adsabs/SciX_UAT_keywords huggingface dataset:
The Jets and the Neutron Star Kick Velocity of the Supernova Remnant CTB 1

We identify jet-shaped morphology in the core-collapse supernova remnant (SNR) CTB 1 that includes two opposite structural features. We identify these as the imprints of a pair of jets that were among the last jets to explode the massive stellar progenitor of CTB 1. We find the projected angle between the jets' axis and the direction of the pulsar velocity, which is the neutron star natal kick, to be α = 78°. We tentatively identify possible signatures of a second pair of opposite jets along a different direction. If this identification holds, SNR CTB 1 has a point-symmetric structure. The morphology and large angle of the jets' axis to kick velocity are expected in the jittering jets explosion mechanism of core-collapse supernovae.

Keywords: supernova remnants; stellar jets; core-collapse supernovae; neutron stars
Data-constrained MHD Simulation of a Multi-ribbon Flare Corresponding to a Successful and a Confined Eruption

The formation and eruption mechanisms of multi-ribbon flares are extremely complicated, especially when the flare is associated with homologous eruptions in the same region. In this paper, we investigate such an event, corresponding to a successful eruption and a confined eruption. This is an M7.1 flare, starting at 12:33 UT on 2011 September 24 in active region NOAA 11302. We obtain the coronal magnetic configuration for this region, using a nonlinear force-free field extrapolation based on the photospheric magnetogram at 12:00 UT. Taking this as the initial condition, we perform a data-constrained MHD simulation to study the evolution of the magnetic topology for this region. We analyze the magnetic null points and the 3D squashing degree for this region, indicating the existence of three flux ropes and two spine-fan structures. The model reproduces the rising processes of the two flux ropes, which form two homologous eruptions consistent with the observations as shown in 94 Å: a large-scale successful eruption that is followed by a small-scale confined eruption. By analyzing the magnetic configuration, the Lorentz force, and the decay index, we find that the torus instability plays an important role in driving the successful eruption of the large flux rope. The magnetic reconnection above the medium flux rope changes the direction of the overlying magnetic field, which provides a downward component of the Lorentz force to confine the eruption of the medium flux rope.

Keywords: solar flares; magnetic fields; solar magnetic reconnection; magnetohydrodynamical simulations
Multi-wave band Synchrotron Polarization of Gamma-Ray Burst Afterglows

Multi-wave band synchrotron linear polarization of gamma-ray burst (GRB) afterglows is studied under the assumption of an anisotropic turbulent magnetic field with a coherence length of the plasma skin-depth scale in the downstream of forward shocks. We find that for typical GRBs, in comparison to optical polarization, the degree of radio polarization shows a similar temporal evolution but a significantly smaller peak value. This results from differences in observed intensity image shapes between the radio and optical bands. We also show that the degree of the polarization spectrum undergoes a gradual variation from the low- to the high-polarization regime above the intensity of the spectral peak frequency, and that the difference in polarization angles in the two regimes is zero or 90°. Thus, simultaneous multi-wave band polarimetric observations of GRB afterglows would be a new determinative test of the plasma-scale magnetic field model. We also discuss theoretical implications from the recent detection of radio linear polarization in GRB 171205A with the Atacama Large Millimeter/submillimeter Array and other models of magnetic field configuration.

Keywords: astrophysical processes; jets; high energy astrophysics; particle astrophysics
Formation of Coronal Mass Ejection and Posteruption Flow of Solar Wind on 2010 August 18 Event

The state of the space environment plays a significant role in the forecasting of geomagnetic storms produced by disturbances of the solar wind (SW). Coronal mass ejections (CMEs) passing through the heliosphere often have a prolonged (up to several days) trail with declining speed, which affects propagation of the subsequent SW streams. We studied the CME and posteruption plasma flows behind the CME rear in the event on 2010 August 18 that was observed in quadrature by several space-based instruments. Observations of the eruption in the corona with EUV telescopes and coronagraphs revealed several discrete outflows followed by a continuous structureless posteruption stream. The interplanetary coronal mass ejection (ICME) associated with this CME was registered by the Plasma and Suprathermal Ion Composition instrument aboard the Solar Terrestrial Relations Observatory between August 20, 16:14 UT and August 21, 13:14 UT, after which the SW disturbance was present over 3 days. Kinematic consideration with the use of the gravitational and drag-based models has shown that the discrete plasma flows can be associated with the ICME, whereas the posteruption outflow arrived in the declining part of the SW transient. We simulated the Fe ion charge distributions of the ICME and post-CME parts of the SW using the plasma temperature and density in the ejection region derived from the differential emission measure analysis. The results demonstrate that in the studied event, the post-ICME trailing region was associated with the posteruption flow from the corona rather than with the ambient SW entrained by the CME.

Keywords: solar corona; solar wind; solar physics; solar coronal mass ejections
Unraveling the Nature of the Deeply Embedded Wolf-Rayet Star WR 121a

An X-ray study of the deeply embedded Wolf-Rayet star WR 121a has been carried out using long-term (spanning over ∼12 yr) archival observations from Chandra and XMM-Newton. For the first time, a periodic variation of 4.1 days has been detected in the X-ray light curve of WR 121a. No companion is seen in a merged and exposure-corrected Chandra X-ray image of WR 121a, as found in other previous observations in the J band. The X-ray spectrum of WR 121a is well explained by a thermal plasma emission model with temperatures of 0.98 ± 0.34 keV and 3.55 ± 0.69 keV for the cool and hot components, respectively, and nonsolar abundances. The present study indicates that WR 121a is an X-ray-bright massive binary with an X-ray luminosity of ∼1034 erg s-1, which can be explained by active wind collision between its components. Phase-locked modulations have been seen in the flux variation of WR 121a where the flux increases by a factor of ∼1.6 from minimum to maximum in the 0.3-10.0 keV energy band. These variations could be caused by the wind collision region being eclipsed by the secondary star in a binary orbit. The winds of both components of WR 121a appear to be radiative. Radiative inhibition and radiative braking are the most likely processes that are severely affecting the wind collision in this short-period massive binary system.

Keywords: wolf-rayet stars; wn stars; binary stars; early-type stars; x-ray stars; stellar winds
Effects of Full-sphere Convection on M-dwarf Dynamo Action, Flux Emergence, and Spin-down

We present an analysis of 21 global MHD simulations of the dynamo action taking place in the interiors of fully convective M4 stars. We leverage our past work involving 45 simulations of shell-convecting-type M2 stars in a very similar parameter space to identify properties that their dynamos share and ways in which they differ. We find that the parameter scalings of many fundamental dynamo measures including the ratio of magnetic to kinetic energy and the cycle period are shared not only between the two sets of M-dwarf models but also with the broader literature on K and G dwarfs, suggesting that their convective dynamos are similar in nature. We find that the surface fields of the fully convective stars are stronger and more organized than those in the shell-convecting models and indicate faster spin-down than is observed, for which we suggest possible remediations. We note an abundance of dynamo states that are localized within one hemisphere at a time and find that such states are well described by a quasi-linear superposition of even- and odd-parity eigenmodes with similar amplitudes. We observe that the turbulent stirring of the deep fields of the fully convective models allows them to attain far higher peak amplitudes than those in the tachoclines of the partially convective models. We employ our AI-enabled pipeline, LoopNet, to search for buoyant, fibril magnetic fields in the simulated stars and find nearly twice as many such structures forming in the M4 models, in good agreement with observed differences in their flaring rates.

Keywords: m dwarf stars; stellar magnetic fields; stellar evolution; magnetohydrodynamical simulations; stellar rotation; emerging flux tubes; convolutional neural networks
Indication of a Pulsar Wind Nebula in the Hard X-Ray Emission from SN 1987A

Since the day of its explosion, SN 1987A (SN87A) was closely monitored with the aim to study its evolution and to detect its central compact relic. The detection of neutrinos from the supernova strongly supports the formation of a neutron star (NS). However, the constant and fruitless search for this object has led to different hypotheses on its nature. To date, the detection in the Atacama Large Millimeter/submillimeter Array data of a feature that is somehow compatible with the emission arising from a proto-pulsar wind nebula (PWN) is the only hint of the existence of such elusive compact object. Here we tackle this 33 yr old issue by analyzing archived observations of SN87A performed by Chandra and NuSTAR in different years. We firmly detect nonthermal emission in the 10-20 kev energy band, due to synchrotron radiation. The possible physical mechanism powering such emission is twofold: diffusive shock acceleration (DSA) or emission arising from an absorbed PWN. By relating a state-of-the-art magnetohydrodynamic simulation of SN87A to the actual data, we reconstruct the absorption pattern of the PWN embedded in the remnant and surrounded by cold ejecta. We found that, even though the DSA scenario cannot be firmly excluded, the most likely scenario that well explains the data is that of PWN emission.

Keywords: supernova remnants; compact objects; neutron stars; x-ray astronomy; x-ray sources; x-ray point sources; x-ray observatories; shocks; interstellar synchrotron emission; plasma astrophysics
Using Chandra Localizations and Gaia Distances and Proper Motions to Classify Hard X-Ray Sources Discovered by INTEGRAL

Here, we report on X-ray observations of ten 17-60 keV sources discovered by the International Gamma-Ray Astrophysics Laboratory satellite. The primary new information is sub-arcsecond positions obtained by the Chandra X-ray Observatory. In six cases (IGR J17040-4305, IGR J18017-3542, IGR J18112-2641, IGR J18434-0508, IGR J19504+3318, and IGR J20084+3221), a unique Chandra counterpart is identified with a high degree of certainty, and for five of these sources (all but J19504), Gaia distances or proper motions indicate that they are Galactic sources. For four of these, the most likely classifications are that the sources are magnetic cataclysmic variables (CVs). J20084 could be either a magnetic CV or a high-mass X-ray binary. We classify the sixth source (J19504) as a likely active galactic nucleus (AGN). In addition, we find likely Chandra counterparts to IGR J18010-3045 and IGR J19577+3339, and the latter is a bright radio source and probable AGN. The other two sources, IGR J12529-6351 and IGR J18013-3222, do not have likely Chandra counterparts, indicating that they are transient, highly variable, or highly absorbed.

Keywords: high energy astrophysics; surveys; astrometry
TIC 278956474: Two Close Binaries in One Young Quadruple System Identified by TESS

We have identified a quadruple system with two close eclipsing binaries in Transiting Exoplanet Survey Satellite (TESS) data. The object is unresolved in Gaia and appears as a single source at parallax 1.08 ± 0.01 mas. Both binaries have observable primary and secondary eclipses and were monitored throughout TESS Cycle 1 (sectors 1-13), falling within the TESS Continuous Viewing Zone. In one eclipsing binary (P = 5.488 days), the smaller star is completely occluded by the larger star during the secondary eclipse; in the other (P = 5.674 days) both eclipses are grazing. Using these data, spectroscopy, speckle photometry, spectral energy distribution analysis, and evolutionary stellar tracks, we have constrained the masses and radii of the four stars in the two eclipsing binaries. The Li I equivalent width indicates an age of 10-50 Myr and, with an outer period of ${858}_{-5}^{+7}$ days, our analysis indicates this is one of the most compact young 2 + 2 quadruple systems known.

Keywords: close binary stars; eclipsing binary stars; young stellar objects; multiple stars
On the Nature of Ultracool White Dwarfs: Not so Cool after All

A recent analysis of the 100 pc white dwarf sample in the SDSS footprint demonstrated for the first time the existence of a well-defined ultracool-or IR-faint-white dwarf sequence in the Hertzsprung-Russell diagram. Here we take advantage of this discovery to enlarge the IR-faint white dwarf sample threefold. We expand our selection to the entire Pan-STARRS survey footprint as well as the Montreal White Dwarf Database 100 pc sample and identify 37 candidates with strong flux deficits in the optical. We present follow-up Gemini optical spectroscopy of 30 of these systems and confirm all of them as IR-faint white dwarfs. We identify an additional set of 33 objects as candidates based on their colors and magnitudes. We present a detailed model atmosphere analysis of all 70 newly identified IR-faint white dwarfs together with 35 previously known objects reported in the literature. We discuss the physics of model atmospheres and show that the key physical ingredient missing in our previous generation of model atmospheres was the high-density correction to the He- free-free absorption coefficient. With new model atmospheres calculated for the purpose of this analysis, we now obtain significantly higher effective temperatures and larger stellar masses for these IR-faint white dwarfs than the T eff and M values reported in previous analyses, thus solving a two-decade-old problem. In particular, we identify in our sample a group of ultramassive white dwarfs in the Debye cooling phase with stellar parameters never measured before.

Keywords: white dwarf stars; stellar properties; hertzsprung russell diagram; stellar remnants; stellar atmospheric opacity
A Forecast of the Sensitivity on the Measurement of the Optical Depth to Reionization with the GroundBIRD Experiment

We compute the expected sensitivity on measurements of optical depth to reionization for a ground-based experiment at Teide Observatory. We simulate polarized partial sky maps for the GroundBIRD experiment at the frequencies 145 and 220 GHz. We perform fits for the simulated maps with our pixel-based likelihood to extract the optical depth to reionization. The noise levels of polarization maps are estimated as 110 $\mu {\rm{K}}\,\mathrm{arcmin}$ and 780 $\mu {\rm{K}}\,\mathrm{arcmin}$ for 145 and 220 GHz, respectively, by assuming a three-year observing campaign and sky coverages of 0.537 for 145 GHz and 0.462 for 220 GHz. Our sensitivities for the optical depth to reionization are found to be στ = 0.030 with the simulated GroundBIRD maps, and στ = 0.012 by combining with the simulated QUIJOTE maps at 11, 13, 17, 19, 30, and 40 GHz.

Keywords: early universe; cosmic microwave background radiation; cosmological parameters; photon decoupling
Particle Acceleration and Transport during 3D CME Eruptions

We calculate particle acceleration during coronal mass ejection (CME) eruptions using combined magnetohydrodynamic and test-particle models. The 2.5D/3D CMEs are generated via the breakout mechanism. In this scenario a reconnection at the "breakout" current sheet (CS) above the flux rope initiates the CME eruption by destabilizing a quasi-static force balance. Reconnection at the flare CS below the erupting flux rope drives the fast acceleration of the CME, which forms flare loops below and produces the energetic particles observed in flares. For test-particle simulations, two times are selected during the impulsive and decay phases of the eruption. Particles are revealed to be accelerated more efficiently in the flare CS rather than in the breakout CS even in the presence of large magnetic islands. Particles are first accelerated in the CSs (with or without magnetic islands) by the reconnection electric field mainly through particle curvature drift. We find, as expected, that accelerated particles precipitate into the chromosphere, become trapped in the loop top by magnetic mirrors, or escape to interplanetary space along open field lines. Some trapped particles are reaccelerated, either via reinjection to the flare CS or through a local Betatron-type acceleration associated with compression of the magnetic field. The energetic particles produce relatively hard energy spectra during the impulsive phase. During the gradual phase, the relaxation of magnetic field shear reduces the guiding field in the flare CS, which leads to a decrease in particle energization efficiency. Important implications of our results for observations of particle acceleration in the solar coronal jets are also discussed.

Keywords: solar flares; solar magnetic reconnection; solar coronal mass ejections
Mantle Degassing Lifetimes through Galactic Time and the Maximum Age Stagnant-lid Rocky Exoplanets Can Support Temperate Climates

The ideal exoplanets to search for life are those within a star's habitable zone. However, even within the habitable zone, planets can still develop uninhabitable climate states. Sustaining a temperate climate over geologic (~gigayear) timescales requires a planet to contain sufficient internal energy to power a planetary-scale carbon cycle. A major component of a rocky planet's energy budget is the heat produced by the decay of radioactive elements, especially 40K, 232Th, 235U, and 238U. As the planet ages and these elements decay, this radiogenic energy source dwindles. Here we estimate the probability distribution of the amount of these heat-producing elements that enter into rocky exoplanets through Galactic history by combining the system-to-system variation seen in stellar abundance data with the results from Galactic chemical evolution models. From this, we perform Monte Carlo thermal evolution models that maximize the mantle cooling rate, thus allowing us to create a pessimistic estimate of lifetime a rocky, stagnant-lid exoplanet can support a global carbon cycle through Galactic history. We apply this framework to a sample of 17 likely rocky exoplanets with measured ages, seven of which we predict are likely to be actively degassing today, despite our pessimistic assumptions. For the remaining planets, including those orbiting TRAPPIST-1, we cannot confidently assume that they currently contain sufficient internal heat to support mantle degassing at a rate sufficient to sustain a global carbon cycle or temperate climate without additional tidal heating or undergoing plate tectonics.

Keywords: exoplanet evolution; exoplanet astronomy
Geometry of the Draco C1 Symbiotic Binary

Draco C1 is a known symbiotic binary star system composed of a carbon red giant and a hot, compact companion—likely a white dwarf—belonging to the Draco dwarf spheroidal galaxy. From near-infrared spectroscopic observations taken by the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2), part of Sloan Digital Sky Survey IV, we provide updated stellar parameters for the cool, giant component, and constrain the temperature and mass of the hot, compact companion. Prior measurements of the periodicity of the system, based on only a few epochs of radial velocity data or relatively short baseline photometric observations, were sufficient only to place lower limits on the orbital period (P > 300 days). For the first time, we report precise orbital parameters for the binary system: with 43 radial velocity measurements from APOGEE spanning an observational baseline of more than 3 yr, we definitively derive the period of the system to be ${1220.0}_{-3.5}^{+3.7}$ days. Based on the newly derived orbital period and separation of the system, together with estimates of the radius of the red giant star, we find that the hot companion must be accreting matter from the dense wind of its evolved companion.

Keywords: draco dwarf galaxy; radial velocity; symbiotic binary stars; white dwarf stars; carbon stars; binary stars; spectroscopy
Dynamical and Thermal Manifestations of the Region above the Top of the Post-flare Loops: MHD Simulations

Observations proved that a distributed structure named a supra-arcade fan (SAF) exists above post-flare loops in solar eruptions. The locations of the SAF are spatially consistent with various emission sources. Termination shocks (TSs) that are often regarded as an efficient driver for particle acceleration possibly exist in the SAF. We performed the numerical simulations of solar flares based on the standard flare model to study the dynamical and thermal manifestations of the SAF, as well as the possibility of detecting TSs in extreme-ultraviolet (EUV) images. In the simulations, the SAF and TSs can be clearly identified. The motion history and temperature evolution of plasmas inside the SAF indicate that the mass of the SAF comes from the corona and the plasmas are heated in the current sheet. The height of the SAF decreases with the speed of about 64.6 km s-1 when the rate of magnetic reconnection quickly increases, and then increases with a slightly lower velocity of about 50.5 km s-1 after the peak of the rate of magnetic reconnection. The descent-ascent path of the SAF is due to the unbalance of the Lorentz force and the pressure force inside the magnetic loops. In synthetic EUV images, emission intensity variations in the area surrounding TSs are significant, indicating that, depending on the viewing angle, TSs could be identifiable in EUV observations. The results of numerical simulations are generally consistent with observations, helping us to better understand the characteristics of the SAF and the physical natures behind it.

Keywords: solar flares; solar magnetic reconnection; termination shock; magnetohydrodynamical simulations
Examining the Properties of Low-luminosity Hosts of Type Ia Supernovae from ASAS-SN

We present a spectroscopic analysis of 44 low-luminosity host galaxies of Type Ia supernovae (SNe Ia) detected by the All-Sky Automated Survey for Supernovae (ASAS-SN), using hydrogen, oxygen, and sulfur emission lines to measure metallicities and star formation rates. We find no statistically significant evidence that the star formation activity and metallicities of the galaxies in our sample are inconsistent with galaxies of similar luminosities and masses. We identify two 3σ outlier galaxies that have high metallicities for their stellar masses, but find that their other properties are consistent with general galaxies. The overall consistency between our sample and general galaxy samples further strengthens the evidence from more luminous SN Ia host galaxy samples that SN Ia host galaxies are typical.

Keywords: type ia supernovae; supernovae; galaxy abundances