No description available.

No description available.

No description available.

No description available.

No description available.

We study the integral Galactic extinction and reddening based on the galaxy catalog of the South Galactic Cap u-band Sky Survey (SCUSS), where u-band galaxy number counts and u - r color distribution are used to derive the Galactic extinction and reddening respectively. We compare these independent statistical measurements with the reddening map of Schlegel et al. (SFD) and find that both the extinction and reddening from the number counts and color distribution are in good agreement with the SFD results at low extinction regions (E(B - V)(SFD) < 0.12 mag). However, for high extinction regions (E(B - V)(SFD) > 0.12 mag), the SFD map overestimates the Galactic reddening systematically, which can be approximated by a linear relation Delta E(B - V)= 0.43[ E(B - V)(SFD) - 0.12]. By combining the results from galaxy number counts and color distribution, we find that the shape of the Galactic extinction curve is in good agreement with the standard R-V = 3.1 extinction law of O'Donnell.

Debris discs are typically revealed through the presence of excess emission at infrared wavelengths. Most discs exhibit excess at mid- and far-infrared wavelengths, analogous to the solar system's Asteroid and Edgeworth-Kuiper belts. Recently, stars with strong (similar to 1%) excess at near-infrared wavelengths were identified through interferometric measurements. Using the HIgh Precision Polarimetric Instrument, we examined a sub-sample of these hot dust stars (and appropriate controls) at parts-per-million sensitivity in SDSS g' (green) and r' (red) filters for evidence of scattered light. No detection of strongly polarized emission from the hot dust stars is seen. We, therefore, rule out scattered light from a normal debris disk as the origin of this emission. A wavelength-dependent contribution from multiple dust components for hot dust stars is inferred from the dispersion (the difference in polarization angle in red and green) of southern stars. Contributions of 17 ppm (green) and 30 ppm (red) are calculated, with strict 3-sigma upper limits of 76 and 68 ppm, respectively. This suggests weak hot dust excesses consistent with thermal emission, although we cannot rule out contrived scenarios, e.g., dust in a spherical shell or face-on discs. We also report on the nature of the local interstellar medium (ISM), obtained as a byproduct of the control measurements. Highlights include the first measurements of the polarimetric color of the local ISM and the discovery of a southern sky region with a polarization per distance thrice the previous maximum. The data suggest that lambda(max), the wavelength of maximum polarization, is bluer than typical.

The Large Binocular Telescope Interferometer (LBTI) is a versatile instrument designed for high angular resolution and high-contrast infrared imaging (1.5-13 mu m). In this paper, we focus on the mid-infrared (8-13 mu m) nulling mode and present its theory of operation, data reduction, and on-sky performance as of the end of the commissioning phase in 2015 March. With an interferometric baseline of 14.4 m, the LBTI nuller is specifically tuned to resolve the habitable zone of nearby main-sequence stars, where warm exozodiacal dust emission peaks. Measuring the exozodi luminosity function of nearby main-sequence stars is a key milestone to prepare for future exo-Earth direct imaging instruments. Thanks to recent progress in wavefront control and phase stabilization, as well as in data reduction techniques, the LBTI demonstrated in 2015 February a calibrated null accuracy of 0.05% over a 3 hr long observing sequence on the bright nearby A3V star beta Leo. This is equivalent to an exozodiacal disk density of 15-30. zodi for a Sun-like star located at 10 pc, depending on the adopted disk model. This result sets a new record for high-contrast mid-infrared interferometric imaging and opens a new window on the study of planetary systems.

A purpose-built cylindrical resuspension chamber (V=0.437 m3 , S=0.35 m2 , S/V=8.38) was used for the dispersion of samples of soil and various kinds of dust. The samples were studied from the point of view of the number and mass distribution of aerosol particles which could affect the concentration of atmospheric aerosol. The samples were taken from lignite, power plant flue ash and from overburden soil in the North Bohemian surface mine Nastup. The individual samples were pneumatically dispersed inside the chamber under defined temperature-humidity conditions (20řC and relative humidity (RH) 50 %). An APS (Aerodynamic Particle Sizer) processing provided us with average size distributions of particle mass and number. Lignite and flue ash probably have the greatest potential impact on the concentration of atmospheric aerosol in the studied locality. The amount of the resuspended mass of the samples varied between 0.001 % (overburden soil) and 0.32 % (mine road). The lignite and flue ash samples were then analyzed by gravimetric methods using the HI (Harvard Impactor) and the SCI (Sioutas Cascade Impactor). The flue ash contained higher amounts of fine particles than the lignite. Subsequent chemical analysis by electron microscope of the filters with deposits of power plant flue ash showed that the PM2.5...

ABSTRACT Looking up at the sky, we would never guess that our atmosphere contains between one and three billion tons of dust and other particles at any given time.1 Wind assists in keeping this dust airborne, but gravity wins most of the time, forcing the dust particles earthward, proving the old adage: “what goes up, must come down.” Precipitant dust levels in the Western Cape do not follow the same pattern as the precipitant dust levels in the summer rainfall areas of South Africa. Due to the very dry summer conditions in the Western Cape, the precipitant dust levels can be very high, especially if sources of fugitive dust are ignored. An environmental consulting company positioned precipitant dust monitoring units at strategic locations, taking process and open dust sources into account. Both wet and dry depositions have been reported on in this report as one figure. Seasonal changes in, and long-term trends of, the amount of precipitant dust were documented and statistically analysed to determine if the precipitantdust levels were above the South African legislated action levels. The particle size analysis performed on the precipitant dust indicated that the dust was predominantly less than 100_μm and that about 22 percent of the particles by volume were under 15_μm. No significant decline in the precipitant dust levels around the calcining industry was noted. Recommendations are that they increase the dust control measures on site, especially near to the DHF sampling location. There was a significant decrease in the precipitant dust levels to the north and south of the smelting industry from October 2001 to April 2005, p-value 0.005 and 0.048. The recommendations for the smelting industry are that they continue to eliminate fugitive dust sources and that they continue to maintain a high awareness of dust control.