The response of the Sao Paulo Continental Shelf, Brazil, to synoptic winds

The response of the Sao Paulo Continental Shelf (SPCS) to synoptic wind forcing has been analyzed. Two different methods are used for this purpose, one based on hydrographic data, bottom topography, and geographical characteristics, and a second on analyzing currentmeter data directly and using empirical orthogonal functions. Both methods show similar results for an essentially barotropic shelf. The SPCS response in the subinertial frequency band appears to be trapped on the continental shelf. Numerical experiments have also been carried out showing results that qualitatively agree with the observations, including the velocity component parallel to the coastline. Supported by CAPES.     

New 1982 — 1990 photometry of λ Andromedae and its 11-year cycle

We present photoelectric photometry of λ And never before published, obtained between February 1982 and December 1990 at 29 different observatories. Then we combine it with all other photometry available to us (previously published, contained in the I.A.U. Commission 27 Archives, and obtained with the Vanderbilt 16-inch automatic telescope but not yet published), to yield a 14.8-year data base. Analysis reveals a long-term cycle in mean brightness, with a full range of 0^m.15 and a period of 11.4 ± 0.4 years. Because most of our new photometry was concentrated in the 1983-84 observing season, we analyze that one well-defined light curve with a two-spot model. Spot A keeps a 0^m.04 amplitude throughout four rotation cycles whereas the amplitude of spot B diminishes from 0^m.09 down almost to 0^m.03. The spot rotation periods were 55^d.9 ± 0^d.6 and 520^d.8 ± 1^d.0, respectively.     

Carbon,hydrogen and nitrogen isotopes in solvent-extractable organic matter from carbonaceous chondrites

Solvent extractions were done on the carbonaceous chondrites Murray, Murchison, Orgueil and Renazzo, using CCl₄ and CH₃OH. Between 2 and 10% of the total carbon in these meteorites is extractable by ordinary techniques, most of it in CH₃OH. After demineralization with HF, perhaps as much as 30% of the total carbon in Murray may be extractable with CH₃OH. The extracts from Renazzo have isotopic ratios which suggest that they are mainly terrestrial organic matter, with lesser contributions from indigenous organics. The CH₃OH-soluble organic matter from Murchison and both untreated and HF-treated Murray has δ¹³C values of about +5 to + 10%. and δ¹⁵N values of about +90 to +100%., both of which are significantly higher than the bulk meteorite values. The Orgueil CH₃OH-extract also has a δ¹⁵N value well above the value in residual organic matter. Values for δD of +300 to +500%. are found for the CH₃OH-soluble organic matter. The combined data for C, H and N isotopes makes it highly unlikely that the CH₃OH-soluble components are derivable from, or simply related to, the insoluble organic polymer found in the same meteorites. A relationship is suggested between the event that formed hydrous minerals in CI1 and CM2 meteorites and the introduction of water-soluble (methanol-soluble) organic compounds. Organic matter soluble in CCl₄ has essentially no nitrogen, and δ³C and δD values are lower than for CH₃OH-soluble phases. Either there are large isotopic fractionations for carbon and hydrogen between different soluble organic phases, or the less polar components are partially of terrestrial origin.     

Automated classification of interplanetary dust particles: Johnson Space Center Cosmic Dust Catalog Volume 15

Abstract– The “Cosmic Dust Catalog,” published by the NASA Johnson Space Center (JSC), describes thousands of interplanetary dust particles subjected to preliminary analysis and with labels indicating their origin. However, only about 80% of the particles are assigned unambiguous labels, the labels of the remaining 20% being uncertain. In addition, the Stardust mission results opened up the possibility that some particles classified as terrestrial contaminants are instead of cosmic (cometary) origin. In this article, we present a methodology for automatic classification of particles on the basis of similarity of their X‐ray energy dispersive spectrometry spectra. The method is applied to the 467 particles constituting Volume 15 of the catalog. A first part of the analysis is to digitize the spectra from their scanned images. The digitized spectra are subjected to agglomerative clustering, which reveals 16 distinct clusters or compositional types of particles. The Sammon’s map is used to visualize the relationship between different clusters; 6 clusters corresponding to cosmic particles and 10 clusters corresponding to terrestrial contaminants are clearly separated on the map indicating overall differences between diverse spectra of cosmic and terrestrial particles. By reconciling labels with the clustering structures, we propose the relabeling of 155 particles including the relabeling of 31 terrestrial contaminants into cosmic particles. The proposed relabeling needs to be confirmed by in‐depth study of these particles. The paucity of particles with firmly determined cometary or asteroidal origin makes it difficult to establish whether the spectra based autoclassification can be utilized to discriminate between cometary and asteroidal particles. The methodology presented here can be used to classify all particles published in the catalog, as well as different samples for which comparable spectra are available.