August 10, 2010
Auditorio de la Facultad de Ciencias
Dr. Tobias Schmidt
Astrophysics Department Jena University, Germany
"(Sub-)stellar companions in the star forming regions of Chamaeleon "
We performed a direct imaging search for stellar and sub-stellar companions among 51 members of the ~ 2 Myr old Cha I region at approximately 165 pc distance as well as other slightly older parts of the Chamaeleon star forming regions using the Adaptive Optics instrument NACO at the Very Large Telescope (VLT) of the European Southern Observatory (ESO) in Chile. Here we present the results of this survey spanning in total 10 nights of imaging at the VLT, being expanded by follow-up spectrscopy of the most interesting objects using the AO-assisted integral field spectrograph SINFONI, as well mounted on Unit Telescope 4 (UT4) of ESO's VLT. In addition to 15 stellar companions that could be confirmed as members of double or multiple systems by common proper motion, partially showing first signs of orbital motion, a few new M stars could be found as companions of single up to a triple star, composing the first quadruple system within Cha I. Finally two sub-stellar companions could be identified, one of them, being close to the deuterium burning mass limit often used to distinguish between brown dwarfs and planetary mass objects, next to the classical T Tauri star CT Cha, very recently found to harbour a disk by 3 mm observations using the Australian Telecope Compact Array (ATCA).

August 10, 2010
Auditorio de la Facultad de Ciencias
Dr. Ingeniero Ricardo Marotti
Grupo de Física del Estado Sólido, Instituto de Física, Facultad de Ingeniería, Universidad de la República. Centro Interdisciplinario de Nanotecnología, Química y Física de Materiales, Universidad de la República. Montevideo, URUGUAY 
"Propiedades Ópticas de Nanomateriales "  
Los Nanomateriales, o materiales nanoestructurados, son materiales cuya estructura o composición cambia en longitudes del orden de entre 1 a 100 nm, en al menos una dimensión. Las propiedades físicas macroscópicas de algunos nanomateriales pueden cambiar drásticamente respecto a los materiales homogéneos de “grandes” dimensiones (micrométricos) correspondientes. Se ejemplificarán estos cambios estudiando las propiedades ópticas de semiconductores y metales nanoestructurados. En el caso de los semiconductores estas propiedades están gobernadas principalmente por confinamiento cuántico de portadores moviéndose en su interior. Un caso especialmente importante en que se observan estos cambios es el ZnO (óxido de zinc). Se trata de un óxido semiconductor transparente con muchas y diversas potenciales aplicaciones que ha despertado gran interés en la literatura científica en los últimos años. En el caso de los metales la posibilidad de preparación de estructuras metalodieléctricas a través del uso de moldes nanoporosos permite un camino para estudiar resonancias de plasmones superficiales, así como la posibilidad de preparar cristales fotónicos. Otros materiales en que la interferencia óptica gobierna sus propiedades pueden ser usados como superficies selectivas en colectores de conversión de energía solar en térmica.

July 15, 2010
Auditorio de la Facultad de Ciencias
Dr. Todor Popov
Bulgarian Academy of Sciences, Sofia, Bulgaria 
"Creation-Annihilation Algebras and Young Tableau "
We start by recalling the bosonic (fermionic) canonical (anti)commutation relations of creation-annihilation operators. Then we consider the field theoretical formalism introduced by H.S. Green as a generalization of the Bose-Fermi alternative. In the so called Green parastatistics the exchange symmetry of the operators is governed by cubic relations instead of the canonical (anti)commutation relations. The "Fock space" of the parastatistics creation-annihilation algebra carries a representation of the (particle-)permutation group. The irreducible representations thereof are labeled by Young diagrams and the states in the parastatistics "Fock space" are in one-to-one correspondence with Young tableaux(and their supersymmetric counterparts). We show how the permutation symmetry can be deformed into a braid group symmetry into the framework of deformed Green parastatistics. Finally we use the "Fock space" of the deformed parastatistics algebra in order to get algebraic structures on combinatorial objects such as Young Tableaux. We are aimed to keep the exposition as simple as possible: the preriquisite are only a basic notion of field theory, permutation and linear group, Young tableaux will be introduced, students are wellcome.

July 13, 2010
Auditorio de la Facultad de Ciencias
Dr. Alberto Rebassa
Universidad de Valparaíso
"El origen de las enanas blancas de baja masa"
Low-mass white dwarfs (M < 0.5Msun) are thought to have formed in binaries as a consequence of strong mass transfer interactions. However, recent radial velocity and infrared studies of apparently single low-mass white dwarfs reveal that a significant fraction of these do not have close companions. In this work we present the first white dwarf mass distributions directly obtained from observations of a large sample of post-common envelope binaries (PCEBs) and wide white dwarf-main sequence binaries (WDMS). The two distributions differ significantly. Whilst the PCEB sample is dominated by systems containing low-mass white dwarfs, the white dwarf mass distribution of the wide WDMS binaries is similar to that of single white dwarfs. Taking into account observational biases we find that the vast majority of low-mass white dwarfs must have formed in close binaries.

July 2,  2010
Auditorio de la Facultad de Ciencias
Dr. Margaret Hanson
Professor of Physics, University of Cincinnati 
"Improving Mass and Age EStimates of Unresolved Stellar Clsuters"
Stellar clusters provide astronomers with powerful diagnostics to derive the history and evolution of the galaxies they reside in. Even with the Hubble Space Telescope, galaxies beyond our Local Group are too distant for the individual stars within these clusters to be resolved. The entire stellar cluster must be studied as a single unresolved entity. Interpreting the integrated photometry of stellar clusters relies entirely on models to generate predicted colors of unresolved stellar systems. However, previous methods can lead to inaccurate estimates of cluster age because of the statistical fluctuations in the cluster1s stellar mass function that leads to real and large ranges in integrated stellar cluster photometry. I will introduce a new stellar cluster-modeling program we have designed that populates and evolves a realistic sample of stars and derives integrated properties as a function of age and total cluster mass. We have used our model to generate a Monte Carlo database of 50 million stellar clusters to derive likelihood photometric properties as a function of cluster age and mass. This allows the user to work back, through statistical inference, to find the most probable age and mass of their stellar cluster based on integrated photometry alone.

June 29,  2010
Auditorio de la Facultad de Ciencias
Dr. Roberto González
Universidad de Chile
"Filaments in the large-scale structure"
We present a new method to identify large-scale filaments, and apply it to a cosmological simulation. The method actually looks for filaments using DM haloes, but it is also applicable to a galaxy distribution. We show some novel statistical properties of filaments, and we study some halo properties in filaments which can influence the galaxy properties in such regions.

June 22,  2010
Auditorio de la Facultad de Ciencias
Dr. Ricardo Salinas
Universidad de Concepción, Chile
"Heart of darkness: Dynamics of Abell 545 and its 'star pile' "
The universal shape of dark matter profiles predicted by cosmological simulations may be altered by the presence of baryons, in particular, by a cD galaxy. The massive cluster Abell 545 hosts in its center a large low surface brightness structure, known as the star pile, which contributes little to the baryonic budget, but at the same time can be used as a dynamical tracer for the innermost region of the cluster, where the halo density gradient is largest. The star pile has a marginally mildly rising velocity dispersion profile with $\sigma_{LOS}\sim$ 300 km s$^{-1}$ at $\sim$ 20 kpc from its center, while the galaxy cluster has $\sigma_{v}\sim$ 1000 km s$^{-1}$ in the projected innermost 150 kpc. We discuss these results within the controversy between cuspy and cored dark matter halos. Additionally, I will present first results of our on-going projects on the dynamics of cD halos and isolated elliptical galaxies

June 15,  2010
Auditorio de la Facultad de Ciencias
Dr. Thomas Eisenbeiss
Astronomical Institute of the Jena University, Germany
"Observations of isolated neutron stars"
With their almost thermal radiation and their small distance the seven ROSAT detected isolated neutron stars are great laboratories to study the equation of state of dense matter. Due to an (so far unexplained) optical excess these neutron stars are also detectable in optical wavelengths, giving the opportunity of precise astrometry and multi wavelength photometric measurements. In this talk the so far achieved results of optical observations of the "magnificent Seven" (as they are often called) are summarized. Two important additions, a new V magnitude and proper motion measurement of RX J0720.4-3125 as well as a new parallax of RX J1856.5-3754 are explained in more detail. Other methods of obtaining the distance as well as applications and conclusions are briefly discussed. thermal radiation and their small distance the seven ROSAT detected isolated neutron stars are great laboratories to study the equation of state of dense matter. Due to an (so far unexplained) optical excess these neutron stars are also detectable in optical wavelengths, giving the opportunity of precise astrometry and multi wavelength photometric measurements. In this talk the so far achieved results of optical observations of the "magnificent Seven" (as they are often called) are summarized. Two important additions, a new V magnitude and proper motion measurement of RX J0720.4-3125 as well as a new parallax of RX J1856.5-3754 are explained in more detail. Other methods of obtaining the distance as well as applications and conclusions are briefly discussed.

May 25, 2010
Dr. Luis Vega
Universidad de Valparaíso
"Blue featureless continuum in Seyfert 2 nuclei: Young stars or non-stellar continuum?"
El profesor Vega analiza la importancia del Triplete del Calcio (CaT) en la cinemática y en el diagnóstico de las poblaciones estelares en una muestra de 78 galaxias, la mayoría con núcleo activo del tipo Seyfert 2. Se complementa el estudio observacional con modelos de síntesis evolutiva de poblaciones estelares simples y compuestas, para diferentes metalicidades.

May 12, 2010
Dr. Emilio Falco
Arizona Observatory Director
Harvard Smithsonian Whipple Observatory
"Gravitational Lenses"
Dr. Falco offers us an interesting talk on recent developments in ongoing  investigations regarding Gravitational Lensing, natural  telescopes that allow us to see objects that are much further away than those discovered in the last decades.

May 11, 2010
Dr. Markus Mugrauer
Astronomical Institute of the Jena University, Germany
"The University Observatory Jena, astronomical observations and research in the heart of Germany"
The University Observatory Jena is located about 20km west of the city of Jena, where we operate a 90cm reflector telescope, as well as a 25cm Cassegrain and a 20cm refractor auxiliary telescope. After its modernization phase, between 2006 and 2007, regular observations take place again at the observatory in each clear night of a year. Today, the observatory is equipped with a state of the art telescope control system, and modern instruments for imaging and spectroscopy are in use at all of its telescopes. Several observing projects were already started, whose first results were published in 12 refereed articles, filling the whole May 2009 issue of the astronomical journal "Astronomical Notes". In this talk I will present the observatory with its instrumentation, as well as the ongoing observing campaigns together with their results, which could be obtained, so far. Among them the spectro-photometric monitoring of young stars, lucky-imaging observations of close binaries, transit time and duration variation studies of transit planets, the photometric search for transit planets in young open clusters, as well as deep imaging observations to detect sub-stellar objects in these clusters.

May 4, 2010
Dr.  Ronald Mennickent
"Restricciones observacionales para la evolución no
conservativa de estrellas binarias de masa intermedia"
En esta charla se presentan las características observacionales de un centenar de estrellas binarias que muestran dos ciclos fotométricos ligados. El ciclo corto se interpreta como debido al movimiento orbital de un sistema semiseparado en proceso de intercambio de masa. El ciclo largo se interpreta como un ciclo de pérdida de masa al medio interestelar. Se analizan estos sistemas en el contexto de evolución no conservativa de binarias de masa intermedia y se postula una relación evolutiva con los sistemas tipo Algol y W Serpentids.

December 11, 2009
Dr. Gastón Follatelli
Universidad de Chile
"Low-Redshift Type Ia Supernovae by the Carnegie Supernova Project"
I will present the analysis of the first set of 35 low-redshift (z<0.08) Type Ia supernovae (SNe Ia) studied by the Carnegie Supernova Project. The data consist of densely-sampled, high-precision light curves obtained with a uniform, well-characterized photometric system comprising the u'g'r'i'BVYJHKs bands. I will show how we used these data to derive light-curve parameters and to build template light curves that are applicable for fitting other SNe-Ia data. Also, I will present our calibration of intrinsic colors at maximum light and color excesses which allowed us to study the properties of the reddening law in the host galaxies, with the advantage of combining optical and NIR bands. The main goal of the analysis was to produce a calibration of absolute peak magnitudes in all bands versus decline rates and color (or reddening). The results of these multi-band fits suggest that SNe Ia provide distances with a precision *as good as 3%--4%*. I will further discuss the validity of Type-Ia supernovae as true *standard candles* (i.e. requiring no correction for decline rate) in the NIR.

December 4, 2009
Dr. José Gallardo
Universidad de Chile
"Estudios de evolución temprana de estrellas de baja masa"
Uno de los escenarios más aceptados durante la formación de objetos estelares y sub/estelares corresponde a que material circumestelar es acretado por un periodo de alrededor de 1 millón de años. En la charla se discutirá fenomenológicamente este proceso y resultados teóricos del efecto de la acreción en la evolución de estrellas, particularmente de baja masa y en objetos sub-estelares en edades tempranas. Adicionalmente analizaremos los ritmos de acrecion obtenidos recientemente para algunos miembros del cúmulo joven NGC 6523 de la nebulosa M8 usando espectros visuales de baja resolución de Gemini-Sur+GMOS.

December 3, 2009
Dr. Alfredo J. Santillán
Centro de Cómputo-DGSC, UNAM
"Turbulencia en las partes externas de galaxias espirales"
Es sabido que muchos procesos físicos pueden estar asociados a la turbulencia que se produce en los discos galácticos. El hidrógeno neutro que se observa en discos de galaxias espirales puede proporcionar información valiosa sobre la eficiencia y dominio de los diversos procesos físicos a diferentes radios galácticos. Varios de estos mecanismos físicos pueden producir turbulencia aun cuando no exista formación de estrellas, por ejemplo, inestabilidades hidrodinámicas, interacción de pequeñas nubes satélites con las galaxias, etc. En esta plática presentaremos simulaciones numéricas magnetohidrodinámicas para estudiar la interacción de nubes de alta velocidad con las partes externas de discos galácticos. Con nuestras simulaciones demostraremos que una lluvia de pequeñas nubes de alta velocidad, además de estar alimentado al disco de material, es un excelente mecanismo para producir movimientos aleatorios en las partes externas de discos galácticos.

December 2, 2009
MSc. Liliana Hernández-Cervantes
Instituto de Astronomía, UNAM.
"Nuevas Tecnologías de la Información vs Observatorios Virtuales Astrofísicos"
Uno de los principales retos que tiene actualmente la investigación en astrofísica es el manejar y analizar el crecimiento exponencial y complejidad de datos observacionales, junto con el enorme volumen de resultados computacionales que se han generando en todo el mundo en las últimas décadas. El concepto de Observatorio Virtual (OV) es la mejor respuesta a este problema, ya que permite el acceso transparente y distribuido de las bases de datos a través del Internet, además de proporcionar poderosas herramientas para analizarlos y visualizarlos. En esta charla hablaremos de la importancia que tienen las nuevas tecnologías de la Información en el desarrollo de los Observatorios Virtuales Astrofísicos.

November 23, 2009
Dr. Félix Mirabel
Comisión de Energía Atómica, Francia & CONICET, Argentina
"Agujeros Negros en el Universo"
En esta conferencia se presentarán las evidencias que se han obtenido en los últimos años sobre la existencia de agujeros negros en el universo a través de sus tres manifestaciones como quasares, microquasares y fuentes de destellos gamma. Luego se describirá los fenómenos observados en las inmediaciones de estos objetos, algunos de los cuales pueden ser utilizados para contrastar por esas observaciones las teorías físicas en el límite de los campos gravitacionales mas intensos. Finalmente se describirá el rol que han tenido los agujeros negros en la evolución de las estructuras cósmicas.

October 16, 2009
Dr. Rodrigo Parra
Staff Astronomer Atacama Pathfinder Experiment (ALMA)
"Observing Starburst Activity at radio and mm Wavelengths"
I will show results obtained with two (very) different types of instruments. First, I will talk about recent radio interferometric observations of the prototypical ULIRG Arp220 and how we can use such data to infer what's really going on in the hidden nucleus of this remarkable object. Then I will show our new sub-mm spectroscopy data obtained from observations towards the southern starburst NGC253 and ellaborate on how this information can be used to learn about the ionized gas inside its obscured nucleus.

October 6, 2009
Dr. Ralf-Juergen Dettmar, Director del Instituto de Astronomia de la Universidad Ruhr de Bochum, Alemania y presidente de la "Astronomische Gesellschaft" (Sociedad Alemana de Astronomia)
"Gaseous Halos of Spiral Galaxies and the Interstellar Disk-Halo Connection"
Multi-wavelength studies of edge-on disk galaxies show the presence of the various phases of the interstellar medium (ISM) in galactic halos. This includes the ionized gas, the hot medium, as well as the cosmic ray component coupled to the large scale magnetic field. The properties of these ISM components in halos are discussed in the framework of the disk-halo interaction, the large scale circulation of matter in a supernova driven ISM.

October 2, 2009
Dr. Roberto Muñoz, Universidad de Valparaíso
"The growth of the red-sequence in clusters since z~1" ("El desarrollo de la secuencia roja en cúmulos de galaxias desde z=1")
Galaxy clusters are gravitationally bounded structures in the Universe, which are inhabited by several thousands of galaxies in a very small region in the sky and filled by a hot X-ray emitting gas. The central megaparsec of clusters is dominated by early type galaxies, which are observed to obey tight empirical scaling relations as the Fundamental plane and the Red-sequence. For many years the red-sequence in clusters has been thought to be in place since very early cosmic times, but recent works have found a deficit of faint red-sequence galaxies in clusters at z>0.4. In this work, we present deep Js and Ks-band imaging of 15 galaxy clusters at z~1, which were discovered in the Red-Sequence Cluster Survey (RCS-1) and followed up using the VLT/ISAAC instrument. The Ks-band luminosity function (LF) for the composite cluster was derived down to M*+2.5 through the application of a statistical background subtraction method, and it can be described by a Schechter function with Ks*=18.82 and \alpha=-0.42. Furthermore, we built the color-magnitude diagram for the composite cluster at z~1, and found that the ratio of luminous-to-faint red-sequence galaxies evolves as function of redshift. Our results suggest that bright cluster galaxies formed most of their stellar content at z_f=3, that faint cluster galaxies are still forming stars at z=1, and that the red-sequence is not yet fully in place at z=1.

September 9, 2009
Dr. Nidia Morrell, Las Campanas Observatory
"Binarias Masivas"
Las estrellas masivas son objetos inusuales que se forman en menores cantidades y viven vidas mucho más cortas que las de las estrellas menos masivas. Además, se encuentran con frecuencia en regiones muy oscurecidas, difíciles de acceder a las observaciones ópticas. Por estos motivos el conocimiento de sus parámetros fundamentales es impreciso. Entre esos parámetros, la masa juega un papel determinante sobre las características y la evolución de esas estrellas. El único método empírico de determinar masas estelares es el análisis simultáneo de curvas de luz y velocidad radial de binarias eclipsantes de espectro doble. Hasta el momento, las mayores masas "medidas" con este método rondan las 100 masas solares, siendo algo inferiores al límite superior estimado estadísticamente para las masas estelares. Un hecho curioso es que, para las estrellas más masivas, las masas predichas por los modelos evlutivos son frecuentemente más grandes (hasta un factor 2) que las derivadas del ajuste de modelos de atmósferas a los espectros observados de esas estrellas, un efecto conocido como la "discrepancia de masas". La multiplicidad no detectada es una de las grandes causas de incertezas en las determinaciones de masa, pues hace que objetos múltiples aparezcan como objetos simples de mayor luminosidad, y por lo tanto, de mayor masa evolutiva. En esta presentación se describirán brevemente algunos de estos problemas, avances realizados recientemente en el estudio de binarias con componentes masivas, y proyectos dedicados a estudiar la multiplicidad de objetos con espectros O y WN, la discrepancia de masas y la determinación empírica del límite superior de masas estelares.

September 4, 2009
Dr. Alessio Romeo, Universidad Andres Bello
"Evolution of the galaxy Red-Sequence in cosmological simulations of clusters and groups"
The Colour-Magnitude relation is a useful tool to study the evolution of elliptical galaxies, helping to estimate the relevance of passive over dynamical (mergers) evolution of their
stellar populations. By means of cosmological and hydrodynamical simulations, we studied the building of the Red Sequence in clusters and groups, confirming that it is mostly driven by the specific star formation rate: galaxies move to the RS as they get aged and redder and eventually set upon a ``dead sequence'' once they have stopped their bulk star formation activity -perhaps as a result of mechanisms related to AGN feedback.

August 21, 2009
Dr. Alberto Rebassa, Universidad de Valparaíso
"Actividad magnética en estrellas secundarias de baja masa"
In this  talk I report on  the analysis of magnetic  activity in white dwarf-low-mass main  sequence binaries.  The seminar  focuses on three different  issues. The first  is the  comparison between  the activity fractions at a given spectral type in both field M-dwarfs and M-dwarfs that  form part  of a  binary system.   In the  second part  I discuss whether the calculated secondary star distances  can  give  insight on the magnetic  properties  of  these  companions.   Finally  I  provide an empirical  spectral type-radius  relation for  low-mass stars  that is compared both  to the theoretical  expectations, and a  compilation of directly measured low-mass radii.

August 7, 2009
Dr. Carol A. Grady, Eureka Scientific and Goddard Space Flight Center
"Recent Advances in the Study of Protoplanetary Disks"
As stars form, high angular momentum material cannot immediately accrete onto the protostars, and forms circumstellar disks. While molecular gas initially dominates the mass of circumstellar disks, by 8-12 million years, the remnant dust disks show signs of dynamical sculpting by Jovian-mass planets. While the overall timescale for the transformation of disk material is now clear, how circumstellar disks clear away the bulk of their material is still not well-understood. In this talk, I review our understanding of circumstellar disks, and in particular, how the combination of integrated-light photometry and spectroscopy coupled with high contrast imaging of the disk allows us to constrain disk properties. Multi-epoch imaging of a few systems has revealed unexpected changes in the visibility of the outer disk which are tentatively linked with changes in the amount and geometry of material within 1 AU of the star.

July 15, 2009
Dr. Rainer Schödel
Instituto de Astrofísica de Andalucía, España
"The star cluster at the center of the Milky Way"
The Galactic center is a unique target for studying the properties of the nuclei of galaxies in general. The supermassive black hole, Sagittarius A*, that is located at the dynamical center of the Milky Way is surrounded by the densest and most massive star cluster of our Galaxy. In this talk I will focus on the most recent results of research on the structure and kinematics of the Milky Way's nuclear star cluster. Adaptive optics imaging is a necessary pre-requisite for this kind of work, which relies heavily on imaging data taken with NACO at the ESO VLT. In the past years enormous progress has been made in our understanding of the Galactic center. However, it is also surprising that several fundamental aspects of the nuclear star cluster have yet to be explored.

July 10, 2009
Melina Bersten
Universidad de Chile
"Modelos hidrodinámicos de Supernovas de Tipo II Plateau"
I will present a study of the main physical parameters that influence the light curves of supernovae type II plateau (SNe II-P) using a newly developed hydrodynamical code. Two main reasons motivate our work. First, the few existing general studies of SN~II-P light curve modeling are based on simplified assumptions and are difficult to relate with observations. Second, the availability of a large database of highly precise and well-sampled observations of SN II-P from ongoing surveys such as the CSP affords a unique opportunity to characterize the properties of such objects.

June 26, 2009
Dr. Karen Kinemuchi
Universidad de Concepción
"Probing the Outer Halo Galactic Formation: The new SDSS dSph
galaxies and their variable stars"
With the discovery of new dwarf spheroidal galaxies from the Sloan Digital Sky Survey, we have a larger pool of possible candidate objects that may have influenced the formation of our Galaxy.  We studied six of these new galaxies for their variable star content, specifically for the RR Lyrae variables.  RR Lyrae variable stars, which belong to an old stellar population, are effectively eyewitnesses to the formation of the Galaxy, as well as useful distance indicators.  I will discuss our results from our studies for six of these dwarf galaxies.

June 17, 2009
Dr. Diah Y.A. Setia Gunawan
"Cygnus OB2 association at 1400 and 350 MHz: In search of massive
colliding-wind binaries"
A radio continuum survey at 1400 and 350 MHz using the Westerbork Synthesis Radio Telescope (WSRT) of a region of 2° × 2° centered on the Cygnus OB2 association is presented.  The resulting 5 &#963; flux-density limits of, respectively, ~2 mJy and ~10-15 mJy are a significant improvement over previous surveys. More than 200 discrete sources with sizes less than 1.9&#952;beam (beam size) were detected, 98 of which at both frequencies. We also detected 28 resolved sources (sizes > 1.9&#952;beam) still having well-defined peak intensities. The observed spectral index and source count strongly suggest an excess of sources of Galactic origin in the direction of Cyg OB2. Positional coincidences of the detected sources in our list were checked against other radio, infrared, and optical objects from various surveys by using the likelihood ratio (LR) method. Furthermore, we looked for objects that show characteristics of either optically thick stellar winds or non-thermal emission and/or variable spectral flux density. More than 100 identifications were found. Of the unidentified sources, ~2/3, show characteristics of sources of Galactic origin,=2 0 ten of which may be stars. The remaining unidentified sources are probably of extragalactic origin.

June 12, 2009
Dr. Saurabh Sharma
Universidad de Valparaíso
"Galactic open star clusters: star formation and IMF"
High-mass star forming regions have been known for many years as OB associations and HII regions and they have been observed quite extensively on various aspects. However, the census of low mass stars in such regions has not been possible until recently. Recent advancement in detectors have permitted the detection of substantial population of low mass stars in OB associations. In this talk, I will discuss the comprehensive multi-wavelength study of young star forming regions containing the low mass pre-main sequence stars to understand the scenario of star formation in greater details. Deep optical and near-infrared imaging of star forming regions in broad (UBVRIJHK) & narrow bands (H&#945;, [S II], molecular hydrogen & Brakett gamma), spectroscopic observations along with mid- & far-infrared (MSX, Spitzer, IRAS-HIRES), X-ray (Chandra and xmm) and radio (VLA-NVSS) archival data set is used to study the star formation and age spread in young star forming regions, Effect of massive star(s) on star formation, Initial mass function at stellar/sub stellar mass range and K-band luminosity function.

June 5, 2009
Dra. Paulina Lira
Universidad de Chile
"AGN Variability"
Variability is one of the most important and recognizable traits in Active Galactic Nuclei (AGN). Variations allow us to determine characteristic time scales and the system size. Some time scales can in fact be related to basic physical properties of the systems. In this talk I will review what can be learnt from studying flux variations in AGN and present a progress report on 2 projects: one that seeks to determine the Black Hole mass in high-z AGN and another which is trying to further understand the accretion process in Active Nuclei.

May 29, 2009
Dr.  Mark Gieles
ESO
"The Universality of the Globular Cluster Mass Function - Can Dynamical Evolution Explain It?"
The young massive clusters (YMC) observed in the star-burst environments such as the ``Antennae" galaxies are thought to be the progenitors of globular clusters (GCs) that are found in almost all galaxies. The respective mass functions (MF), however, are strikingly different: YMCs form with a power-law MF with an index of -2, while the GCs have a typical mass of ~200.000 M_sun. The most popular explanation is that the low mass GCs have been eroded by tidal disruption over the course of nearly a Hubble time. Dynamical models predict that indeed a power-law MF can be converted into a bell-shaped MF, but they also show that the turn-over mass depends on the strength of the tidal field. This is at odds with the empirical finding that the turn-over mass in the GC MF is independent of environment (galacto-centric distance and/or galaxy type). To overcome this problem, an analytical model was recently introduced in which the mass-loss rate scales with cluster density, that is, the internal relaxation dominates the evolution and sets the mass loss rate. I present result from a large set of N-body simulations with which we study this. The rather surprising result is that for a cluster of a given mass at a given orbit, the dissolution time is independent of its radius, and hence density. This is due to a balance between internal relaxation and the effect of the tidal field, which have an opposite effect, but of similar magnitude, on the mass loss rate of clusters with different radii. It implies that the cluster dissolution time depends only on cluster mass and angular velocity around the galaxy centre, which makes it hard, if not impossible, to explain the universality of the GCMF by dynamical evolution. Several alternatives, based on existing theories on the early evolution of clusters, will be discussed.

May 11, 2009
Dr.  Nicolas Lodieu
Instituto de Astrofísica de Canarias, España
"Latest results from the UKIDSS Galactic Clusters Survey: the IMF of 4 young clusters and star-forming regions"
In this seminar, I will focus on the latest results obtained from the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Surveys (GCS) in 4 regions: Pleiades (125 Myr; 130 pc), IC 4665 (27 Myr; 350 pc), Upper Sco (5 Myr; 145 pc), and sigma Orionis (3 Myr; 352 pc). I will briefly describe the UKIDSS survey and the GCS component. Then, I will detail the photometric and proper motion selections used in each region to identify very low-mass star (M <= 0.5 Msun) and brown dwarf member candidates. Finally, I will compare the mass functions in the 0.5-0.03 Msun mass range with the field mass function derived by Kroupa (2002) and Chabrier (2003). I will discuss the similarities and differences.

April 27, 2009
Dr. David Floyd
OCIW, Observatorio Las Campanas
"Examining Quasar Accretion Discs through Microlensing"
I present a novel method of constraining AGN emission region size and emission mechanism, using recent optical--NIR imaging from the Magellan telescopes of  ``anomalous'' lensed quasars.
Anomalous lensed quasars have an image pair in which one of the images is unusually ("anomalously") dim. We rule out millilensing and partial obscuration as causes for the anomalous flux ratio in each of our quasars, leaving microlensing as the only plausible alternative. We generate magnification maps for each image using a range of smooth-to-clumpy matter fractions. We then randomly select source positions on the map and calculate the magnifications of a set of Gaussian sources of varying width.  We are thus able to constrain statistically, both the proportion of smooth to-clumpy lensing material, and the size of the emitting region of the lensed source.
Using this technique we have probed down to unprecedented scale lengths in the central engine (< 7 light days in r' band) and have begun to explore the change with wavelength. We find clear evidence of a decrease in source size with wavelength, and can place meaningful constraints on possible emission mechanisms. The alpha-disk prescriptions (e.g. Shakura-Sunyaev 1973, Gaskell 2008) are strongly excluded.

Abril 3, 2009
Dr.  Tomás Verdugo
Universidad de Valparaíso
"Laes a través de lentes gravitatorias"
En esta charla presentaré dos modelos de lentes gravitatorias fuertes para los cúmulos de galaxias MS2053 y MS0440, realizados con el código LENSTOOL. Seleccionando los mejores modelos de ambos cúmulos y aprovechando el efecto de amplificación de estos objetos, hemos construido una estadística para fuentes lenteadas. Para ello simulamos seiscientas mil fuentes entre 1 < z < 7 distribuidas según las funciones de luminosidad para LAES y Lyalfa-blobs. Encontramos que la función de luminosidad se transmite a la probabilidad de encontrar emisores lenteados con una amplificación mayor a 10, preservándose incluso el corrimiento al rojo para el máximo de las dos funciones. De esta manera resulta posible en principio estudiar ambas poblaciones de objetos y mostrar si existe una asociación entre ambos fenómenos.

November 4,  2008
Dr. Danielle Alloin
CEA/DSM/IRFU, Université Paris 7, CEA/Saclay & ESO
Visiting Scientist
"Extremely massive young stellar clusters"
At the inner Lindblad resonance in the barred spiral active galaxy NGC1365, we have discovered a number of new sources, compact and bright, which popup at mid-infrared and radio wavelengths, while they are invisible in the optical and near-infrared. Imaging and spectroscopy in the mid-infrared have been collected at the VLT with VISIR, and are used to unveil the nature of such sources. Using several age indicators and two modelling tools (STARBURST and GRASIL), we find that these sources correspond to star clusters at an age of about 7 Myrs, extremely massive, 107 Mo, and still embedded in their parent molecular material. This poses a number of key-questions: How could they be so massive? How is it that at this age they are still embedded in cold material? What is their lifetime?

October 28, 3.10 PM
Dr. Thierry Montmerle
Laboratoire d'Astrophysique de Grenoble, Eso visiting scientist
"What happened to the solar system 4.5685 billion years ago?"
Our knowledge of the chronology of events that took place at the earliest stages of evolution of the solar system derives from two very different bodies of evidence: (i) the observation of young, solar-type stars in various regions of star formation, isolated or in associations; (ii) the deciphering of the meteoritic record of "anomalous" abundances of some elements in the solar system. Along with an extremely precise age of the birth of the solar system (4.5685 Gyr ± 0.5 Myr), meteorites tell us that something dramatic happened at that time: a supernova explosion in its vicinity. Was this a unique event ? Or are young, forming planetary systems frequently exposed to such events ? The topic is currently highly controversial, and I will discuss the present state of the art.

October 23, 2008
Dra. Mariana Orellana, FCAG-Universidad Nacional de La Plata, Argentina
"Radiación Gamma en binarias con acreción"
A lo largo de la investigación vinculada con esta tesis se estudiaron modelos de binarias de rayos gamma con acreción. Este tema ha experimentado un progreso radical durante los últimos años debido a los resultados obtenidos por telescopios Cherenkov.
Específicamente, hemos estudiado el caso de un objeto compacto de bajo campo magnético, capaz de efectuar eyecciones de masa confinadas en chorros de partículas relativistas (microcuásares). Al suponer un contenido de protones relativistas en el jet, se producen interacciones hadrónicas con protones fríos que a modo de blanco provee el viento estelar. Se consideró, entre otras aplicaciones, a la controvertida fuente LSI +61 303. En los casos contemplados, donde la binaria contiene una estrella de tipo espectral joven, la propagación de los rayos gamma muy energéticos generados en el volumen del sistema binario puede inducir el desarrollo de cascadas electromagnéticas dominadas por el mecanismo de dispersión Compton inversa. Hemos desarrollado un código para la simulación Monte Carlo de tales cascadas. Se exponen algunos de los resultados obtenidos, poniendo en relieve la importancia de este problema para la correcta estimación de un espectro detectable a energías mayores que algunos GeV.

October 14, 2008
Dr. Nelson Padilla, PUC
"Understanding local and global influences on the galaxy population"
Reports on the detection of local and global modulations of star formation in galaxies are reviewed and compared to results from semi-analytic models.  The latter are used for the following main objectives, i) to study the expected extent of the influence of individual galaxies on their neighbors, ii) to assess the influence of the halo merger histories on the properties of the galaxies, and iii) to characterise the relation between halo assembly and local/global environments.  

August 26, 2008
Dr. Miguel Verdugo
Institut für Astrophysik Göttingen
"The star formation activity in the outskirts of intermediate redshift clusters"
Al observar cúmulos de galaxias se observa que su contenido de tipos de galaxias es diferente al observado en el campo, mientras que al observar cúmulos distantes se observa que sus poblaciones de galaxies son tambien diferentes.  Esto puede ser causado por la tardía época de formación de los cúmulos, en concordancia con los modelos jerárquicos de formación de estructuras, o por fenómenos de transformación de galaxias específicos de los cúmulos. Presentaré resultados de observaciones de galaxias, en cúmulos a z~0.25, a grandes distancias desde el centro. Es en esas regiones en donde las galaxias son por primera vez afectadas por el medioambiente presente en los cúmulos. Para esto, se tomaron espectros de centenares de galaxias y su actividad de formación estelar fue comparada con el medioambiente global y local de las galaxias.

June 19, 2008

Dra. Margaret Hanson, Department of Physics, University of Cincinnati, USA

"One Hundred 30 Dors: Is the Milky Way different or are we somehow missing them?"
There are a few ways to estimate the number of massive open clusters expected in the disk of the Milky Way, such as the total star formation rate of the Galaxy, or the open cluster mass function extrapolated to include the entire Galaxy.  Surprisingly, they give similar predictions:  the Milky Way should contain about 100 clusters as massive as 30 Doradus in the Large Magellanic Cloud, and even several clusters with 10 times that mass.  Are we seeing them? This talk will first look closely at these predictions and compare that to what we have found so far in our Galaxy. I will then present sophisticated Monte Carlo imaging simulations our group is doing to estimate the selection biases faced by current near-infrared searches for these massive clusters.

June 13, 2008
Matías Gómez, Universidad de Concepción, Chile:
"Globular Clusters in the giant elliptical NGC5128"
I will present our program to study Globular Clusters in the giant elliptical NGC5128 (Centaurus A). Using Magellan/IMACS images covering a 1.2 × 1.2 deg2 field of view with seeing of 0.4"-0.6", we have applied convolution techniques to analyze the light distribution of 364 confirmed globular clusters in the field of NGC 5128 and to obtain their structural parameters. Combining these parameters with existing Washington photometry from Harris et al., we are able to examine the size difference between metal-poor (blue) and metal-rich (red) globular clusters. For the first time, this can be addressed on a sample of confirmed clusters that extends to galactocentric distances about 8 times the effective radius, R_eff, of the galaxy. Within 1R_eff, red clusters are about 30% smaller on average than blue clusters, in agreement with the vast majority of extragalactic globular cluster systems studied. As the galactocentric distance increases, however, this difference becomes negligible. Thus, our results indicate that the differences between the effective radii, r_e, of the clusters could be explained purely by projection effects, with red clusters being more centrally concentrated than blue ones, and by an intrinsic r_e-R_gc dependence, like the one observed for the Galaxy.
I will also discuss our additional programs on the same target galaxy to better understand its kinematics and dynamics using GCs as tracers of their host galaxy potential and episodes of star formation.

May 27, 2008
Isaura Fuentes-Carrera from Observatorio de Paris-Meudon:
"Interacción de galaxias espirales: el caso de Arp 240"
En la actualidad es ampliamente aceptado que las galaxias, tal y como se conocen ahora, se formaron a partir de la fusión de sistemas de menor tamaño. La interacción de galaxias es un fenómeno comun que juega un papel importante en la formación y evolución de estos sistemas,
determinando su tipo morfológico y su historia de formación estelar. En esta charla presentaré observaciones del par de galaxias espirales en interacción Arp 240 (NGC 55257/58) obtenidas con un interferómetro Fabry-Perot de barrido. Se hara una breve descripción de esta técnica observacional, seguida del análisis de la cinemática del gas ionizado de este sistema. Los resultados se comparán con observaciones en el infrarrojo, CO(1-0) y HI tomadas de la literatura.

March 14, 2008
Dr. Hans Zinnecker from Astrophysikalisches Institut, Postdam, Germany
"Direct imaging search for giant planets around white dwarfs"

November 23, 2007
Alfredo Santillán, Universidad Autónoma de México
"Mexican Virtual Solar Observatory"
The Virtual Solar Observatory (VSO) concept contains software tools for searching, manipulating, and analyzing data from archives of solar data at many different observatories around the world (Hill 2000). The VSO not only provides fast and reliable access to the existing solar data, but also represents a powerful and unique machinery to perform numerical simulations for the evolution of a variety of different phenomena associated with the solar activity. Two Mexican Universities, Universidad Nacional Autónoma de México (UNAM) and the Universidad de Sonora (USON), are working together to create the Mexican Virtual Solar Observatory (MVSO) that will be part of a wider national effort. In this site we present a general description and advances obtained in the development of Graphical User Interfaces (GUI) to Remotely Perform Numerical Simulation of the Evolution of Coronal Mass Ejection in the Interplanetary Medium. This tool was developed by scientists and programmers of the Computer Center (DGSCA) & Instituto de Astronomía of the UNAM.

November 21, 2007
Dr.  Henny Lamers, Utrecht University, ESO
"The formation and destruction of star clusters in (interacting) galaxies"
Star clusters do not live forever.  Within about 10 Myr after their birth out of giant molecular clouds,  the remaining gas is expelled by  stellar winds and supernova explosions. As a result, the majority of the clusters dissolve within about 10 – 20 Myr. This is called “infant mortality”.
The  clusters that survive infant mortality slowly dissolve on a very long time scale of Gyrs due to various  internal and external effects such as two-body stellar encounters,  the external tidal field, encounters  with giant molecular clouds and shocks by galactic spiral arms.
Recent studies, based on HST images of large numbers of clusters in different galaxies, have shown that the survival times of clusters depends very strongly on the local conditions.
It can differ by orders of magnitude between clusters in quiet galaxies, such as the Magellanic Clouds, or clusters in interacting galaxies, such as the Antenna galaxies.
I will give a review of our present knowledge of the formation and destruction of star clusters in the Milky Way and in normal and interacting galaxies. I will discuss how we can “measure” the destruction rates of star clusters and the physical processes that are responsible for it.
I will demonstrate some of these effects by movies based on numerical simulations.
These studies help us to understand the populations of field stars in our galaxy
and the difference between the Galactic open clusters and the globular cluster.
 
August 27, 2007
Alberto Rebassa, University of Warwick, UK
"Post Common Envelope Binaries (PCEBs) with SDSS"
In this seminar I am going to provide an introduction of Post Common Envelope Binaries (PCEBs), essentially what they are, where they come from and why they are important. The main body of the talk, nevertheless, will be focused on
(1) the identification of PCEBs from the Sloan Digital Sky Survey, and
(2) the analysis of the stellar components (main sequence and white dwarf) of the sample.

August 10, 2007
Valentin Ivanov, ESO

July 3, 2007
Markus Mugrauer, Yena University
"The multiplicity of planet host stars"
During the last decade more than two hundred planets were indirectly detected around stars in the solar neighborhood. Some of these so-called exoplanets were also found around stars which are themselves members of double or triple star systems. Today more than 30 of these stellar systems with exoplanets are known. A large fraction of them was revealed by us in a systematic imaging survey carried out during the last years mainly at La Silla observatory with the NTT (southern sky) and with UKIRT (northern sky) on Hawaii. In this talk I will summarize the detections of our imaging survey and discuss the impact of stellar multiplicity on the planet formation process in general. Furthermore, I will present apparent differences between the properties of exoplanets which revolve around single stars and those which reside in stellar systems.

June 8, 2007
Ricardo Demarco,  Johns Hopkins University
"Observaciones pancromaticas de cumulos de galaxias en el universo joven"
Cúmulos de galaxias son las estructuras gravitacionalmente ligadas, más grandes del universo. Ofrecen la oportunidad de estudiar en detalle el comportamiento de la materia en las regiones de mayor densidad de materia oscura. Su fuerte emisión en rayos X los hace detectables a un alto corrimiento al rojo del espectro, en épocas cuando el universo tenía solo un tercio de su edad actual. Usando el VLT y el Telescopio Espacial Hubble, entre otros, hemos realizado observaciones pancromaticas de cúmulos de galaxias con corrimientos al rojo cercanos a uno, permitiendonos hacer un estudio detallado no tan
sólo de la distribución de materia oscura y bariónica en estas estructuras, sino que también de las propiedades de las galaxias que los componen.  En esta oportunidad, presentaré los resultados obtenidos del estudio de dos de los cúmulos más masivos y distantes conocidos en el hemisferio sur celeste y discutiré sus implicancias sobre la formación de estructuras a gran escala y la formación y evolución de galaxias.

May 11, 2007
Rainer Schodel, Coeln University
"The (quite dark) stellar cluster around the supermassive black hole
Sagittarius A* in the centre of the Milky Way"

May 4, 2007
Swetlana Hubrig, ESO, Chile
"Magnetic fields in massive stars"
I will mention Herbig, Be, Bp, SPB, and O stars.

March 9, 2007
Tobias Schmidt, Yena University
"Adaptive Optics, applied to observations of young T Tauri stars"
Today several advanced telescopes use Adaptive Optics to increase the quality of their astronomical images. With this technique we now are able to compensate a lot of the atmospheric turbulence using mirrors which can be altered in their shape several times per second. In this talk I would like to present examples of AO applications used today by NACO at the ESO Very Large Telescope (VLT), as well as results of the work we recently did on the young T Tauri star TWA 5 in the TW Hydrae association, a very young association with an age of approximately 7 million years located in the southern hemisphere.

November 24, 2006
Marceau Limousin, Dark Cosmology Centre, Niels Bohr Institute
"Mapping Dark Matter in Galaxy Clusters: From Weak Galaxy-Galaxy lensing to Cluster lensing"