adsabs/SciX_UAT_keywords huggingface dataset:
Fundamental Properties of Sheared/Guide Field MHD Magnetic Reconnection

The properties of the sheared/guide field magnetic reconnection (MRX) are investigated with two-dimensional MHD simulation. We simulate the spontaneous evolution from the isothermal current sheet (CS) equilibrium in which distribution of the thermodynamical quantities is symmetric about the CS. The magnetic shear is characterized by two parameters: the shear parameter and the asymmetry parameter. The asymmetry of the Alfvén speed (VA0x) perpendicular to the X-line along the CS is essential. We focus on the asymptotic self-similarly expanding phase of the evolution. This research is unique for the discussion based on the consistency across the entire MRX system, although the sheared MRX has been studied since the early 1980s. In addition to reconfirmation of the previously reported properties of the sheared MRX, the following new properties are found. (1) The reconnection jet changes to the "core-envelope structure" (a high-density core with a low-density envelope) for the sheared symmetric VA0x case but the "two-layered structure" (the high-speed, low-density layer and the medium-speed, high-density layer) for the asymmetric VA0x case. (2) The parameter dependence of the reconnection rate is clarified. The MRX is fastest for the symmetric case and slows as the asymmetry increases for any fixed shear angle. For the symmetric case, the reconnection rate has a monotonically decreasing dependence on the shear angle. (3) In the asymmetric case, the plasmas from both sides of the CS coexist on the same magnetic field lines in the larger VA0x side plasmoid. This characteristic structure suggests an efficient plasma mixing when the plasmoid breaks.

Keywords: plasma astrophysics; solar magnetic reconnection
Atomic Oxygen Escape on Mars Driven by Electron Impact Excitation and Ionization

Neutral escape on Mars is well known to be dominated by atomic oxygen (O) escape via the dissociative recombination (DR) of ${{\rm{O}}}_{2}^{+}$ , the most abundant ion species in the Martian upper atmosphere. In this study, we suggest an alternative mechanism due to the impact excitation and ionization of CO2 by photoelectrons on the dayside or precipitating solar wind electrons on the nightside. These electron impact (EI) processes are capable of producing hot O atoms via the predissociation of CO2 and ${\mathrm{CO}}_{2}^{+}$ in electronically excited states. An evaluation with the aid of the combined data set accumulated by several instruments on board the Mars Atmosphere and Volatile Evolution spacecraft reveals that CO2 EI makes a non-negligible contribution to total atomic O escape on Mars, with a median EI-to-DR escape flux ratio of 10% on the dayside and 20% on the nightside. CO2 EI is found to be able to drive stronger O escape than atmospheric sputtering, an alternative escape mechanism well studied on Mars. Our results highlight the importance of a neutral escape mechanism largely ignored in previous studies.

Keywords: planetary atmospheres; upper atmosphere; electron impact ionization
Systematic KMTNet Planetary Anomaly Search. X. Complete Sample of 2017 Prime-field Planets

We complete the analysis of planetary candidates found by the KMT AnomalyFinder for the 2017 prime fields that cover ∼13 deg2. We report three unambiguous planets: OGLE-2017-BLG-0640, OGLE-2017-BLG-1275, and OGLE-2017-BLG-1237. The first two of these were not previously identified, while the last was not previously published due to technical complications induced by a nearby variable. We further report that a fourth anomalous event, the previously recognized OGLE-2017-BLG-1777, is very likely to be planetary, although its light curve requires unusually complex modeling because the lens and source both have orbiting companions. One of the three unambiguous planets, OGLE-2017-BLG-1275, is the first AnomalyFinder discovery that has a Spitzer microlens parallax measurement, π E ≃ 0.045 ± 0.015, implying that this planetary system almost certainly lies in the Galactic bulge. In the order listed, the four planetary events have planet-host mass ratios q and normalized projected separations s of $(\mathrm{log}q,s)=(-2.31,0.61)$ , (‑2.06, 0.63/1.09), (‑2.10, 1.04), and (‑2.86, 0.72). Combined with previously published events, the 2017 prime fields contain 11 unambiguous planets with well-measured q and one very likely candidate, of which three are AnomalyFinder discoveries. In addition to these 12, there are three other unambiguous planets with large uncertainties in q.

Keywords: gravitational microlensing
XMM-Newton and INTEGRAL Observations of the Bright GRB 230307A: Vanishing of the Local Absorption and Limits on the Dust in the Magellanic Bridge

GRB 230307A is the second brightest gamma-ray burst detected in more than 50 years of observations and is located in the direction of the Magellanic Bridge. Despite its long duration, it is most likely the result of the merger of a compact binary ejected from a galaxy in the local universe (redshift z = 0.065). Our XMM-Newton observation of its afterglow at 4.5 days shows a power-law spectrum with photon index Γ = 1.73 ± 0.10, unabsorbed flux F 0.3-10 keV = (8.8 ± 0.5) × 10-14 erg cm-2 s-1, and no absorption in excess of that produced in our Galaxy and in the Magellanic Bridge. We derive a limit of ${N}_{{\rm{H}}}^{{\rm{HOST}}}\lt 5\times {10}^{20}$ cm-2 on the absorption at the GRB redshift, which is a factor ~5 below the value measured during the prompt phase. We searched for the presence of dust scattering rings with negative results and set an upper limit of the order of A V < 0.05 on the absorption from dust in the Magellanic Bridge.

Keywords: gamma-ray bursts; interstellar dust; magellanic clouds
Convex Shape and Rotation Model of Lucy Target (11351) Leucus from Lightcurves and Occultations

We report new photometric lightcurve observations of the Lucy Mission target (11351) Leucus acquired during the 2017, 2018, and 2019 apparitions. We use these data in combination with stellar occultations captured during five epochs to determine the sidereal rotation period, the spin axis orientation, a convex shape model, the absolute scale of the object, its geometric albedo, and a model of the photometric properties of the target. We find that Leucus is a prograde rotator with a spin axis located within a sky-projected radius of 3° (1σ) from J2000 Ecliptic coordinates (λ = 208°, β = +77°) or J2000 Equatorial Coordinates (R.A. = 248°, decl. = +58°). The sidereal period is refined to Psid = 445.683 ± 0.007 h. The convex shape model is irregular, with maximum dimensions of 60.8, 39.1, and 27.8 km. The convex model accounts for global features of the occultation silhouettes, although minor deviations suggest that local and global concavities are present. We determine a geometric albedo of pV = 0.043 ± 0.002. The derived phase curve supports a D-type classification for Leucus.

Keywords: light curves; stellar occultation; jupiter trojans; ccd photometry
In Search of Infall Motion in Molecular Clumps. V. HCO+ (1–0) and HCN (1–0) Observations toward 210 Infall Candidates

We have carried out HCO+(J = 1–0) and HCN (J = 1–0) line observations towards 210 infall candidates selected from the CO blue-profile catalog by Jiang et al., using the Purple Mountain Observatory 13.7 m telescope. Out of the 210 targets, 42 sources are further confirmed to have infall signatures in HCO+ and/or HCN lines, with a confirmation rate of ∼20%. According to the line profiles, we classify them into two categories: double-peaked and peak-shoulder. Some physical properties are estimated through profile fitting using the RATRAN model. We find that the two types are separated in parameter space, indicating they may be of different properties. The median values of kinetic temperature, infall velocity, and mass infall rate for the two types are 10.5 K and 40.8 K, 0.40 km s‑1 and 1.00 km s‑1, and 4.6 × 10‑5 M ⊙ yr‑1 and 3.5 × 10‑4 M ⊙ yr‑1, respectively. The infall velocities and mass-infall rates of peak-shoulder sources are slightly larger than those of double-peaked ones, suggesting they tend to form more massive stars. We also discuss the association of the 42 confirmed sources with other star formation activities such as maser and outflow, which supports this result.

Keywords: star formation; interstellar medium; molecular clouds; collapsing clouds
Phase-space Analysis of Ordered and Disordered Nonthermal Ion Energization during Magnetic Reconnection

Anomalous ion heating is frequently observed to accompany magnetic reconnection, yet there is little consensus on its origin. Instead of the usual velocity-space analysis, we use phase-space analysis to exhaustively explain how ions are nonthermally energized during collisionless, antiparallel magnetic reconnection. There are both ordered and disordered aspects in the process; the former is explained in terms of conservative quantities, and the latter is explained by demonstrating chaos through a direct calculation of Lyapunov exponents. The former induces "multibeam-like heating" in all three directions, whereas the latter induces stochastic bulk heating. Profiles of the ion temperature tensor components during reconnection can be easily understood by the phase-space distributions of ions in different motional stages.

Keywords: solar magnetic reconnection; solar coronal heating
Observation of S4716-a Star with a 4 yr Orbit around Sgr A*

The ongoing monitoring of the Galactic center and Sgr A*, the central supermassive black hole, produces surprising and unexpected findings. This goes hand in hand with the technical evolution of ground- and space-based telescopes and instruments, but also with the progression of image filter techniques such as the Lucy-Richardson algorithm. As we continue to trace the members of the S cluster close to Sgr A* on their expected trajectory around the supermassive black hole, we present the finding of a new stellar source, which we call S4716. The newly found star orbits Sgr A* in about 4.0 yr and can be detected with NIRC2 (Keck), OSIRIS (Keck), SINFONI (VLT), NACO (VLT), and GRAVITY (VLTI). With a periapse distance of about 100 au, S4716 shows an equivalent distance toward Sgr A* as S4711. These fast-moving stars undergo a similar dynamical evolution, since S4711-S4716 share comparable orbital properties. We will furthermore draw a connection between the recent finding of a new faint star called S300 and the data presented here. Additionally, we observed a blend-star event with S4716 and another newly identified S star S148 in 2017.

Keywords: galactic center; star clusters; stellar dynamics; supermassive black holes
Appearance of a New Nebula in the Constellation Puppis after an Outburst in 2015 around WISEA J075915.26-310844.6

Here I report the appearance of a new nebula in the constellation Puppis. The nebula was discovered in archived DECam images from 2017 January. Additionally the central source shows an outburst between 2015 February and 2015 April in archived unWISE images. The outburst reached the current brightness in 2016 November (W1 ∼ 3.6 mag, W2 ∼ 1.5 mag). The pre-outburst images from the VST (2012 March) and PanSTARRS (2015 February) do not show any nebulosity around this source. The appearance of reflection nebulae overlapping with the outburst of the central source is known for pre-main sequence stars, such as FU Orionis variables. Follow-up spectroscopy is desired for the central source.

Keywords: fu orionis stars; reflection nebulae; infrared astronomy; star formation; pre-main sequence stars
Breaking Boundaries: A Universal Wavefront Reconstruction Approach for High-resolution Solar Imaging

This Letter proposes a universal wavefront reconstruction approach based on a coupled data set and neural network, aiming to overcome the limitations of current algorithms in terms of universality and wavefront sensing accuracy for variable imaging objects. First, a novel data set, Multi-Object Wavefront Coupling Dataset (MOCD-Dataset), is developed to provide diverse data and enable the network to learn universal wavefront features. Next, a new universal wavefront reconstruction network called Object-Independent Wavefront Decoupling Network (OIWD-Net) is introduced, aiming to separate imaging object information from multiple variable images. Our algorithm eliminates the need for specialized wavefront sensors, has a simple system, high light energy utilization, and does not require customized models for each different type of imaging objects, making it highly practical. By combining the MOCD-Dataset and the OIWD-Net, excellent accuracy in wavefront reconstruction of different imaging objects has been achieved. This research provides a new solution for high-resolution image restoration in fields such as solar structure observation and astronomical high-resolution imaging.

Keywords: solar activity
Determining the Spectral Content of MOSES Images

The Multi-Order Solar Extreme Ultraviolet Spectrograph (MOSES) sounding rocket was launched from White Sands Missile Range on 2006 February 8th, to capture images of the Sun in the He II 303.8 Å emission line. MOSES is a slitless spectrograph that forms images in multiple spectral orders simultaneously using a concave diffraction grating in an effort to measure line profiles over a wide field of view from a single exposure. Early work on MOSES data showed evidence of solar features composed of neither He II 303.8 Å nor the nearby Si XI 303.3 Å spectral lines. We have built a forward model that uses cotemporal EIT images and the Chianti atomic database to fit synthetic images with known spectra to the MOSES data in order to quantify this additional spectral content. Our fit reveals a host of dim lines that alone are insignificant but combined contribute a comparable intensity to MOSES images as Si XI 303.3 Å. In total, lines other than He II 303.8 Å and Si XI 303.3 Å contribute approximately 10% of the total intensity in the MOSES zero order image. This additional content, if not properly accounted for, could significantly impact the analysis of MOSES and similar slitless spectrograph data, especially those using a zero-order (undispersed) image. More broadly, this serves as a reminder that multilayer EUV imagers are sensitive to a host of weak contaminant lines.

Keywords: solar transition region; solar instruments
Response of the High-latitude Upper Mesosphere to Energetic Electron Precipitation

We carried out a statistical study on the effects of strong geomagnetic activity on the mesopause over the auroral region from 2002 to 2018. When the auroral electrojet index increased significantly, the energetic electron precipitation from the Medium Energy Proton and Electron Detector was enhanced by several multiples of 10 for the 55°-70° geomagnetic latitude band. The temperatures measured by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument increased immediately in the mesopause region, together with a descent of the mesopause of about 0.5-2 km. Due to the depth that the precipitation can affect, we conclude that the mesopause is mainly influenced by electrons in the energy range 30-100 keV. The maximum temperature increment at 95 km can reach 4 K and the delay of the response can be up to 1 day. In general, we find that the temperatures significantly respond to the electron precipitation at as low as 93 km, within the mesopause region in most of a year.

Keywords: earth atmosphere; mesopause; mesosphere; aeronomy
Detecting Lipids on Planetary Surfaces with Laser Desorption Ionization Mass Spectrometry

In the search for extraterrestrial life, biosignatures (e.g., organic molecules) play an important role, of which lipids are one considerable class. If detected, these molecules can be strong indicators of the presence of life, past or present, as they are ubiquitous in life on Earth. However, their detection is challenging, depending on, e.g., instrument performance, as well as the selected site. In this contribution, we demonstrate that, using laser desorption ionization mass spectrometry, detection of lipids is feasible. Using our space prototype instrument designed and built in-house, six representative lipids were successfully detected: cholecalciferol, phylloquinone, menadione, 17α-ethynylestradiol, α-tocopherol, and retinol, both as pure substances and as mixtures additionally containing amino acids or polycyclic aromatic hydrocarbons. Observed limits of detection for lipids already meet the requirements stated in the Enceladus Orbilander mission concept. The current performance of our LDI-MS system allows for the simultaneous identification of lipids, amino acids, and polycyclic aromatic hydrocarbons, using a single instrument. We therefore believe that the LDI-MS system is a promising candidate for future space exploration missions devoted to life detection.

Keywords: mass spectrometry; time-of-flight mass spectrometry; astrobiology; biosignatures; space vehicle instruments
Effects of Total Solar Eclipse on Ionospheric Total Electron Content over Antarctica on 2021 December 4

The effects of a total solar eclipse that occurred on 2021 December 4 on ionospheric total electron content (TEC) over Antarctic stations were studied. The study was based on GPS data obtained over Antarctica on the day of the eclipse and the days before and after the eclipse over six GPS stations. The findings of this study show that a total solar eclipse lowers the amount of ionization reaching the Earth's surface with TEC values dropping across the stations. Finally, the enhancement of ΔTEC is quite different from one station to another station. This may also be due to the effect of solar heating conditions and the density of the Sun as exerted over the stations with the Sun side over one station and the clouded part over the others.

Keywords: solar eclipses
Response of Electric Field in Terrestrial Magnetosphere to Interplanetary Shock

Electric field impulses generated by interplanetary shocks can cause a series of dynamic processes in the Earth's magnetosphere and were previously explained by either fast-mode wave propagation or flow related to compression of the magnetopause. Based on a Space Weather Modeling Framework simulation, we suggest a new scenario in which the evolution of the impulse is due to both the propagation of the fast-mode wave and the compression of the magnetopause, which can explain the simulation and observations in previous related studies. The onset of the electric field impulse is determined by the propagation of the fast-mode wave in the magnetosphere while the peak of the impulse is determined by the propagation of the compression of the magnetopause. The new understanding of the impulse is important for the generation of subsequent ultralow frequency waves through the coupling of the fast-mode to Alfvén waves and field line resonances and related radiation-belt electron acceleration.

Keywords: space plasmas; space weather; van allen radiation belts; planetary magnetospheres; magnetohydrodynamical simulations; magnetohydrodynamics; solar-terrestrial interactions; solar-planetary interactions; interplanetary shocks
The EDGE-CALIFA Survey: Molecular Gas and Star Formation Activity across the Green Valley

We present a 12CO(J = 2‑1) survey of 60 local galaxies using data from the Atacama Compact Array as part of the Extragalactic Database for Galaxy Evolution: the ACA EDGE survey. These galaxies all have integral field spectroscopy from the CALIFA survey. Compared to other local galaxy surveys, ACA EDGE is designed to mitigate selection effects based on CO brightness and morphological type. Of the 60 galaxies in ACA EDGE, 36 are on the star formation main sequence, 13 are on the red sequence, and 11 lie in the "green valley" transition between these sequences. We test how star formation quenching processes affect the star formation rate (SFR) per unit molecular gas mass, SFEmol = SFR/M mol, and related quantities in galaxies with stellar masses 10 ≤ log[M ⋆/M ⊙] ≤ 11.5 covering the full range of morphological types. We observe a systematic decrease of the molecular-to-stellar mass fraction ( ${R}_{\star }^{\mathrm{mol}}$ ) with a decreasing level of star formation activity, with green valley galaxies also having lower SFEmol than galaxies on the main sequence. On average, we find that the spatially resolved SFEmol within the bulge region of green valley galaxies is lower than in the bulges of main-sequence galaxies if we adopt a constant CO-to-H2 conversion factor, α CO. While efficiencies in main-sequence galaxies remain almost constant with galactocentric radius, in green valley galaxies, we note a systematic increase of SFEmol, ${R}_{\star }^{\mathrm{mol}}$ , and specific SFR with increasing radius. As shown in previous studies, our results suggest that although gas depletion (or removal) seems to be the most important driver of the star formation quenching in galaxies transiting through the green valley, a reduction in star formation efficiency is also required during this stage.

Keywords: extragalactic astronomy
The Enceladus Orbilander Mission Concept: Balancing Return and Resources in the Search for Life

Enceladus's long-lived plume of ice grains and water vapor makes accessing oceanic material readily achievable from orbit (around Saturn or Enceladus) and from the moon's surface. In preparation for the National Academies of Sciences, Engineering and Medicine 2023-2032 Planetary Science and Astrobiology Decadal Survey, we investigated four architectures capable of collecting and analyzing plume material from orbit and/or on the surface to address the most pressing questions at Enceladus: Is the subsurface ocean inhabited? Why, or why not? Trades specific to these four architectures were studied to allow an evaluation of the science return with respect to investment. The team found that Orbilander, a mission concept that would first orbit and then land on Enceladus, represented the best balance. Orbilander was thus studied at a higher fidelity, including a more detailed science operations plan during both orbital and landed phases, landing site characterization and selection analyses, and landing procedures. The Orbilander mission concept demonstrates that scientifically compelling but resource-conscious Flagship-class missions can be executed in the next decade to search for life at Enceladus.

Keywords: saturnian satellites; planetary science; remote sensing; astrobiology; biosignatures; natural satellite surfaces
The Crab Nebula as a Calibrator for Wide-beam Cosmic Microwave Background Polarization Surveys

We analyze the effect of polarized diffuse emission in the calibration of wide-beam millimeter-wave polarimeters, when using the Crab Nebula as a reference source for both polarized brightness and polarization angle. We show that, for CMB polarization experiments aiming at detecting B-mode in a scenario with a tensor to scalar ratio r ~ 0.001, wide (a few degrees in diameter), precise ( ${\sigma }_{Q},{\sigma }_{U}\sim 20\,\mu {{\rm{K}}}_{\mathrm{CMB}}\mathrm{arcmin}$ ), high angular resolution (<FWHM) reference maps are needed to properly take into account the effects of diffuse polarized emission and avoid significant bias in the calibration.

Keywords: observational cosmology; dust continuum emission; cmbr detectors; cosmic microwave background radiation; polarimetry