The disagreement between evolutionary and dynamical time scales for the evolution of the central stars of planetary nebulae (CSPN) through the H-R diagram is investigated. Three possible reasons for the disagreement are examined: (1) the nebulae could have experienced a phase of rapid photoionization of material ejected previously while the stars

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Ionic abundances for two irregular dwarf galaxies belonging to the Local Group, GR 8 and Sextans B, are presented. The oxygen abundances have been found to be 0.055 solar masses and 0.16 solar mass, respectively. The Ne(2+)/O(2+) abundance ratio is within the range of what is observed for other irregular galaxies but the N(+)/O(+) and the S(+)/O(+)

A new procedure to separate the instrumental and atmospheric components of stray light is presented. It is based on the dependence of the aureole's atmospheric component on the air mass and is applied to measurements taken with the Vacuum Newton Telescope (VNT) at the Observatorio del Teide (Tenerife). The resulting instrumental part is independent

Although spiral structure in grand design galaxies is generally present in the young and old stellar components and also in both atomic and molecular gas, the issue of whether the spiral structure is merely "organized" by a density wave, or whether star formation is triggered preferentially in the arms is still an open question. Here we present