adsabs/SciX_UAT_keywords huggingface dataset:
Modeling a Coronal Mass Ejection from an Extended Filament Channel. I. Eruption and Early Evolution

We present observations and modeling of the magnetic field configuration, morphology, and dynamics of a large-scale, high-latitude filament eruption observed by the Solar Dynamics Observatory. We analyze the 2015 July 9-10 filament eruption and the evolution of the resulting coronal mass ejection (CME) through the solar corona. The slow streamer-blowout CME leaves behind an elongated post-eruption arcade above the extended polarity inversion line that is only poorly visible in extreme ultraviolet (EUV) disk observations and does not resemble a typical bright flare-loop system. Magnetohydrodynamic (MHD) simulation results from our data-inspired modeling of this eruption compare favorably with the EUV and white-light coronagraph observations. We estimate the reconnection flux from the simulation's flare-arcade growth and examine the magnetic-field orientation and evolution of the erupting prominence, highlighting the transition from an erupting sheared-arcade filament channel into a streamer-blowout flux-rope CME. Our results represent the first numerical modeling of a global-scale filament eruption where multiple ambiguous and complex observational signatures in EUV and white light can be fully understood and explained with the MHD simulation. In this context, our findings also suggest that the so-called stealth CME classification, as a driver of unexpected or "problem" geomagnetic storms, belongs more to a continuum of observable/nonobservable signatures than to separate or distinct eruption processes.

Keywords: quiet sun; magnetohydrodynamical simulations; quiescent solar prominence; solar filament eruptions; solar magnetic reconnection; solar extreme ultraviolet emission; solar coronal mass ejections
On the Origin of the North Celestial Pole Loop

The North Celestial Pole Loop (NCPL) provides a unique laboratory for studying the early-stage precursors of star formation. Uncovering its origin is key to understanding the dynamical mechanisms that control the evolution of its contents. In this study, we explore the 3D geometry and the dynamics of the NCPL using high-resolution dust extinction data and H I data, respectively. We find that material toward Polaris and Ursa Major is distributed along a plane similarly oriented to the Radcliffe wave. The Spider projected in between appears disconnected in 3D, a discontinuity in the loop shape. We find that the elongated cavity that forms the inner part of the NCPL is a protrusion of the Local Bubble (LB) likely filled with warm (possibly hot) gas that passes through and goes beyond the location of the dense clouds. An idealized model of the cavity as a prolate spheroid oriented toward the observer, reminiscent of the cylindrical model proposed by Meyerdierks et al., encompasses the protrusion and fits into arcs of warm H I gas expanding laterally to it. As first argued by Meyerdierks et al., the nonspherical geometry of the cavity and the lack of OB stars interior to it disfavor an origin caused by a single point-like source of energy or multiple supernovae. Rather, the formation of the protrusion could be related to the propagation of warm gas from the LB into a pre-existing nonuniform medium in the lower halo, the topology of which was likely shaped by past star formation activity along the Local Arm.

Keywords: interstellar dust extinction; interstellar medium; solar neighborhood
Dark Matter in Fractional Gravity. I. Astrophysical Tests on Galactic Scales

We explore the possibility that the dark matter (DM) component in galaxies may originate fractional gravity. In such a framework, the standard law of inertia continues to hold, but the gravitational potential associated with a given DM density distribution is determined by a modified Poisson equation including fractional derivatives (i.e., derivatives of noninteger type) that are meant to describe nonlocal effects. We analytically derive the expression of the potential that in fractional gravity corresponds to various spherically symmetric density profiles, including the Navarro-Frenk-White (NFW) distribution that is usually exploited to describe virialized halos of collisionless DM as extracted from N-body cosmological simulations. We show that in fractional gravity, the dynamics of a test particle moving in a cuspy NFW density distribution is substantially altered with respect to the Newtonian case, mirroring what in Newtonian gravity would instead be sourced by a density profile with an inner core. We test the fractional gravity framework on galactic scales, showing that (i) it can provide accurate fits to the stacked rotation curves of spiral galaxies with different properties, including dwarfs; (ii) it can reproduce to reasonable accuracy the observed shape and scatter of the radial acceleration relation over an extended range of galaxy accelerations; and (iii) it can properly account for the universal surface density and the core radius versus disk scale length scaling relations. Finally, we discuss the possible origin of the fractional gravity behavior as a fundamental or emerging property of the elusive DM component.

Keywords: cosmology; dark matter; non-standard theories of gravity
Revealing Callisto's Carbon-rich Surface and CO2 Atmosphere with JWST

We analyzed spectral cubes of Callisto's leading and trailing hemispheres, collected with the NIRSpec Integrated Field Unit (G395H) on the James Webb Space Telescope. These spatially resolved data show strong 4.25 μm absorption bands resulting from solid-state 12CO2, with the strongest spectral features at low latitudes near the center of its trailing hemisphere, consistent with radiolytic production spurred by magnetospheric plasma interacting with native H2O mixed with carbonaceous compounds. We detected CO2 rovibrational emission lines between 4.2 and 4.3 μm over both hemispheres, confirming the global presence of CO2 gas in Callisto's tenuous atmosphere. These results represent the first detection of CO2 gas over Callisto's trailing side. The distribution of CO2 gas is offset from the subsolar region on either hemisphere, suggesting that sputtering, radiolysis, and geologic processes help sustain Callisto's atmosphere. We detected a 4.38 μm absorption band that likely results from solid-state 13CO2. A prominent 4.57 μm absorption band that might result from CN-bearing organics is present and significantly stronger on Callisto's leading hemisphere, unlike 12CO2, suggesting these two spectral features are spatially antiassociated. The distribution of the 4.57 μm band is more consistent with a native origin and/or accumulation of dust from Jupiter's irregular satellites. Other, more subtle absorption features could result from CH-bearing organics, CO, carbonyl sulfide, and Na-bearing minerals. These results highlight the need for preparatory laboratory work and improved surface–atmosphere interaction models to better understand carbon chemistry on the icy Galilean moons before the arrival of NASA's Europa Clipper and ESA's JUICE spacecraft.

Keywords: infrared spectroscopy; galilean satellites; callisto; james webb space telescope; natural satellite atmospheres; natural satellite surfaces; complex organic molecules; carbon dioxide; irregular satellites
A Mini-Neptune from TESS and CHEOPS Around the 120 Myr Old AB Dor Member HIP 94235

The Transiting Exoplanet Survey Satellite (TESS) mission has enabled discoveries of the brightest transiting planet systems around young stars. These systems are the benchmarks for testing theories of planetary evolution. We report the discovery of a mini-Neptune transiting a bright star in the AB Doradus moving group. HIP 94235 (TOI-4399, TIC 464646604) is a V mag = 8.31 G-dwarf hosting a ${3.00}_{-0.28}^{+0.32}\,{R}_{\oplus }$ mini-Neptune in a 7.7 day period orbit. HIP 94235 is part of the AB Doradus moving group, one of the youngest and closest associations. Due to its youth, the host star exhibits significant photometric spot modulation, lithium absorption, and X-ray emission. Three 0.06% transits were observed during Sector 27 of the TESS Extended Mission, though these transit signals are dwarfed by the 2% peak-to-peak photometric variability exhibited by the host star. Follow-up observations with the Characterising Exoplanet Satellite confirmed the transit signal and prevented the erosion of the transit ephemeris. HIP 94235 is part of a 50 au G-M binary system. We make use of diffraction limited observations spanning 11 yr, and astrometric accelerations from Hipparcos and Gaia, to constrain the orbit of HIP 94235 B. HIP 94235 is one of the tightest stellar binaries to host an inner planet. As part of a growing sample of bright, young planet systems, HIP 94235 b is ideal for follow-up transit observations, such as those that investigate the evaporative processes driven by high-energy radiation that may sculpt the valleys and deserts in the Neptune population.

Keywords: exoplanet astronomy; exoplanet evolution; exoplanet detection methods
Gamma-Ray Diagnostics of r-process Nucleosynthesis in the Remnants of Galactic Binary Neutron-star Mergers

We perform a full nuclear-network numerical calculation of the r-process nuclei in binary neutron-star mergers (NSMs), with the aim of estimating gamma-ray emissions from the remnants of Galactic NSMs up to 106 yr old. The nucleosynthesis calculation of 4070 nuclei is adopted to provide the elemental composition ratios of nuclei with an electron fraction Y e between 0.10 and 0.45. The decay processes of 3237 unstable nuclei are simulated to extract the gamma-ray spectra. As a result, the NSMs have different spectral colors in the gamma-ray band from various other astronomical objects at less than 105 yr old. In addition, we propose a new line diagnostic method for Y e that uses the line ratios of either 137mBa/85K or 243Am/60mCo, which become larger than unity for young and old r-process sites, respectively, with a low-Y e environment. From an estimation of the distance limit for gamma-ray observations as a function of age, the high sensitivity in the sub-megaelectronvolt band, at approximately 10-9 photons s-1 cm-2 or 10-15 erg s-1 cm-2, is required to cover all the NSM remnants in our Galaxy, if we assume that the population of NSMs by Wu et al. A gamma-ray survey with sensitivities of 10-8-10-7 photons s-1 cm-2 or 10-14-10-13 erg s-1 cm-2 in the 70-4000 keV band is expected to find emissions from at least one NSM remnant under the assumption of an NSM rate of 30 Myr-1. The feasibility of gamma-ray missions observing Galactic NSMs is also studied.

Keywords: r-process; gravitational wave sources; neutron stars; nuclear astrophysics; nucleosynthesis
Small-scale Dynamo in Supernova-driven Interstellar Turbulence

Magnetic fields grow quickly even at early cosmological times, suggesting the action of a small-scale dynamo (SSD) in the interstellar medium of galaxies. Many studies have focused on idealized turbulent driving of the SSD. Here we simulate more realistic supernova-driven turbulence to determine whether it can drive an SSD. Magnetic field growth occurring in our models appears inconsistent with simple tangling of magnetic fields, but consistent with SSD action, reproducing and confirming models by Balsara et al. that did not include physical resistivity η. We vary η, as well as the numerical resolution and supernova rate, $\dot{\sigma }$ <!-- --> , to delineate the regime in which an SSD occurs. For a given $\dot{\sigma }$ <!-- --> we find convergence for SSD growth rate with resolution of a parsec. For $\dot{\sigma }\simeq {\dot{\sigma }}_{\mathrm{sn}}$ <!-- --> , with ${\dot{\sigma }}_{\mathrm{sn}}$ <!-- --> the solar neighborhood rate, the critical resistivity below which an SSD occurs is $0.005\gt {\eta }_{\mathrm{crit}}\gt 0.001\,\mathrm{kpc}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ <!-- --> , and this increases with the supernova rate. Across the modeled range of 0.5-4 pc resolution we find that for $\eta \lt {\eta }_{\mathrm{crit}}$ <!-- --> , the SSD saturates at about 5% of kinetic energy equipartition, independent of growth rate. In the range $0.2\,{\dot{\sigma }}_{\mathrm{sn}}\leqslant \dot{\sigma }\leqslant 8\,{\dot{\sigma }}_{\mathrm{sn}}$ <!-- --> growth rate increases with $\dot{\sigma }$ <!-- --> . SSDs in the supernova-driven interstellar medium commonly exhibit erratic growth.

Keywords: astrophysical fluid dynamics; magnetohydrodynamical simulations; supernova dynamics; interstellar medium; interstellar magnetic fields; supernova remnants; magnetohydrodynamics
Formation of Macroscale Flux Transfer Events at Mercury

Flux transfer events (FTEs) are magnetic flux ropes that are produced via magnetic reconnection at the planetary magnetopause where the solar wind directly interacts with the magnetosphere. Previous observations show that FTEs with a duration of several seconds, corresponding to a spatial scale of ∼0.5-1 RM, can occur at Mercury. However, the formation of these macroscale FTEs at a small dimensional magnetopause with a radius of ∼1.5 RM remains unclear. Here, we report the observations of active magnetic reconnection events at Mercury's magnetopause by the MESSENGER spacecraft. The reconnection process is dominated by the formation of a series of multi-scale FTEs. Ion-scale flux ropes, typically with durations of ∼1 s or less, may be produced by the tearing instability in the thin current sheet near the subsolar position. Moreover, the commonly observed macroscale FTEs consist of three to tens of successive small-scale FTEs. We propose that macroscale FTEs at Mercury are generated by the interaction and merging of multiple ion-scale flux ropes, probably through two or more steps. This is distinct from the formation of typical FTEs, mainly between a pair of X-lines, at Earth's magnetopause. Thus, the formation and evolution of FTEs may differ among planetary magnetospheres with a vast range of scale sizes. We further conclude that Mercury's magnetopause is a natural plasma laboratory to study flux rope dynamics and evolution for the upcoming Bepi-Colombo mission.

Keywords: planetary magnetospheres; mercury (planet); solar magnetic reconnection; planetary boundary layers; solar-planetary interactions
The McDonald Accelerating Stars Survey (MASS): Discovery of a Long-period Substellar Companion Orbiting the Old Solar Analog HD 47127

Brown dwarfs with well-determined ages, luminosities, and masses provide rare but valuable tests of low-temperature atmospheric and evolutionary models. We present the discovery and dynamical mass measurement of a substellar companion to HD 47127, an old (≈7-10 Gyr) G5 main-sequence star with a mass similar to the Sun. Radial velocities of the host star with the Harlan J. Smith Telescope uncovered a low-amplitude acceleration of 1.93 ± 0.08 m s-1 yr-1 based on 20 years of monitoring. We subsequently recovered a faint (ΔH = 13.14 ± 0.15 mag) comoving companion at 1"95 (52 au) with follow-up Keck/NIRC2 adaptive optics imaging. The radial acceleration of HD 47127 together with its tangential acceleration from Hipparcos and Gaia EDR3 astrometry provide a direct measurement of the three-dimensional acceleration vector of the host star, enabling a dynamical mass constraint for HD 47127 B (67.5-177 MJup at 95% confidence) despite the small fractional orbital coverage of the observations. The absolute H-band magnitude of HD 47127 B is fainter than the benchmark T dwarfs HD 19467 B and Gl 229 B but brighter than Gl 758 B and HD 4113 C, suggesting a late-T spectral type. Altogether the mass limits for HD 47127 B from its dynamical mass and the substellar boundary imply a range of 67-78 MJup assuming it is single, although a preference for high masses of ≈100 MJup from dynamical constraints hints at the possibility that HD 47127 B could itself be a binary pair of brown dwarfs or that another massive companion resides closer in. Regardless, HD 47127 B will be an excellent target for more refined orbital and atmospheric characterization in the future.

Keywords: brown dwarfs; t dwarfs; companion stars; substellar companion stars
Revisiting the Oldest Stars as Cosmological Probes: New Constraints on the Hubble Constant

Despite the tremendous advance of observational cosmology, the value of the Hubble constant (H 0) is still controversial (the so-called "Hubble tension") because of the inconsistency between local/late-time measurements and those derived from the cosmic microwave background. As the age of the Universe is very sensitive to H 0, we explored whether the present-day oldest stars could place independent constraints on the Hubble constant. To this purpose, we selected from the literature the oldest objects (globular clusters, stars, white dwarfs, and ultrafaint and dwarf spheroidal galaxies) with accurate age estimates. Adopting a conservative prior on their formation redshifts (11 ≤ z f ≤ 30) and assuming Ω M = 0.3 ± 0.02, we developed a method based on Bayesian statistics to estimate the Hubble constant. We selected the oldest objects (>13.3 Gyr) and estimated H 0 both for each of them individually and for the average ages of homogeneous subsamples. Statistical and systematic uncertainties were properly taken into account. The constraints based on individual ages indicate that H 0 < 70.6 km s-1 Mpc-1 when selecting the most accurate estimates. If the ages are averaged and analyzed independently for each subsample, the most stringent constraints imply H 0 < 73.0 km s-1 Mpc-1 with a probability of 90.3% and errors around 2.5 km s-1 Mpc-1. We also constructed an "accuracy matrix" to assess how the constraints on H 0 become more stringent with further improvements in the accuracy of stellar ages and Ω M . The results show the great potential of the oldest stars as independent and competitive cosmological probes not limited to just the Hubble constant.

Keywords: cosmology; observational cosmology; cosmological parameters; hubble constant; stellar ages
A Feature Representation Method for X-Ray Pulsar Signals Based on Cyclostationarity Theory

X-ray pulsar signals commonly have a very low amplitude and suffer from high observation noise and statistical correlation interference, which seriously degrade the signal detection performance given finite observation times. Here, noise refers to the uncertainty distribution of the photon Poisson statistics, and interference refers to time-dependent broadband or narrowband signals, which may originate from some artificial interference source or other pulsars. To address the above problems, this paper proposes a feature representation method for pulsar signal detection based on high-order cyclostationarity theory. First, we establish a photon signal model of an X-ray detector based on the cyclostationary characteristics of pulsar signals, considering period jitter, correlation interference, and Gaussian noise in the pulsar emission process. By introducing cyclic statistics, we use a direct estimation method for the high-order spectrum, including a nonuniform sampling strategy, to accurately extract signal features and effectively suppress correlation interference and noise. Finally, we use simulation data and Rossi X-ray Timing Explorer observation data to verify the proposed method. The results show that the proposed method is a promising feature modeling solution that is superior to traditional one-dimensional spectra and epoch folding in counteracting interference and noise. While such feature modeling is particularly useful for applications such as pulsar navigation, we believe that this method has general promise for a wide range of pulsar-related research.

Keywords: rotation powered pulsars; x-ray stars; astronomy data analysis; astronomy data modeling
Reaction Rate Sensitivity of the Production of γ-Ray Emitting Isotopes in Core-collapse Supernovae

Radioactive isotopes produced in core-collapse supernovae (CCSNe) provide useful insights into the underlying processes driving the collapse mechanism and the origins of elemental abundances. Their study generates a confluence of major physics research, including experimental measurements of nuclear reaction rates, astrophysical modeling, and γ-ray observations. Here we identify the key nuclear reaction rates to the nucleosynthesis of observable radioactive isotopes in explosive silicon burning during CCSNe. Using the nuclear reaction network calculator SkyNet and current REACLIB reaction rates, we evolve temperature-density-time profiles of the innermost 0.45 M⊙ ejecta from the core collapse and explosion of a 12 M⊙ star. Individually varying 3403 reaction rates by factors of 100, we identify 141 reactions that cause significant differences in the isotopes of interest, namely, 43K, 47Ca, 44,47Sc, 44Ti, 48,51Cr, 48,49V, 52,53Mn, 55,59Fe, 56,57Co, and 56,57,59Ni. For each of these reactions, we present a novel method to extract the temperature range pertinent to the nucleosynthesis of the relevant isotope; the resulting temperatures lie within the range T = 0.47-6.15 GK. Limiting the variations to within 1σ of STARLIB reaction rate uncertainties further reduces the identified reactions to 48 key rates, which can be used to guide future experimental research. Complete results are presented in tabular form.

Keywords: explosive nucleosynthesis; nucleosynthesis; core-collapse supernovae; gamma-rays; nuclear astrophysics; reaction rates
Sequential Star Formation in the Young SMC Region NGC 602: Insights from ALMA

NGC 602 is a young, low-metallicity star cluster in the "Wing" of the Small Magellanic Cloud. We reveal the recent evolutionary past of the cluster through analysis of high-resolution (~0.4 pc) Atacama Large Millimeter/submillimeter Array observations of molecular gas in the associated H II region N90. We identify 110 molecular clumps (R < 0.8 pc) traced by CO emission, and study the relationship between the clumps and associated young stellar objects (YSOs) and pre-main-sequence (PMS) stars. The clumps have high virial parameters (typical α vir = 4-11) and may retain signatures of a collision in the last ≲8 Myr between H I components of the adjacent supergiant shell SMC-SGS 1. We obtain a CO-bright-to-H2 gas conversion factor of X CO,B = (3.4 ± 0.2) × 1020 cm-2 (K km s-1)-1, and correct observed clump properties for CO-dark H2 gas to derive a total molecular gas mass in N90 of 16,600 ± 2400 M ⊙. We derive a recent (≲1 Myr) star formation rate of 130 ± 30 M ⊙ Myr-1 with an efficiency of 8% ± 3% assessed through comparing total YSO mass to total molecular gas mass. Very few significant radial trends exist between clump properties or PMS star ages and distance from NGC 602. We do not find evidence for a triggered star formation scenario among the youngest (≲2 Myr) stellar generations, and instead conclude that a sequential star formation process in which NGC 602 did not directly cause recent star formation in the region is likely.

Keywords: small magellanic cloud; interstellar medium; molecular clouds; h ii regions; star formation