Joint formation of QSOs and spheroids: QSOs as clocks of star formation in spheroids     

G.L. Granato  L. Silva  P. Monaco  P. Panuzzo  P. Salucci  G. De Zotti  L. Danese 《Monthly notices of the Royal Astronomical Society》2001,324(3):757-768

Direct and indirect observational evidence leads to the conclusion that high-redshift QSOs did shine in the core of early-type protogalaxies during their main episode of star formation. Exploiting this fact, we derive the rate of formation of this kind of stellar system at high redshift by using the QSO luminosity function. The elemental proportions in elliptical galaxies, the descendants of the QSO hosts, suggest that the star formation was more rapid in more massive objects. We show that this is expected to occur in dark matter haloes, when the processes of cooling and heating are considered. This is also confirmed by comparing the observed submm counts with those derived by coupling the formation rate and the star formation rate of the spheroidal galaxies with a detailed model for their SED evolution. In this scenario SCUBA galaxies and Lyman-break galaxies are early-type protogalaxies forming the bulk of their stars before the onset of QSO activity.  相似文献   

Time-resolved spectroscopy of the sdBV V338 Serpentis     

R. H. Østensen  J. H. Telting  R. Oreiro  U. Heber  E. De Beck  M. Reed 《Astrophysics and Space Science》2010,329(1-2):167-174

We obtained 1955 high-resolution spectra of the high-amplitude pulsating subdwarf B star V338 Ser with the FIES spectrograph at the 2.5 m Nordic Optical Telescope covering 4 full nights in May–June 2009. Here we present the first results from phase-folding the data on the main pulsation mode, as revealed by simultaneous B-band photometry obtained with the Mercator 1.25 m and Baker 0.4 m telescopes. We compare the results with a sample line-profile model produced with LTE atmospheres and bruce+kylie.  相似文献   

Shape and obliquity effects on the thermal evolution of the Rosetta target 67P/Churyumov-Gerasimenko cometary nucleus     

M.C. De Sanctis  J. Lasue  M.T. Capria  D. Turrini 《Icarus》2010,207(1):341-494

This work is dedicated to the application to 67P/Churyumov-Gerasimenko of a new quasi-3D approach for non-spherically shaped comet nuclei with the aim to interpret the current activity of the comet in terms of initial characteristics and to predict shape and internal stratification evolution of the nucleus. The model is applied to differently shaped nuclei taking into account the characteristics of Comet 67P/Churyumov-Gerasimenko deduced from observations. We focus our attention on the combined effects that shapes and obliquity have on the comet surface and sub-surface evolution. We discuss the results in terms of activity, local dust mantle formation and disruption, erosion of the surface and internal stratigraphy.The results show that differently shaped nuclei can have different internal structures leading to different activity patterns and behaviors. Our calculations have shown that local variations in the dust and gas fluxes can be induced by the nucleus shape. The distribution of “active” areas on Comet 67P/Churyumov-Gerasimenko is different because of different shapes, reflecting the illumination conditions on the surface. These shapes can influence the structure of the inner coma, but the coma far away from the nucleus is only marginally affected by the nucleus shape. However, different comet behaviors can arise from differently shaped comet nuclei, especially in terms of local activity, surface and sub-surface characteristics and properties. The water flux local distribution is the most influenced by the shape as it is directly linked to the illumination. Irregular shapes have large shadowing effects that can result in activity patterns on the comet surface.The effects of different pole directions are discussed to see the relations with the nucleus activity and internal structure. It is shown that the orientation of the rotation axis plays a strong role on the surface evolution of 67P/Churyumov-Gerasimenko, determining seasonal effects on the fluxes. The activity of the comet changes greatly with the nucleus obliquity leading to pre-post-perihelion differences in the activity and seasonal effects. The effects of the dust deposition and crust formation on the cometary activity have also been simulated and are discussed with respect to 67P/Churyumov-Gerasimenko observations. The dust mantling is also strongly obliquity dependent, with different surface distributions of the dust-covered regions according to the different comet pole orientations. Finally, we show that our model can reproduce the fluxes behavior near perihelion in terms of amplitude and asymmetry, and we estimate 20% of the illuminated surface to be active.  相似文献   

New orbital solutions and absolute elements of the eclipsing binary TV Cet     

Z. Bozkurt  Ö.L. Değirmenci 《New Astronomy》2010,15(4):356-361

We present new differential, four-color photoelectric photometry for the eclipsing binary TV Cet. UBVR light curves and radial velocities published previously are solved simultaneously using the Wilson–Devinney computer program. Our solutions indicate that TV Cet includes a third light contribution with 2.3% in U, 1.9% in B, 1.3% in V and 1.6% in R. The masses of the component stars are $1.34\pm 0.05$ and $1.23\pm 0.05M\odot$, while the radii are $1.47\pm 0.02$ and $1.21\pm 0.01R\odot$ for the primary and secondary components, respectively. Using new absolute properties and our previous results from period analysis, we calculated the observational and theoretical internal structure constants to be ${\overline{k}}_{2\text{,}\mathit{obs}}=-1.66$ and ${\overline{k}}_{2\text{,}\mathit{theo}}=-2.25$, respectively. Taking into account the third light contribution from the Wilson–Devinney solution and properties of the third body orbit from period analysis, the mass of the third body is obtained as $0.56M\odot$, corresponding to the inclination value $i_3=20°$. Evolutionary status of the component stars is also studied. We present the position of the stars in an H–R diagram for solar compositions.  相似文献   

Spectroscopic study of the O-type runaway supergiant HD 195592     

M. De Becker  N. Linder  G. Rauw 《New Astronomy》2010,15(1):76-82

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Groundwater Chemistry of the Mornag Aquifer System in NE Tunisia     

Boutheina Farhat  Abdallah Ben Mammou  Lamia Kouzana  Ismail Chenini  Francesca Podda  Giovanni De Giudici 《Resource Geology》2010,60(4):377-388

The present paper investigates hydrochemical processes and water quality in the Mornag aquifer in NE Tunisia. Groundwater samples were collected during a field campaign, and were analysed for major and trace elements. The collected waters have a chemical facies rich in Ca²⁺, Na⁺ and Cl^-. Piper diagram shows a progressive increase in chloride ions along with increasing salinity. Saturation indexes calculated by using PHREEQC (USGS) show that the Mornag waters are slightly saturated with respect to carbonates (calcite and dolomite), while undersaturated with respect to gypsum, halite and other evaporitic minerals. The current composition of waters takes place via dissolution of halite and Ca-sulfates, where the increase in calcium is partially balanced by possible calcite precipitation. The relevant recorded pollutant is nitrate, which was likely dispersed from agricultural soils, while heavy metals were generally far below values of pollution thresholds, indicating no influence by mining activity.  相似文献   

Interaction between tectonic and erosion processes on the morphogenesis of an Alpine valley: geological and geophysical investigations in the lower Romanche valley (Belledonne massif, western Alps)     

Olivier Le Roux  Stéphane Schwartz  Jean François Gamond  Denis Jongmans  Pierre Tricart  Michel Sebrier 《International Journal of Earth Sciences》2010,99(2):427-441

In the Belledonne massif, the steep Paleozoic Belledonne Middle Fault (BMF) separates micaschists, displaying numerous landslides, from amphibolites. The massif is incised by the lower Romanche river valley. When crossing the BMF, the valley widens into a lozenge-shaped basin recently interpreted as an active pull-apart type structure associated with a major N110 striking Quaternary fault. Multidisciplinary investigations were carried out in the basin to check if this model has implications on the seismic and landslide hazard assessment. This study demonstrated the existence of a N80 sinistral strike slip Séchilienne Fault Zone (SFZ). This fault zone is suspected to offset the BMF by 375 m across the basin. Geophysical experiments revealed that the bedrock depth increases strongly in the basin, up to 350 m. Our study invalidates the active pull-apart origin of the basin and suggests it results from Quaternary glacial and fluvial erosion processes, magnified by the intersection of two inherited structures, the BMF and the SFZ.  相似文献   

Recent Trends Towards Oligotrophication of the Northern Adriatic: Evidence from Chlorophyll <Emphasis Type="Italic">a</Emphasis> Time Series     

Patricija Mozetič  Cosimo Solidoro  Gianpiero Cossarini  Giorgio Socal  Robert Precali  Janja Francé  Franco Bianchi  Cinzia De Vittor  Nenad Smodlaka  Serena Fonda Umani 《Estuaries and Coasts》2010,33(2):362-375

The results of the updated and quality-checked data base of field observations on chlorophyll a (Chl a) collected in the period 1970–2007 in the Northern Adriatic Sea are presented. From the last decade, SeaWiFS satellite information was also considered. Results demonstrate a global tendency towards Chl a reduction in the period of investigation, which is more marked in the eutrophic area under the influence of the Po River. In the rest of the basin, which presents meso- or oligotrophic characteristics, long-term changes are more difficult to detect. The long-term field dataset can be divided into two periods: the last decade characterized by the strong decrease observed in the whole northern Adriatic and the earlier period with no or slight increase. The recent substantial reduction of Chl a concentrations is confirmed all over the basin (−0.11 mg m⁻³ year⁻¹) from satellite-derived information. Results are consistent with recently evidenced decrease in concentrations of phosphate and ammonia and point to the existence of oligotrophication in the Northern Adriatic. Results indicate forcefully that the still common perception of the Adriatic Sea as a very eutrophic basin is no longer appropriate, at least for its northern part and in recent years.  相似文献   

Comparative Analysis of Phytoplankton Composition and Abundance over a Two-Decade Period at the Land–Ocean Boundary of a Tropical Mangrove Ecosystem     

Haimanti Biswas  Mitali Dey  Dipnarayan Ganguly  Tarun K. De  Sandip Ghosh  Tapan K. Jana 《Estuaries and Coasts》2010,33(2):384-394

Inter-annual variations of phytoplankton abundance and community organization were observed over a two-decade period along with the ancillary parameters at the land–ocean boundary associated with the Sundarban mangrove forest (21°32′ and 22°40′ N and 88°05′ and 89° E), along the NE Coast of the Bay of Bengal. The number of definable Bacillariophyceae species exceeded Dinophyceae taxa, and the total number of bloom-forming species declined from a maximum of ten in 2000 and a minimum of two in 2007. Blooms of the diatom Coscinodiscus radiatus were common in 2000 and 2007. Tide cycles and the onset of the monsoon season played important roles in diurnal and seasonal variability of phytoplankton. Phytoplankton biovolume showed seasonality, with the highest levels during post-monsoon periods and lowest levels during the monsoon period. Phytoplankton abundance was correlated to rainfall patterns, which may be altered by long-term changes in climate.  相似文献   

Alpine paleostress reconstruction and active faulting in Western Iberia     

Loreto Antón  Alfonso Muñoz-Martin  Gerardo De Vicente 《Central European Journal of Geosciences》2010,2(2):152-164

The study of intraplate tectonics is crucial for understanding the deformation within plates, far from active plate boundaries and associated stress transmission to the plate interiors. This paper examines the tectonic evolution of the Variscan basement at the western margin of the Cenozoic Duero basin. Located east of the Vilariça Fault System in NW Iberia, this intraplate zone is a relatively flat but elevated area with an intense NNE-SSW trending fault system and associated moderate seismicity. Although the area has played an important role in the Duero basin configuration, its Alpine to present-day tectonic evolution has not been well constrained. In order to characterize the successive paleostress fields, 1428 pairs of fault-striae were measured at 56 sites and two focal mechanisms were used. Stress inversion methods have been applied to analyze paleostress regimes. Results show the existence of three dominant maximum horizontal stress (Shmax) trends: N-S, NE-SW and E-W. Relative and absolute dating of the activated faults for each Shmax shows that the clearly predominant N-S paleostress field in the zone has been active since the Oligocene up to the present day; while a NE-SW stress field is found to have been active during the Cretaceous and an older E-W paleostress field was active in the earlier Alpine cycle (Late Triassic).  相似文献