The new observational O/Fe vs Fe/H relationship in halo dwarfs is analyzed in terms of a model of chemical evolution for the solar neighborhood. The role of nucleosynthesis prescriptions for SN II and SN I (both Ia and Ib) is analyzed. It is shown that, by adopting iron yields for SN II according to the observations of SN 1987A and by assuming

Deep spectra of the planetary nebula IC 418 were obtained in the wavelength range 4190-5850 A. The data made it possible to map an extended halo about the source, evaluate the variation in halo intensity with radius, and model the results in terms of a radially symmetric dust scatter envelope. It is suggested that the nebula is in a relatively

IAUC 5077 available at Central Bureau for Astronomical Telegrams. IAUC 5077 available at Central Bureau for Astronomical Telegrams.

IAUC 5079 available at Central Bureau for Astronomical Telegrams.

IAUC 5078 available at Central Bureau for Astronomical Telegrams.

The effect of a spiral-like perturbation in the orbits of an axisymmetric galactic potential is studied using surfaces of section. It is found that the perturbation induces stochasticity and diffusion of orbits in phase space.