adsabs/SciX_UAT_keywords huggingface dataset:
Parsec-scale Properties of Steep- and Flat-spectrum Extragalactic Radio Sources from a VLBA Survey of a Complete North Polar Cap Sample

We observed with the Very Long Baseline Array (VLBA) at 2.3 and 8.6 GHz a complete flux-density-limited sample of 482 radio sources with decl. > +75° brighter than 200 mJy at 1.4 GHz drawn from the NVSS catalog. A total of 34% of the sources show parsec-scale emission above the flux density detection limit of 30 mJy; their accurate positions and parsec-scale structure parameters are determined. Among all the sources detected at least at the shortest VLBA baselines, the majority, or 72%, have a steep single-dish spectrum. The fraction of the sources with a detectable parsec-scale structure is above 95% among the flat-spectrum objects and close to 25% among the steep-spectrum objects. We identified 82 compact steep-spectrum source candidates, which make up 17% of the sample; most of them are reported for the first time. The compactness and the brightness temperature of the sources in our sample show a positive correlation with single-dish and VLBA spectral indices. All the sources with a significant 8 GHz variability were detected by the VLBA snapshot observations, which independently confirmed their compactness. We demonstrated that 54% of the sources detected by the VLBA at 2.3 GHz in our sample have a steep VLBA spectrum. The compact radio emission of these sources is likely dominated by optically thin jets or mini-lobes, not by an opaque jet core. These results show that future VLBI surveys aimed at searching for new sources with parsec-scale structure should include not only flat-spectrum sources but also steep-spectrum ones in order to reach an acceptable level of completeness.

Keywords: galaxy jets; active galactic nuclei; radio astrometry; radio astronomy; radio continuum emission; radio sources; very long baseline interferometry; radio interferometry
Generalized Peas in a Pod: Extending Intra-system Mass Uniformity to Non-TTV Systems via the Gini Index

It has been demonstrated that planets belonging to the same close-in, compact multiple-planet system tend to exhibit a striking degree of uniformity in their sizes. A similar trend has also been found to hold for the masses of such planets, but considerations of such intra-system mass uniformity have generally been limited to statistical samples wherein a majority of systems have constituent planetary mass measurements obtained via analysis of transit timing variations (TTVs). Since systems with strong TTV signals typically lie in or near mean motion resonance, it remains to be seen whether intra-system mass uniformity is still readily emergent for nonresonant systems with non-TTV mass provenance. We thus present in this work a mass uniformity analysis of 17 non-TTV systems with masses measured via radial velocity measurements. Using the Gini index, a common statistic for economic inequality, as our primary metric for uniformity, we find that our sample of 17 non-TTV systems displays intra-system mass uniformity at a level of ~2.5σ confidence. We provide additional discussion of possible statistical and astrophysical underpinnings for this result. We also demonstrate the existence of a correlation (r = 0.25) between characteristic solid surface density (Σ0) of the minimum-mass extrasolar nebula and system mass Gini index, suggesting that more-massive disks may generally form systems with more-unequal planetary masses.

Keywords: exoplanets; super earths; exoplanet systems; planetary system formation; mini neptunes
Heavy-ion Acceleration in 3He-rich Solar Energetic Particle Events: New Insights from Solar Orbiter

We present Solar Orbiter energetic particle observations of two 3He-rich events with features more clearly observed than in prior studies. The event of 2022 November 9 observed from 0.59 au contained hundreds of ultraheavy (UH; mass >78 amu) ions whereas previous observations at 1 au have shown only an occasional count or two. The event of 2023 April 8 observed from 0.29 au fortuitously had very low ambient activity, making it possible to observe spectra from the 3He acceleration mechanism without contamination, revealing extremely low H and 4He intensities arriving simultaneously with other ions observed in typical 3He-rich events. Taken together with previous studies, we believe these data show that 3He-rich events have a single acceleration mechanism that is responsible for the unique abundance features of 3He, heavy ions, and UH ions. Considering the acceleration model of Roth & Temerin that heats the ions over a broad range of gyrofrequencies away from those damped by H and 4He, we calculate reasonable fits to the observed abundances O-Fe. A key result is that high values of, e.g., Fe/O typical of such events is not due to preferential Fe heating, but on the contrary is due mainly to the depletion of O, which at elevated temperatures has a charge-to-mass ratio in the region of the waves damped by 4He. The model also naturally incorporates features of high-ionization states and neutron-rich isotope enhancements that have been long-standing puzzles in observations of this type of flare.

Keywords: solar flares; solar energetic particles; solar particle emission; solar abundances; solar magnetic fields; solar magnetic reconnection
Knowledge Inventory of Foundational Data Products in Planetary Science

Some of the key components of any Planetary Spatial Data Infrastructure (PDSI) are the data products that end-users wish to discover, access, and interrogate. One precursor to the implementation of a PSDI is a knowledge inventory that catalogs what products are available, from which data producers, and at what initially understood data qualities. We present a knowledge inventory of foundational PSDI data products: geodetic coordinate reference frames, elevation or topography, and orthoimages or orthomosaics. Additionally, we catalog the available gravity models that serve as critical data for the assessment of spatial location, spatial accuracy, and ultimately spatial efficacy. We strengthen our previously published definitions of foundational data products to assist in solidifying a common vocabulary that will improve communication about these essential data products.

Keywords: planetary science; photogrammetry
Where are the Water Worlds?: Self-consistent Models of Water-rich Exoplanet Atmospheres

It remains to be ascertained whether sub-Neptune exoplanets primarily possess hydrogen-rich atmospheres or whether a population of H2O-rich water worlds lurks in their midst. Addressing this question requires improved modeling of water-rich exoplanetary atmospheres, both to predict and interpret spectroscopic observations and to serve as upper boundary conditions on interior structure calculations. Here, we present new models of hydrogen-helium-water atmospheres with water abundances ranging from solar to 100% water vapor. We improve upon previous models of high-water-content atmospheres by incorporating updated prescriptions for water self-broadening and a nonideal gas equation of state. Our model grid (https://umd.box.com/v/water-worlds) includes temperature-pressure profiles in radiative-convective equilibrium, along with their associated transmission and thermal emission spectra. We find that our model updates primarily act at high pressures, significantly impacting bottom-of-atmosphere temperatures, with implications for the accuracy of interior structure calculations. Upper-atmosphere conditions and spectroscopic observables are less impacted by our model updates, and we find that, under most conditions, retrieval codes built for hot Jupiters should also perform well on water-rich planets. We additionally quantify the observational degeneracies among both thermal emission and transmission spectra. We recover standard degeneracies with clouds and mean molecular weight for transmission spectra, and we find thermal emission spectra to be more readily distinguishable from one another in the water-poor (i.e., near-solar) regime.

Keywords: exoplanet atmospheres; exoplanet astronomy; exoplanets; mini neptunes; radiative transfer
Limiting Spectral Resolution of a Reflection Grating Made via Electron-beam Lithography

Gratings enable dispersive spectroscopy from the X-ray to the optical, and feature prominently in proposed flagships and SmallSats alike. The exacting performance requirements of these future missions necessitate assessing whether the present state-of-the-art in grating manufacture will limit spectrometer performance. In this work, we manufacture a 1.5 mm thick, 1000 nm period (1000 gr mm-1) flat grating using electron-beam lithography (EBL), a promising lithographic technique for patterning gratings for future astronomical observatories. We assess the limiting spectral resolution of this grating by interferometrically measuring the diffracted wavefronts produced in ± first order. Our measurements show this grating has a performance of at least R ∼ 14,600, and that our assessment is bounded by the error of our interferometric measurement. The impact of EBL stitching error on grating performance is quantified, and a path to measuring the period error of customized, curved gratings is presented.

Keywords: spectrometers; astronomical instrumentation; astronomical optics
Relativistic Magnetic Explosions

Many explosive astrophysical events, like magnetars' bursts and flares, are magnetically driven. We consider dynamics of such magnetic explosions-relativistic expansion of highly magnetized and highly magnetically overpressurized clouds. The corresponding dynamics are qualitatively different from fluid explosions due to the topological constraint of the conservation of the magnetic flux. Using analytical, relativistic MHD as well as force-free calculations, we find that the creation of a relativistically expanding, causally disconnected flow obeys a threshold condition: it requires sufficiently high initial overpressure and a sufficiently quick decrease of the pressure in the external medium (the preexplosion wind). In the subcritical case the magnetic cloud just "puffs up" and quietly expands with the preflare wind. We also find a compact analytical solution to Prendergast's problem-expansion of force-free plasma into a vacuum.

Keywords: magnetars; soft gamma-ray repeaters; relativistic fluid dynamics
X-Ray and Radio Observations of Central Black Holes in Nearby Low-mass Early-type Galaxies: Preliminary Evidence for Low Eddington Fractions

We present new radio and X-ray observations of two nearby (<4 Mpc) low-mass early-type galaxies with dynamically confirmed central black holes: NGC 5102 and NGC 205. NGC 5102 shows a weak nuclear X-ray source and has no core radio emission. However, for the first time we demonstrate that it shows luminous extended radio continuum emission in low-resolution, low-frequency (<3 GHz) data, consistent with jet lobes on scales ≳100 pc formed from past accretion and jet activity. By contrast, in new, extremely deep, strictly simultaneous Very Large Array and Chandra observations, no radio or X-ray emission is detected from the black hole in NGC 205. We consider these measurements and upper limits in the context of the few other low-mass early-type galaxies with dynamically confirmed black holes, and show that the mean ratio of bolometric to Eddington luminosity in this sample is only $\mathrm{log}\,({L}_{\mathrm{bol}}/{L}_{\mathrm{Edd}})=-6.57\pm 0.50$ . These Eddington ratios are lower than typical in a comparison sample of more massive early-type galaxies, though this conclusion is quite tentative due to our small sample of low-mass galaxies and potential biases in the comparison sample. This preliminary result is in mild tension with previous work using less sensitive observations of more distant galaxies, which predict higher X-ray luminosities than we observe for low-mass galaxies. If it is confirmed that central black holes in low-mass galaxies typically have low Eddington ratios, this presents a challenge to measuring the occupation fraction of central black holes with standard optical emission line, X-ray, or radio surveys.

Keywords: early-type galaxies; radio active galactic nuclei; x-ray active galactic nuclei
Enhanced Hydrogen Escape on Mars during the 2018 Global Dust Storm: Impact of Horizontal Wind Field

Mars has undergone a substantial water loss, transforming from the early warm and wet state to the current cold and arid state. Observations and modeling efforts suggest that hydrogen escape is a metric of water loss on Mars. As a consequence of the vertical transport of water vapor by deep convection, hydrogen escape is significantly enhanced during Martian global dust storms. Motivated by the established scenario that the horizontal wind field could substantially enhance thermal escape, here we evaluate, for the first time, how the escape of H and H2 on Mars during a typical global dust storm is modified by the enhanced horizontal wind field during the period. By combining kinetic model calculations and the Mars Climate Database outputs, we reach the conclusion that a nonnegligible enhancement of the H and H2 escape flux could be driven by horizontal winds near the exobase, reaching 15% for H and 60% for H2 at dawn near the equator during the dust storm. Although the enhancement of the global hydrogen escape rate by the horizontal wind is insignificant, it plays a crucial role in the redistribution of H and H2 escape flux. The results presented here make useful contributions to a thorough understanding of enhanced hydrogen escape during the global dust storms.

Keywords: mars; upper atmosphere; exosphere; planetary atmospheres; solar system planets
Orbital Evolution of Close-in Super-Earths Driven by Atmospheric Escape

The increasing number of super-Earths close to their host stars have revealed a scarcity of close-in small planets with 1.5-2.0 R ⊕ in the radius distribution of Kepler planets. The atmospheric escape of super-Earths by photoevaporation can explain the origin of the observed "radius gap." Many theoretical studies have considered the in situ mass loss of a close-in planet. Planets that undergo atmospheric escape, however, move outward due to the change in the orbital angular momentum of their star-planet systems. In this study, we calculate the orbital evolution of an evaporating super-Earth with a H2/He atmosphere around FGKM-type stars under stellar X-ray and extreme-UV irradiation (XUV). The rate of increase in the orbital radius of an evaporating planet is approximately proportional to that of the atmospheric mass loss during a high stellar XUV phase. We show that super-Earths with a rocky core of ≲10 M ⊕ and a H2/He atmosphere at ≲0.03-0.1 au (≲0.01-0.03 au) around G-type stars (M-type stars) are prone to outward migration driven by photoevaporation. Although the changes in the orbits of the planets would be small, they would rearrange the orbital configurations of compact, multiplanet systems, such as the TRAPPIST-1 system. We also find that the radius gap and the so-called "Neptune desert" in the observed population of close-in planets around FGK-type stars still appear in our simulations. On the other hand, the observed planet population around M-type stars can be reproduced only by a high stellar XUV luminosity model.

Keywords: exoplanets; exoplanet evolution; exoplanet formation; exoplanet atmospheres; super earths
The Energy Conversion Rate of an Active Region Transient Brightening Estimated by Hinode Spectroscopic Observations

We statistically estimate the conversion rate of the energy released during an active region transient brightening to Doppler motion and thermal and nonthermal energies. We used two types of data sets for the energy estimation and detection of transient brightenings. One includes spectroscopic images of Fe XIV, Fe XV, and Fe XVI lines observed by the Hinode/EUV Imaging Spectrometer. The other includes images obtained from the 211 Å channel of the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA). The observed active region was NOAA 11890 on 2013 November 9 and 10. As a result, the released Doppler motion and nonthermal energies were found to be approximately 0.1%-1% and 10%-100% of the change in the amount of thermal energy in each enhancement, respectively. Using this conversion rate, we estimated the contribution of the total energy flux of AIA transient brightenings to the active region heating to be at most 2% of the conduction and radiative losses.

Keywords: active sun; solar physics; the sun; solar flare spectra; solar flares; solar active region velocity fields; solar active regions; spectroscopy
Conditions for Chromospheric Plasma Acceleration or Trigger of Chromospheric Mass Ejections by Magnetic-field-aligned Electric Fields

Backward-propagating or reverse fluctuations in Alfvénic turbulence were recently found to produce magnetic-field-aligned (MFA) electric fields that can easily transfer their energy to the plasma, either in the form of heat (or electron beams that quickly dissipate their energy as heat) if electrons absorb most of the MFA energy, or in the form of translational motion of the plasma if the ions absorb most of the MFA energy. Conditions for the direct proton acceleration (jet formation) in the quiet chromosphere included a temperature ≤104 K and a magnetic field between about 10 and 100 G, conditions very similar to those under which chromospheric plasma jets or dynamic jet-like spicules are observed with the Interface Region Imaging Spectrograph. Here the conditions for direct ion acceleration by MFA electric fields are determined for a much broader range of electron densities and plasma temperatures, to include both quiet and flaring conditions of the chromospheric plasma. For the higher chromospheric electron densities of solar flaring conditions, direct ion and therefore plasma acceleration by MFA electric fields is found to be possible in the much stronger (kG) magnetic fields of active regions, provided the plasma temperature remains less than about 105 K. Under flaring conditions, the MFA electric fields may cause the acceleration or at least trigger the upward motion of dense (>1012-1013 cm-3) chromospheric plasma. It is also suggested that chromospheric nonresonant MFA acceleration, by producing local electron beams, may eliminate the need for electron beams to propagate from the flaring corona down to the denser chromosphere.

Keywords: solar coronal mass ejections; solar chromosphere; solar flares; solar physics; solar transition region; alfven waves; plasma astrophysics; magnetic fields
GRB 221009A: An Ordinary Nearby GRB with Extraordinary Observational Properties

The gamma-ray burst GRB 221009A, known as the "brightest of all time," is the closest energetic burst detected so far, with an energy of E γ,iso ~ 1055 erg. This study aims to assess its compatibility with known GRB energy and luminosity distributions. Our analysis indicates that the energy/luminosity function of GRBs is consistent across various redshift intervals, and that the inclusion of GRB 221009A does not significantly impact the function at low redshifts. Additionally, our evaluation of the best-fitting result of the entire GRB sample suggests that the expected number of GRBs with energy greater than 1055 erg at a low redshift is 0.2, so that the emergence of GRB 221009A is consistent with expected energy/luminosity functions within ~2σ Poisson fluctuation error, still adhering to the principles of small number statistics. Furthermore, we find that GRB 221009A and other energetic bursts, defined as E γ,iso ≳ 1054 erg, exhibit no significant differences in terms of distributions of T 90, minimum timescale, Amati relation, E γ,iso-E X,iso relation, L γ,iso-Γ0 relation, E γ,iso-Γ0 relation, L γ,iso-E p,i-Γ0 relation, and host galaxy properties, compared to normal long GRBs. This suggests that energetic GRBs (including GRB 221009A) and other long GRBs likely have similar progenitor systems and undergo similar energy dissipation and radiation processes. The generation of energetic GRBs may be due to more extreme central engine properties or, more likely, a rarer viewing configuration of a quasi-universal structured jet.

Keywords: gamma-ray bursts
JWST Sneaks a Peek at the Stellar Morphology of z 2 Submillimeter Galaxies: Bulge Formation at Cosmic Noon

We report morphological analyses of seven submillimeter galaxies (SMGs) at z ~ 2 using the James Webb Space Telescope NIRCam images taken as part of the public CEERS and PRIMER surveys. Through two-dimensional surface brightness profile fitting we find evidence of compact reddened stellar structures in all the SMGs, in particular in the F444W filter, suggesting an ubiquitous presence of stellar bulges. The median size of these bulges at F444W with a bootstrapped uncertainty is found to be 0.7 ± 1.0 kpc (0.6-0.7-3.9 kpc for 14th-50th-86th percentiles) and the median Sérsic index is 0.7 ± 0.9 (0.4-0.7-2.8 for 14th-50th-86th percentiles). Structures akin to spiral arms and bars are also identified, and their asymmetric shapes, tidal features, as well as evidence of nearby galaxies at consistent redshifts as those of corresponding SMGs suggest that these SMGs are undergoing dynamical interactions, likely responsible for the triggering of their star-forming activity. Via a curve-of-growth analysis we deduce half-light radii for the NIRCam wave bands, finding that sizes are significantly smaller at longer wavelengths in all cases, in particular that the median size ratio between F444W and F150W is 0.6 ± 0.1. However, we also find that F444W sizes, roughly corresponding to rest-frame H band, are not smaller than those of submillimeter continuum as measured by the Atacama Large Millimeter/submillimeter Array, contradicting certain recent predictions from theoretical models. Our results suggest that while stellar bulges are undergoing an active formation phase in SMGs at z ~ 2, the total stellar masses of SMGs are still dominated by their disks, not bulges.

Keywords: high-redshift galaxies; galaxy structure; ultraluminous infrared galaxies; galaxy interactions; galaxy formation
Needle in a Haystack: Finding Supermassive Black Hole-related Flares in the Zwicky Transient Facility Public Survey

Transient accretion events onto supermassive black holes (SMBHs), such as tidal disruption events (TDEs), Bowen Fluorescence Flares (BFFs), and active galactic nuclei (AGNs), which are accompanied by sudden increases of activity, offer a new window onto the SMBH population, accretion physics, and stellar dynamics in galaxy centers. However, such transients are rare and finding them in wide-field transient surveys is challenging. Here we present the results of a systematic real-time search for SMBH-related transients in Zwicky Transient Facility (ZTF) public alerts, using various search queries. We examined 345 rising events coincident with a galaxy nucleus, with no history of previous activity, of which 223 were spectroscopically classified. Of those, five (2.2%) were TDEs, one (0.5%) was a BFF, and two (0.9%) were AGN flares. Limiting the search to blue events, the fraction of TDEs nearly doubles to 4.1%, and no TDEs are missed. Limiting the search further to candidate post-starburst galaxies increases the relative number of TDEs to 16.7%, but the absolute numbers in such a search are small. The main contamination source is supernovae (95.1% of classified events), of which the majority (82.2% of supernovae) are of Type Ia. In a comparison set of 39 events with limited photometric history, the AGN contamination increases to ~30%. Host galaxy offset is not a significant discriminant of TDEs in current ZTF data, but might be useful in higher-resolution data. Our results can be used to quantify the efficiency of various SMBH-related transient search strategies in optical surveys such as ZTF and the Legacy Survey of Space and Time.

Keywords: supernovae; tidal disruption; supermassive black holes; active galactic nuclei; astronomical methods