Isolated and mildly interacting spiral galaxies: Rotation curves and metallicities     

Isabel Márquez  Josefa Masegosa  Mariano Moles  Jesús Varela  Daniella Bettoni  Giusseppe Galletta 《Astrophysics and Space Science》2003,284(2):711-714

We present the study of long slit spectra in the region ofHα emission line of a sample of 111 spiral galaxies with recognizable and well defined spiral morphology and with a well determined environmental status, ranging from isolation to non-disruptive interaction with satellites or companions. The form and properties of the rotation curves (RC) are considered as a function of the isolation degree, morphological type, t, and luminosity. The line ratios are used to estimate the metallicity of all the detected HII regions, thus producing a composite metallicity profile for different types of spirals. We have found that isolated galaxies (ISO) tend to be of later types and lower luminosity than the interacting galaxies (INT). The outer parts of the RC of ISO tend to be flatter than in INT, but they show similar relations between global parameters. The scatter of the Tully-Fisher (TF) relation defined by ISO is significantly lower than that of INT. The [NII]/Hα ratios, used as a metallicity indicator, show a clear trend between Z and t, with earlier spirals showing higher ratios; this trend is tighter when instead of t the gradient of the inner RC, G, is used; no trend is found with the change in interaction status. The Z-gradient of the disks depends on the type, being almost flat for early spirals, and increasing for later types. The [NII]/Hα ratios measured for disk HII regions of INT are higher than for normal/ISO objects, even if all the galaxy families present similar distributions of Hα Equivalent Width. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Glass-bearing inclusions in Nakhla(SNC meteorite) augite: heterogeneouslytrapped phases     

M. E. Varela  G. Kurat  R. Clocchiatti 《Mineralogy and Petrology》2001,71(3-4):155-172

Summary Nakhla augite and olivine grains commonly contain glass-bearing inclusions. In contrast to olivines, augites host only one type of multiphase inclusions which consists of euhedral to subhedral augite, Ti-magnetite and pigeonite plus silica-rich glass and a bubble. No fractures surround these inclusions, making it likely that they are of a pristine composition. Heating experiments with a final temperature of 1150 °C were done for the first time with Nakhla augite inclusions. During heating the glass melted and crystals inside the inclusions were dissolved in the melt whereby its chemical composition changed. The quenched glass is poorer in SiO₂ and Al₂O₃ and richer in CaO, FeO and MgO compared to unheated inclusion glass. Our in situ analyses allowed us to estimate the initial composition of a liquid co-existing with Nakhla augite at 1150 °C and 1 atm pressure. Several features of Nakhla, such as the high Fe/Mg ratio of the augite, which is out of equilibrium with the glass, the highly variable alkali content and the Na/K ratio of the glasses are incompatible with the standard model that states that SNC meteorites are all igneous rocks formed from basaltic magmas. Our results on re-melted glasses suggest a more complex and possibly non-magmatic genesis of Nakhla. Both types of glass-bearing inclusions (those hosted by augite or olivine) could represent heterogeneously trapped mineral + glass inclusions. Those hosted by augites mimic at least in part parental melt inclusions. However, the quenched glass is out of equilibrium with the host with respect to the Fe/Mg ratio and has too much compositional variation to be representative of a parental melt.

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Zusammenfassung Glasführende Einschlüsse im Augit von Nakhla (SNC-Meteorit): Heterogeneingeschlossene Phasen Augite und Olivine im Achondriten Nakhla enthalten h?ufig glasführende Einschlüsse. Im Gegensatz zu den Olivinen enthalten die Augite nur einen Typ Multiphasen-Einschlu?, welcher aus idiomorphem bis subidiomorphem Augit, Ti-Magnetit, Pigeonit und einem SiO₂-reichen Glas mit Blase besteht. Diese Einschlüsse sind nicht von Sprüngen umgeben, was es wahrscheinlich macht, dass sie ihre ursprüngliche Zusammensetzung unver?ndert erhalten haben. Erstmals wurden Schmelz-Experimente mit Endtemperaturen von 1150 °C an Nakhla Augiten durchgeführt. In diesen Experimenten schmolz das Glas der Einschlüsse, l?ste die koexistierenden kristallinen Phasen auf und ?nderte dabei seine chemische Zusammensetzung. Das durch Abschrecken dieser Schmelze erzeugte Glas ist ?rmer an SiO₂ und Al₂O₃ und reicher an CaO, FeO und MgO als das ursprüngliche Einschlu?glas. Diese in situ-Analyse erlaubt eine Absch?tzung der ursprünglichen Zusammensetzung einer Schmelze im Gleichgewicht mit Nakhla Augit bei 1150 °C und 1 atm Druck. Einige Eigenschaften von Nakhla, wie das hohe Fe/Mg-Verh?ltnis des Augites, welches nicht im Gleichgewicht mit dem Glas ist, die variablen Alkali-Gehalte und die Na/K-Verh?ltnisse im Glas sind inkompatibel mit dem Standard-Modell für die SNC-Meteorite, welches diese als magmatische Gesteine basaltischer Herkunft sieht. Unsere Ergebnisse weisen auf eine komplexe, m?glicherweise nicht-magmatische Entstehung von Nakhla hin. Sowohl die glasführenden Einschlüsse im Olivin als auch jene im Augit von Nakhla k?nnten Produkte eines heterogenen Aufsammelns von Mineral plus Glas sein. Die Einschlüsse im Augit imitieren zumindest zum Teil Schmelzeinschlüsse. Allerdings sind sie mit ihrem Fe/Mg – Verh?ltnis nicht im Gleichgewicht mit dem Augit und sind auch in ihrer Zusammensetzung zu inhomogen, um für ein m?gliches Mutter-Magma repr?sentativ zu sein.

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Received April 10, 2000; revised version accepted October 19, 2000  相似文献   

Lavras do Sul: A New Equilibrated Ordinary L5 Chondrite from Rio Grande do Sul,Brazil     

M. E. Zucolotto  L. L. Antonello  M. E. Varela  R. B. Scorzelli  Isabel P. Ludka  P. Munayco  E. dos Santos 《Earth, Moon, and Planets》2012,108(2):139-150

The new Brazilian chondrite, Lavras do Sul, was found in 1985 at Lavras do Sul, Rio Grande do Sul State-Brazil (33°30′48″S; 53°54′65″W). It consists of a single mass weighing about 1 kg, covered by a black fusion crust with grayish interior. Four polished thin sections were prepared from a slice weighing 67 g on deposit at the Museu Nacional/UFRJ. It consists mostly of chondrules and chondrule fragments dispersed in a recrystallized matrix. Most chondrules are poorly defined and range in size from 300 to 2,000 μm, although some of them show distinct outlines, particularly when viewed under cross-polarized transmitted and reflected light. The texture of chondrules varies from non-porphyritic (e.g., barred-olivine, radial-pyroxene) to porphyritic ones (e.g., granular olivine as well as olivine-pyroxene). The meteorite contains mainly olivine (Fa_24.9), low-Ca pyroxene (Fs_22.6) and metal phases, with minor amounts of plagioclase, chromite and magnetite. Mössbauer Spectroscopy studies indicate that the metal phase is kamacite, tetrataenite and antitaenite. Veins of secondary iddingsite crosscut the thin section and some ferromagnesian silicates. The chemical composition indicates that Lavras do Sul is a member of the low iron L chondrite group. The poorly delineated chondritic texture with few well-defined chondrules, the occurrence of rare clinopyroxene and plagioclase (and maskelynite) with apparent diameters ranging from 5 to 123 μm led us to classify Lavras do Sul as an equilibrated petrologic type 5. The shock features of some minerals suggest a shock stage S3, and the presence of a small amount of secondary minerals such as iddingsite and goethite, a degree of weathering W₁. The meteorite name was approved by the Nomenclature Committee (Nom Com) of the Meteoritical Society (Meteoritic Bulletin Nº99).  相似文献   

Diet and dietary variation of New Zealand hoki Macruronus novaezelandiae     

AM Connell  J Forman 《新西兰海洋与淡水研究杂志》2013,47(4):289-308

The diet of hoki was determined from examination of stomach contents of 1992 fish of 26–112 cm total length (TL) sampled at depths of 209–904m on Chatham Rise, New Zealand, from summer research trawl surveys and seasonal commercial fishing trawls, during 2004–2008. Prey was predominantly euphausiids, mesopelagic fishes and natant decapods. Multivariate analyses using distance-based linear models, non-parametric multi-dimensional scaling and similarity percentages indicated that the best predictors of diet variability were the position of the fish in relation to the subtropical front (STF), fish size and longitude. Pasiphaeids were more important to the north of the STF, and sternoptychid fishes and euphausiids more important in the STF convergence area. Euphausiids and sternoptychid fishes were important for smaller hoki (26–55 cm TL), myctophid fishes and natant decapods for larger hoki, and macrourids for the largest hoki (>84 cm TL). The longitudinal effect was characterised by pasiphaeids, euphausiids and sternoptychids to the west, and myctophids in the centre of Chatham Rise. Feeding activity was analysed using generalised additive models, and was found to vary with time of day, sample source (research or commercial), longitude, hoki size and depth. The variability in diet suggested hoki forage opportunistically within their preferred habitat and biological limits.  相似文献   

Variations of phytoplankton productivity and biomass over an annual cycle in Saanich Inlet,a British Columbia fjord     

Damian S. Grundle  David A. Timothy  Diana E. Varela 《Continental Shelf Research》2009

Saanich Inlet is a highly productive temperate fjord with the capability to record inter-annual patterns of water-column primary production in undisturbed laminated sediments. We investigated spatial and temporal variations in primary productivity, total and size-fractionated phytoplankton chl a, dissolved nutrients, temperature and salinity at the head and mouth of Saanich Inlet from May 2005 to November 2006. New primary productivity was also measured from May to October 2006. During the growing season (spring, summer and fall), primary productivity was 1.5 times higher at the mouth than at the head of Saanich Inlet and, averaged across stations, total productivity was 460 g C m⁻² y⁻¹. Average new productivity was 53% and 58% of total primary productivity at the head and mouth of the inlet, respectively, and during the growing season micro-phytoplankton (>20 μm; mainly diatoms) was the most abundant size-class of phytoplankton. These rates of primary production are as high as or higher than those measured in other fjords, possibly because of a tidally-driven fortnightly gravity exchange that supplies nutrients to surface waters that enhance biological production when nutrients would otherwise be limiting. This exchange delivers nutrients at least as far inland as the head station, while nutrients associated with an eddy near the mouth may be the cause of even higher productivity there. We discuss the impact of these nutrient sources to Saanich Inlet on the records of paleoproduction generated from two Ocean Drilling Program cores extracted from this fjord, and suggest that the fortnightly exchange buffers variations in nutrient supply occurring on sub-decadal or decadal scales.  相似文献   

Current state and trends in Canadian Arctic marine ecosystems: I. Primary production     

Jean-éric Tremblay  Dominique Robert  Diana E. Varela  Connie Lovejoy  Gérald Darnis  R. John Nelson  Akash R. Sastri 《Climatic change》2012,115(1):161-178

During the International Polar Year (IPY), large international research programs provided a unique opportunity for assessing the current state and trends in major components of arctic marine ecosystems at an exceptionally wide spatio-temporal scale: sampling covered most regions of the Canadian Arctic (IPY-Canada??s Three Oceans project), and the coastal and offshore areas of the southeastern Beaufort Sea were monitored over almost a full year (IPY-Circumpolar Flaw Lead project). The general goal of these projects was to improve our understanding of how the response of arctic marine ecosystems to climate warming will alter the productivity and structure of the food web and the ecosystem services it provides to Northerners. The present paper summarizes and discusses six key findings related to primary production (PP), which determines the amount of food available to consumers. (1) Offshore, the warming and freshening of the surface layer is leading to the displacement of large nanophytoplankton species by small picophytoplankton cells, with potentially profound bottom-up effects within the marine food web. (2) In coastal areas, PP increases as favourable winds and the deeper seaward retreat of ice promote upwelling. (3) Multiple upwelling events repeatedly provide food to herbivores throughout the growth season. (4) A substantial amount of pelagic PP occurs under thinning ice and cannot be detected by orbiting sensors. (5) Early PP in the spring does not imply a trophic mismatch with key herbivores. (6) The epipelagic ecosystem is very efficient at retaining carbon in surface waters and preventing its sedimentation to the benthos. While enhanced PP could result in increased fish and marine mammal harvests for Northerners, it will most likely be insufficient for sustainable large-scale commercial fisheries in the Canadian Arctic.  相似文献   

Structure and Dynamics of NGC 1300     

J.A.L. Aguerri  M. Prieto  A.M. Varela  C. Muñoz-Tuñón 《Astrophysics and Space Science》2001,276(2-4):611-618

The isophotal profiles and colour maps of a sample of 12 spiral galaxies allowed us to analyse the different structural components that compose them. These components were parameterized by performing a decomposition of the galaxy brightness profiles. Inferring the geometry for each component, we have obtained the spatial mass distribution and the gravitational potential for each object. Here we present the detailed analysis for one of the galaxies in the sample, the barred galaxy NGC 1300. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A winter upwelling event in the Northern Galician Rias: Frequency and oceanographic implications     

I. Alvarez  N. Ospina-Alvarez  Y. Pazos  M. deCastro  P. Bernardez  M.J. Campos  J.L. Gomez-Gesteira  M.T. Alvarez-Ossorio  M. Varela  M. Gomez-Gesteira  R. Prego   《Estuarine, Coastal and Shelf Science》2009,82(4):1362

A winter shelf-water upwelling evidence (February 2008) is described by first time in the Northern Galician Rias (NW Iberian Peninsula). On February 20, after 9 consecutive days of upwelling favorable conditions, inside the O Barqueiro Ria was observed the presence of seawater below 10 m depth which replaced the less saline water previously observed in January. This situation was in agreement with the analyzed Ekman transport close to the northern Galician coast. Salinity and temperature distribution revealed that the upwelled water inside the rias corresponds to shelf bottom seawater which is not associated with Eastern North Atlantic Central Water or the Iberian Poleward Current. In addition, TS diagram indicated a higher influence of upwelling eastward (Viveiro–Barqueiro–Ortigueira). Nutrient salts' concentrations also suggested the presence of seawater from subsurface origin with a small variation with regard to the winter mixing in this marine area. Plankton showed the existence of spring conditions related to solar radiation increase associated to upwelling favorable winds. Some species also corroborated the intrusion of shelf-water inside the ria. Results from the analysis of Ekman transport data from 1967 to 2007 revealed that this event cannot be considered an isolated episode. In fact, the number of days per month under upwelling favorable conditions in winter (January–March) was not negligible (8–10 days) showing that upwelling events along the northern Galician coast are also possible during winter.  相似文献   

Salmon aquaculture and coastal ecosystem health in Chile: Analysis of regulations,environmental impacts and bioremediation systems     

Alejandro H. Buschmann  Felipe Cabello  Kyle Young  Juan Carvajal  Daniel A. Varela  Luis Henríquez 《Ocean & Coastal Management》2009,52(5):243-249

In 2007 salmon, mollusk and seaweed aquaculture production in Chile totaled 904 thousand tonnes, making the nation the leading marine aquaculture producer in the western world. Salmonids grown in open cage net pens account for over 73% of the production. This review summarizes the current status of Chilean aquaculture and proposes the establishment of new regulations and monitoring programmes that encourage and accommodate emerging bioremediation technologies. In contrast to a rapidly expanding, well-financed and technologically advanced industry, the regulatory structure in Chile is outdated and based on insufficient science. The number of publications on the environmental impacts of salmon aquaculture in Chile is low relative to its production level. Nevertheless, the impacts of organic and inorganic waste on benthic communities, pelagic organisms and bird populations are documented. The technology to reduce these impacts using integrated multi-trophic aquaculture (IMTA) strategies exists, but has not been implemented at commercial scales. We call on the government and industry to support the creation of a well-financed and politically independent agency responsible for developing and enforcing science-based environmental regulations in Chile. The agency's immediate goal should be to fund research required to develop a transparent, ecosystem-based regulatory framework that promotes IMTA. Monitoring programs and licensing procedures must consider the impacts of individual sites and the cumulative impacts from multiple sites across a wide range of spatial scales. Before such changes are realized, environmental threats and human health risks will remain unacceptably high and salmon farming in Chile will not meet any reasonable definition of sustainability.  相似文献   

Hydrolytic ectoenzyme activity associated with suspended and sinking organic particles within the anoxic Cariaco Basin     

Gordon T. Taylor  Robert Thunell  Ramon Varela  Claudia Benitez-Nelson  Mary I. Scranton 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(8):1266-1283

Ectohydrolase activities of suspended microbiota were compared to those associated with sinking particles (sed-POM) retrieved from sediment traps deployed in the permanently anoxic Cariaco Basin. In shore-based assays, activities of aminopeptidase, β-glucosidase, chitinase and alkaline phosphatase were measured in samples obtained from oxic and anoxic depths using MUF- and MCA-labeled fluorogenic substrate analogs. Hydrolysis potentials for these enzymes in the seston varied widely over the nine cruises sampled (8 Nov 1996–3 May 2000) and among depths (15–1265 m); from <10 to over 1600 nM d^?1 hydrolysate released, generally co-varying with one another and with suspended particulate organic carbon (POC) and particulate nitrogen (PN). Hydrolytic potentials, prokaryotic abundances and POC/PN concentrations in sinking debris were 400–1.3×10⁷ times higher than in comparable volumes of seawater. However when normalized to PN, hydrolytic potentials in sediment trap samples were not demonstrably higher than in Niskin bottle samples. We estimate that PN pools in sediment trap samples were turned over 2–1400 times (medians=7–26x) slower by hydrolysis than were suspended PN pools. Median prokaryotic growth rates (divisions d^?1) in sinking debris were also ～150 times slower than for bacterioplankton. Hydrolytic potentials in surface oxic waters were generally faster than in underlying anoxic waters on a volumetric basis (nM hydrolysate d^?1), but were not significantly (p>0.05) different when normalized to PN or prokaryote abundances. Alkaline phosphatase was consistently the most active ectohydrolase in both sample types, suggesting that Cariaco Basin assemblages were adapted to decomposing phosphate esters in organic polymers. However, phosphorus limitation was not evident from nutrient inventories in the water column. Results support the hypothesis that efficiencies of polymer hydrolysis in anoxic waters are not inherently lower than in oxic waters.  相似文献