adsabs/SciX_UAT_keywords huggingface dataset:
Rapid Refilling of the Lunar Wake under Transonic Plasma Flow: ARTEMIS Observations

The lunar wake is usually rapidly refilled when the background plasma is substantially subsonic. Here we present observational case studies, by the two ARTEMIS spacecraft, of the lunar wakes in the magnetosheath near the magnetopause under transonic plasma flows with relatively large plasma beta and different magnetic field orientations. The associated background plasma betas are near 1, suggesting that the plasmas are not strongly controlled by the magnetic fields. As a result, the part of the lunar wake under subsonic plasma was rapidly refilled. Pitch angle distributions reveal that a significant portion of the refilling ions are from the downstream wake. This is consistent with the fact that higher sound speed than bulk speed of the background plasma enables downstream particles to get access to upstream wake due to the pressure gradient. The other part under supersonic plasma remains a typical wake structure with high plasma density or flux depletions. Our results show that the Mach number and plasma beta primarily determine the rapid refilling of the lunar wake, which is allowed only in subsonic plasma with plasma beta greater than or close to 1 and hardly influenced at all by the magnetic field orientation.

Keywords: the moon; lunar science; plasma physics
Lithium and Beryllium in NGC 752-an Open Cluster Twice the Age of the Hyades

The surface abundances of the light elements lithium (Li) and beryllium (Be) reveal information about the physical processes taking place in stellar interiors. The investigation of the amount of these two elements in stars in open clusters shows the effect of age on those mechanisms. We have obtained spectra of both Li and Be in main-sequence stars in NGC 752 at high spectral resolution and high signal-to-noise ratios with HIRES on the Keck I telescope. In order to make meaningful comparisons with other clusters, we have determined the stellar parameters on a common scale. We have found abundances of Li and Be by spectral synthesis techniques. NGC 752 is twice the age of the well-studied Hyades. We find that (1) the Li dip centered near 6500 K is wider in NGC 752, having expanded toward cooler temperatures; (2) the Be dip is deeper in the older NGC 752; (3) the Li "peak" near 6200 K is lower by about 0.3 dex; (4) although there is little Be depletion in the cooler stars, it is possible that Be may be lower in NGC 752 than in the Hyades; and (5) the Li content in both clusters declines with decreasing temperature, but there is less Li in NGC 752 at a given temperature by ~0.4 dex. These differences are consistent with the transport of the light-element nuclei below the surface convection zone as predicted by theory. That connection to rotational spin-down is indicated by the pattern of rotation with temperature in the two clusters.

Keywords: open star clusters; chemical abundances; stellar evolution
Is the Atmosphere of the Ultra-hot Jupiter WASP-121 b Variable?

We present a comprehensive analysis of the Hubble Space Telescope observations of the atmosphere of WASP-121 b, an ultra-hot Jupiter. After reducing the transit, eclipse, and phase-curve observations with a uniform methodology and addressing the biases from instrument systematics, sophisticated atmospheric retrievals are used to extract robust constraints on the thermal structure, chemistry, and cloud properties of the atmosphere. Our analysis shows that the observations are consistent with a strong thermal inversion beginning at ∼104 Pa on the dayside, solar to subsolar metallicity Z (i.e., $-0.77\lt \mathrm{log}({\text{}}Z)\lt 0.05$ ), and supersolar C/O ratio (i.e., 0.59 < C/O < 0.87). More importantly, utilizing the high signal-to-noise ratio and repeated observations of the planet, we identify the following unambiguous time-varying signals in the data: (i) a shift of the putative hotspot offset between the two phase curves and (ii) varying spectral signatures in the transits and eclipses. By simulating the global dynamics of WASP-121 b's atmosphere at high resolution, we show that the identified signals are consistent with quasiperiodic weather patterns, hence atmospheric variability, with signatures at the level probed by the observations (∼5% to ∼10%) that change on a timescale of ∼5 planet days; in the simulations, the weather patterns arise from the formation and movement of storms and fronts, causing hot (as well as cold) patches of atmosphere to deform, separate, and mix in time.

Keywords: exoplanet atmospheric variability; exoplanet atmospheric composition; bayesian statistics; astrophysical fluid dynamics; astronomy data analysis
Catalog of the Galactic Population of X-Ray Pulsars in High-mass X-Ray Binary Systems

A catalog of the Galactic population of X-ray pulsars in high-mass X-ray binary (HMXB) systems is presented. It contains information about 82 confirmed sources: 18 persistent and 64 transient pulsars. Their basic parameters include spin period, spin evolution with global and local spin-up/spin-down and duration, orbital period, X-ray luminosity, magnetic field strength measured by cyclotron line analysis, distance, spectral and luminosity class, and observable parameters of massive companions, which are shown in the tables provided, with corresponding references. Candidates of HMXB pulsars are also listed for further careful consideration.

Keywords: high mass x-ray binary stars; neutron stars; pulsars; accretion; high energy astrophysics
Can Cooling and Heating Functions Be Modeled with Homogeneous Radiation Fields?

Cooling and heating functions describe how radiative processes impact the thermal state of a gas as a function of its temperature and other physical properties. In a most general case the functions depend on the detailed distributions of ionic species and on the radiation spectrum. Hence, these functions may vary on a very wide range of spatial and temporal scales. In this paper, we explore cooling and heating functions between 5 ≤ z ≤ 10 in simulated galaxies from the Cosmic Reionization On Computers project. We compare three functions: (1) the actual cooling and heating rates of hydrodynamic cells as a function of cell temperature, (2) the median cooling and heating functions computed using median interstellar medium (ISM) properties (median ISM), and (3) the median of the cooling and heating functions of all gas cells (instantaneous). We find that the median ISM and instantaneous approaches to finding a median cooling and heating function give identical results within the spread due to cell-to-cell variation. However, the actual cooling (heating) rates experienced by the gas at different temperatures in the simulations do not correspond to either summarized cooling (heating) functions. In other words, the thermodynamics of the gas in the simulations cannot be described by a single set of a cooling plus a heating function with a spatially constant radiation field that could be computed with common tools, such as CLOUDY.

Keywords: galaxies; high-redshift galaxies; galaxy formation; cosmology; computational methods; interstellar radiation field
Doppler-velocity Drifts Detected in a Solar Prominence

We analyzed multiline observations of a quiescent prominence from the slit spectrograph located at the Ondřejov Observatory. Dopplergrams and integrated intensity maps of the whole prominence were obtained from observations in six spectral lines: Ca II H, Hϵ, Hβ, He I D3, Hα, and Ca II IR. By combining integrated intensity maps with non-LTE radiative-transfer modeling, we carefully identified areas in an optically thin regime. The comparison of the Doppler-velocity maps and scatterplots from different lines shows the existence of differences in the velocity of ions and neutrals called velocity drift. The drift is of a local nature, present mostly at prominence edges in the area with a large velocity gradient, as can be tentatively expected based on multifluid MHD models. We could not explore the time evolution of the drift, since our data set consists of a single scan only. Our paper brings another contribution to a rather controversial problem of the detection of multifluid effects in solar prominences.

Keywords: solar prominences
Jet Reorientation in Central Galaxies of Clusters and Groups: Insights from VLBA and Chandra Data

Recent observations of galaxy clusters and groups with misalignments between their central active galactic nucleus jets and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet-bubble connection in cooling cores, and the processes responsible for jet realignment. To investigate the frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and groups. Using Very Long Baseline Array radio data, we measure the parsec-scale position angle of the jets, and compare it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample and selected subsets, we consistently find that there is a 30%-38% chance to find a misalignment larger than ΔΨ = 45° when observing a cluster/group with a detected jet and at least one cavity. We determine that projection may account for an apparently large ΔΨ only in a fraction of objects (~35%), and given that gas dynamical disturbances (such as sloshing) are found in both aligned and misaligned systems, we exclude environmental perturbation as the main driver of cavity-jet misalignment. Moreover, we find that large misalignments (up to ~90°) are favored over smaller ones (45° ≤ ΔΨ ≤ 70°), and that the change in jet direction can occur on timescales between one and a few tens of Myr. We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we discuss several engine-based mechanisms that may cause these dramatic changes.

Keywords: galaxy clusters; intracluster medium; radio galaxies; galaxy groups; relativistic jets; supermassive black holes
Pulsational Pair-instability Supernovae. II. Neutrino Signals from Pulsations and Their Detection by Terrestrial Neutrino Detectors

A Pulsational Pair-instability supernova (PPISN) evolves from a massive star with a mass ∼80-140 M⊙ that develops electron-positron pair-instability after hydrostatic He-burning in the core has finished. In Leung et al. (Paper I), we examined the evolutionary tracks and the pulsational mass-loss history of this class of stars. In this paper, we analyze the thermodynamical history to explore the neutrino observables of PPISNe. We compute the neutrino light curves and spectra during pulsation. We then study the detailed neutrino emission profiles of these stars and estimate the expected neutrino detection count for different terrestrial neutrino detectors, including, e.g., KamLAND and Super-Kamiokande. Finally, we compare the neutrino pattern of PPISN with other types of supernovae based on a canonical 10 kt detector. The predicted neutrino signals can provide an early warning for telescopes to trace for the early time optical signals. The implications of neutrino physics on the expected detection are also discussed.

Keywords: supernova neutrinos; stellar pulsations; supernovae
Search for TiO and Optical Nightside Emission from the Exoplanet WASP-33b

With a temperature akin to an M dwarf, WASP-33b is among the hottest Jupiters known, making it an ideal target for high-resolution optical spectroscopy. By analyzing both transmission and emission spectra, we aim to substantiate previous reports of atmospheric TiO and a thermal inversion within the planet's atmosphere. We observed two transits and six arcs of the phase curve with the Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) on the Canada-France-Hawaii Telescope and High Resolution Echelle Spectrometer (HIRES) on the Keck telescope, which provide high spectral resolution and ample wavelength coverage. We employ the Doppler cross-correlation technique to search for the molecular signatures of TiO and H2O in these spectra, using models based on the TiO line list of Plez. Though we cannot exclude line-list-dependent effects, our data do not corroborate previous indications of a thermal inversion. Instead we place a 3σ upper limit of 10-9 on the volume mixing ratio of TiO for the T-P profile we consider. While we are unable to constrain the volume mixing ratio of water, our strongest constraint on TiO comes from dayside emission spectra. This apparent absence of a stratosphere sits in stark contrast to previous observations of WASP-33b as well as theoretical predictions for the atmospheres of highly irradiated planets. The discrepancy could be due to variances between line lists, and we stress that detection limits are only as good as the line list employed, and are only valid for the specific T-P profile considered due to the strong degeneracy between lapse rate ( ${dT}/d\mathrm{log}P$ ) and molecular abundance.

Keywords: astronomy data analysis; exoplanet atmospheres; high resolution spectroscopy; hot jupiters; transmission spectroscopy; exoplanet atmospheric composition; exoplanets; extrasolar gaseous giant planets
Rankine-Hugoniot Relations and Magnetic Field Enhancement in Turbulent Shocks

In fast collisionless shocks, the density and magnetic field increase and the plasma is heated. The compression and heating are ultimately determined by the Rankine-Hugoniot relations connecting the upstream and downstream parameters. The standard Rankine-Hugoniot relations take into account only mean upstream and downstream parameters. Observations at the Earth's bow shock show that the downstream magnetic field does not always relax to a uniform state, but large amplitude magnetic oscillations persist. Here, these Rankine-Hugoniot relations are extended to such turbulent shocks where the mean downstream magnetic field is accompanied by magnetic fluctuations. It is shown that the turbulent magnetic field pressure may substantially exceed the pressure of the mean field, while the density compression and heating may be only weakly affected. Thus, strong amplification of the rms magnetic field can be achieved at the expense of a modest reduction of plasma heating.

Keywords: shocks; planetary bow shocks; interplanetary shocks; space plasmas; plasma astrophysics
Hydrodynamical Modeling of the Light Curves of Core-collapse Supernovae with HYPERION. I. The Mass Range 13-25 M⊙, the Metallicities -3 ≤ [Fe/H] ≤ 0, and the Case of SN 1999em

We present the last version of HYdrodynamic Ppm Explosion with Radiation diffusION (HYPERION), a hydrodynamic code designed to calculate the explosive nucleosynthesis, remnant mass, and light curve associated with the explosion of a massive star. By means of this code, we compute the explosion of a subset of red supergiant models taken from the database published by Limongi & Chieffi for various explosion energies in the range ∼0.20-2.00 × 1051 erg. The main outcomes of these simulations, i.e., remnant mass, synthesized 56Ni, luminosity, and length of the plateau of the bolometric light curve, are analyzed as a function of the initial parameters of the star (mass and metallicity) and the explosion energy. As a first application of HYPERION, we estimated the mass and metallicity of the progenitor star of SN 1999em, a well-studied Type IIP supernova, by means of the light-curve fitting. In particular, if the adopted distance to the host galaxy NGC 1637 is 7.83 Mpc, the properties of the light curve point toward a progenitor with an initial mass of 13 M⊙ and a metallicity [Fe/H] = -1. If, on the contrary, the adopted distance modulus is 11.7 Mpc, all models with initial mass 13 ≤ M/M⊙ ≤ 15 and metallicities -1 ≤ [Fe/H] ≤ 0 are compatible with the progenitor of SN 1999em.

Keywords: stellar remnants; core-collapse supernovae; supernova dynamics; hydrodynamical simulations; hydrodynamics
A Nearby Repeating Fast Radio Burst in the Direction of M81

We report on the discovery of FRB 20200120E, a repeating fast radio burst (FRB) with a low dispersion measure (DM) detected by the Canadian Hydrogen Intensity Mapping Experiment FRB project. The source DM of 87.82 pc cm-3 is the lowest recorded from an FRB to date, yet it is significantly higher than the maximum expected from the Milky Way interstellar medium in this direction (∼50 pc cm-3). We have detected three bursts and one candidate burst from the source over the period 2020 January-November. The baseband voltage data for the event on 2020 January 20 enabled a sky localization of the source to within ≃14 arcmin2 (90% confidence). The FRB localization is close to M81, a spiral galaxy at a distance of 3.6 Mpc. The FRB appears on the outskirts of M81 (projected offset ∼20 kpc) but well inside its extended H I and thick disks. We empirically estimate the probability of a chance coincidence with M81 to be <10-2. However, we cannot reject a Milky Way halo origin for the FRB. Within the FRB localization region, we find several interesting cataloged M81 sources and a radio point source detected in the Very Large Array Sky Survey. We search for prompt X-ray counterparts in Swift Burst Alert Telescope and Fermi/GBM data, and, for two of the FRB 20200120E bursts, we rule out coincident SGR 1806-20-like X-ray bursts. Due to the proximity of FRB 20200120E, future follow-up for prompt multiwavelength counterparts and subarcsecond localization could be constraining of proposed FRB models.

Keywords: radio transient sources; radio bursts; transient sources; radio pulsars
COLDz: Deep 34 GHz Continuum Observations and Free-Free Emission in High-redshift Star-forming Galaxies

The high-frequency radio sky has historically remained largely unexplored due to the typical faintness of sources in this regime, and the modest survey speed compared to observations at lower frequencies. However, high-frequency radio surveys offer an invaluable tracer of high-redshift star formation, as they directly target the faint radio free-free emission. We present deep continuum observations at 34 GHz in the COSMOS and GOODS-North fields from the Karl G. Jansky Very Large Array (VLA), as part of the COLDz survey. The deep COSMOS mosaic spans $\sim 10\,{\mathrm{arcmin}}^{2}$ down to σ = 1.3 μJy beam-1, while the wider GOODS-N observations cover $\sim 50\,{\mathrm{arcmin}}^{2}$ to σ = 5.3 μJy beam-1. We detect a total of 18 galaxies at 34 GHz, of which nine show radio emission consistent with being powered by star formation; although for two sources, this is likely due to thermal emission from dust. Utilizing deep ancillary radio data at 1.4, 3, 5, and 10 GHz, we decompose the spectra of the remaining seven star-forming galaxies into their synchrotron and thermal free-free components, and find typical thermal fractions and synchrotron spectral indices comparable to those observed in local star-forming galaxies. We further determine free-free star formation rates (SFRs), and show that these are in agreement with SFRs from spectral energy distribution-fitting and the far-infrared/radio correlation. Our observations place strong constraints on the high-frequency radio emission in typical galaxies at high redshift, and provide some of the first insights into what is set to become a key area of study with future radio facilities, such as the Square Kilometer Array Phase 1 and next-generation VLA.

Keywords: high-redshift galaxies; galaxy evolution; galaxy formation; radio continuum emission
Setting the Stage for Cosmic Chronometers. II. Impact of Stellar Population Synthesis Models Systematics and Full Covariance Matrix

The evolution of differential ages of passive galaxies at different redshifts (cosmic chronometers) has been proved to be a method potentially able to constrain the Hubble parameter in a cosmology-independent way, but the systematic uncertainties must be carefully evaluated. In this paper, we compute the contribution to the full covariance matrix of systematic uncertainties due to the choice of initial mass function, stellar library, and metallicity, exploring a variety of stellar population synthesis models. Through simulations in the redshift range 0 < z < 1.5, we find that the choice of the stellar population synthesis model dominates the total error budget on H(z), with contributions at a level of ∼4.5%, discarding the most discordant model. The contribution due to the choice of initial mass function is <0.5%, while that due to the stellar library is ∼6.6%, on average. We also assess the impact of an uncertainty in the stellar metallicity determination, finding that an error of ∼10% (5%) on the stellar metallicity propagates to a 9% (4%) error on H(z). These results are used to provide the combined contribution of these systematic effects on the error budget. For current H(z) measurements, where the uncertainties due to metallicity and star formation history were already included, we show that, using the more modern stellar libraries, the additional systematic uncertainty is between 5.4% (at z = 0.2) and 2.3% (at z = 1.5). To reach the goal of keeping the systematic error budget below the 1% level, we discuss the efforts needed to obtain higher resolution and signal-to-noise spectra and improvements in the modeling of stellar population synthesis.

Keywords: galaxy evolution; galaxy stellar content; observational cosmology; cosmological parameters
Magnetohydrodynamical Torsional Oscillations from Thermoresistive Instability in Hot Jupiters

Hot Jupiter atmospheres may be subject to a thermoresistive instability where an increase in the electrical conductivity due to ohmic heating results in runaway of the atmospheric temperature. We introduce a simplified one-dimensional model of the equatorial substellar region of a hot Jupiter that includes the temperature dependence and time dependence of the electrical conductivity, as well as the dynamical back-reaction of the magnetic field on the flow. This model extends our previous one-zone model to include the radial structure of the atmosphere. Spatial gradients of electrical conductivity strongly modify the radial profile of Alfvénic oscillations, leading to steepening and downward transport of magnetic field, enhancing dissipation at depth. We find unstable solutions that lead to self-sustained oscillations for equilibrium temperatures in the range T eq ≈ 1000-1200 K and radial magnetic field strength in the range ≈10-100 G. For a given set of parameters, self-sustained oscillations occur in a narrow range of equilibrium temperatures that allow the magnetic Reynolds number to alternate between large and small values during an oscillation cycle. With our simplified geometry, outside of this temperature window the system reaches a steady state in which the effect of the magnetic field can be approximated as a magnetic drag term. Our results show that thermoresistive instability is a possible source of variability in magnetized hot Jupiters at colder temperatures and emphasize the importance of including the temperature dependence of electrical conductivity in models of atmospheric dynamics.

Keywords: astrophysical fluid dynamics; magnetohydrodynamics; exoplanet atmospheric variability; exoplanet atmospheric dynamics