FeO represents an important end-member for planetary interiors mineralogy. However, its properties in the liquid state under high pressure are poorly constrained. Here, in situ high-pressure and high-temperature X-ray diffraction experiments, ab initio simulations, and thermodynamic calculations are combined to study the local structure and density evolution of liquid FeO under extreme conditions. Our results highlight a strong shortening of the Fe-Fe distance, particularly pronounced between ambient pressure and similar to 40 GPa, possibly related with the insulator to metal transition occurring in solid FeO over a similar pressure range. Liquid density is smoothly evolving between 60 and 150 GPa from values calculated for magnetic liquid to those calculated for non-magnetic liquid, compatibly with a continuous spin crossover in liquid FeO. The present findings support the potential decorrelation between insulator/metal transition and the high-spin to low-spin continuous transition, and relate the changes in the microscopic structure with macroscopic properties, such as the closure of the Fe-FeO miscibility gap. Finally, these results are used to construct a parameterized thermal equation of state for liquid FeO providing densities up to pressure and temperature conditions expected at the Earth's core-mantle boundary.

Accurate and precise measurements of spectroradiometric temperature are crucial for many high pressure experiments that use diamond anvil cells or shock waves. In experiments with sub-millisecond timescales, specialized detectors such as streak cameras or photomultiplier tubes are required to measure temperature. High accuracy and precision are difficult to attain, especially at temperatures below 3000 K. Here, we present a new spectroradiometry system based on multianode photomultiplier tube technology and passive readout circuitry that yields a 0.24 mu s rise-time for each channel. Temperature is measured using five color spectroradiometry. During high pressure pulsed Joule heating experiments in a diamond anvil cell, we document measurement precision to be +/- 30 K at temperatures as low as 2000 K during single-shot heating experiments with 0.6 mu s time-resolution. Ambient pressure melting tests using pulsed Joule heating indicate that the accuracy is +/- 80 K in the temperature range 1800-2700 K.

Solid iron-silicon alloys play an important role in planetary cores, especially for planets that formed under reducing conditions, such as Mercury. The CsCl (B2) structure occupies a considerable portion of the Fe-Si binary phase diagram at pressure and temperature conditions relevant for the core of Mercury, yet its thermodynamic and thermoelastic properties are poorly known. Here, we report in situ X-ray difraction measurements on iron-silicon alloys with 7-30 wt% Si performed in laser-heated diamond-anvil cells up to similar to 120 GPa and similar to 3000 K. Unit-cell volumes of the B2 phase at high pressures and high temperatures have been used to obtain a composition-dependent thermal equation of state of this phase. In turn, the thermal equation of state is exploited to determine the composition of the B2 phase in hcp+B2 mixtures at 30-100 GPa and to place constraints on the hcp+B2/B2 phase boundary, determined to vary between similar to 13-18 wt% Si in the considered pressure and temperature range. The hcp+B2/B2 boundary of Fe-Si alloys is observed to be dependent on pressure but weakly dependent on temperature. Our results, coupled with literature data on liquid equations of state, yield an estimation of the density contrast between B2 solid and liquid under Mercury's core conditions, which directly relates to the buoyancy of the crystallizing material. While the density contrast may be large enough to form a solid inner core by the gravitational sinking of B2 alloys in a Si-rich core, the density of the B2 solid is close to that of the liquid at solidus conditions for Si concentration approaching similar to 10 wt% Si.

In this study, we conduct extensive high-pressure experiments to investigate phase stability in the cobalt-nitrogen system. Through a combination of synthesis in a laser-heated diamond anvil cell, first-principles calculations, Raman spectroscopy, and single-crystal X-ray diffraction, we establish the stability fields of known high-pressure phases, hexagonal NiAs-type CoN, and marcasite-type CoN2 within the pressure range of 50-90 GPa. We synthesize and characterize previously unknown nitrides, Co3N2, Pnma-CoN and two polynitrides, CoN3 and CoN5, within the pressure range of 90-120 GPa. Both polynitrides exhibit novel types of polymeric nitrogen chains and networks. CoN3 feature branched-type nitrogen trimers (N3) and CoN5 show pi-bonded nitrogen chain. As the nitrogen content in the cobalt nitride increases, the CoN6 polyhedral frameworks transit from face-sharing (in CoN) to edge-sharing (in CoN2 and CoN3), and finally to isolated (in CoN5). Our study provides insights into the intricate interplay between structure evolution, bonding arrangements, and high-pressure synthesis in polynitrides, expanding the knowledge for the development of advanced energy materials.

We present the JWST Resolved Stellar Populations Early Release Science (ERS) program. We obtained 27.5 hr of NIRCam and NIRISS imaging of three targets in the Local Group (Milky Way globular cluster M92, ultrafaint dwarf galaxy Draco II, and star-forming dwarf galaxy WLM), which span factors of similar to 10(5) in luminosity, similar to 10(4) in distance, and similar to 10(5) in surface brightness. We describe the survey strategy, scientific and technical goals, implementation details, present select NIRCam color-magnitude diagrams (CMDs), and validate the NIRCam exposure time calculator (ETC). Our CMDs are among the deepest in existence for each class of target. They touch the theoretical hydrogen-burning limit in M92 (<0.08 M-circle dot; M-F090W similar to +13.6), include the lowest-mass stars observed outside the Milky Way in Draco II (0.09M(circle dot); M-F090W similar to +12.1), and reach similar to 1.5 mag below the oldest main-sequence turnoff in WLM (M-F090W similar to +4.6). The PARSEC stellar models provide a good qualitative match to the NIRCam CMDs, though they are similar to 0.05 mag too blue compared to M92 F090W - F150W data. Our CMDs show detector-dependent color offsets ranging from similar to 0.02 mag in F090W - F150W to similar to 0.1 mag in F277W - F444W; these appear to be due to differences in the zero-point calibrations among the detectors. The NIRCam ETC (v2.0) matches the signal-to-noise ratios based on photon noise in uncrowded fields, but the ETC may not be accurate in more crowded fields, similar to what is known for the Hubble Space Telescope. We release the point-source photometry package DOLPHOT, optimized for NIRCam and NIRISS, for the community.

KELT-9b is an ultra-hot Jupiter observed to be undergoing extreme mass-loss. Its A0-type host star has a radiative envelope, which makes its surface layers prone to retaining recently accreted material. To search for potential signs of planetary material polluting the stellar surface, we carry out the most comprehensive chemical characterization of KELT-9 to-date. New element detections include Na and Y, which had previously been detected in the ultra-hot Jupiter but not studied in the star; these detections complete the set of ten elements measured in both star and planet. In comparing KELT-9 with similar open cluster stars we find no strong anomalies. This finding is consistent with calculations of photospheric pollution accounting for stellar mixing and using observationally estimated KELT-9b mass-loss rates. We also rule out recent, short-lived intensive mass transfer such as the stellar ingestion of an Earth-mass exomoon.

The two prevailing planet formation scenarios, core accretion and disk instability, predict distinct planetary mass-metallicity relations. Yet, the detection of this trend remains challenging due to inadequate data on planet atmosphere abundance and inhomogeneities in both planet and host stellar abundance measurements. Here we analyze high-resolution spectra for the host stars of 19 transiting exoplanets to derive the C, O, Na, S, and K abundances, including planetary types from cool mini-Neptunes to hot Jupiters (T-eq similar to 300-2700 K; planet radius similar to 0.1-2 R-J). Our Monte Carlo simulations suggest that the current data set, updated based on Welbanks et al., is unable to distinguish between a linear relation and an independent distribution model for the abundance-mass correlation for water, Na, or K. To detect a trend with strong evidence (Bayes factor > 10) at the 2 sigma confidence interval, we recommend a minimum sample of 58 planets with Hubble Space Telescope measurements of water abundances coupled with [O/H] of the host stars, or 45 planets at the JWST precision. Coupled with future JWST or ground-based high-resolution data, this well-characterized sample of planets with precise host-star abundances constitute an important ensemble of planets to further probe the abundance-mass correlation.

Prompt rho proportional to r-1.5 density cusps are the densest and most abundant dark matter systems. If the dark matter is a weakly interacting massive particle (WIMP), recent studies have shown that prompt cusps dominate the aggregate dark matter annihilation rate. This article explores whether individual prompt cusps could be detected as gamma-ray sources. At the Fermi Telescope's point-source sensitivity, WIMPs with the canonical annihilation cross section could form detectable prompt cusps if the particle mass is of order 10 GeV. These objects could be 10-100 pc away and weigh under a solar mass; they would subtend around 0.1 degrees on the sky. For GeV-scale dark matter particles with below-canonical cross sections, searches for individual prompt cusps can be more sensitive than searches for the annihilation signals from galactic dark matter halos.

Aims. We explore different scenarios to explain the chemical difference found in the remarkable giant-giant binary system HD 138202 + CD-30 12303. For the first time, we suggest how to distinguish these scenarios by taking advantage of the extensive convective envelopes of giant stars. Methods. We carried out a high-precision determination of stellar parameters and abundances by applying a full line-by-line differential analysis on GHOST high-resolution spectra. We used the FUNDPAR program with ATLAS12 model atmospheres and specific opacities calculated for an arbitrary composition through a doubly iterated method. Physical parameters were estimated with the isochrones package and evolutionary tracks were calculated via MIST models. Results. We found a significant chemical difference between the two stars (Delta[Fe/H] similar to 0.08 dex), which is largely unexpected considering the insensitivity of giant stars to planetary ingestion and diffusion effects. We tested the possibility of engulfment events by using several different combinations of stellar mass, ingested mass, metallicity of the engulfed object and different convective envelopes. However, the planetary ingestion scenario does not seem to explain the observed differences. For the first time, we distinguished the source of chemical differences using a giant-giant binary system. By ruling out other possible scenarios such as planet formation and evolutionary effects between the two stars, we suggest that primordial inhomogeneities might explain the observed differences. This remarkable result implies that the metallicity differences that were observed in at least some main-sequence binary systems might be related to primordial inhomogeneities rather than engulfment events. We also discuss the important implications of finding primordial inhomogeneities, which affect chemical tagging and other fields such as planet formation. We strongly encourage the use of giant-giant pairs. They are a relevant complement to main-sequence pairs for determining the origin of the observed chemical differences in multiple systems.

Excursion set theory is a powerful and widely used tool for describing the distribution of dark matter haloes, but it is normally applied with simplifying approximations. We use numerical sampling methods to study the mass functions predicted by the theory without approximations. With a spherical top-hat window and a constant delta = 1.5 threshold, the theory accurately predicts mass functions with the M-200 mass definition, both unconditional and conditional, in simulations of a range of matter-dominated cosmologies. For Lambda cold dark matter at the present epoch, predictions lie between the M-200m and M-200c mass functions. In contrast, with the same window function, a non-constant threshold based on ellipsoidal collapse predicts uniformly too few haloes. This work indicates a new way to simply and accurately evaluate halo mass functions, clustering bias, and assembly histories for a range of cosmologies. We provide a fitting function that accurately represents the predictions of the theory for a wide range of parameters.