HDE 245059: A Weak-Lined T Tauri Binary Revealed by Chandra and Keck

We present the Chandra High Energy Transmission Grating Spectrometer (HETGS) and Keck observations of HDE 245059, a young weak-lined T Tauri star (WTTS), member of the pre-main sequence group in the Lambda Orionis Cluster. Our high spatial resolution, near-infrared observations with Keck reveal that HDE 245059 a binary separated by 0.87". Based on this new information we have obtained an estimate of the masses of the binary components; 3M_{sun} and 2.5M_{sun} for the north and south components, respectively. We have estimated the age of the system to be ~2-3 Myr. We detect both components of the binary in the zeroth order Chandra image and in the grating spectra. Our fits to the spectrum of the binary have shown that the emission is dominated by a plasma between 8 and 15 MK, a soft component at 4 MK and a hard component at 50 MK are also detected. The value of the hydrogen column density was low, 8 x 10^{19} cm^{-2}, likely due to the clearing of the inner region of the Lambda Orionis cloud. The abundance pattern shows an inverse First Ionization Potential (FIP) effect for all elements from O to Fe, the only exception being Ca. A 3-T model was fitted to the individual zeroth order spectra using the abundances derived for the binary. We have also obtained several lines fluxes from the grating spectra. The fits to the triplets show no evidence of high densities. We conclude that the X-ray properties of the weak-lined T Tau binary HDE 245059 are similar to those generally observed in other weak-lined T Tau stars. Although its accretion history may have been affected by the clearing of the interstellar material around Lambda Ori, its coronal properties appears not to have been strongly modified.Comment: 12 pages, 10 figures Accepted for publication in Ap

Omnivoria e repartição de recursos em águas pobres em nutrientes da Bacia do Rio Negro

Amazonian biodiversity is notorious, this is also valid for the fauna of the mineral-deficient waters of the Rio Negro System. Some 25 years of research on the benthic fauna of Central Amazonian streams resulted in species-rich foodwebs with a high degree of omnivory within dense animal communities. To exemplify the taxonomic range of omnivorous consumers, the detailed resource spectra of 18 consumer species, including Protozoa (2 species), Platyhelminthes (1 species), insects (2 species), fish (6 species) and shrimps (Decapoda, 7 species), associated primarily with the benthic habitats of Rio Negro tributaries, are presented. Special features of omnivory are characterized, and the importance of litter-decomposing fungi as essential energy input into the foodwebs is documented. It is shown that general omnivory -diverse omnivore consumers sharing most of the resource types- is a prevalent feature. The relevance of this general omnivory for the maintenance of biodiversity is discussed.A biodiversidade do Amazonas é notório e isto também é válido para as águas pobres em nutrientes da bacia do Rio Negro. Uma pesquisa de 25 anos da fauna béntica de igarapés da Amazônia Central resultou em redes alimentares caraterizadas por alta diversidade de espécies, por intensa omnivoria e por alta densidade populacional. Para demonstrar a generalidade taxonômica de omnivoria no bentos dos igarapés, são apresentados as listas de presas / recursos de 18 espécies de consumidores, sendo Protozoa (2 epécies), Platyhelminthes (1 espécie), insetos (2 espécies), peixes (6 espécies) e camarões (Decapoda, 7 espécies). Diferentes categorias de omnivoria são apresentados, e a importância de fungos decompositores da liteira submersa como input básico de energia nas redes alimentares é demonstrada. É prevalente a omnivoria geral, sendo que as diferentes espécies omnívoros estão utilizando os mesmos recursos. Considera- se a relevância desta omnivoria geral para a manutenção da biodiversidade