Emission-line and UV continuum observations of the type I Seyfert galaxy NGC 5548 were carried out for a period of 8 months with the IUE satellite. It was found that both the continuum shape and the line ratios of NGC 5548, while being not unusual for type I Seyfert galaxies, are strongly variable. The UV continuum flux and broad emission line

A circular analyzer has been used at the focal plane of a telescope in days of absence of instrumental polarization to simultaneously record I±V spectrograms at two different wavelength ranges: ≡6300 Å and ≡3930 - 3970 Å. The observations have been analyzed within two, also different, frames: on the one hand, an empirical relationship between

The chromatic behaviour of the IAC analyzer, commonly used at the German Vacuum Gregory-Coude telesope at the Spanish Observatorio del Teide (Canary Islands), is investigated. It is shown that, through careful alignment of the optical components, a nearly perfect circular analysis can be obtained at wavelengths of 4000 Å and 6000 Å. For other

The new observational O/Fe versus Fe/H abundance relationship for halo stars is studied in terms of several models of chemical evolution for the solar neighborhood. Nucleosynthesis products from type I (both Ia and Ib) and Type II SNs are taken into account. The behavior of the O/Fe ratio for halo and disk stars is well reproduced by assuming (1) a

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The GOLF experiment on the SOHO mission will study the internal structure of the sun by measuring the spectrum of global oscillations in the frequency range 10-7 to 6 10-3 Hz. Both p and g mode oscillations will be investigated, with the emphasis on the low order long period waves which penetrate the solar core. The instrument employs an extension