adsabs/SciX_UAT_keywords huggingface dataset:
Kinematical Constraint on Eccentricity in the Protoplanetary Disk MWC 758 with ALMA

We analyzed the archival data of the 13CO and C18O J = 3 - 2 emission lines in the protoplanetary disk around MWC 758 obtained with the Atacama Large Millimeter/submillimeter Array to discuss possible planet-disk interaction and non-Keplerian motion in the disk. We performed fitting of a Keplerian disk model to the observational data and measured the velocity deviations from the Keplerian rotation. We found significant velocity deviations around the inner cavity in the MWC 758 disk. We examined several possibilities that may cause the velocity deviations, such as pressure gradient, height of the emitting layer, infall motion, inner warp, and eccentricity in the disk. We found that the combination of an eccentric orbital motion with eccentricity of 0.1 ± 0.04 at the radius of the inner cavity and an infalling flow best explains the observed velocity deviations. Our kinematically constrained eccentricity of the gas orbital motion close to the inner cavity is consistent with the eccentricity of the dust ring around the inner cavity measured in the submillimeter continuum emission. Our results hint at strong dust-gas coupling around the inner cavity and presence of a gas giant planet inside the inner cavity in the MWC 758 disk.

Keywords: protoplanetary disks; eccentricity; planet formation; planetary-disk interactions
Magnetocentrifugal Origin for Protostellar Jets Validated through Detection of Radial Flow at the Jet Base

Jets can facilitate the mass accretion onto the protostars in star formation. They are believed to be launched from accretion disks around the protostars by magnetocentrifugal force, as supported by the detections of rotation and magnetic fields in some of them. Here we report a radial flow of the textbook-case protostellar jet HH 212 at the base to further support this jet-launching scenario. This radial flow validates a central prediction of the magnetocentrifugal theory of jet formation and collimation, namely, the jet is the densest part of a wide-angle wind that flows radially outward at distances far from the (small, sub-au) launching region. Additional evidence for the radially flowing wide-angle component comes from its ability to reproduce the structure and kinematics of the shells detected around the HH 212 jet. This component, which can transport material from the inner to outer disk, could account for the chondrules and Ca-Al-rich inclusions detected in the solar system at large distances.

Keywords: interstellar medium; star formation; jets
The Drivers of Active Region Outflows into the Slow Solar Wind

Plasma outflows from the edges of active regions have been suggested as a possible source of the slow solar wind. Spectroscopic measurements show that these outflows have an enhanced elemental composition, which is a distinct signature of the slow wind. Current spectroscopic observations, however, do not have sufficient spatial resolution to distinguish what structures are being measured or determine the driver of the outflows. The High-resolution Coronal Imager (Hi-C) flew on a sounding rocket in 2018 May and observed areas of active region outflow at the highest spatial resolution ever achieved (250 km). Here we use the Hi-C data to disentangle the outflow composition signatures observed with the Hinode satellite during the flight. We show that there are two components to the outflow emission: a substantial contribution from expanded plasma that appears to have been expelled from closed loops in the active region core and a second contribution from dynamic activity in active region plage, with a composition signature that reflects solar photospheric abundances. The two competing drivers of the outflows may explain the variable composition of the slow solar wind.

Keywords: solar corona; slow solar wind
Avalanches and the Distribution of Reconnection Events in Magnetized Circumstellar Disks

Cosmic rays produced by young stellar objects can potentially alter the ionization structure, heating budget, chemical composition, and accretion activity in circumstellar disks. The inner edges of these disks are truncated by strong magnetic fields, which can reconnect and produce flaring activity that accelerates cosmic radiation. The resulting cosmic rays can provide a source of ionization and produce spallation reactions that alter the composition of planetesimals. These reconnection and particle acceleration processes are analogous to the physical processes that produce flaring in and the heating of stellar coronae. Flaring events on the surface of the Sun exhibit a power-law distribution of energy, reminiscent of those measured for earthquakes and avalanches. Numerical lattice reconnection models are capable of reproducing the observed power-law behavior of solar flares under the paradigm of self-organized criticality. One interpretation of these experiments is that the solar corona maintains a nonlinear attractor-or "critical"-state by balancing energy input via braided magnetic fields and output via reconnection events. Motivated by these results, we generalize the lattice reconnection formalism for applications in the truncation region of magnetized disks. Our numerical experiments demonstrate that these nonlinear dynamical systems are capable of both attaining and maintaining criticality in the presence of Keplerian shear and other complications. The resulting power-law spectrum of flare energies in the equilibrium attractor state is found to be nearly universal in magnetized disks. This finding indicates that magnetic reconnection and flaring in the inner regions of circumstellar disks occur in a manner similar to the activity on stellar surfaces. These results, in turn, have ramifications for the spallation-driven injection of radionuclides in planetesimals, disk ionization, and the subsequent planetary formation process.

Keywords: planet formation; exoplanet formation; circumstellar disks; solar magnetic reconnection; nucleosynthesis; cosmic ray nucleosynthesis
Drivers of Magnetic Field Amplification at Oblique Shocks: In Situ Observations

Collisionless shocks are ubiquitous structures throughout the Universe. Shock waves in space and astrophysical plasmas convert the energy of a fast-flowing plasma to other forms of energy, including thermal and magnetic energies. Plasma turbulence and high-amplitude electric and magnetic fluctuations are necessary for effective energy conversion and particle acceleration. We survey and characterize in situ observations of reflected ions and magnetic field amplification rates at quasiperpendicular shocks under a wide range of upstream conditions. We report magnetic amplification rates as high as 25 in our current data set. Reflected ions interacting with the incoming plasma create magnetic perturbations that cause magnetic amplification in upstream and downstream regions of quasiperpendicular shocks. Our observations show that, in general, magnetic amplification increases with the fraction of reflected ions, which itself increases with Mach number. Both parameters plateau once full reflection is reached. Magnetic amplification continuously increases with the inverse of the magnetization parameter of the upstream plasma. We find that the extended foot region upstream of shocks and nonlinear processes within that region are key factors for intense magnetic amplification. Our observations at nonrelativistic shocks provide the first experimental evidence that below a certain magnetization threshold, the magnetic amplification efficiency at quasiperpendicular shocks becomes comparable to that at the quasiparallel shocks.

Keywords: solar wind; space plasmas; shocks
A Search for Extragalactic Fast Blue Optical Transients in ZTF and the Rate of AT2018cow-like Transients

We present a search for extragalactic fast blue optical transients (FBOTs) during Phase I of the Zwicky Transient Facility (ZTF). We identify 38 candidates with durations above half-maximum light 1 day < t 1/2 < 12 days, of which 28 have blue (g - r ≲ -0.2 mag) colors at peak light. Of the 38 transients (28 FBOTs), 19 (13) can be spectroscopically classified as core-collapse supernovae (SNe): 11 (8) H- or He-rich (Type II/IIb/Ib) SNe, 6 (4) interacting (Type IIn/Ibn) SNe, and 2 (1) H&He-poor (Type Ic/Ic-BL) SNe. Two FBOTs (published previously) had predominantly featureless spectra and luminous radio emission: AT2018lug (The Koala) and AT2020xnd (The Camel). Seven (five) did not have a definitive classification: AT 2020bdh showed tentative broad Hα in emission, and AT 2020bot showed unidentified broad features and was 10 kpc offset from the center of an early-type galaxy. Ten (eight) have no spectroscopic observations or redshift measurements. We present multiwavelength (radio, millimeter, and/or X-ray) observations for five FBOTs (three Type Ibn, one Type IIn/Ibn, one Type IIb). Additionally, we search radio-survey (VLA and ASKAP) data to set limits on the presence of radio emission for 24 of the transients. All X-ray and radio observations resulted in nondetections; we rule out AT2018cow-like X-ray and radio behavior for five FBOTs and more luminous emission (such as that seen in the Camel) for four additional FBOTs. We conclude that exotic transients similar to AT2018cow, the Koala, and the Camel represent a rare subset of FBOTs and use ZTF's SN classification experiments to measure the rate to be at most 0.1% of the local core-collapse SN rate.

Keywords: transient sources; time domain astronomy; core-collapse supernovae; surveys
Investigation of the Long-term Variation of Solar Ca II K Intensity. I. Density-to-intensity Calibration Formula for Historical Photographic Plates

This paper presents a novel formula to convert photographic density into intensity for historical photographic plates of the Sun. Photographic photometry is of great importance as the very first step of analyzing century-long archived photographic data to study the long-term variation. The calibration formula is newly developed by using the intensity fluctuation originating in the network pattern in the quiet region, taking into consideration the nonlinearity between the density and the intensity. The formula is useful especially when experimentally obtained characteristic curves are insufficient for homogeneous analysis of a whole long-term data set. An example procedure of the calibration using the formula is demonstrated. Resultant intensity images calibrated from the photographic data can reproduce both the fluctuation and the center-to-limb variation of modern reference data. The calibration procedure is also tested with a whole twentieth century data set and shows good performance, while the preliminary result of the long-term intensity variation seems to be partially affected by the quality of the original plates. The resultant solar Ca II K intensity variation will be updated and discussed in a subsequent paper with the comparison to the solar UV variation related to the terrestrial environment.

Keywords: astronomy data analysis; photoheliographs; solar chromosphere; solar cycle; solar electromagnetic emission
Cloud Identification from All-sky Camera Data with Machine Learning

Most ground-based observatories are equipped with wide-angle all-sky cameras to monitor the night sky conditions. Such camera systems can be used to provide an early warning of incoming clouds that can pose a danger to the telescope equipment through precipitation, as well as for sky quality monitoring. We investigate the use of different machine-learning approaches for automating the identification of mostly opaque clouds in all-sky camera data as a cloud warning system. In a deep-learning approach, we train a residual neural network (ResNet) on pre-labeled camera images. Our second approach extracts relevant and localized image features from camera images and uses these data to train a gradient-boosted tree-based model (lightGBM). We train both model approaches on a set of roughly 2000 images taken by the all-sky camera located at Lowell Observatory's Discovery Channel Telescope, in which the presence of clouds has been labeled manually. The ResNet approach reaches an accuracy of 85% in detecting clouds in a given region of an image, but requires a significant amount of computing resources. Our lightGBM approach achieves an accuracy of 95% with a training sample of ∼1000 images and rather modest computing resources. Based on different performance metrics, we recommend the latter feature-based approach for automated cloud detection. Code that was built for this work is available online.

Keywords: observational astronomy; astronomy data analysis; astronomy software; astronomical site protection; convolutional neural networks; all-sky cameras; open source software
TeV and keV-MeV Excesses as Probes for Hadronic Process in BL Lacertaes

A hard TeV γ-ray component excess over the single-zone leptonic model prediction (TeV excess) is observed in the spectral energy distributions (SEDs) of some BL Lacs. Its origin is uncertain. We revisit this issue with four BL Lacs (1ES 0229+200, 1ES 0347-121, 1ES 1101-232, and H2356-309), in which the TeV excess is detected in their intrinsic SEDs. We represent their SEDs with a single-zone leptohadronic model, where radiations of the electrons and protons as well as the cascade electrons produced by the γγ and pγ interactions within their jets are considered. We show that the observed SEDs below the GeV gamma-ray band are attributed to the synchrotron radiations and self-Compton process of the primary electrons, and the TeV excess is explained with the γ-ray emission from the pγ process via the π 0 decay. The cascade emission of the electrons produced via the γγ and pγ interactions results in a keV-MeV excess in the SEDs, illustrated as a bump or plateau. This extra photon field enhances the production of TeV photons from the p γ process, resulting in a reduction of the proton power by about one order of magnitude. However, the derived powers are still 3-4 orders of magnitude larger than the Eddington limit, being challenged by the current black hole accretion physics. Applying our model to Mrk 421, we propose that synergic observations with current and upcoming TeV and keV-MeV telescopes for its tentative TeV and MeV excesses can give insights to the hadronic process in its jet.

Keywords: blazars; relativistic jets; non-thermal radiation sources
A Geologically Robust Procedure for Observing Rocky Exoplanets to Ensure that Detection of Atmospheric Oxygen Is a Modern Earth-like Biosignature

In the next decades, the astrobiological community will debate whether the first observations of oxygen in an exoplanet's atmosphere signify life, so it is critical to establish procedures now for collection and interpretation of such data. We present a step-by-step observational strategy for using oxygen as a robust biosignature to prioritize exoplanet targets and design future observations. It is premised on avoiding planets lacking subaerial weathering of continents, which would imply geochemical cycles drastically different from modern Earth's, precluding use of oxygen as a biosignature. The strategy starts with the most readily obtained data: orbital semimajor axis and stellar luminosity to ensure residence in the habitable zone and stellar X-ray/ultraviolet flux to ensure an exoplanet can retain a secondary (outgassed) atmosphere. Next, high-precision mass and radius information should be combined with high-precision stellar abundance data to constrain the exoplanet's water content; those incompatible with <0.1 wt% H2O can be deprioritized. Then, reflectance photometry or low-resolution transmission spectroscopy should confirm an optically thin atmosphere. Subsequent long-duration, high-resolution transmission spectroscopy should search for oxygen and ensure that water vapor and CO2 are present only at low (∼102-104 ppm levels). Assuming oxygen is found, attribution to life requires the most difficult step, acquisition of a detailed, multispectral light curve of the exoplanet, to ensure both surface land and water. Exoplanets failing some of these steps might be habitable, even have observable biogenic oxygen, but should be deprioritized because oxygen could not be attributed unambiguously to life, and life therefore would not be detectable on such planets. Finally, we show how to use this scheme for the solar system, the 55 Cnc system, and the TRAPPIST-1 system, in which only the Earth and TRAPPIST-1e successfully pass through our procedure.

Keywords: exoplanet systems; exoplanet structure; exoplanet astronomy; stellar astronomy; astrobiology; biosignatures
Modeling of Joint Parker Solar Probe-Metis/Solar Orbiter Observations

We present the first theoretical modeling of joint Parker Solar Probe (PSP)-Metis/Solar Orbiter (SolO) quadrature observations. The combined observations describe the evolution of a slow solar wind plasma parcel from the extended solar corona (3.5-6.3 R ⊙) to the very inner heliosphere (23.2 R ⊙). The Metis/SolO instrument remotely measures the solar wind speed finding a range from 96 to 201 km s-1, and PSP measures the solar wind plasma in situ, observing a radial speed of 219.34 km s-1. We find theoretically and observationally that the solar wind speed accelerates rapidly within 3.3-4 R ⊙ and then increases more gradually with distance. Similarly, we find that the theoretical solar wind density is consistent with the remotely and in-situ observed solar wind density. The normalized cross helicity and normalized residual energy observed by PSP are 0.96 and -0.07, respectively, indicating that the slow solar wind is very Alfvénic. The theoretical NI/slab results are very similar to PSP measurements, which is a consequence of the highly magnetic field-aligned radial flow ensuring that PSP can measure slab fluctuations and not 2D ones. Finally, we calculate the theoretical 2D and slab turbulence pressure, finding that the theoretical slab pressure is very similar to that observed by PSP.

Keywords: the sun; solar wind; interplanetary turbulence
A Helium-flash-induced Mixing Event Can Explain the Lithium Abundances of Red Clump Stars

Observations demonstrate that the surface abundance of ${}^{7}\mathrm{Li}$ in low-mass stars changes dramatically between the tip of the red giant branch and the red clump. This naturally suggests an association with the helium core flash, which occurs between these two stages. Using stellar evolution models and a simple, ad hoc mixing prescription, we demonstrate that the ${}^{7}\mathrm{Li}$ enhancement can be explained by a brief chemical mixing event that occurs at the time of the first, strongest He subflash. The amount of ${}^{7}\mathrm{Be}$ already present above the H-burning shell just before the flash, once it mixes into the cooler envelope and undergoes an electron capture converting it to ${}^{7}\mathrm{Li}$ , is sufficient to explain the observed abundance at the red clump. We suggest that the excitation of internal gravity waves by the vigorous turbulent convection during the flash may provide a physical mechanism that can induce such mixing.

Keywords: stellar evolution; stellar abundances; red giant clump
LensWatch. I. Resolved HST Observations and Constraints on the Strongly Lensed Type Ia Supernova 2022qmx ("SN Zwicky")

Supernovae (SNe) that have been multiply imaged by gravitational lensing are rare and powerful probes for cosmology. Each detection is an opportunity to develop the critical tools and methodologies needed as the sample of lensed SNe increases by orders of magnitude with the upcoming Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope. The latest such discovery is of the quadruply imaged Type Ia SN 2022qmx (aka, "SN Zwicky") at z = 0.3544. SN Zwicky was discovered by the Zwicky Transient Facility in spatially unresolved data. Here we present follow-up Hubble Space Telescope observations of SN Zwicky, the first from the multicycle "LensWatch (www.lenswatch.org)" program. We measure photometry for each of the four images of SN Zwicky, which are resolved in three WFC3/UVIS filters (F475W, F625W, and F814W) but unresolved with WFC3/IR F160W, and present an analysis of the lensing system using a variety of independent lens modeling methods. We find consistency between lens-model-predicted time delays (≲1 day), and delays estimated with the single epoch of Hubble Space Telescope colors (≲3.5 days), including the uncertainty from chromatic microlensing (~1-1.5 days). Our lens models converge to an Einstein radius of ${\theta }_{{\rm{E}}}=({0.168}_{-0.005}^{+0.009})^{\prime\prime} $ , the smallest yet seen in a lensed SN system. The "standard candle" nature of SN Zwicky provides magnification estimates independent of the lens modeling that are brighter than predicted by $\sim {1.7}_{-0.6}^{+0.8}$ mag and $\sim {0.9}_{-0.6}^{+0.8}$ mag for two of the four images, suggesting significant microlensing and/or additional substructure beyond the flexibility of our image-position mass models.

Keywords: type ia supernovae; strong gravitational lensing
FORCAST Imaging of Two Small Nearby Clusters: The Coronet and B 59

We present mid-infrared imaging of two young clusters, the Coronet in the CrA cloud core and B 59 in the Pipe Nebula, using the FORCAST camera on the Stratospheric Observatory for Infrared Astronomy. We also analyze Herschel Space Observatory4 PACS and SPIRE images of the associated clouds. The two clusters are at similar, and very close, distances. Star formation is ongoing in the Coronet, which hosts at least one Class 0 source and several pre-stellar cores, which may collapse and form stars. The B 59 cluster is older, although it still has a few Class I sources, and is less compact. The CrA cloud has a diameter of ~0.16 pc, and we determine a dust temperature of 15.7 K and a star formation efficiency of ~27%. The B 59 core is approximately twice as large, with a dust temperature of ~11.4 K and a star formation efficiency of ~14%. We infer that the gas densities are much higher in the Coronet, which has also formed intermediate-mass stars, while B 59 has only formed low-mass stars.

Keywords: star formation; protostars; pre-main sequence stars; protoplanetary disks; circumstellar disks
Testing the Limits of Biosignature Detection in Ca-sulphate Mixtures Through a Simulated Martian Environment

Mixtures of cyanobacterial microbial mat and Ca-sulphate minerals were exposed to a simulated Martian environment via the Thales Alenia Space's "MARSBalloon" Project in partnership with St Bernard's High School via the Orbyts science inclusivity program. FTIR spectroscopic analyses identified that at 50% Ca-sulphate, most microbial mat biosignatures were obscured under Earth conditions, except for the C-O stretch and polysaccharide O-H vibrational modes. At 75% Ca-sulphate concentrations, no spectral biosignatures were observed. However, after exposure to a simulated stratospheric Martian environment, partial dehydration of the Ca-sulphate occurred to reveal the spectral biosignatures. This has implications in the search for life on Mars, particularly within evaporite-rich environments similar to those being investigated by the Curiosity rover.

Keywords: astrobiology; biosignatures; mars; solar system terrestrial planets; stratosphere; infrared spectroscopy; spectroscopy