adsabs/SciX_UAT_keywords huggingface dataset:
A Study of Equatorial Coronal Holes during the Maximum Phase of Four Solar Cycles

The 11 yr solar cycle (SC) is characterized by periodic changes in solar activity indicators such as the number of sunspots, coronal holes, and active regions (ARs), as well as the occurrence rate of solar energetic events such as filament eruptions, flares, and coronal mass ejections. In this work we performed a statistical study of the equatorial coronal holes (ECHs) and ARs during the maximum phase of the last four SCs: SC 21 (1979-1982), SC 22 (1989-1992), SC 23 (1999-2002), and SC 24 (2012-2015). We compared the number of ECHs and ARs, separations between their centroids, solar wind speed, pressure, and the number of intense geomagnetic storm (IGS) data over these four cycles. We note a strong anticorrelation between the number of ARs and ECHs. We found that the number of close ARs and ECHs, solar wind speed, and the number of IGS increases with average sunspot maximum number for even cycles and decreases with average sunspot maximum for odd cycles. Also, we find strong odd-even trends in the relation between the wind properties and the numbers of close AR and ECH. These results obtained from the annual average data suggest a possible link between ECH and AR proximity and the solar wind phenomena, though odd-even trends point to the importance of other effects (e.g., Sun-Earth magnetic alignment) as well.

Keywords: solar coronal holes; solar active regions; solar wind; solar storm; solar cycle; solar evolution; solar activity
A New Way to Explore Cosmological Tensions Using Gravitational Waves and Strong Gravitational Lensing

In recent years, a crisis in the standard cosmology has been caused by inconsistencies in the measurements of some key cosmological parameters, the Hubble constant H 0 and cosmic curvature parameter Ω K , for example. It is necessary to remeasure them with the cosmological model-independent methods. In this paper, based on the distance sum rule, we present such a way to constrain H 0 and Ω K simultaneously in the late universe from strong gravitational lensing time-delay (SGLTD) data and gravitational wave (GW) standard siren data simulated from the future observation of the Einstein Telescope (ET). Based on the data for six currently observed SGLTDs, we find that the constraint precision of H 0 from the combined 100 GW events can be comparable with the measurement from the SH0ES collaboration. As the number of GW events increases to 700, the constraint precision of H 0 will exceed that of the Planck 2018 results. Considering 1000 GW events as the conservative estimation of ET in the 10 yr observation, we obtain H 0 = 73.69 ± 0.36 km s-1 Mpc-1 with a 0.5% uncertainty and ${{\rm{\Omega }}}_{K}={0.076}_{-0.087}^{+0.068}$ . In addition, we simulate 55 strong gravitational lensing (SGL) systems with a 6.6% uncertainty for the measurement of time-delay distance. By combining with 1000 GWs, we infer that H 0 = 73.65 ± 0.35 km s-1 Mpc-1 and Ω K = 0.008 ± 0.048. Our results suggest that this approach can play an important role in exploring cosmological tensions.

Keywords: cosmological parameters; gravitational waves; strong gravitational lensing; hubble constant
Incompleteness Matters Not: Inference of H0 from Binary Black Hole-Galaxy Cross-correlations

We show how the angular clustering between gravitational-wave (GW) standard sirens and galaxies with known redshifts allows an inference of the Hubble constant regardless of whether the host galaxies of any of these sirens are present in the galaxy catalog. We demonstrate this for the first time with realistic simulations of GW signals from binary black holes in a three-detector network with Advanced LIGO and Advanced Virgo sensitivities. We show that with such a network, the cross-correlation technique can be used to infer the Hubble parameter with a precision of less than 10% (2%) at 90% confidence with 50 (500) sources, even with a 100% incomplete catalog, which does not contain the hosts of any of the GW events. We compare our method with the current state-of-the-art techniques used for the inference of the Hubble parameter from real data. We argue that, if the clustering information is not used explicitly, the inference of H0 from real data is expected to be prior-dominated.

Keywords: hubble constant; large-scale structure of the universe
Evidence for a Transient Emission Feature at 1524 Å in the Far Ultraviolet Spectrum of 21 Com

Evidence is presented for the presence of a transient emission feature at 1524 Å in the far ultraviolet spectrum of 21 Com recorded by the International Ultraviolet Explorer during the 1979 event. This event is characterized by he sudden appearance of broad and intense absorption features shortwards of 1720 Å. The emission feature at 1524 Å is tentatively identified as a Si I line also present in the FUV spectra of quiescent dMe dwarfs. During the event, the flux level in the continuum adjacent to this line is about 1.6 times higher than in the mean spectrum outside event.

Keywords: chemically peculiar stars; ap stars
Hypothetical Hyperbolic Encounters between Venus and Proto-Mercury that Partially Stripped Away Proto-Mercury’s Mantle

Compared to all other terrestrial planets in the solar system, Mercury has an unusually large metal core, comprising ∼70% of its mass. Giant impacts could have removed a significant fraction of the silicate mantle of a chondritic proto-Mercury, forming the iron-rich present-day Mercury. However, such high-temperature giant impacts seem at odds with the retention of moderately volatile elements on present-day Mercury. We simulated a series of hyperbolic encounters between proto-Mercury and proto-Venus, which may have occurred in the chaotic early solar system. Tidal disruption of proto-Mercury always removes a portion of its silicate mantle, while its iron core remains intact. We find, in favorable cases, four close encounters with fast-spinning projectiles (resulting from previous encounters) that could lead to Mercury’s present-day iron fraction. More encounters are needed when the spin and orbital angular momentum are not always aligned. These hyperbolic encounters have various outcomes, such as orbital decay, binary planets, and change of spin rates. These results suggest the importance of the proper treatment of close encounters in N-body simulations of planetary accretion.

Keywords: impact phenomena; tidal disruption; computational astronomy; solar system formation
Multiwavelength Imaging and Spectral Analysis of Jet-like Phenomena in a Solar Active Region Using IRIS and AIA

High-resolution observations of dynamic phenomena give insights into the properties and processes that govern the low solar atmosphere. We present an analysis of jet-like phenomena emanating from a penumbral footpoint in active region (AR) 12192 using imaging and spectral observations from the Interface Region Imaging Spectrograph (IRIS) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. These jets are associated with line-of-sight Doppler speeds of ±10-22 km s-1 and bright fronts that seem to move across the plane-of-sky at speeds of 23-130 km s-1. Such speeds are considerably higher than the expected sound speed in the chromosphere. The jets have signatures that are visible both in the cool and hot channels of IRIS and AIA. Each jet lasts on average 15 minutes and occurs 5-7 times over a period of 2 hr. Possible mechanisms to explain this phenomenon are suggested, the most likely of which involve p-mode or Alfvén wave shock trains impinging on the transition region and corona as a result of steepening photospheric wavefronts or gravity waves.

Keywords: solar chromosphere; solar active regions; jets; shocks; sunspots; solar spicules; solar transition region; solar photosphere
Mapping the Hidden Magnetic Field of the Quiet Sun

The Sun is the only star where we can resolve the intricate magnetism that all convective stars harbor. Yet, more than 99% of its visible surface along the solar cycle (the so-called quiet Sun) is filled with a tangled, unresolved magnetism. These "hidden" fields are thought to store enough magnetic energy to play a role in the heating of the Sun's outer atmosphere, but its field strength is still not constrained. Previous investigations based on the Hanle effect in atomic lines claim a strong magnetization of about 100 G, while the same effect in molecules show a factor of 10 weaker fields. The discrepancy disappears if the magnetic field strength of the hidden field is not homogeneous in the solar surface. In this Letter, we prove using magnetohydrodynamical simulations that it is possible to infer the average field strength of the hidden quiet-Sun magnetic fields using multiline inversions of intensity profiles in the Zeeman regime. Using this technique with 15 spectral lines in the 1.5 μm spectral range, we reveal that the spatial distribution of the hidden field is strongly correlated with convection motions, and that the average magnetization is about 46 G. Reconciling our findings with the Hanle ones is not obvious and will require future work on both sides, since it implies an increase of the field strength with height, something that is physically questionable.

Keywords: solar magnetic fields; solar photosphere; spectropolarimetry
Interpreting the Equatorially Antisymmetric Gravitational Field of Saturn Measured by the Cassini Grand Finale

The equatorially antisymmetric gravitational field of Saturn, represented by the four gravitational coefficients J3, J5, J7, and J9, has been measured by the Cassini Grand Finale. Since the rotational distortion and the internal structure do not contribute to the asymmetric gravity field, the spectrum of the odd coefficients offers a direct window into the structure and amplitude of fluid motion in Saturn. We show that the observed cloud-top asymmetric winds extending into Saturn's interior cannot produce the measured gravity field, suggesting that the cloud-top winds are confined within a thin weather layer and hence do not contribute to the observed gravity. We interpret the asymmetric gravitational field by searching for an a priori unknown zonal circulation taking place in the molecular envelope. We find that a zonal circulation confined in the 20,000 km thick molecular layer produces the coefficients J3, J5, J7, J9 in agreement with measurements. The depth of the circulation is consistent with that inferred from the equatorially symmetric gravitational field of Saturn.

Keywords: solar system gas giant planets; saturn; gravitational fields; gravity anomaly; deep space probes; planetary atmospheres; hydrodynamics; magnetohydrodynamical simulations
Unstable Mass Transfer from a Main-sequence Star to a Supermassive Black Hole and Quasiperiodic Eruptions

We discuss the formation and evolution of systems composed of a low-mass (M ⋆ ≲ 4 M ⊙) main-sequence star orbiting a 105-107 M ⊙ supermassive black hole with an orbital period of order ~hours and a mild eccentricity (e ≈ 0.1-0.2), episodically shedding mass at each pericenter passage. We argue that the resulting mass transfer is likely unstable, with Roche lobe overflow initially driven by gravitational-wave emission, but then being accelerated by the star's expansion in response to its mass loss, undergoing a runaway process. We show that such systems are naturally produced by two-body gravitational encounters within the inner parsec of a galaxy, followed by gravitational-wave circularization and inspiral from initially highly eccentric orbits. We argue that such systems can produce recurring flares similar to the recently identified class of X-ray transients known as quasiperiodic eruptions, observed at the centers of a few distant galaxies.

Keywords: gravitational waves; supermassive black holes; roche lobe overflow; x-ray transient sources; tidal disruption; stellar dynamics
Improved Period Variations of 32 Contact Binaries with Rapidly Decreasing Periods in the Galactic Bulge

We present detailed analyses of updated eclipse timing diagrams for 32 contact binary merger candidates in the Galactic bulge. The photometric data was obtained from 2016 to 2021 using the Korea Microlensing Telescope Network with the 1.6 m telescopes located at three southern sites (CTIO, SAAO, and SSO). The times of minimum lights were determined by applying the binary-star model to full light curves created at half-year intervals from the observations. The orbital period variations of the binary systems were analyzed using the O - C diagrams from our new timings with the others published in the literature, which are based on the OGLE observations from 2001 to 2015. As results, the orbital periods and period-decreasing rates of 32 binary systems were located to be in the ranges of 0.370 to 1.238 days and from -3.0 to -13.1 × 10-6 day yr-1, respectively. Out of these stars, 24 systems show a combination effect of a parabola and a light travel time caused by a third body, and their outer orbital periods are in the range of 9.1-26.5 yr. We propose that all of our merger candidates need additional monitoring observations to study a luminous-red nova progenitor.

Keywords: contact binary stars; eclipsing binary minima timing method; eclipsing binary stars; galactic bulge; stellar mergers
Changes in Photospheric Lorentz Force in Eruptive and Confined Solar Flares

Solar flares are known to leave imprints on the magnetic field in the photosphere, often manifested as an abrupt and permanent change in the downward-directed Lorentz force in localized areas inside the active region. Our study aims to differentiate eruptive and confined solar flares based on the variations in vertical Lorentz force. We select 26 eruptive and 11 confined major solar flares (stronger than the GOES M5 class) observed during 2011–2017. We analyze these flaring regions using SHARP vector magnetograms obtained from NASA's Helioseismic and Magnetic Imager. We also compare data corresponding to two synthetic flares from a δ-sunspot simulation reported by Chatterjee et al. We estimate the change in the horizontal magnetic field and the total Lorentz force integrated over an area around the polarity inversion line (PIL) that encompasses the location of the flare. Our results indicate a rapid increase in the horizontal magnetic field along the flaring PIL, accompanied by a significant change in the downward-directed Lorentz force in the same vicinity. Notably, we find that all the confined events under study exhibit a total change in Lorentz force of <1.8 × 1022 dyn. This threshold plays an important role in effectively distinguishing eruptive and confined flares. Further, our analysis suggests that the change in total Lorentz force also depends on the reconnection height in the solar corona at the associated flare onset. The results provide significant implications for understanding the flare-related upward impulse transmission for the associated coronal mass ejection.

Keywords: solar magnetic fields; solar coronal mass ejections; solar flares
The Solar Probe Cup on the Parker Solar Probe

Solar Probe Cup (SPC) is a Faraday cup instrument on board NASA's Parker Solar Probe (PSP) spacecraft designed to make rapid measurements of thermal coronal and solar wind plasma. The spacecraft is in a heliocentric orbit that takes it closer to the Sun than any previous spacecraft, allowing measurements to be made where the coronal and solar wind plasma is being heated and accelerated. The SPC instrument was designed to be pointed directly at the Sun at all times, allowing the solar wind (which is flowing primarily radially away from the Sun) to be measured throughout the orbit. The instrument is capable of measuring solar wind ions with an energy between 100 and 6000 V (protons with speeds from 139 to 1072 km s-1). It also measures electrons with an energy/charge between 100 and 1500 V. SPC has been designed to have a wide dynamic range that is capable of measuring protons and alpha particles at the closest perihelion (9.86 solar radii from the center of the Sun) and out to 0.25 au. Initial observations from the first orbit of PSP indicate that the instrument is functioning well.

Keywords: solar wind; solar instruments; space plasmas; space vehicle instruments; solar corona
Disruption of a Planetary Nitrogen Cycle as Evidence of Extraterrestrial Agriculture

Agriculture is one of the oldest forms of technology on Earth. The cultivation of plants requires a terrestrial planet with active hydrological and carbon cycles and depends on the availability of nitrogen in soil. The technological innovation of agriculture is the active management of this nitrogen cycle by applying fertilizer to soil, at first through the production of manure excesses but later by the Haber-Bosch industrial process. The use of such fertilizers has increased the atmospheric abundance of nitrogen-containing species such as NH3 and N2O as agricultural productivity intensifies in many parts of the world. Both NH3 and N2O are effective greenhouse gases, and the combined presence of these gases in the atmosphere of a habitable planet could serve as a remotely detectable spectral signature of technology. Here we use a synthetic spectral generator to assess the detectability of NH3 and N2O that would arise from present-day and future global-scale agriculture. We show that present-day Earth abundances of NH3 and N2O would be difficult to detect, but hypothetical scenarios involving a planet with 30-100 billion people could show a change in transmittance of about 50%-70% compared to preagricultural Earth. These calculations suggest the possibility of considering the simultaneous detection of NH3 and N2O in an atmosphere that also contains H2O, O2, and CO2 as a technosignature for extraterrestrial agriculture. The technology of agriculture is one that could be sustainable across geologic timescales, so the spectral signature of such an "ExoFarm" is worth considering in the search for technosignatures.

Keywords: technosignatures; astrobiology; biosignatures; habitable planets; spectroscopy
2SXPS: An Improved and Expanded Swift X-Ray Telescope Point-source Catalog

We present the 2SXPS (Swift-XRT Point Source) catalog, containing 206,335 point sources detected by the Swift X-ray Telescope (XRT) in the 0.3-10 keV energy range. This catalog represents a significant improvement over 1SXPS, with double the sky coverage (now 3790 deg2), and several significant developments in source detection and classification. In particular, we present for the first time techniques to model the effect of stray light - significantly reducing the number of spurious sources detected. These techniques will be very important for future, large effective area X-ray missions, such as the forthcoming Athena X-ray observatory. We also present a new model of the XRT point-spread function and a method for correctly localizing and characterizing piled-up sources. We provide light curves - in four energy bands, two hardness ratios, and two binning timescales - for every source, and from these deduce that over 80,000 of the sources in 2SXPS are variable in at least one band or hardness ratio. The catalog data can be queried or downloaded via a web interface at https://www.swift.ac.uk/2SXPS, via HEASARC, or in Vizier (IX/58).

Keywords: catalogs; x-ray astronomy; x-ray identification
Runaway OB Stars in the Small Magellanic Cloud: Dynamical versus Supernova Ejections

Runaway OB stars are ejected from their parent clusters via two mechanisms, both involving multiple stars: the dynamical ejection scenario (DES) and the binary supernova scenario (BSS). We constrain the relative contributions from these two ejection mechanisms in the Small Magellanic Cloud (SMC) using data for 304 field OB stars from the spatially complete Runaways and Isolated O-Type Star Spectroscopic Survey of the SMC (RIOTS4). We obtain stellar masses and projected rotational velocities ${v}_{r}\sin \ i$ for the sample using RIOTS4 spectra, and we use transverse velocities ${v}_{\mathrm{loc}}$ from Gaia DR2 proper motions. Kinematic analyses of the masses, ${v}_{r}\sin \ i$ , noncompact binaries, high-mass X-ray binaries, and Oe/Be stars largely support predictions for the statistical properties of the DES and BSS populations. We find that dynamical ejections dominate over supernova ejections by a factor of ∼2-3 in the SMC, and our results suggest a high frequency of DES runaways and binary ejections. Objects seen as BSS runaways also include two-step ejections of binaries that are reaccelerated by supernova kicks. We find that two-step runaways likely dominate the BSS runaway population. Our results further imply that any contribution from in situ field OB star formation is small. Finally, our data strongly support the post-mass-transfer model for the origin of classical Oe/Be stars, providing a simple explanation for the bimodality in the ${v}_{r}\sin \ i$ distribution and high, near-critical, Oe/Be rotation velocities. The close correspondence of Oe/Be stars with BSS predictions implies that the emission-line disks are long-lived.

Keywords: runaway stars; massive stars; small magellanic cloud; field stars; stellar kinematics; binary stars; star clusters; be stars; stellar rotation; high mass x-ray binary stars
An Empirically Derived Formula for the Shape of Planet-induced Gaps in Protoplanetary Disks

This study uses numerical hydrodynamics calculations and a novel method for densely sampling parameter space to measure the precise shape of a gap opened by a planet in a gaseous disk, as a function of planet-to-star mass ratio, disk Mach number, and disk viscosity. Formulas for gap depth and width are determined, which are combined to form a complete formula for surface density as a function of radius in the disk. This new analytical formula is compared with numerically derived gaps opened by planets ranging from very low masses up to a few times Jupiter's mass, and excellent agreement is found over a wide range of parameter space relevant to planet-disk interactions. A simple-to-use code is presented to rapidly generate synthetic disk profiles.

Keywords: exoplanet formation; hydrodynamical simulations; hydrodynamics; protoplanetary disks; planet formation; astrophysical fluid dynamics
A Measurement of the Kuiper Belt's Mean Plane From Objects Classified By Machine Learning

Mean plane measurements of the Kuiper Belt from observational data are of interest for their potential to test dynamical models of the solar system. Recent measurements have yielded inconsistent results. Here we report a measurement of the Kuiper Belt's mean plane with a sample size more than twice as large as in previous measurements. The sample of interest is the nonresonant Kuiper Belt objects, which we identify by using machine learning on the observed Kuiper Belt population whose orbits are well determined. We estimate the measurement error with a Monte Carlo procedure. We find that the overall mean plane of the nonresonant Kuiper Belt (semimajor axis range of 35-150 au) and also that of the classical Kuiper Belt (semimajor axis range of 42-48 au) are both close to (within ~0.°7) but distinguishable from the invariable plane of the solar system to greater than 99.7% confidence. When binning the sample into smaller semimajor axis bins, we find the measured mean plane is mostly consistent with both the invariable plane and the theoretically expected Laplace surface forced by the known planets. Statistically significant discrepancies are found only in the semimajor axis ranges 40.3-42 au and 45-50 au; these ranges are in proximity to the ν 8 secular resonance and Neptune's 2:1 mean motion resonance where the theory for the Laplace surface is likely to be inaccurate. These results do not support a previously reported anomalous warp at semimajor axes above 50 au.

Keywords: classical kuiper belt objects; kuiper belt; orbital theory; celestial mechanics