The Stellar Halo in the Large Magellanic Cloud: Mass, Luminosity, and Microlensing Predictions

Recently obtained kinematic data has shown that the Large Magellanic Cloud (LMC) possesses an old stellar halo. In order to further characterize the properties of this halo, parametric King models are fit to the surface density of RR Lyrae stars. Using data from both the MACHO and OGLE II microlensing surveys, the model fits yield the center of their distribution at RA = 05:21.1+-0.8, Dec = -69:45+-6 (J2000) and a core radius of 1.42+-0.12 kpc. As a check the halo model is compared with RR Lyrae star counts in fields near the LMC's periphery previously surveyed with photographic plates. These data, however, require a cautious interpretation. Several topics regarding the LMC stellar halo are discussed. First, the properties of the halo imply a global mass-to-light ratio of M/L_V = 5.3+-2.1 and a total mass of 1.6+-0.6 10^10 M_sun for the LMC in good agreement with estimates based on the rotation curve. Second, although the LMC's disk and halo are kinematically distinct, the shape of the surface density profile of the halo is remarkably similar to that of the young disk. For example, the best-fit exponential scale length for the RR Lyrae stars is 1.47+-0.08 kpc, which compares to 1.46 kpc for the LMC's blue light. In the Galaxy, the halo and disk do not resemble each other like this. Finally, a local maximum in the LMC's microlensing optical depth due to halo-on-disk stellar self-lensing is predicted. For the parameters of the stellar halo obtained, this maximum is located near MACHO events LMC-4 and LMC-23, and is large enough to possibly account for these two events, but not for all of the observed microlensing.Comment: 11 pages, 1 figure, accepted to ApJ Letter

Low frequency measurements of synchrotron absorbing HII regions and modeling of observed synchrotron emissivity

Cosmic rays (CRs) and magnetic fields are dynamically important components in the Galaxy, and their energy densities are comparable to that of the turbulent interstellar gas. The interaction of CRs and Galactic magnetic fields produces synchrotron radiation clearly visible in the radio regime. Detailed measurements of synchrotron radiation averaged over the line-of-sight (LOS), so-called synchrotron emissivities, can be used as a tracer of the CR density and Galactic magnetic field (GMF) strength. Our aim is to model the synchrotron emissivity in the Milky Way using a 3 dimensional dataset instead of LOS-integrated intensity maps on the sky. Using absorbed HII regions we can measure the synchrotron emissivity over a part of the LOS through the Galaxy, changing from a 2 dimensional to a 3 dimensional view. Performing these measurements on a large scale is one of the new applications of the window opened by current low frequency arrays. Using various simple axisymmetric emissivity models and a number of GMF-based emissivity models we can simulate the synchrotron emissivities and compare them to the observed values in the catalog. We present a catalog of low-frequency absorption measurements of HII regions, their distances and electron temperatures, compiled from literature. These data show that the axisymmetric emissivity models are not complex enough, but the GMF-based emissivity models deliver a reasonable fit. These models suggest that the fit can be improved by either an enhanced synchrotron emissivity in the outer reaches of the Milky Way, or an emissivity drop near the Galactic center. State-of-the-art GMF models plus a constant CR density model cannot explain low-frequency absorption measurements, but the fits improved with slight (ad-hoc) adaptations. It is clear that more detailed models are needed, but the current results are very promising.Comment: 14 pages, 9 figures, accepted for publication in A&

A sedimentação fluvial cenozóica na região do Entre-Douro-e-Minho (NW de Portugal)

Na região foram identificados cinco ciclos de glipto/sedimentogénese fluvial cenozóicos, de importância regional, decorridos no Pliocénico superior (Placenciano) e Quaternário. A cada um destes ciclos de glipto/sedimentogénese correspondeu escavação de novo talvegue no substrato seguida de colmatação do paleovale. Esta interpretação baseia-se num conjunto de informações que têm sido obtidas através do estudo dos sedimentos, das paleoalterações associadas e das observações de campo acompanhando as frentes de exploração dos depósitos. Os testemunhos destas etapas de sedimentação fossilizam vales fluviais largos, com orientação transversal à fachada atlântica e ocorrem nas bacias dos rios Minho, Lima e Cávado e ainda nos depósitos de Alvarães. Os sedimentos cenozóicos contactam directamente, por inconformidade, as rochas do substrato. As litofácies depositadas variam desde conglomerados com matriz areno-lutítica a arenitos lutíticos e lutitos. O tipo e organização das litofácies são típicas de sistemas fluviais do tipo entrançado. São do tipo entrançado em areias na maioria das bacias e predominantemente do tipo entrançado em cascalho na bacia do rio Minho. Os canais fluviais estavam confinados aos respectivos vales e ocupavam-nos durante as inundações. O primeiro ciclo está representado pela Formação de Alvarães, Formação de Barrocas (bacia do rio Minho) e unidade inferior de Prado (bacia do rio Cávado). Estas formações apresentam características sedimentares e conteúdo paleontológico climaticamente equivalentes, indicadores de clima quente e húmido. Esta etapa de sedimentação, mais antiga, é atribuída ao intervalo entre o Placenciano e Plistocénico inferior. O segundo ciclo de gliptogénese cenozóica deve ter decorrido antes do Plistocénico médio, durante o arrefecimento que atingiu a Europa. Esta interpretação cronológica baseia-se no conteúdo florístico descrito na jazida de Corgos (bacia do rio Minho). A composição sedimentar nos três primeiros ciclos é semelhante, siliciosa e caulinítica, afectada por alterações diagenéticas que expressam condições favoráveis à meteorização química. A sedimentação do quarto ciclo cenozóico difere dos anteriores. O enchimento contém clastos de rochas e minerais quimicamente alteráveis e/ou com menor grau de alteração, frequentemente caulinite de baixa cristalinidade e interestratificados entre outros. O último ciclo cenozóico, o quinto, tem início com o arrefecimento climático do último período glaciário, do qual existem vestígios de glaciações nas serras da Peneda e Gerês. Provocou o ravinamento de um novo talvegue, esvaziando os enchimentos anteriores, do qual resultaram os actuais vales dos rios do Entre-Douro-e- Minho. As aluviões que preenchem estes vales indicam a manutenção de condições climáticas menos propícias à meteorização química, tendo sido depositadas no pós-glaciar

Análise dimensional de sedimentos fluviais : formação de Alvarães e depósitos de terraços da bacia do rio Lima (NW de Portugal)

Trata-se dum estudo das distribuições dimensionais de sedimentos fluviais Plio-Quaternários do NW de Portugal pertencendo: à Formação de Alvarâes (enchimento da «bacia de Alvarães»), aos depósitos dos terraços do rio Lima e depósitos dos terraços dos afluentes deste rio. As distribuições dimensionais foram obtidas por: crivação dos sedimentos>62 µm num agitador mecânico de tipo RO-TAP, segundo uma escala dimensional com intervalos iguais a √2, e pipetagem das suspensões62 µm on a RO-TAP equipment, following a √2 grade scale, and pipetting the particles<62 µm with Andreasen pipette. The interpretation is based on the statistical parameters, graphic mean (MzØ), inclusive graphic standard deviation (σΙ), inclusive graphic skewness (SkI), graphic kurtosis (KG), computed following the formulas of FOLK-WARD (1957), and on the CM diagrams (PASSEGA 1957)

Discontinuous operation promotes efficient continuous anaerobic treatment of effluents with high lipid content

A mixture of skim milk and sodium oleate was fed to an upflow sludge bed reactor operated in cycles. Each cycle had a feeding phase under continuous operation and a reaction phase in batch. Five cycles were performed with organic loading rates applied during feeding phases varying between 4.4 and 8 kg COD.mˉ³.dˉ¹ and a constant hydraulic retention time of 1.6 days. In the first two cycles, 70% of the methane-COD was produced in the reaction batch phase, whereas from the third to the fifth cycles, biogas production in the reaction phase was less than 3% of total production. Overall methane yields increased steadily, from 0.67 to 0.91 kg COD-CH4.kg COD removedˉ¹. LCFA accumulated into the sludge in the first two cycles, being palmitate and stearate the dominant intermediates quantified. In the subsequent cycles no LCFA were detected in the solid or liquid phases. The specific methanogenic activity in the presence of acetate and H2/CO2 increased significantly along the operation, particularly between time zero and the end of the third cycle. These results show that a discontinuous operation promoted the development of an active anaerobic community able to efficiently convert a continuous organic load of 8.2 kg COD.mˉ³.dˉ¹, from which 50% was oleate.European Commission - LIFE03 ENV/P/000501.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/CTA/46328/2002

Microbial syngas conversion by mesophilic and thermophilic anaerobic mixed-cultures

Synthesis gas (or syngas) can be produced from the gasification of a variety of recalcitrant or biodegradable wastes. Syngas is a mixture composed of mainly H2, CO and CO2 that can be used in a biological process for the production of fuels or usable chemicals. The main goal of this work was to study the physiology and microbial composition of anaerobic cultures able to utilize syngas. The results indicated that the thermophilic sludge inoculum presents a promising carboxydotrophic potential comparing to the mesophilic sludge inoculum. Monitoring of microbial structure of thermophilic enriched cultures by using PCR-DGGE and cloning techniques showed that bacterial community profiles clustered in three different groups