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Abstract
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 (0.09 M-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.
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Abstract
The chemical interaction of Sn with H-2 by X-ray diffraction methods at pressures of 180-210 GPa is studied. A previously unknown tetrahydride SnH4 with a cubic structure (fcc) exhibiting superconducting properties below T-C = 72 K is obtained; the formation of a high molecular C2/m-SnH14 superhydride and several lower hydrides, fcc SnH2, and C2-Sn12H18, is also detected. The temperature dependence of critical current density C-J(T) in SnH4 yields the superconducting gap 2 Delta(0) = 21.6 meV at 180 GPa. SnH4 has unusual behavior in strong magnetic fields: B,T-linear dependences of magnetoresistance and the upper critical magnetic field B-C2(T) proportional to(T-C - T). The latter contradicts the Wertheimer-Helfand-Hohenberg model developed for conventional superconductors. Along with this, the temperature dependence of electrical resistance of fcc SnH4 in non-superconducting state exhibits a deviation from what is expected for phonon-mediated scattering described by the Bloch-Gruneisen model and is beyond the framework of the Fermi liquid theory. Such anomalies occur for many superhydrides, making them much closer to cuprates than previously believed.
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Abstract
Physical laws-such as the laws of motion, gravity, electromagnetism, and thermodynamics-codify the general behavior of varied macroscopic natural systems across space and time. We propose that an additional, hitherto-unarticulated law is required to characterize familiar macroscopic phenomena of our complex, evolving universe. An important feature of the classical laws of physics is the conceptual equivalence of specific characteristics shared by an extensive, seemingly diverse body of natural phenomena. Identifying potential equivalencies among disparate phenomena-for example, falling apples and orbiting moons or hot objects and compressed springs-has been instrumental in advancing the scientific understanding of our world through the articulation of laws of nature. A pervasive wonder of the natural world is the evolution of varied systems, including stars, minerals, atmospheres, and life. These evolving systems appear to be conceptually equivalent in that they display three notable attributes: 1) They form from numerous components that have the potential to adopt combinatorially vast numbers of different configurations; 2) processes exist that generate numerous different configurations; and 3) configurations are preferentially selected based on function. We identify universal concepts of selection-static persistence, dynamic persistence, and novelty generation-that underpin function and drive systems to evolve through the exchange of information between the environment and the system. Accordingly, we propose a "law of increasing functional information": The functional information of a system will increase (i.e., the system will evolve) if many different configurations of the system undergo selection for one or more functions.
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Abstract
This paper reports the first measurement of the relationship between turbulent velocity and cloud size in the diffuse circumgalactic medium (CGM) in typical galaxy halos at redshift z approximate to 0.4-1. Through spectrally resolved absorption profiles of a suite of ionic transitions paired with careful ionization analyses of individual components, cool clumps of size as small as l(cl) similar to 1 pc and density lower than n(H) =10(-3) cm(-3) are identified in galaxy halos. In addition, comparing the line widths between different elements for kinematically matched components provides robust empirical constraints on the thermal temperature T and the nonthermal motions b(NT), independent of the ionization models. On average, b(NT) is found to increase with lcl following bNT mu l(cl)(0.3)over three decades in spatial scale from l(cl) approximate to 1 pc to l(cl) approximate to 1 kpc. Attributing the observed b(NT) to turbulent motions internal to the clumps, the best-fit b(NT)-l(cl) relation shows that the turbulence is consistent with Kolmogorov at <1 kpc with a roughly constant energy transfer rate per unit mass of epsilon approximate to 0.003 cm(2) s(-3) and a dissipation timescale of less than or similar to 100 Myr. No significant difference is found between massive quiescent and star-forming halos in the sample on scales less than 1 kpc. While the inferred epsilon is comparable to what is found in C IV absorbers at high redshift, it is considerably smaller than observed in star-forming gas or in extended line-emitting nebulae around distant quasars. A brief discussion of possible sources to drive the observed turbulence in the cool CGM is presented.
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Sachi Weerasooriya

Postdoctoral Fellow

Observatories
Ca-silicate inclusion inside a diamond from Kankan, Guinea. Photo credit: Margo Regier.
October 18, 2023

Superdeep diamonds provide a window on supercontinent growth

Opalized ammonite. Credit: ARKENSTONE/Rob Lavinsky

Opalized ammonite: A beautiful example from Alberta, Canada of the intersection of biological evolution and mineral evolution — the interplay between minerals and life. A hundred million years ago, the ammonite deposited its own hard carbonate shell — a "biomineral." In this rare case, that original carbonate shell was later replaced by the fiery mineral opal. Credit: ARKENSTONE/Rob Lavinsky

October 16, 2023

Scientists and philosophers team up to study concept of evolution beyond biological context

Abstract
The Mars Environmental Dynamics Analyzer (MEDA) on board Perseverance includes first-of-its-kind sensors measuring the incident and reflected solar flux, the downwelling atmospheric IR flux, and the upwelling IR flux emitted by the surface. We use these measurements for the first 350 sols of the Mars 2020 mission (L-s similar to 6 degrees-174 degrees in Martian Year 36) to determine the surface radiative budget on Mars and to calculate the broadband albedo (0.3-3 mu m) as a function of the illumination and viewing geometry. Together with MEDA measurements of ground temperature, we calculate the thermal inertia for homogeneous terrains without the need for numerical thermal models. We found that (a) the observed downwelling atmospheric IR flux is significantly lower than the model predictions. This is likely caused by the strong diurnal variation in aerosol opacity measured by MEDA, which is not accounted for by numerical models. (b) The albedo presents a marked non-Lambertian behavior, with lowest values near noon and highest values corresponding to low phase angles (i.e., Sun behind the observer). (c) Thermal inertia values ranged between 180 (sand dune) and 605 (bedrock-dominated material) SI units. (d) Averages of albedo and thermal inertia (spatial resolution of similar to 3-4 m(2)) along Perseverance's traverse are in very good agreement with collocated retrievals of thermal inertia from Thermal Emission Imaging System (spatial resolution of 100 m per pixel) and of bolometric albedo in the 0.25-2.9 mu m range from (spatial resolution of similar to 300 km(2)). The results presented here are important to validate model predictions and provide ground-truth to orbital measurements.
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Abstract
We present new maps of the Milky Way disk showing the distribution of metallicity ([Fe/H]), alpha-element abundances ([Mg/Fe]), and stellar age, using a sample of 66,496 red giant stars from the final data release (DR17) of the Apache Point Observatory Galactic Evolution Experiment survey. We measure radial and vertical gradients, quantify the distribution functions for age and metallicity, and explore chemical clock relations across the Milky Way for the low-a disk, high-alpha disk, and total population independently. The low-alpha disk exhibits a negative radial metallicity gradient of -0.06 +/- 0.001 dex kpc(-1), which flattens with distance from the midplane. The high-alpha disk shows a flat radial gradient in metallicity and age across nearly all locations of the disk. The age and metallicity distribution functions shift from negatively skewed in the inner Galaxy to positively skewed at large radius. Significant bimodality in the [Mg/Fe]-[Fe/H] plane and in the [Mg/Fe]-age relation persist across the entire disk. The age estimates have typical uncertainties of similar to 0.15 in log(age) and may be subject to additional systematic errors, which impose limitations on conclusions drawn from this sample. Nevertheless, these results act as critical constraints on galactic evolution models, constraining which physical processes played a dominant role in the formation of the Milky Way disk. We discuss how radial migration predicts many of the observed trends near the solar neighborhood and in the outer disk, but an additional more dramatic evolution history, such as the multi-infall model or a merger event, is needed to explain the chemical and age bimodality elsewhere in the Galaxy.
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James Johnson

Postdoctoral Fellow

Observatories

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