associations