Internal colour gradients for E/S0 galaxies in Abell 2218

We determine colour gradients of  −0.15 ± 0.08  mag per decade in radius in F450W−F606W and  −0.07 ± 0.06 mag  per decade in radius in F606W−F814W for a sample of 22 E/S0 galaxies in Abell 2218. These gradients are consistent with the existence of a mild (  ∼−0.3  dex per decade in radius) gradient in metal abundance (cf. previous work at lower and higher redshifts for field and cluster galaxies). The size of the observed gradients is found to be independent of luminosity over a range spanning   M *−1  to   M *+1.5  and also to be independent of morphological type. These results suggest a fundamental similarity in the distributions of stellar populations in ellipticals and the bulges of lenticular galaxies. These results are not consistent with simple models of either monolithic collapse or hierarchical mergers.     

Effects of subsurface drainage tiles on streamflow in Iowa agricultural watersheds: Exploratory hydrograph analysis

Flow from artificial subsurface (tile) drainage systems may be contributing to increasing baseflow in Midwestern rivers and increased losses of nitrate‐nitrogen. Standard hydrograph analysis techniques were applied to model simulation output and field monitoring from tile‐drained landscapes to explore how flow from drainage tiles affects stream baseflow and streamflow recession characteristics. DRAINMOD was used to simulate hydrologic response from drained (24 m tile spacing) and undrained agricultural systems. Hydrograph analysis was conducted using programs PART and RECESS. Field monitoring data were obtained from several monitoring sites in Iowa typical of heavily drained and less‐drained regions. Results indicate that flow from tile drainage primarily affects the baseflow portion of a hydrograph, increasing annual baseflow in streams with seasonal increases primarily occurring in the late spring and early summer months. Master recession curves from tile‐drained watersheds appear to be more linear than less‐tiled watersheds although comparative results of the recession index k were inconsistent. Considering the magnitude of non‐point source pollutant loads coming from tile‐drained landscapes, it is critical that more in‐depth research and analysis be done to assess the effects of tile drainage on watershed hydrology if water quality solutions are to be properly evaluated. Copyright © 2008 John Wiley & Sons, Ltd.     

Storm runoff and sediment losses from forest clearcutting and stand re‐establishment with best management practices in East Texas,USA

Nine small (2·5 ha) and four large (70–135 ha) watersheds were instrumented in 1999 to evaluate the effects of intensive silvicultural practices with best management practices (BMPs) on runoff and stream water quality in the Western Gulf Coastal Plain of East Texas, USA. Two treatments were implemented in 2002: a conventional treatment with clearcutting and herbicide site preparation, and an intensive treatment that added subsoiling, fertilization and a release herbicide application. Watershed effects were compared with results from a previously conducted study on the same watersheds in 1981, in which two combinations of harvesting and mechanical site preparation without BMPs were evaluated. Due to the reduction in evapotranspirational demand, total storm runoff increased on all six treated small watersheds following harvest by 0·94 to 13·73 cm in 2003. Runoff increases were not statistically significant on the treated large watersheds. Total first‐year sediment loss was significantly greater on two of the conventional and one of the intensive small watersheds. The greatest first‐year increase was 540·1 kg ha^?1, only one‐fifth of that observed on these watersheds from shearing and windrowing without BMPs in 1981. First‐year sediment loss was significantly greater on the intensive large watershed following harvest, but not on the conventional large watershed. These data suggest that BMPs are very effective in reducing potential water quality impacts from intensive silvicultural practices. Copyright © 2007 John Wiley & Sons, Ltd.     

Book Review: William A. Cassidy (ed.): Meteorites,Ice, and Antarctica: A personal Account,Cambridge University Press, 2003, ISBN: 0-521-25872-0 hardback,Price:GBP 19.95/US$ 30.00.

Earth, Moon, and Planets -     

The radio galaxy Centaurus B

Centaurus B (PKS B1343−601) is one of the brightest and closest radio galaxies, with flux density ∼250 Jy at 408 MHz and redshift 0.01215, but it has not been studied much because of its position (i) close to the Galactic plane (it is also known as G309.6+1.7 and Kes 19) and (ii) in the southern sky. It has recently been suggested as the centre of a highly obscured cluster behind the Galactic plane. We present radio observations made with the Australia Telescope Compact Array and Molonglo Observatory Synthesis Telescope to study the jets and lobes. The total intensity and polarization radio images of the FR I jets are used to determine the jet brightness and width variations, magnetic field structure and fractional polarization. The equipartition pressure calculated along the jets declines rapidly over the first 1 arcmin from the galaxy reaching a constant pressure of 10⁻¹³  h ^−4/7 Pa in the lobes blown in the intracluster medium.     

Ground-based visible and near-IR observations of Comet 9P/Tempel 1 during the Deep Impact encounter

We present the results of our visible and near-IR observations of Comet 9P/Tempel 1 during the Deep Impact encounter. The comet was observed before, during, and after impact from Kitt Peak National Observatory (J, H, K) and Observatorio Astronómico Nacional-San Pedro Mártir, Mexico (B, V, R, I). High time-resolution images in R, J, H, and K the night of impact with a 3^.″5 radius aperture revealed a rapid brightening which had multiple slopes and lasted for approximately 25 min before leveling off. The brightness decreased on subsequent nights and returned to near pre-impact levels by July 8 UT. The R-J, R-H, R-K, J-H, J-K, and H-K colors became bluer the night of impact. The R-J, R-H, and R-K colors remained blue on the night after impact while the J-H, J-K, and H-K colors returned to baseline levels. The observed color changes suggest the bluening was due to an increase in small grains relative to the ambient coma, an increase in ice relative to refractory dust in the coma, or a combination of the two. The ejecta were initially directed towards the southwest but had been driven southeast by solar radiation pressure by the second night after impact. The mean projected ejecta velocity was estimated at 0.20-0.23 km s⁻¹ over the first 24 h after impact.