Based on O II recombination lines we present a new calibration (called O II_{RL}) of Pagel's O_{23} indicator to determine the O/H abundance ratio in extragalactic H II regions and emission line galaxies. The O II_{RL} calibration produces O/H abundances about a factor of two higher than those derived from the T(4363) method with t^2 = 0.00. The O

The term overshooting is used to describe two situations: the chemical mixing induced by the convective elements crossing the boundary given by Schwarzschild's criterion (overshooting), or, in addition to that mixing, the change in the temperature gradient in the overshoot region when convection is efficient enough (penetration; Zahn 1991). We show

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We present time-series optical photometry of five new cataclysmic variables (CVs) identified by the Hamburg Quasar Survey (HQS). The deep eclipses observed in HS 0129+2933 (= TT Tri), HS 0220+0603 and HS 0455+8315 provided very accurate orbital periods of 3.35129827(65), 3.58098501(34) and 3.56937674(26) h, respectively. HS 0805+3822 shows grazing

A new theoretical calibration of surface-brightness fluctuations (SBF) for single age, single metallicity stellar populations is presented for the optical and near-IR broad-band filters, as well as for the HST WFPC2 filters. The IAC-star code is used together with two Padua and the Teramo stellar evolution libraries. A set of single-burst stellar

¿Las supernovas (SN/SNs) son herramientas útiles para el estudio del polvo en otras galaxias? ¿Tienden a explotar en regiones donde las propiedades de los granos de polvo son diferentes de las estándares? Contestar a estas preguntas fue el principal objetivo de esta tesis. Durante la primera parte de este trabajo, se recopilaron, reducieron y