adsabs/SciX_UAT_keywords huggingface dataset:
A Census of the Low Accretors. II. Accretion Properties

Much is known about the processes driving accretion from protoplanetary disks onto low-mass pre-main-sequence stars (T Tauri stars). Nevertheless, it is unclear how accretion stops. To determine the accretion properties and their relation to stellar properties and gain insight into the last stages of accretion, we present a detailed analysis of 24 low and possible accretors, previously identified using the He I λ10830 line. We model moderate-resolution Hα profiles of these stars using magnetospheric accretion flow models that account for the chromospheric contribution at the line center. Based on parameters derived from the fits of 20 stars that can be reproduced with the models, we find a power-law relation between the disk truncation radius and the mass accretion rate consistent with predictions from theory and simulations. Comparing the corotation and truncation radii, we find that most of our targets are accreting in the unstable regime and rule out the propeller as the main process stopping accretion. For the truncation radius to be the same as the magnetic radius, the dipole magnetic field and/or the efficiency parameter ξ need to be smaller than previously determined, suggesting that higher-order fields dominate in low accretion rates. Lastly, we determine that the lowest accretion rates that can be detected by Hα line modeling are (1-3) × 10-11 M ☉ yr-1 for M3 stars and (3-5) × 10-11 M ☉ yr-1 for K5 stars. These limits are lower than the observed accretion rates in our sample, suggesting that we have reached a physical lower limit. This limit, $\dot{M}\sim {10}^{-10}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ , is consistent with EUV-dominated photoevaporation.

Keywords: stellar accretion; h i line emission; protoplanetary disks; t tauri stars
The Photospheric Footpoints of Solar Coronal Hole Jets

We study the photospheric footpoints of a set of 35 coronal jets in a coronal hole as observed by Hinode/EIS. We use SDO/AIA data to coalign the spectroscopic EIS data with SDO/HMI line-of-sight magnetograms and calculate the plane-of-sky flow field using local correlation tracking (LCT) on SDO/HMI white light images. The jets are put into categories according to the changes observed in the photospheric magnetic flux at the footpoints of the coronal bright point where the jets originate: flux cancellation, complex flux changes (flux appearance/emergence and cancellation), and no flux changes. We also present three jets in detail. Observed magnetic flux evolution, LCT flow field structure and location of the jet footpoints at supergranular boundaries do not support the flux emergence scenario used in most jet simulations and are also not consistent with a rotational photospheric driver. Detailed numerical jet simulations using our observed photospheric features, in particular converging flows and flux cancellation do not currently exist, although such models would provide a realistic eruptive event scenario.

Keywords: solar magnetic fields; solar physics; solar coronal holes; solar photosphere; eruptive phenomena; solar ultraviolet emission; solar magnetic reconnection; solar magnetic bright points; solar coronal transients; solar atmospheric motions; solar corona
A Swift X-Ray View of the SMS4 Sample-X-Ray Properties of 31 Quasars and Radio Galaxies

We present Neil Gehrels Swift Observatory (hereafter Swift) observations of 31 sources from the SMS4 catalog, a sample of 137 bright radio sources originally designed to extend the well-studied 3CRR radio sample to the Southern Hemisphere. All these sources had no Chandra or XMM-Newton observations: 24 of these were observed with Swift through a dedicated proposal in 2015, and data for the remaining seven were retrieved from the Swift archive. The reduction and analysis of data collected by the Swift X-ray Telescope (XRT) led to 20 detections in the 0.3-10 keV band. We provide details of the X-ray emission in this band for these 20 detections, as well as upper limits for the remaining 11 SMS4 sources. When statistics allowed, we investigated the extent of the X-ray emission and the hardness ratio, and we carried out a spectral analysis. We matched the 20 X-ray-detected sources with infrared (AllWISE, CatWISE2020) and optical (GSC 2.3.2, DES DR2) catalogs to establish associations with infrared and optical sources and compared our results with previously published counterparts in these bands. Requiring a detection in both the infrared and optical bands to establish a candidate counterpart for our X-ray detections, we obtain reliable counterparts for 18 sources, while the remaining two sources need further investigation to establish firm identifications. In the infrared, we confirm 12 previously established counterparts and provide six new candidates. In the optical, we find agreement with 13 previously established counterparts, while we provide an alternative candidate for five SMS4 sources. We find that ~35% of all the SMS4 sources lie below the lower limit of 10.9 Jy for the flux density at 178 MHz established for the 3CRR sample, at variance with the values extrapolated using measurements at higher frequencies. Therefore, for future studies where flux-density-limited samples are needed, we encourage the use of the more recent G4Jy sample. We present the list of 56 SMS4 sources that in 2022 March remain to be observed in the X-rays with narrow-field instruments, to highlight interesting sources and organize further observational campaigns to achieve complete X-ray coverage for the whole SMS4 in the forthcoming years.

Keywords: active galaxies; extragalactic radio sources; x-ray astronomy
The Importance of Optical Wavelength Data on Atmospheric Retrievals of Exoplanet Transmission Spectra

Exoplanet transmission spectra provide rich information about the chemical composition, clouds, and temperature structure of exoplanet atmospheres. Most exoplanet transmission spectra only span infrared wavelengths (≳1 μm), which can preclude crucial atmospheric information from shorter wavelengths. Here, we explore how retrieved atmospheric parameters from exoplanet transmission spectra change with the addition of optical data. From a sample of 14 giant planets with transit spectra from 0.3–4.5 μm, primarily from the Hubble and Spitzer space telescopes, we apply a free chemistry retrieval to planetary spectra for wavelength ranges of 0.3–4.5 μm, 0.6–4.5 μm, and 1.1–4.5 μm. We analyze the posterior distributions of these retrievals and perform an information content analysis, finding wavelengths below 0.6 μm are necessary to constrain cloud scattering slope parameters ( $\mathrm{log}a$ and γ) and alkali species Na and K. There is limited improvement in the constraints on the remaining atmospheric parameters. Across the population, we find that limb temperatures are retrieved colder than planetary equilibrium temperatures but have an overall good agreement with Global Circulation Models. As the JWST extends to a minimum wavelength of 0.6 μm, we demonstrate that exploration into complementing JWST observations with optical HST data is important to further our understanding of aerosol properties and alkali abundances in exoplanet atmospheres.

Keywords: exoplanet atmospheres; transmission spectroscopy; hubble space telescope
Indirect Evidence for Dark Matter Density Spikes around Stellar-mass Black Holes

It has been suggested for a long time that dark matter would form a density spike around a black hole. However, no promising evidence has been observed so far to verify this theoretical suggestion. Here, we report the existence of a dark matter density spike around each of the two nearby stellar-mass black holes (A0620-00 and XTE J1118+480). The dynamical friction between dark matter and the companion stars can satisfactorily explain the abnormally fast orbital decays in the two binaries. The calculated spike index for A0620-00 and XTE J1118+480 is $\gamma ={1.71}_{-0.02}^{+0.01}$ and $\gamma ={1.85}_{-0.04}^{+0.04}$ , respectively, which are close to the lower regime predicted by the stellar heating model. It may provide possible indirect evidence for the existence of dark matter density spikes around stellar-mass black holes. We anticipate that analyzing observational data of nearby black hole X-ray binaries would be a new way to reveal the nature of dark matter.

Keywords: dark matter distribution; black holes
A Broad Grid of 2D Kilonova Emission Models

Depending upon the properties of their compact remnants and the physics included in the models, simulations of neutron star mergers can produce a broad range of ejecta properties. The characteristics of this ejecta, in turn, define the kilonova emission. To explore the effect of ejecta properties, we present a grid of two-component 2D axisymmetric kilonova simulations that vary mass, velocity, morphology, and composition. The masses and velocities of each component vary, respectively, from 0.001 to 0.1 M⊙ and 0.05 to 0.3 c, covering much of the range of results from the neutron star merger literature. The set of 900 models is constrained to have a toroidal low electron fraction (Ye) ejecta with a robust r-process composition and either a spherical or lobed high-Ye ejecta with two possible compositions. We simulate these models with the Monte Carlo radiative transfer code SuperNu using a full suite of lanthanide and fourth-row element opacities. We examine the trends of these models with parameter variation, show how they can be used with statistical tools, and compare the model light curves and spectra to those of AT2017gfo, the electromagnetic counterpart of GW170817.

Keywords: transient sources; infrared sources; radiative transfer simulations; neutron stars; r-process
Hidden Hearts of Neutrino Active Galaxies

Recent multimessenger studies have provided evidence for high-energy neutrino sources that are opaque to GeV-TeV gamma rays. We present model-independent studies on the connection between neutrinos and gamma rays in the active galaxy NGC 1068, and find that the neutrinos most likely come from regions within ~30-100 Schwarzschild radii. This is especially the case if neutrinos are produced via the photomeson production process, although the constraints could be alleviated if hadronuclear interactions are dominant. We consider the most favorable neutrino production regions, and discuss coronae, jets, winds, and their interactions with dense material. The results strengthen the importance of understanding dissipation mechanisms near the coronal region and the outflow base. There could be a connection between active galactic nuclei with near-Eddington accretion and tidal disruptions events, in that neutrinos are produced in the obscured vicinity of supermassive black holes.

Keywords: neutrino astronomy; active galactic nuclei; gamma-ray astronomy; particle astrophysics
Equator to Pole Solar Chromospheric Differential Rotation Using Ca-K Features Derived from Kodaikanal Data

Differential rotation is one of the basic characteristics of the Sun, and it plays an important role in generating the magnetic fields and its activities. We investigated rotation rate using chromospheric features such as plages, enhanced network (EN), active network (AN), and quiet network (QN) separately (for the first time). The digitized Ca-K images from Kodaikanal Observatory for 1907–1996 are used to study rotation over 0°–80° latitudes at an interval of 10°. We find that plages and all types of networks exhibit the differential rotation of the chromosphere. Furthermore, the rotation rate shows a decreasing pattern as one move from the equator to the higher polar latitudes for all the features used in the study. At the equator the rotation rate (rotation period) is obtained to be ∼13.98° day‑1 (25.74 days), ∼13.91° day‑1 (25.88 days), ∼13.99° day‑1 (25.74 days), and ∼14.11° day‑1 (25.51 days) for plage, EN, AN, and QN areas, respectively. By analyzing how the area of chromospheric features varies over time, we can effectively map the Sun's rotation rate at all latitudes, including the polar regions. Interestingly, both plages and small-scale networks exhibit a similar differential rotation rate. This suggests these features likely rooted at the same layer below the visible surface of the Sun. Therefore, the long-term Ca-K data is very useful for studying the solar rotation rate at all latitudes including the polar regions.

Keywords: solar chromosphere; plages; solar rotation; solar differential rotation
Europa Clipper Preparatory Photometry to Constrain Surface Properties

We infer the surface reflectance properties of Europa using multispectral data sets available from previous missions. We use 21 full-disk images of Europa from Voyager's Imaging Science System, Galileo's Solid State Imaging, and New Horizons' Long Range Reconnaissance Imager at differing observation geometries (10°-128° (phase angle)) to compute disk-integrated surface-scattering properties over various geologic units. The derived empirical photometric models will serve the practical goals of data acquisition, aid in the calculation of instrument integration times, and facilitate quick-look data products for images acquired by Europa Clipper and other future missions to Europa. We use the Minneart and Lommel-Seeliger plus Lambert reflectance models to constrain the photometric parameters of Europa's surface. We find that the surface albedo parameter, B0, in the Minneart function gradually decreases with increasing phase angles. We also note that the photometric properties of Europa (geometric albedo at 0.47 μm is 0.72 on the leading side and 0.62 on the trailing side) require a significant "Lambert" term (A < 1) in the Lommel-Seeliger plus Lambert reflectance model. We also observe that the photometric parameters are not highly dependent on the geologic terrain type despite their visibly different albedos.

Keywords: europa; planetary surfaces; photometry
Differential Rotation of the Chromosphere in the He I Absorption Line

Differential rotation is the basis of the solar dynamo theory. Synoptic maps of He I intensity from Carrington rotations 2032-2135 are utilized to investigate the differential rotation of the solar chromosphere in the He I absorption line. The chromosphere is surprisingly found to rotate faster than the photosphere below it. The anomalous heating of the chromosphere and corona has been a big problem in modern astronomy. It is speculated that the small-scale magnetic elements with magnetic flux in the range of (2.9-32.0) × 1018 Mx, which are anchored in the leptocline, heat the quiet chromosphere to present the anomalous temperature increase, causing it to rotate at the same rate as the leptocline. The differential of rotation rate in the chromosphere is found to be strengthened by strong magnetic fields, but in stark contrast, at the photosphere strong magnetic fields repress the differential of rotation rate. A plausible explanation is given for these findings.

Keywords: solar rotation; solar chromosphere; solar activity
Imaging a Large Coronal Loop Using Type U Solar Radio Burst Interferometry

Solar radio U-bursts are generated by electron beams traveling along closed magnetic loops in the solar corona. Low-frequency (<100 MHz) U-bursts serve as powerful diagnostic tools for studying large-sized coronal loops that extend into the middle corona. However, the positive frequency drift component (descending leg) of U-bursts has received less attention in previous studies, as the descending radio flux is weak. In this study, we utilized LOFAR interferometric solar imaging data from a U-burst that has a significant descending leg component, observed between 10 and 90 MHz on 2020 June 5th. By analyzing the radio source centroid positions, we determined the beam velocities and physical parameters of a large coronal magnetic loop that reached just about 1.3 R ⊙ in altitude. At this altitude, we found the plasma temperature to be around 1.1 MK, the plasma pressure around 0.20 mdyn, cm‑2, and the minimum magnetic field strength around 0.07 G. The similarity in physical properties determined from the image suggests a symmetric loop. The average electron beam velocity on the ascending leg was found to be 0.21c, while it was 0.14c on the descending leg. This apparent deceleration is attributed to a decrease in the range of electron energies that resonate with Langmuir waves, likely due to the positive background plasma density gradient along the downward loop leg.

Keywords: solar corona; solar coronal loops; solar coronal radio emission; solar particle emission; solar energetic particles
Assessment of Variability of the TEC in the Equatorial Anomaly Region with a Focus over Africa Using Rz and F10.7 as Input Drivers

This paper mainly intends to address the assessment of altitudinal variability of the vertical total electron content (VTEC) extracted from the Global Positioning System (GPS), the new versions of the International Reference Ionosphere Extended to the Plasmasphere (IRI-Plas 2017), and a quick-run ionospheric electron density (NeQuick 2) model in the equatorial anomaly region with a focus over Africa. This is manipulated employing the daily sunspot number (Rz) and 10.7 cm solar radio flux (F10.7) indices as the driver for the models during 2013-2016. The results show that the GPS-derived VTEC values are generally smaller than the modeled VTEC (IRI-Plas 2017 and NeQuick 2 VTEC) values, especially while utilizing the models with the Rz index. The modeled VTEC values are closer to the GPS VTEC values while using the models with the F10.7 index than Rz. The VTEC values obtained while using both models with the F10.7 index tend to increase while traversing from the high to the low solar activity years (especially in the March equinox and December solstice). The top-side ionospheric and plasmaspheric layers contribute the highest and lowest values to the total VTEC. Hence, the signal propagation through the ionosphere is largely affected when the signal crosses the top-side layer. Unlike other layers, due to the limited impact of the EUV on the ionization of neutral particles in the plasmasphere, the VTEC in the plasmaspheric layer (ECpl) shows smooth pattern with similar hourly values. Moreover, the IRI-Plas 2017 model does not effectively respond to the geomagnetic storm time variability of the VTEC with altitude.

Keywords: atmospheric variability; atmospheric composition; solar x-ray emission; solar electromagnetic emission; solar extreme ultraviolet emission; solar gamma-ray emission; solar radio emission; solar ultraviolet emission; solar physics
Semi-analytical Expression of G-mode Period Spacing: The Case of Brunt-Väisälä Frequency with Not a Jump but a Ramp

To decipher complex patterns of gravity-mode period spacings observed for intermediate-mass main-sequence stars is an important step toward a better understanding of the structure and dynamics in the deep radiative region of the stars. In this study, we apply the JWKB approximation to derive a semi-analytical expression of the g-mode period spacing pattern, for which the gradient in the Brunt-Väisälä frequency is taken into account. The formulation includes the term P -1 B ⋆, where P and B ⋆ represent the g-mode period and degree of the structural variation, the latter of which especially is related to the steepness of the gradient of the Brunt-Väisälä frequency. Tests with one-dimensional stellar models show that the semi-analytical expression derived in this study is useful for inferring the degree of the structural variation B ⋆ with an accuracy of ~10 % in the case of relatively massive intermediate-mass models with the mass M larger than 3 M ⊙. The newly formulated expression will possibly allow us to put further constraints on, e.g., mixing processes inside intermediate-mass main-sequence g-mode pulsators such as β Cep, SPB, and γ Dor stars that have been principal targets in asteroseismology.

Keywords: stellar evolution; stellar cores; stellar interiors; stellar oscillations; asteroseismology
Eruption of Solar Magnetic Flux Ropes Caused by Flux Feeding

Large-scale solar eruptions are believed to have a magnetic flux rope as the core structure. However, it remains elusive as to how the flux rope builds up and what triggers its eruption. Recent observations found that a prominence erupted following multiple episodes of "flux feeding." During each episode, a chromospheric fibril rose and merged with the prominence lying above. In this Letter, we carried out 2.5-dimensional magnetohydrodynamic (MHD) numerical simulations to investigate whether the flux-feeding mechanism can explain such an eruption. The simulations demonstrate that the discrete emergence of small flux ropes can initiate eruptions by feeding axial flux into the preexistent flux rope until its total axial flux reaches a critical value. The onset of the eruption is dominated by an ideal MHD process. Our simulation results corroborate that the flux feeding is a viable mechanism to cause the eruption of solar magnetic flux ropes.

Keywords: solar prominences; solar filaments; solar flares; solar magnetic flux emergence; solar coronal mass ejections; solar filament eruptions
Molecules in the Carbon-rich Protoplanetary Nebula CRL 2688

We present observations of the carbon-rich protoplanetary nebula CRL 2688 made with the Institut de Radioastronomie Millimétrique 30 m telescope in the 3 and 2 mm bands. In total, 196 transition lines belonging to 38 molecular species and isotopologues are detected, among which, to the best of our knowledge, 153 transition lines and 13 species are the first reported for this object. Additionally, in order to contribute to future research, we have collected observational data on the molecular lines of CRL 2688 from the literature and compiled them into a single unified catalog. We find that the molecular abundance of CRL 2688 cannot be explained by the standard model of a circumstellar envelope. The implications of metal-bearing molecules on circumstellar chemistry are discussed.

Keywords: molecular gas; molecular spectroscopy; circumstellar matter; protoplanetary nebulae; circumstellar envelopes; circumstellar gas; circumstellar shells
First Detection of CO2 Emission in a Centaur: JWST NIRSpec Observations of 39P/Oterma

Centaurs are minor solar system bodies with orbits transitioning between those of trans-Neptunian scattered disk objects and Jupiter-family comets (JFCs). 39P/Oterma (39P) is a frequently active centaur that has recently held both centaur and JFC classifications and was observed with the JWST NIRSpec instrument on 2022 July 27 UTC while it was 5.82 au from the Sun. For the first time, CO2 gas emission was detected in a centaur, with a production rate of ${Q}_{{\mathrm{CO}}_{2}}$ = (5.96 ± 0.80) × 1023 molecules s-1. This is the lowest detection of CO2 of any centaur or comet. CO and H2O were not detected down to constraining upper limits. Derived mixing ratios of Q CO/Q ${}_{{\mathrm{CO}}_{2}}$ ≤ 2.03 and ${Q}_{{\mathrm{CO}}_{2}}$ /Q ${}_{{{\rm{H}}}_{2}{\rm{O}}}$ ≥ 0.60 are consistent with CO2 and/or CO outgassing playing large roles in driving the activity, but not water, and show a significant difference between the coma abundances of 29P/Schwassmann-Wachmann 1, another centaur at a similar heliocentric distance, which may be explained by thermal processing of 39P's surface during its previous JFC orbit. To help contextualize the JWST data we also acquired visible CCD imaging data on two dates in 2022 July (Gemini-North) and September (Lowell Discovery Telescope). Image analysis and photometry based on these data are consistent with a point-source detection and an estimated effective nucleus radius of 39P in the range of R nuc = 2.21-2.49 km.

Keywords: centaur group; comets; james webb space telescope; infrared observatories; carbon dioxide