adsabs/SciX_UAT_keywords huggingface dataset:
Sharp Alfvénic Impulses in the Near-Sun Solar Wind

Measurements of the near-Sun solar wind by the Parker Solar Probe have revealed the presence of large numbers of discrete Alfvénic impulses with an anti-sunward sense of propagation. These are similar to those previously observed near 1 au, in high speed streams over the Sun's poles and at 60 solar radii. At 35 solar radii, however, they are typically shorter and sharper than seen elsewhere. In addition, these spikes occur in "patches" and there are also clear periods within the same stream when they do not occur; the timescale of these patches might be related to the rate at which the spacecraft magnetic footpoint tracks across the coronal hole from which the plasma originated. While the velocity fluctuations associated with these spikes are typically under 100 km s-1, due to the rather low Alfvén speeds in the streams observed by the spacecraft to date, these are still associated with large angular deflections of the magnetic field—and these deflections are not isotropic. These deflections do not appear to be related to the recently reported large-scale, pro-rotation solar wind flow. Estimates of the size and shape of the spikes reveal high aspect ratio flow-aligned structures with a transverse scale of ≈104 km. These events might be signatures of near-Sun impulsive reconnection events.

Keywords: solar wind; solar corona; space plasmas
Evolution of the Interplanetary Turbulence and the Associated Turbulence Anisotropy in the Outer Heliosphere: VOYAGER 2 Observations

We study the radial evolution of the inertial-range solar wind plasma turbulence and its anisotropy in the outer heliosphere. We use magnetic field ( B ) measurements from the Voyager 2 spacecraft for heliocentric distances R from 1 to 33 au. We find that the perpendicular and trace power spectral densities (PSDs) of the magnetic field ( ${E}_{{{\rm{B}}}_{\perp }}$ and ${E}_{{{\rm{B}}}_{\mathrm{Tr}}}$ ) still follow a Kolmogorov-like spectrum until 33 au. The parallel magnetic field PSD, ${E}_{{B}_{\parallel }}$ , transits from a power-law index of ‑2 to ‑5/3 as the distance crosses R ∼ 10 au. The PSD at frequencies 0.01 Hz < f < 0.2 Hz flattens at R > 20 au, gradually approaching an f ‑1 spectrum, probably due to instrument noise. At 0.002 Hz < f < 0.1 Hz, quasi-parallel propagation dominates at 1 au < R < 7 au, with quasi-perpendicular propagation gradually emerging at R > 5 au. For R > 7 au, oblique propagation becomes the primary mode of propagation. At smaller frequencies of f < 0.01 Hz, ${E}_{{{\rm{B}}}_{\perp }}$ increases with propagation angle at 1 au < R < 5 au, and in contrast decreases with propagation angle at R > 5 au due to the enhanced power level at propagation angles smaller than 20°. Such enhancement may derive from the injection of wave energy from the pickup ion source into the background turbulent cascade, and the injected wave energy is transferred across scales without leaving local enhancements in ${E}_{{{\rm{B}}}_{\perp }}$ or ${E}_{{{\rm{B}}}_{\mathrm{Tr}}}$ .

Keywords: heliosphere; interplanetary turbulence; solar wind
DAMPE Proton Spectrum Indicates a Slow-diffusion Zone in the nearby ISM

The hardening and softening features in the DAMPE proton spectrum are very likely to have originated from a nearby supernova remnant (SNR). The proton spectrum from the nearby SNR is required to be very hard below ≈10 TeV. To reproduce this feature, we illustrate that an anomalously slow-diffusion zone for cosmic rays (CRs) must exist in the local interstellar medium (ISM) after also taking the dipole anisotropy of CRs into account. Assuming that the diffusion coefficient is homogeneous in the nearby ISM, we show that the diffusion coefficient is constrained to the magnitude of 1026 cm2 s-1 when normalized to 1 GeV, which is about 100 times smaller than the average value in the Galaxy. We further discuss the spatial distribution of the slow diffusion and find two distinct possibilities. In one case, the SNR is several hundred parsecs away from the solar system, and both the SNR and the solar system must be included in a large slow-diffusion zone. In the other case, the SNR is very close with a distance of ∼50 pc and the slow-diffusion zone is only limited around the SNR, while the current multiwavelength observations do not indicate such a close source. This work provides a new way of studying the CR diffusion in the local ISM.

Keywords: cosmic rays; supernova remnants; interstellar medium
The Abundances of Helium, Magnesium and Phosphorus in the Atmosphere of HD144844

Abundances of helium and magnesium are derived in LTE for the B9 Mn P Ga star HD 144844 using the group of He I lines near 4470.40 Å and the Mg II triplet at 4481.22 Å. Both elements are found to be very underabundant, about 2% of the solar helium and magnesium abundances. The profile of the Mg II line at 4481.22 Å clearly shows two components and confirms that this star is a double-lined spectroscopic binary. The synthesis of three P II lines at 6024.18, 6034.04 and 6043.88 Å yields phosphorus abundances from 150 up to 200 times the solar phosphorus abundance. A NLTE synthesis is necessary to derive more accurate abundances.

Keywords: chemically peculiar stars; mercury-manganese stars
Consistency of the Parkes Pulsar Timing Array Signal with a Nanohertz Gravitational-wave Background

Pulsar timing array experiments have recently reported strong evidence for a common-spectrum stochastic process with a strain spectral index consistent with that expected of a nanohertz-frequency gravitational-wave background, but with negligible yet non-zero evidence for spatial correlations required for a definitive detection. However, it was pointed out by the Parkes Pulsar Timing Array (PPTA) collaboration that the same models used in recent analyses resulted in strong evidence for a common-spectrum process in simulations where none is present. In this work, we introduce a methodology to distinguish pulsar power spectra with the same amplitude from noise power spectra of similar but distinct amplitudes. The former is the signature of a spatially uncorrelated pulsar term of a nanohertz gravitational-wave background, whereas the latter could represent ensemble pulsar noise properties. We test the methodology on simulated data sets. We find that the reported common process in PPTA pulsars is indeed consistent with the spectral feature of a pulsar term. We recommend this methodology as one of the validity tests that the real astrophysical and cosmological backgrounds should pass, as well as for inferences about the spatially uncorrelated component of the background.

Keywords: gravitational waves; millisecond pulsars; pulsar timing method; astronomy data analysis; bayesian statistics; importance sampling; supermassive black holes; gravitational wave astronomy; hierarchical models; high energy astrophysics; astronomical methods
Ions in the Thermosphere of Exoplanets: Observable Constraints Revealed by Innovative Laboratory Experiments

With the upcoming launch of space telescopes dedicated to the study of exoplanets, the Atmospheric Remote-Sensing Infrared Exoplanet Large-survey (ARIEL) and the James Webb Space Telescope (JWST), a new era is opening in exoplanetary atmospheric explorations. However, especially in relatively cold planets around later-type stars, photochemical hazes and clouds may mask the composition of the lower part of the atmosphere, making it difficult to detect any chemical species in the troposphere or understand whether there is a surface or not. This issue is particularly exacerbated if the goal is to study the habitability of said exoplanets and search for biosignatures. This work combines innovative laboratory experiments, chemical modeling, and simulated observations at ARIEL and JWST resolutions. We focus on the signatures of molecular ions that can be found in upper atmospheres above cloud decks. Our results suggest that ${{\rm{H}}}_{3}^{+}$ along with H3O+ could be detected in the observational spectra of sub-Neptunes based on a realistic mixing ratio assumption. This new parametric set may help to distinguish super-Earths with a thin atmosphere from H2-dominated sub-Neptunes to address the critical question of whether a low-gravity planet around a low-mass active star is able to retain its volatile components. These ions may also constitute potential tracers to certain molecules of interest, such as H2O or O2, to probe the habitability of exoplanets. Their detection will be an enthralling challenge for the future JWST and ARIEL telescopes.

Keywords: exoplanet atmospheres; photoionization; space telescopes; laboratory astrophysics
Bulk Properties of PSR J0030+0451 Inferred with the Compactness Measurement of NICER

In 2019, the Neutron star Interior Composition ExploreR (NICER) mission released its findings on the mass and radius of the isolated neutron star (INS) PSR J0030+0451, revealing a mass of approximately 1.4 solar masses (M ⊙) and a radius near 13 km. However, the recent reanalysis by the NICER collaboration suggests that the available data primarily yield a precise inference of the compactness for this source while the resulting mass and radius are strongly model-dependent and diverse (the 68.3% credible regions just overlap slightly for the ST+PDT and PDT-U models). By integrating this compactness data with the equation of state (EOS) refined by our latest investigations, we have deduced the mass and radius for PSR J0030+0451, delivering estimates of $M={1.48}_{-0.10}^{+0.09}\,{M}_{\odot }$ and $R={12.38}_{-0.70}^{+0.51}\,\mathrm{km}$ for the compactness found in the ST+PDT model, alongside $M={1.47}_{-0.20}^{+0.14}\,{M}_{\odot }$ and $R={12.37}_{-0.69}^{+0.50}\,\mathrm{km}$ for the compactness in the PDT-U model. These two groups of results are well consistent with each other and the direct X-ray data inference within the ST+PDT model seems to be favored. Additionally, we have calculated the tidal deformability, moment of inertia, and gravitational binding energy for this neutron star. Furthermore, employing these refined EOS models, we have updated mass–radius estimates for three INSs with established gravitational redshifts.

Keywords: neutron stars; nuclear physics; compact objects
The Role of Alfvén Wave Dynamics on the Large-scale Properties of the Solar Wind: Comparing an MHD Simulation with Parker Solar Probe E1 Data

During Parker Solar Probe's first orbit, the solar wind plasma was observed in situ closer than ever before, the perihelion on 2018 November 6 revealing a flow that is constantly permeated by large-amplitude Alfvénic fluctuations. These include radial magnetic field reversals, or switchbacks, that seem to be a persistent feature of the young solar wind. The measurements also reveal a very strong, unexpected, azimuthal velocity component. In this work, we numerically model the solar corona during this first encounter, solving the MHD equations and accounting for Alfvén wave transport and dissipation. We find that the large-scale plasma parameters are well reproduced, allowing the computation of the solar wind sources at Probe with confidence. We try to understand the dynamical nature of the solar wind to explain both the amplitude of the observed radial magnetic field and of the azimuthal velocities.

Keywords: solar wind; solar physics; alfven waves; magnetohydrodynamics; magnetohydrodynamical simulations
Observable Signatures of Stellar-mass Black Holes in Active Galactic Nuclei

Stellar-mass black holes (BHs) are predicted to be embedded in the disks of active galactic nuclei (AGNs) due to gravitational drag and in situ star formation. However, clear evidence for AGN disk-embedded BHs is currently lacking. Here, as possible electromagnetic signatures of these BHs, we investigate breakout emission from shocks emerging around Blandford-Znajek jets launched from accreting BHs in AGN disks. We assume that most of the highly super-Eddington flow reaches the BH and produces a strong jet, and the jet produces feedback that shuts off accretion and thus leads to episodic flaring. These assumptions, while poorly understood at present, yield observable consequences that can probe the presence of AGN-embedded BHs as well as the accretion process itself. They predict a breakout emission characterized by luminous thermal emission in the X-ray bands and bright broadband nonthermal emission from the infrared to the gamma-ray bands. The flare duration depends on the BH's distance r from the central supermassive BH, varying between 103-106 s for r ~ 0.01-1 pc. This emission can be discovered by current and future infrared, optical, and X-ray wide-field surveys and monitoring campaigns of nearby AGNs.

Keywords: astrophysical black holes; active galactic nuclei; transient sources; time domain astronomy; high energy astrophysics
WISE J141530.7+592234: A Very Low Mass Ratio Contact Binary with Significant Light Curve Variations

Multi-band photometric observations and period investigations of the total eclipsing binary WISE J141530.7+592234 (hereinafter J141530), whose mass ratio close to the low mass ratio limit, were carried out for the first time. The stellar atmospheric parameters of the primary component were calculated by the spectral fitting, yielding the following results: T eff = 5890 ± 22 K, [Fe/H] = 0.01 ± 0.03 dex, log g = 4.53 ± 0.04 cm s-2. Our observations show that the light curve of V-band on May 2 is about 0.1 mag brighter than that observed in February and March at phase 0.6. Comparing with the small amplitude (about 0.2 mag), the variations are remarkable. Meanwhile, obvious light curve variations and quick reversal of O'Connell effects are found in Transiting Exoplanet Survey Satellite data, which is likely caused by magnetic activity. Photometric solutions derived from multi-band light curves indicate that J141530 has a high contact degree (f ~ 70%) and a very low mass ratio (q ~ 0.0546). Based on the O - C diagram, a long-term period increase was found. The period increase rate is calculated to be dP/dt = 3.90 × 10-7 day yr-1, which can be explained by mass transfer from the low mass component to the large mass component. By analyzing the merging criterion, such as the ratio of spin angular momentum (J spin) to the orbital angular momentum (J orb), the instability separation and the instability mass ratio, J141530 can be regarded as a potential progenitor of luminous red novae.

Keywords: binary stars; contact binary stars; spectroscopy
Shockingly Bright Warm Carbon Monoxide Molecular Features in the Supernova Remnant Cassiopeia A Revealed by JWST

We present JWST NIRCam (F356W and F444W filters) and MIRI (F770W) images and NIRSpec Integral Field Unit (IFU) spectroscopy of the young Galactic supernova remnant Cassiopeia A (Cas A) to probe the physical conditions for molecular CO formation and destruction in supernova ejecta. We obtained the data as part of a JWST survey of Cas A. The NIRCam and MIRI images map the spatial distributions of synchrotron radiation, Ar-rich ejecta, and CO on both large and small scales, revealing remarkably complex structures. The CO emission is stronger at the outer layers than the Ar ejecta, which indicates the re-formation of CO molecules behind the reverse shock. NIRSpec-IFU spectra (3–5.5 μm) were obtained toward two representative knots in the NE and S fields that show very different nucleosynthesis characteristics. Both regions are dominated by the bright fundamental rovibrational band of CO in the two R and P branches, with strong [Ar VI] and relatively weaker, variable strength ejecta lines of [Si IX], [Ca IV], [Ca V], and [Mg IV]. The NIRSpec-IFU data resolve individual ejecta knots and filaments spatially and in velocity space. The fundamental CO band in the JWST spectra reveals unique shapes of CO, showing a few tens of sinusoidal patterns of rovibrational lines with pseudocontinuum underneath, which is attributed to the high-velocity widths of CO lines. Our results with LTE modeling of CO emission indicate a temperature of ∼1080 K and provide unique insight into the correlations between dust, molecules, and highly ionized ejecta in supernovae and have strong ramifications for modeling dust formation that is led by CO cooling in the early Universe.

Keywords: supernova remnants; metal-containing molecules; co line emission; supernovae; james webb space telescope; ejecta; astrochemistry; dust formation
Exploring the Chemistry Induced by Energetic Processing of the H2-bearing, CO-rich Apolar Ice Layer

Interstellar ice mantles on the surfaces of dust grains are thought to have a bilayered structure, with a H2O-rich polar layer, covered by a CO-rich apolar layer that probably harbors H2 and other volatiles such as N2. In this work, we explore the chemistry induced by 2 keV electrons and Lyα photons in H2:CO:15N2 ice analogs of the CO-rich layer when exposed to similar fluences to those expected from the cosmic-ray-induced secondary electrons and UV photons during the typical lifetime of dense clouds. Six products were identified upon 2 keV electron irradiation: CO2, C2O (and other carbon chain oxides), CH4, H2CO, H2C2O, and H15NCO. The total product abundances corresponded to 5%-10% of the initial CO molecules exposed to electron irradiation. Lyα photon irradiation delivered one to two orders of magnitude lower yields with a similar product branching ratio, which may be due to the low UV-photon absorption cross section of the ice sample at this wavelength. Formation of additional N-bearing species, namely C215N2 and 15NH3, was only observed in the absence of H2 and CO molecules, respectively, suggesting that reactants derived from H2 and CO molecules preferentially react with each other instead of with 15N2 and its dissociation products. In summary, ice chemistry induced by energetic processing of the CO-rich apolar ice layer provides alternative formation pathways for several species detected in the interstellar medium, including some related to the complex organic molecule chemistry. Further quantification of these pathways will help astrochemical models constrain their relative contribution to the interstellar budget of, especially, the organic species H2CO and HNCO.

Keywords: interstellar molecules; dense interstellar clouds; cosmic rays; laboratory astrophysics; experimental techniques
ExoCubed: A Riemann-solver-based Cubed-sphere Dynamic Core for Planetary Atmospheres

The computational fluid dynamics on a sphere is relevant to global simulations of geophysical fluid dynamics. Using the conventional spherical–polar (or lat–lon) grid results in a singularity at the poles, with orders-of-magnitude-smaller cell sizes at the poles in comparison to the equator. To address this problem, we developed a general circulation model (dynamic core) with a gnomonic equiangular cubed-sphere configuration. This model is developed based on the Simulating Nonhydrostatic Atmospheres on Planets model, using a finite-volume numerical scheme with a Riemann-solver-based dynamic core and the vertical implicit correction scheme. This change of the horizontal configuration gives a 20-time acceleration of global simulations compared to the lat–lon grid with a similar number of cells at medium resolution. We presented standard tests ranging from 2D shallow-water models to 3D general circulation tests, including Earth-like planets and shallow hot Jupiters, to validate the accuracy of the model. The method described in this article is generic to transform any existing finite-volume hydrodynamic model in the Cartesian geometry to the spherical geometry.

Keywords: exoplanet atmospheres; planetary atmospheres; hydrodynamical simulations
The ALCHEMI Atlas: Principal Component Analysis Reveals Starburst Evolution in NGC 253

Molecular lines are powerful diagnostics of the physical and chemical properties of the interstellar medium (ISM). These ISM properties, which affect future star formation, are expected to differ in starburst galaxies from those of more quiescent galaxies. We investigate the ISM properties in the central molecular zone of the nearby starburst galaxy NGC 253 using the ultrawide millimeter spectral scan survey from the Atacama Large Millimeter/submillimeter Array Large Program ALCHEMI. We present an atlas of velocity-integrated images at a 1.″6 resolution of 148 unblended transitions from 44 species, including the first extragalactic detection of HCNH+ and the first interferometric images of C3H+, NO, and HCS+. We conduct a principal component analysis (PCA) on these images to extract correlated chemical species and to identify key groups of diagnostic transitions. To the best of our knowledge, our data set is currently the largest astronomical set of molecular lines to which PCA has been applied. The PCA can categorize transitions coming from different physical components in NGC 253 such as (i) young starburst tracers characterized by high-excitation transitions of HC3N and complex organic molecules versus tracers of on-going star formation (radio recombination lines) and high-excitation transitions of CCH and CN tracing photodissociation regions, (ii) tracers of cloud-collision-induced shocks (low-excitation transitions of CH3OH, HNCO, HOCO+, and OCS) versus shocks from star formation-induced outflows (high-excitation transitions of SiO), as well as (iii) outflows showing emission from HOC+, CCH, H3O+, CO isotopologues, HCN, HCO+, CS, and CN. Our findings show these intensities vary with galactic dynamics, star formation activities, and stellar feedback.

Keywords: astrochemistry; starburst galaxies; interstellar medium; interstellar molecules
Inspecting the Cepheid Distance Ladder: the Hubble Space Telescope Distance to the SN Ia Host Galaxy NGC 5584

The current tension between the direct and the early-universe measurements of the Hubble constant, H0, requires detailed scrutiny of all the data and methods used in the studies on both sides of the debate. The Cepheids in the Type Ia supernova (SN Ia) host galaxy NGC 5584 played a key role in the local measurement of H0. The SH0ES project used the observations of this galaxy to derive a relation between the Cepheids' periods and ratios of their amplitudes in different optical bands of the Hubble Space Telescope and used these relations to analyze the light curves of the Cepheids in around half of the current sample of local SN Ia host galaxies. In this work, we present an independent detailed analysis of the Cepheids in NGC 5584. We employ different tools for our photometric analysis and a completely different method for our light-curve analysis, and we do not find a systematic difference between our period and mean magnitude measurements compared to those reported by SH0ES. By adopting a period-luminosity relation calibrated by the Cepheids in the Milky Way, we measure a distance modulus μ = 31.810 ± 0.047 (mag), which is in agreement with μ = 31.786 ± 0.046 (mag) measured by SH0ES. In addition, the relations we find between the periods and amplitude ratios of the Cepheids in NGC 5584 are significantly tighter than those of SH0ES, and their potential impact on the direct H0 measurement will be investigated in future studies.

Keywords: observational cosmology; cosmological parameters; hubble constant; cepheid distance; galaxies; type ia supernovae; variable stars; photometry; light curves; stellar photometry; astronomy data analysis; galaxy distances