The emissivity was calculated for the pair production of helicity-flipped neutrinos, in a way that can be used in supernova calculations. Also presented are simple estimates which show that such process can act as an efficient energy-loss mechanism in the shocked supernova core, and this fact is used to extract neutrino mass limits from SN 1987A

Intermediate resolution CCD spectra of the oxygen triplet at 7770 A have been analyzed to determine oxygen abundances in a sample of metal-deficient stars with metallicities covering the range of Fe/H values between -0.2 and -2.5. Important oxygen overabundances (O/F values of not less than 1) are found in the more metal deficient stars of the

The identification of two new southern planetary nebulae, IRAS 16455-3455 and IRAS 15154-5258, via low resolution spectroscopy, is reported. IRAS 16455-3455 is a high excitation planetary nebula with an extension of 9 arcsec, m(V) = 8.95 and E(B-V) = 1.21. Chemical abundances in this nebula are similar to the mean values for planetaries in the

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The use of long-slit spectroscopy at high spectral and spatial resolution has made it possible to measure gradients of gaseous excitation and also velocity fields in a sample of four bright nuclear starburst galaxies selected from the sample of Balzano (1983). Variations are found not only in the intensity but also in the quality of the emission

Preliminary results of a program aimed at investigating the presence of H II regions around Seyfert nuclei are presented. Extended zones of ionized gas have been detected around some classical Seyfert galaxies. It is thought that the ionizing mechanism in these extended regions is UV radiation from young stars formed in a recent burst of star