adsabs/SciX_UAT_keywords huggingface dataset:
Characterization of the DART Impact Ejecta Plume on Dimorphos from LICIACube Observations

We modeled the geometry and the three-dimensional orientation of the ejecta cone triggered by the impact of the DART spacecraft on the asteroid Dimorphos. We used eight LUKE images of the impact acquired by the CubeSat LICIACube that flew by the Didymos system shortly after the impact. These images, which show the ejecta cone in both face-on and side-on profiles, enabled us to reconstruct the ejecta cone in inertial space. We started our model as a simple cone with a circular base and developed it to a rotated cone with an elliptical base that best fit the data. The cone axis points to R.A., decl. (in J2000): ${147}_{-10^\circ }^{+1^\circ }$ , + ${16}_{-6^\circ }^{+4^\circ }$ . The cone is characterized by two perpendicular half-angles of $\eta ={69}_{-3^\circ }^{+1^\circ },\gamma ={51}_{-11^\circ }^{+1^\circ }$ and a rotation of ω = 12° around its axis. The apex of the cone is located near the center of Dimorphos within 15 m. The intersection of the cone and the surface of Dimorphos (surface enclosed by the cone) would correspond to a crater with a maximum radius of about 65 m. The characterization of the cone axis is directly related to the computation of the momentum enhancement factor (β) of the impact, and it hence proves the crucial need of studying impacts in the context of planetary defence scenarios. The results of this work could potentially be used to constrain whether the impact took place in a strength-dominated or a gravity-dominated regime. This work shows the important scientific return of the LICIACube CubeSat in the context of planetary defence.

Keywords: asteroids
Magnetic Fields and Fragmentation of Filaments in the Hub of California-X

We present 850 μm polarization and C18O (3-2) molecular line observations toward the X-shaped nebula in the California molecular cloud using James Clerk Maxwell Telescope (JCMT)'s SCUBA-2/POL-2 and HARP instruments. The 850 μm emission shows that the observed region includes two elongated filamentary structures (Fil1 and Fil2) having chains of regularly spaced cores. We measured the mass per unit length of the filaments and found that Fil1 and Fil2 are thermally super- and subcritical, respectively, but both are subcritical if nonthermal turbulence is considered. The mean projected spacings ( ${\rm{\Delta }}\bar{S}$ ) of the cores in Fil1 and Fil2 are 0.13 and 0.16 pc, respectively. ${\rm{\Delta }}\bar{S}$ is smaller than 4× the filament width expected in the classical cylinder fragmentation model. The large-scale magnetic field orientations shown by Planck are perpendicular to the long axes of Fil1 and Fil2, while those in the filaments obtained from the high-resolution polarization data of JCMT are disturbed, but those in Fil1 tend to have longitudinal orientations. Using the modified Davis–Chandrasekhar–Fermi method, we estimated the magnetic field strengths (B pos) of the filaments, which are 110 ± 80 and 90 ± 60 μG, respectively. We calculated the gravitational, kinematic, and magnetic energies of the filaments, and found that the fraction of magnetic energy is larger than 60% in both filaments. We propose that the dominant magnetic energy may lead the filament to be fragmented into aligned cores as suggested by Tang et al., and the shorter core spacing can be due to a projection effect via the inclined geometry of the filaments or due to nonnegligible longitudinal magnetic fields in the case of Fil1.

Keywords: interstellar magnetic fields; interstellar medium; polarimetry; submillimeter astronomy; star forming regions
Clouds and Clarity: Revisiting Atmospheric Feature Trends in Neptune-size Exoplanets

Over the last decade, precise exoplanet transmission spectroscopy has revealed the atmospheres of dozens of exoplanets, driven largely by observatories like the Hubble Space Telescope. One major discovery has been the ubiquity of atmospheric aerosols, often blocking access to exoplanet chemical inventories. Tentative trends have been identified, showing that the clarity of planetary atmospheres may depend on equilibrium temperature. Previous work has often grouped dissimilar planets together in order to increase the statistical power of any trends, but it remains unclear from observed transmission spectra whether these planets exhibit the same atmospheric physics and chemistry. We present a reanalysis of a smaller, more physically similar sample of 15 exo-Neptune transmission spectra across a wide range of temperatures (200-1000 K). Using condensation cloud and hydrocarbon haze models, we find that the exo-Neptune population is best described by low cloud sedimentation efficiency (f sed ~ 0.1) and high metallicity (100 × solar). There is an intrinsic scatter of ~0.5 scale height, perhaps evidence of stochasticity in these planets' formation processes. Observers should expect significant attenuation in transmission spectra of Neptune-size exoplanets, up to 6 scale heights for equilibrium temperatures between 500 and 800 K. With JWST's greater wavelength sensitivity, colder (<500 K) planets should be high-priority targets given their clearer atmospheres, and the need to distinguish between the "super-puffs" and more typical gas-dominated planets.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; exoplanet atmospheric dynamics; transmission spectroscopy; hubble space telescope; james webb space telescope
A Comparison of Solar X-Ray Flare Timescales and Peak Temperatures with Associated Coronal Mass Ejections

Recent work has shown that plots of solar flare X-ray peak temperatures, Tm, versus log peak fluxes, Fp, show statistically significant separations of lower Tm flares with fast (Vcme ≥ 1000 km s-1) and wide (Wcme = 360°) strong coronal mass ejections (CMEs) from higher Tm flares with no CMEs or slow (Vcme < 1000 km s-1) or narrow (<360°) weak CMEs. We extend that statistical separation to CME kinetic energies, Ecme. Flares with long-duration timescales also have well-known associations with fast CMEs and solar energetic (E > 10 MeV) particle events. Using a data set of 585 ≥ M3.0 GOES X-ray flares, we ask whether longer flare timescales (rise times, TR; durations from onset to half-power decay, TD; decay times to half power, Td; and decay times to C2, TC2) also statistically discriminate among the three groups of CMEs for speeds, widths, and energies. All log-log plots of flare timescales versus Fp produce significant separations of the three groups of CMEs generally better than those of Tm versus log Fp. We use separations of CME distribution medians to sort the four flare timescales as effective discriminants among the three CME groups. Separations between the confined flares (no-CMEs) and weak CMEs are generally smaller than those between the weak CMEs and strong CMEs. A combination of Tm and TC2 provides optimum group separations, but Tm and log TD or log Td appears best for CME forecasting purposes.

Keywords: the sun; solar x-ray flares
Large-amplitude Prominence Oscillations following Impact by a Coronal Jet

Observational evidence shows that coronal jets can hit prominences and set them in motion. The impact leads to large-amplitude oscillations (LAOs) in the prominence. In this paper, we attempt to understand this process via 2.5D MHD numerical experiments. In our model, the jets are generated in a sheared magnetic arcade above a parasitic bipolar region located in one of the footpoints of the filament channel (FC) supporting the prominence. The shear is imposed at velocities not far above the observed photospheric values; this leads to a multiple reconnection process, as obtained in previous jet models. Both a fast Alfvénic perturbation and a slower supersonic front preceding a plasma jet are issued from the reconnection site; in the later phase, a more violent (eruptive) jet is produced. The perturbation and jets run along the FC; they are partially reflected at the prominence, and partially transmitted through it. This results in a pattern of counter-streaming flows along the FC, and oscillations in the prominence. The oscillations are LAOs (i.e., with amplitudes above 10 km s-1) in some areas of the prominence, both in the longitudinal and transverse directions. In some field lines, the impact is so strong that the prominence mass is brought out of the dip and down to the chromosphere along the FC. Two cases are studied, with respect to arcades at different heights above the parasitic bipolar region, leading to different heights for the region of the prominence perturbed by the jets. The obtained oscillation amplitudes and periods are in general agreement with the observations.

Keywords: solar prominences; plasma jets; solar coronal waves; solar corona; solar filaments; jets
The ΛCDM-NG Cosmological Model: A Possible Resolution of the Hubble Tension

We offer a cosmological model based on conventional general relativity (no speculative physics) that may resolve the Hubble tension. A reanalysis of the foundation of the Lambda-CDM model shows that general relativity alone does not specify what fraction of the mass density acts as the source term in Friedmann's equation and what fraction acts as the source of the gravitational potential of condensed objects. This observation opens the way to alternative cosmological models within conventional general relativity, and it proves that the ΛCDM model is not the unique solution of Einstein's equations for the usual cosmological sources of gravitation. We emphasize that the source of the gravitation potential in the ΛCDM model is the deviation δ ρ m of the mass density away from its average value, and not the total density of condensed masses as in Newtonian theory. Though not often stated, this is a modification of Newtonian gravitation within the ΛCDM model. The ΛCDM-NG model uses the freedom to move matter between source terms to restore the source of gravitational potential to its Newtonian form. There is no Hubble tension in the ΛCDM-NG model if the gravitational potential of condensed objects (stars, galaxies, and dark matter clouds) falls in a certain range, a range that does not seem unreasonable for the actual Universe. The deceleration parameter in the ΛCDM-NG model differs from that in the ΛCDM model, suggesting a test to distinguish between the two models.

Keywords: cosmology; cosmological models; relativistic cosmology; observational cosmology
H2O2-induced Greenhouse Warming on Oxidized Early Mars

The existence of liquid water within an oxidized environment on early Mars has been inferred by the Mn-rich rocks found during recent explorations on Mars. The oxidized atmosphere implied by the Mn-rich rocks would basically be comprised of CO2 and H2O without any reduced greenhouse gases such as H2 and CH4. So far, however, it has been thought that early Mars could not have been warm enough to sustain water in liquid form without the presence of reduced greenhouse gases. Here, we propose that H2O2 could have been the gas responsible for warming the surface of the oxidized early Mars. Our one-dimensional atmospheric model shows that only 1 ppm of H2O2 is enough to warm the planetary surface because of its strong absorption at far-infrared wavelengths, in which the surface temperature could have reached over 273 K for a CO2 atmosphere with a pressure of 3 bar. A wet and oxidized atmosphere is expected to maintain sufficient quantities of H2O2 gas in its upper atmosphere due to its rapid photochemical production in slow condensation conditions. Our results demonstrate that a warm and wet environment could have been maintained on an oxidized early Mars, thereby suggesting that there may be connections between its ancient atmospheric redox state and possible aqueous environment.

Keywords: solar system terrestrial planets; mars; planetary atmospheres
Evolution of Magnetic Fields and Energy Release Processes during Homologous Eruptive Flares

We explore the processes of the repetitive buildup and the explosive release of magnetic energy, together with the formation of magnetic flux ropes, which eventually resulted in three homologous eruptive flares of successively increasing intensities (i.e., M2.0, M2.6, and X1.0). The flares originated from NOAA active region 12017 between 2014 March 28 and 29. EUV observations and magnetogram measurements, together with coronal magnetic field modeling, suggest that the flares were triggered by the eruption of flux ropes that were embedded in a densely packed system of loops within a small part of the active region. In X-rays, the first and second events show similar evolutions, with single compact sources, while the third event exhibits multiple emission centroids, with a set of strong nonthermal conjugate sources at 50-100 keV during the hard X-ray peak. Over an interval of ≈ 44 hr, the photospheric magnetic field encompassing the three flares undergoes important phases of emergence and cancellation, together with significant changes near the polarity inversion lines within the flaring region. Our observations point toward the tether-cutting mechanism being the plausible triggering process of the eruptions. Between the second and third events, we observe a prominent phase of flux emergence that temporally correlates with the buildup phase of free magnetic energy in the active region corona. In conclusion, our analysis reveals efficient coupling between the rapidly evolving photospheric and coronal magnetic fields in the active region, leading to a continued phase of the buildup of free energy, which results in the homologous flares of successively increasing intensities.

Keywords: solar coronal mass ejections; solar flares; solar magnetic flux emergence; solar x-ray emission
Photospheric Emission in Gamma-Ray Bursts. I. Variability

It is generally believed that the variability of photospheric emission in gamma-ray bursts (GRBs) traces that of the jet power. This work further investigates the variability of photospheric emission in a variable jet. By setting a constant η (dimensionless entropy of the jet), we find that the light curve of the photospheric emission shows a "tracking" pattern on the time profile of jet power. However, the relative variability is significantly low in the photospheric emission compared with that in the jet power. If the η is genetic variable, the variability of the photospheric emission is not only limited by the jet power but also affected by η strongly. It becomes complex and is generally different from that of the jet power. Moreover, the opposite phase may stand in the variabilities of the photospheric emission at different photon energies. We also find that the relative variability does not remain constant over the photon energies with an obvious reduction at a certain energy. This is consistent with the analysis of GRB 090902B in which an appreciable thermal component has been detected in a wide energy range. For several other GRBs coupling with the thermal component, we conservatively evaluate the variability of the thermal and nonthermal emission, respectively. Our results show that the relative variability of the thermal emission is likely comparable to that of the nonthermal emission for these bursts. In addition, the analysis of GRB 120323A reveals that the variability of the photospheric emission may be of the opposite phase from that of the nonthermal emission.

Keywords: gamma-ray bursts; jets; astronomy data analysis; non-thermal radiation sources
Searches after Gravitational Waves Using ARizona Observatories (SAGUARO): Observations and Analysis from Advanced LIGO/Virgo's Third Observing Run

With the conclusion of the third observing run for Advanced LIGO/Virgo (O3), we present a detailed analysis of both triggered and serendipitous observations of 17 gravitational-wave (GW) events (7 triggered and 10 purely serendipitous) from the Searches After Gravitational-waves Using ARizona Observatories (SAGUARO) program. We searched a total of 4935 deg2 down to a median 5σ transient detection depth of 21.1 AB mag using the Mt. Lemmon 1.5 m telescope, the discovery engine for SAGUARO. In addition to triggered events within 24 hr, our transient search encompassed a time interval following GW events of <120 hr, providing observations on ∼1/2 of the events accessible to the Mt. Lemmon 1.5 m telescope. We covered 2.1%-86% of the LVC total probability (Ptotal) for individual events, with a median Ptotal ≈ 8% within <120 hr. Following improvements to our pipeline and the addition of serendipitous observations, we find a total of seven new optical candidates across five GW events, which we are unable to rule out after searching for additional information and comparing to kilonova models. Using both publicly available and our own late-time data, we investigated a total of 252 optical candidates for these 17 events, finding that only 65% were followed up in some capacity by the community. Of the total 252 candidates, we are able to rule out an additional 12 previously reported counterpart candidates. In light of these results, we discuss lessons learned from the SAGUARO GW counterpart search. We discuss how community coordination of observations and candidate follow-up, as well as the role of archival data, are crucial to improving the efficiency of follow-up efforts and preventing unnecessary duplication of effort with limited electromagnetic resources.

Keywords: gravitational waves; observational astronomy
Experimental Constraints on Deliquescence of Calcium Perchlorate Mixed with a Mars Regolith Analog

Hygroscopic salts within the Martian regolith may actively participate in the near-surface water cycle by exchanging water vapor via solid-state salt hydration and deliquescence. To elucidate this process, experimental work has constrained the phase diagram of Mars-relevant salts and the stability of the resultant brines. However, salt interactions with a Mars-like regolith, which itself can exchange water vapor with the atmosphere via adsorption, has not yet been well explored. Here, to better understand water exchange with a salty Mars-like regolith and, particularly, the potential to form brines, we have conducted a series of experiments using JSC Mars-1 regolith simulant mixed with calcium perchlorate in a Mars simulation chamber at a temperature <5°C and a relative humidity <20%. During the experiments, we measured the sample mass, as well as the temperature and relative humidity of the sample and the chamber. We found that the water uptake of a salty Mars-like regolith is about twice as fast as that of a salt-free regolith. Furthermore, we found evidence to suggest that deliquescence occurred; however, not all the salt within the sample may have entered solution. The amount of water in solution was small and did not lead to regolith darkening. Our results suggest that, under the tested experimental conditions, salt deliquescence and regolith adsorption can occur simultaneously.

Keywords: mars; water vapor; surface processes; astrobiology
Long-term Study of the First Galactic Ultraluminous X-Ray Source Swift J0243.6+6124 Using NICER

We present the results obtained from detailed X-ray timing and spectral studies of X-ray pulsar Swift J0243.6+6124 during its giant and normal X-ray outbursts between 2017 and 2023 observed by the Neutron star Interior Composition Explorer (NICER). We focused on a timing analysis of the normal outbursts. A distinct break is found in the power density spectra of the source. The corresponding break frequency and slopes of the power laws around the break vary with luminosity, indicating a change in the accretion dynamics with the mass accretion rate. Interestingly, we detected quasiperiodic oscillations within a specific luminosity range, providing further insights into the underlying physical processes. We also studied the neutron star spin period evolution and a luminosity variation in the pulse profile during the recent 2023 outburst. The spectral analysis was conducted comprehensively for the giant and all other normal outbursts. We identified a double transition at luminosities of ≈7.5 × 1037 and 2.1 × 1038 erg s‑1 in the evolution of continuum parameters like the photon index and cutoff energy with luminosity. This indicates three distinct accretion modes experienced by the source, mainly during the giant X-ray outburst. A soft blackbody component with a temperature of 0.08–0.7 keV is also detected in the spectra. The observed temperature undergoes a discontinuous transition when the pulsar evolves from a sub- to super-Eddington state. Notably, in addition to an evolving 6–7 keV iron line complex, a 1 keV emission line was observed during the super-Eddington state of the source, implying X-ray reflection from the accretion disk or outflow material.

Keywords: neutron stars; compact objects; ultraluminous x-ray sources; pulsars
Infrared Spectroscopic and Physical Properties of Methanol Ices—Reconciling the Conflicting Published Band Strengths of an Important Interstellar Solid

Infrared spectroscopic observations have established the presence of solid methanol (CH3OH) in the interstellar medium and in solar system ices, but the abundance of frozen CH3OH cannot be deduced without accurate band strengths, optical constants, and reference spectra. In this paper we identify disagreements, omissions, and gaps in the literature on infrared (IR) intensities of methanol ices, including unaddressed concerns that reach back several decades. New spectra are presented with intensity measurements aided by new data on the index of refraction and density of solid CH3OH. The result is that the large discordant results from different laboratory groups can now be reconciled. Multiple ices have been used to determine, apparently for the first time, IR intensities of H2O + CH3OH mixtures of accurately known composition for use with observations of interstellar ices. Also for the first time, measurements on CH3OH ices with different thicknesses have allowed us to report both near-IR band strengths and optical constants for two near-IR features used by planetary scientists. We have used our new IR results to determine vapor pressures of solid CH3OH and have compared them to measurements made with a quartz-crystal microbalance. Thermal annealings of methanol ices have been carried out and phase changes in the solid state examined. Comparisons of our results to earlier work are presented where possible, and electronic versions of our new results are made available.

Keywords: interstellar molecules; astrochemistry; laboratory astrophysics; chemical abundances; ice spectroscopy
Multiwavelength Analysis of the Supernova-associated Low-luminosity GRB 171205A

Multiwavelength properties of the nearby supernova (SN)-associated low-luminosity GRB 171205A are investigated in depth to constrain its physical origin synthetically. The pulse width is found to be correlated with energy with a power-law index of ‑0.24 ± 0.07, which is consistent with the indices of other SN-associated gamma-ray bursts (SN/GRBs) but larger than those of long GRBs. By analyzing the overall light curve of its prompt gamma rays and X-ray plateaus simultaneously, we infer that the early X-rays together with the gamma-rays should reflect the activities of the central engine, while the late X-rays may be dominated by the interaction of external shocks with circumburst material. In addition, we find that the host radio flux and offset of GRB 171205A are similar to those of other nearby low-luminosity GRBs. We adopt nine SN/GRBs with measured offset to build a relation between peak luminosity (L γ,p ) and spectral lag (τ) as L γ,p ∝ τ ‑1.91±0.33. The peak luminosity and the projected physical offset of 12 SN/GRBs and 10 kilonova-associated GRBs are found to be moderately correlated, suggesting their different progenitors. The multiwavelength afterglow fitted with a top-hat jet model indicates that the jet half-opening angle and the viewing angle of GRB 171205A are ∼34.°4 and 41.°8, respectively, which implies that the off-axis emissions are dominated by the peripheral cocoon rather than the jet core.

Keywords: gamma-ray bursts