adsabs/SciX_UAT_keywords huggingface dataset:
Uranus Orbiter and Probe: A Radio Science Investigation to Determine the Planet's Gravity Field, Depth of the Winds, and Tidal Deformations

The most recent Planetary Science and Astrobiology Decadal Survey has proposed Uranus as the target for NASA's next large-scale mission. The interior structure and atmosphere of the planet are currently poorly understood, and objectives for investigating Uranus's deeper regions and composition are highly ranked. Traditionally, gravity science has served as one of the primary means for probing the depths of planetary bodies and inferring their internal density distributions. In this work, we present precise numerical simulations of an onboard radio science experiment designed to determine Uranus's gravity field and tidal deformations, which would offer a rare view into the planet's interior. We focus on the mission's orbital planning, discussing crucial parameters such as the number of pericenter passes, orbital inclination, and periapsis altitude necessary to meet the gravity measurement requirements for a Uranus orbiter. Our findings suggest that eight close encounters may be sufficient to determine the zonal gravity field up to J 8 with a relative accuracy of 10%, if the trajectory is optimized. This would allow for the decoupling of the gravity field components due to interior structure and zonal winds. Additionally, we find that the expected end-of-mission uncertainty on Uranus's Love number k 22 is of order ∼0.01 (3σ). This level of accuracy may offer crucial information about Uranus's inner state and allow for discriminating between a liquid and solid core, thus shedding light on crucial aspects of the planet's formation and evolution.

Keywords: uranus; gravitational fields; tides; orbiters; space probes; atmospheric dynamics
Search for Optically Dark Infrared Galaxies without Counterparts of Subaru Hyper Suprime-Cam in the AKARI North Ecliptic Pole Wide Survey Field

We present the physical properties of AKARI sources without optical counterparts in optical images from the Hyper Suprime-Cam (HSC) on the Subaru telescope. Using the AKARI infrared (IR) source catalog and HSC optical catalog, we select 583 objects that do not have HSC counterparts in the AKARI North Ecliptic Pole wide survey field (∼5 deg2). Because the HSC limiting magnitude is deep (gAB ∼ 28.6), these are good candidates for extremely red star-forming galaxies (SFGs) and/or active galactic nuclei (AGNs), possibly at high redshifts. We compile multiwavelength data out to 500 μm and use them for fitting the spectral energy distribution with CIGALE to investigate the physical properties of AKARI galaxies without optical counterparts. We also compare their physical quantities with AKARI mid-IR selected galaxies with HSC counterparts. The estimated redshifts of AKARI objects without HSC counterparts range up to z ∼ 4, significantly higher than for AKARI objects with HSC counterparts. We find that (i) 3.6 - 4.5 μm color, (ii) AGN luminosity, (iii) stellar mass, (iv) star formation rate, and (v) V-band dust attenuation in the interstellar medium of AKARI objects without HSC counterparts are systematically larger than those of AKARI objects with counterparts. These results suggest that our sample includes luminous, heavily dust-obscured SFGs/AGNs at z ∼ 1-4 that are missed by previous optical surveys, providing very interesting targets for the coming era of the James Webb Space Telescope.

Keywords: active galactic nuclei; infrared galaxies; infrared photometry; bayesian statistics
Effects of Magnetic Perturbation on Reconnection and Heating in the Solar Corona

The solar corona exhibits unusually high temperatures (∼106 K) compared to the photosphere (∼5800 K). This coronal heating is one of the fundamental problems in solar physics that has yet to be resolved. Magnetic reconnection is thought to play a critical role in driving this enigmatic heating process. We address the interplay between reconnection in the solar corona and the photospheric footpoint motion. The effect of the latter is modeled to generate an external magnetic perturbation that is added to the main coronal field. Resistive magnetohydrodynamics is used where sources and sinks terms due to the perturbation are explicitly obtained in the equations. We set the perturbation to be sinusoidal in space while remaining time independent. The equations are solved using openFOAM. Our results show that magnetic reconnection with perturbation, even with a very small amplitude, leads to (1) more complex formation and evolution of X-points and plasmoids, (2) a transition from slow to fast reconnection rate, (3) a stronger increase of the temperature, and (4) a quicker formation of high-speed jets driving the hot plasma outside the simulation domain with a Mach number that is six times greater compared to the case without perturbation. Moreover, we also find that a magnetic perturbation with shorter wavelength promotes even a faster temporal evolution of the reconnection process than for the longer wavelength. Therefore, the heating and the dynamics of plasma particles in the solar corona are significantly enhanced when the reconnection process is externally disturbed by even a very small perturbation.

Keywords: solar magnetic reconnection; solar coronal heating; magnetohydrodynamics
Radio Evolution of a Type IIb Supernova SN 2016gkg

We present extensive radio monitoring of a Type IIb supernova (SN IIb), SN 2016gkg during t ~ 8-1429 days postexplosion at frequencies ν ~ 0.33-25 GHz. The detailed radio light curves and spectra are broadly consistent with self-absorbed synchrotron emission due to the interaction of the SN shock with the circumstellar medium. The model underpredicts the flux densities at t ~ 299 days postexplosion by a factor of 2, possibly indicating a density enhancement in the circumstellar medium due to a nonuniform mass loss from the progenitor. Assuming a wind velocity v w ~ 200 km s-1, we estimate the mass-loss rate to be $\dot{M}\sim $ (2.2, 3.6, 3.8, 12.6, 3.7, and 5.0) ×10-6 M ⊙ yr-1 during ~8, 15, 25, 48, 87, and 115 yr, respectively, before the explosion. The shock wave from SN 2016gkg is expanding from R ~ 0.5 × 1016 to 7 × 1016 cm during t ~ 24-492 days postexplosion indicating a shock deceleration index, m ~ 0.8 (R ∝ t m ), and mean shock velocity v ~ 0.1c. The radio data are inconsistent with a free-free absorption model and higher shock velocities are in support of a relatively compact progenitor for SN 2016gkg.

Keywords: supernovae; circumstellar matter; radio continuum emission
The Search for Binary Supermassive Black Holes among Quasars with Offset Broad Lines Using the Very Long Baseline Array

In several previous studies, quasars exhibiting broad emission lines with ≳1000 km s-1 velocity offsets with respect to the host galaxy rest frame have been discovered. One leading hypothesis for the origin of these velocity-offset broad lines is the dynamics of a binary supermassive black hole (SMBH). We present high-resolution radio imaging of 34 quasars showing these velocity-offset broad lines with the Very Long Baseline Array (VLBA), aiming to find evidence for the putative binary SMBHs (such as dual radio cores), and testing the competing physical models. We detect exactly half of the target sample from our VLBA imaging, after implementing a 5σ detection limit. While we do not resolve double radio sources in any of the targets, we obtain limits on the instantaneous projected separations of a radio-emitting binary for all of the detected sources under the assumption that a binary still exists within our VLBA angular resolution limits. We also assess the likelihood that a radio-emitting companion SMBH exists outside of our angular resolution limits, but its radio luminosity is too weak to produce a detectable signal in the VLBA data. Additionally, we compare the precise sky positions afforded by these data to optical positions from both the SDSS and Gaia DR2 source catalogs. We find projected radio/optical separations on the order of ~10 pc for three quasars. Finally, we explore how future multi-wavelength campaigns with optical, radio, and X-ray observatories can help discriminate further between the competing physical models.

Keywords: active galactic nuclei; active galaxies; radio active galactic nuclei; radio cores; supermassive black holes
Chandra High Energy Transmission Gratings Spectra of V3890 Sgr

The recurrent nova (RN) V3890 Sgr was observed during the seventh day after the onset of its most recent outburst, with the Chandra ACIS-S camera and High Energy Transmission Gratings. A rich emission line spectrum was detected, due to transitions of Fe-L and K-shell ions ranging from neon to iron. The measured absorbed flux is ≈10-10 erg cm-2 s-1 in the 1.4-15 Šrange (0.77-8.86 keV). The line profiles are asymmetric, blueshifted, and skewed toward the blue side, as if the ejecta moving toward us are less absorbed than the receding ejecta. The full width at half-maximum of most emission lines is 1000-1200 km s-1, with some extended blue wings. The spectrum is thermal and consistent with a plasma in collisional ionization equilibrium with column density 1.3 × 1022 cm-2 and at least two components at temperatures of about 1 and 4 keV, possibly a forward and a reverse shock, or regions with differently mixed ejecta and a red giant wind. The spectrum is remarkably similar to the symbiotic RNe V745 Sco and RS Oph, but we cannot distinguish whether the shocks occurred at a distance of a few au from the red giant, or near the giant's photosphere, in a high-density medium containing only a low mass. The ratios of the flux in lines of aluminum, magnesium, and neon relative to the flux in lines of silicon and iron probably indicate a carbon-oxygen white dwarf.

Keywords: novae; recurrent novae; cataclysmic variable stars; x-ray astronomy; atomic spectroscopy; high resolution spectroscopy
Physical Constraints on Motility with Applications to Possible Life on Mars and Enceladus

Motility is a ubiquitous feature of microbial life on Earth, and is widely regarded as a promising biosignature candidate. In the search for motile organisms, it is therefore valuable to have rough estimates for the number of such microbes that one may expect to find in a given area or volume. In this work, we explore this question by employing a simple theoretical model that takes into account the amount of free energy available in a given environment and the energetic cost of motility. We present heuristic upper bounds for the average biomass density and the number density of motile lifeforms for the Martian subsurface and the ocean of Enceladus by presuming that the motile microbes in question derive their energy from methanogenesis. We consequently demonstrate that the resultant densities of motile organisms might be potentially comparable to, or much lower than, the total microbial densities documented in various extreme environments on Earth.

Keywords: astrobiology; xenobiology; biosignatures; mars; saturnian satellites; galilean satellites; ocean planets
Breaking Resonant Chains: Destabilization of Resonant Planets Due to Long-term Mass Evolution

Recent exoplanet observations reported a large number of multiple-planet systems, in which some of the planets are in a chain of resonances. The fraction of resonant systems to non-resonant systems provides clues about their formation history. We investigated the orbital stability of planets in resonant chains by considering the long-term evolution of planetary mass and stellar mass and using orbital calculations. We found that while resonant chains were stable, they can be destabilized by a change of ∼10% in planetary mass. Such a mass evolution can occur by atmospheric escape due to photoevaporation. We also found that resonant chains can be broken by a stellar mass loss of ≲1%, which would be explained by stellar winds or coronal mass ejections. The long-term mass change of planets and stars plays an important role in the orbital evolutions of planetary systems, including super-Earths.

Keywords: exoplanet dynamics; exoplanet formation; exoplanet evolution
Are Large Sunspots Dominant in Naked-eye Sunspot Observations for 1819-1918?

This article explores the sizes of sunspots as determined by naked-eye sunspot observations (NSOs). The international sunspot number (ISN), the group sunspot number, and the Greenwich photo-heliographic results (GPR) were utilized. According to the ISN results, 64% of NSOs from 1819 to 1918 have been identified as large sunspots. We found that the sunspot sizes had been considerably underestimated using the ISN data (compared to using the GPR data). About 40% of NSOs from 1819 to 1918 have been identified as giant sunspots, which have ranks of sunspot areas smaller than 5%. The results in this article indicate that the majority of NSOs are large sunspots. This calls into question the previous understanding that NSOs include sunspots of all sizes above the visibility limit.

Keywords: sunspots; sunspot cycle; sunspot number; maunder minimum
OGLE-2013-BLG-0911Lb: A Secondary on the Brown-dwarf Planet Boundary around an M Dwarf

We present the analysis of the binary-lens microlensing event OGLE-2013-BLG-0911. The best-fit solutions indicate the binary mass ratio of q ≃ 0.03, which differs from that reported in Shvartzvald et al. The event suffers from the well-known close/wide degeneracy, resulting in two groups of solutions for the projected separation normalized by the Einstein radius of s ∼ 0.15 or s ∼ 7. The finite source and the parallax observations allow us to measure the lens physical parameters. The lens system is an M dwarf orbited by a massive Jupiter companion at very close ( ${M}_{\mathrm{host}}={0.30}_{-0.06}^{+0.08}{M}_{\odot }$ , ${M}_{\mathrm{comp}}={10.1}_{-2.2}^{+2.9}{M}_{\mathrm{Jup}}$ , ${a}_{\exp }={0.40}_{-0.04}^{+0.05}\,\mathrm{au}$ ) or wide ( ${M}_{\mathrm{host}}={0.28}_{-0.08}^{+0.10}{M}_{\odot }$ , ${M}_{\mathrm{comp}}={9.9}_{-3.5}^{+3.8}{M}_{\mathrm{Jup}}$ , ${a}_{\exp }={18.0}_{-3.2}^{+3.2}\,\mathrm{au}$ ) separation. Although the mass ratio is slightly above the planet-brown dwarf (BD) mass-ratio boundary of q = 0.03, which is generally used, the median physical mass of the companion is slightly below the planet-BD mass boundary of 13MJup. It is likely that the formation mechanisms for BDs and planets are different and the objects near the boundaries could have been formed by either mechanism. It is important to probe the distribution of such companions with masses of ∼13MJup in order to statistically constrain the formation theories for both BDs and massive planets. In particular, the microlensing method is able to probe the distribution around low-mass M dwarfs and even BDs, which is challenging for other exoplanet detection methods.

Keywords: gravitational microlensing; exoplanet astronomy; brown dwarfs; exoplanet systems; exoplanets; extrasolar gaseous giant planets; exoplanet detection methods; m dwarf stars
Formation of Gaps in Self-gravitating Debris Disks by Secular Resonance in a Single-planet System. II. Toward a Self-consistent Model

High-resolution observations of several debris disks reveal structures such as gaps and spirals, suggestive of gravitational perturbations induced by underlying planets. Most existing studies of planet-debris disk interactions ignore the gravity of the disk, treating it as a reservoir of massless planetesimals. In this paper, we continue our investigation into the long-term interaction between a single eccentric planet and an external, massive debris disk. Building upon our previous work, here we consider not only the axisymmetric component of the disk's gravitational potential, but also the nonaxisymmetric torque that the disk exerts on the planet (ignoring for now only the nonaxisymmetric component of the disk self-gravity). To this goal, we develop and test a semianalytic "N-ring" framework that is based on a generalized (softened) version of the classical Laplace-Lagrange secular theory. Using this tool, we demonstrate that even when the disk is less massive than the planet, not only can a secular resonance be established within the disk that leads to the formation of a wide gap, but that the very same resonance also damps the planetary eccentricity e p via a process known as resonant friction. The resulting gap is initially nonaxisymmetric (akin to those observed in HD 92945 and HD 206893), but evolves to become more axisymmetric (similar to that in HD 107146) as e p (t) → 0 with time. We also develop analytic understanding of these findings, finding good quantitative agreement with the outcomes of the N-ring calculations. Our results may be used to infer both the dynamical masses of (gapped) debris disks and the dynamical history of the planets interior to them, as we exemplify for HD 206893.

Keywords: exoplanet dynamics; circumstellar disks; debris disks; planetary dynamics; astrodynamics; celestial mechanics; planetary system evolution; dynamical evolution
Mapping Stellar Surfaces. II. An Interpretable Gaussian Process Model for Light Curves

The use of Gaussian processes (GPs) as models for astronomical time series data sets has recently become almost ubiquitous, given their ease of use and flexibility. In particular, GPs excel at marginalization over the stellar signal when the variability due to starspots is treated as a nuisance, as in exoplanet transit modeling. However, these effective models are less useful in cases where the starspot signal is of primary interest, since it is not obvious how the parameters of the GP relate to physical parameters like the spot size, contrast, and latitudinal distribution. Instead, it is common practice to explicitly model the effect of individual starspots on the light curve and attempt to infer their properties via optimization or posterior inference. Unfortunately, this process is ill-posed and often computationally intractable when applied to stars with more than a few spots and/or to ensembles of many stars. Here we derive a closed-form expression for a GP that describes the light curve of a rotating, evolving stellar surface conditioned on a given distribution of starspot sizes, contrasts, and latitudes. We demonstrate that this model is correctly calibrated, allowing one to robustly infer physical parameters of interest from one or more light curves, including the typical spot radii and latitudes. Our GP has far-ranging implications for understanding the variability and magnetic activity of stars from light curves and radial velocity measurements, as well as for modeling correlated noise in exoplanet searches. Our implementation is efficient, user-friendly, and open-source, available in the package starry_process.

Keywords: analytical mathematics; time series analysis; gaussian processes regression; starspots
The Effect of Inefficient Accretion on Planetary Differentiation

Pairwise collisions between terrestrial embryos are the dominant means of accretion during the last stage of planet formation. Hence, their realistic treatment in N-body studies is critical to accurately model the formation of terrestrial planets and to develop interpretations of telescopic and spacecraft observations. In this work, we compare the effects of two collision prescriptions on the core-mantle differentiation of terrestrial planets: a model in which collisions are always completely accretionary ("perfect merging"), and a more realistic model based on neural networks that has been trained on hydrodynamical simulations of giant impacts. The latter model is able to predict the loss of mass due to imperfect accretion and the evolution of nonaccreted projectiles in hit-and-run collisions. We find that the results of the neural network model feature a wider range of final core mass fractions and metal-silicate equilibration pressures, temperatures, and oxygen fugacities than the assumption of perfect merging. When used to model collisions in N-body studies of terrestrial planet formation, the two models provide similar answers for planets more massive than ≈0.1 M⊕ (Earth masses). For less massive final bodies, however, the inefficient-accretion model predicts a higher degree of compositional diversity. This phenomenon is not reflected in planet formation models of the solar system that use perfect merging to determine collisional outcomes. Our findings confirm the role of giant impacts as important drivers of planetary diversity and encourage a realistic implementation of inefficient accretion in future accretion studies.

Keywords: planetary system formation; solar system terrestrial planets; planetary interior
Multiwavelength Polarization Observations of Mrk 501

Mrk 501 is a prototypical high-synchrotron-peaked blazar and serves as one of the primary targets for the Imaging X-ray Polarimetry Explorer (IXPE). In this study, we report X-ray polarization measurements of Mrk 501 based on six IXPE observations. The detection of X-ray polarization at a confidence level exceeding 99% is achieved in four out of the six observations conducted across the entire energy range (2–8 keV) of IXPE. The maximum polarization degree (ΠX) is measured to be 15.8% ± 2.8%, accompanied by a polarization angle (ψ X) of 98.°0 ± 5.°1 at a confidence level of 5.6σ. During the remaining two observations, only an upper limit of ΠX < 12% could be derived at the 99% confidence level. No temporal variability in polarization is observed throughout all six IXPE observations for Mrk 501. A discernible trend of energy-dependent variation in the polarization degree is detected in optical spectropolarimetry; however, no analogous indication is observed in ΠX. The chromatic behavior of Π and the consistent values of ψ across different frequencies from X-ray to radio bands, along with the agreement between ψ and jet position angle, strongly support the interpretation of the energy-stratified model with shock-accelerated particles in the jet of Mrk 501. Additionally, the possibility of the presence of a global helical magnetic field in the jet of Mrk 501 is discussed.

Keywords: relativistic jets; x-ray active galactic nuclei; active galactic nuclei; blazars; spectropolarimetry
X-Ray Redshifts of Obscured Chandra Source Catalog Active Galactic Nuclei

We have computed obscured active galactic nuclei (AGN) redshifts using the XZ method, adopting a broad treatment in which we employed a wide-ranging data set and worked primarily at the XZ counts sensitivity threshold, culminating with a redshift catalog containing 121 sources that lack documented redshifts. We considered 363 obscured AGN from the Chandra Source Catalog Release 2.0, 59 of which were selected using multiwavelength criteria while 304 were X-ray selected. One third of the data set had crossmatched spectroscopic or photometric redshifts. These sources, dominated by low-z and low-N H AGN, were supplemented by 1000 simulations to form a data set for testing the XZ method. We used a multilayer perceptron neural network to examine and predict cases in which XZ fails to reproduce the known redshift, yielding a classifier that can identify and discard poor redshift estimates. This classifier demonstrated a statistically significant ~3σ improvement over the existing XZ redshift information gain filter. We applied the machine-learning model to sources with no documented redshifts, resulting in the 121 source new redshift catalog, all of which were X-ray selected. Our neural network's performance suggests that nearly 90% of these redshift estimates are consistent with hypothetical spectroscopic or photometric measurements, strengthening the notion that redshifts can be reliably estimated using only X-rays, which is valuable to current and future missions such as Athena. We have also identified a possible Compton-thick candidate that warrants further investigation.

Keywords: active galactic nuclei; x-ray active galactic nuclei; redshift surveys; x-ray astronomy; x-ray sources