Could the Hercules satellite be a stellar stream in the Milky Way halo?

We investigate the possibility that Hercules, a recently discovered Milky Way (MW) satellite, is a stellar stream in the process of formation. This hypothesis is motivated by Hercules' highly elongated shape as well as the measurement of a tentative radial velocity gradient along its body. The application of simple analytical techniques on radial velocity data of its member stars provides tight constraints on the tangential velocity of the system (v_t = -16^{+6}_{-22} km/s, relative to the Galactic Standard of Rest). Combining this with its large receding velocity (145 km/s) and distance (138 kpc) yields an orbit that would have taken Hercules to within 6^{+9}_{-2} kpc of the Galactic centre approximately 0.6 Gyr ago. This very small perigalacticon can naturally explain the violent tidal destruction of the dwarf galaxy in the MW's gravitational potential, inducing its transformation into a stellar stream.Comment: Conference proceedings of "A Universe of dwarf galaxies: Observations, Theories, Simulations" held in Lyon, France (June 14-18, 2010

A study of the Hercules dwarf spheroidal galaxy

Parts of large spiral galaxies, such as the Milky Way and Andromeda, are believed to have formed from the accretion of several smaller galaxies. Remnants of this chaotic merging era, such as dwarf spheroidal (dSph) galaxies, are visible in the outskirts of large galaxies. dSph galaxies are characterized by their low luminosity, low surface brightness and high fraction of dark matter. Determining the properties, such as mass, luminosity and metallicity, of the dSph galaxies provides key information in our understanding of galaxy formation and evolution. In this thesis, we combine Strömgren photometry with low and high resolution spectroscopy, of the recently discovered Hercules dSph galaxy, to provide information about the evolutionary state of the stars and their radial velocities and metallicities. This enables us to select a clean sample of red-giant branch stars that belong to the Hercules dSph galaxy. Based on the stars identified as members of the Hercules, we find: 1) a galaxy mass that is significantly lower than previous estimates: 2) an abundance trend such that [Ca/Fe] is higher for more metal-poor stars, and lower for more metal-rich stars. This trend suggests an early rapid enrichment through supernovae type II: 3) a tentative evidence for a velocity gradient in our kinematic data. Additionally, we provide a study of the Draco, Sextans and UMaII dSph galaxies using Strömgren photometry. This enables us to establish a new metallicity calibration, based on [Fe/H] determined from high-resolution spectroscopy, from which we derive metallicity distribution functions for the Draco, Sextans and UMaII dSph galaxies

A new low mass for the Hercules dSph: the end of a common mass scale for the dwarfs?

We present a new mass estimate for the Hercules dwarf spheroidal galaxy (dSph), based on the revised velocity dispersion obtained by Aden et al. (2009, arXiv:0908.3489). The removal of a significant foreground contamination using newly acquired Stromgren photometry has resulted in a reduced velocity dispersion. Using this new velocity dispersion of 3.72 +/- 0.91 km/s, we find a mass of M_300=1.9^{+1.1}_{-0.8} 10^6 M_sun within the central 300 pc, which is also the half-light radius, and a mass of M_433=3.7_{-1.6}^{+2.2} 10^6 M_sun within the reach of our data to 433 pc, significantly lower than previous estimates. We derive an overall mass-to-light ratio of M_433/L=103^{+83}_{-48} M_sun/L_sun. Our mass estimate calls into question recent claims of a common mass scale for dSph galaxies. Additionally, we find tentative evidence for a velocity gradient in our kinematic data of 16 +/- 3 km/s/kpc, and evidence of an asymmetric extension in the light distribution at about 0.5 kpc. We explore the possibility that these features are due to tidal interactions with the Milky Way. We show that there is a self-consistent model in which Hercules has an assumed tidal radius of r_t = 485 pc, an orbital pericentre of r_p = 18.5 +/- 5 kpc, and a mass within r_t of M_{tid,r_t}=5.2 +/- 2.7 10^6 M_sun. Proper motions are required to test this model. Although we cannot exclude models in which Hercules contains no dark matter, we argue that Hercules is more likely to be a dark matter dominated system which is currently experiencing some tidal disturbance of its outer parts.Comment: 10 pages, 3 figures, Accepted for publication by ApJ

An abundance study of red-giant-branch stars in the Hercules dwarf spheroidal galaxy

Using high-resolution spectroscopy, we provide a determination of [Fe/H] and [Ca/H] for confirmed red-giant branch member stars of the Hercules dwarf spheroidal galaxy. Based on this we explore the ages of the prevailing stellar populations in Hercules, and the enrichment history from supernovae. Additionally, we provide a new simple metallicity calibration for Stromgren photometry for metal-poor, red giant branch stars. We find that the red-giant branch stars of the Hercules dSph galaxy are more metal-poor than estimated in our previous study that was based on photometry alone. Additionally, we find an abundance trend such that [Ca/Fe] is higher for more metal-poor stars, and lower for more metal-rich stars, with a spread of about 0.8 dex. The [Ca/Fe] trend suggests an early rapid chemical enrichment through supernovae of type II, followed by a phase of slow star formation dominated by enrichment through supernovae of type Ia. A comparison with isochrones indicates that the red giants in Hercules are older than 10 Gyr.Comment: 12 pages, 11 figures. Accepted for publication in A&

Bloqueo radicular lumbar selectivo guiado por TAC. Alternativa para diagnóstico y tratamiento de radiculopatías originadas por hernias discales y/o artrosis facetarías

El presente estudio muestra nuestra experiencia en la realización de bloqueos facetarios periarticulares y radiculares lumbares guiados por Tomografía Axial Computada (TAC), en pacientes con dolor lumbar, o lumbociático provocados por estenosis foraminales de diversas causas, especialmente las secundarias a hernias discales foraminales sin manifestaciones de déficit motor y artrosis facetarías, en estos casos, la causa del dolor se supone se debe a la isquemia que afecta directamente las raíces nerviosas y produce síntomas.Se realizó la evaluación de 55 pacientes a los que se les efectuó este procedimiento entre los años 2007-2010 con diagnóstico de radiculopatía lumbar provocados por estenosis foraminales secundarias a hernias discales foraminales sin manifestaciones de déficit motor y artrosis facetarías y que no mejoraron con tratamiento médico-kinésico en 4 a 6 semanas. 40 Hombres y 15 mujeres con edades entre 35 y 84 años. Se realizaron 45 bloqueos de raíces nerviosas, a 10pacientes se les realizó en dos espacios simultáneos en forma homolateral, y 10 facetarios periarticulares, 8 en forma bilateral. El 90% de los pacientes refirió mejoría inmediata después del procedimiento, con resultados variables a largo plazo. La duración de la mejoría del dolor fue variable y osciló en un rango entre 15 días hasta en forma permanente en el 80% de los casos. Los procedimientos en su mayoría se realizaron con internación de 24 horas. No se presentaron complicaciones técnicas, ni posteriores a la inyección. En nuestra experiencia los mejores resultados se encuentran en el dolor radicular con el diagnóstico de hernia discal foraminal. Se concluye que los bloqueos facetarios y radiculares constituyen un método diagnóstico y terapéutico que puede realizarse con mucha precisión y seguridad utilizando la  ayuda de imágenes diagnósticas, especialmente la TAC siendo útiles para la localización del origen del dolor y para decidir un eventual tratamiento definitivo.

Propuesta de diseño de aula virtual en plataforma Moodle de contenidos de Matemática I, Facultad de Ciencias Agropecuarias (UNC)

Ponencia presentada en la I Jornadas Nacionales y III Jornadas sobre Experiencias e Investigación en Educación a Distancia y Tecnología Educativa en la UNC. Córdoba, Argentina, 14 y 15 de marzo de 2013.La inclusión de tecnologías de información y comunicación (TICs) en los procesos formativos profesionales han ocasionado cambios sustanciales en el modo en que se aprende, se enseña y se construye el conocimiento. El modelo de aprendizaje mixto combina la enseñanza presencial con la enseñanza virtual tratando de reemplazar algunas actividades por otras apoyadas con tecnología. Las propuestas educativas mediante la utilización de aulas virtuales son cada vez más sólidas, amplias y diversificadas. Una de las tecnologías más utilizadas para el desarrollo de estos entornos de aprendizaje son las plataformas virtuales. En particular la plataforma MOODLE (Modular Object-Oriented Dynamic Learning Environment) es un software libre, en continuo desarrollo y de costo nulo para su instalación y empleo. El objetivo de este trabajo fue diseñar un aula virtual en plataforma educativa Moodle como apoyo al desarrollo de clases presenciales de la asignatura Matemática I perteneciente a la Facultad de Ciencias Agropecuarias de la UNC. El espacio virtual se dividió en unidades didácticas de aprendizaje: una de presentación de la asignatura y el resto coincidentes con las unidades temáticas del programa analítico. Se incorporan ejercicios prácticos como complemento a las clases presenciales. También foros de consulta y de discusión de temas, secciones de novedades y encuestas. Todos los diseños para la elaboración de materiales y recursos didácticos se confeccionaron teniendo en cuenta pautas de accesibilidad para la elaboración de los mismos.Fil: Adén, María del Huerto. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias. Departamento de Ingeniería y Mecanización Rural. Cátedra de Matemática I; Argentina.Fil: González, Valeria Mariel. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias. Departamento de Ingeniería y Mecanización Rural. Cátedra de Matemática I; Argentina.Fil: Bocco, Mónica. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias. Departamento de Ingeniería y Mecanización Rural. Cátedra de Matemática I; Argentina

External Mass Accumulation onto Core Potentials: Implications for Star Clusters, Galaxies and Galaxy Clusters

Accretion studies have been focused on the flow around bodies with point mass gravitational potentials, but few general results are available for non-point mass distributions. Here, we study the accretion flow onto non-divergent, core potentials moving through a background medium. We use Plummer and Hernquist potentials as examples to study gas accretion onto star clusters, dwarf and large galaxy halos and galaxy clusters in a variety of astrophysical environments. The general conditions required for a core potential to collectively accrete large quantities of gas from the external medium are derived using both simulations and analytic results. The consequences of large mass accumulation in galaxy nuclei, dwarf galaxies and star clusters are twofold. First, if the gas cools effectively star formation can be triggered, generating new stellar members in the system. Second, if the collective potential of the system is able to alter the ambient gas properties before the gas is accreted onto the individual core members, the augmented mass supply rates could significantly alter the state of the various accreting stellar populations and result in an enhanced central black hole accretion luminosity.Comment: 24 pages, 15 figures, accepted to Ap

The ability of intermediate-band Stromgren photometry to correctly identify dwarf, subgiant, and giant stars and provide stellar metallicities and surface gravities

[Abridged] Several large scale photometric and spectroscopic surveys are being undertaken to provide a more detailed picture of the Milky Way. Given the necessity of generalisation in the determination of, e.g., stellar parameters when tens and hundred of thousands of stars are considered it remains important to provide independent, detailed studies to verify the methods used in the surveys. We evaluate available calibrations for deriving [M/H] from Stromgren photometry and develop the standard sequences for dwarf stars to reflect their metallicity dependence and test how well metallicities derived from ugriz photometry reproduce metallicities derived from the well-tested system of Stromgren photometry. We use a catalogue of dwarf stars with both Stromgren uvby photometry and spectroscopically determined iron abundances (in total 451 dwarf stars with 0.3<(b-y)_0<1.0). We also evaluate available calibrations that determine log g. A larger catalogue, in which metallicity is determined directly from uvby photometry, is used to trace metallicity-dependent standard sequences for dwarf stars. We derive new standard sequences in the c_1,0 versus (b-y)_0 plane and in the c_1,0 versus (v-y)_0 plane for dwarf stars with 0.40 < (b-y)_0 < 0.95 and 1.10 < (v-y)_0 < 2.38. We recommend the calibrations by Ramirez & Me'endez (2005) for deriving metallicities from Stromgren photometry and find that intermediate band photometry, such as Stromgren photometry, more accurately than broad band photometry reproduces spectroscopically determined [Fe/H]. Stromgren photometry is also better at differentiating between dwarf and giant stars. We conclude that additional investigations of the differences between metallicities derived from ugriz photometry and intermediate-band photometry, such as Stromgren photometry, are required.Comment: Accepted for publication in A&A, 34 pages, including on-line materia

Signatures of an intermediate-age metal-rich bulge population

We have determined detailed elemental abundances and stellar ages for a sample of now 38 microlensed dwarf and subgiant stars in the Galactic bulge. Stars with sub-solar metallicities are all old and have enhanced alpha-element abundances -- very similar to what is seen for local thick disk stars. The metal-rich stars on the other hand show a wide variety of stellar ages, ranging from 3-4 Gyr to 12 Gyr, and an average around 7-8 Gyr. The existence of young and metal-rich stars are in conflict with recent photometric studies of the bulge which claim that the bulge only contains old stars.Comment: Poster contribution at Galactic archeology, near-field cosmology and the formation of the Milky Way, Shuzenji, Japan, 1-4 November 2011, to be published in ASP Conference Serie