Early-time Spitzer observations of the type II-Plateau supernova, 2004dj

We present mid-infrared observations with the Spitzer Space Telescope of the nearby type II-P supernova, SN 2004dj, at epochs of 89 to 129 days. We have obtained the first mid-IR spectra of any supernova apart from SN 1987A. A prominent [NiII] 6.64 micron line is observed, from which we deduce that the mass of stable nickel must be at least 2.2e10(-4) Msun. We also observe the red wing of the CO-fundamental band. We relate our findings to possible progenitors and favour an evolved star, most likely a red supergiant, with a probable initial mass between ~10 and 15 Msun.Comment: ApJ Letters (accepted

Spitzer measurements of atomic and molecular abundances in the Type IIP SN 2005af

We present results based on Spitzer Space Telescope mid-infrared (3.6-30 micron) observations of the nearby IIP supernova 2005af. We report the first ever detection of the SiO molecule in a Type IIP supernova. Together with the detection of the CO fundamental, this is an exciting finding as it may signal the onset of dust condensation in the ejecta. From a wealth of fine-structure lines we provide abundance estimates for stable Ni, Ar, and Ne which, via spectral synthesis, may be used to constrain nucleosynthesis models.Comment: ApJ Letters (accepted

Impact of urban canopy meteorological forcing on aerosol concentrations

The regional climate model RegCM4 extended with the land surface model CLM4.5 was coupled to the chemistry transport model CAMx to analyze the impact of urban meteorological forcing on surface fine aerosol (PM2.5) concentrations for summer conditions over the 2001–2005 period, focusing on the area of Europe. Starting with the analysis of the meteorological modifications caused by urban canopy forcing, we found a significant increase in urban surface temperatures (up to 2–3&thinsp;K), a decrease of specific humidity (by up to 0.4–0.6&thinsp;gkg−1), a reduction of wind speed (up to −1&thinsp;ms−1) and an enhancement of vertical turbulent diffusion coefficient (up to 60–70&thinsp;m2s−1).These modifications translated into significant changes in surface aerosol concentrations that were calculated by a cascading experimental approach. First, none of the urban meteorological effects were considered. Then, the temperature effect was added, then the humidity and the wind, and finally, the enhanced turbulence was considered in the chemical runs. This facilitated the understanding of the underlying processes acting to modify urban aerosol concentrations. Moreover, we looked at the impact of the individual aerosol components as well. The urbanization-induced temperature changes resulted in a decrease of PM2.5 by −1.5 to −2&thinsp;µg m−3, while decreased urban winds resulted in increases by 1–2&thinsp;µg m−3. The enhanced turbulence over urban areas resulted in decreases of PM2.5 by −2&thinsp;µg m−3. The combined effect of all individual impact depends on the competition between the partial impacts and can reach up to −3&thinsp;µg m−3 for some cities, especially when the temperature impact was stronger in magnitude than the wind impact. The effect of changed humidity was found to be minor. The main contributor to the temperature impact is the modification of secondary inorganic aerosols, mainly nitrates, while the wind and turbulence impact is most pronounced in the case of primary aerosol (primary black and organic carbon and other fine particle matter). The overall as well as individual impacts on secondary organic aerosol are very small, with the increased turbulence acting as the main driver. The analysis of the vertical extent of the aerosol changes showed that the perturbations caused by urban canopy forcing, besides being large near the surface, have a secondary maximum for turbulence and wind impact over higher model levels, which is attributed to the vertical extent of the changes in turbulence over urban areas. The validation of model data with measurements showed good agreement, and we could detect a clear model improvement in some areas when including the urban canopy meteorological effects in our chemistry simulations.</p

Improved Laboratory Transition Probabilities for Neutral Chromium and Re-determination of the Chromium Abundance for the Sun and Three Stars

Branching fraction measurements from Fourier transform spectra in conjunction with published radiative lifetimes are used to determine transition probabilities for 263 lines of neutral chromium. These laboratory values are employed to derive a new photospheric abundance for the Sun: log $\epsilon$(Cr I)$_{\odot}$ = 5.64$\pm$0.01 ($\sigma = 0.07$). These Cr I solar abundances do not exhibit any trends with line strength nor with excitation energy and there were no obvious indications of departures from LTE. In addition, oscillator strengths for singly-ionized chromium recently reported by the FERRUM Project are used to determine: log $\epsilon$(Cr II)$_{\odot}$ = 5.77$\pm$0.03 ($\sigma = 0.13$). Transition probability data are also applied to the spectra of three stars: HD 75732 (metal-rich dwarf), HD 140283 (metal-poor subgiant), and CS 22892-052 (metal-poor giant). In all of the selected stars, Cr I is found to be underabundant with respect to Cr II. The possible causes for this abundance discrepancy and apparent ionization imbalance are discussed.Comment: 44 pages, 6 figure

Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV

We describe the measurement of the depth of maximum, Xmax, of the longitudinal development of air showers induced by cosmic rays. Almost four thousand events above 10^18 eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/- 0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.Comment: Accepted for publication by PR