adsabs/SciX_UAT_keywords huggingface dataset:
Accretion and Extinction Variations in the Low-mass Pre-main-sequence Binary System WX Cha

Light curves of young star systems show photometric variability due to different kinematic and physical processes. One of the main contributors to the photometric variability is the changing mass accretion rate, which regulates the interplay between the forming young star and the protoplanetary disk. We collected high-resolution spectroscopy in eight different epochs, as well as ground-based and space-borne multiepoch optical and infrared photometry of WX Cha, an M0 binary system, with an almost edge-on disk (i = 87°) in the Chamaeleon I star-forming region. Spectroscopic observations cover 72 days, the ground-based optical monitoring covers 42 days while space-borne TESS photometry extends for 56 days. The multiwavelength light curves exhibit quasi-periodic variability of 0.35-0.53 mag in the near-infrared, and of 1.3 mag in the g band. We studied the variability of selected emission lines that trace the accretion, computed the accretion luminosity and the mass accretion rate using empirical relations, and obtained values between L acc ~ 1.6 L ⊙ - 3.2 L ⊙ and ${\dot{M}}_{\mathrm{acc}}\sim 3.31\times {10}^{-7}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}-7.76\,\times {10}^{-7}$ M ⊙ yr-1. Our results show that WX Cha is accreting at a rate larger than what is typical for T Tauri stars in the same star-forming region with the same stellar parameters. We theorize that this is due to the higher disk mass of WX Cha than what is usual for stars with similar stellar mass and to the binary nature of the system. Daily changes in the accretion luminosity and in the extinction can explain the photometric variability. * Based on observations collected at the European Southern Observatory under ESO programs 2103.C-5025, 0103.A-9008, and 0100.C-0708(A).

Keywords: stellar accretion; star formation; binary stars; spectroscopy; light curves; classical t tauri stars; photometry
Exploring Solar Wind Origins and Connecting Plasma Flows from the Parker Solar Probe to 1 au: Nonspherical Source Surface and Alfvénic Fluctuations

The magnetic field measurements of the FIELDS instrument on the Parker Solar Probe (PSP) have shown intensities, throughout its first solar encounter, that require a very low source surface (SS) height ( ${R}_{\mathrm{SS}}\leqslant 1.8\,{R}_{\odot }$ ) to be reconciled with magnetic field measurements at the Sun via potential field extrapolation (PFSS). However, during PSP's second encounter, the situation went back to a more classic SS height ( ${R}_{\mathrm{SS}}\leqslant 2.5\,{R}_{\odot }$ ). Here we use high-resolution observations of the photospheric magnetic field (Solar Dynamics Observatory/Helioseismic and Magnetic Imager) to calculate neutral lines and boundaries of the open field regions for SS heights from 1.2 to 2.5 R⊙ using an evolving PFSS model and the measured solar wind speed to trace the source of the wind observed by PSP to the low corona and photosphere. We adjust RSS to get the best match for the field polarity over the period 2018 October-November and 2019 March-April, finding that the best fit for the observed magnetic field polarity inversions requires a nonspherical SS. The geometry of the coronal hole boundaries for different RSS is tested using the PSP perihelion passes, 3D PFSS models, and LASCO/C2 observations. We investigate the sources of stronger-than-average magnetic fields and times of Alfvénic fast and slow wind. Only some of the strongly Alfvénic slow wind streams seen by PSP survive and are observed at 1 au: the origins and peculiar topology of the background in which they propagate is discussed.

Keywords: the sun; slow solar wind; alfven waves; space plasmas; solar activity; solar magnetic fields; solar corona; fast solar wind; solar coronal holes; solar coronal mass ejections; solar coronal streamers; solar filaments
Emission-line Outflows from the Circumnuclear to Circumgalactic Scales in a Partially Obscured Quasar

We present a detailed analysis of the rest-frame UV and optical emission-line spectrum of the partially obscured quasar J121704.70+023417.1 (hereafter J1217+0234). Here the obscuring material, very likely the dusty torus invoked by the AGN unification models, acts as a natural coronagraph, which greatly suppresses both the continuum and broad-line emission in the UV and enables a clear detection of three emission-line components at and beyond the dusty torus scale: (1) The component, with a blueshift of v ≈ 1200 km s-1 and a line width of FWHM ≈ 2600 km s-1, shows exceptionally large intensity ratios, such as N V/Lyα ≈ 2.3 and O VI/Lyα ≈ 1.4, indicating that the emitting gas is highly ionized and has a very high density up to n H ~ 1013 cm-3, possibly associated with the dusty torus. (2) The largely unshifted narrow-line component, with FWHM ≈ 510 km s-1, is completely absent in all UV lines but Lyα and is significantly detected in the forbidden lines of [O III], [O II], and [Ne III] in the optical, implying massive low-density (n H ~ 102 cm-3) gas ~40 kpc from the galactic center. (3) The intermediate component is only detected in [O III] with a blueshift and line width between (1) and (2), which might bridge the gases from the circumnuclear to the circumgalactic scales. Follow-up observations with high spatial resolution and high sensitivity are needed to confirm the speculation and are helpful to reveal outflows at multiscales in J1217+0234.

Keywords: active galaxies; agn host galaxies; quasars
Numerical Modeling and Physical Interplay of Stochastic Turbulent Acceleration for Nonthermal Emission Processes

Particle acceleration is a ubiquitous phenomenon in astrophysical and space plasma. Diffusive shock acceleration (DSA) and stochastic turbulent acceleration (STA) are known to be the possible mechanisms for producing very highly energetic particles, particularly in weakly magnetized regions. An interplay of different acceleration processes along with various radiation losses is typically observed in astrophysical sources. While DSA is a systematic acceleration process that energizes particles in the vicinity of shocks, STA is a random energizing process, where the interaction between cosmic ray particles and electromagnetic fluctuations results in particle acceleration. This process is usually interpreted as a biased random walk in energy space, modeled through a Fokker-Planck equation. In the present work, we describe a novel Eulerian algorithm, adopted to incorporate turbulent acceleration in the presence of DSA and radiative processes like synchrotron and inverse Compton emission. The developed framework extends the hybrid Eulerian-Lagrangian module in a full-fledged relativistic Magneto-hydrodynamic (RMHD) code PLUTO. From our validation tests and case studies, we showcase the competing and complementary nature of both acceleration processes. Axisymmetric simulations of an RMHD jet with this extended hybrid framework clearly demonstrate that emission due to shocks is localized, while that due to turbulent acceleration originates in the backflow and is more diffuse, particularly in the high-energy X-ray band.

Keywords: non-thermal radiation sources; computational methods; plasma astrophysics; magnetohydrodynamical simulations; shocks
Quasiperiodic Behavior in the γ-Ray Light Curve of the Blazar PKS 0405-385

We analyze the quasiperiodic oscillation (QPO) of the historical light curve of flat-spectrum radio quasars PKS 0405-385 detected by the Fermi Large Area Telescope from 2008 August to 2021 November. To identify and determine the QPO signal of PKS 0405-385 in the γ-ray light curve, we use four time series analysis techniques based on frequency and time domains, i.e., the Lomb-Scargle periodogram (LSP), the weighted wavelet z-transform (WWZ), the REDFIT, and the epoch folding. The results show that PKS 0405-385 has a quasiperiodic behavior of ~2.8 yr with the significance of ~4.3σ in Fermi long-term monitoring. Remarkably, we also performed QPO analysis in the G-band light curve observed from 2014 October to 2021 October using LSP and WWZ technology, and the results (~4σ of significance) are consistent with the periodic detection in γ-ray. This may imply that the optical emission is radiated by an electron population in the same way as the γ-ray emission. In discussing the possible mechanism of quasiperiodic behavior, either the helical motion within a jet or the supermassive black hole binary system provides a viable explanation for the QPO of 2.8 yr, and the relevant parameters have been estimated.

Keywords: blazars; flat-spectrum radio quasars; period search
Bioverse: A Comprehensive Assessment of the Capabilities of Extremely Large Telescopes to Probe Earth-like O2 Levels in Nearby Transiting Habitable-zone Exoplanets

Molecular oxygen is a strong indicator of life on Earth and may indicate biological processes on exoplanets too. Recent studies proposed that Earth-like O2 levels might be detectable on nearby exoplanets using high-resolution spectrographs on future extremely large telescopes (ELTs). However, these studies did not consider constraints like relative velocities, planet occurrence rates, and target observability. We expanded on past studies by creating a homogeneous catalog of 286,391 main-sequence stars within 120 pc using Gaia DR3 and used the Bioverse framework to simulate the likelihood of finding nearby transiting Earth analogs. We also simulated a survey of M dwarfs within 20 pc accounting for η ⊕ estimates, transit probabilities, relative velocities, and target observability to determine how long ELTs and theoretical 50-100 m ground-based telescopes need to observe to probe for Earth-like O2 levels with an R = 100,000 spectrograph. This would only be possible within 50 yr for up to ~21% of nearby M-dwarf systems if a suitable transiting habitable-zone Earth analog was discovered, assuming signals from every observable partial transit from each ELT can be combined. If so, Earth-like O2 levels could be detectable on TRAPPIST-1 d-g within 16-55 yr, respectively, and about half that time with an R = 500,000 spectrograph. These results have important implications for whether ELTs can survey nearby habitable-zone Earth analogs for O2 via transmission spectroscopy. Our work provides the most comprehensive assessment to date of the ground-based capabilities to search for life beyond the solar system.

Keywords: fundamental parameters of stars; exoplanet systems; exoplanets; exoplanet atmospheres; biosignatures
Thermocline Depth on Water-rich Exoplanets

Water-rich exoplanets are a type of terrestrial planet that is water-rich and whose ocean depth can reach tens to hundreds of kilometers with no exposed continents. Due to the lack of exposed continents, neither western boundary current nor coastal upwelling exists, and ocean overturning circulation becomes the most important way to return the nutrients deposited in the deep ocean back to the thermocline and to the surface ocean. Here we investigate the depth of the thermocline in both wind-dominated and mixing-dominated systems on water-rich exoplanets using the global ocean model MITgcm. We find that the wind-driven circulation is dominated by overturning cells through Ekman pumping and subduction and by zonal (west-east) circum-longitudinal currents, similar to the Antarctic Circumpolar Current on Earth. The wind-influenced thermocline depth shows little dependence on the ocean depth, and under a large range of parameters, the thermocline is restricted within the upper layers of the ocean. The mixing-influenced thermocline is limited within the upper 10 km of the ocean and cannot reach the bottom of the ocean even under extremely strong vertical mixing. The scaling theories for the thermocline depth on Earth are applicable for the thermocline depth on water-rich exoplanets. However, due to the lack of exposed continents, the zonal and meridional flow speeds are not in the same magnitude as that in the oceans of Earth, which results in scaling relationships for water-rich exoplanets being a little different from that used on Earth.

Keywords: ocean planets; exoplanet dynamics; habitable planets
Statistics of Water-group Band Ion Cyclotron Waves in Saturn's Inner Magnetosphere Based on 13 yr of Cassini Measurements

Based on Cassini observations from 2004 to 2016, we perform a comprehensive analysis of the statistical distribution of the occurrence rate, averaged amplitude, wave normal angle (WNA), ellipticity, and power spectral intensity of ion cyclotron waves in Saturn's inner magnetosphere. Our results show that ion cyclotron waves mainly occur between the orbits of Enceladus and Dione near the equatorial region (∣λ∣ < 20°), with higher occurrence rates in the northern hemisphere than the southern hemisphere. The averaged wave amplitudes vary between 0.1 and 2 nT with a strong day-night asymmetry and a pronounced minimum at the equator. Saturnian ion cyclotron waves are predominantly left-handed polarized with small WNAs near the equator and become linearly polarized with larger WNAs at higher latitudes. The major wave power occurs frequently at frequencies of 0.5-1.2 ${f}_{{w}^{+}}$ , where ${f}_{{w}^{+}}$ is the equatorial gyrofrequency of H2O+ ions, with the strongest intensity (>~10 nT2 Hz-1) at L ~ 6.5 statistically present in the midnight sector.

Keywords: saturn; planetary science; planetary magnetospheres
On the Collisional Disalignment of Dust Grains in Illuminated and Shaded Regions of IC 63

Interstellar dust grain alignment causes polarization from UV to mm wavelengths, allowing the study of the geometry and strength of the magnetic field. Over the last couple of decades, observations and theory have led to the establishment of the radiative alignment torque mechanism as a leading candidate to explain the effect. With a quantitatively well constrained theory, polarization can be used not only to study the interstellar magnetic field, but also the dust and other environmental parameters. Photodissociation regions, with their intense, anisotropic radiation fields, consequent rapid H2 formation, and high spatial density-contrast provide a rich environment for such studies. Here we discuss an expanded optical, NIR, and mm-wave study of the IC 63 nebula, showing strong H2 formation-enhanced alignment and the first direct empirical evidence for disalignment due to gas-grain collisions using high-resolution HCO+(J = 1-0) observations. We find that a relative amount of polarization is marginally anticorrelated with column density of HCO+. However, separating the lines of sight of optical polarimetry into those behind, or in front of, a dense clump as seen from γ Cas, the distribution separates into two well defined sets, with data corresponding to "shaded" gas having a shallower slope. This is expected if the decrease in polarization is caused by collisions since collisional disalignment rate is proportional to ${R}_{C}\propto n\sqrt{T}$ . Ratios of the best-fit slopes for the "illuminated" and "shaded" samples of lines of sight agrees, within the uncertainties, with the square root of the two-temperature H2 excitation in the nebula seen by Thi et al.

Keywords: interstellar dust; polarimetry
Modeling the Solar Corona with an Implicit High-order Reconstructed Discontinuous Galerkin Scheme

The present study aims to apply an implicit high-order reconstructed discontinuous Galerkin (DG) scheme (rDG(P 1 P 2)) to simulate the steady-state solar corona. In this scheme, a piecewise quadratic polynomial solution, P 2, is obtained from the underlying piecewise linear DG solution, P 1, by least-squares reconstruction with a weighted essentially nonoscillatory limiter. The reconstructed quadratic polynomial solution is then used for the computation of the fluxes and source terms. In addition, an implicit time integration method with large time steps is considered in this work. The resulting large linear algebraic system of equations from the implicit discretization is solved by the cellwise relaxation implicit scheme which can make full use of the compactness of the DG scheme. The code of the implicit high-order rDG scheme is developed in Fortran language with message passing interface parallelization in Cartesian coordinates. To validate this code, we first test a problem with an exact solution, which confirms the expected third-order accuracy. Then we simulate the solar corona for Carrington rotations 2167, 2183, and 2210, and compare the modeled results with observations. We find that the numerical results basically reproduce the large-scale observed structures of the solar corona, such as coronal holes, helmet streamers, pseudostreamers, and high- and low-speed streams, which demonstrates the capability of the developed scheme.

Keywords: solar corona; solar magnetic fields; magnetohydrodynamical simulations
Energy Repartition and Entropy Generation across the Earth's Bow Shock: MMS Observations

The evolution of plasma entropy and the process of plasma energy redistribution at the collisionless plasma shock front are evaluated based on the high temporal resolution data from the four Magnetospheric Multiscale spacecraft during the crossing of the terrestrial bow shock. The ion distribution function has been separated into the populations with different characteristic behaviors in the vicinity of the shock: the upstream core population, the reflected ions, the gyrating ions, the ions trapped in the vicinity of the shock, and the downstream core population. The values of ion and electron moments (density, bulk velocity, and temperature) have been determined separately for these populations. It is shown that the solar wind core population bulk velocity slows down mainly in the ramp with the electrostatic potential increase but not in the foot region as it was supposed. The reflected ion population determines the foot region properties, so the proton temperature peak in the foot region is an effect of the relative motion of the different ion populations, rather than an actual increase in the thermal speed of any of the ion population. The ion entropy evaluated showed a significant increase across the shock: the enhancement of the ion entropy occurs in the foot of the shock front and at the ramp, where the reflected ions are emerging in addition to the upstream solar wind ions, the anisotropy growing to generate the bursts of ion-scale electrostatic waves. The entropy of electrons across the shock does not show a significant change: electron heating goes almost adiabatically.

Keywords: solar wind; planetary bow shocks
The Evolving AGN Duty Cycle in Galaxies Since z ∼ 3 as Encoded in the X-Ray Luminosity Function

We present a new modeling of the X-ray luminosity function (XLF) of active galactic nuclei (AGNs) out to z ∼ 3, dissecting the contributions of main-sequence (MS) and starburst (SB) galaxies. For each galaxy population, we convolved the observed galaxy stellar mass (M⋆) function with a grid of M⋆-independent Eddington ratio (λEDD) distributions, normalized via empirical black hole accretion rate (BHAR) to star formation rate (SFR) relations. Our simple approach yields an excellent agreement with the observed XLF since z ∼ 3. We find that the redshift evolution of the observed XLF can only be reproduced through an intrinsic flattening of the λEDD distribution and with a positive shift of the break λ*, consistent with an antihierarchical behavior. The AGN accretion history is predominantly made by massive (1010 < M⋆ < 1011 M⊙) MS galaxies, while SB-driven BH accretion, possibly associated with galaxy mergers, becomes dominant only in bright quasars, at log(LX/erg s-1) > 44.36 + 1.28 × (1 + z). We infer that the probability of finding highly accreting (λEDD > 10%) AGNs significantly increases with redshift, from 0.4% (3.0%) at z = 0.5%-6.5% (15.3%) at z = 3 for MS (SB) galaxies, implying a longer AGN duty cycle in the early universe. Our results strongly favor a M⋆-dependent ratio between BHAR and SFR, as BHAR/SFR ∝ M\star0.73[+0.22,-0.29], supporting a nonlinear BH buildup relative to the host. Finally, this framework opens potential questions on super-Eddington BH accretion and different λEDD prescriptions for understanding the cosmic BH mass assembly.

Keywords: agn host galaxies; starburst galaxies; active galactic nuclei; active galaxies; galaxy evolution
Identification of White Dwarfs from Gaia EDR3 via Spectra from LAMOST DR7

We cross-matched 1.3 million white dwarf (WD) candidates from Gaia EDR3 with spectral data from LAMOST DR7 within 3″. Applying machine learning described in our previous work, we spectroscopically identified 6190 WD objects after visual inspection. 32 detailed classes were adopted for them, including but not limited to DAB and DB+M. We estimated the atmospheric parameters for the DA and DB type WD using Levenberg-Marquardt least-squares algorithm. Finally, a catalog of WD spectra from LAMOST is provided online.

Keywords: white dwarf stars
A New Metal-poor Globular Cluster and Resolved Stars in the Outer Disk of the Black Eye Galaxy M64: Implication for the Origin of the Type III Disk Break

M64 is a nearby spiral galaxy with a Type III antitruncation component. To trace the origin of the Type III component, we present Hubble Space Telescope/Advanced Camera for Surveys (ACS) F606W/F814W photometry of resolved stars in a field located in the outer disk ( $2\buildrel{\,\prime}\over{.} 5\lesssim r\lesssim 6\buildrel{\,\prime}\over{.} 5$ ) of M64. At $r\approx 5\buildrel{\,\prime}\over{.} 5$ (7 kpc) to the east, we discover a new metal-poor globular cluster ( ${R}_{\mathrm{eff}}=5.73\pm 0.02$ pc and MV = -9.54 ± 0.09 mag), M64-GC1. This is the first globular cluster found in M64. The color-magnitude diagram (CMD) of the resolved stars in M64-GC1 is well matched by 12 Gyr isochrones with [Fe/H] = -1.5 ± 0.2, showing that this cluster belongs to a halo. The CMD of the resolved stars in the entire ACS field shows two distinguishable red giant branches (RGBs): a curved metal-rich RGB and a vertical metal-poor RGB. The metal-rich RGB represents an old metal-rich ([Fe/H] ≈ -0.4) disk population. In contrast, the CMD of the metal-poor RGB stars is very similar to the CMD of M64-GC1, showing that the metal-poor RGB represents a halo population. The radial number-density profile of the metal-rich RGB stars is described by an exponential disk law, while the profile of the metal-poor RGB stars is described by a de Vaucouleurs's law. From these, we conclude that the origin of the Type III component in M64 is a halo that has a much lower metallicity than the disk or bulge population.

Keywords: galaxy stellar halos; galaxy disks; spiral galaxies; galaxy distances; galaxy stellar content; globular star clusters
On the Proposed Interstellar Origin of the USG 20140108 Fireball

A critical review of the evidence for the interstellar origin of the USG 20140108 fireball is presented. Examining United States Government (USG) fireball velocities where independent data are available shows the former to have significant (10-15 km s-1) uncertainties at large speeds and highly variable radiant accuracy, with average errors in excess of 10°. The ablation model fits to the observed lightcurve are possible for normal chondritic impactors only assuming low speeds. To match the high speed and low fragmentation height of the USG 20140108 fireball would require a high-density/strength object with low drag and a highly aerodynamic shape not made of iron. We suggest the simplest explanation for the unusual characteristics of USG 20140108 is that the speed, in particular, is substantially overestimated.

Keywords: interstellar objects; meteoroids