Large-scale structure in the NIR-selected MUNICS survey

The Munich Near-IR Cluster Survey (MUNICS) is a wide-area, medium-deep, photometric survey selected in the K' band. The project's main scientific aims are the identification of galaxy clusters up to redshifts of unity and the selection of a large sample of field early-type galaxies up to z < 1.5 for evolutionary studies. We created a Large Scale Structure catalog, using a new structure finding technique specialized for photometric datasets, that we developed on the basis of a friends-of-friends algorithm. We tested the plausibility of the resulting galaxy group and cluster catalog with the help of Color-Magnitude Diagrams (CMD), as well as a likelihood- and Voronoi-approach. This revised version was published online in August 2006 with corrections to the Cover Date.     

The ultrashort period dwarf nova SW ursae majoris

SW UMa is an unusual dwarf nova in several respects. Recent observations by Robinsonet al. (1986) have established that SW UMa is an SU UMa system, while Shafter, Szkody, and Thorstensen (1986) have presented evidence suggesting that SW UMa may be a DQ Her system as well. If the DQ Her classification is confirmed then SW UMa will be the only system to have this dual classification. Finally, time resolved spectroscopy of SW UMa has revealed the presence of an S-wave component in the H emission which has an unexpected phasing relative to the line wings.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Preliminary observations of solar radio sources with the Culgoora radioheliograph operating at four frequencies

The Culgoora radioheliograph has been modified for observing at 327.4 MHz, which is in addition to the three frequencies (43.25, 80, and 160 MHz) previously available. At the new frequency the array beamwidth is 56, which represents the highest resolution yet available for metre-wavelength solar mapping.At 327.4 MHz the sources of radio emission are mainly in the lowest layers of the corona. Some preliminary four-frequency observations have been made of type I storms. It is found that the source size generally decreases with increasing observing frequency. This result confirms earlier suggestions that the sources of both type I and type III emission are contained in structures whose boundaries diverge outwards in the corona.     

Variability in the power spectrum of solar five-minute oscillations

Two-dimensional power spectra of solar five-minute oscillations display prominent ridge structures in (k, ω) space, where k is the horizontal wavenumber and ω is the temporal frequency. The positions of these ridges in k and ω can be used to probe temperature and velocity structures in the subphotosphere. We have been carrying out a continuing program of observations of five-minute oscillations with the diode array instrument on the vacuum tower telescope at Sacramento Peak Observatory (SPO). We have sought to establish whether power spectra taken on separate days show shifts in ridge locations; these may arise from different velocity and temperature patterns having been brought into our sampling region by solar rotation. Power spectra have been obtained for six days of observations of Doppler velocities using the Mgi λ5173 and Fei λ5434 spectral lines. Each data set covers 8 to 11 hr in time and samples a region 256″ × 1024″ in spatial extent, with a spatial resolution of 2″ and temporal sampling of 65 s. We have detected shifts in ridge locations between certain data sets which are statistically significant. The character of these displacements when analyzed in terms of eastward and westward propagating waves implies that changes have occurred in both temperature and horizontal velocity fields underlying our observing window. We estimate the magnitude of the velocity changes to be on the order of 100 m s^-1; we may be detecting the effects of large-scale convection akin to giant cells.     

Late Quaternary Bison diminution on the Great Plains of North America: evaluating the role of human hunting versus climate change

Body size changes of Bison and mortality age structure data document the effects of climate-driven environmental change and human hunting pressure on large mammals in North America. Morphometric and mortality data are drawn from 58 archaeological and 9 paleontological localities dating between 37,000 and 250 calBP. Proxy information on body size is based on measurements recorded on 901 adult calcanei (os calcis) and 1026 humeri. In addition, published mortality profiles from 24 archaeological faunal assemblages spanning the last 14,000 years were used to approximate the age structure of bison populations. These results suggest that dramatic diminution in bison body size occurred in several short bursts, rather than a continuous gradual decline. These periods of rapid size reduction correlate with times of ecological reorganization, when aridity-driven changes in grasslands decreased forage quality and availability. Mortality age data indicate that the decrease in body size occurred in a context where there was no evidence for a progressively severe juvenile bias in bison populations. Overall, it appears that the changes in body size were a reaction to environmental conditions rather than the result of human predation pressure.     

Spring and summer phytoplankton communities in the Chukchi and Eastern Beaufort Seas

Phytoplankton pigments and size-fractionated biomass in the Chukchi and Beaufort Seas showed spatial and temporal variation during the spring and summer of 2002. Cluster analysis of pigment ratios revealed different assemblages over the shelf, slope and basin regions. In spring, phytoplankton with particle sizes greater than 5 μm, identified as diatoms and/or haptophytes, dominated over the shelf. Smaller (<5 μm) phytoplankton containing chlorophyll b, most likely prasinophytes, were more abundant over the slope and basin. Due to extensive ice cover at this time, phytoplankton experienced low irradiance, but nutrients were near maximal for the year. By summer, small prasinophytes and larger haptophytes and diatoms co-dominated in near-surface assemblages in largely ice-free waters when nitrate was mostly depleted. Deeper in the water column at 1–15% of the surface irradiance larger sized diatoms were still abundant in the upper nutricline. Phytoplankton from the shelf appeared to be advected through Barrow Canyon to the adjacent basin, explaining similar composition between the two areas in spring and summer. Off-shelf advection was much less pronounced for other slope and basin areas, which are influenced by the low-nutrient Beaufort gyre circulation, leading to a dominance of smaller prasinophytes and chlorophytes. The correlation of large-sized fucoxanthin containing phytoplankton with the higher primary production measurements shows promise for trophic status to be estimated using accessory pigment ratios.     

Charged dust in the outer planetary magnetospheres

We assume that typical interplanetary grains are fragile, aggregates of the Brownlee type, and discuss the physical and dynamical processes associated with their entry into the Jovian magnetosphere. Limiting ourselves to the equatorial plane of the planet, we show that grains traversing the outer edge of the co-rotating magnetodisc (r35R _J ) are rapidly charged up to large negative potentials on both the day and the night sides. A parent grain of radiusR _g 20 is electrostatically disrupted when it attains a potential of about –220 V. While the eventual potential achieved by the smallest fragments (R _g 0.1 ) are controlled by the rapid field emission of electrons, those of the larger fragments (R _g 1 ) are set by the plasma and photoemission currents.All the negatively charged fragments are strongly attracted towards the planet by the (radial) corotational electric field and some are stably trapped. We suggest that the sudden enhancement by about 2 orders of magnitude of the interplanetary dust flux measured by Pioneer 10, at about 30R _J from Jupiter result from the combination of these two effects.The different brightness asymmetries between the leading and the trailing sides of the outer and inner Galilean satellites appear to be a natural consequence of the way the trajectories of these charged dust grains intersect these satellite surfaces. Finally, the similarity in the brightness asymmetries between the Jovian and Saturnian satellites, and our belief that they have a similar cause, leads us to the expectation that Saturn's magnetic momentM and spin , are parallel as in the case of Jupiter, with the limit of plasma co-rotation lying between the satellites Rhea and Iapetus.     

Quantitative analysis of variations in depositional sequence thickness from submarine channel levees

Abstract Thickness variations across‐levee and downchannel in acoustically defined depositional sequences from six submarine channel‐levee systems show consistent and quantifiable patterns. The thickness of depositional sequences perpendicular to the channel trend, i.e. across the levee, decreases exponentially, as characterized by a spatial decay constant, k. Similarly, the thickness of sediment at the levee crest decreases exponentially down the upper reaches of submarine channels and can be characterized by a second spatial decay constant, λ. The inverse of these decay constants has units of length and defines depositional length scales such that k^?1 is a measure of levee width and λ^?1 is a measure of levee length. Quantification of levee architecture in this way allowed investigation of relationships between levee architecture and channel dimensions. It was found that these measures of levee e‐folding width and levee e‐folding length are directly related to channel width and relief. The dimensions of channels and levees are thus intimately related, thereby limiting the range of potential channel‐levee morphologies, regardless of allocyclic forcing. A simple sediment budget model relates the product of the levee e‐folding width and e‐folding length to through‐channel volume discharge. A classification system based on the quantitative downchannel behaviour of levee architecture allows identification of a ‘mid‐channel’ reach, where sediment is passively transferred from the through‐channel flow to the levees as an overspilling flow. Downstream from this reach, the channel gradually looses its control on guiding turbidity currents, and the resulting flow can be considered as an unconfined or spreading flow.     

Inferring the mass fraction of floc-deposited mud: application to fine-grained turbidites

Fine sediment deposition in the ocean is complicated by the cohesive nature of muds and their tendency to flocculate. The result is disaggregated inorganic grain size (DIGS) distributions of bottom sediment that are influenced by single‐grain and floc deposition. This study outlines a parametric model that characterizes bottom sediment DIGS distributions. Modelled parameters are then used to infer depositional conditions that account for the regional variation in the grain sizes deposited by turbidity currents on the Laurentian Fan–Sohm Abyssal Plain, offshore south‐eastern Canada. Results indicate that, on the channellized Laurentian Fan, the mass fraction of floc‐deposited mud increases only slightly downslope. The small evolution in this fraction arises because sediment concentration and turbulent energy are associated in turbidity currents. On the Sohm Abyssal Plain, however, the mass fraction of floc‐deposited mud decreases, probably as a result of lower sediment concentration at this source‐distal site. Estimates of the mass fraction of mud deposited as flocs suggest that floc deposition is the dominant mode by which sediment is lost from suspension, although single‐grain deposition contributes more to the depositional flux in proximal areas where high energy breaks flocs and in distal areas where low sediment concentration limits floc formation. It is concluded that, throughout the dispersal system, changes in the fraction of flocculated mud deposited from turbidity currents reflect changes in sediment concentration and energy downslope.