Eclipsing Binary Stars in Nearby Galaxies

We briefly discuss the survey programme we are conducting to detect eclipsing binaries in local group galaxies. Some lightcurves from studies of M31, IC 1613 and NGC 6822 are presented along with details of future work.     

THUNDERSTORM CLIMATOLOGY BASED ON LIGHTNING DETECTOR DATA,MANITOBA, CANADA

Comparisons are made between thunderstorm data collected from a lightning detector network and from conventional climatic stations for the province of Manitoba, Canada. The greater resolution in time and space of lightning detector (direction finder) data makes it a valuable source of thunderstorm information and lends itself to some important applications. Data were collected for the forest fire season of 1985 using a network of 7 lightning direction finders distributed throughout the province. Some 67,912 cloud-to-ground lightning strikes were recorded by time and location during 122 thunderstorm days. July was the most active month with 27,260 strikes over 28 days. Two regions of the province had the greatest concentration of lightning strikes, indicating some influence by topography and position of large lakes. Case studies are presented of the most active lightning storms of 1985 and 1986. These storms are exclusively frontal storms, with most having similar synoptic weather patterns to those of large hailstorms and tornadoes in Manitoba. Relationships between meteorological parameters and lightning strike distribution are presented. These relationships may prove useful in the suppression of lightning-caused forest fires, especially in remote areas of the province. [Key words: lightning, thunderstorm, synoptic climatology, natural hazards, fire prevention.]     

The 2dF Galaxy Redshift Survey: galaxy luminosity functions per spectral type

We calculate the optical b _J luminosity function (LF) of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are defined using a new parameter, η , which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter η identifies the average emission- and absorption-line strength in the galaxy rest frame spectrum, and hence is a useful indicator of the present star formation. We use a total of 75 000 galaxies in our calculations, chosen from a sample of high signal-to-noise ratio, low-redshift galaxies observed before 2001 January. We find that there is a systematic steepening of the faint-end slope ( α ) as one moves from passive  ( α =-0.54)  to active  ( α =-1.50)  star-forming galaxies, and that there is also a corresponding faintening of the rest frame characteristic magnitude   M *-5 log₁₀( h )  (from −19.6 to −19.2). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies  [ M _{b J}-5 log₁₀( h )  fainter than −16.0], perhaps suggesting the presence of a significant dwarf population. The LFs presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample, and in other surveys. We also present a new procedure for determining self-consistent k -corrections, and investigate possible fibre-aperture biases.     

Geomorphic and sedimentologic evidence for the separation of Lake Superior from Lake Michigan and Huron

A common break was recognized in four Lake Superior strandplain sequences using geomorphic and sedimentologic characteristics. Strandplains were divided into lakeward and landward sets of beach ridges using aerial photographs and topographic surveys to identify similar surficial features and core data to identify similar subsurface features. Cross-strandplain, elevation-trend changes from a lowering towards the lake in the landward set of beach ridges to a rise or reduction of slope towards the lake in the lakeward set of beach ridges indicates that the break is associated with an outlet change for Lake Superior. Correlation of this break between study sites and age model results for the strandplain sequences suggest that the outlet change occurred sometime after about 2,400 calendar years ago (after the Algoma phase). Age model results from one site (Grand Traverse Bay) suggest an alternate age closer to about 1,200 calendar years ago but age models need to be investigated further. The landward part of the strandplain was deposited when water levels were common in all three upper Great Lakes basins (Superior, Huron, and Michigan) and drained through the Port Huron/Sarnia outlet. The lakeward part was deposited after the Sault outlet started to help regulate water levels in the Lake Superior basin. The landward beach ridges are commonly better defined and continuous across the embayments, more numerous, larger in relief, wider, have greater vegetation density, and intervening swales contain more standing water and peat than the lakeward set. Changes in drainage patterns, foreshore sediment thickness and grain size help in identifying the break between sets in the strandplain sequences. Investigation of these breaks may help identify possible gaps in the record or missing ridges in strandplain sequences that may not be apparent when viewing age distributions and may justify the need for multiple age and glacial isostatic adjustment models. This is the third in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue. The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

Experimental stability of magnesium sulfate hydrates that may be present on Mars

Since the Viking missions in 1976, magnesium sulfates have been predicted to exist on the surface of Mars. Recent orbital measurements suggest that Mg-sulfates are rather ubiquitous on the martian surface. Chemical analyses by landers support the inference that Mg-sulfate hydrates may be one source of the significant quantities of equatorial near-surface hydrogen observed by the neutron and γ-ray spectrometers on the Mars Odyssey spacecraft. The present study was undertaken to examine stability relations among the various Mg-sulfate hydrates. Using saturated salt solutions to control water-vapor pressure at temperatures of 3, 23, 50, 63, and 75 °C, Mg-sulfate phases were allowed to equilibrate from 2 to 3 months to see which hydration states were formed or were stable. Starting materials consisted of hexahydrite (6H₂O), starkeyite (4H₂O), kieserite (1H₂O), a second monohydrate-polymorph available as a chemical reagent, and an anhydrous MgSO₄ reagent. Products created in this study included these minerals, along with epsomite (7H₂O), sanderite (2H₂O), amorphous MgSO₄ (1-2H₂O), several previously undescribed phases, one of which was quite persistent (2.4H₂O), and trace amounts of pentahydrite (5H₂O). As expected, Mg-sulfate stability is strongly dependent on water vapor pressure and temperature. Lower temperatures favor the more hydrated Mg-sulfates. However, the MgSO₄ system was found to be surprisingly complicated and is strongly dominated by metastability, sluggish kinetics, and reaction pathways. Unexpected results were frequently encountered, in addition to the formation of previously undescribed phases. Several of the hydrates also show significant metastable extensions, such that phase boundaries can only be approximated. For example, kieserite, which has been reported on Mars from OMEGA data, in addition to having a distinct stability region, is resistant to transformation and persists throughout temperature-RH space until very high relative humidities are achieved. Results of this study show that MgSO₄ hydrates in addition to epsomite, hexahydrite, and kieserite can persist and should not be overlooked when assessing possible Mg-sulfate minerals that can occur on Mars.     

The application of GIS in the lands sector of a developing country: Challenges facing land administrators in Ghana

The Government of Ghana is about to take steps under its Land Administration Project to initiate the adoption of geographical information systems (GIS) in the administration of land. This paper identifies some of the challenges for Ghana's leading lands agency, the Lands Commission Secretariat, and highlights problems such as the paucity of reliable data sets and lack of standards. One of the major planning issues in Accra is that of building encroachments, for which no digital information is currently available. The paper reports on a pilot study to record encroachments on public land and demonstrates the type of inconsistencies that are apparent between the planning and cadastral data sets that do exist. The paper emphasizes that appropriate applications of GIS in Ghana's land sector are those that consider the political, social and institutional contexts within which GIS is to be operationalized.     

Earthquake-induced burial of archaeological sites along the southern Washington coast about A.D. 1700

Although inhabited by thousands of people when first reached by Europeans, the Pacific coast of southern Washington has little recognized evidence of prehistoric human occupation. This apparent contradiction may be explained partly by geologic evidence for coastal submergence during prehistoric earthquakes on the Cascadia subduction zone. Recently discovered archaeological sites, exposed in the banks of two tidal streams, show evidence for earthquake-induced submergence and consequent burial by intertidal mud about A.D. 1700. We surmise that, because of prehistoric earthquakes, other archaeological sites may now lie hidden beneath the surfaces of modern tidelands. Such burial of archaeological sites raises questions about the estimation of prehistoric human population densities along coasts subject to earthquake-induced submergence. © 1996 John Wiley & Sons, Inc.