adsabs/SciX_UAT_keywords huggingface dataset:
Three-dimensional Simulations of Magnetospheric Accretion in a T Tauri Star: Accretion and Wind Structures Just Around the Star

We perform three-dimensional (3D) magnetohydrodynamic simulations of magnetospheric accretion in a T Tauri star to study the accretion and wind structures in the close vicinity of the star. The gas accreting onto the star consists of the gas from the magnetospheric boundary and the failed disk winds. The accreting gas is commonly found as a multi-column accretion, which is consistent with observations. A significant fraction of the angular momentum of the accreting flows is removed by the magnetic fields of conical disk winds and turbulent failed winds inside and near the magnetosphere. As a result, the accretion torque is significantly reduced compared to the simple estimation based on the mass accretion rate. The stellar spin affects the time variability of the conical disk wind by changing the stability condition of the magnetospheric boundary. However, the time-averaged magnetospheric radius only weakly depends on the stellar spin, which is unlike the prediction of classical theories that the stellar spin controls the magnetospheric radius through the magnetic torque. The ratio of the toroidal to the poloidal field strengths at the magnetospheric boundary, which is a key parameter for the magnetic torque, is also insensitive to the spin; it is rather determined by the disk dynamics. Considering newly found 3D effects, we obtain a scaling relation of the magnetospheric radius very similar to the Ghosh & Lamb relation from the steady angular momentum transport equation.

Keywords: pre-main sequence stars; star formation; magnetohydrodynamical simulations; stellar magnetic fields; stellar accretion disks; protostars; protoplanetary disks
How Likely Are Snowball Episodes Near the Inner Edge of the Habitable Zone?

Understanding when global glaciations occur on Earth-like planets is a major challenge in climate evolution research. Most models of how greenhouse gases like CO2 evolve with time on terrestrial planets are deterministic, but the complex, nonlinear nature of Earth's climate history motivates study of nondeterministic climate models. Here a maximally simple stochastic model of CO2 evolution and climate on an Earth-like planet with an imperfect CO2 thermostat is investigated. It is shown that as stellar luminosity is increased in this model, the decrease in the average atmospheric CO2 concentration renders the climate increasingly unstable, with excursions to a low-temperature state common once the received stellar flux approaches that of present-day Earth. Unless climate feedbacks always force the variance in CO2 concentration to decline rapidly with received stellar flux, this means that terrestrial planets near the inner edge of the habitable zone may enter Snowball states quite frequently. Observations of the albedos and color variation of terrestrial-type exoplanets should allow this prediction to be tested directly in the future.

Keywords: earth (planet); exoplanets; habitable planets; habitable zone; greenhouse gases; surface ices
OASI: A Brazilian Observatory Dedicated to the Study of Small Solar System Bodies—Some Results on NEO's Physical Properties

The distribution of professional observatories around the world is quite biased toward the Northern Hemisphere, and this tendency is even more pronounced when considering those dedicated only to the study of small solar system bodies. In the Southern Hemisphere, the IMPACTON project deployed the Observatório Astronômico do Sertão de Itaparica (OASI), dedicated to the observation of minor bodies of the solar system with emphasis on Near-Earth Objects (NEOs). The observatory is located at the county of Itacuruba, in the Pernambuco State of Brazil, and operate a 1 m Cassegrain telescope. Here, we present a complete characterization of the OASI instruments and the sky conditions during the first eight years of operations. The limiting magnitudes are determined in the different available filters. The median seeing results to be 1"22, with a higher number of photometric nights from April to October. We also give an overview of the results obtained from the OASI observations and discuss them in the light of similar data from the literature. In particular, the rotational periods of 23 NEOs, and the spin directions and shapes of 9 NEOs, have been determined for the very first time using our observations. Analyzing rotational periods, sizes and taxonomic classification from the literature and OASI, we conclude that the fast rotating NEOs are predominantly S-type objects. However, rotational periods obtained at the OASI and with similar value from LCDB database allowed to identify the first fast rotator C-type NEO: asteroid 436724. With an estimated tensile strength as low as 0.5 KPa, this asteroid allows us to suggest that it defines the border between the C- and S-type fast rotators in the size versus period diagram. Although this hypothesis is based on a very small sample it is compatible with all presently available data. Only new observations, however, can prove if this hypothesis is correct.

Keywords: telescopes; surveys; near-earth objects
Classifying Intermediate-redshift Galaxies in SDSS: Alternative Diagnostic Diagrams

We select a sample of 1437 active galactic nuclei (AGN) from the catalog of the Sloan Digital Sky Survey galaxy properties from the Portsmouth group by detection of the high-ionization [Ne V] 3426 Å emission line. We compare the fluxes of [Ne III] 3869 Å, [O III] 5007 Å, [O II] 3726, 3728 Å, and [O I] 6300 Å to that of [Ne v]. All four lines show a strong linear correlation with [Ne v], although lines from ions with lower ionization potentials have a lower correlation coefficient. We investigate the use of two forbidden line ratio diagnostic diagrams that do not rely on Hα in order to classify high-redshift galaxies. These use the [Ne III]/[O II] line ratio plotted against [O III]/[O I] and [O III]/[O II], respectively. We use photoionization modeling to characterize the behavior of the narrow-line region in AGN and star-forming regions and test the validity of our diagnostic diagrams. We also use a luminosity cutoff of log L [O III] [erg s‑1] = 42, which lowers the contamination of the AGN region by star-forming galaxies down to 10% but does not remove green pea and purple grape galaxies from the AGN region. We also investigate the OHNO diagram, which uses [Ne III]/[O II] plotted against [O III]/Hβ. Using our new diagnostic diagrams, we are able to reliably classify AGN up to a redshift of z ≤ 1.06 and add more than 822 new AGN to the [Ne v]-selected AGN sample.

Keywords: active galactic nuclei; classification systems; starburst galaxies
The Near-Earth Object Surveyor Mission

The Near-Earth Object (NEO) Surveyor mission is a NASA Observatory designed to discover and characterize asteroids and comets. The mission's primary objective is to find the majority of objects large enough to cause severe regional impact damage (>140 m in effective spherical diameter) within its 5 yr baseline survey. Operating at the Sun-Earth L1 Lagrange point, the mission will survey to within 45° of the Sun in an effort to find objects in the most Earth-like orbits. The survey cadence is optimized to provide observational arcs long enough to distinguish near-Earth objects from more distant small bodies that cannot pose an impact hazard reliably. Over the course of its survey, NEO Surveyor will discover ~200,000-300,000 new NEOs down to sizes as small as ~10 m and thousands of comets, significantly improving our understanding of the probability of an Earth impact over the next century.

Keywords: asteroids; near-earth objects; comets; surveys; sky surveys; infrared astronomy
Blue Coma and Red Surface of 174P/Echeclus: Two Sides of the Same Coin?

Seccull et al. (2019) report a dramatic difference in the color of the coma and surface of Centaur 174P/Echeclus. While the coma was blue in appearance, the surface was red. A similar phenomenon was found in laboratory optical measurements of single-scattering feldspar particles and of a surface comprised of these same particles. Thus, the observations do not necessarily suggest different chemical composition and size distribution of dust in the coma and surface of 174P/Echeclus. Instead, the observed difference could arise from multiple-scattering phenomena that makes a significant contribution to light scattering by a regolith, but does not appear in an optically thin coma.

Keywords: comet surfaces; comae; multi-color photometry; coma dust; centaur group
Visible and Infrared Spectroscopy of the Planetary Nebula M4-18

0.47-2.45 μm spectroscopy is reported for the compact planetary nebula Minkowski 4-18 (PK146+07), filling some spectral gaps and presenting uniform and simultaneous observation of this entire spectral range. While the strongest features are the H I lines, the most prevalent are those of carbon, principally of C II, commensurate with the carbon rich, Wolf-Rayet nature of the exciting star.

Keywords: planetary nebulae
Interplanetary Protons versus Interacting Protons in the 2017 September 10 Solar Eruptive Event

We analyze the relativistic proton emission from the Sun during the eruptive event on 2017 September 10, which caused a ground-level enhancement (GLE 72) registered by the worldwide network of neutron monitors. Using the neutron monitor data and interplanetary transport modeling both along and across interplanetary magnetic field (IMF) lines, we deduce parameters of the proton injection into the interplanetary medium. The inferred injection profile of the interplanetary protons is compared with the profile of the >100 MeV γ-ray emission observed by the Fermi Large Area Telescope, attributed to pion production from the interaction of >300 MeV protons at the Sun. GLE 72 started with a prompt component that arrived along the IMF lines. This was followed by a more prolonged enhancement caused by protons arriving at the Earth across the IMF lines from the southwest. The interplanetary proton event is modeled using two sources—one source at the root of the Earth-connected IMF line and another source situated near the solar western limb. The maximum phase of the second injection of interplanetary protons coincides with the maximum phase of the prolonged >100 MeV γ-ray emission that originated from a small area at the solar western limb, below the current sheet trailing the associated coronal mass ejection (CME). A possible common source of interacting protons and interplanetary protons is discussed in terms of proton acceleration at the CME bow shock versus coronal (re-)acceleration in the wake of the CME.

Keywords: solar coronal mass ejections; solar energetic particles; solar particle emission; solar coronal mass ejection shocks; solar flares; solar gamma-ray emission
Cross Helicity of the 2018 November Magnetic Cloud Observed by the Parker Solar Probe

Magnetic clouds are large-scale transient structures in the solar wind with low plasma-β, low-amplitude magnetic field fluctuations, and twisted field lines with both ends often connected to the Sun. Their inertial-range turbulent properties have not been examined in detail. In this Letter, we analyze the normalized cross helicity, σc, and residual energy, σr, of plasma fluctuations in the 2018 November magnetic cloud observed at 0.25 au by the Parker Solar Probe. A low value of $| {\sigma }_{c}| $ was present in the cloud core, indicating that wave power parallel and antiparallel to the mean field was approximately balanced, while the cloud's outer layers displayed larger amplitude Alfvénic fluctuations with high $| {\sigma }_{c}| $ values and σr ∼ 0. These properties are discussed in terms of the cloud's solar connectivity and local interaction with the solar wind. We suggest that low $| {\sigma }_{c}| $ is likely a common feature of magnetic clouds given their typically closed field structure. Antisunward fluctuations propagating immediately upstream of the cloud had strongly negative σr values.

Keywords: interplanetary turbulence; solar wind; solar coronal mass ejections; interplanetary magnetic fields
Testing the Momentum-driven Supernova Feedback Paradigm in M31

Momentum feedback from isolated supernova remnants (SNRs) have been increasingly recognized by modern cosmological simulations as a resolution-independent means to implement the effects of feedback in galaxies, such as turbulence and winds. However, the integrated momentum yield from SNRs is uncertain due to the effects of SN clustering and interstellar medium (ISM) inhomogeneities. In this paper, we use spatially resolved observations of the prominent 10 kpc star-forming ring of M31 to test models of mass-weighted ISM turbulence driven by momentum feedback from isolated, nonoverlapping SNRs. We use a detailed stellar age distribution (SAD) map from the Panchromatic Hubble Andromeda Treasury survey, observationally constrained SN delay-time distributions, and maps of the atomic and molecular hydrogen to estimate the mass-weighted velocity dispersion using the Martizzi et al. ISM turbulence model. Our estimates are within a factor of two of the observed mass-weighted velocity dispersion in most of the ring, but exceed observations at densities ≲0.2 cm-3 and SN rates >2.1 × 10-4 SN yr-1 kpc-2, even after accounting for plausible variations in SAD models and ISM scale height assumptions. We conclude that at high SN rates the momentum deposited is most likely suppressed by the nonlinear effects of SN clustering, while at low densities, SNRs reach pressure equilibrium before the cooling phase. These corrections should be introduced in models of momentum-driven feedback and ISM turbulence.

Keywords: interstellar medium; stellar feedback; supernovae; supernova remnants; stellar-interstellar interactions
New Insights into the First Two PSP Solar Encounters Enabled by Modeling Analysis with ADAPT-WSA

Parker Solar Probe's (PSP's) unique orbital path allows us to observe the solar wind closer to the Sun than ever before. Essential to advancing our knowledge of solar wind and energetic particle formation is identifying the sources of PSP observations. We report on results for the first two PSP solar encounters derived using the Wang-Sheeley-Arge (WSA) model driven by Air Force Data Assimilative Photospheric Flux Transport (ADAPT) model maps. We derive the coronal magnetic field and the 1 R ⊙ source regions of the PSP-observed solar wind. We validate our results with the solar wind speed and magnetic polarity observed at PSP. When modeling results are very reliable, we derive time series of model-derived spacecraft separation from the heliospheric current sheet, magnetic expansion factor, coronal hole boundary distance, and photospheric field strength along the field lines estimated to be connected to the spacecraft. We present new results for Encounter 1, which show time evolution of the far-side mid-latitude coronal hole that PSP corotates with. We discuss how this evolution coincides with solar wind speed, density, and temperature observed at the spacecraft. During Encounter 2, a new active region emerges on the solar far side, making it difficult to model. We show that ADAPT-WSA output agrees well with PSP observations once this active region rotates onto the near side, allowing us to reliably estimate the solar wind sources retrospectively for most of the encounter. We close with ways in which coronal modeling enables scientific interpretation of these encounters that would otherwise not have been possible.

Keywords: solar wind; solar magnetic fields; solar corona
The Discovery of a Remnant Radio Galaxy in A2065 Using GMRT

The upgraded Giant Metrewave Radio Telescope (GMRT) has been used to map the cluster A2065 at z = 0.0726. We report the discovery of a remnant radio galaxy at the peripheral cluster region. The spatially resolved radio emission from the remnant radio galaxy shows an elongated, bar-shaped structure, whose size is ≈52″ × 110″ (≃72 × 152 kpc2). Our study with multiwavelength GMRT data and Chandra data shows that across the remnant radio galaxy there is a hint of a surface-brightness edge in the hot X-ray gas. We detect tentative flattening of the radio spectral index as the old plasma at the near end of the surface-brightness edge is reinvigorated by the passage of a possible shock front and shows the expected change in radio emission characteristics. We suggest that the remnant radio galaxy has been seeded by the lobes of the active galactic nucleus (AGN) hosted by the WISEA J152228.01+274141.3 source, demonstrating the connection between AGNs and remnant radio sources. Although the number of known remnant radio sources is beginning to increase, we emphasize the need for better data to understand the physics and nature of poorly understood remnant radio sources.

Keywords: active galactic nuclei; extragalactic radio sources; fanaroff-riley radio galaxies; galaxy structure; radio continuum emission; galaxy clusters
A Statistical Study of IRIS Observational Signatures of Nanoflares and Nonthermal Particles

Nanoflares are regarded as one of the major mechanisms of magnetic energy release and coronal heating in the solar outer atmosphere. We conduct a statistical study on the response of the chromosphere and transition region to nanoflares, as observed by the Interface Region Imaging Spectrograph (IRIS), by using an algorithm for the automatic detection of these events. The initial atmospheric response to these small heating events is observed, with IRIS, as transient brightening at the foot points of coronal loops heated to high temperatures (>4 MK). For four active regions, observed over 143 hr, we detected 1082 footpoint brightenings under the IRIS slit, and for those we extracted physical parameters from the IRIS Mg II and Si IV spectra that are formed in the chromosphere and transition region, respectively. We investigate the distributions of the spectral parameters, and the relationships between the parameters, also comparing them with predictions from RADYN numerical simulations of nanoflare-heated loops. We find that these events, and the presence of nonthermal particles, tend to be more frequent in flare productive active regions, and where the hot 94 Å emission measured by the Atmospheric Imaging Assembly is higher. We find evidence for highly dynamic motions characterized by strong Si IV nonthermal velocities (not dependent on the heliocentric x-coordinate, i.e., on the angle between the magnetic field and the line of sight) and asymmetric Mg II spectra. These findings provide tight new constraints on the properties of nanoflares and nonthermal particles in active regions, and their effects on the lower atmosphere.

Keywords: solar chromosphere; solar transition region; solar active regions; solar physics; solar coronal heating
DeepZipper: A Novel Deep-learning Architecture for Lensed Supernovae Identification

Large-scale astronomical surveys have the potential to capture data on large numbers of strongly gravitationally lensed supernovae (LSNe). To facilitate timely analysis and spectroscopic follow-up before the supernova fades, an LSN needs to be identified soon after it begins. To quickly identify LSNe in optical survey data sets, we designed ZipperNet, a multibranch deep neural network that combines convolutional layers (traditionally used for images) with long short-term memory layers (traditionally used for time series). We tested ZipperNet on the task of classifying objects from four categories-no lens, galaxy-galaxy lens, lensed Type-Ia supernova, lensed core-collapse supernova-within high-fidelity simulations of three cosmic survey data sets: the Dark Energy Survey, Rubin Observatory's Legacy Survey of Space and Time (LSST), and a Dark Energy Spectroscopic Instrument (DESI) imaging survey. Among our results, we find that for the LSST-like data set, ZipperNet classifies LSNe with a receiver operating characteristic area under the curve of 0.97, predicts the spectroscopic type of the lensed supernovae with 79% accuracy, and demonstrates similarly high performance for LSNe 1-2 epochs after first detection. We anticipate that a model like ZipperNet, which simultaneously incorporates spatial and temporal information, can play a significant role in the rapid identification of lensed transient systems in cosmic survey experiments.

Keywords: supernovae; strong gravitational lensing; neural networks
Future Approach Distances and Times of Gliese 710 and R Cra to the Solar System Using Gaia DR2

I present the future approach distances and times of the stars Gliese 710 and R Cra run toward the future under a global galactic model with input parameters from the Gaia repositories. I found that the star Gliese 710 will approach the Sun closer than previously estimated. These results can confirm other calculations done to find the remarkable differences between the results of models with pre-Gaia and Gaia databases.

Keywords: stellar kinematics; stellar motion; solar neighborhood; stellar dynamics; solar system
Color Transformations of Photometric Measurements of Galaxies in Optical and Near-infrared Wide-field Imaging Surveys

Over the past 2 decades, wide-field photometric surveys in optical and infrared domains reached a nearly all-sky coverage thanks to numerous observational facilities operating in both hemispheres. However, subtle differences among exact realizations of Johnson and SDSS photometric systems require one to convert photometric measurements into the same system prior to analysis of composite data sets originating from multiple surveys. It turns out that the published photometric transformations lead to substantial biases when applied to integrated photometry of galaxies from the corresponding catalogs. Here we present photometric transformations based on piece-wise linear approximations of integrated photometry of galaxies in the optical surveys SDSS, DECaLS, BASS, MzLS, DES, DELVE, KiDS, VST ATLAS, and the near-infrared surveys UKIDSS, UHS, VHS, and VIKING. We validate our transformations by constructing k-corrected color-magnitude diagrams of non-active galaxies and measuring the position and tightness of the "red sequence." We also provide transformations for aperture magnitudes and show how they are affected by the image quality difference among the surveys. We present the implementation of the derived transformations in PYTHON and IDL and also a web-based color transformation calculator for galaxies. By comparing DECaLS and DES, we identified systematic issues in DECaLS photometry for extended galaxies, which we attribute to the photometric software package used by DECaLS. As an application of our method, we compiled two multi-wavelength photometric catalogs for over 200,000 low- and intermediate-redshift galaxies originating from CfA FAST and Hectospec spectral archives. *An online color transformation calculator is available at: https://colors.voxastro.org/.

Keywords: color equation; photometric systems; galaxy photometry; galaxy colors
Observational Evidence for Fast Mode Periodic Small-scale Shocks: A New Type of Plasma Phenomenon

We show observational evidence for a new form of collisionless shock in interplanetary space near Mars, small-scale shocks with periodic spacings. Pickup of new ionized hydrogen atoms in a magnetic field aligned with the solar wind direction causes the generation of a magnetosonic wave train through an ion beam instability. The waves have a frequency close to the local proton gyrofrequency. This is a similar physical process as for the formation of cometary plasma waves/turbulence. However, for the case of proton pickup near Mars, each individual magnetosonic wave cycle develops into a small-scale shock. So there is a string of fast mode shocks formed with proton gyroperiod spacings. These small-scale shocks display dissipation in the ions and dispersive whistlers. A fraction of ions trapped/reflected at the small-scale shocks are accelerated by the motional electric field. Observational results demonstrate that periodic shocks can perform the same functions as a single supercritical shock in a high-speed flow.

Keywords: interplanetary shocks; planetary bow shocks; solar coronal mass ejection shocks; stellar bow shocks