adsabs/SciX_UAT_keywords huggingface dataset:
Ultra-wideband, Multiepoch Radio Study of the First Discovered "Main-sequence Radio Pulse Emitter" CU Vir

The presence of a large-scale surface magnetic field in early-type stars leads to several unique electromagnetic phenomena producing radiation over X-ray to radio bands. Among them, the rarest type of emission is electron cyclotron maser emission (ECME) observed as periodic, circularly polarized radio pulses. The phenomenon was first discovered in the hot magnetic star CU Vir. Past observations of this star led to the consensus that the star produces only right circularly polarized ECME, suggesting that only one magnetic hemisphere takes part in the phenomenon. Here we present the first ultra-wideband (0.4-4 GHz) study of this star using the upgraded Giant Metrewave Radio telescope and the Karl G. Jansky Very Large Array, which led to the surprising discovery of ECME of both circular polarizations up to around 1.5 GHz. The GHz observations also allowed us to infer that the upper ECME cutoff frequency is at ≳5 GHz. The sub-GHz observation led to the unexpected observation of more than two pairs of ECME pulses per rotation cycle. In addition, we report the discovery of a "giant pulse" and transient enhancements, which are potentially the first observational evidence of "centrifugal breakout" of plasma from the innermost part of the stellar magnetosphere. The stark contrast between the star's behavior at GHz and sub-GHz frequencies could either be due to propagation effects, a manifestation of varying magnetic field topology as a function of height, or a signature of an additional "ECME engine."

Keywords: magnetic stars; b stars; magnetospheric radio emissions; astrophysical masers; radio astronomy; transient detection
Solar Bayesian Analysis Toolkit—A New Markov Chain Monte Carlo IDL Code for Bayesian Parameter Inference

We present the Solar Bayesian Analysis Toolkit (SoBAT), which is a new easy to use tool for Bayesian analysis of observational data, including parameter inference and model comparison. SoBAT is aimed (but not limited) to be used for the analysis of solar observational data. We describe a new IDL code designed to facilitate the comparison of a user-supplied model with data. Bayesian inference allows prior information to be taken into account. The use of Markov Chain Monte Carlo sampling allows efficient exploration of large parameter spaces and provides reliable estimation of model parameters and their uncertainties. The Bayesian evidence for different models can be used for quantitative comparison. The code is tested to demonstrate its ability to accurately recover a variety of parameter probability distributions. Its application to practical problems is demonstrated using studies of the structure and oscillation of coronal loops.

Keywords: solar physics; bayesian statistics; astronomy data analysis; astronomy software; markov chain monte carlo
Depth of Jupiter's Zonal Flow under the "Shallow-wind" Assumption

In this article, the depth of Jupiter's zonal flow in the molecular-hydrogen region is for the first time explored in the context of the so-called "shallow-wind" scenario, which means the internal zonal circulation is kinematically different from the fast atmospheric jet stream. A gravitationally constrained zonal flow of typical speed $O(1)\,{\rm{m}}\,{{\rm{s}}}^{-1}$ is adopted. The zonal flow is examined in the semiconducting region for its MHD interaction with Jupiter's main magnetic field and the resulting ohmic dissipation. Our calculations indicate that the zonal flow in Jupiter might be permitted to reach downward to the radial location at $r=0.937{R}_{J}$ , deeper than previous estimations obtained by assuming the fast cloud-top zonal wind extended straightforward into Jupiter's interior. On the other hand, it is also concluded that Jupiter's zonal flow likely cannot penetrate any deeper to where electrical conductivity is greater than $O(10)\,{\rm{S}}\,{{\rm{m}}}^{-1}$ ; though, fluid motion might be slow under the "shallow-wind" model assumption.

Keywords: magnetic fields; gravitation; jupiter; planetary atmospheres; magnetohydrodynamics
Bayesian Accretion Modeling: Axisymmetric Equatorial Emission in the Kerr Spacetime

The Event Horizon Telescope (EHT) has produced images of two supermassive black holes, Messier 87* (M 87*) and Sagittarius A* (Sgr A*). The EHT collaboration used these images to indirectly constrain black hole parameters by calibrating measurements of the sky-plane emission morphology to images of general relativistic magnetohydrodynamic (GRMHD) simulations. Here, we develop a model for directly constraining the black hole mass, spin, and inclination through signatures of lensing, redshift, and frame dragging, while simultaneously marginalizing over the unknown accretion and emission properties. By assuming optically thin, axisymmetric, equatorial emission near the black hole, our model gains orders of magnitude in speed over similar approaches that require radiative transfer. Using 2017 EHT M 87* baseline coverage, we use fits of the model to itself to show that the data are insufficient to demonstrate existence of the photon ring. We then survey time-averaged GRMHD simulations fitting EHT-like data, and find that our model is best-suited to fitting magnetically arrested disks, which are the favored class of simulations for both M 87* and Sgr A*. For these simulations, the best-fit model parameters are within ~10% of the true mass and within ~10° for inclination. With 2017 EHT coverage and 1% fractional uncertainty on amplitudes, spin is unconstrained. Accurate inference of spin axis position angle depends strongly on spin and electron temperature. Our results show the promise of directly constraining black hole spacetimes with interferometric data, but they also show that nearly identical images permit large differences in black hole properties, highlighting degeneracies between the plasma properties, spacetime, and, most crucially, the unknown emission geometry when studying lensed accretion flow images at a single frequency.

Keywords: accretion; astrophysical black holes; gravitational lensing; very long baseline interferometry
An Ancient Martian Dynamo Driven by Hemispheric Heating: Effect of Thermal Boundary Conditions

Magnetic field observations from the MGS, MAVEN, and InSight missions reveal that a dynamo was active in Mars's early history. One unique feature of Mars's magnetic crustal field is its hemispheric dichotomy, where magnetic fields in the southern hemisphere are much stronger than those in the northern hemisphere. Here we use numerical dynamo simulations to investigate the potential hemispheric nature of Mars's ancient dynamo. Previous studies show that a hemispheric heat flux perturbation at the core-mantle boundary could result in either a stable hemispherical magnetic field or a constantly reversing field, depending on choices of parameters used in those models. These two scenarios lead to different implications for the origin of crustal fields. Here we test the dynamo sensitivity to varying hemispheric heat flux perturbations at the core-mantle boundary in a broader parameter regime to understand whether a hemispheric dynamo is likely for early Mars. We find that features of the dynamo change from stable, hemispheric magnetic fields to reversing, hemispheric fields, with increasing hemispheric heat flux perturbations at the core-mantle boundary. We also find that magnetic fields powered by bottom heating are more stable and transition from a nonreversing, hemispheric magnetic field to a multipolar field at higher hemispheric heat flux perturbations, while the transition happens at a much lower heat flux perturbation for magnetic fields powered by internal heating.

Keywords: planetary interior; magnetic fields; mars; magnetohydrodynamics
Four Eccentric Mergers Increase the Evidence that LIGO-Virgo-KAGRA's Binary Black Holes Form Dynamically

The growing population of compact binary mergers detected with gravitational waves contains multiple events that are challenging to explain through isolated binary evolution. Such events have higher masses than are expected in isolated binaries, component spin tilt angles that are misaligned, and/or nonnegligible orbital eccentricities. We investigate the orbital eccentricities of 62 binary black hole candidates from the third gravitational-wave transient catalog of the LIGO-Virgo-KAGRA Collaboration with an aligned-spin, moderate-eccentricity waveform model. Within this framework, we find that at least four of these events show significant support for eccentricity e 10 ≥ 0.1 at a gravitational-wave frequency of 10 Hz (>60% credibility, under a log-uniform eccentricity prior that spans the range 10-4 < e 10 < 0.2). Two of these events are new additions to the population: GW191109 and GW200208_22. If the four eccentric candidates are truly eccentric, our results suggest that densely populated star clusters may produce 100% of the observed mergers. However, it remains likely that other formation environments with higher yields of eccentric mergers-for example, active galactic nuclei-also contribute. We estimate that we will be able to confidently distinguish which formation channel dominates the eccentric merger rate after ≳80 detections of events with e 10 ≥ 0.05 at LIGO-Virgo sensitivity, with only ~5 detectably eccentric events required to distinguish formation channels with third-generation gravitational-wave detectors.

Keywords: black holes; compact objects; high energy astrophysics; astrophysical black holes; gravitational waves; gravitational wave astronomy; gravitational wave detectors; gravitational wave sources; globular star clusters; star clusters; bayesian statistics; active galactic nuclei
CAHA/PPAK Integral-field Spectroscopic Observations of M81. I. Circumnuclear Ionized Gas

Galactic circumnuclear environments of nearby galaxies provide unique opportunities for our understanding of the coevolution between supermassive black holes and their host galaxies. Here, we present a detailed study of ionized gas in the central kiloparsec region of M81, which hosts the closest prototype low-luminosity active galactic nucleus, based on optical integral-field spectroscopic observations taken with the CAHA 3.5 m telescope. It is found that much of the circumnuclear ionized gas is concentrated within a bright core of ~200 pc in extent and a surrounding spiral-like structure known as the nuclear spiral. The total mass of the ionized gas is estimated to be ~2 × 105 M ⊙, which corresponds to a few percent of the cold gas mass in this region, as traced by co-spatial dust extinction features. Plausible signature of a biconical outflow along the disk plane is suggested by a pair of blueshifted/redshifted low-velocity features, symmetrically located at ~120-250 pc from the nucleus. The spatially resolved line ratios of [N II]/Hα and [O III]/Hβ demonstrate that much of the circumnuclear region can be classified as a LINER. However, substantial spatial variations in the line intensities and line ratios strongly suggest that different ionization/excitation mechanisms, rather than just a central dominant source of photoionization, are simultaneously at work to produce the observed line signatures.

Keywords: liner galaxies; galaxy nuclei; warm ionized medium
Semianalytic Expressions for the Isolation and Coupling of Mixed Modes

In the oscillation spectra of giant stars, nonradial modes may be seen to undergo avoided crossings, which produce a characteristic "mode bumping" of the otherwise uniform asymptotic p- and g-mode patterns in their respective echelle diagrams. Avoided crossings evolve very quickly relative to typical observational errors and are therefore extremely useful in determining precise ages of stars, particularly in subgiants. This phenomenon is caused by coupling between modes in the p- and g-mode cavities that are near resonance with each other. Most theoretical analyses of the coupling between these mode cavities rely on the Jeffreys-Wentzel-Kramers-Brillouin approach, which is strictly speaking inapplicable to the low-order g modes observed in subgiants or the low-order p modes seen in very evolved red giants. We present both a nonasymptotic prescription for isolating the two mode cavities, as well as a perturbative (and also nonasymptotic) description of the coupling between them, which we show to hold good for the low-order g and p modes in these physical situations. Finally, we discuss how these results may be applied to modeling subgiant stars and determining their global properties from oscillation frequencies. We also make our code for all of these computations publicly available.

Keywords: asteroseismology; stellar oscillations; computational methods
Compact Groups of Galaxies in Sloan Digital Sky Survey and LAMOST Spectral Survey. I. The Catalogs

A compact group (CG) is a kind of special galaxy system where the galaxy members are separated at distances of the order of galaxy size. The strong interaction between the galaxy members makes CGs ideal labs for studying the environmental effects on galaxy evolution. The traditional photometric selection algorithm biases against the CG candidates at low redshifts, while the spectroscopic identification technique is affected by the spectroscopic incompleteness of sample galaxies and typically biases against the high redshift candidates. In this study, we combine these two methods and select CGs in the main galaxy sample of the Sloan Digital Sky Survey, where we also have taken the advantages of the complementary redshift measurements from the LAMOST spectral and GAMA surveys. We have obtained the largest and most complete CG samples to date. Our samples include 6144 CGs and 8022 CG candidates, which are unique in the studies of the nature of the CGs and the evolution of the galaxies inside.

Keywords: galaxy groups; hickson compact group; galaxy environments
Millimeter to THz Spectroscopy of HC18O+ and HC17O+: Accurate Rest Frequencies for Astrophysical Studies

Heavy oxygen isotopic species of HCO+ are important optically thin astrophysical tracers. The ground-state rotational spectrum of HC18O+, DC18O+, HC17O+, and DC17O+ has been recorded in the laboratory in the frequency range from 85 GHz to 1.3 THz. The ions have been produced in the negative column of a glow-discharge plasma, and their spectrum has been recorded in absorption using a frequency-modulation submillimeter-wave spectrometer. Various sources of systematic error have been carefully accounted for in order to obtain highly accurate line-position measurements. Theoretical estimates of the molecular parameters and of the collision effects on the line shape have been obtained by high-level ab initio calculations. The analysis yielded much improved rotational and centrifugal distortion constants, thus bringing the spectroscopic characterization of these rare isotopic variants to the same level of the parent species. Also, the first experimental rotational data for DC17O+ have been provided. These results allow for the calculation of an updated set of rest frequencies to support current and future astrophysical studies. The derived data set for the widely used HC18O+ tracer reaches an accuracy of a few parts in 109 up to 1.5 THz. Such accuracy is important for the analysis of astrophysical objects targeted by Atacama Large Millimeter/submillimeter Array observations at the submillimeter regime.

Keywords: laboratory astrophysics; spectral line lists; collisional broadening
ROME. IV. An Arecibo Search for Substellar Magnetospheric Radio Emissions in Purported Exoplanet-hosting Systems at 5 GHz

Plasma flow–obstacle interactions, such as those between an exoplanet's magnetosphere and the host star's stellar wind, may lead to detectable radio emissions. Despite many attempts to detect magnetospheric (auroral) radio emissions from exoplanets, a reproducible, unambiguous detection remains elusive. This fourth paper of the Radio Observations of Magnetized Exoplanets (ROME) series presents the results of a targeted radio survey of nine nearby systems that host exoplanet, brown dwarf, or low-mass-stellar companions conducted with the Arecibo radio telescope at ∼5 GHz. This search for magnetospheric radio emissions has the greatest sensitivity (∼1 mJy during <1 s integration times) and collected full Stokes parameters over the largest simultaneous bandpass of any survey to date. It is also the first survey to search for radio emission from brown dwarfs of spectral class Y, which may illuminate open questions regarding their magnetism, interior and atmospheric structure, and formation histories. No magnetospheric radio emissions from substellar companions were detected. These results are examined within the context of recent theoretical work on plasma flow–obstacle interactions, and radio emissions observed from the solar system planets and ultracool dwarfs.

Keywords: magnetospheric radio emissions; y dwarfs; brown dwarfs; exoplanets; planetary magnetospheres; non-thermal radiation sources; magnetic fields; spectropolarimetry; aurorae; natural satellites (extrasolar)
Hydrodynamic Escape of Water Vapor Atmospheres near Very Active Stars

When exposed to the high-energy X-ray and ultraviolet radiation of a very active star, water vapor in the upper atmospheres of planets can be photodissociated and rapidly lost to space. In this paper, I study the chemical, thermal, and hydrodynamic processes in the upper atmospheres of terrestrial planets, concentrating on water-vapor-dominated atmospheres orbiting in the habitable zones of active stars. I consider different stellar activity levels and find very high levels of atmospheric escape in all cases, with the outflowing gas being dominated by atomic hydrogen and oxygen in both their neutral and ion forms. In the lower activity cases, I find that the accumulation of O2 and increases in the D/H ratios in the atmospheres due to mass fractionation are possible, but in the higher activity cases, no mass fractionation takes place. Connecting these results to stellar activity evolution tracks for solar-mass stars, I show that huge amounts of water vapor can be lost, and both the losses and the amount of O2 that can be accumulated in the atmosphere depend sensitively on the star's initial rotation rate. For an Earth-mass planet in the habitable zone of a low-mass M dwarf, my results suggest that the accumulation of atmospheric O2 is unlikely unless water loss can take place after the star's most active phase.

Keywords: exoplanet atmospheres; planetary atmospheres; upper atmosphere; water vapor; stellar activity
Characterizing and Mitigating Intraday Variability: Reconstructing Source Structure in Accreting Black Holes with mm-VLBI

The extraordinary physical resolution afforded by the Event Horizon Telescope has opened a window onto the astrophysical phenomena unfolding on horizon scales in two known black holes, M87* and Sgr A*. However, with this leap in resolution has come a new set of practical complications. Sgr A* exhibits intraday variability that violates the assumptions underlying Earth aperture synthesis, limiting traditional image reconstruction methods to short timescales and data sets with very sparse (u, v) coverage. We present a new set of tools to detect and mitigate this variability. We develop a data-driven, model-agnostic procedure to detect and characterize the spatial structure of intraday variability. This method is calibrated against a large set of mock data sets, producing an empirical estimator of the spatial power spectrum of the brightness fluctuations. We present a novel Bayesian noise modeling algorithm that simultaneously reconstructs an average image and statistical measure of the fluctuations about it using a parameterized form for the excess variance in the complex visibilities not otherwise explained by the statistical errors. These methods are validated using a variety of simulated data, including general relativistic magnetohydrodynamic simulations appropriate for Sgr A* and M87*. We find that the reconstructed source structure and variability are robust to changes in the underlying image model. We apply these methods to the 2017 EHT observations of M87*, finding evidence for variability across the EHT observing campaign. The variability mitigation strategies presented are widely applicable to very long baseline interferometry observations of variable sources generally, for which they provide a data-informed averaging procedure and natural characterization of inter-epoch image consistency.

Keywords: galactic center; black holes; radio astronomy; very long baseline interferometry; time domain astronomy; astronomy data analysis; computational astronomy
Detection of a Broad 8 μm UIR Feature in the Mid-infrared Spectrum of WR 125 Observed with Subaru/COMICS

We present the detection of a broad 8 μm feature in newly formed dust around the carbon-rich Wolf-Rayet (WC) binary WR 125 from N-band low-resolution (NL; R ~ 250) spectroscopy between 7.3 and 13.6 μm and N-band (11.7 μm) and Q-band (18.8 μm) imaging with Subaru/COMICS in 2019 October. WR 125 is a colliding-wind binary (WC7 + O9) that exhibited renewed dust formation starting in 2018, ~28 yr after its first dust formation episode had been observed. We also compare our infrared photometry with historical observations and revise the dust formation period of WR 125 to 28.1 yr. Archival infrared spectra of five dusty WC stars, WR 48a, WR 98a, WR 104, WR 112, and WR 118, obtained with Infrared Space Observatory/Short-Wavelength Spectrometer are reanalyzed and compared with the WR 125 spectrum to search for a similar feature. We analyze the dusty WC spectra using two different extinction curves to investigate the impact of interstellar extinction correction on the presence and/or properties of the 8 μm feature. All of the dusty WC spectra dereddened with the two different extinction curves show a broad feature around 8 μm (FWHM ~ 1-2 μm). We suggest that these 8 μm features seen in the dusty WC spectra are related to the Class C unidentified infrared features.

Keywords: infrared astronomy; astrochemistry; circumstellar dust; wolf-rayet stars
Orbital Precession in the Distant Solar System: Further Constraining the Planet Nine Hypothesis with Numerical Simulations

The longitudes of perihelia and orbital poles of the solar system's dozen or so most remote detected objects are clustered in a manner inconsistent with that of a random sample of uniformly distributed orbits. While small number statistics and observational biases may explain these features, the statistical significance of the clustering has led to the recent development of the "Planet Nine hypothesis." In the proposed scenario, orbits in the distant solar system are shepherded via secular perturbations from an undetected massive planet on an eccentric orbit. However, the precession of perihelia and nodes in the outer Kuiper Belt and inner Oort cloud are also affected by the giant planets, passing stars, and the galactic tide. We perform a large suite of numerical simulations designed to study the orbital alignment of extreme trans-Neptunian objects (ETNOs) and inner Oort cloud objects (IOCOs). In our various integrations that include Planet Nine, we consistently find that ≳60% of ETNOs and IOCOs that are detectable after 4 Gyr are also anti-aligned in perihelia with the distant massive perturber. However, when we randomly select 17 objects from this sample of remaining orbits, there is significant scatter in the degree of longitude of perihelion and orbital pole clustering that might be observed. Furthermore, we argue that, in the absence of Planet Nine, 17 randomly drawn orbits should still exhibit some clustering even if the underlying distribution is uniform. Thus, we find that still more ETNO and IOCO detections are required to confidently infer the presence of Planet Nine.

Keywords: solar system; solar system gas giant planets; solar system formation; small solar system bodies