adsabs/SciX_UAT_keywords huggingface dataset:
Can Stochastic Resonance Explain Recurrence of Grand Minima?

The amplitude of the 11 yr solar cycle is well known to be subject to long-term modulation, including sustained periods of very low activity known as Grand Minima. Stable long-period cycles found in proxies of solar activity have given new momentum to the debate about a possible influence of the tiny planetary tidal forcing. Here, we study the solar cycle by means of a simple zero-dimensional dynamo model, which includes a delay caused by meridional circulation as well as a quenching of the α-effect at toroidal magnetic fields exceeding an upper threshold. Fitting this model to the sunspot record, we find a set of parameters close to the bifurcation point at which two stable oscillatory modes emerge. One mode is a limit cycle resembling normal solar activity including a characteristic kink in the decaying limb of the cycle. The other mode is a weak sub-threshold cycle that could be interpreted as Grand Minimum activity. Adding noise to the model, we show that it exhibits Stochastic Resonance, which means that a weak external modulation can toss the dynamo back and forth between these two modes, whereby the periodicities of the modulation get strongly amplified.

Keywords: solar dynamo; solar cycle
Forced Measurement of Astronomical Sources at Low Signal-to-noise

We propose a modified moment matching algorithm to avoid catastrophic failures for sources with a low signal to noise ratio. The proposed modifications include a method to eliminate nonphysical negative pixel values and a forced single iteration with an initial guess derived from coadd measurements when iterative methods are unstable. We correct for all biases in measurements introduced by the method. We find that the proposed modifications allow the algorithm to avoid catastrophic failures in nearly 100% of the cases, especially at low SNR. Additionally, with a reasonable guess from coadd measurements, the algorithm measures the flux, centroid, size, shape, and ellipticity with a bias statistically consistent with zero. We show that the proposed method allows us to measure sources 7 times fainter than traditional methods when applied to images obtained from WIYN-ODI. We also present a scheme to find uncertainties in measurements when using the new method to measure astronomical sources.

Keywords: algorithms; astronomical methods; interdisciplinary astronomy
Two Young Planetary Systems around Field Stars with Ages between 20 and 320 Myr from TESS

Planets around young stars trace the early evolution of planetary systems. We report the discovery and validation of two planetary systems with ages ≲300 Myr from observations by the Transiting Exoplanet Survey Satellite (TESS). The $40\mbox{--}320$ Myr old G star TOI-251 hosts a ${2.74}_{-0.18}^{+0.18}\,{R}_{\oplus }$ mini-Neptune with a $4.94$ day period. The $20\mbox{--}160$ Myr old K star TOI-942 hosts a system of inflated Neptune-sized planets, with TOI-942b orbiting in a period of $4.32$ days with a radius of ${4.81}_{-0.20}^{+0.20}\,{R}_{\oplus }$ and TOI-942c orbiting in a period of $10.16$ days with a radius of ${5.79}_{-0.18}^{+0.19}\,{R}_{\oplus }$ . Though we cannot place either host star into a known stellar association or cluster, we can estimate their ages via their photometric and spectroscopic properties. Both stars exhibit significant photometric variability due to spot modulation, with measured rotation periods of ∼3.5 days. These stars also exhibit significant chromospheric activity, with age estimates from the chromospheric calcium emission lines and X-ray fluxes matching that estimated from gyrochronology. Both stars also exhibit significant lithium absorption, similar in equivalent width to well-characterized young cluster members. TESS has the potential to deliver a population of young planet-bearing field stars, contributing significantly to tracing the properties of planets as a function of their age.

Keywords: exoplanet evolution; exoplanets
Deciphering the Local Interstellar Spectra of Secondary Nuclei with the Galprop/Helmod Framework and a Hint for Primary Lithium in Cosmic Rays

Local interstellar spectra (LIS) of secondary cosmic-ray (CR) nuclei, lithium, beryllium, boron, and partially secondary nitrogen, are derived in the rigidity range from 10 MV to ∼200 TV using the most recent experimental results combined with state-of-the-art models for CR propagation in the Galaxy and in the heliosphere. The lithium spectrum appears somewhat flatter at high energies compared to other secondary species, which may imply a primary lithium component. Two propagation packages, GALPROP and HelMod, are combined to provide a single framework that is run to reproduce direct measurements of CR species at different modulation levels, and at both polarities of the solar magnetic field. An iterative maximum-likelihood method is developed that uses GALPROP-predicted LIS as input to HelMod, which provides the modulated spectra for specific time periods of the selected experiments for the model-data comparison. The proposed LIS accommodates the low-energy interstellar spectra measured by Voyager 1, the High Energy Astrophysics Observatory-3 (HEAO-3), and the Cosmic Ray Isotope Spectrometer on board of the Advanced Composition Explorer (ACE/CRIS), as well as the high-energy observations by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA), Alpha Magnetic Spectrometer-02 (AMS-02), and earlier experiments that are made deep in the heliosphere. The interstellar and heliospheric propagation parameters derived in this study are consistent with our earlier results for propagation of CR protons, helium, carbon, oxygen, antiprotons, and electrons.

Keywords: cosmic rays; heliosphere; interstellar medium; interplanetary medium; particle astrophysics; isotopic abundances
A New Approach for the Regression of the Center Coordinates and Radius of the Solar Disk Using a Deep Convolutional Neural Network

This paper presents a new approach for the regression of the center coordinates and radius of the solar disk in Hα solar full-disk images by using a Deep Convolutional Neural Network. We use ∼100,000 original Hα solar full-disk images obtained from Huairou Solar Observing Station as the experimental data set. The data set includes two parts: the original image and three numeric values (center coordinates and radius). In order to deal with the uneven distribution of the solar disk position in the original image, we randomly shift the solar disk during image preprocessing. Furthermore, data augmentation is also used to increase the robustness of the model. By evaluating the model with R-square and relative error, the center coordinates and the radius of the solar disk are proved to be effectively regressed. The data sets we constructed and source code are available as open source on GitHub.

Keywords: solar radius; solar physics; astronomy data analysis; convolutional neural networks; regression
The Optically Thick Rotating Magnetic Wind from a Massive White Dwarf Merger Product. II. Axisymmetric Magnetohydrodynamic Simulations

We numerically construct a series of axisymmetric rotating magnetic wind solutions, aiming at exploring the observation properties of massive white dwarf (WD) merger remnants with a strong magnetic field, a fast spin, and an intense mass loss, as inferred for WD J005311. We investigate the magnetospheric structure and the resultant spin-down torque exerted to the merger remnant with respect to the surface magnetic flux Φ*, spin angular frequency Ω* and the mass-loss rate $\dot{M}$ . We confirm that the wind properties for $\sigma \equiv {{\rm{\Phi }}}_{* }^{2}{{\rm{\Omega }}}_{* }^{2}/\dot{M}{v}_{\mathrm{esc}}^{3}\gtrsim 1$ significantly deviate from those of the spherical Parker wind, where v esc is the escape velocity at stellar surface. For such a rotating magnetic wind sequence, we find (i) a quasiperiodic mass eruption triggered by magnetic reconnection along with the equatorial plane and (ii) a scaling relation for the spin-down torque $T\approx (1/2)\times \dot{M}{{\rm{\Omega }}}_{* }{R}_{* }^{2}{\sigma }^{1/4}$ . We apply our results to discuss the spin-down evolution and wind anisotropy of massive WD merger remnants, the latter of which could be probed by a successive observation of WD J005311 using Chandra.

Keywords: stellar winds; white dwarf stars; stellar rotation; magnetohydrodynamics
The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems I: High-contrast Imaging of the Exoplanet HIP 65426 b from 2 to 16 μm

We present JWST Early Release Science coronagraphic observations of the super-Jupiter exoplanet, HIP 65426b, with the Near-Infrared Camera (NIRCam) from 2 to 5 μm, and with the Mid-Infrared Instrument (MIRI) from 11 to 16 μm. At a separation of ~0.″82 (87 ${}_{-31}^{+108}$ au), HIP 65426b is clearly detected in all seven of our observational filters, representing the first images of an exoplanet to be obtained by JWST, and the first-ever direct detection of an exoplanet beyond 5 μm. These observations demonstrate that JWST is exceeding its nominal predicted performance by up to a factor of 10, depending on separation and subtraction method, with measured 5σ contrast limits of ~1 × 10-5 and ~2 × 10-4 at 1″ for NIRCam at 4.4 μm and MIRI at 11.3 μm, respectively. These contrast limits provide sensitivity to sub-Jupiter companions with masses as low as 0.3M Jup beyond separations of ~100 au. Together with existing ground-based near-infrared data, the JWST photometry are fit well by a BT-SETTL atmospheric model from 1 to 16 μm, and they span ~97% of HIP 65426b's luminous range. Independent of the choice of model atmosphere, we measure an empirical bolometric luminosity that is tightly constrained between $\mathrm{log}\left({L}_{\mathrm{bol}}/{L}_{\odot }\right)$ = -4.31 and -4.14, which in turn provides a robust mass constraint of 7.1 ± 1.2 M Jup. In totality, these observations confirm that JWST presents a powerful and exciting opportunity to characterize the population of exoplanets amenable to high-contrast imaging in greater detail.

Keywords: exoplanets; exoplanet astronomy; extrasolar gaseous planets
The Composition, Excitation, and Physical State of Atomic Gas in the Debris Disk Surrounding 51 Oph

We measured 304 absorption features in the ultraviolet and visible spectra of the star 51 Oph, which is known to have a debris disk with a high inclination. We analyzed the relative populations of atoms in excited fine-structure and metastable levels that are maintained by optical pumping and collisional excitation by electrons, and we found that most of the gas is situated at about 6 au from the star, has an electron volume density 105 < n(e) < 3 × 106 cm-3, and a temperature T = 8000 K. Our interpretations reveal that the gas is partly ionized, has a column density of neutral hydrogen equal to 1021 cm-2, and has a composition similar to that of a mildly depleted interstellar medium or that of Jupiter-family comets. Compared to results for disks around some other stars, such as β Pic and 49 Cet, we find surprisingly little neutral carbon. No molecular features were detected, which indicates that our line of sight misses the molecule-rich central plane of the disk. The tilt of the disk is also validated by our being able to detect resonant scattering of the starlight by oxygen atoms. ∗ Based on observations with the NASA/ESA Hubble Space Telescope obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Associations of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.

Keywords: debris disks; circumstellar gas; abundance ratios
Electron-scale Magnetic Peaks Upstream of Mercury's Bow Shock: MESSENGER Observations

Electron-scale magnetic peaks (ESMPs) with spatial sizes less than one local ion gyroradius have been recently revealed to exist in the terrestrial magnetosheath and solar wind at 1 au. Whether they widely exist in the astrophysical plasma is unclear. Here, we investigate the magnetic peaks with a period of 0.1-100 s upstream of Mercury's bow shock by using the magnetic field data from the MESSENGER spacecraft. Based on the distribution of their durations, these magnetic peaks can be divided into two groups: one with durations less than 0.6 s and the other with durations larger than 0.6 s. The durations in each group obey a log-normal distribution. The magnetic peaks with durations less than 0.6 s are inferred to be electron scale, suggesting that ESMPs exist in the solar wind at Mercury's orbit. The median duration of these ESMPs is ~0.3 s. The ESMPs have a larger occurrence rate near the bow shock and prefer to occur when the ambient interplanetary magnetic field (IMF) can be connected to the bow shock, which suggests that the foreshock could be one source region of these ESMPs. Their occurrence rate also tends to be larger when the IMF strength is weaker. Our observations also suggest that some ESMPs originate from the upstream solar wind. The properties of the ESMPs found here could help to shed light on their generation mechanisms and their roles in the astrophysical plasma.

Keywords: solar wind; interplanetary magnetic fields
DDO68 C: The Actual Appearance of a Ghost Satellite Dwarf through Adaptive Optics at the Large Binocular Telescope

Through adaptive optics (AO) imaging with the SOUL+LUCI instrument at the Large Binocular Telescope we were able to resolve, for the first time, individual stars in the gas-rich galaxy DDO68 C. This system was already suggested to be interacting with the extremely metal-poor dwarf DDO68, but its nature has remained elusive so far because of the presence of a bright foreground star close to its line of sight that hampers a detailed study of its stellar population and distance. In our study, we turned this interloper star into an opportunity to have a deeper insight on DDO68 C, using it as a guide star for the AO correction. Although the new data do not allow for a direct distance measurement through the red giant branch tip method, the combined analysis of the resolved-star color-magnitude diagram, of archival GALEX far-UV and near-UV photometry, and of Hα data provides a self-consistent picture in which DDO68 C is at the same ~13 Mpc distance as its candidate companion DDO68. These results indicate that DDO68 is a unique case of a low-mass dwarf, less massive than the Magellanic Clouds, interacting with three satellites (DDO68 C and two previously confirmed accreting systems), providing useful constraints on cosmological models and a potential explanation for its anomalous extremely low metallicity.

Keywords: dwarf galaxies; dwarf irregular galaxies; interacting galaxies; galaxy stellar content; adaptive optics
Anthropogenic Coal Ash as a Contaminant in an Underwater Search. II. Beyond Beryllium, Lanthanum, and Uranium

It has been shown that the Beryllium, Lanthanum and Uranium concentrations in the "BeLaU" spherules are in the expected ranges of coal ash. It is reported that the average elemental concentration of 12 microspherules can be found in the COALQUAL database in 98% (49/50) of the elements examined. The "BeLaU pattern" is found to be not unique, it can be reproduced using a coal ash standard (SRM1633a) and a chondritic normalization. The ratio of rare-earth elements in the "BeLaU" spherules and the SMR1633a sample is of order unity. Comparisons against SRM1633a return only two elements with abundances statistically significantly lower than the coal ash standard of reference (or fractions of order unity), agreeing in 96% (52/54) of the elements tested. No elements show higher abundance than 10× the reference standard. Terrestrial coal ash is curiously very similar to the collected spherules. Origin from a recent meteoritic event remains uncertain.

Keywords: meteorite composition; micrometeorites; chondrites
Discovery and Timing of Pulsars in the Globular Cluster M13 with FAST

We report the discovery of a binary millisecond pulsar (namely PSR J1641+3627F or M13F) in the globular cluster (GC) M13 (NGC 6205) and timing solutions of M13A to F using observations made with the Five-hundred-meter Aperture Spherical radio Telescope. PSR J1641+3627F has a spin period of 3.00 ms and an orbital period of 1.4 days. The most likely companion mass is 0.13 M⊙. M13A to E all have short spin periods and small period derivatives. We also confirm that the binary millisecond pulsar PSR J1641+3627E (also M13E) is a black widow with a companion mass around 0.02 M⊙. We find that all the binary systems have low eccentricities compared to those typical for GC pulsars and that they decrease with distance from the cluster core. This is consistent with what is expected, as this cluster has a very low encounter rate per binary.

Keywords: millisecond pulsars; pulsar timing method; period search
Dust Resurgence in Protoplanetary Disks Due to Planetesimal-Planet Interactions

Observational data on the dust content of circumstellar disks show that the median dust content in disks around pre-main-sequence stars in nearby star-forming regions seems to increase from ~1 to ~2 Myr and then decline with time. This behavior challenges the models where the small dust grains steadily decline by accumulating into larger bodies and drifting inwards on a short timescale (≤1 Myr). In this Letter we explore the possibility to reconcile this discrepancy in the framework of a model where the early formation of planets dynamically stirs the nearby planetesimals and causes high-energy impacts between them, resulting in the production of second-generation dust. We show that the observed dust evolution can be naturally explained by this process within a suite of representative disk-planet architectures.

Keywords: protoplanetary disks; planetary-disk interactions; planetary migration; planetary system formation; planetesimals; circumstellar disks
Misalignment of Terrestrial Circumbinary Planets as an Indicator of Their Formation Mechanism

Circumbinary gas disks are often observed to be misaligned with the binary orbit, suggesting that planet formation may proceed in a misaligned disk. With n-body simulations, we consider the formation of circumbinary terrestrial planets from a particle disk that is initially misaligned. We find that if terrestrial planets form in this way, in the absence of gas, they can only form close to coplanar or close to polar to the binary orbit. Planets around a circular binary form coplanar while planets around an eccentric binary can form coplanar or polar depending on the initial disk misalignment and the binary eccentricity. The more massive a terrestrial planet is, the more aligned it is (to coplanar or polar) because it has undergone more mergers that lead on average to smaller misalignment angles. Nodal precession of particle disks with very large initial inclinations lead to high mutual inclinations between the particles. This produces high relative velocities between particles that lead to mass ejections that can completely inhibit planet formation. Misaligned terrestrial circumbinary planets may be able to form in the presence of a misaligned circumbinary gas disk that may help to nodally align the particle orbits and maintain the inclination of the planets during their formation.

Keywords: binary stars; extrasolar rocky planets; planet formation; exoplanet formation
Thermal Components in Gamma-Ray Bursts. II. Constraining the Hybrid Jet Model

In explaining the physical origin of the jet composition of gamma-ray bursts (GRBs), a more general picture, I.e., the hybrid jet model (which introduced another magnetization parameter σ0 on the basis of the traditional fireball model), has been well studied in Gao & Zhang. However, it still has not yet been applied to a large GRB sample. Here, we first employ the "top-down" approach of Gao & Zhang to diagnose the photosphere properties at the central engine to see how the hybrid model can account for the observed data as well, through applying a Fermi GRB sample (eight bursts) with the detected photosphere component, as presented in Li (our Paper I). We infer all physical parameters of a hybrid problem with three typical values of the radius of the jet base (r0 = 107, 108, and 109 cm). We find that the dimensionless entropy for all the bursts shows η ≫ 1 while the derived (1+σ0) for five bursts (GRB 081224, GRB 110721A, GRB 090719, GRB 100707, and GRB 100724) is larger than unity, indicating that in addition to a hot fireball component, another cold Poynting-flux component may also play an important role. Our analysis also shows that in a few time bins for all r0 in GRB 081224 and GRB 110721A, the magnetization parameter at ∼1015 cm (1+σr15) is greater than unity, which implies that internal-collision-induced magnetic reconnection and turbulence may be the mechanism to power the nonthermal emission, rather than internal shocks. We conclude that the majority of bursts (probably all) can be well explained by the hybrid jet problem.

Keywords: gamma-ray bursts; astronomy data analysis; relativistic jets
Locations and Morphologies of Jellyfish Galaxies in A2744 and A370

We present a study of the orbits, environments, and morphologies of 13 ram-pressure stripped galaxies in the massive, intermediate redshift (z ~ 0.3-0.4) galaxy clusters A2744 and A370, using MUSE integral-field spectroscopy and Hubble Space Telescope imaging from the Frontier Fields Program. We compare different measures of the locations and morphologies of the stripped sample with a sample of six post-starburst galaxies identified within the same clusters, as well as the general cluster population. We calculate the phase-space locations of all cluster galaxies and carry out a substructure analysis, finding that the ram-pressure stripped galaxies in A370 are not associated with any substructures, but are likely isolated infalling galaxies. In contrast, the ram-pressure stripped galaxies in A2744 are strictly located within a high-velocity substructure, moving through a region of dense X-ray emitting gas. We conclude that their ram-pressure interactions are likely to be the direct result of the merger between two components of the cluster. Finally, we study the morphologies of the stripped and post-starburst galaxies, using numerical measures to quantify the level of visual disturbances. We explore any morphological deviations of these galaxies from the cluster population, particularly the weaker cases that have been confirmed via the presence of ionized gas tails to be undergoing ram-pressure stripping, but are not strongly visually disturbed in the broadband data. We find that the stripped sample galaxies are generally divergent from the general cluster sample, with post-starburst galaxies being intermediary in morphology between stripped galaxies and red passive cluster members.

Keywords: galaxy clusters; intracluster medium; galaxy interactions; galaxy environments; galaxy encounters; galaxy evolution; post-starburst galaxies