This paper presents the detailed abundances and r-process classifications of 126 newly identified metal-poor stars as part of an ongoing collaboration, the R-Process Alliance. The stars were identified as metal-poor candidates from the RAdial Velocity Experiment (RAVE) and were followed up at high spectral resolution (R similar to 31,500) with the 3.5 m telescope at Apache Point Observatory. The atmospheric parameters were determined spectroscopically from Fe I lines, taking into account < 3D > non-LTE corrections and using differential abundances with respect to a set of standards. Of the 126 new stars, 124 have [Fe/H] < -1.5, 105 have [Fe/H] < -2.0, and 4 have [Fe/H] < -3.0. Nine new carbon-enhanced metal-poor stars have been discovered, three of which are enhanced in r-process elements. Abundances of neutron-capture elements reveal 60 new r-I stars (with +0.3 <= [Eu/Fe] <= +1.0 and [Ba/Eu] < 0) and 4 new r-II stars (with [Eu/Fe] > +1.0). Nineteen stars are found to exhibit a "limited-r" signature ([Sr/Ba] > +0.5, [Ba/Eu] < 0). For the r-II stars, the second- and third-peak main r-process patterns are consistent with the r-process signature in other metal-poor stars and the Sun. The abundances of the light, alpha, and Fe-peak elements match those of typical Milky Way (MW) halo stars, except for one r-I star that has high Na and low Mg, characteristic of globular cluster stars. Parallaxes and proper motions from the second Gaia data release yield UVW space velocities for these stars that are consistent with membership in the MW halo. Intriguingly, all r-II and the majority of r-I stars have retrograde orbits, which may indicate an accretion origin.

We present results from an observing campaign to identify low-metallicity stars in the Best & Brightest Survey. From medium-resolution (R similar to 1200-2000) spectroscopy of 857 candidates, we estimate the stellar atmospheric parameters (T-eff, log g, and [Fe/H]), as well as carbon and alpha-element abundances. We find that 69% of the observed stars have [Fe/H] <= -1.0, 39% have [Fe/H] <= -2.0, and 2% have [Fe/H] <= -3.0. There are also 133 carbon-enhanced metal-poor (CEMP) stars in this sample, with 97 CEMP Group. I and 36 CEMP Group. II stars identified in the A(C) versus [Fe/H] diagram. A subset of the confirmed low-metallicity stars were followed-up with high-resolution spectroscopy, as part of the R-process Alliance, with the goal of identifying new highly and moderately r-process-enhanced stars. Comparison between the stellar atmospheric parameters estimated in this work and from high-resolution spectroscopy exhibit good agreement, confirming our expectation that medium-resolution observing campaigns are an effective way of selecting interesting stars for further, more targeted, efforts.

We report on the spectroscopic analysis of RAVE J183013.5-455510, an extremely metal-poor star, highly enhanced in CNO, and with discernible contributions from the rapid neutron-capture process. There is no evidence of binarity for this object. At [Fe/H] = -3.57, this star has one of the lowest metallicities currently observed, with 18 measured abundances of neutron-capture elements. The presence of Ba, La, and Ce abundances above the solar system r-process predictions suggests that there must have been a non-standard source of r-process elements operating at such low metallicities. One plausible explanation is that this enhancement originates from material ejected at unusually high velocities in a neutron star merger event. We also explore the possibility that the neutron-capture elements were produced during the evolution and explosion of a rotating massive star. In addition, based on comparisons with yields from zero-metallicity faint supernova, we speculate that RAVE J1830-4555 was formed from a gas cloud pre-enriched by both progenitor types. From analysis based on Gaia DR2 measurements, we show that this star has orbital properties similar to the Galactic metal-weak thick-disk stellar population.

Binary neutron star mergers (NSMs) have been confirmed as one source of the heaviest observable elements made by the rapid neutron-capture (r-) process. However, modeling NSM outflows-from the total ejecta masses to their elemental yields-depends on the unknown nuclear equation of state (EOS) that governs neutron star structure. In this work, we derive a phenomenological EOS by assuming that NSMs are the dominant sources of the heavy element material in metal-poor stars with r-process abundance patterns. We start with a population synthesis model to obtain a population of merging neutron star binaries and calculate their EOS-dependent elemental yields. Under the assumption that these mergers were responsible for the majority of r-process elements in the metal-poor stars, we find parameters representing the EOS for which the theoretical NSM yields reproduce the derived abundances from observations of metal-poor stars. For our proof-of-concept assumptions, we find an EOS that is slightly softer than, but still in agreement with, current constraints, e.g., by the Neutron Star Interior Composition Explorer, with R (1.4) = 12.25 +/- 0.03 km and M (TOV) = 2.17 +/- 0.03 M (circle dot) (statistical uncertainties, neglecting modeling systematics).

We are building an image slicer integral field unit (IFU) to go on the IMACS wide-field imaging spectrograph on the Magellan Baade Telescope at Las Campanas Observatory, the Reformatting Optically-Sensitive IMACS Enhancement IFU, or ROSIE IFU. The 50.4 '' x 53.5 '' field of view will be pre-sliced into four 12.6 '' x 53.5 '' subfields, and then each subfield will be divided into 21 0.6 '' x 53.5 '' slices. The four main image slicers will produce four pseudo-slits spaced six arcminutes apart across the IMACS f/2 camera field of view, providing a wavelength coverage of 1800 Angstroms at a spectral resolution of 2000. Optics are in-hand, the first image slicer is being aluminized, mounts are being designed and fabricated, and software is being written. This IFU will enable the efficient mapping of extended objects such as nebulae, galaxies, or outflows, making it a powerful addition to IMACS.

The plant kingdom contains a stunning array of complex morphologies easily observed above-ground, but more challenging to visualize below-ground. Understanding the magnitude of diversity in root distribution within the soil, termed root system architecture (RSA), is fundamental in determining how this trait contributes to species adaptation in local environments. Roots are the interface between the soil environment and the shoot system and therefore play a key role in anchorage, resource uptake, and stress resilience. Previously, we presented the GLO-Roots (Growth and Luminescence Observatory for Roots) system to study the RSA of soil-grown Arabidopsis thaliana plants from germination to maturity (Rellan-alvarez et al., 2015). In this study, we present the automation of GLO-Roots using robotics and the development of image analysis pipelines in order to examine the temporal dynamic regulation of RSA and the broader natural variation of RSA in Arabidopsis, over time. These datasets describe the developmental dynamics of two independent panels of accessions and reveal highly complex and polygenic RSA traits that show significant correlation with climate variables of the accessions' respective origins.

We present a spectroscopic analysis of the low-mass binary star system GJ 660.1AB, a pair of nearby M dwarfs for which we have obtained separated near-infrared spectra (0.9-2.5 mu m) with the SpeX spectrograph. The spectrum of GJ 660.1B is distinctly peculiar, with a triangular-shaped 1.7 mu m peak that initially suggests that it is a low-surface- gravity, young brown dwarf. However, we rule out this hypothesis and determine instead that this companion is a mild subdwarf (d/sdM7) based on the subsolar metallicity of the primary, [Fe/H] = -0.63 +/- 0.06. Comparison of the near-infrared spectrum of GJ 660.1B to two sets of spectral models yields conflicting results, with a common effective temperature of T-eff = 2550-2650 K, but alternately low surface gravity (log g = 4.4(-0.5)(+0.5)) and very low metallicity ([M/H] = -0.96(-0.24)(+0.19)), or high surface gravity (log g = 5.0-5.5) and slightly subsolar metallicity ([M/H] = -0.20(-0.19)(+0.13)). We conjecture that insufficient condensate opacity and excessive collision-induced H-2 absorption in the models bias them toward low surface gravities and a metallicity that is inconsistent with the primary and points toward improvements needed in the spectral modeling of metal-poor, very-low-mass dwarfs. The peculiar spectral characteristics of GJ. 660.1B emphasize that care is needed when interpreting surface gravity features in the spectra of ultracool dwarfs.

The 32 Orionis group is a co-moving group of roughly 20 young (24 Myr) M3-B5 stars 100. pc from the Sun. Here we report the discovery of its first substellar member, WISE. J052857.69+090104.2. This source was previously reported to be an M giant star based on its unusual near-infrared spectrum and lack of measureable proper motion. We re-analyze previous data and new moderate-resolution spectroscopy from Magellan/Folded-port InfraRed Echellette to demonstrate that this source is a young near-infrared L1 brown dwarf with very low surface gravity features. Spectral model fits indicate T-eff = 1880(-70)(+150) K and log g = 3.8(-0.2)(+0.2), consistent with a 15-22 Myr object with a mass near the deuterium-burning limit. Its sky position, estimated distance, kinematics (both proper motion and radial velocity), and spectral characteristics are all consistent with membership in 32 Orionis, and its temperature and age imply a mass (M = 14(-3)(+4) M-J) that straddles the brown dwarf/planetary-mass object boundary. The source has a somewhat red J - W2 color compared to other L1 dwarfs, but this is likely a low-gravity-related temperature offset; we find no evidence of significant excess reddening from a disk or cool companion in the 3-5 mu m waveband.

We investigate stellar metallicity distribution functions (MDFs), including Fe and alpha-element abundances, in dwarf galaxies from the Feedback in Realistic Environment (FIRE) project. We examine both isolated dwarf galaxies and those that are satellites of a MilkyWay-mass galaxy. In particular, we study the effects of including a sub-grid turbulent model for the diffusion of metals in gas. Simulations that include diffusion have narrower MDFs and abundance ratio distributions, because diffusion drives individual gas and star particles towards the average metallicity. This effect provides significantly better agreement with observed abundance distributions in dwarf galaxies in the Local Group, including small intrinsic scatter in [alpha/Fe] versus [Fe/H] of less than or similar to 0.1 dex. This small intrinsic scatter arises in our simulations because the interstellar medium in dwarf galaxies is well mixed at nearly all cosmic times, such that stars that form at a given time have similar abundances to less than or similar to 0.1 dex. Thus, most of the scatter in abundances at z = 0 arises from redshift evolution and not from instantaneous scatter in the ISM. We find similar MDF widths and intrinsic scatter for satellite and isolated dwarf galaxies, which suggests that environmental effects play a minor role compared with internal chemical evolution in our simulations. Overall, with the inclusion of metal diffusion, our simulations reproduce abundance distribution widths of observed low-mass galaxies, enabling detailed studies of chemical evolution in galaxy formation.

We use cosmological hydrodynamical simulations of Milky Way-mass galaxies from the FIRE project to evaluate various strategies for estimating the mass of a galaxy's stellar halo from deep, integrated-light images. We find good agreement with integrated-light observations if we mimic observational methods to measure the mass of the stellar halo by selecting regions of an image via projected radius relative to the disk scale length or by their surface density in stellar mass. However, these observational methods systematically underestimate the accreted stellar component, defined in our (and most) simulations as the mass of stars formed outside of the host galaxy, by up to a factor of 10, since the accreted component is centrally concentrated and therefore substantially obscured by the galactic disk. Furthermore, these observational methods introduce spurious dependencies of the estimated accreted stellar component on the stellar mass and size of galaxies that can obscure the trends in accreted stellar mass predicted by cosmological simulations, since we find that in our simulations, the size and shape of the central galaxy are not strongly correlated with the assembly history of the accreted stellar halo. This effect persists whether galaxies are viewed edge-on or face-on. We show that metallicity or color information may provide a way to more cleanly delineate in observations the regions dominated by accreted stars. Absent additional data, we caution that estimates of the mass of the accreted stellar component from single-band images alone should be taken as lower limits.