O papel das populações tradicionais na conservação da biodiversidade.

bitstream/CNPF-2009-09/42622/1/Doc153.pdf1 CD-ROM

Research Update on Extreme-Mass-Ratio Inspirals

The inspirals of stellar-mass mass compact objects into massive black holes in the centres of galaxies are one of the most important sources of gravitational radiation for space-based detectors like LISA or eLISA. These extreme-mass-ratio inspirals (EMRIs) will enable an ambitious research program with implications for astrophysics, cosmology, and fundamental physics. This article is a summary of the talks delivered at the plenary session on EMRIs at the 10th International LISA Symposium. It contains research updates on the following topics: astrophysics of EMRIs; EMRI science potential; and EMRI modeling.Comment: 17 pages, no figures. Proceedings of the LISA Symposium X, to be published at the Journal of Physic

The Challenges in Gravitational Wave Astronomy for Space-Based Detectors

The Gravitational Wave (GW) universe contains a wealth of sources which, with the proper treatment, will open up the universe as never before. By observing massive black hole binaries to high redshifts, we should begin to explore the formation process of seed black holes and track galactic evolution to the present day. Observations of extreme mass ratio inspirals will allow us to explore galactic centers in the local universe, as well as providing tests of General Relativity and constraining the value of Hubble's constant. The detection of compact binaries in our own galaxy may allow us to model stellar evolution in the Milky Way. Finally, the detection of cosmic (super)strings and a stochastic background would help us to constrain cosmological models. However, all of this depends on our ability to not only resolve sources and carry out parameter estimation, but also on our ability to define an optimal data analysis strategy. In this presentation, I will examine the challenges that lie ahead in GW astronomy for the ESA L3 Cosmic Vision mission, eLISA.Comment: 12 pages. Plenary presentation to appear in the Proceedings of the Sant Cugat Forum on Astrophysics, Sant Cugat, April 22-25, 201

The impact of realistic models of mass segregation on the event rate of extreme-mass ratio inspirals and cusp re-growth

One of the most interesting sources of gravitational waves (GWs) for LISA is the inspiral of compact objects on to a massive black hole (MBH), commonly referred to as an "extreme-mass ratio inspiral" (EMRI). The small object, typically a stellar black hole (bh), emits significant amounts of GW along each orbit in the detector bandwidth. The slowly, adiabatic inspiral of these sources will allow us to map space-time around MBHs in detail, as well as to test our current conception of gravitation in the strong regime. The event rate of this kind of source has been addressed many times in the literature and the numbers reported fluctuate by orders of magnitude. On the other hand, recent observations of the Galactic center revealed a dearth of giant stars inside the inner parsec relative to the numbers theoretically expected for a fully relaxed stellar cusp. The possibility of unrelaxed nuclei (or, equivalently, with no or only a very shallow cusp) adds substantial uncertainty to the estimates. Having this timely question in mind, we run a significant number of direct-summation $N-$body simulations with up to half a million particles to calibrate a much faster orbit-averaged Fokker-Planck code. We then investigate the regime of strong mass segregation (SMS) for models with two different stellar mass components. We show that, under quite generic initial conditions, the time required for the growth of a relaxed, mass segregated stellar cusp is shorter than a Hubble time for MBHs with $M_\bullet \lesssim 5 \times 10^6 M_\odot$ (i.e. nuclei in the range of LISA). SMS has a significant impact boosting the EMRI rates by a factor of $\sim 10$ for our fiducial models of Milky Way type galactic nuclei.Comment: Accepted by CQG, minor changes, a bit expande

The scientific potential of space-based gravitational wave detectors

The millihertz gravitational wave band can only be accessed with a space-based interferometer, but it is one of the richest in potential sources. Observations in this band have amazing scientific potential. The mergers between massive black holes with mass in the range 10 thousand to 10 million solar masses, which are expected to occur following the mergers of their host galaxies, produce strong millihertz gravitational radiation. Observations of these systems will trace the hierarchical assembly of structure in the Universe in a mass range that is very difficult to probe electromagnetically. Stellar mass compact objects falling into such black holes in the centres of galaxies generate detectable gravitational radiation for several years prior to the final plunge and merger with the central black hole. Measurements of these systems offer an unprecedented opportunity to probe the predictions of general relativity in the strong-field and dynamical regime. Millihertz gravitational waves are also generated by millions of ultra-compact binaries in the Milky Way, providing a new way to probe galactic stellar populations. ESA has recognised this great scientific potential by selecting The Gravitational Universe as its theme for the L3 large satellite mission, scheduled for launch in ~2034. In this article we will review the likely sources for millihertz gravitational wave detectors and describe the wide applications that observations of these sources could have for astrophysics, cosmology and fundamental physics.Comment: 18 pages, 2 figures, contribution to Gravitational Wave Astrophysics, the proceedings of the 2014 Sant Cugat Forum on Astrophysics; v2 includes one additional referenc

Effective source approach to self-force calculations

Numerical evaluation of the self-force on a point particle is made difficult by the use of delta functions as sources. Recent methods for self-force calculations avoid delta functions altogether, using instead a finite and extended "effective source" for a point particle. We provide a review of the general principles underlying this strategy, using the specific example of a scalar point charge moving in a black hole spacetime. We also report on two new developments: (i) the construction and evaluation of an effective source for a scalar charge moving along a generic orbit of an arbitrary spacetime, and (ii) the successful implementation of hyperboloidal slicing that significantly improves on previous treatments of boundary conditions used for effective-source-based self-force calculations. Finally, we identify some of the key issues related to the effective source approach that will need to be addressed by future work.Comment: Invited review for NRDA/Capra 2010 (Theory Meets Data Analysis at Comparable and Extreme Mass Ratios), Perimeter Institute, June 2010, CQG special issue - 22 pages, 8 figure

Influence of rainfall on the discharge, nutrient concentrations and loads of a stream of the "Pampa Ondulada" (Buenos Aires, Argentina)

The basin area of the Durazno Stream covers approx. 360 km2 of a plain with a gentle slope, mainly devoted to cattle farming and agriculture. This study examines the variability of chemical composition of surface water of the stream in relation to stream discharge, estimated from a hydrological deterministic model from rainfall data. Fifteen samplings were carried out, four in high flow condition and the rest in baseline flow. In each sampling, the main physico-chemical variables were determined. Since discharge data from this stream were not available, it was estimated in situ through an instantaneous unitary hydrograph model. Both estimations of stream discharge were similar. The main forms of dissolved inorganic nitrogen were ammonium and nitrate. The four significant components of PCA that explained 84.4 % of total variance were: mineral component, particulate matter content, ammonium and dissolved phosphorus levels, and nitrates' level. The decreased concentrations of major ions and conductivity during high flow condition suggest solutes' dilution by the massive inflow of water originated by rainfalls. The highest concentrations and loads of suspended solids (SS) (86 mg/l and 22638 kg/day) and particulate organic carbon (POC) (3.1 mg/l and 832 kg/day) were observed in the sample obtained during the rising limb of the hydrograph following a drought period, suggesting that basin erosive processes are more important during the first hours of the storm. Three of the samplings that were carried out in high flow conditions showed low mineral and nutrient content that revealed better water quality. In contrast, the sampling with the greatest total runoff (14.1 mm) showed high concentrations of ammonium (1205 μg/l) and dissolved phosphorus (561 μg/l), suggesting that a long stagnant period on soils with low permeability, could favor reduction processes of nitrate to ammonium and mobilization of dissolved phosphorus to overlying water. The nutrients' loads increased in high flow conditions most likely due to runoff from the riverbank soils. The rise of nutrients, SS, POC and total organic carbon (TOC), loads in the same or in higher proportion than the stream discharge, alerts on the risk of contamination of surface water in an agricultural basin.La cuenca del Arroyo Durazno abarca aproximadamente 360 km2 de una llanura con suave pendiente, dedicada principalmente a ganadería y agricultura. Este estudio examina la variabilidad en la composición química del agua superficial del arroyo en relación con el caudal estimado a través de un modelo hidrológico determinístico a partir de los datos de lluvia. Se realizaron quince muestreos: cuatro en condiciones de alto caudal, los restantes en caudal base. En cada muestreo se determinaron las principales variables fisico-químicas. Dado que no existen datos publicados de caudal de este arroyo, se lo estimó in situ, y a partir del modelo de hidrograma unitario. Ambas estimaciones resultaron similares. Las principales formas de nitrógeno inorgánico disuelto fueron amonio y nitrato. Los primeros 4 factores extraídos del PCA que explicaron 84.4 % de la varianza total fueron: componente mineral, contenido de material particulado, niveles de amonio y fósforo disuelto y nivel de nitratos. El decrecimiento de iones mayoritarios y conductividad durante las condiciones de alto caudal sugiere su dilución por la entrada masiva de agua por lluvias. Las mayores concentraciones y cargas de sólidos suspendidos (SS) (86 mg/l y 22638 kg/día) y carbono orgánico particulado (COP) (3.1 mg/l y 832 kg/día) se hallaron en el muestreo realizado durante la rama ascendente del hidrograma posterior a un período de sequía, sugiriendo que los procesos erosivos de la cuenca son más importantes en las primeras horas de la tormenta. Tres de los muestreos realizados en condiciones de alto caudal presentaron bajo contenido mineral y de nutrientes, indicando mejor calidad de agua. En cambio en el muestreo de mayor lámina de escorrentía acumulada (14.1 mm) las concentraciones de amonio (1205μg/l) y fósforo disuelto (561μg/l) fueron elevadas, sugiriendo que un prolongado periodo de estancamiento en un suelo de baja permeabilidad favorecería los procesos de reducción de nitratos a amonio y la movilización de fósforo disuelto al agua de inundación. Las cargas de nutrientes aumentaron en condiciones de alto caudal probablemente debido al aporte por escorrentía de suelos ribereños. El ascenso en las cargas de nutrientes, SS, COP y carbono orgánico total en igual o mayor magnitud que el caudal alerta sobre el riesgo de contaminación de las aguas superficiales en una cuenca agrícola