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The GALAH+ survey: Third data release
(Oxford University Press on behalf of Royal Astronomical Society, 2021) Buder, Sven; Sharma, Sanjib; Kos, J.; Amarsi, A. M.; Nordlander, Thomas; Lind, Karin; Martell, S. L.; Asplund, Martin; Bland-Hawthorn, Jonathan; Casey, Andrew; De Silva, Gayandhi M; D’Orazi, Valentina; Freeman, Kenneth; Hayden, Michael R.; Lewis, Geraint Francis; lin, jane; Schlesinger, Katharine; Simpson, Jeffrey D; Stello, Dennis; Zucker, Daniel; Casagrande, Luca; Da Costa, Gary; Nandakumar, Govind; Ting, Yuan-Sen; Zerjal, Marusa
The ensemble of chemical element abundance measurements for stars, along with precision distances and orbit properties, provides high-dimensional data to study the evolution of the Milky Way. With this third data release of the Galactic Archaeology with HERMES (GALAH) survey, we publish 678 423 spectra for 588 571 mostly nearby stars (81.2 per cent of stars are within <2 kpc), observed with the HERMES spectrograph at the Anglo-Australian Telescope. This release (hereafter GALAH+ DR3) includes all observations from GALAH Phase 1 (bright, main, and faint survey, 70 per cent), K2-HERMES (17 per cent), TESS-HERMES (5 per cent), and a subset of ancillary observations (8 per cent) including the bulge and >75 stellar clusters. We derive stellar parameters T-eff, logg, [Fe/H], v(mic), v(broad), and v(rad) using our modified version of the spectrum synthesis code Spectroscopy Made Easy (SME) and 1D MARCS model atmospheres. We break spectroscopic degeneracies in our spectrum analysis with astrometry from Gaia DR2 and photometry from 2MASS. We report abundance ratios [X/Fe] for 30 different elements (11 of which are based on non-LTE computations) covering five nucleosynthetic pathways. We describe validations for accuracy and precision, flagging of peculiar stars/measurements and recommendations for using our results. Our catalogue comprises 65 per cent dwarfs, 34 per cent giants, and 1 per cent other/unclassified stars. Based on unflagged chemical composition and age, we find 62 per cent young low-alpha, 9 per cent young high-alpha, 27 per cent old high-alpha, and 2 per cent stars with [Fe/H] <= -1. Based on kinematics, 4 per cent are halo stars. Several Value-Added-Catalogues, including stellar ages and dynamics, updated after Gaia eDR3, accompany this release and allow chrono-chemodynamic analyses, as we showcase.
Direct zircon U-Pb evidence for pre-Himalayan HT metamorphism in the Higher Himalayan Crystallines, eastern Garhwal Himalaya, India
(John Wiley & Sons Inc, 2022-01-02) Mohan, Shashank Prabha; Williams, Ian; Singh, Sandeep
The high-grade Higher Himalayan Crystallines (HHC), located between the South Tibetan Detachment System and Main Central Thrust in the collision zone between the Indo-Australian and Eurasian plates, have been subject to at least four significant phases of deformation and metamorphism. The earliest of those significantly predates the Cenozoic continent-continent collision, but has been difficult to date isotopically because of later overprinting. Migmatitic paragneiss from the Badrinath Formation in the Dhauliganga Valley, northern Uttarakhand, some of the highest-grade rocks in the HHC, preserves direct evidence of mid-Ordovician metamorphism in the form of 465.8 +/- 6.4 Ma zircon overgrowths with extremely low Th/U (0.0038-0.0074). The overgrowths have formed on ca. 2.63-0.71 Ga detrital zircon cores and are themselves overgrown by two generations of Miocene metamorphic zircon with mean Pb/U ages of ca. 21.5 and 18.2 Ma. Monazite from the same sample has a mean Pb/Th age of 19.4 +/- 0.2 Ma. The oxygen isotopic compositions of the monazite (delta O-18: 7.69 +/- 0.08 parts per thousand) and youngest zircon overgrowths (delta O-18: 7.95 +/- 0.12, 8.24 +/- 0.09 parts per thousand) are consistent with mineral growth in a metasediment, but either of the two minerals did not grow in isotopic equilibrium with each other, or the original composition of the monazite has not been preserved. If the quartz (delta O-18: 13.29 +/- 0.11 parts per thousand) equilibrated with the youngest zircon and its composition has been preserved, then the last episode of zircon growth took place at low temperature, ca. 420 degrees C, after the migmatization. The protolith of the Badrinath migmatite was a Neoproterozoic or Early Palaeozoic metasediment partially melted (and probably migmatized) in the Middle Ordovician. The strong planar foliation currently present in the migmatite is probably the result of mid-crustal extrusional channel flow and HT decompressional partial melting in the Miocene.
Quantifying the nature of ore-forming fluids in the Dalucao carbonatite-related REE deposit, Southwest China: implication for the transport and deposition of REEs
(Springer Verlag, 2022-08) Zhang, Wei; Chen, Wei Terry; Mernagh, Terry; Zhou, Li
Carbonatite-related rare earth element (REE) deposits are major hosts of REE resources. REE mineralization in these deposits is generally associated with hydrothermal systems at late stages of carbonatite evolution, but the nature of ore-forming fluids and their role in concentrating REEs are not well understood. In this study, we quantified the nature of ore-forming fluids by conducting a detailed investigation on the fluid inclusions of the Dalucao carbonatite–related REE deposit, Southwest China. Based on the phases present at room temperature, three types of fluid inclusions, namely, high-density, CO2-rich inclusions, solid-bearing brine inclusions, and aqueous liquid inclusions, have been distinguished in the deposit. High-resolution Raman mapping reveals that the daughter minerals in the earliest brine inclusions are dominantly composed of sulfate (average mass proportion of 92.3%) with minor chloride (3.1%), carbonate (4.4%), and silicate (0.2%). In addition, a Raman peak of SO42– has been detected in the liquid phase of the aqueous inclusions. These new results suggest that the early, high-temperature ore-forming fluids are unique for containing extremely high concentrations of sulfate. Such sulfate-rich fluids are confirmed to be responsible for transporting appreciable amounts of REEs in the forms of REE-sulfate complexes. We further propose that deposition of REE minerals was mainly triggered by decreasing temperatures, which, as a result, reduced the solubility of sulfate in the fluids. Our new findings highlight the fact that sulfate-rich fluids tend to be more common in carbonatite-related REE deposits and play key roles in REE mineralization.
Algebraic Characterization of Fixed Modes in Decentralized Control
(1981) Anderson, Brian D.O.; Clements, David J.
Algebraic characterizations are presented for the existence of fixed modes of a linear closed-loop system with decentralized feedback control. The class of controllers for which fixed modes are present is extended beyond that currently known.
First extragalactic measurement of the turbulence driving parameter: ALMA observations of the star-foing region N159E in the Large Magellanic Cloud
(Oxford University Press on behalf of Royal Astronomical Society, 2021) Sharda, Piyush; Harimohan Menon, Shyam; Federrath, Christoph; Krumholz, Mark; Beattie, James; Jameson, K.; Tokuda, K.; Burkhart, Blakesley; Crocker, Roland; Law, Charles J.; Seta, Amit; Gaetz, Terrance, J.; Pingel, Nickolas; Seitenzahl, Ivo R; Sano, Hidetoshi; Fukui, Yasuo
Studying the driving modes of turbulence is important for characterizing the impact of turbulence in various astrophysical environments. The driving mode of turbulence is parametrized by b, which relates the width of the gas density PDF to the turbulent Mach number; b approximate to 1/3, 1, and 0.4 correspond to driving that is solenoidal, compressive, and a natural mixture of the two, respectively. In this work, we use high-resolution (sub-pc) ALMA (CO)-C-12 (J = 2-1), (CO)-C-13 (J = 2-1), and (CO)-O-18 (J = 2-1) observations of filamentary molecular clouds in the star-forming region N159E (the Papillon Nebula) in the Large Magellanic Cloud (LMC) to provide the first measurement of turbulence driving parameter in an extragalactic region. We use a non-local thermodynamic equilibrium (NLTE) analysis of the CO isotopologues to construct a gas density PDF, which we find to be largely lognormal in shape with some intermittent features indicating deviations from lognormality. We find that the width of the lognormal part of the density PDF is comparable to the supersonic turbulent Mach number, resulting in b approximate to 0.9. This implies that the driving mode of turbulence in N159E is primarily compressive. We speculate that the compressive turbulence could have been powered by gravo-turbulent fragmentation of the molecular gas, or due to compression powered by Hi flows that led to the development of the molecular filaments observed by ALMA in the region. Our analysis can be easily applied to study the nature of turbulence driving in resolved star-forming regions in the local as well as the high-redshift Universe.