adsabs/SciX_UAT_keywords huggingface dataset:
Data-driven MHD Simulation of the Formation and Initiation of a Large-scale Preflare Magnetic Flux Rope in AR 12371

Solar eruptions are the most powerful drivers of space weather. To understand their cause and nature, it is crucial to know how the coronal magnetic field evolves before eruption. Here we study the formation process of a relatively large-scale magnetic flux rope (MFR) in active region NOAA 12371 that erupts with a major flare and coronal mass ejection on 2015 June 21. A data-driven numerical magnetohydrodynamic model is employed to simulate three-dimensional coronal magnetic field evolution of 1 day duration before the eruption. Comparison between the observed features and our modeled magnetic field discloses how the pre-eruption MFR forms. Initially, the magnetic field lines were weakly twisted as being simple sheared arcades. Then a long MFR was formed along the polarity inversion line due to the complex photospheric motion, which is mainly shearing rather than twisting. The presence of the MFR is evidenced by a coherent set of magnetic field lines with twist number above unity. Below the MFR a current sheet is shown in the model, suggesting that tether-cutting reconnection plays a key role in the MFR formation. The MFR's flux grows as more and more field lines are twisted due to continuous injection of magnetic helicity by the photospheric motions. Meanwhile, the height of the MFR's axis increases monotonely from its formation. By an analysis of the decay index of its overlying field, we suggest that this is because the MFR runs into the torus instability regime and becomes unstable, which finally triggers the eruption.

Keywords: solar flares; solar coronal mass ejections; solar filament eruptions; solar active regions; magnetohydrodynamical simulations; quasars
X-Rays from the Nearby Compact Emission-line Galaxy NGC 2366

Luminous, compact emission-line galaxies (LCGs) are the most abundant class of confirmed Lyman continuum (LyC) emitters. An optical integral field study of the nearby LCG NGC 2366 reveals an outflow originating at the star cluster "knot B" thought to clear a channel via mechanical feedback that enables LyC escape. We observed NGC 2366 with the Chandra X-ray Observatory and detected X-ray emission from a point source coincident with the apex of the outflow at knot B. The pointlike nature and variability of the X-ray emission suggests accretion onto a compact object. The accretion could produce sufficient kinetic energy to power the outflow.

Keywords: blue compact dwarf galaxies; galaxy winds; h ii regions; x-ray binary stars; reionization; starburst galaxies
ALMA Observations of Quasar Host Galaxies at z ≃ 4.8

We present ALMA Band 7 data of the [C II] $\lambda 157.74\,\mu {\rm{m}}$ emission line and underlying far-IR (FIR) continuum for 12 luminous quasars at $z\simeq 4.8$ powered by fast-growing supermassive black holes (SMBHs). Our total sample consists of 18 quasars, 12 of which are presented here for the first time. The new sources consist of six Herschel/SPIRE-detected systems, which we define as "FIR-bright" sources, and six Herschel/SPIRE-undetected systems, which we define as "FIR-faint" sources. We determine dust masses for the quasars hosts of ${M}_{\mathrm{dust}}\leqslant 0.2\mbox{--}25.0\times {10}^{8}{M}_{\odot }$ , implying interstellar medium gas masses comparable to the dynamical masses derived from the [C II] kinematics. It is found that, on average, the Mg II line is blueshifted by $\sim 500\,\mathrm{km}\,{{\rm{s}}}^{-1}$ with respect to the [C II] emission line, which is also observed when complementing our observations with data from the literature. We find that all of our FIR-bright subsample and most of the FIR-faint objects lie above the main sequence of star-forming galaxies at $z\sim 5$ . We detect companion submillimeter galaxies for two sources, both FIR-faint, with a range of projected distances of $\sim 20\mbox{--}60$ kpc and typical velocity shifts of $\left|{\rm{\Delta }}V\right|\lesssim 200\,\mathrm{km}\,{{\rm{s}}}^{-1}$ from the quasar hosts. Of our total sample of 18 quasars, 5/18 are found to have dust-obscured star-forming companions.

Keywords: active galaxies; high-redshift galaxies; galaxy interactions; quasars; star formation
VERTICO. VII. Environmental Quenching Caused by the Suppression of Molecular Gas Content and Star Formation Efficiency in Virgo Cluster Galaxies

We study how environment regulates the star formation cycle of 33 Virgo Cluster satellite galaxies on 720 pc scales. We present the resolved star-forming main sequence for cluster galaxies, dividing the sample based on their global H I properties and comparing to a control sample of field galaxies. H I-poor cluster galaxies have reduced star formation rate (SFR) surface densities with respect to both H I-normal cluster and field galaxies (~0.5 dex), suggesting that mechanisms regulating the global H I content are responsible for quenching local star formation. We demonstrate that the observed quenching in H I-poor galaxies is caused by environmental processes such as ram pressure stripping (RPS), simultaneously reducing the molecular gas surface density and star formation efficiency (SFE) compared to regions in H I-normal systems (by 0.38 and 0.22 dex, respectively). We observe systematically elevated SFRs that are driven by increased molecular gas surface densities at fixed stellar mass surface density in the outskirts of early stage RPS galaxies, while SFE remains unchanged with respect to the field sample. We quantify how RPS and starvation affect the star formation cycle of inner and outer galaxy disks as they are processed by the cluster. We show both are effective quenching mechanisms, with the key difference being that RPS acts upon the galaxy outskirts while starvation regulates the star formation cycle throughout disk, including within the truncation radius. For both processes, the quenching is caused by a simultaneous reduction in the molecular gas surface densities and SFE at fixed stellar mass surface density.

Keywords: galaxy environments; galaxy clusters; star formation; interstellar medium
The International Astronomical Search Collaboration (IASC)—Citizen Scientist System for Asteroid Discovery

We describe a citizen science asteroid detection system developed by the International Astronomical Search Collaboration (IASC) and the Institute for Astronomy at the University of Hawaii, utilizing data from the Pan-STARRS telescopes. The goals of this project are to (i) educate and engage citizen scientists (mostly high school students) in science and astronomy, (ii) search for new asteroids to extend the limiting magnitudes of existing asteroid surveys, and (iii) find missed Near-Earth Objects (NEOs—objects with perihelia q < 1.3 au) to support planetary defense efforts. Over the past 15 yr, 50,000 citizen scientists from 96 countries around the world have detected ∼12,000 main-belt asteroids and ∼5 NEOs. Citizen scientists use the software Astrometrica during scheduled campaigns to search for and measure asteroid astrometry and photometry, and submit the data to IASC for vetting. Candidate detections not already submitted by Pan-STARRS are then submitted to the Minor Planet Center, and are typically ∼0.30 ± 0.07 mag fainter.

Keywords: surveys; near-earth objects; asteroids; main belt asteroids
Joint Observations of Energy Transport and Dissipation during Plasma Flow Vortex in the Terrestrial Magnetotail

Plasma flow vorticity is ubiquitous in space and plays a key role in material mixing and energy transfer. The five THEMIS satellites orbiting in different regions of the terrestrial magnetotail provide an unprecedented opportunity to study the temporal–spatial evolution characteristics of a plasma flow vortex on large spatial scales. We present an analysis of the flow vorticity that occurred between 05:50 and 06:30 UT on 2009 March 23 during a quiet time of the terrestrial magnetotail. The uneven distributions of the density and temperature of the vortex observed by the three near-Earth satellites (THA, THD, and THE) indicate that the plasma in the solar wind gradually mixed into the near-Earth magnetotail through a series of nonequilibrium processes. Both the flow vortices and dipolarization observed by the three near-Earth satellites were about 10 minutes earlier than those observed by the two satellites (THB and THC) in the mid-magnetotail. Further analysis of the relationship between vorticity, field-aligned current, and energy transport reveals that the flow vortex interacted with the surrounding plasma during its tailward propagation. The field-aligned current related to the vorticity could only generate a pseudo-breakup of the aurora in the ionosphere. Thus, we speculate that this flow vortex mainly transports mass and energy from the solar wind to the near-magnetotail, propagates tailward to the mid-magnetotail, and heats the encountered plasma by dissipating its bulk flow and dominant thermal energy. These results shed light on the mass mixing, energy transport, and dissipation of the plasma flow vortex during quiet levels of geomagnetic activity on large spatial scales.

Keywords: geomagnetic fields; magnetohydrodynamics
Stellar Variability in a Forming Massive Star Cluster

We present a near-infrared (NIR) variability analysis for a 6' × 6' region, which encompasses the massive protocluster G286.21+0.17. The total sample comprises more than 5000 objects, of which 562 show signs of a circumstellar disk based on their infrared colors. The data includes Hubble Space Telescope observations taken in two epochs separated by 3 yr in the F110W and F160W bands. 363 objects (7% of the sample) exhibit NIR variability at a significant level (Stetson index >1.7), and a higher variability fraction (14%) is found for the young stellar objects with disk excesses. We identified four high amplitude (>0.6 mag) variables seen in both NIR bands. Follow-up and archival observations of the most variable object in this survey (G286.2032+0.1740) reveal a rising light curve over 8 yr from 2011 to 2019, with a K band brightening of 3.5 mag. Overall the temporal behavior of G286.2032+0.1740 resembles that of typical FU Ori objects; however, its pre-burst luminosity indicates it has a very low mass (<0.12 M⊙), making it an extreme case of an outburst event that is still ongoing.

Keywords: pre-main sequence stars; accretion; stellar accretion disks; young stellar objects; variable stars
Imaging the 44 au Kuiper Belt Analog Debris Ring around HD 141569A with GPI Polarimetry

We present the first polarimetric detection of the inner disk component around the pre-main-sequence B9.5 star HD 141569A. Gemini Planet Imager H-band (1.65 μm) polarimetric differential imaging reveals the highest signal-to-noise ratio detection of this ring yet attained and traces structure inward to 0.″25 (28 au at a distance of 111 pc). The radial polarized intensity image shows the east side of the disk, peaking in intensity at 0.″40 (44 au) and extending out to 0.″9 (100 au). There is a spiral arm-like enhancement to the south, reminiscent of the known spiral structures on the outer rings of the disk. The location of the spiral arm is coincident with 12CO J = 3-2 emission detected by ALMA and hints at a dynamically active inner circumstellar region. Our observations also show a portion of the middle dusty ring at ∼220 au known from previous observations of this system. We fit the polarized H-band emission with a continuum radiative transfer Mie model. Our best-fit model favors an optically thin disk with a minimum dust grain size close to the blowout size for this system, evidence of ongoing dust production in the inner reaches of the disk. The thermal emission from this model accounts for virtually all of the far-infrared and millimeter flux from the entire HD 141569A disk, in agreement with the lack of ALMA continuum and CO emission beyond ∼100 au. A remaining 8-30 μm thermal excess a factor of ∼2 above our model argues for an as-yet-unresolved warm innermost 5-15 au component of the disk.

Keywords: debris disks; circumstellar disks; polarimetry; astronomical techniques; coronagraphic imaging; direct imaging
Pulsar Double Lensing Sheds Light on the Origin of Extreme Scattering Events

In extreme scattering events, the brightness of a compact radio source drops significantly, as light is refracted out of the line of sight by foreground plasma lenses. Despite recent efforts, the nature of these lenses has remained a puzzle, because any roughly round lens would be so highly overpressurized relative to the interstellar medium that it could only exist for about a year. This, combined with a lack of constraints on distances and velocities, has led to a plethora of theoretical models. We present observations of a dramatic double-lensing event in pulsar PSR B0834+06 and use a novel phase-retrieval technique to show that the data can be reproduced remarkably well with a two-screen model: one screen with many small lenses and another with a single, strong one. We further show that the latter lens is so strong that it would inevitably cause extreme scattering events. Our observations show that the lens moves slowly and is highly elongated on the sky. If similarly elongated along the line of sight, as would arise naturally from a sheet of plasma viewed nearly edge-on, no large overpressure is required and hence the lens could be long-lived.

Keywords: interstellar medium; radio pulsars; interstellar scattering; radio astronomy; radio spectroscopy; warm ionized medium
X-Ray Emission from GW170817 ∼2.5 years After the Merger

The binary neutron star merger GW170817 is the first and only astronomical object with a joint detection of gravitational waves and electromagnetic radiation. Here we report the results from deep Chandra X-ray observations of GW170817 at δt ∼ 940 days post merger. We find evidence for X-ray emission with flux Fx = $({2.24}_{+0.97}^{-0.96})\times {10}^{-15}\,\mathrm{erg}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ (Lx = ${4.29}_{+1.86}^{-1.84}\times {10}^{38}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ , 0.3-10 keV). This flux is consistent with the expected late-time evolution of non-thermal emission from an off-axis structured jet and it is now approaching the sensitivity threshold of current X-ray instrumentation. Future observations might reveal the emergence of the kilonova afterglow.

Keywords: neutron stars; gravitational waves
Investigating the Condensation of Benzene (C6H6) in Titan's South Polar Cloud System with a Combination of Laboratory, Observational, and Modeling Tools

We have combined laboratory, modeling, and observational efforts to investigate the chemical and microphysical processes leading to the formation of the cloud system that formed at an unusually high altitude (>250 km) over Titan's south pole after the northern spring equinox. We present here a study focused on the formation of C6H6 ice clouds at 87°S. As the first step of our synergistic approach, we have measured, for the first time, the equilibrium vapor pressure of pure crystalline C6H6 at low temperatures (134-158 K) representative of Titan's atmosphere. Our laboratory data indicate that the experimental vapor pressure values are larger than those predicted by extrapolations found in the literature calculated from higher-temperature laboratory measurements. We have used our experimental results along with temperature profiles and C6H6 mixing ratios derived from observational data acquired by the Cassini Composite Infrared Spectrometer (CIRS) as input parameters in the coupled microphysics radiative transfer Community Aerosol and Radiation Model for Atmospheres (CARMA). CARMA simulations constrained by these input parameters were conducted to derive C6H6 ice particle size distribution, gas volume mixing ratios, gas relative humidity, and cloud altitudes. The impact of the vapor pressure on the CIRS data analysis and in the CARMA simulations was investigated and resulted in both cases in benzene condensation occurring at lower altitude in the stratosphere than previously thought. In addition, the stratospheric C6H6 gas abundances predicted with the new saturation relationship are ~1000× higher than previous calculations between 150-200 km, which results in larger particle sizes.

Keywords: titan; experimental techniques; laboratory astrophysics
Solar Filament Eruptions in H α Doppler Velocity

We use observations taken with a novel solar telescope spectroheliograph to investigate the association between the early filament rise and coronal mass ejections (CMEs). The instrument allows the H α full line profile to be registered in each pixel of the solar disk with a time cadence of about 1 minute. We analyze observations of three eruptive filaments in 2021 and show that patrol telescope measurements of the H α line profile with a spectral resolution R = 40,000 can be used to detect precursors of filament eruptions with an advance of several hours and to estimate the initial acceleration of CMEs. Our limited case study also suggests that while detecting an early filament rise may serve as an indicator of a possible eruption, the filament ascent alone is not a definite sign of a CME.

Keywords: solar filament eruptions; solar filaments; solar instruments; astronomical instrumentation
Hidden Companions to Intermediate-mass Stars. X. Solving for the Mass Ratio in the Spectroscopic Binary Zubenelgenubi = α 2 Librae

Zubenelgenubi = α 2 Librae is a nearby double-lined spectroscopic binary that forms a quadruple system with α 1 Librae. The radial velocity amplitude for the rapidly rotating primary is subject to a systematic uncertainty and as a result only a lower limit q = 0.81 to the mass ratio has been previously reported. Here we present a VLTI/GRAVITY interferometric observation of Zubenelgenubi in which we measured a K band flux ratio of 74.7%, resulting in isochrone masses M Aa = 1.95 M ⊙ and M Ab = 1.79 M ⊙ (q = 0.92). The fact that the projected rotational velocities differ by a factor of three despite the similar masses suggests that the stellar spin axes are significantly misaligned in spite of the small semimajor axis a = 0.52 au or alternatively that the primary is a merger product. *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Keywords: multiple stars; spectroscopic binary stars; a stars; optical interferometry
Forecasting the Ambient Solar Wind with Numerical Models. II. An Adaptive Prediction System for Specifying Solar Wind Speed near the Sun

The ambient solar wind flows and fields influence the complex propagation dynamics of coronal mass ejections in the interplanetary medium and play an essential role in shaping Earth's space weather environment. A critical scientific goal in the space weather research and prediction community is to develop, implement, and optimize numerical models for specifying the large-scale properties of solar wind conditions at the inner boundary of the heliospheric model domain. Here we present an adaptive prediction system that fuses information from in situ measurements of the solar wind into numerical models to better match the global solar wind model solutions near the Sun with prevailing physical conditions in the vicinity of Earth. In this way, we attempt to advance the predictive capabilities of well-established solar wind models for specifying solar wind speed, including the Wang-Sheeley-Arge model. In particular, we use the Heliospheric Upwind eXtrapolation (HUX) model for mapping the solar wind solutions from the near-Sun environment to the vicinity of Earth. In addition, we present the newly developed Tunable HUX (THUX) model, which solves the viscous form of the underlying Burgers equation. We perform a statistical analysis of the resulting solar wind predictions for the period 2006-2015. The proposed prediction scheme improves all the investigated coronal/heliospheric model combinations and produces better estimates of the solar wind state at Earth than our reference baseline model. We discuss why this is the case and conclude that our findings have important implications for future practice in applied space weather research and prediction.

Keywords: solar wind; solar coronal holes; solar corona; solar photosphere; heliosphere; corotating streams
Tying the Geometrical Traits of Massive Young Stellar Objects and Their Disks to a Potential Evolutionary Sequence Using Infrared Observations

Young massive stars influence their surroundings from local to galactic scales, but the observational challenges associated with their distance and embedded nature has, until the recent decade, made high-resolution studies of these objects difficult. In particular, comparative analyses of massive young stellar object (MYSO) disks are currently lacking and our understanding of their evolution is limited. Here, we combine the results of two studies with the aim to attribute geometrical features to an evolutionary sequence for a sample of seven MYSOs. The time evolution is based on near-infrared spectral features, while the geometry is determined from a multi-size-scale study of MYSOs. We find that MYSO disks with determined geometrical substructure turn out to be also spectroscopically more evolved. This implies that disk evolution and dispersal occur within MYSOs similarly to low-mass young stellar object (YSO) disk evolution, despite their faster formation timescales.

Keywords: star formation; massive stars; circumstellar disks; infrared astronomy; interferometry; observational astronomy
The Habitable Zone Planet Finder Reveals a High Mass and Low Obliquity for the Young Neptune K2-25b

Using radial velocity data from the Habitable Zone Planet Finder, we have measured the mass of the Neptune-sized planet K2-25b, as well as the obliquity of its M4.5 dwarf host star in the 600-800 Myr Hyades cluster. This is one of the youngest planetary systems for which both of these quantities have been measured and one of the very few M dwarfs with a measured obliquity. Based on a joint analysis of the radial velocity data, time-series photometry from the K2 mission, and new transit light curves obtained with diffuser-assisted photometry, the planet's radius and mass are 3.44 ± 0.12 R⊕ and ${24.5}_{-5.2}^{+5.7}{M}_{\oplus }$ . These properties are compatible with a rocky core enshrouded by a thin hydrogen-helium atmosphere (5% by mass). We measure an orbital eccentricity of e = 0.43 ± 0.05. The sky-projected stellar obliquity is λ = 3° ± 16°, compatible with spin-orbit alignment, in contrast to other "hot Neptunes" that have been studied around older stars.

Keywords: exoplanet astronomy; exoplanet systems; radial velocity; exoplanet detection methods; transit photometry; photometry; exoplanet formation; mini neptunes; low mass stars; near infrared astronomy