Characterizing octagonal and rectangular fibers for MAROON-X

We report on the scrambling performance and focal-ratio-degradation (FRD) of various octagonal and rectangular fibers considered for MAROON-X. Our measurements demonstrate the detrimental effect of thin claddings on the FRD of octagonal and rectangular fibers and that stress induced at the connectors can further increase the FRD. We find that fibers with a thick, round cladding show low FRD. We further demonstrate that the scrambling behavior of non-circular fibers is often complex and introduce a new metric to fully capture non-linear scrambling performance, leading to much lower scrambling gain values than are typically reported in the literature (<1000 compared to 10,000 or more). We find that scrambling gain measurements for small-core, non-circular fibers are often speckle dominated if the fiber is not agitated.Comment: 10 pages, 8 figures, submitted to SPIE Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation 2016 (9912-185

Optimal non-circular fiber geometries for image scrambling in high-resolution spectrographs

Optical fibers are a key component for high-resolution spectrographs to attain high precision in radial velocity measurements. We present a custom fiber with a novel core geometry - a 'D'-shape. From a theoretical standpoint, such a fiber should provide superior scrambling and modal noise mitigation, since unlike the commonly used circular and polygonal fiber cross sections, it shows chaotic scrambling. We report on the fabrication process of a test fiber and compare the optical properties, scrambling performance, and modal noise behavior of the D-fiber with those of common polygonal fibers.Comment: 7 pages, 6 figures, submitted to SPIE Astronomical Telescopes & Instrumentation 2016 (9912-192

Exploration of the Hydrogen Sulfide−Germanium Sulfide System

In the present work, the (x)H2S + (1−x)GeS2 system has been systematically investigated to determine the incorporation of hydrogen into the tetrahedral germanium sulfide network. Reactions between gaseous H2S and glassy-GeS2 have been explored over a range of temperatures and pressures. Reactions for shorter times and lower temperatures (ambient through 250 °C) produced the protonated thiogermanic acid H4Ge4S10 with an adamantane-like microstructure. In contrast, longer reaction times produced the unprotonated low-temperature three-dimensional α-GeS2 crystal structure. At higher temperatures (750 °C), sublimation reactions produced weakly protonated amorphous materials in the form of spherical particles (100 nm to a few μm). Structural characterizations of the obtained amorphous and crystalline materials have been performed using IR and Raman spectroscopies, thermogravimetric analysis, ac impedance spectroscopy, and SEM. Thermal mass loss measurements and quantitative IR of the S−H stretching region 2500 cm-1 were used to determine the amount of hydrogen incorporated into the GeS2 network

Crystal Structure of Thiogermanic Acid H4Ge4S10

X-ray diffraction analysis reveals the thiogermanic acid H4Ge4S10 possesses discrete adamantane-like Ge4S104- complex anions. Each thioanion is composed of four corner shared GeS2.5- tetrahedral units. Crystals were grown from anhydrous liquid hydrogen sulfide reactions with glassy germanium sulfide at room temperature. The crystal structure was solved and refined from single crystal diffractometer data (Mo Kα radiation) obtained at 173 K. H4Ge4S10 is triclinic, centrosymmetric space group P1̄, with a = 8.621(4) Å, b = 9.899(4) Å,c = 10.009(4) Å, α = 85.963(7)°, β = 64.714(7)°, γ = 89.501(8)°, and Z = 2. Average bridging and terminal d̄(Ge−S) distances are 2.229 and 2.206 Å, respectively. Vibrational mode assignments are reported from Raman scattering and IR absorption spectra of polycrystalline samples. The νs(Ge−S−Ge) and νs(Ge−S-) stretching modes are observed at 354 and 405 cm-1, respectively

Synthesis and Characterization of the Thiogermanic Acids H4Ge4S10 and H2Ge4S9

The synthesis and structure of the thiogermanic acids H4Ge4S10 and H2Ge4S9 are reported. A novel preparation method consisting of reacting germanium oxide with liquid hydrogen sulfide containing a trace amount of water is used to form Ge4S104- ions. Evaporating the hydrogen sulfide solution at room temperature leaves an unstable H4Ge4S10·xH2O product. The stoichiometry and structure of the thermally stable anhydrous phase are dependent on reaction time. An H4Ge4S10 product with an adamantane-like cage structure is obtained at shorter reaction times. Longer reaction times produce an H2Ge4S9 product with a more complex cage unit, a higher symmetry unit cell, and increased thermal stability. Raman, infrared, powder X-ray diffraction, and thermogravimetric data are reported for both structures

Density and Velocity Fields from the PSCz Survey

We present the results for the predicted density and peculiar velocity fields and the dipole from the PSCz survey of 15,000 IRAS galaxies over 84% of the sky. We find a significant component to the dipole arising between 6000 and 15,000 km/s, but no significant component from greater distances. The misalignment with the CMB is 20 degrees. The most remarkable feature of the PSCz model velocity field is a coherent large-scale flow along the baseline connecting Perseus-Pisces, the Local Supercluster, Great Attractor and the Shapley Concentration. We have measured the parameter beta using the amplitude of the dipole, bulk flow and point by point comparisons between the individual velocities of galaxies in the MarkIII and SFI datasets, and the large-scale clustering distortion in redshift space.All our results are consistent with beta = 0.6 +- 0.1.Comment: 8 pages, 8 figures. To appear in 'Towards an Understanding of Cosmic Flows', Victoria, July 1999, eds Courteau,S., Strauss,M., Willick,J. PAS