Galactic Wind in the Nearby Starburst Galaxy NGC 253 Observed with the Kyoto3DII Fabry-Perot Mode

We have observed the central region of the nearby starburst galaxy NGC 253 with the Kyoto Tridimensional Spectrograph II (Kyoto3DII) Fabry-Perot mode in order to investigate the properties of its galactic wind. Since this galaxy has a large inclination, it is easy to observe its galactic wind. We produced the Ha, [N II]6583, and [S II]6716,6731 images, as well as those line ratio maps. The [N II]/Ha ratio in the galactic wind region is larger than those in H II regions in the galactic disk. The [N II]/Ha ratio in the southeastern filament, a part of the galactic wind, is the largest and reaches about 1.5. These large [N II]/Ha ratios are explained by shock ionization/excitation. Using the [S II]/Ha ratio map, we spatially separate the galactic wind region from the starburst region. The kinetic energy of the galactic wind can be sufficiently supplied by supernovae in a starburst region in the galactic center. The shape of the galactic wind and the line ratio maps are non-axisymmetric about the galactic minor axis, which is also seen in M82. In the [N II]6583/[S II]6716,6731 map, the positions with large ratios coincide with the positions of star clusters found in the Hubble Space Telescope (HST) observation. This means that intense star formation causes strong nitrogen enrichment in these regions. Our unique data of the line ratio maps including [S II] lines have demonstrated their effectiveness for clearly distinguishing between shocked gas regions and starburst regions, determining the extent of galactic wind and its mass and kinetic energy, and discovering regions with enhanced nitrogen abundance.Comment: 22 pages, 5 figures, 1 table, accepted for publication in Ap

Chemical Abundances Of Open Clusters From High-Resolution Infrared Spectra. I. NGC 6940

We present near-infrared spectroscopic analysis of 12 red giant members of the Galactic open cluster NGC 6940. High-resolution (R$\simeq$45000) and high signal-to-noise ratio (S/N > 100) near-infrared H and K band spectra were gathered with the Immersion Grating Infrared Spectrograph (IGRINS) on the 2.7m Smith Telescope at McDonald Observatory. We obtained abundances of H-burning (C, N, O), ${\alpha}$ (Mg, Si, S, Ca), light odd-Z (Na, Al, P, K), Fe-group (Sc, Ti, Cr, Fe, Co, Ni) and neutron-capture (Ce, Nd, Yb) elements. We report the abundances of S, P, K, Ce, and Yb in NGC 6940 for the first time. Many OH and CN features in the H band were used to obtain O and N abundances. C abundances were measured from four different features: CO molecular lines in the K band, high excitation C I lines present in both near-infrared and optical, CH and $C_2$ bands in the optical region. We have also determined $^{12}C/^{13}C$ ratios from the R-branch band heads of first overtone (2-0) and (3-1) $^{12}CO$ (2-0) $^{13}CO$ lines near 23440 \overset{\lower.5em\circ}{\mathrm{A}} and (3-1) $^{13}CO$ lines at about 23730 \overset{\lower.5em\circ}{\mathrm{A}}. We have also investigated the HF feature at 23358.3 \overset{\lower.5em\circ}{\mathrm{A}}, finding solar fluorine abundances without ruling out a slight enhancement. For some elements (such as the ${\alpha}$ group), IGRINS data yield more internally self-consistent abundances. We also revisited the CMD of NGC 6940 by determining the most probable cluster members using Gaia DR2. Finally, we applied Victoria isochrones and MESA models in order to refine our estimates of the evolutionary stages of our targets.Comment: 16 pages, 10 figure

Observational Constraints on Superbubble X-ray Energy Budgets

The hot, X-ray-emitting gas in superbubbles imparts energy and enriched material to the interstellar medium (ISM) and generates the hot ionized medium, the ISM's high-temperature component. The evolution of superbubble energy budgets is not well understood, however, and the processes responsible for enhanced X-ray emission in superbubbles remain a matter of debate. We present Chandra ACIS-S observations of two X-ray-bright superbubbles in the Large Magellanic Cloud (LMC), DEM L50 (N186) and DEM L152 (N44), with an emphasis on disentangling the true superbubble X-ray emission from non-related diffuse emission and determining the spatial origin and spectral variation of the X-ray emission. An examination of the superbubble energy budgets shows that on the order of 50% of the X-ray emission comes from regions associated with supernova remnant (SNR) impacts. We find some evidence of mass-loading due to swept-up clouds and metallicity enrichment, but neither mechanism provides a significant contribution to the X-ray luminosities. We also find that one of the superbubbles, DEM L50, is likely not in collisional ionization equilibrium. We compare our observations to the predictions of the standard Weaver et al. model and to 1-D hydrodynamic simulations including cavity supernova impacts on the shell walls. Our observations show that mass-loading due to thermal evaporation from the shell walls and SNR impacts are the dominant source of enhanced X-ray luminosities in superbubbles. These two processes should affect most superbubbles, and their contribution to the X-ray luminosity must be considered when determining the energy available for transport to the ISM.Comment: 25 pages, 11 figures, accepted for publication in Ap

Effect of dynamic stall on the aerodynamics of vertical-axis wind turbines

Accurate simulations of the aerodynamic performance of vertical-axis wind turbines pose a significant challenge for computational fluid dynamics methods. The aerodynamic interaction between the blades of the rotor and the wake that is produced by the blades requires a high-fidelity representation of the convection of vorticity within the wake. In addition, the cyclic motion of the blades induces large variations in the angle of attack on the blades that can manifest as dynamic stall. The present paper describes the application of a numerical model that is based on the vorticity transport formulation of the Navier–Stokes equations, to the prediction of the aerodynamics of a verticalaxis wind turbine that consists of three curved rotor blades that are twisted helically around the rotational axis of the rotor. The predicted variation of the power coefficient with tip speed ratio compares very favorably with experimental measurements. It is demonstrated that helical blade twist reduces the oscillation of the power coefficient that is an inherent feature of turbines with non-twisted blade configurations

Ferromagnetic redshift of the optical gap in GdN

We report measurements of the optical gap in a GdN film at temperatures from 300 to 6K, covering both the paramagnetic and ferromagnetic phases. The gap is 1.31eV in the paramagnetic phase and red-shifts to 0.9eV in the spin-split bands below the Curie temperature. The paramagnetic gap is larger than was suggested by very early experiments, and has permitted us to refine a (LSDA+U)-computed band structure. The band structure was computed in the full translation symmetry of the ferromagnetic ground state, assigning the paramagnetic-state gap as the average of the majority- and minority-spin gaps in the ferromagnetic state. That procedure has been further tested by a band structure in a 32-atom supercell with randomly-oriented spins. After fitting only the paramagnetic gap the refined band structure then reproduces our measured gaps in both phases by direct transitions at the X point.Comment: 5 pages, 4 figure