adsabs/SciX_UAT_keywords huggingface dataset:
FIRST Winged Radio Galaxies with X and Z Symmetry

X-shaped radio galaxies (XRGs) are a subclass of radio sources that exhibit a pair of secondary low surface brightness radio lobes oriented at an angle to the primary high surface brightness lobes. Sometimes, the secondary low brightened lobes emerge from the edges of the primary high brightened lobes and form a Z-symmetric morphology. We present a systematical search result for XRGs and Z-shaped radio galaxies (ZRGs) from the VLA Faint Images of the Radio Sky at Twenty-Centimeters (VLA FIRST) Survey at 1.4 GHz. Our search yields a total of 296 number of radio sources, out of which 161 are XRGs and 135 are ZRGs. We have also made optical identification of these sources from the different available literature. J1124 + 4325 and J1319 + 0502 are the farthest known XRG and ZRG, respectively. We have estimated spectral index and radio luminosity of these radio sources and made a comparative study with previously detected XRGs and ZRGs. The average value of luminosities for XRGs is higher than that of ZRGs. With the help of a large sample size of the newly discovered XRGs and ZRGs, various statistical properties of these sources are studied. Out of 161 XRGs presented in the current paper, 70% (113) are FR II radio galaxies and 13% (20) are FR I radio galaxies. For 28 XRGs, the morphology is complex and could not be classified. For XRGs, the statistical studies are done on the angle between the major axis and minor axis and the relative size of the major and minor axes. For the ZRGs a statistical study is done on the angular size.

Keywords: active galactic nuclei; catalogs; interferometric correlation; quasars; radio continuum emission; surveys
Roaring to Softly Whispering: X-Ray Emission after ∼3.7 yr at the Location of the Transient AT2018cow and Implications for Accretion-powered Scenarios

We present the first deep X-ray observations of luminous fast blue optical transient (LFBOT) AT 2018cow at ∼3.7 yr since discovery, together with the reanalysis of the observation at δ t ∼ 220 days. X-ray emission is significantly detected at a location consistent with AT 2018cow. The very soft X-ray spectrum and sustained luminosity are distinct from the spectral and temporal behavior of the LFBOT in the first ∼100 days and would possibly signal the emergence of a new emission component, although a robust association with AT 2018cow can only be claimed at δ t ∼ 220 days, while at δ t ∼ 1350 days contamination of the host galaxy cannot be excluded. We interpret these findings in the context of the late-time panchromatic emission from AT 2018cow, which includes the detection of persistent, slowly fading UV emission with ν L ν ≈ 1039 erg s‑1. Similar to previous works (and in analogy with arguments for ultraluminous X-ray sources), these late-time observations are consistent with thin disks around intermediate-mass black holes (with M • ≈ 103–104 M ☉) accreting at sub-Eddington rates. However, differently from previous studies, we find that smaller-mass black holes with M • ≈ 10–100 M ☉ accreting at ≳the Eddington rate cannot be ruled out and provide a natural explanation for the inferred compact size (R out ≈ 40 R ☉) of the accretion disk years after the optical flare. Most importantly, irrespective of the accretor mass, our study lends support to the hypothesis that LFBOTs are accretion-powered phenomena and that, specifically, LFBOTs constitute electromagnetic manifestations of super-Eddington accreting systems that evolve to ≲Eddington over a ≈100-day timescale. *Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

Keywords: accretion; stellar accretion disks; supernovae; black holes; high energy astrophysics; x-ray astronomy; transient sources; x-ray transient sources
TOI-1859b: A 64 Day Warm Jupiter on an Eccentric and Misaligned Orbit

Warm Jupiters are close-in giant planets with relatively large planet-star separations (i.e., 10 < a/R ⋆ < 100). Given their weak tidal interactions with their host stars, measurements of stellar obliquity may be used to probe the initial obliquity distribution and dynamical history for close-in gas giants. Using spectroscopic observations, we confirm the planetary nature of TOI-1859b and determine the stellar obliquity of TOI-1859 to be λ = 38.9 ${}_{-2.7}^{+2.8}$ ° relative to its planetary companion using the Rossiter-McLaughlin effect. TOI-1859b is a 64 day warm Jupiter orbiting around a late F dwarf and has an orbital eccentricity of 0.57 ${}_{-0.16}^{+0.12}$ inferred purely from transit light curves. The eccentric and misaligned orbit of TOI-1859b is likely an outcome of dynamical interactions, such as planet-planet scattering and planet-disk resonance crossing.

Keywords: extrasolar gaseous giant planets; exoplanet dynamics; radial velocity; transit photometry
An Automatic Identification Method for the Photoelectron Boundary at Mars

The photoelectron boundary (PEB) at Mars is defined to be the boundary separating the photoelectron-dominated ionosphere from the external plasma environment. Extensive studies have been presented to analyze the PEB variation in the Martian dayside ionosphere. However, the PEB was identified manually in previous studies because of the difficulty in detecting the faint photoelectron features at high altitudes. In this study, we develop an algorithm to detect these faint features and identify the location of PEB from energetic electron measurements automatically. We apply the algorithm to the measurements by the Solar Wind Electron Analyzer instrument on board the Mars Atmosphere and Volatile Evolution mission and identify a total number of 15,681 PEB crossing events accumulated from 2015 January to 2019 October, of which 9169 PEB are on the dayside and 6912 are on the nightside. Our analysis indicates that the altitude of the identified PEB tends to increase with solar extreme ultraviolet radiation and crustal magnetic field strength, in agreement with previous findings. By contrast, the PEB altitude on the nightside tends to increase dramatically with solar zenith angle but is found to be weakly influenced by the crustal magnetic field strength.

Keywords: mars; planetary ionospheres
Unveiling the Dynamics of Dense Cores in Cluster-forming Clumps: A 3D Magnetohydrodynamics Simulation Study of Angular Momentum and Magnetic Field Properties

We conducted isothermal magnetohydrodynamics simulations with self-gravity to investigate the properties of dense cores in cluster-forming clumps. Two different setups were explored: a single rotating clump and colliding clumps. We focused on determining the extent to which the rotation and magnetic field of the parental clump are inherited by the formed dense cores. Our statistical analysis revealed that the alignment between the angular momentum of dense cores, ${{\boldsymbol{L}}}_{\mathrm{core}}$ , and the rotational axis of the clump is influenced by the strength of turbulence and the simulation setup. In single rotating clumps, we found that ${{\boldsymbol{L}}}_{\mathrm{core}}$ tends to align with the clump's rotational axis if the initial turbulence is weak. In colliding clumps, however, this alignment does not occur, regardless of the initial turbulence strength. This misalignment in colliding clumps is due to the induced turbulence from the collision and the isotropic gas inflow into dense cores. Our analysis of colliding clumps also revealed that the magnetic field globally bends along the shock-compressed layer, and the mean magnetic field of dense cores, ${{\boldsymbol{B}}}_{\mathrm{core}}$ , aligns with it. Both in single rotating clumps and colliding clumps, we found that the angle between ${{\boldsymbol{B}}}_{\mathrm{core}}$ and ${{\boldsymbol{L}}}_{\mathrm{core}}$ is generally random, regardless of the clump properties. We also analyzed the dynamical states of the formed cores and found a higher proportion of unbound cores in colliding clumps. In addition, the contribution of rotational energy was only approximately 5% of the gravitational energy, regardless of the model parameters for both single and colliding cases.

Keywords: molecular gas; star formation; magnetohydrodynamical simulations
Are There Higher Electron Densities in Narrow Emission Line Regions of Type-1 AGNs than in Type-2 AGNs?

In the manuscript, we check properties of electron densities n e traced by flux ratio R sii of [S II]λ6716 Å to [S II]λ6731 Å in narrow emission line regions (NLRs) between Type-1 active galactic nucleus (AGN) and Type-2 AGN in SDSS Data Release 12 (DR12). Under the framework of unified model considering kiloparsec-scale structures, similar n e in NLRs should be expected between Type-1 AGN and Type-2 AGN. Based on reliable measurements of the [S II] doublet with measured parameters at least 5 times larger than corresponding uncertainties, there are 6039 Type-1 AGN and 8725 Type-2 AGN (excluding the Type-2 LINERs and the composite galaxies) collected from SDSS DR12. Then, lower R sii (higher n e ) in NLRs can be well confirmed in Type-1 AGN than in Type-2 AGN, with the confidence level higher than 5σ, even after considering the necessary effects including effects of electron temperatures traced by [O III]λ4364,4959,5007 Å on estimating n e in NLRs. Two probable methods are proposed to explain the higher n e in NLRs in Type-1 AGN. First, the higher n e in NLRs of Type-1 AGN could indicate longer time durations of AGN activities in Type-1 AGN than in Type-2 AGN, if AGN activities triggering galactic-scale outflows leading to more electrons injecting into NLRs were accepted to explain the higher n e in NLRs of Type-2 AGN than H II galaxies. Second, the lower n e in NLRs of Type-2 AGN could be explained by stronger star-forming contributions in Type-2 AGN, considering lower n e in H II regions. The results provide interesting challenges to the commonly and widely accepted unified model of AGN.

Keywords: active galaxies; active galactic nuclei; emission line galaxies; seyfert galaxies
Tilting Uranus via Spin-Orbit Resonance with Planet Nine

Uranus's startlingly large obliquity of 98° has yet to admit a satisfactory explanation. The most widely accepted hypothesis involving a giant impactor that tipped Uranus onto its side encounters several difficulties with regard to Uranus's spin rate and prograde satellite system. An obliquity increase that was driven by capture of Uranus into a secular spin-orbit resonance remains a possible alternative hypothesis that avoids many of the issues associated with a giant impact. We propose that secular spin-orbit resonance could have excited Uranus's obliquity to its present-day value if it was driven by the outward migration of an as-yet-undetected outer solar system body commonly known as Planet Nine. We draw support for our hypothesis from an analysis of 123 N-body simulations with varying parameters for Planet Nine and its migration. We find that in multiple instances, a simulated Planet Nine drives Uranus's obliquity past 98°, with a significant number falling within 10% of this value. We note a significant caveat to our results in that a much faster than present-day spin axis precession rate for Uranus is required in all cases for it to reach high obliquities. We conclude that while it was, in principle, possible for Planet Nine (if it exists) to have been responsible for Uranus's obliquity, the feasibility of such a result hinges on Uranus's primordial precession rate.

Keywords: celestial mechanics; trans-neptunian objects; solar system gas giant planets
The Center of Expansion and Age of the Oxygen-rich Supernova Remnant 1E 0102.2-7219

We present new proper-motion measurements of optically emitting oxygen-rich knots of supernova remnant 1E 0102.2-7219 (E0102), which are used to estimate the remnant's center of expansion and age. Four epochs of high-resolution Hubble Space Telescope images spanning 19 yr were retrieved and analyzed. We found a robust center of expansion of α = 1h04m02.48 s and δ = -72°01'53"92 (J2000) with 1σ uncertainty of 1"77 using 45 knots from images obtained with the Advanced Camera for Surveys using the F475W filter in 2003 and 2013 having the highest signal-to-noise ratio. We also estimate an upper limit explosion age of 1738 ± 175 yr by selecting the knots with the highest proper motions and these knots are assumed to be the least decelerated. We find evidence of an asymmetry in the proper motions of the knots as a function of position angle. We conclude that these asymmetries were most likely caused by interaction between E0102's original supernova blast wave and an inhomogeneous surrounding environment, as opposed to intrinsic explosion asymmetry. The observed nonhomologous expansion suggests that the use of a free expansion model inaccurately offsets the center of expansion and leads to an overestimated explosion age. We discuss our findings as they compare to previous age and center of expansion estimates of E0102, as well as their relevance to a recently identified candidate central compact object.

Keywords: supernova remnants; interstellar medium
Detecting Technosignatures from Earth-scale Civilizations

Assuming civilizations have similar interplanetary communications and radar capability to NASA's Deep Space Network, what is the feasibility of intercepting their communications? Interplanetary conjunctions between Earth-like exoplanets, their stars, and other planets in their systems provide one of the most unique and pragmatic opportunities for detecting technosignatures. While eavesdropping on terrestrial communications becomes limited by a planet's rotation, the beams of satellite communications and interplanetary radar transmissions are tracked, providing the most persistent and powerful opportunity for signal interception. In this study, we present a framework for assessing exoplanet habitability and establishing quantitative bounds for detecting Earth-scale technosignatures from Earth-like planets. These constraints for time, frequency, sky positions, and observatory sensitivity provide recommended observational guidelines for using state-of-the-art and future ground-based radio observatories toward technosignature detection. Applying this framework, 16 exoplanet targets are proposed for radio observation.

Keywords: exoplanets; technosignatures; radio astronomy
A Template-based Approach to the Photometric Classification of SN 1991bg-like Supernovae in the SDSS-II Supernova Survey

The use of SNe Ia to measure cosmological parameters has grown significantly over the past two decades. However, there exists a significant diversity in the SN Ia population that is not well understood. Overluminous SN 1991T-like and subluminous SN 1991bg-like objects are two characteristic examples of peculiar SNe. The identification and classification of such objects is an important step in studying what makes them unique from the remaining SN population. With the upcoming Vera C. Rubin Observatory promising on the order of a million new SNe over a 10 year survey, spectroscopic classifications will be possible for only a small subset of observed targets. As such, photometric classification has become an increasingly important concern in preparing for the next generation of astronomical surveys. Using observations from the Sloan Digital Sky Survey II (SDSS-II) SN Survey, we apply here an empirically based classification technique targeted at the identification of SN 1991bg-like SNe in photometric data sets. By performing dedicated fits to photometric data in the rest-frame redder and bluer bandpasses, we classify 16 previously unidentified 91bg-like SNe. Using SDSS-II host galaxy measurements, we find that these SNe are preferentially found in host galaxies with an older average stellar age than the hosts of normal SNe Ia. We also find that these SNe are found at a further physical distance from the center of their host galaxies. We find no statistically significant bias in host galaxy mass or specific star formation rate for these targets.

Keywords: observational astronomy; supernovae; light curve classification; type ia supernovae
Generation and Life Cycle of Solar Spicules

The physical mechanism for the creation of solar spicules is proposed with three stages of their life cycle. It is assumed that at stage I the density hump is formed locally in the x-y plane in the lower chromosphere in the presence of temperature gradients of electrons and ions along the z-axis (the vertical direction). In this region, the density structure of quasi-neutral (n i ≃ n e = n) plasma after taking birth is accelerated in the vertical direction owing to the thermal force F th ∝ ∇n(x, y, t) × (∇T e + ∇T i ). The exact time-dependent analytical solution of two-fluid plasma equations is presented assuming that density is maximum at the center of the density structure and decays away from it gradually. The 2D density structure is created as a step function H(t) in time at the bottom of the chromosphere, and consequently, the vertical plasma velocity turns out to be the ramp function of time R(t) = tH(t), whereas the source term S(x, y, t) for the density follows the delta function δ(t) form. The upward acceleration ${\boldsymbol{a}}=a\,(x,y\,)\,\hat{z}$ produced in this density structure is greater than the downward constant solar acceleration ‑ g ⊙ in the chromosphere. In the transition region, the temperature gradients are steeper; therefore, the upward acceleration increases in magnitude g ⊙ ≪ a and the density hump spends less time there. This is stage II of its life cycle. In stage III, the density structure enters into the corona, where the gradients of temperatures vanish and the structure decelerates to zero velocity under the action of the solar gravitational force.

Keywords: solar spicules; solar chromosphere
Observations of Mini Coronal Dimmings Caused by Small-scale Eruptions in the Quiet Sun

Small-scale eruptions could play an important role in coronal heating, generation of solar energetic particles (SEPs), and mass source of the solar wind. However, they are poorly observed, and their characteristics, distributions, and origins remain unclear. Here a mini coronal dimming was captured by the recently launched Solar Orbiter spacecraft. The observations indicate that a minifilament eruption results in the dimming and takes away approximately (1.65 ± 0.54) × 1013 g of mass, which also exhibits similar features as the sources of SEP events. The released magnetic free energy is of the order of ~1027 erg. Our results suggest that weak constraining force makes the flux rope associated with the minifilament easily enter a torus-unstable domain. We discuss that weak magnetic constraints from low-altitude background fields may be a general condition for the quiet-Sun eruptions, which provide a possible mechanism for the transport of coronal material and energy from the lower to the middle or even higher corona.

Keywords: quiet sun; solar coronal transients; solar magnetic fields; solar filaments
Sensitivity Testing of Stereophotoclinometry for the OSIRIS-REx Mission. II. Effective Observation Geometry for Digital Terrain Modeling

The OSIRIS-REx mission used stereophotoclinometry (SPC) to generate digital terrain models (DTMs) of its target asteroid, Bennu. Here we present a suite of preflight tests conducted to identify the observing geometry and number of images needed to create DTMs that would enable successful navigation around and to the surface of the asteroid. We demonstrate that high-quality DTMs can be generated by using only five images: four that are focused on topography, in which the spacecraft's viewing geometry brackets the target (north, south, east, and west), and a fifth that measures the target's albedo variation, taken from near local noon. We further show that the first 10 iterations of the SPC process can meaningfully improve DTM quality, including in the case of a suboptimal input image set, whereas after 10 iterations the DTM quality approaches an asymptotic maximum. We distill our findings into recommendations for observation planning that can be applied by other missions intending to use SPC to model the shape and terrain of their target.

Keywords: asteroid surfaces; asteroids; near-earth objects
MIRC-X: A Highly Sensitive Six-telescope Interferometric Imager at the CHARA Array

Michigan InfraRed Combiner-eXeter (MIRC-X) is a new highly sensitive six-telescope interferometric imager installed at the CHARA Array that provides an angular resolution equivalent of up to a 330 m diameter baseline telescope in J- and H-band wavelengths ( $\tfrac{\lambda }{2B}\sim 0.6$ mas). We upgraded the original Michigan InfraRed Combiner (MIRC) instrument to improve sensitivity and wavelength coverage in two phases. First, a revolutionary sub-electron noise and fast-frame-rate C-RED ONE camera based on an SAPHIRA detector was installed. Second, a new-generation beam combiner was designed and commissioned to (i) maximize sensitivity, (ii) extend the wavelength coverage to J band, and (iii) enable polarization observations. A low-latency and fast-frame-rate control software enables high-efficiency observations and fringe tracking for the forthcoming instruments of the CHARA Array. Since mid-2017, MIRC-X has been offered to the community and has demonstrated best-case H-band sensitivity down to 8.2 correlated magnitude. MIRC-X uses single-mode fibers to coherently combine the light from six telescopes simultaneously with an image-plane combination scheme and delivers a visibility precision better than 1%, and closure phase precision better than 1°. MIRC-X aims at (i) imaging protoplanetary disks, (ii) detecting exoplanets with precise astrometry, and (iii) imaging stellar surfaces and starspots at an unprecedented angular resolution in the near-infrared. In this paper, we present the instrument design, installation, operation, and on-sky results, and demonstrate the imaging capability of MIRC-X on the binary system ι Peg. The purpose of this paper is to provide a solid reference for studies based on MIRC-X data and to inspire future instruments in optical interferometry.

Keywords: very long baseline interferometry; michelson interferometry; astronomical detectors; binary stars; astronomy data reduction; astronomical instrumentation; astronomy data acquisition; interferometers; young stellar objects; exoplanet detection methods; starspots; astronomy data analysis
X-Ray Polarized View of the Accretion Geometry in the X-Ray Binary Circinus X-1

Cir X-1 is a neutron star X-ray binary characterized by strong variations in flux during its eccentric ~16.6 day orbit. There are also strong variations in the spectral state, and it has historically shown both atoll and Z state properties. We observed the source with the Imaging X-ray Polarimetry Explorer during two orbital segments, 6 days apart, for a total of 263 ks. We find an X-ray polarization degree in these segments of 1.6% ± 0.3% and 1.4% ± 0.3% at polarization angles of 37° ± 5° and -12° ± 7°, respectively. Thus, we observed a rotation of the polarization angle by 49° ± 8° along the orbit. Because variations of accretion flow, and then of the hardness ratio, are expected during the orbit, we also studied the polarization binned in hardness ratio and found the polarization angle differing by 67° ± 11° between the lowest and highest values of the hardness ratio. We discuss possible interpretations of this result that could indicate a possible misalignment between the symmetry axes of the accretion disk and the Comptonizing region caused by the misalignment of the neutron star's angular momentum with respect to the orbital one.

Keywords: x-ray binary stars; polarimetry; x-ray astronomy; x-ray sources