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1.
Roberto F. Viotti Lucio Angelo Antonelli Sonja Rebecchi Corinne Rossi 《Journal of Astrophysics and Astronomy》2002,23(1-2):19-22
We have investigated with BeppoSAX the long term behaviour of the harder X-ray component of the supposed supermassive binary
system η Car along its 5.52 year cycle. We have found that in March 1998 during egress from the last December 1997 eclipse,
this component was the same as outside eclipse, but for a large (×3.5) increase of NH
h
, that can be attributed to the presence or formation of opaque matter in front of the source near periastron. Unexpectedly,
at that time the iron 6.7 keV emission line was 40% stronger. BeppoSAX has for the first time found ahard X-ray tail extending to at least 50 keV, that cannot be adequately fitted with an additional hotter thermal component. The 2–100 keV
spectrum of η Car is instead well fitted with an absorbed powerlaw spectrum with photon index 2.53, suggesting non-thermal
emission as an alternative model for the core source. 相似文献
2.
Roberto F. Viotti Rosario González-Riestra Takashi Iijima Stefano Bernabei Riccardo Claudi Jochen Greiner Michael Friedjung Vito Francesco Polcaro Corinne Rossi 《Astrophysics and Space Science》2005,296(1-4):435-439
We review the main characteristics of the symbiotic system AG Draconis, with special emphasis on its optical and X-ray variations.
We also discuss the X-ray to visual energy distribution during quiescence and outburst and describe our spectroscopic and
X-ray observations during the 2003 outburst.
Based on X-ray observations collected with the XMM–Newton Observatory, on INES data from the IUE satellite, and on optical
spectra collected with the Asiago–Cima Ekar, Bologna–Loiano and La Palma–Galileo Italian telescopes. 相似文献
3.
Abstract. The temperate, symbiotic coral Cladocora caespitosa occurs naturally with variable numbers of zooxanthellae. This allows us to study differences in the physiology of symbiotic and "non-symbiotic" polyps and to correlate them with zooxanthellae activities.
Zooxanthellae density in "dark" (normal-colored) polyps was 50 times higher than in "white" (bleached) polyps.
The chlorophyll a content per zooxanthella was 3 times, and Chi c was 13 times higher in white polyps than in dark ones. O2 -flux experiments were conducted with colonies in situ and with single polyps - dark and white - under laboratory conditions. Two approaches were used to evaluate the contribution of zooxanthellae translocation products to animal respiration. Both revealed that the animal tissues derive a higher benefit from the zooxanthellae during periods of low water temperature than during warm periods. 相似文献
Zooxanthellae density in "dark" (normal-colored) polyps was 50 times higher than in "white" (bleached) polyps.
The chlorophyll a content per zooxanthella was 3 times, and Chi c was 13 times higher in white polyps than in dark ones. O
4.
5.
Britta Planer-Friedrich Corinne Lehr Jörg Matschullat Darrell Kirk Nordstrom 《Geochimica et cosmochimica acta》2006,70(10):2480-2491
Geothermal features in the Yellowstone National Park contain up to several milligram per liter of aqueous arsenic. Part of this arsenic is volatilized and released into the atmosphere. Total volatile arsenic concentrations of 0.5-200 mg/m3 at the surface of the hot springs were found to exceed the previously assumed nanogram per cubic meter range of background concentrations by orders of magnitude. Speciation of the volatile arsenic was performed using solid-phase micro-extraction fibers with analysis by GC-MS. The arsenic species most frequently identified in the samples is (CH3)2AsCl, followed by (CH3)3As, (CH3)2AsSCH3, and CH3AsCl2 in decreasing order of frequency. This report contains the first documented occurrence of chloro- and thioarsines in a natural environment. Toxicity, mobility, and degradation products are unknown. 相似文献
6.
Corinne Sonzogni Edouard Bard Frauke Rostek Denis Dollfus Antoni Rosell-Melé Geoffrey Eglinton 《Quaternary Research》1997,47(3):344-355
We compare alkenone unsaturation ratios measured on recent sediments from the Indian Ocean (20°N–45°S) with modern sea oceanographic parameters. For each of the core sites we estimated average seasonal cycles of sea surface temperature (SST) and salinity, which we then weighted with the seasonal productivity cycle derived from chlorophyll satellite imagery. The unsaturation index (U37K′) ranges from 0.2 to 1 and correlates with water temperature but not with salinity. TheU37K′versus SST relationship for Indian Ocean sediments (U37K′= 0.033 SST + 0.05) is similar to what has been observed for core tops from the Pacific and Atlantic oceans and the Black Sea. A global compilation for core tops givesU37K′= 0.031 T + 0.084 (R= 0.98), which is close to a previously reported calibration based on particulate organic matter from the water column. For temperatures between 24° and 29°C, however, the slope seems to decrease to about 0.02U37K′unit/°C. For Indian Ocean core tops, the ratios of total C37alkenones/total C38alkenones and the slope of theU37K′-SST relationship are similar to those previously observed for cultures ofEmiliania huxleyibut different from those previously published forGephyrocapsa oceanica.EitherE. huxleyiis a major producer of alkenones in the Indian Ocean or strains ofG. oceanicaliving in the northern Indian Ocean behave differently from the one cultured. In contrast with coccolithophorid assemblages, the ratios of C37alkenones to total C38alkenones lack clear geographic pattern in the Indian Ocean. 相似文献
7.
Sren Grube Pedersen Martin Schiller James N. Connelly Martin Bizzarro 《Meteoritics & planetary science》2019,54(6):1215-1227
Planetary bodies a few hundred kilometers in radii are the precursors to larger planets but it is unclear whether these bodies themselves formed very rapidly or accreted slowly over several millions of years. Ordinary H chondrite meteorites provide an opportunity to investigate the accretion time scale of a small planetary body given that variable degrees of thermal metamorphism present in H chondrites provide a proxy for their stratigraphic depth and, therefore, relative accretion times. We exploit this feature to search for nucleosynthetic isotope variability of 54Cr, which is a sensitive tracer of spatial and temporal variations in the protoplanetary disk's solids, between 17 H chondrites covering all petrologic types to obtain clues about the parent body accretionary rate. We find no systematic variability in the mass‐biased corrected abundances of 53Cr or 54Cr outside of the analytical uncertainties, suggesting very rapid accretion of the H chondrite parent body consistent with turbulent accretion. By utilizing the μ54Cr–planetary mass relationship observed between inner solar system planetary bodies, we calculate that the H chondrite accretion occurred at 1.1 ± 0.4 or 1.8 ± 0.2 Myr after the formation of calcium‐aluminum‐rich inclusions (CAIs), assuming either the initial 26Al/27Al abundance of inner solar system solids determined from angrite meteorites or CAIs from CV chondrites, respectively. Notably, these ages are in agreement with age estimates based on the parent bodies’ thermal evolution when correcting these calculations to the same initial 26Al/27Al abundance, reinforcing the idea of a secular evolution in the isotopic composition of inner disk solids. 相似文献
8.
Juana Mireya Mendoza-Vera Samba K Corinne Cuoc Marc Bouvy Marc Pagano 《Estuarine, Coastal and Shelf Science》2008,79(4):740-750
Pseudodiaptomus hessei is a key species in many water bodies in the Senegal River hydrosystem but it became rare or completely disappeared from two ecosystems (Lake Guiers and Dakar Bango Reservoir; Senegal, West Africa) after major hydrological changes caused by human action, mainly impoundments on the river in 1985, and the opening of a new estuary mouth in 2003. Kâ et al. [Kâ, S., Pagano, M., Ba, N., Bouvy, M., Leboulanger, C., Arfi, R., Thiaw, O.T., Ndour, E.H.M., Corbin, D., Defaye, D., Cuoc, C., Kouassi, E., 2006. Zooplankton distribution related to environmental factors and phytoplankton in a shallow tropical lake (Lake Guiers, Senegal, West Africa). International Review of Hydrobiology 91(5), 389–405] put forward several hypotheses to explain the reasons for this decline: salinity and chemical changes in the water, predation by a cyclopid predator Mesocyclops ogunnus and/or the inhibiting effects of cyanobacteria and/or diatoms (allelopathy). This study assessed these hypotheses by studying the distribution of P. hessei in 13 stations (including the Dakar Bango reservoir and Lake Guiers) in relation to physical, chemical and biological (phyto- and zooplanktons) factors at each station. We produced a distribution pattern for this species in the Senegal River hydrosystem. Rank correlations and principal component analysis showed that P. hessei was not correlated with conductivity but was positively correlated with pH and alkalinity, suggesting chemical effects. The clear association with two filamentous cyanobacteria (Cylindrospermopsis raciborskii and Anabaena sp.) did not appear to support the hypothesis of cyanobacteria inhibition but blooming conditions were never encountered during the study. Negative correlation with diatoms (especially with Fragilaria sp.) suggested that aldehyde producing diatoms had a negative effect. Negative correlations with cyclopids such as Mesocyclops supported the hypothesis of cyclopid predation to explain the decline of P. hessei. This study proposes several lines of research for future studies to test these hypotheses. 相似文献
9.
Martin Schiller James N. Connelly Martin Bizzarro 《Meteoritics & planetary science》2017,52(6):1233-1243
The large collection of howardite‐eucrite‐diogenite (HED) meteorites allows us to study the initial magmatic differentiation of a planetesimal. We report Pb‐Pb ages of the unequilibrated North West Africa (NWA) 4215 and Dhofar 700 diogenite meteorites and their mass‐independent 26Mg isotope compositions (26Mg*) to better understand the timing of differentiation and crystallization of their source reservoir(s). NWA 4215 defines a Pb‐Pb age of 4484.5 ± 7.9 Myr and has a 26Mg* excess of +2.3 ± 1.6 ppm whereas Dhofar 700 has a Pb‐Pb age of 4546.4 ± 4.7 Myr and a 26Mg* excess of +25.5 ± 1.9 ppm. We interpret the young age of NWA 4215 as a thermal overprint, but the age of Dhofar 700 is interpreted to represent a primary crystallization age. Combining our new data with published Mg isotope and trace element data suggests that approximately half of the diogenites for which such data are available crystallized within the first 1–2 Myr of our solar system, consistent with a short‐lived, early‐formed magma ocean undergoing convective cooling. The other half of the diogenites, including both NWA 4215 and Dhofar 700, are best explained by their crystallization in slowly cooled isolated magma chambers lasting over at least ~20 Myr. 相似文献
10.
Carole Cordier Martial Caroff Thierry Juteau Corinne Fleutelot Christophe Hmond Marion Drouin Joseph Cotten Claire Bollinger 《Lithos》2007,99(3-4):289-311
The present study is based on a set of lavas and crosscutting dikes collected by dives along detailed vertical transects on the northern flank of the western part of the Blanco Transform Fault, Northeast Pacific. The studied area consists of a small basin, the Western Blanco Depression (WBD), extending from the southern end of the Juan de Fuca ridge to a pseudofault trace 60 km eastward. The Northern Scarp of the WBD comprises a volcanic unit overlying a sheeted-dike complex. Major and trace element data, coupled with Sr–Nd isotope ratios, reveal a two-component mantle source, composed by an isotopically depleted matrix variably veined by more enriched material. One chemical group (NS2), indistinguishable from the other Northern Scarp samples on the basis of trace element data, has an unusually depleted isotopic composition typical of a nearly pure mantle end-member. Some cogenetic samples of the Northern Scarp have been used to constrain the differentiation modalities. Anorthite and MgO content profiles in plagioclase xenocrysts and phenocrysts reveal (i) the existence of H2O-bearing evolved melts in the mushy zones and (ii) the occurrence of mixing process between these melts and anhydrous mafic liquids. The hydration is supported by other petrographic features such as high magmatic fO2 values, calculated from Fe–Ti oxide pairs, and the presence of pyroxene inclusions in plagioclase phenocrysts. Mixing, consistent with the existence of Ni-rich ferrobasalts, is interpreted to be the consequence of the reservoir refilling by mafic liquids (Mg# = 70). These petrological and geochemical evidences are combined with the evolution of Mg# with depth to suggest a periodic open-system magma chamber evolution beneath the southern end of the Juan de Fuca ridge. 相似文献