adsabs/SciX_UAT_keywords huggingface dataset:
Inferring Exoplanet Disequilibria with Multivariate Information in Atmospheric Reaction Networks

Inferring properties of exoplanets from their atmospheres presents technical challenges in data collection due to low resolution and low signal-to-noise ratio (S/N) and theoretical challenges in the predictions made from forward-modeling due to errors introduced via incomplete or inaccurate assumptions in atmospheric physics and chemistry. The combination of these factors makes developing techniques to identify the most predictive features robust to low S/N and model error an increasingly important challenge for exoplanet science. Here we implement a multivariate approach to identify optimal predictors of the state of disequilibria. As a case study we focus on the prediction of vertical mixing (parameterized as eddy diffusion) in hot Jupiter atmospheres. We use multivariate information contained in molecular abundances, reaction network topology, and Gibbs free energy to demonstrate the variation in prediction efficacy of the vertical mixing coefficient (K zz) from different model information. While current approaches target inferring molecular abundances from spectral data, our results indicate that the set of optimal predictors of K zz varies with planetary properties such as irradiation temperature and metallicity. In most cases, multivariate data composed of network topological variables, which capture system-level features, perform as well as the set of optimal predictors and better than any individual variable. We discuss future directions, where identifying the set of optimal predictors should be useful for quantitatively ranking atmospheres in terms of their distance from thermochemical equilibrium, provide target variables for the development of new tools for inverse modeling, and provide applications to the longer-term goal of detection of disequilibria associated with life.

Keywords: exoplanet atmospheres
Bipolar Ephemeral Active Regions, Magnetic Flux Cancellation, and Solar Magnetic Explosions

We examine the cradle-to-grave magnetic evolution of 10 bipolar ephemeral active regions (BEARs) in solar coronal holes, especially aspects of the magnetic evolution leading to each of 43 obvious microflare events. The data are from the Solar Dynamics Observatory: 211 Å coronal EUV images and line-of-sight photospheric magnetograms. We find evidence that (1) each microflare event is a magnetic explosion that results in a miniature flare arcade astride the polarity inversion line (PIL) of the explosive lobe of the BEAR's anemone magnetic field; (2) relative to the BEAR's emerged flux-rope Ω loop, the anemone's explosive lobe can be an inside lobe, an outside lobe, or an inside-and-outside lobe; (3) 5 events are confined explosions, 20 events are mostly confined explosions, and 18 events are blowout explosions, which are miniatures of the magnetic explosions that make coronal mass ejections (CMEs); (4) contrary to the expectation of Moore et al., none of the 18 blowout events explode from inside the BEAR's Ω loop during the Ω loop's emergence; and (5) before and during each of the 43 microflare events, there is magnetic flux cancellation at the PIL of the anemone's explosive lobe. From finding evident flux cancellation at the underlying PIL before and during all 43 microflare events-together with BEARs evidently being miniatures of all larger solar bipolar active regions-we expect that in essentially the same way, flux cancellation in sunspot active regions prepares and triggers the magnetic explosions for many major flares and CMEs.

Keywords: solar magnetic fields; solar active regions; jets; solar magnetic flux emergence; solar magnetic reconnection; solar coronal holes; ephemeral active regions
The Most Predictive Physical Properties for the Stellar Population Radial Profiles of Nearby Galaxies

We present a study on the radial profiles of the D4000, luminosity-weighted stellar ages τL, and luminosity-weighted stellar metallicities [Z/H]L of 3654 nearby galaxies (0.01 < z < 0.15) using the IFU spectroscopic data from the MaNGA survey available in the SDSS DR15, in an effort to explore the connection between median stellar population radial gradients (I.e., ∇D4000, ∇τL, ∇[Z/H]L) out to ∼1.5 Re and various galaxy properties, including stellar mass (M⋆), specific star formation rate (sSFR), morphologies, and local environment. We find that M⋆ is the single most predictive physical property for ∇D4000 and ∇[Z/H]L. The most predictive properties for ∇τL are sSFR and, to a lesser degree, M⋆. The environmental parameters, including local galaxy overdensities and central-satellite division, have virtually no correlation with stellar population radial profiles for the whole sample, but the ∇D4000 of star-forming satellite galaxies with M⋆ ≲ 1010 M⊙ exhibit a significant positive correlation with galaxy overdensities. Galaxies with lower sSFR have on average steeper negative stellar population gradients, and this sSFR dependence is stronger for more massive star-forming galaxies. The negative correlation between the median stellar population gradients and M⋆ are best described largely as segmented relationships, whereby median gradients of galaxies with log M⋆ ≲ 10.0 (with the exact value depending on sSFR) have much weaker mass dependence than galaxies with higher M⋆. While the dependence of the radial gradients of ages and metallicities on T-Types and central stellar mass surface densities are generally not significant, galaxies with later T-Types or lower central mass densities tend to have significantly lower D4000, younger τL, and lower [Z/H]L across the radial ranges probed in this study.

Keywords: galaxy evolution; galaxies; star formation; galaxy stellar content
New Constraints on the Future Evaporation of the Young Exoplanets in the V1298 Tau System

Transiting planets at young ages are key targets for improving our understanding of the evolution of exo-atmospheres. We present results of a new X-ray observation of V 1298 Tau with XMM-Newton, aimed to determine more accurately the high-energy irradiation of the four planets orbiting this pre-main-sequence star, and the possible variability due to magnetic activity on short and long timescales. Following the first measurements of planetary masses in the V 1298 Tau system, we revise early guesses of the current escape rates from the planetary atmospheres, employing our updated atmospheric evaporation models to predict the future evolution of the system. Contrary to previous expectations, we find that the two outer Jupiter-sized planets will not be affected by any evaporation on Gyr timescales, and the same occurs for the two smaller inner planets, unless their true masses are lower than ~40 M ⊕. These results confirm that relatively massive planets can reach their final position in the mass-radius diagram very early in their evolutionary history.

Keywords: exoplanet systems; exoplanet atmospheres; pre-main sequence stars; x-ray stars
A Simulation of Radius-frequency Mapping for PSR J1848-0123 with an Inverse Compton Scattering Model

The radio radiation mechanism is one of the open questions for pulsars. Multiband observations are very helpful to constrain pulsar radiation models. We observed PSR J1848-0123 at the 5 GHz band with the Shanghai Tianma 65 m radio telescope (TMRT). The 5 GHz observation together with the European Pulsar Network (EPN) and CSIRO ATNF Data Archives databases provides a broadband evolution property of the pulse profiles for this pulsar. We reprocessed these data sets to obtain the multiband pulse profiles. It was found that the pulse profile of PSR J1848-0123 narrows with increasing emission frequency. We separated the emission components of each pulse profile with a multi-Gaussian fitting method, and then calculated the beaming angle and emission radius of each component with the basic radiation geometry of pulsar. With the calculated beam angles and radiation radii, we simulated the radius-frequency mapping of this pulsar with an inverse Compton scatting model (ICS). It was found that the observed radio radiation could be generated in the core gap region above the polar cap of the pulsar. The beaming angle and emission radius versus frequency for PSR J1848-0123 can be explained well with the ICS model.

Keywords: rotation powered pulsars; pulsars
Efficient Energy Conversion through Vortex Arrays in the Turbulent Magnetosheath

Turbulence is often enhanced when transmitted through a collisionless plasma shock. We investigate how the enhanced turbulent energy in the Earth's magnetosheath effectively dissipates via vortex arrays. This research topic is of great importance as it relates to particle energization at astrophysical shocks across the universe. Wave modes and intermittent coherent structures are the key candidate mechanisms for energy conversion in turbulent plasmas. Here, by comparing in-situ measurements in the Earth's magnetosheath with a theoretical model, we find the existence of vortex arrays at the transition between the downstream regions of the Earth's bow shock. Vortex arrays consist of quasi-orthogonal kinetic waves and exhibit both high volumetric filling factors and strong local energy conversion, thereby showing a greater dissipative energization than traditional waves and coherent structures. Therefore, we propose that vortex arrays are a promising mechanism for efficient energy conversion in the sheath regions downstream of astrophysical shocks.

Keywords: space plasmas; interplanetary turbulence; planetary bow shocks
Chandra X-Ray Observations of PSR J1849-0001, Its Pulsar Wind Nebula, and the TeV Source HESS J1849-000

We obtained a 108 ks Chandra X-ray Observatory (CXO) observation of PSR J1849-0001 and its pulsar wind nebula (PWN) coincident with the TeV source HESS J1849-000. By analyzing the new and old (archival) CXO data, we resolved the pulsar from the PWN, explored the PWN morphology on arcsecond and arcminute scales, and measured the spectra of different regions of the PWN. Both the pulsar and the compact inner PWN spectra are hard with power-law photon indices of 1.20 ± 0.07 and 1.49 ± 0.20, respectively. The jet-dominated PWN has a relatively low luminosity, lack of γ-ray pulsations, relatively hard and nonthermal spectrum of the pulsar, and sine-like pulse profile, which indicates a relatively small angle between the pulsar's spin and magnetic dipole axis. In this respect, it shares similar properties with a few other so-called MeV pulsars. Although the joint X-ray and TeV spectral energy distribution can be roughly described by a single-zone model, the obtained magnetic field value is unrealistically low. A more realistic scenario is the presence of a relic PWN, no longer emitting synchrotron X-rays but still radiating in TeV via inverse-Compton upscattering. We also serendipitously detected surprisingly bright X-ray emission from a very wide binary whose components should not be interacting.

Keywords: pulsars; rotation powered pulsars; pulsar wind nebulae; gamma-ray sources; x-ray astronomy
An Optical Distortion Solution for the Keck I OSIRIS Imager

The astrometric precision and accuracy of an imaging camera is often limited by geometric optical distortions. These must be calibrated and removed to measure precise proper motions, orbits, and gravitationally lensed positions of interesting astronomical objects. Here, we derive a distortion solution for the OSIRIS Imager fed by the Keck I adaptive optics system at the W. M. Keck Observatory. The distortion solution was derived from images of the dense globular clusters M15 and M92 taken with OSIRIS in 2020 and 2021. The set of 403 starlists, each containing ~1000 stars, were compared to reference Hubble catalogs to measure the distortion-induced positional differences. OSIRIS was opened and optically realigned in 2020 November and the distortion solutions before and after the opening show slight differences at the ~20 mas level. We find that the OSIRIS distortion closely matches the designed optical model: large, reaching 20 pixels at the corners, but mostly low order, with the majority of the distortion in the 2nd-order mode. After applying the new distortion correction, we find a median residual of [x, y] = [0.052, 0.056] pixels ([0.51, 0.56] mas) for the 2020 solution, and [x, y] = [0.081, 0.071] pixels ([0.80, 0.71] mas) for the 2021 solution. Comparison between NIRC2 images and OSIRIS images of the Galactic center show that the mean astrometric difference between the two instruments reduces from 10.7 standard deviations to 1.7 standard deviations when the OSIRIS distortion solution is applied. The distortion model is included in the Keck AO Imaging data-reduction pipeline and is available for use on OSIRIS data.

Keywords: astronomical instrumentation; optical aberration; optical position
Searching for Intragroup Light in Deep U-band Imaging of the COSMOS Field

We present the results of deep, ground based U-band imaging with the Large Binocular Telescope of the Cosmic Evolution Survey field as part of the near-UV imaging program, UVCANDELS. We utilize a seeing sorted stacking method along with night-to-night relative transparency corrections to create optimal depth and optimal resolution mosaics in the U-band, which are capable of reaching point source magnitudes of AB~26.5 mag at 3σ. These ground-based mosaics bridge the wavelength gap between the Hubble Space Telescope WFC3 F275W and ACS F435W images and are necessary to understand galaxy assembly in the last 9-10 Gyr. We use the depth of these mosaics to search for the presence of U-band intragroup light (IGrL) beyond the local universe. Regardless of how groups are scaled and stacked, we do not detect any U-band IGrL to unprecedented U-band depths of ~29.1-29.6 mag arcsec-2, which corresponds to an IGrL fraction of ≲1% of the total group light. This stringent upper limit suggests that IGrL does not contribute significantly to the Extragalactic Background Light at short wavelengths. Furthermore, the lack of UV IGrL observed in these stacks suggests that the atomic gas observed in the intragroup medium is likely not dense enough to trigger star formation on large scales. Future studies may detect IGrL by creating similar stacks at longer wavelengths or by pre-selecting groups which are older and/or more dynamically evolved similar to past IGrL observations of compact groups and loose groups with signs of gravitational interactions.

Keywords: galaxy groups; astronomical techniques
Massive Interacting Binaries as an Enrichment Source for Multiple Populations in Star Clusters

We present a suite of binary evolution models with massive primaries (10 ≤ M 1 ≤ 40 M ⊙) and periods and mass ratios chosen such that the systems undergo nonconservative mass transfer while the primaries have helium cores. We track the total mass and chemical composition of the ejecta from these systems. This material shows the abundance signatures of hot hydrogen burning that are needed to explain the abundance patterns seen in multiple populations in massive star clusters. We then calculate the total yield of a population of binary stars with masses, mass ratios, and periods consistent with their distribution in a field population. We show that the overall abundance of this material is enriched in helium, nitrogen, sodium, and aluminum, and depleted in carbon, oxygen, and magnesium, by amounts that are consistent with observations. We also show that such a population of binaries will return approximately 25% of its mass in this ejecta (compared to 4% if all the stars were single), over a characteristic timescale of about 12 Myr. We argue that massive binaries must be seriously considered as a contributor to the source of enriched material needed to explain the multiple populations in massive clusters, since essentially all massive stars are formed in binaries or higher-order multiples, massive binaries are primarily formed in clusters, and massive binaries naturally produce material of the right composition.

Keywords: binary stars
New Evidence for Extended He I> Reionization at z ≳ 3.5 from He II Lyman Alpha and Beta Transmission Spikes

We present new high-resolution (R = λ/Δλ ∼ 14,000) spectra of the two brightest He II-transparent quasars in the far-UV at zem > 3.5, HE2QS J2311-1417 (zem = 3.70) and HE2QS J1630+0435 (zem = 3.81), obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. In the predominantly saturated He II absorption spectra, both sight lines show several isolated resolved (FWHM ≳ 50 km s-1) transmission spikes in He II Lyα and He II Lyβ. The incidence of such spikes decreases with increasing redshift, but both sight lines show significant spikes at z ≳ 3.5, signaling the presence of fully ionized regions in the z ≳ 3.5 intergalactic medium (IGM). We employ an automated algorithm to compare the number of detected He II transmission spikes to predictions from mock spectra created from the outputs of a cubic (146 cMpc)3 optically thin Nyx hydrodynamical simulation, assuming a range of UV background photoionization rates ΓHe II. From the incidence of Lyα and Lyβ transmission spikes we infer similar photoionization rates of ${{\rm{\Gamma }}}_{\mathrm{He}{\rm\small{II}}}=({2.0}_{-0.5}^{+0.6})\times {10}^{-15}\,{{\rm{s}}}^{-1}$ at 3.51 < z < 3.66 and ΓHe II = (0.9 ± 0.3) × 10-15 s-1 at 3.460 < z < 3.685, respectively. Because the transmission spikes indicate fully ionized regions at z ≳ 3.5 along both lines of sight, our observations provide further evidence that He II reionization had substantially progressed at these redshifts. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program 15356.

Keywords: cosmic background radiation; hubble space telescope; intergalactic medium; quasar absorption line spectroscopy; reionization; ultraviolet astronomy
A Fresh Look at AGB Stars in Galactic Open Clusters with Gaia: Impact on Stellar Models and the Initial-Final Mass Relation

Benefiting from the Gaia second and early third releases of photometric and astrometric data, we examine the population of asymptotic giant branch (AGB) stars that appear in the fields of intermediate-age and young open star clusters. We identify 49 AGB star candidates, brighter than the tip of the red giant branch, with a good to high cluster membership probability. Among them, we find 19 TP-AGB stars with known spectral type: 4 M stars, 3 MS/S stars, and 12 C stars. By combining observations, stellar models, and radiative transfer calculations that include the effect of circumstellar dust, we characterize each star in terms of initial mass, luminosity, mass-loss rate, core mass, period, and mode of pulsation. The information collected helps us shed light on the TP-AGB evolution at solar-like metallicity, placing constraints on the third dredge-up process, the initial masses of carbon stars, stellar winds, and the initial-final mass relation (IFMR). In particular, we find that two bright carbon stars, MSB 75 and BM IV 90, members of the clusters NGC 7789 and NGC 2660 (with similar ages of ≃ 1.2-1.6 Gyr and initial masses 2.1 ≳ M i /M ⊙ ≳ 1.9), have unusually high core masses, M c ≈ 0.67-0.7 M ⊙. These results support the findings of a recent work (Marigo et al. 2020) that identified a kink in the IFMR, which interrupts its monotonic trend just at the same initial masses. Finally, we investigate two competing scenarios to explain the M c data: the role of stellar winds in single-star evolution, and binary interactions through the blue straggler channel.

Keywords: asymptotic giant branch stars
Investigating the Low-flux States in Six Intermediate Polars

We present optical photometry of six intermediate polars that exhibit transitions to a low-flux state. For four of these systems, DW Cnc, V515 And, V1223 Sgr, and RX J2133.7+5107, we are able to perform timing analysis in and out of the low states. We find that, for DW Cnc and V515 And, the dominant periodicities in the light curves change as the flux decreases, indicating a change in the sources' accretion properties as they transition to the low state. For V1223 Sgr, we find that the variability is almost completely quenched at the lowest flux, but we do not find evidence for a changing accretion geometry. For RX J2133.7+5107, the temporal properties do not change in the low state, but we do see a period of enhanced accretion that is coincident with increased variability on the beat frequency, which we do not associate with a change in the accretion mechanisms in the system.

Keywords: cataclysmic variable stars; dq herculis stars; accretion; white dwarf stars; stellar accretion disks
First M87 Event Horizon Telescope Results. VIII. Magnetic Field Structure near The Event Horizon

Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales. This polarized synchrotron radiation probes the structure of magnetic fields and the plasma properties near the black hole. Here we compare the resolved polarization structure observed by the EHT, along with simultaneous unresolved observations with the Atacama Large Millimeter/submillimeter Array, to expectations from theoretical models. The low fractional linear polarization in the resolved image suggests that the polarization is scrambled on scales smaller than the EHT beam, which we attribute to Faraday rotation internal to the emission region. We estimate the average density ne ∼ 104-7 cm-3, magnetic field strength B ∼ 1-30 G, and electron temperature Te ∼ (1-12) × 1010 K of the radiating plasma in a simple one-zone emission model. We show that the net azimuthal linear polarization pattern may result from organized, poloidal magnetic fields in the emission region. In a quantitative comparison with a large library of simulated polarimetric images from general relativistic magnetohydrodynamic (GRMHD) simulations, we identify a subset of physical models that can explain critical features of the polarimetric EHT observations while producing a relativistic jet of sufficient power. The consistent GRMHD models are all of magnetically arrested accretion disks, where near-horizon magnetic fields are dynamically important. We use the models to infer a mass accretion rate onto the black hole in M87 of (3-20) × 10-4 M⊙ yr-1.

Keywords: accretion; black holes; event horizons; jets; kerr black holes; magnetic fields; magnetohydrodynamics; plasma astrophysics; polarimetry; radiative transfer; radio jets; relativistic jets
A Radio Pinwheel Emanating from WR 147

Wolf-Rayet (WR) stars are evolved massive stars, presumably on their way to becoming supernovae. They are characterized by high luminosities and fast and dense stellar winds. We have detected signs of a radio continuum pinwheel associated with WR 147, a nitrogen-rich WR star with spectral subtype WN8. These structures are known to exist around a handful of late-type carbon-rich WR stars with massive companions where dust has formed in the zone where the two winds collide and produced a plume of dense gas and dust that is carried out with the WR wind. As the binary system rotates, an Archimedean spiral detectable in the infrared is formed. The resulting pinwheel contains information on wind speeds, wind-momentum ratio, and orbital parameters. However, WR 147 is a WN star and the formation of dust is unlikely, so a different emission mechanism must be at work. Our analysis of the data suggests that in this case the emission is dominantly of a nonthermal nature (synchrotron), although we cannot exclude the possibility that some clumps could be brighter in free-free emission. It is possible that the pinwheels associated with WN stars will be detectable only as nonthermal emitters at radio wavelengths. From the characteristics of the pinwheel we estimate a period of 1.7 yr for the binary system (the WN8 star and a companion yet undetected directly) that is responsible for the pinwheel.

Keywords: binary stars; wolf-rayet stars; stellar winds