Kinematics of the Gum nebula region

To investigate the kinematics of the neutral material around the Gum nebula, emission from hydroxyl at 1667 MHz was observed at many positions over the region. Fitting models of expanding shells to these data together with previously published molecular line data shows that the diffuse molecular clouds and cometary globules form a single expanding shell centred on G261−2.5. The mean angular radius is 10.5° and its maximum radius is 14°. The models show that the distance range to the expansion centre is from 200 pc to 500 pc.
The path of the runaway O-star ζ Puppis passed within <0.5° of the expansion centre of the neutral shell ∼1.5 Myr ago. The supernova of the erstwhile binary companion of ζ Puppis is the probable origin of the Gum nebula and the swept up expanding neutral shell. The 500-pc distance to the supernova is adopted as the distance to the expansion centre of the neutral shell. At this distance the energy required to produce the observed expansion could have been met with a single supernova. The radii of the front and back faces of the shell are 130 and 70 pc respectively. The front face is expanding faster than the back face, at 14 and 8.5 km s⁻¹ respectively.
The extent of the neutral shell matches the radio continuum and H α emission of the Gum nebula well. The photoionized gas in the nebula is probably primarily ionized by ζ Puppis, which is still within the neutral shell. No evidence was found for the IRAS -Vela shell as a separate expanding shell.     

The NOAA Goes-12 Solar X-Ray Imager (SXI) 1. Instrument, Operations, and Data

The Solar X-ray Imager (SXI) was launched 23 July 2001 on NOAAs GOES-12 satellite and completed post-launch testing 20 December 2001. Beginning 22 January 2003 it has provided nearly uninterrupted, full-disk, soft X-ray solar images, with a continuous frame rate significantly exceeding that for previous similar instruments. The SXI provides images with a 1 min cadence and a single-image (adjustable) dynamic range near 100. A set of metallic thin-film filters provides temperature discrimination in the 0.6 – 6.0 nm bandpass. The spatial resolution of approximately 10 arcsec FWHM is sampled with 5 arcsec pixels. Three instrument degradations have occurred since launch, two affecting entrance filters and one affecting the detector high-voltage system. This work presents the SXI instrument, its operations, and its data processing, including the impacts of the instrument degradations. A companion paper (Pizzo et al., this issue) presents SXI performance prior to an instrument degradation that occurred on 5 November 2003 and thus applies to more than 420000 soft X-ray images of the Sun.     

Mineralogy,geochemistry and petrogenesis of the V-Ti-bearing and chromiferous magnetite deposits hosted by Neoarchaean Channagiri Mafic-Ultramafic Complex,Western Dharwar Craton,India: Implications for emplacement in differentiated pulses

The Channagiri Mafic-Ultramafic Complex occupies lowermost section of the Neoarchaean Shimoga supracrustal group in the Western Dharwar Craton. It is a segmented body occupying the interdomal troughs of granitoids. The magnetite deposits occur in the northeastern portion; typically occupying the interface zone between gabbro and anorthositic. Mineralogically, the deposits are simple with abundant magnetite and ilmenite. Hogbomite is a consistent minor mineral. Magnetites are typically vanadiferous (0.7–1.25% V₂O₅). Ilmenite consistently analyses more MgO and MnO than coexisting magnetite. Chlorite, almost the only silicate present; lies in the range of ripidolite, corundophilite and sheridanite. The chromiferous suit occupying eastern side of Hanumalapur block (HPB) contains Fe-Cr-oxide analysing 37.8–11.9% Cr₂O₃ and 40.5–80% FeO ^t . In these too, chlorite, typically chromiferous (0.6–1.2% Cr₂O₃), is the most dominant silicate mineral. Geochemistry of V-Ti-magnetite is dominated by Fe, Ti and V with Al, Si, Mg and Mn contributing most of the remaining. Cr, Ni, Zn, Co, Cu, Ga and Sc dominate trace element geochemistry. The Cr-magnetite is high in Cr₂O₃ and PGE. Two separate cycles of mafic magmatism are distinguished in the CMUC. The first phase of first cycle, viz., melagabbro-gabbro, emplaced in the southeastern portion, is devoid of magnetite deposits. The second phase, an evolved ferrogabbroic magma emplaced in differentiated pulses, occupying northeastern portion of the complex, consists of melagabbro→gabbro-anorthosite→V-Ti magnetite→ferrogabbro sequence. Increase in oxygen fugacity facilitated deposition of V-Ti magnetite from ferrogabbroic magma pulse emplaced in late stages. The second cycle of chromiferous PGE mineralized suite comprises fine-grained ultramafite→alternation of pyroxinite-picrite→Crmagnetite sequence formed from fractionation of ferropicritic magma. HPB also includes >65m thick sill-like dioritic phase at the base of the ferriferous suit and a sinuous band of coarse-grained ultramafite enclosed within the chromiferous suit; both unrelated to the two mafic magmatic cycles.     

Détermination par la Méthode K/Ar de l'âge des Intrusions et des Minéralisations Associées dans le Porphyre Cuprifère de Quellaveco (Sud Ouest du Pérou)

Résumé Les âges K-Ar des roches granodioritiques du stock de Quellaveco, des rhyolites encaissantes et d'un dyke subvolcanique sont compris entre le Paléocène et le début de l'Eocène, avec un âge moyen de 53.7 M.A. Ces résultats concordent avec ceux obtenus pour bon nombre d'autres porphyres cuprifères du Sud-Ouest des Etats Unis et du Nord du Chili qui ont été formés au cours de l'orogenèse Laramienne. De plus, il n'y a quasiment pas de différence entre l'âge du substratum et celui de l'intrusif, ce qui semble indiquer que ces roches sont cogénétiques.

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Granodioritic rocks from the stock of Quellaveco, their surrounding rhyolites and a subvolcanic dyke give K-Ar ages between Paleocene and lower Eocene, with an mean age of 53.7 M.Y. These results agree with those of other porphyry-copper deposits in the South-Western USA, in Northern Chile, and, which have been generated during Laramian orogenesis. Furthermore, no significant age difference between the pluton and the basement, have been observed, is interpreted as indicative of a consanguineous origin for both rock types.

     

Biases of submerged bulk and freeze‐core samples

Freeze‐coring and bulk sampling are routine methods used to sample subsurface spawning gravel under shallow water. Both methods have limitations. Freeze‐coring is not believed to representatively sample coarse grain sizes and the sample volumes are relatively small. Conversely, when bulk sampling, even within an enclosure, some fine sediment is suspended and washed away from the sample. This paper assesses the biases in sampling performance between the two methods and determines whether the loss of fines that occurs when bulk sampling could be predicted and thus corrected for. At six riffles the spawning substrate was sampled under approximately 50 cm of water with a bulk sample and three adjacent freeze‐cores. For each riffle, data from the two samples were combined using the method of Fripp and Diplas (1993) and the resultant composite sample was compared with the original freeze‐core and bulk samples to assess the relative precision and biases of the two techniques. On average, the D₅₀ of the bulk samples was 4 mm larger and a one‐third loss of the <2 mm fraction occurred compared with the composite samples. In contrast, freeze‐core samples contain on average 32% more sediment >16 mm compared with composite samples. Based on six samples, taken from six riffles, the amount of sediment finer than 0·5 mm lost using our bulk sampling technique with an enclosure appears to be predictable and correctable. Copyright © 2005 John Wiley & Sons, Ltd.     

Trübeströme in Seen: Sauerstoffeintrag durch grundnah eingeschichtetes Flusswasser

Near-bottom current measurements in the main delta areas of the Walensee (Switzerland) and of Lake Constance yielded evidence that sporadic high influxes of clastic suspensions caused by flood stage discharges of tributaries generate turbidity underflows. Turbid suspensions plunge down the delta front as hyperpycnal inflows with speeds up to 130cm/s. These periodic intrusions of well oxygenated river water may influence the oxygen budget of the basal hypolimnion, thus possibly antagonizing eutrophication in marginal cases, supported by the adsorption of phosphate by suspended clay particles.      

Ages K-Ar de l'Événement Hydrothermal et des Intrusions Associées dans le District Minéralisé Miocène d'Aīn-Barbar (Est Constantinois,Algérie)

The Ain-Barbar district (Edough — Cap de Fer massif, northeastern Algeria) displays numerous microgranitic plugs and several rhyolitic dykes. These intrusives are cross-cut by polymetallic ore veins (Fe-Cu-Zn-Pb), and are hydrothermally altered in association with the mineralization. K-Ar measurements were carried out in order to determine the age of this event. Measurements gave conventional “ages” in the interval 15 to 16 M.Y., as well as two “isochron ages”, respectively at 15.1 and 16.0 M.Y. The 16.0 M.Y. age could be representative for the intrusion of microgranites, and one of the rhyolitic dykes. The 15.1 M.Y. one is clearly the age of the intrusion for two other rhyolitic dykes, and is coeval with the age of their hydrothermal alteration. The 15.1 M.Y. age is equally the one for the hydrothermal alteration affecting previous intrusive rocks. These results are compatible with previous data concerning magmatic events within the Edough — Cap de Fer massif. They show that hydrothermal process occurred very close after the end of intrusion in the Ain-Barbar district. They give also indirect evidence for the age of the last folding event in the area.