Detection of a long-duration solar gamma-ray flare on Jun. 11, 1991 with EGRET on Compton-GRO

On 11 Jun. 1991, the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (Comption-GRO) observed high energy gamma radiation above 30 MeV from the Sun following an intense flare around 2:00 Universal Time (UT). After the decay of most of the x ray flare, which caused nearly complete deadtime losses in EGRET, high energy emission was registered during the interval from about 3:30 UT to at least 10:30 UT. Gamma rays were detected up to energies above 1 GeV. The solar origin of the emission is assured by the time profile of the gamma ray count rate and by time resolved sky maps, which show a clear maximum at the position of the sun. The gamma ray lightcurve of the flare can be described with two components: a fast decaying emission with an e-folding time constant of about 25 minutes and a slow decay with about 255 minutes. There are indications for a spectral evolution with time, such that the emission below 100 MeV fades away earlier than the 100 to 300 MeV radiation, roughly in the time scale of the fast component. The spectrum of the flare can be fitted with a composite of a proton generated pion neutral spectrum and an electron bremsstrahlung component. The latter can be identified with the fast decaying component of the lightcurve

Long-term field studies of lemurs, lorises, and tarsiers

Lemurs, lorises, and tarsiers are socially and ecologically diverse primates that include some of the most endangered mammals. We review results of long-term studies of 15 lemur species from 7 sites in Madagascar and 1 species each of loris and tarsier in Indonesia. We emphasize that the existence of long-term study populations is a crucial prerequisite for planning and conducting shorter studies on specific topics, as exemplified by various ecophysiological studies of lemurs. Extended studies of known individuals have revealed variation in social organization within and between ecologically similar species. Even for these primates with relatively fast life histories, it required more than a decade of paternity data to characterize male reproductive skew. The long-term consequences of female rank on reproductive success remain poorly known, however. Long-term monitoring of known individuals is the only method to obtain data on life-history adaptations, which appear to be shaped by predation in the species covered here; long-term studies are also needed for addressing particular questions in community ecology. The mere presence of long-term projects has a positive effect on the protection of study sites, and they generate unique data that are fundamental to conservation measures, such as close monitoring of populations. Los lémures, lorises y tarseros son grupos de primates, muy diversos social y ecológicamente, que incluyen algunas de las especies de mamíferos más amenazadas. Se revisaron los resultados de estudios a largo plazo de 15 especies de lémures en 7 áreas de estudio en Madagascar y una especie de loris y otra de tarsero, en Indonesia. Se resalta la importancia de las áreas de estudio a largo plazo como prerrequisito esencial para planear y llevar a cabo estudios de menor duración sobre temas especificos, como lo ejemplifican varios estudios eco-fisiológicos en lemurs. Estudios a largo plazo de individuos conocidos, han revelado variacion en la organizacion social dentro y entre especies ecologicamente similares. Incluso en estos primates, con un ciclo de vida relativamente corto, se necesita recopilar más de una década de datos de paternidad para determinar el sesgo reproductivo de los machos. Sin embargo, aún se sabe poco de las consecuencias a largo plazo que la posición de las hembras en la jerarquía social puede tener en su éxito reproductivo. El monitoreo a largo plazo de individuos conocidos es el unico metodo para obtener datos sobre adaptaciones en su history natural, las cuales aparentemente son moduladas en function de la predacion a las especies estudiadas en este trabajo. Estos estudios a largo plazo son tambien necesarios para afrontar temas específicos sobre la ecología de estas comunidades. La simple presencia de proyectos a largo plazo tienen un efecto positive en la proteccion de los lugares de studio, como asi tambien generan datos unicos que son fundamentals para apoyar medidas de conservacion tales como el monitoreo de poblaciones

The effect of increasing helium content and disk dwarfs evolution on the chemical enrichment of the Galaxy

The paper deals with two main effects: First the empirical metal abundance distribution in Main Sequence disk dwarfs of the solar neighborhood, and second, the theoretical possibility of (a) increased helium content as the Galaxy evolves, and (b) the presence of evolutionary effects in disk dwarfs. A linear increase of helium content with metal content is taken into account, and some constraints are imposed relative to initial, solar and present day observed values of Y and Z, and to observed relative helium to heavy element enrichment, Delta Y/Delta Z. 'Evolved' and 'unevolved' theoretical metal abundance distributions are derived by accounting for a two-phase model of chemical evolution of galaxies and for a linear mass dependence of star lifetimes in the spectral range G2V-G8V, and are compared with the empirical distribution. Finally, models of chemical evolution invoking homogeneous collapse without infall and inhomogeneous collapse with infall, are briefly discussed relative to the empirical metal abundance distribution in Main Sequence disk dwarfs of the solar neighborhood