adsabs/SciX_UAT_keywords huggingface dataset:
Infrared Band Strengths of Dangling OH Features in Amorphous Water at 20 K

Infrared (IR) spectra of vapor-deposited amorphous water at low temperatures show two weak peaks at around 3720 and 3696 cm‑1 assigned to free-OH stretching modes of two- and three-coordinated water molecules (so-called "dangling" OH bonds), respectively, on the ice surface. A recent JWST observation first succeeded in detection of a potential dangling OH feature at 3664 cm‑1 for ices in molecular clouds, highlighting the importance of dangling OH bonds in interstellar ice chemistry. A lack of band strengths of these features at low temperatures restricts the quantification of dangling OH bonds from IR spectra, hindering development of a molecular-level understanding of the surface structure and chemistry of ice. Using IR multiple-angle incidence resolution spectrometry, we quantified the band strengths of two- and three-coordinated dangling OH features in amorphous water at 20 K as being 4.6 ± 1.6 × 10‑18 and 9.1 ± 1.0 × 10‑18 cm molecule‑1, respectively. These values are more than an order of magnitude lower than band strengths of bulk-water molecules in ice and liquid water and are similar to those of H2O monomers confined in solid matrices. Adsorption of carbon monoxide with dangling OH bonds results in the appearance of a new broad dangling OH feature at 3680–3620 cm‑1, with a band strength of 1.8 ± 0.1 × 10‑17 cm molecule‑1. The band strengths of dangling OH features determined in this study advance our understanding of the surface structure of interstellar ice analogs and recent IR observations of the JWST.

Keywords: optical constants (ice); ice physics; physical properties (ice); surface ices; ice spectroscopy; vibrational spectroscopy; spectroscopy; infrared spectroscopy; dust physics; interstellar dust; solid matter physics; interstellar clouds
Modeling the Extragalactic Background Light and the Cosmic Star Formation History

We present an updated model for the extragalactic background light (EBL) from stars and dust, over wavelengths ≈0.1-1000 μm. This model uses accurate theoretical stellar spectra, and tracks the evolution of star formation, stellar mass density, metallicity, and interstellar dust extinction and emission in the universe with redshift. Dust emission components are treated self-consistently, with stellar light absorbed by dust reradiated in the infrared as three blackbody components. We fit our model, with free parameters associated with star formation rate and dust extinction and emission, to a wide variety of data: luminosity density, stellar mass density, and dust extinction data from galaxy surveys; and γ-ray absorption optical depth data from γ-ray telescopes. Our results strongly constraint the star formation rate density and dust photon escape fraction of the universe out to redshift z = 10, about 90% of the history of the universe. We find our model result is, in some cases, below lower limits on the z = 0 EBL intensity, and below some low-z γ-ray absorption measurements.

Keywords: diffuse radiation; gamma-rays; gamma-ray astronomy; gamma-ray sources; blazars
Living with Neighbors. IV. Dissecting the Spin-Orbit Alignment of Dark Matter Halos: Interacting Neighbors and the Local Large-scale Structure

Spin-orbit alignment (SOA; i.e., the vector alignment between the halo spin and the orbital angular momentum of neighboring halos) provides an important clue to how galactic angular momenta develop. For this study, we extract virial-radius-wise contact halo pairs with mass ratios between 1/10 and 10 from a set of cosmological N-body simulations. In the spin-orbit angle distribution, we find a significant SOA in that 52.7% ± 0.2% of neighbors are on the prograde orbit. The SOA of our sample is mainly driven by low-mass target halos (<1011.5 h-1 M⊙) with close merging neighbors, corroborating the notion that tidal interaction is one of the physical origins of SOA. We also examine the correlation of SOA with the adjacent filament and find that halos closer to the filament show stronger SOA. Most interestingly, we discover for the first time that halos with the spin parallel to the filament experience most frequently prograde polar-interaction (i.e., fairly perpendicular but still prograde interaction; spin-orbit angle ~70°). This instantly invokes the spin-flip event and the prograde-polar interaction will soon flip the spin of the halo to align it with the neighbor's orbital angular momentum. We propose that SOA originates from the local cosmic flow along the anisotropic large-scale structure, especially that along the filament, and grows further by interactions with neighbors.

Keywords: n-body simulations; dark matter; galaxy kinematics; cosmic web; large-scale structure of the universe; galaxy dark matter halos; galaxy encounters; galaxy interactions
Hadronic versus Leptonic Models for γ-Ray Emission from VER J2227+608

Recent observations of VER J2227+608 reveal a broken power γ-ray spectrum with the spectral index increasing from ∼1.8 in the GeV energy range to ∼2.3 in the TeV range. Such a spectral break can be attributed to radiative energy loss of energetic electrons in the leptonic scenario for the γ-ray emission, which, in combination with the characteristic age of the nearby pulsar, can be used to constrain the magnetic field in the emission region. We show that the radio and X-ray observations can also be explained in such a scenario. In the hadronic scenario, the spectral break can be attributed to diffusion of energetic ions in a turbulent medium and detailed spectral measurement can be used to constrain the diffusion coefficient. These two models, however, predict drastically different spectra above 100 TeV, which will be uncovered with future high-resolution observations, such as Large High Altitude Air Shower Observatory (LHAASO) and/or Cherenkov Telescope Array (CTA).

Keywords: rotation powered pulsars; gamma-ray astronomy; diffuse nebulae; ultra-high-energy cosmic radiation; astrophysical processes; gamma-ray sources; non-thermal radiation sources; galactic cosmic rays; extended radiation sources; supernova remnants; cosmic ray astronomy; cosmic ray sources
Proton Energy Spectra of Energetic Storm Particle Events and Relation with Shock Parameters and Turbulence

The proton energy spectra of 23 energetic storm particle (ESP) events of various types, occurring either in association with (16 events) or in the absence of (7 events) solar energetic particles (SEPs), are investigated by using data from particle instruments aboard STEREO A in the energy range from 84.1 keV to 100 MeV. The obtained spectra were fitted with several known functions. Out of the 12 ESP events occurring in association with SEPs and quasi-perpendicular shocks, the Weibull distribution provides good fits to the spectra over the whole energy range in five cases. For the other seven events it fits the high energy tail, with lower energies explained by the power law predicted by the diffusive shock acceleration (DSA). Conversely, for the four SEP-associated ESPs at quasi-parallel shocks, a double power law better reproduces the observed spectra. Moreover, a significant correlation of the downstream turbulence level is found with the background subtracted Weibull parameters for quasi-perpendicular shocks, and with the proton peak value in the intermediate energy range of 4-6 MeV for all 16 considered shocks. Our results suggest that the downstream turbulence is a relevant factor in particle acceleration and that stochastic acceleration (SA) can be a plausible mechanism for reacceleration at interplanetary shocks. In the seven cases not associated with SEPs, an Ellison-Ramaty form fits the observed spectra, consistently with a DSA process, suggesting that a strong shock and/or a high energy particle background should be present for the SA to be at work.

Keywords: interplanetary particle acceleration; interplanetary turbulence; interplanetary shocks
CHAOS IV: Gas-phase Abundance Trends from the First Four CHAOS Galaxies

The chemical abundances of spiral galaxies, as probed by H II regions across their disks, are key to understanding the evolution of galaxies over a wide range of environments. We present Large Binocular Telescope/Multi-Object Double Spectrographs spectra of 52 H II regions in NGC 3184 as part of the CHemical Abundances Of Spirals (CHAOS) project. We explore the direct-method gas-phase abundance trends for the first four CHAOS galaxies, using temperature measurements from one or more auroral-line detections in 190 individual H II regions. We find that the dispersion in ${T}_{e}-{T}_{e}$ relationships is dependent on ionization, as characterized by ${F}_{\lambda 5007}/{F}_{\lambda 3727}$ , and so we recommend ionization-based temperature priorities for abundance calculations. We confirm our previous results that [N II] and [S III] provide the most robust measures of electron temperature in low-ionization zones, while [O III] provides reliable electron temperatures in high-ionization nebula. We measure relative and absolute abundances for O, N, S, Ar, and Ne. The four CHAOS galaxies marginally conform with a universal O/H gradient, as found by empirical integral field unit studies when plotted relative to effective radius. However, after adjusting for vertical offsets, we find a tight universal N/O gradient of ${\alpha }_{{\rm{N}}/{\rm{O}}}=-0.33$ dex/Re with σtot. = 0.08 for Rg/Re < 2.0, where N is dominated by secondary production. Despite this tight universal N/O gradient, the scatter in the N/O-O/H relationship is significant. Interestingly, the scatter is similar when N/O is plotted relative to O/H or S/H. The observable ionic states of S probe lower ionization and excitation energies than O, which might be more appropriate for characterizing abundances in metal-rich H II regions.

Keywords: chemical abundances; galaxy abundances; interstellar abundances; metallicity; spiral galaxies; galaxy chemical evolution; galaxy evolution; interstellar medium
Credit Lost: Two Decades of Software Citation in Astronomy

Software has been a crucial contributor to scientific progress in astronomy for decades, but practices that enable machine-actionable citations have not been consistently applied to software itself. Instead, software citation behaviors developed independently from standard publication mechanisms and policies, resulting in human-readable citations that remain hidden over time and that cannot represent the influence software has had in the field. These historical software citation behaviors need to be understood in order to improve software citation guidance and develop relevant publishing practices that fully support the astronomy community. To this end, a 23 year retrospective analysis of software citation practices in astronomy was developed. Astronomy publications were mined for 410 aliases associated with nine software packages and analyzed to identify past practices and trends that prevent software citations from benefiting software authors.

Keywords: astronomy software
Two Warm Super-Earths Transiting the Nearby M Dwarf TOI-2095

We report the detection and validation of two planets orbiting TOI-2095 (TIC 235678745). The host star is a 3700 K M1V dwarf with a high proper motion. The star lies at a distance of 42 pc in a sparsely populated portion of the sky and is bright in the infrared (K = 9). With data from 24 sectors of observation during Cycles 2 and 4 of the Transiting Exoplanet Survey Satellite, TOI-2095 exhibits two sets of transits associated with super-Earth-sized planets. The planets have orbital periods of 17.7 days and 28.2 days and radii of 1.30 R ⊕ and 1.39 R ⊕, respectively. Archival data, preliminary follow-up observations, and vetting analyses support the planetary interpretation of the detected transit signals. The pair of planets have estimated equilibrium temperatures of approximately 400 K, with stellar insolations of 3.23 and 1.73 S ⊕, placing them in the Venus zone. The planets also lie in a radius regime signaling the transition between rock-dominated and volatile-rich compositions. They are thus prime targets for follow-up mass measurements to better understand the properties of warm, transition-radius planets. The relatively long orbital periods of these two planets provide crucial data that can help shed light on the processes that shape the composition of small planets orbiting M dwarfs.

Keywords: exoplanets; m stars
On the Granulation and Irregular Variation of Red Supergiants

The mechanisms and characteristics of the irregular variations of red supergiants (RSGs) are studied based on the RSG samples in the Small Magellanic Cloud (SMC), Large Magellanic Cloud (LMC), and M31. With the time-series data from the All-Sky Automated Survey for SuperNovae and Intermediate Palomar Transient Factory survey, we use the continuous time autoregressive moving average model to estimate the variability features of the light curves and their power spectral density (PSD). The characteristic evolution timescale and amplitude of granulations are further derived from fitting the posterior PSD with the COR function, which is a Harvey-like granulation model. The consistency of theoretical predictions and results is checked to verify the correctness of the assumption that granulations on RSGs contribute to irregular variation. The relations between granulation and stellar parameters are obtained and compared with the results of red giant branch (RGB) stars and Betelgeuse. It is found that the relations are in agreement with predictions from basic physical process of granulation and fall close to the extrapolated relations of RGB stars. The granulations in most of the RSGs evolve at a timescale of several days to a year with a characteristic amplitude of 10-1000 mmag. The results imply that the irregular variations of RSGs can be attributed to the evolution of granulations. When comparing the results from the SMC, LMC, and M31, the timescale and amplitude of granulation seem to increase with metallicity. The analytical relations of the granulation parameters with stellar parameters are derived for the RSG sample of each galaxy.

Keywords: late-type stars; stellar pulsations; stellar oscillations; red supergiant stars
Probing Cosmic-Ray Transport with Radio Synchrotron Harps in the Galactic Center

Recent observations with the MeerKAT radio telescope reveal a unique population of faint nonthermal filaments pervading the central molecular zone, a region rich in molecular gas near the Galactic center. Some of those filaments are organized into groups of almost parallel filaments, seemingly sorted by their length, so that their morphology resembles a harp with radio-emitting "strings." We argue that the synchrotron-emitting GeV electrons of these radio harps have been consecutively injected by the same source (a massive star or pulsar) into spatially intermittent magnetic fiber bundles within a magnetic flux tube or via time-dependent injection events. After escaping from this source, the propagation of cosmic-ray (CR) electrons inside a flux tube is governed by the theory of CR transport. We propose to use observations of radio harp filaments to gain insight into the specifics of CR propagation along magnetic fields of which there are two principle modes: CRs could either stream with self-excited magnetohydrodynamic waves or diffuse along the magnetic field. To disentangle these possibilities, we conduct hydrodynamical simulations of either purely diffusing or streaming CR electrons and compare the resulting brightness distributions to the observed synchrotron profiles of the radio harps. We find compelling evidence that CR streaming is the dominant propagation mode for GeV CRs in one of the radio harps. Observations at higher angular resolution should detect more radio harps and may help to disentangle projection effects of the possibly three-dimensional flux-tube structure of the other radio harps.

Keywords: galactic center; non-thermal radiation sources; cosmic rays; computational methods
Evidence for Plasmoid-mediated Magnetic Reconnection during a Small-scale Flare in the Partially Ionized Low Solar Atmosphere

Magnetic reconnection plays a crucial role in the energy release process for different kinds of solar eruptions and activities. The rapid solar eruption requires a fast reconnection model. Plasmoid instability in the reconnecting current sheets is one of the most acceptable fast reconnection mechanisms for explaining the explosive events in the magnetohydrodynamics (MHD) scale, which is also a potential bridge between the macroscopic MHD reconnection process and microscale dissipations. Plenty of high-resolution observations indicate that the plasmoid-like structures exist in the high-temperature solar corona, but such evidences are very rare in the lower solar atmosphere with partially ionized plasmas. Utilizing joint observations from the Goode Solar Telescope and the Solar Dynamics Observatory, we discovered a small-scale eruptive phenomenon in NOAA Active Region 13085, characterized by clear reconnection cusp structures, supported by nonlinear force-free field extrapolation results. The plasmoid-like structures with a size of about 150 km were observed to be ejected downward from the current sheet at a maximum velocity of 24 km s‑1 in the Hα line wing images, followed by enhanced emissions at around the postflare loop region in multiple wavelengths. Our 2.5D high-resolution MHD simulations further reproduced such a phenomenon and revealed reconnection fine structures. These results provide comprehensive evidences for the plasmoid-mediated reconnection in partially ionized plasmas, and suggest a unified reconnection model for solar flares with different length scales from the lower chromosphere to the corona.

Keywords: solar magnetic reconnection; solar chromospheric heating; solar activity
Velocity Offset Between Emission and Absorption Lines Might Be an Effective Indicator of a Dual Core System

This paper presents the detection of a significant velocity offset between the emission and absorption lines of a dual core system in SDSS J155708.82+273518.74 (=SDSS J1557). The photometric image of SDSS J1557 exhibits two clear cores with a projected separation of ~2.″2 (4.9 kpc) determined by GALFIT. Based on the applications of the commonly accepted pPXF code with 636 theoretical SSP templates, the host galaxy contribution can be well determined. Then, the emission-line features of SDSS J1557 can be well measured after subtraction of the host starlight. It is found that the velocity offset of emission lines with respect to absorption lines reaches 458 ± 13 km s-1. According to a Baldwin-Phillips-Terlevich diagram, SDSS J1557 is a composite galaxy. In addition, SDSS J1557 can well fit the M BH - σ * relation of bulges, and a galaxy merger would not change this relation. Two reasonable models (an AGN-driven outflow versus a dual core system) are discussed to explain this velocity offset. The model of an AGN-driven outflow fails to interpret the systematic redshift of the emission lines and similar velocity offsets for the various emission lines of SDSS J1557. Instead, the significant velocity offset between the emission and absorption lines might be an effective indicator of a dual core system.

Keywords: active galactic nuclei; active galaxies; emission line galaxies; supermassive black holes; galaxy mergers; quasar absorption line spectroscopy
PIC Simulations of Microinstabilities and Waves at Near-Sun Solar Wind Perpendicular Shocks: Predictions for Parker Solar Probe and Solar Orbiter

Microinstabilities and waves excited at moderate-Mach-number perpendicular shocks in the near-Sun solar wind are investigated by full particle-in-cell simulations. By analyzing the dispersion relation of fluctuating field components directly issued from the shock simulation, we obtain key findings concerning wave excitations at the shock front: (1) at the leading edge of the foot, two types of electrostatic (ES) waves are observed. The relative drift of the reflected ions versus the electrons triggers an electron cyclotron drift instability (ECDI) that excites the first ES wave. Because the bulk velocity of gyro-reflected ions shifts to the direction of the shock front, the resulting ES wave propagates oblique to the shock normal. Immediately, a fraction of incident electrons are accelerated by this ES wave and a ring-like velocity distribution is generated. They can couple with the hot Maxwellian core and excite the second ES wave around the upper hybrid frequency. (2) From the middle of the foot all the way to the ramp, electrons can couple with both incident and reflected ions. ES waves excited by ECDI in different directions propagate across each other. Electromagnetic (EM) waves (X mode) emitted toward upstream are observed in both regions. They are probably induced by a small fraction of relativistic electrons. Results shed new insight on the mechanism for the occurrence of ES wave excitations and possible EM wave emissions at young coronal mass ejection-driven shocks in the near-Sun solar wind.

Keywords: plasma astrophysics; space plasmas; plasma physics; interplanetary shocks
Cloudy and Cloud-free Thermal Phase Curves with PICASO: Applications to WASP-43b

We present new functionality within PICASO, a state-of-the-art radiative transfer model for exoplanet and brown dwarf atmospheres, by developing a new pipeline that computes phase-resolved thermal emission (thermal phase curves) from three-dimensional (3D) models. Because PICASO is coupled to Virga, an open-source cloud code, we are able to produce cloudy phase curves with different sedimentation efficiencies (f sed) and cloud condensate species. We present the first application of this new algorithm to hot Jupiter WASP-43b. Previous studies of the thermal emission of WASP-43b from Kataria et al. found good agreement between cloud-free models and dayside thermal emission, but an overestimation of the nightside flux, for which clouds have been suggested as a possible explanation. We use the temperature and vertical wind structure from the cloud-free 3D general circulation models of Kataria et al. and post-process it using PICASO, assuming that clouds form and affect the spectra. We compare our models to results from Kataria et al., including Hubble Space Telescope Wide-Field Camera 3 (WFC3) observations of WASP-43b from Stevenson et al. In addition, we compute phase curves for Spitzer at 3.6 and 4.5 μm and compare them to observations from Stevenson et al. We are able to closely recover the cloud-free results, even though PICASO utilizes a coarse spatial grid. We find that cloudy phase curves provide much better agreement with the WFC3 and Spitzer nightside data, while still closely matching the dayside emission. This work provides the community with a convenient, user-friendly tool to interpret phase-resolved observations of exoplanet atmospheres using 3D models.

Keywords: exoplanet astronomy; extrasolar gaseous planets; hot jupiters; exoplanet atmospheres; planetary atmospheres; atmospheric clouds