Microvariations (magnitude changes of several hundredths in timescales ranging from minutes to hours) may arise from three sources: jet and accretion instabilities and gravitational microlensing events. Each may produce different changes on the quasars continuous spectra. For this reason, BVR observations can yield a high degree of discrimination

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The ISO mission has shown the importance of establishing a reliable spectrophotometric calibration over the range of wavelengths covered by its multiple observing modes. We examine the needs for infrared calibration with the new generation of 8-10 metre class telescopes in the light of this experience, in particular the 10-m Gran Telescopio

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Through observations and modeling, we demonstrate how the recently discovered large-scale bar in NGC 5248 generates spiral structure that continues from 10 kpc down to 100 pc. Deep inside the bar, two massive CO spirals with streaming motions of 20--40 km/s cover nearly 180 deg in azimuth and connect to two narrow K-band spirals which delineate the

We present the spatial distribution of chemical species in M 31, as derived from intermediate resolution spectra of seven B-type supergiants, lying within four OB associations, covering a galactocentric distance of 5 - 12 kpc. We do not detect any systematic oxygen gradient across this galactocentric range. We find that the inner regions of M 31