We present far- and near-ultraviolet absorption spectroscopy of the similar to 23 Myr edge-on debris disk surrounding the A0V star eta Telescopii, obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph. We detect absorption lines from C i, C ii, O i, Mg ii, Al ii, Si ii, S ii, Mn ii, Fe ii, and marginally N i. The lines show two clear absorption components at -22.7 +/- 0.5 km s(-1) and -17.8 +/- 0.7 km s(-1), which we attribute to circumstellar (CS) and interstellar gas, respectively. CO absorption is not detected, and we find no evidence for star-grazing exocomets. The CS absorption components are blueshifted by -16.9 +/- 2.6 km s(-1) in the star's reference frame, indicating that they are outflowing in a radiatively driven disk wind. We find that the C/Fe ratio in the eta Tel CS gas is significantly higher than the solar ratio, as is the case in the beta Pic and 49 Cet debris disks. Unlike those disks, however, the measured C/O ratio in the eta Tel CS gas is consistent with the solar value. Our analysis shows that because eta Tel is an earlier type star than beta Pic and 49 Cet, with more substantial radiation pressure at the dominant C ii transitions, this species cannot bind the CS gas disk to the star as it does for beta Pic and 49 Cet, resulting in the disk wind.

Earth's core is composed of iron (Fe) alloyed with light elements, e.g., silicon (Si). Its thermal conductivity critically affects Earth's thermal structure, evolution, and dynamics, as it controls the magnitude of thermal and compositional sources required to sustain a geodynamo over Earth's history. Here we directly measured thermal conductivities of solid Fe and Fe-Si alloys up to 144GPa and 3300K. 15 at% Si alloyed in Fe substantially reduces its conductivity by about 2 folds at 132GPa and 3000K. An outer core with 15 at% Si would have a conductivity of about 20Wm(-1) K-1, lower than pure Fe at similar pressure-temperature conditions. This suggests a lower minimum heat flow, around 3 TW, across the core-mantle boundary than previously expected, and thus less thermal energy needed to operate the geodynamo. Our results provide key constraints on inner core age that could be older than two billion-years. Thermal conductivity of Earth's core affects Earth's thermal structure, evolution and dynamics. Based on thermal conductivity measurements of iron-silicon alloys at high pressure and temperature conditions, the authors here propose Earth's inner core could be older than previously expected.

The synthesis of polynitrogen compounds is of great importance due to their potential as high-energy-density materials (HEDM), but because of the intrinsic instability of these compounds, their synthesis and stabilization is a fundamental challenge. Polymeric nitrogen units which may be stabilized in compounds with metals at high pressure are now restricted to non-branched chains with an average N-N bond order of 1.25, limiting their HEDM performances. Herein, we demonstrate the synthesis of a novel polynitrogen compound TaN5 via a direct reaction between tantalum and nitrogen in a diamond anvil cell at circa 100 GPa. TaN5 is the first example of a material containing branched all-single-bonded nitrogen chains [N-5(5-)](infinity). Apart from that we discover two novel Ta-N compounds: TaN4 with finite N-4(4-) chains and the incommensurately modulated compound TaN2-x, which is recoverable at ambient conditions.

We present a detailed characterization of the extremely dusty main-sequence star TYC 8830 410 1. This system hosts inner planetary system dust (T (dust) approximate to 300 K) with a fractional infrared luminosity of similar to 1%. Mid-infrared spectroscopy reveals a strong, mildly crystalline solid-state emission feature. TYC 8830 410 1 (spectral type G9 V) has a 49.5 '' separation M4-type companion comoving and co-distant with it, and we estimate a system age of similar to 600 Myr. TYC 8830 410 1 also experiences "dipper"-like dimming events as detected by the All-Sky Automated Survey for Supernovae, Transiting Exoplanet Survey Satellite, and characterized in more detail with the Las Cumbres Observatory Global Telescope. These recurring eclipses suggest at least one roughly star-sized cloud of dust orbits the star in addition to assorted smaller dust structures. The extreme properties of the material orbiting TYC 8830 410 1 point to dramatic dust-production mechanisms that likely included something similar to the giant impact event thought to have formed the Earth-Moon system, although hundreds of millions of years after such processes are thought to have concluded in the solar system. TYC 8830 410 1 holds promise to deliver significant advances in our understanding of the origin, structure, and evolution of extremely dusty inner planetary systems.

Following the discovery of high-temperature superconductivity in the La-H system, we studied the formation of new chemical compounds in the barium-hydrogen system at pressures from 75 to 173GPa. Using in situ generation of hydrogen from NH3BH3, we synthesized previously unknown superhydride BaH12 with a pseudocubic (fcc) Ba sublattice in four independent experiments. Density functional theory calculations indicate close agreement between the theoretical and experimental equations of state. In addition, we identified previously known P6/mmm-BaH2 and possibly BaH10 and BaH6 as impurities in the samples. Ab initio calculations show that newly discovered semimetallic BaH12 contains H-2 and H-3(-) molecular units and detached H-12 chains which are formed as a result of a Peierls-type distortion of the cubic cage structure. Barium dodecahydride is a unique molecular hydride with metallic conductivity that demonstrates the superconducting transition around 20K at 140GPa. Metallization of pure hydrogen via overlapping of electronic bands requires high pressure above 3 Mbar. Here the authors study the Ba-H system and discover a unique superhydride BaH12 that contains molecular hydrogen, which demonstrates metallic properties and superconductivity below 1.5 Mbar.

We present near-infrared Large Binocular Telescope LMIRCam imagery of the disk around the Herbig Ae/Be star AB Aurigae. A comparison of the surface brightness at K-s (2.16 itm), H2O narrowband (3.08 mu m), and L' (3.7 mu m) allows us to probe the presence of icy grains in this (pre)transitional disk environment. By applying reference differential imaging point-spread function subtraction, we detect the disk at high signal-to-noise ratios in all three bands. We find strong morphological differences between the bands, including asymmetries consistent with the observed spiral arms within 100 au in . An apparent deficit of scattered light at 3.08 mu m relative to the bracketing wavelengths (K-s and L') is evocative of ice absorption at the disk surface layer. However, the Delta(K-s - H2O) color is consistent with grains with little to no ice (0%-5% by mass). The Delta(H2O - L') color, conversely, suggests grains with a much higher ice mass fraction (-0.68), and the two colors cannot be reconciled under a single grain population model. Additionally, we find that the extremely red Delta(K-s - L') disk color cannot be reproduced under conventional scattered light modeling with any combination of grain parameters or reasonable local extinction values. We hypothesize that the scattering surfaces at the three wavelengths are not colocated, and that the optical depth effects in each wavelength result from probing the grain population at different disk surface depths. The morphological similarity between K-s and H2O suggests that their scattering surfaces are near one another, lending credence to the Delta(K-s - H2O) disk color constraint of <5% ice mass fraction for the outermost scattering disk layer.

Carbon-bearing phases show a rich variety of structural transitions as an adaptation to pressure. Of particular interest is the crossover from sp(2) carbon to sp(3) carbon, as physical and chemical properties of carbon in these distinct electronic configurations are very different. In this chapter we review pressure-induced sp(2)-sp(3) transitions in elemental carbon, carbonates, and hydrocarbons.

We present follow-up photometry and spectroscopy of ZTF J0328-1219, strengthening its status as a white dwarf exhibiting transiting planetary debris. Using TESS and Zwicky Transient Facility photometry, along with follow-up high-speed photometry from various observatories, we find evidence for two significant periods of variability at 9.937 and 11.2 hr. We interpret these as most likely the orbital periods of different debris clumps. Changes in the detailed dip structures within the light curves are observed on nightly, weekly, and monthly timescales, reminiscent of the dynamic behavior observed in the first white dwarf discovered to harbor a disintegrating asteroid, WD 1145+017. We fit previously published spectroscopy along with broadband photometry to obtain new atmospheric parameters for the white dwarf, with M-star = 0.731 +/- 0.023 M-circle dot, T-eff = 7630 +/- 140 K, and [Ca/He] = - 9.55 +/- 0.12. With new high-resolution spectroscopy, we detect prominent and narrow Na D absorption features likely of circumstellar origin, with velocities 21.4 +/- 1.0 km s(-1) blueshifted relative to atmospheric lines. We attribute the periodically modulated photometric signal to dusty effluents from small orbiting bodies such as asteroids or comets, but we are unable to identify the most likely material that is being sublimated, or otherwise ejected, as the environmental temperatures range from roughly 400 to 700 K.

The application of pressure has been speculated to boost the search for high-temperature superconductors, especially in superhydrides. However, the applied pressure as high as hundreds of GPa needed to create superconductivity in those materials limits their technological application. Finding a route to achieve the high-temperature superconductivity at near-ambient conditions is attractive. By choosing a phase-change alloy Ge2Sb2Te5, we study the phase evolution of this material with pressure from the trigonal phase through the amorphous to the body-centered cubic one by the measurements of x-ray diffraction, Raman scattering, resistivity, and Hall coefficient. Superconductivity is observed to take place in the last two phases and can maintain at nearly ambient pressure in the decompression run. Pressure-induced disorder is found to be the key for holding superconductivity in the compressed phase-change alloy.

We present ALMA 1.3 mm observations of the HD 53143 debris disk-the first infrared or millimeter image produced of this similar to 1 Gyr old solar analog. Previous HST STIS coronagraphic imaging did not detect flux along the minor axis of the disk, which could suggest a face-on geometry with two clumps of dust. These ALMA observations reveal a disk with a strikingly different structure. In order to fit models to the millimeter visibilities and constrain the uncertainties on the disk parameters, we adopt a Markov Chain Monte Carlo approach. This is the most eccentric debris disk observed to date with a forced eccentricity of 0.21 +/- 0.02, nearly twice that of the Fomalhaut debris disk, and also displays an apocenter glow. Although this eccentric model fits the outer debris disk well, significant interior residuals remain, which may suggest a possible edge-on inner disk, which remains unresolved in these observations. Combined with the observed structure difference between HST and ALMA, these results suggest a potential previous scattering event or dynamical instability in this system. We also note that the stellar flux changes considerably over the course of our observations, suggesting flaring at millimeter wavelengths. Using simultaneous TESS observations, we determine the stellar rotation period to be 9.6 +/- 0.1 days.