The infrared [WC] stars

A number of late [WC] stars have unique infrared properties, not foundamong the non-[WC] planetary nebulae, and together define a class of IR-[WC]stars. They have unusual IRAS colours, resembling stars in theearliest post-AGB evolution and possibly related to PAH formation.Most or all show a double chemistry, with both a neutral (molecular)oxygen-rich and an inner carbon-rich region. Their dense nebulae indicaterecent evolution from the AGB, suggesting a fatal-thermal-pulse (FTP)scenario. Although both the colours and the stellar characteristicspredict fast evolution, it is shown that this phase must last for10⁴ yr. The morphologies of the nebulae are discussed. Forone object in Sgr, the progenitor mass (1.3 M_⊙) is known.The stellar temperatures of the IR-[WC] stars appear much higher inlow metallicity systems (LMC, Sgr). This may be indicative of anextended `pseudo' photosphere. It is proposed that re-accretion ofejected gas may slow down the post-AGB evolution and so extend the lifetime of the IR-[WC] stars.     

Phytoplankton blooms and nitrogen productivity in San Francisco Bay

San Francisco Bay has been considered an HNLC or HNLG (high nutrient low chlorophyll or low growth) region with nonlimiting concentrations of inorganic nutrients yet low standing stocks of phytoplankton. Most of the studies leading to this conclusion come from the South Bay and little is known about nutrient processes and phytoplankton productivity in the northern and central parts of the estuary. Data collected over 3 yr (1999–2003) in Suisun, San Pablo, and Central Bays describe the availability of dissolved inorganic nitrogen (DIN), silicate, and phosphate and the seasonal variability in phytoplankton abundance. Rate measurements of fractionated nitrogen productivity provide the relative contributions of different forms of DIN (ammonium and nitrate) and different sized phytoplankton to the development of seasonal phytoplankton blooms. Regional differences in bloom dynamics are observed with Suisun Bay, the least saline, highest nutrient, most turbid region having less phytoplankton biomass and productivity than San Pablo and Central Bays, except in the abnormally wet spring of 2000. Spring blooms in San Francisco Bay are driven primarily by high rates of nitrate uptake by larger phytoplankton cells following a period of increased ammonium uptake that depletes the ambient ammonium. The smaller occasional fall blooms are apparently flueled mostly by ammonium uptake by small sized phytoplankton. The data suggest that the HNLC condition in the northern and central parts of San Francisco Bay is due primarily to light availability modulated by the interaction between ammonium and nitrate, and the relative amounts of the two forms of the DIN pool available to the phytoplankton.     

Contribution de la gravimétrie à l'étude de la structure du bassin de Tadla (Maroc) : Implications hydrogéologiques

This study is based on the analysis and the interpretation of the gravity data of the Tadla basin. Its purpose is to increase the knowledge of this basin structure. A residual anomaly map was first calculated from the Bouguer anomaly data witch are strongly affected by a regional gradient. The computed map provides information on the ground density variation but it does not bring enough of new elements. Data filtering allows us to emphasize the structures affecting the basin. We chose the horizontal gradient coupled to the upward continuation techniques that permit to highlight news structures and to give information on their dip. The elaborated structural map of the study area constitutes a useful document for rationalizing the future groundwater exploration in the Tadla basin. To cite this article: A. Najine et al., C. R. Geoscience 338 (2006).     

A statistical model for foraminiferal paleobathymetry, with application to the middle Miocene of the Hokuroku district, Japan

A paleobathymetric Bayes estimator, based on a uniform prior distribution of foraminiferal species over the depth range from 0 to 5000 m, is developed and calibrated from the occurrence of 35 species of foraminifera from present day sites on the Pacific and Indian Ocean seafloors. The species are grouped into 12 clusters in order to more nearly satisfy the independence assumptions of the model. Objective depth-independent criteria are developed for ruling certain samples inadmissible for estimation. The accuracy of the estimator is assessed by comparing estimated and measured depths for the admissible calibration samples, yielding a mean absolute error of estimation of between 300 and 400 m. The depth estimator is applied to foraminifera-bearing Miocene samples from the Hokuroku district of Japan, where paleobathymetric depths of between 3000 and 4000 m are indicated at the time of massive sulfide ore formation.     

The volume and surface area of a uniformly rotating polytrope

This paper develops algebraic expressions for the volume and surface area of a uniformly rotating polytrope. The expressions depend on an analytic theory for boundary shape developed in previous papers. A comparison with the calculations of James indicates the present theory improves on the original Chandrasekhar theory by a factor 10 or more.     

Surface Integral Formulae for Geomagnetic Studies

Surface integral formulae are derived expressing any one of certain field quantities, namely current functions, magnetic potentials and normal components of magnetic fields, in terms of any one other, for current systems flowing in concentric spherical surfaces. In all, 36 such formulae are obtained, which should prove useful in many geomagnetic studies, especially in geomagnetic induction problems.     

A balloon-borne observation of the X-ray source Cygnus XR-1

An observation of the variable X-ray source Cygnus XR-1 was made with a balloon-borne proportional counter in the energy region 22–70 keV. The resultant spectrum indicates that the source was in a state of maximum flux during the time period 1915–2005 UT, 15 January, 1968. This paper presents results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. NAS7-100, sponsored by the National Aeronautics and Space Administration.     

Rotational distortion of polytropes by analytic approximation

This paper modifies the first-order perturbation theory of Chandrasekhar, for rotational distortion of polytropes. Comparison with numerical integrations by other authors demonstrates that the present analytic theory is as accurate as other published first-order theories. The present theory is in a form permitting rapid calculation of boundary shapes as a function of the rotation parameter,v, and the polytrope index,n. Results are presented for a critically rotating polytrope, for the casen=3.