adsabs/SciX_UAT_keywords huggingface dataset:
SN 2018gj: A Short Plateau Type II Supernova with Persistent Blueshifted Ha Emission

We present an extensive, panchromatic photometric (UV, optical, and near-IR) and low-resolution optical spectroscopic coverage of a Type IIP supernova SN 2018gj that occurred on the outskirts of the host galaxy NGC 6217. From the V-band light curve, we estimate the plateau length to be ~ 70 ± 2 days, placing it among the very few well-sampled short plateau supernovae (SNe). With V-band peak absolute magnitude M V ≤ -17.0 ± 0.1 mag, it falls in the middle of the luminosity distribution of the Type II SNe. The color evolution is typical to other Type II SNe except for an early elbow-like feature in the evolution of V - R color owing to its early transition from the plateau to the nebular phase. Using the expanding photospheric method, we present an independent estimate of the distance to SN 2018gj. We report the spectral evolution to be typical of a Type II SNe. However, we see a persistent blueshift in emission lines until the late nebular phase, not ordinarily observed in Type II SNe. The amount of radioactive nickel (56Ni) yield in the explosion was estimated to be 0.026 ± 0.007 M ⊙. We infer from semianalytical modeling, nebular spectrum, and 1D hydrodynamical modeling that the probable progenitor was a red supergiant with a zero-age-main-sequence mass ≤13 M ⊙. In the simulated hydrodynamical model light curves, reproducing the early optical bolometric light curve required an additional radiation source, which could be the interaction with the proximal circumstellar matter.

Keywords: observational astronomy; type ii supernovae; hydrodynamical simulations; red supergiant stars
Formulating the r-mode Problem for Slowly Rotating Neutron Stars

We revisit the problem of inertial r-modes in stratified stars, drawing on a more precise description of the composition stratification in a mature neutron star. The results highlight issues with the traditional approach to the problem, leading us to rethink the computational strategy for the r-modes of nonbarotropic neutron stars. We outline two strategies for dealing with the problem. For moderate to slowly rotating neutron stars the only viable alternative may be to approach the problem numerically from the outset, while a meaningful slow-rotation calculation can be carried out for the fastest known spinning stars (which may be close to being driven unstable by the emission of gravitational waves). We demonstrate that the latter approach leads to a problem close, but not identical, to that for barotropic inertial modes. We also suggest that these reformulations of the problem likely resolve the long-standing problem of singular behavior associated with a corotation point in rotating relativistic neutron stars. This issue needs to be resolved in order to guide future gravitational-wave searches.

Keywords: neutron stars; astrophysical fluid dynamics; asteroseismology
Implications of High-density, High-temperature Ridges Observed in Some Two-ribbon Flares

Several two-ribbon solar flares observed on the disk, notably including the Bastille flare of 2000 July 14, show an extended ridge of plasma running along the loop tops of the post-reconnection arcade. In that and two more recent examples, the ridge is visible in emission by Fe XXIV at roughly 17 MK, with a high, steadily increasing emission measure suggesting an expanding column of very dense plasma. We find that ridges are consistent with overhead views of long, vertical plasma sheets, such as seen above certain limb flares. Those vertical features show enhanced temperature and density over their entire lengths, making explanations in terms of termination shocks and evaporation collision seem less plausible. We use observations of several ridge events to argue in favor of compression and heating by slow magnetosonic shocks in the reconnection outflow. In this scenario, the ridge is built up as retracting flux piles hot, compressed plasma atop the post-flare arcade. Thanks to the overhead perspective offered by the ridge observations, we are able to measure the reconnection rate and show it to be consistent with the rate of increase in column emission measure across the ridge. This consistency supports the hypothesis that slow shocks and retraction compress the plasma seen in ridges, vertical plasma sheets, and possibly the high-temperature fans through which post-reconnection downflows are observed. Such a unified picture of these diverse features enhances our understanding of the role played by magnetic reconnection in solar flares.

Keywords: solar flares
Detecting Magnetic Fields in Exoplanets with Spectropolarimetry of the Helium Line at 1083 nm

The magnetic fields of the solar system's planets provide valuable insights into their interiors and can have dramatic consequences for the evolution of their atmospheres and interaction with the solar wind. However, we have little direct knowledge of magnetic fields in exoplanets. Here we present a method for detecting magnetic fields in the atmospheres of close-in exoplanets based on spectropolarimetric transit observations at the wavelength of the helium line at 1083 nm. This methodology has been successfully applied for exploring magnetic fields in solar coronal filaments. Strong absorption signatures (transit depths on the order of a few percent) in the 1083 nm line have recently been observed for several close-in exoplanets. We show that in the conditions in these escaping atmospheres, metastable helium atoms should be optically pumped by the starlight and, for field strengths more than a few × 10-4 G, should align with the magnetic field. This results in linearly polarized absorption at 1083 nm that traces the field direction (the Hanle effect), which we explore by both analytic computation and the Hazel numerical code. The linear polarization √{{Q}^{2}+{U}^{2}}/I ranges from ∼10-3 in optimistic cases down to a few × 10-5 for particularly unfavorable cases, with very weak dependence on field strength. The line-of-sight component of the field results in a slight circular polarization (the Zeeman effect), also reaching V/I∼ few × {10}^{-5}({B}_{\parallel }/10 G). We discuss the detectability of these signals with current (SPIRou) and future (Extremely Large Telescope) high-resolution infrared spectropolarimeters, and we briefly comment on possible sources of astrophysical contamination.

Keywords: exoplanet atmospheres; magnetic fields; spectropolarimetry
Sequential Lid Removal in a Triple-decker Chain of CME-producing Solar Eruptions

We investigate the onsets of three consecutive coronal mass ejection (CME) eruptions in 12 hr from a large bipolar active region (AR) observed by the Solar Dynamics Observatory (SDO), the Solar Terrestrial Relations Observatory (STEREO), the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and the Geostationary Operational Environmental Satellite (GOES). Evidently, the AR initially had a "triple-decker" configuration: three flux ropes in a vertical stack above the polarity inversion line (PIL). Upon being bumped by a confined eruption of the middle flux rope, the top flux rope erupts to make the first CME and its accompanying AR-spanning flare arcade rooted in a far apart pair of flare ribbons. The second CME is made by eruption of the previously arrested middle flux rope, which blows open the flare arcade of the first CME and produces a flare arcade rooted in a pair of flare ribbons closer to the PIL than those of the first CME. The third CME is made by blowout eruption of the bottom flux rope, which blows open the second flare arcade and makes its own flare arcade and pair of flare ribbons. Flux cancellation observed at the PIL likely triggers the initial confined eruption of the middle flux rope. That confined eruption evidently triggers the first CME eruption. The lid-removal mechanism instigated by the first CME eruption plausibly triggers the second CME eruption. Further lid removal by the second CME eruption plausibly triggers the final CME eruption.

Keywords: solar flares; solar activity; solar magnetic fields; the sun; solar coronal mass ejections; solar filament eruptions
The Accretion History of EX Lup: A Century of Bursts, Outbursts, and Quiescence

EX Lup is the archetype for the class of young stars that undergoes repeated accretion outbursts of ~5 mag at optical wavelengths that last for months. Despite extensive monitoring that dates back 130 yr, the accretion history of EX Lup remains mostly qualitative and has large uncertainties. We assess historical accretion rates of EX Lup by applying correlations between optical brightness and accretion, developed on multi-band magnitude photometry of the ~2 mag optical burst in 2022. Two distinct classes of bursts occur: major outbursts (ΔV ~ 5 mag) have year-long durations, are rare, reach accretion rates of ${\dot{M}}_{\mathrm{acc}}\sim {10}^{-7}$ M ⊙ yr-1 at peak, and have a total accreted mass of around 0.1 Earth mass. The characteristic bursts (ΔV ~ 2 mag) have durations of ~2-3 months, are more common, reach accretion rates of ${\dot{M}}_{\mathrm{acc}}\sim {10}^{-8}$ M ⊙ yr-1 at peak, and have a total accreted mass of around 10-3 Earth masses. The distribution of total accreted mass in the full set of bursts is poorly described by a power law, which suggests different driving causes behind the major outburst and characteristic bursts. The total mass accreted during two classes of bursts is around 2 times the masses accreted during quiescence. Our analysis of the light curves reveals a color-dependent time lag in the 2022 post-burst light curve, attributed to the presence of both hot and cool spots on the stellar surface.

Keywords: eruptive variable stars; stellar accretion; classical t tauri stars; light curves
Primordial Black Holes in Scalar Field Inflation Coupled to the Gauss–Bonnet Term with Fractional Power-law Potentials

In this study, we investigate the formation of primordial black holes (PBHs) in a scalar field inflationary model coupled to the Gauss–Bonnet term with fractional power-law potentials. The coupling function enhances the curvature perturbations, then results in the generation of PBHs and detectable secondary gravitational waves (GWs). We identify three separate sets of parameters for the potential functions of the form ϕ 1/3, ϕ 2/5, and ϕ 2/3. By adjusting the model parameters, we decelerate the inflaton during the ultra-slow-roll phase and enhance curvature perturbations. Our calculations predict the formation of PBHs with masses of ${ \mathcal O }(10){M}_{\odot }$ , which are compatible with LIGO-Virgo observational data. Additionally, we find PBHs with masses around ${ \mathcal O }({10}^{-6}){M}_{\odot }$ and ${ \mathcal O }({10}^{-5}){M}_{\odot }$ , which can explain ultra-short-timescale microlensing events in OGLE data. Furthermore, our proposed mechanism could lead to the formation of PBHs in mass scales around ${ \mathcal O }({10}^{-14}){M}_{\odot }$ and ${ \mathcal O }({10}^{-13}){M}_{\odot }$ , contributing to approximately 99% of the dark matter in the Universe. We also study the production of secondary GWs in our model. In all cases of the model, the density parameter of secondary GWs ${{\rm{\Omega }}}_{{\mathrm{GW}}_{0}}$ exhibits peaks that intersect the sensitivity curves of GW detectors, providing a means to verify our findings using data of these detectors. Our numerical results demonstrate a power-law behavior for the spectra of ${{\rm{\Omega }}}_{{\mathrm{GW}}_{0}}$ with respect to frequency, given by ${{\rm{\Omega }}}_{{\mathrm{GW}}_{0}}{(f)\sim (f/{f}_{c})}^{n}$ . Additionally, in the infrared regime where f ≪ f c , the power index takes a log-dependent form, specifically $n=3-2/\mathrm{ln}({f}_{c}/f)$ .

Keywords: cosmic inflation; primordial black holes; gravitational waves
Data-constrained Magnetohydrodynamic Simulation of an Intermediate Solar Filament Eruption

Solar eruptive activities could occur in weak magnetic field environments and over large spatial scales, which are especially relevant to eruptions involving intermediate or quiescent solar filaments. To handle the large scales, we implement and apply a flux rope embedding method using regularized Biot-Savart laws in the spherical coordinate system. Combined with a potential field source surface model and a magneto-frictional method, a nonlinear force-free field comprising a flux rope embedded in a potential field is constructed. Using the combined nonlinear force-free field as the initial condition, we then perform a zero-β data-constrained magnetohydrodynamic (MHD) simulation for an M8.7 flare at 03:38 UT on 2012 January 23. The MHD model reproduces the eruption process, flare ribbon evolution (represented by the quasi-separatrix layer evolution), and kinematics of the flux rope. This approach could potentially model global-scale eruptions from weak field regions.

Keywords: solar prominences; solar magnetic fields; magnetohydrodynamics; solar corona
Re-evaluation of the Effect of Brown Dwarfs' Viewing Geometry using a Bayesian Framework

A brown dwarf's viewing geometry can affect measurements of variability amplitudes and emergent spectra. Historically, this angle was derived by combining rotation periods and $v\,\sin \,i$ assuming that they are statistically independent. Recently, Masuda & Winn showed that this assumption could lead to biased results. The same study presented a solution that properly incorporates the correlation between the equatorial and projected rotational velocities. We use this Bayesian framework to re-calculate the viewing angles of 18 variable brown dwarfs with known $v\,\sin \,i$ values and photometric rotation periods. We find that the viewing angle distributions change most significantly in equator-on cases. We re-derive the correlation coefficients between the viewing angle, variability amplitude, and color anomaly. These results confirm and refine these correlations and highlight the importance of proper posterior sampling to determine the inclination angle of the spin axis.

Keywords: brown dwarfs; stellar rotation; bayesian statistics; inclination
Miranda's Thick Regolith Indicates a Major Mantling Event from an Unknown Source

We investigated "muted" craters and scarps across Miranda's cratered terrain. The morphologies of the muted craters are most consistent with modification by regolith deposition instead of erosion or viscous relaxation. We used three techniques to estimate regolith thickness. (1) Analysis of muted crater depth-Diameter (d-D) ratios near the South Polar Terrain Chasma indicates that regolith mantling their floors ranges from 0.3 to 1.2 km thick. Because older craters may have collected more regolith than younger craters, the true thickness may be similar to the highest estimate. (2) Analysis of crater size-frequency distributions across the cratered terrain indicates a thickness of 1.0 ± 0.2 km. (3) Analysis of a central mound within Alonso Crater indicates a thickness of ${1.4}_{-0.4}^{+0.3}$ km near Verona Rupes and may represent an upper limit. These results indicate that Miranda has one of the thickest regoliths in the solar system, which has important implications for Miranda's interior thermal properties. Regolith appears to mantle some scarps within Arden but not Elsinore or Inverness, indicating that Arden may be the oldest corona, contrary to previous relative age estimates. In this scenario, the mantling event was ongoing during Arden's formation but before Elsinore or Inverness formed. We propose three possible sources for Miranda's thick regolith: (1) giant impact ejecta, (2) plume deposits, and (3) Uranian ring deposits. We favor the ring deposit hypothesis, which is consistent with the regolith's large spatial extent, substantial thickness, and Miranda's slightly spectrally blue color. Follow-up studies that rigorously investigate these scenarios are required.

Keywords: uranian satellites; planetary science; regolith; craters; tectonics
Searching for Double-line Spectroscopic Binaries in the LAMOST Medium-resolution Spectroscopic Survey with Deep Learning

Double-line spectroscopic binaries (SB2s) are a vital class of spectroscopic binaries for studying star formation and evolution. Searching for SB2s has been a hot topic in astronomy. Although considerable efforts have been made with fruitful outcomes, limitations in automation and accuracy still persist. In this study, we developed a convolutional neural network model to search for SB2 candidates in LAMOST medium-resolution survey (MRS) data release (DR) 9 v1.0 by detecting double peaks in the cross-correlation function (CCF). We first generated a large number of spectra of single stars and binaries using the iSpec spectral synthesis software. The CCFs of these synthesized spectra were then calculated to form our training set. To efficiently detect the peaks of the CCFs, we applied a Softmax function-based noise reduction method. After testing and validation, the model achieved an accuracy of 97.76% in the testing set and was validated for more than 90% of the sample in several published SB2 catalogs. Finally, by applying the model to examine approximately 1.59 million LAMOST-MRS DR9 spectra, we identified 728 candidate SB2s, including 281 newly discovered ones.

Keywords: convolutional neural networks; spectroscopic binary stars
Estimates of the Early Electromagnetic Emission from Compact Binary Mergers

Compact binary mergers that involve at least one neutron star, either binary neutron star or black hole-neutron star coalescences, are thought to be the potential sources of electromagnetic emission due to the material ejected during the merger or those left outside the central object after the merger. Since the intensity of these electromagnetic transients decays rapidly with time, one should pay more attention to early emissions from such events, which are useful in revealing the nature of these mergers. In this work, we study the early emission of kilonovae, short gamma-ray bursts (GRBs), and cocoons that could be produced in those mergers. We estimate their luminosities and timescales as functions of the chirp mass, which is the most readily constrained parameter from the gravitational wave detections of these events. We focus on the range of chirp mass as 1.3-2.7 M⊙, which is compatible with one of the merging components being a so-called "mass gap" black hole. We show that the electromagnetic observation of these transients could be used to distinguish the types of the mergers when the detected chirp mass falls in the range of 1.5-1.7 M⊙. Applying our analysis to the subthreshold GRB GBM-190816, we found that for this particular event the effective spin should be larger than 0.6 and the mass of the heavier object might be larger than 5.5 M⊙ for the phenomenological Steiner-Fischer-Hempel equation of state.

Keywords: stellar mass black holes; neutron stars; gamma-ray bursts; gravitational wave sources; optical bursts; x-ray bursts
Mini-EUSO Mission to Study Earth UV Emissions on board the ISS

Mini-EUSO is a telescope observing the Earth in the ultraviolet band from the International Space Station. It is a part of the JEM-EUSO program, paving the way to future larger missions, such as K-EUSO and POEMMA, devoted primarily to the observation of ultrahigh-energy cosmic rays from space. Mini-EUSO is capable of observing extensive air showers generated by ultrahigh-energy cosmic rays with an energy above 1021 eV and to detect artificial showers generated with lasers from the ground. Other main scientific objectives of the mission are the search for nuclearites and strange quark matter, the study of atmospheric phenomena such as transient luminous events, meteors, and meteoroids, the observation of sea bioluminescence and of artificial satellites and man-made space debris. Mini-EUSO will map the nighttime Earth in the UV range (290-430 nm), with a spatial resolution of about 6.3 km and a temporal resolution of 2.5 μs, through a nadir-facing UV-transparent window in the Russian Zvezda module. The instrument, launched on 2019 August 22, from the Baikonur Cosmodrome, is based on an optical system employing two Fresnel lenses and a focal surface composed of 36 multianode photomultiplier tubes, 64 channels each, for a total of 2304 channels with single-photon counting sensitivity and an overall field of view of 44°. Mini-EUSO also contains two ancillary cameras to complement measurements in the near-infrared and visible ranges. In this paper, we describe the detector and present the various phenomena observed in the first months of operations.

Keywords: ultra-high-energy cosmic radiation; meteors; ultraviolet telescopes; lightning; earth atmosphere; earth ionosphere
Detecting and Characterizing Young Quasars. I. Systemic Redshifts and Proximity Zone Measurements

In a multiwavelength survey of 13 quasars at 5.8 ≲ z ≲ 6.5, which were preselected to be potentially young, we find five objects with extremely small proximity zone sizes that may imply UV-luminous quasar lifetimes of ≲100,000 yr. Proximity zones are regions of enhanced transmitted flux in the vicinity of quasars that are sensitive to the quasars' lifetimes because the intergalactic gas has a finite response time to their radiation. We combine submillimeter observations from the Atacama Large Millimetre Array and the NOrthern Extended Millimeter Array, as well as deep optical and near-infrared spectra from the medium-resolution spectrograph on the Very Large Telescope and on the Keck telescopes, in order to identify and characterize these new young quasars, which provide valuable clues about the accretion behavior of supermassive black holes in the early universe and pose challenges on current black hole formation models to explain the rapid formation of billion-solar-mass black holes. We measure the quasars' systemic redshifts, black hole masses, Eddington ratios, emission-line luminosities, and star formation rates of their host galaxies. Combined with previous results, we estimate the fraction of young objects within the high-redshift quasar population at large to be 5% ≲ fyoung ≲ 10%. One of the young objects, PSO J158-14, shows a very bright dust continuum flux (Fcont = 3.46 ± 0.02 mJy), indicating a highly starbursting host galaxy with a star formation rate of approximately 1420 M⊙ yr-1.

Keywords: quasars; supermassive black holes; reionization; intergalactic medium; quasar absorption line spectroscopy
Spatial Distribution of Intracluster Light versus Dark Matter in Horizon Run 5

One intriguing approach for studying the dynamical evolution of galaxy clusters is to compare the spatial distributions among various components such as dark matter, member galaxies, gas, and intracluster light (ICL). Utilizing the recently introduced weighted overlap coefficient (WOC), we analyze the spatial distributions of components within 174 galaxy clusters (M tot > 5 × 1013 M ⊙, z = 0.625) at varying dynamical states in the cosmological hydrodynamical simulation Horizon Run 5. We observe that the distributions of gas and the combination of ICL with the brightest cluster galaxy (BCG) closely resembles the dark matter distribution, particularly in more relaxed clusters, characterized by the half-mass epoch. The similarity in spatial distribution between dark matter and BCG+ICL mimics the changes in the dynamical state of clusters during a major merger. Notably, at redshifts >1, BCG+ICL traced dark matter more accurately than the gas. Additionally, we examined the one-dimensional radial profiles of each component, which show that the BCG+ICL is a sensitive component revealing the dynamical state of clusters. We propose a new method that can approximately recover the dark matter profile by scaling the BCG+ICL radial profile. Furthermore, we find a recipe for tracing dark matter in unrelaxed clusters by including the most massive satellite galaxies together with the BCG+ICL distribution. Combining the BCG+ICL and the gas distribution enhances the dark matter tracing ability. Our results imply that the BCG+ICL distribution is an effective tracer for the dark matter distribution, and the similarity of the spatial distribution may be a useful probe of the dynamical state of a cluster.

Keywords: galaxy clusters; galactic and extragalactic astronomy; dark matter; hydrodynamical simulations