Modern theories of galaxy formation predict that the Galactic stellar halo was hierarchically assembled from the accretion and disruption of smaller systems. This hierarchical assembly is expected to produce a high degree of structure in the combined phase and chemistry space; this structure should provide a relatively direct probe of the accretion history of our Galaxy. Revealing this structure requires precise 3D positions (including distances), 3D velocities, and chemistry for large samples of stars. The Gaia satellite is delivering proper motions and parallaxes for > 1 billion stars to G ≈ 20. However, radial velocities and metallicities will only be available to G ≈ 15, which is insufficient to probe the outer stellar halo ( 10 kpc). Moreover, parallaxes will not be precise enough to deliver high-quality distances for stars beyond ∼ 10 kpc. Identifying accreted systems throughout the stellar halo therefore requires a large ground-based spectroscopic survey to complement Gaia. Here we provide an overview of the H3 Stellar Spectroscopic Survey, which will deliver precise stellar parameters and spectrophotometric distances for ≈ 200, 000 stars to r = 18. Spectra are obtained with the Hectochelle instrument at the MMT, which is configured for the H3 Survey to deliver resolution R ≈ 23, 000 spectra covering the wavelength range 5150Å−5300Å. The survey is optimized for stellar halo science and therefore focuses on high Galactic latitude fields (|b| > 30 • ), sparsely sampling 15, 000 sq. degrees. Targets are selected on the basis of Gaia parallaxes, enabling very efficient selection of bone fide halo stars. The survey began in the Fall of 2017 and has collected 88,000 spectra to-date. All of the data, including the derived stellar parameters, will eventually be made publicly available via the survey website: h3survey.rc.fas.harvard.edu.

Photoelectron spectra of a number of sulfur-containing negative ions have been measured, and the following electron affinities are reported: EA(S2) = 1.670 ± 0.015 eV, EA(HS2) = 1.907 ± 0.023 eV, EA(DS2) = 1.912 ± 0.015 eV, EA(CH3S2) = 1.757 ± 0.022 eV, EA(CD3S2) = 1.748 ± 0.022 eV, EA(CH3CH2S) = 1.947 ± 0.013 eV, EA(CH3SCH2) = 0.868 ± 0.051 eV, EA(CH3S) = 1.871 ± 0.012 eV, and EA(CH2S) = 0.465 ± 0.023 eV. For the first five anions, the photoelectron spectra consist of excitation of the S-S stretching mode of the radical. Wherever possible, the spectroscopic information obtained is used to elucidate geometries and thermochemistry of these reactive intermediates. Results from these sulfur-containing ions and radicals are compared with what is known about their oxygen analogues.

We have measured the photoelectron spectra of CH2CN~a nd CD2CN" and report the following electron affinities: EA(CH2CN) = 1.543 ± 0.014 eV and EA(CD2CN) = 1.538 ± 0.012 eV. From an analysis of the peak splittings and intensities, we extract potential-energy curves for the umbrella mode of the CH2CN" negative ion and the CH2CN radical. The radical is found to be a planar, C2¿ species. The structure of the cyanomethide ion is almost described as CH2=C=N", but the hydrogens are bent slightly out of the molecular plane. A Franck-Condon analysis leads to a value of the out-of-plane deformation angle as 30 ± 5°with a very small inversion barrier of 100 ± 50 cm"1, Our structural conclusions are reinforced by a series of ab initio Hartree-Fock and Moller-Plesset perturbation calculations on both the cyanomethyl radical and cyanomethide ion. Using the gas-phase acidity of CH3CN, we obtain the following bond-dissociation energy for acetonitrile: DH°298(H-CH2CN) = 94.2 ± 2.0 kcal/mol.

We present the stellar mass-[Fe/H] and mass-[Mg/H] relation of quiescent galaxies in two galaxy clusters at z ∼ 0.39 and z ∼ 0.54. We derive the age, [Fe/H], and [Mg/Fe] for each individual galaxy using a full-spectrum fitting technique. By comparing with the relations for z ∼ 0 SDSS galaxies, we confirm our previous finding that the mass-[Fe/H] relation evolves with redshift. The mass-[Fe/H] relation at higher redshift has lower normalization and possibly steeper slope. However, based on our sample, the mass-[Mg/H] relation does not evolve over the observed redshift range. We use a simple analytic chemical evolution model to constrain average outflow that these galaxies experience over their lifetime, via the calculation of mass-loading factor. We find that the average mass-loading factor η is a power-law function of galaxy stellar mass, η ∝ M −0.21±0.09 * . The measured mass-loading factors are consistent with the results of other observational methods for outflow measurements and with the predictions where outflow is caused by star formation feedback in turbulent disks.

Binospec is a high-throughput, 370 to 1000 nm, imaging spectrograph that addresses two adjacent 8ʹ by 15ʹ fields of view. Binospec was commissioned in late 2017 at the f/5 focus of the 6.5m MMT and is now available to all MMT observers. Here we describe the Binospec software used for observation planning, instrument control, and data reduction. The software and control systems incorporate a high level of automation to minimize observer workload. Instrument configuration and observation sequencing is implemented using a database-driven approach to maximize observatory efficiency. A web-based interface allows users to define observations, monitor status, and retrieve data products.

A pulse sequence of z-restored spin echo, -pi-beta-tau-pi-tau-, employing a pi pulse in the middle of the delay (2tau) to form a spin echo and the two pi pulses together to restore the residual longitudinal magnetization back to + z direction, is described. (13)C spectra of organic compounds provide a wealth of structural information; however, (13)C 1D spectra acquired using reverse geometry probes can have significant baseline humps or rolls because of pulse ring-down within the coil. The baseline distortions are especially apparent in spectra acquired using cryogenically enhanced probes. The baseline problem may be alleviated by extending the delay between the last pulse and the starting point of acquisition. However, uses of long delay times introduce large negative first-order phase corrections which themselves produce baseline roll. The prescribed experiment can be used to completely remove the hump, roll or dip in the baseline of the (13)C spectrum and at the same time obtain sensitivity similar to the experiment of a single beta pulse. We believe that this experiment will be of general applications in acquiring high-quality (13)C NMR data with reverse geometry probes and spectral interpretation.

Disturbance in seagrass habitats may cause variation in the structure of fish assemblages and individual taxa. One important form of disturbance is wave action associated with strong winds. Total fish abundance and species richness from seagrass beds at 2 sites in Port Phillip Bay, Australia, were sampled during low and high wave disturbance. During high wave action (> 0.25 m) in seagrass beds, abundance of fish at one site decreased significantly, but species richness was unaffected at both sites. Plankton sampling conducted at the same time as seagrass sampling (directly 300 m offshore from the seagrass sites) found that species richness significantly increased during high wave conditions at both sites. Total fish abundance similarly increased in the plankton during high wave conditions at one site. We conclude that variation in assemblage structure during increased physical disturbance is related to variation in a small number of numerically dominant species within the assemblage. At the individual taxon level, numerically dominant species in the seagrass and plankton showed considerable variation in response to disturbance. In the seagrass assemblage, post-larval King George whiting Sillaginodes punctata (Cuvier and Valenciennes), adult weedfish Heteroclinus perspicillatus (Cuvier and Valenciennes), and pipefish juveniles and adults from the genus Stigmatopora decreased in abundance at either one or both sites during high wave conditions. Conversely, in the plankton, adult pipefish Hypelognathus rostratus (Waite and Hale), juvenile Stigmatopora and larval Gymnapistes marmoratus (Cuvier and Valenciennes) significantly increased in abundance during these same physical conditions. It appears that for some taxa physical disturbance may facilitate secondary planktonic dispersal. KEY WORDS: Physical disturbance · Fish transport · Seagrass fishes · Post-settlement processesResale or republication not permitted without written consent of the publisher

The late Miocene was an important time to understand the geological, climatic, and biotic evolution of the ancient New World tropics and the context for the Great American Biotic Interchange (GABI). Despite this importance, upper Miocene deposits containing diverse faunas and floras and their associated geological context are rare in Central America. We present an integrated study of the geological and paleontological context and age of a new locality from Lago Alajuela in northern Panama (Caribbean side) containing late Miocene marine and terrestrial fossils (plants, invertebrates, and vertebrates) from the Alajuela Formation. These taxa indicate predominantly estuarine and shallow marine paleoenvironments, along with terrestrial influences based on the occurrence of land mammals. Sr-isotope ratio analyses of in situ scallop shells indicate an age for the Alajuela Formation of 9.77 ± 0.22 Ma, which also equates to a latest Clarendonian (Cl3) North American Land Mammal Age. Along with the roughly contemporaneous late Miocene Gatun and Lago Bayano faunas in Panama, we now have the opportunity to reconstruct the dynamics of the Central America seaway that existed before final closure coincident with formation of the Isthmus of Panama.