While secondary mass inferences based on single-lined spectroscopic binary (SB1) solutions are subject to sini degeneracies, this degeneracy can be lifted through the observations of eclipses. We combine the subset of Gaia Data Release 3 SB1 solutions consistent with brown dwarf-mass secondaries with the Transiting Exoplanet Survey Satellite (TESS) Object of Interest (TOI) list to identify three candidate transiting brown dwarf systems. Ground-based precision radial velocity follow-up observations confirm that TOI-2533.01 is a transiting brown dwarf with M=72-3+3MJup=0.069-0.003+0.003M circle dot orbiting TYC 2010-124-1 and that TOI-5427.01 is a transiting very low-mass star with M=93-2+2MJup=0.088-0.002+0.002M circle dot orbiting UCAC4 515-012898. We validate TOI-1712.01 as a very low-mass star with M=82-7+7MJup=0.079-0.007+0.007M circle dot transiting the primary in the hierarchical triple system BD+45 1593. Even after accounting for third light, TOI-1712.01 has a radius nearly a factor of 2 larger than predicted for isolated stars with similar properties. We propose that the intense instellation experienced by TOI-1712.01 diminishes the temperature gradient near its surface, suppresses convection, and leads to its inflated radius. Our analyses verify Gaia DR3 SB1 solutions in the low Doppler semiamplitude limit, thereby providing the foundation for future joint analyses of Gaia radial velocities and Kepler, K2, TESS, and PLAnetary Transits and Oscillations light curves for the characterization of transiting massive brown dwarfs and very low-mass stars.

The MSb2 compounds with M = Cr,Fe, Ru, and Os have been investigated under high pressuresby synchrotron powder X-ray diffraction. All compounds, except CrSb2, were found to retain the marcasite structure up to the highestpressures (more than 50 GPa). In contrast, we found that CrSb2 has a structural phase transition around 10 GPa to a metastable,MoP2-type structure with Cr coordinated to seven Sb atoms.In addition, we compared ambient temperature compression with laser-heatingexperiments and found that laser-heating at pressures below and abovethis phase transition results in the known CuAl2-type structure.Density functional theory calculations show that this tetragonal structureis the most stable in the whole pressure interval. However, a crossingof the marcasite's and MoP2-like structure'senthalpies occurs between 5 and 7.5 GPa, which is in good agreementwith the experimental data. The phase transition to the MoP2-type structure observed in this work opens up for discovering othercompounds with this new transition pathway from the marcasite structure.

M & eacute;langes are mixtures of subducted materials and serpentinized mantle rocks that form along the slab-mantle interface in subduction zones. It has been suggested that m & eacute;lange rocks may be able to ascend from the slab-top into the overlying mantle, as solid or partially molten buoyant diapirs, and transfer their compositional signatures to the source regions of arc magmas. However, their ability to buoyantly rise is in part tied to their phase equilibria during melting and residual densities after melt extraction, all of which are poorly constrained. Here, we report a series of piston-cylinder experiments performed at 1.5-2.5 GPa and 500-1050 degrees C on three natural m & eacute;lange rocks that span a range of m & eacute;lange compositions. Using phase equilibria, solidus temperatures, and densities for all experiments, we show that melting of m & eacute;langes is unlikely to occur along the slab-top at pressures <= 2.5 GPa, so that diapirism into the hotter mantle wedge would be required for melting to initiate. For the two metaluminous m & eacute;lange compositions, diapir formation is favored up to pressures of at least 2.5 GPa. For the peraluminous m & eacute;lange composition investigated, diapir buoyancy is possible at 1.5 GPa but limited at 2.5 GPa due to the formation of high-density garnet, primarily at the expense of chlorite. We also evaluate whether thermodynamic modeling (Perple_X) can accurately reproduce the phase equilibria, solidus temperatures, and density evolution of m & eacute;lange compositions. Our analysis shows good agreement between models and experiments in m & eacute;lange compositions with low initial water contents and low-pressure (<= 1.5 GPa) conditions. However, discrepancies between the thermodynamic models and experiments become larger at higher pressures and high-water contents, highlighting the need for an improved thermodynamic database that can model novel bulk compositions beyond the canonical subducting lithologies. This study provides experimental constraints on m & eacute;lange buoyancy that can inform numerical models of m & eacute;lange diapirism and influence the interpretations of both geophysical signals and geochemical characteristics of magmas in subduction zones.(c) 2023 The Author(s). Published by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons .org /licenses /by-nc -nd /4 .0/).

Bimetallic nanoparticles have gained significant attention in catalysis as potential alternatives to expensive catalysts based on noble metals. In this study, we investigate the compositional tuning of Pd-Cu bimetallic nanoparticles using a physical synthesis method called spark ablation. By utilizing pure and alloyed electrodes in different configurations, we demonstrate the ability to tailor the chemical composition of nanoparticles within the range of approximately 80 : 20 at% to 40 : 60 at% (Pd : Cu), measured using X-ray fluorescence (XRF) and transmission electron microscopy energy dispersive X-ray spectroscopy (TEM-EDXS). Time-resolved XRF measurements revealed a shift in composition throughout the ablation process, potentially influenced by material transfer between electrodes. Powder X-ray diffraction confirmed the predominantly fcc phase of the nanoparticles while high-resolution TEM and scanning TEM-EDXS confirmed the mixing of Pd and Cu within individual nanoparticles. X-ray photoelectron and absorption spectroscopy were used to analyze the outermost atomic layers of the nanoparticles, which is highly important for catalytic applications. Such comprehensive analyses offer insights into the formation and structure of bimetallic nanoparticles and pave the way for the development of efficient and affordable catalysts for various applications.

To clarify the effect of oxygen defects on the perovskite structure under high pressure, structural changes in srebrodolskite Ca2Fe2O5 were investigated by using high-pressure Raman spectroscopy and synchrotron powder X-ray diffraction analyses. The result of the high-pressure Raman spectroscopic study showed that with compression, a new Raman band appeared at 12.0 GPa. Furthermore, an additional new Raman band appeared at 16.0 GPa. The phase-transition pressure was approximately consistent with the previous research, and the intensities of these new bands became much stronger with increasing pressure. At least nine Raman bands were observable at 23.0 GPa. A high-pressure synchrotron powder X-ray diffraction study was performed up to 20.2 GPa. The obtained pressure-volume compression curve apparently deviated from the equation-of-state of srebrodolskite determined by the previous study above 9.1 GPa, at which point srebrodolskite began to transform into its high- pressure phase. The Rietveld refinement of the X-ray diffraction data at 12.6 GPa fitted with space group Pn21a yielded agreement factors of Rp = 1.46% and wRp = 2.01%. The second high-pressure phase transition occurred at 14.2 GPa with the emergence of new reflections at d-spacing values of 3.938 and 1.953 angstrom. The powder X-ray diffraction patterns of the second high-pressure phase were characterized by three reflections appearing at approximately d-spacing values of 3.938, 2.609, and 1.953 angstrom. Consequently, the second high-pressure phase is likely to be composed of a new structure that is not included in the known brownmillerite-type structures. The results provide clues for understanding the physical properties of the chemically heterogeneous Earth's mantle.

Mercury has a compositionally diverse surface exhibiting geochemical terranes that represent different periods of igneous activity, suggesting diverse mantle source compositions. Mercury's juvenile mantle likely formed after fractional solidification of a magma ocean, which produced distinct mineralogical horizons with depth. To produce the diversity of observed volcanic terranes, dynamic mixing of materials from distinct mantle horizons is required. One process that could dynamically mix the juvenile cumulate pile is cumulate mantle overturn, where dense layers in shallow planetary mantles sink into deeper, less dense layers as Rayleigh-Taylor instabilities. Gravitationally unstable density stratification is a requisite starting condition for overturn; solidification of the Mercurian magma ocean is likely to have produced such a density inversion, with a relatively dense clinopyroxene-bearing pyroxenite layer atop lower density dunite and harzburgite layers. Sulfides are present in abundance on Mercury's surface and would be additional mantle phase(s) if they are indigenous to the planet's interior. Sulfides have variable densities; they could potentially enhance the formation of gravitational instabilities or prevent them from developing. Exploring physically reasonable mantle density and viscosity structures, we evaluate the potential for cumulate mantle overturn in Mercury and predict the possible timing, scale, and rate of overturn for plausible physical parameter combinations. Our analysis suggests that overturn is possible in Mercury's mantle within 100 Myr of magma ocean solidification, providing a mechanism for producing the mantle sources that would melt to form surface compositions on Mercury, and overturn may control the spatial scale of volcanic provinces observed on the surface today.

Context. Gaps in circumstellar disks can signal the existence of planetary perturbers, making such systems preferred targets for direct imaging observations of exoplanets. Aims. Being one of the brightest and closest stars to the Sun, the photometric standard star Vega hosts a two-belt debris disk structure. Together with the fact that its planetary system is being viewed nearly face-on, Vega has been one of the prime targets for planet imaging efforts. Methods. Using the vector vortex coronagraph on Keck/NIRC2 in the M-s band at 4.67 mu m, we report the planet detection limits from 1 au to 22 au for Vega with an on-target time of 1.8 h. Results. We reach a 3 M-Jupiter limit outward of 12 au, which is nearly an order of magnitude deeper than for other existing studies. Combining our observations with existing radial velocity studies, we can confidently rule out the existence of companions more than similar to 8 M-Jupiter from 22 au down to 0.1 au for Vega. Interior and exterior to similar to 4 au, this combined approach reaches planet detection limits down to similar to 2-3 M-Jupiter using radial velocity and direct imaging, respectively. Conclusions. By reaching multi-Jupiter mass detection limits, our results are expected to be complemented by the planet imaging of Vega in the upcoming observations using the James Webb Space Telescope to obtain a more holistic understanding of the planetary system configuration around Vega.

Giant planets around young stars serve as a clue to unveiling their formation history and orbital evolution. CI Tau is a 2 Myr-old classical T Tauri star hosting an eccentric hot Jupiter, CI Tau b. The standard formation scenario of a hot Jupiter predicts that planets formed further out and migrated inward. A high eccentricity of CI Tau b may be suggestive of high-e migration due to secular gravitational perturbations by an outer companion. Also, the Atacama Large Millimeter/submillimeter Array 1.3 mm-continuum observations show that CI Tau has at least three annular gaps in which unseen planets may exist. We present high-contrast imaging around CI Tau taken from the Keck/NIRC2 -band filter and vortex coronagraph that allows us to search for an outer companion. We did not detect any outer companion around CI Tau from angular differential imaging (ADI) using two deep imaging data sets. The detection limits from ADI-reduced images rule out the existence of an outer companion beyond similar to 30 au that can cause the Kozai-Lidov migration of CI Tau b. Our results suggest that CI Tau b may have experienced type II migration from ?2 au in megayears. We also confirm that no planets with >= 2-4 M-Jup are hidden in two outer gaps.

Planet formation imprints signatures on the physical structures of disks. In this paper, we present high-resolution (similar to 50 mas, 8 au) Atacama Large Millimeter/submillimeter Array observations of 1.3 mm dust continuum and CO line emission toward the disk around the M3.5 star 2MASSJ04124068+2438157. The dust disk consists of only two narrow rings at radial distances of 0 47 and 0 78 (similar to 70 and 116 au), with Gaussian sigma widths of 5.6 and 8.5 au, respectively. The width of the outer ring is smaller than the estimated pressure scale height by similar to 25%, suggesting dust trapping in a radial pressure bump. The dust disk size, set by the location of the outermost ring, is significantly larger (by 3 sigma) than other disks with similar millimeter luminosity, which can be explained by an early formation of local pressure bump to stop radial drift of millimeter dust grains. After considering the disk's physical structure and accretion properties, we prefer planet-disk interaction over dead zone or photoevaporation models to explain the observed dust disk morphology. We carry out high-contrast imaging at the L' band using Keck/NIRC2 to search for potential young planets, but do not identify any source above 5 sigma. Within the dust gap between the two rings, we reach a contrast level of similar to 7 mag, constraining the possible planet below similar to 2-4M(Jup). Analyses of the gap/ring properties suggest that an approximately Saturn-mass planet at similar to 90 au is likely responsible for the formation of the outer ring, which can potentially be revealed with JWST.