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

Biological fermentation of syngas

Este resumo faz parte de: Book of abstracts of the Meeting of the Institute for Biotechnology and Bioengineering, 2, Braga, Portugal, 2010. A versão completa do livro de atas está disponível em: http://hdl.handle.net/1822/1096

LCFA accumulation and biodegradation during anaerobic discontinuous treatment of an oleate-rich wastewater

The dynamics of medium and long-chain fatty acids (LCFA) accumulation and biodegradation was studied during the anaerobic treatment of an oleate-rich wastewater. This treatment was made in an upflow sludge bed reactor operated in cycles during 213 days. Five cycles were performed, each one with a feeding phase in continuous and a reaction phase in batch. Saturated and unsaturated fatty acids from C6 to C18 were extracted and analyzed by gas chromatography on biomass samples collected at different key moments of the reactor operation. These biomass samples were also incubated in batch assays and methane production from the accumulated substrate was followed. LCFA accumulated onto the sludge during the first two cycles, reaching a maximum value of 1.7 gCOD-LCFA.gVSˉ¹. Palmitate and stearate were the dominant intermediates quantified, approximately in equal quantities. On the subsequent cycles only residual amounts of LCFA were detected. Methane production on batch assays was higher than expected from the LCFA accumulated, suggesting that other substrates could also be entrapped with the sludge. The results show that during the first two cycles a specialized microbial consortium developed, able to treat oleate-rich wastewaters.European Commission - LIFE03 ENV/P/000501.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/CTA/46328/2002

Fed-batch anaerobic degradation of long chain fatty acids

Efficient mineralization of effluents with high lipid content is possible in anaerobic digesters when a sequential operation mode is applied, favoring the adsorption of LCFA onto the sludge and then allowing the adsorbed substrate to be biodegraded1-3. The study of adsorption along time can help to optimize the process. Five batch assays were conducted in 160mL vials inoculated with flocculent biomass and fed with sodium oleate (1g CQO/gVSS). Feeding was applied during 10min (0.8ml/min), after which (t=0) a vial was immediately sacrificed and analyzed for soluble COD, VSS and biomass-associated LCFA. After 0.5, 1, 24 and 1000 hours of incubation at 37±1°C, 150rpm, one vial was sacrificed and analyzed for the parameters stated before. Two additional vials prepared and fed in a similar way and two blank controls (without substrate) were incubated in the same conditions to follow cumulative methane production. At the end of the feeding period, soluble COD removal efficiency was 73%, corresponding exclusively to LCFA accumulation onto the sludge. During the first 24 hours, methane or VFA production were negligible probably due to residual substrate degradation. Palmitic acid accounted for 46 to 54% of the biomass-associated LCFA and oleic acid for 31 to 40%. After 1000 hours of incubation soluble COD removal was 86% and palmitic acid accounted for 100% of the biomass-associated LCFA (45mg COD-LCFA/g VSS)