A method is presented to estimate the influence of the atmospheric turbulence and the telescope on the mean power spectra of the granulation brightness distribution at positions outside the disk centre, derived using the determination of Fried's parameter. The procedure is based on the differential degradation suffered by the directions

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A very rapid swing in the polarization position angle (PA) in the optical region was observed in blazar OJ 287 during one night of our five nights UBVRI photopolarimetric monitoring in January 1991 with the Nordic Optical Telescope. During this PA swing the flux increased ~40% in five hours, while the polarization level was very stable and quite

Two years after its outburst in 1989, the William Herschel Telescope has been used to find absorption features in V404 Cyg characteristic of a late G or early K star with a radial velocity curve of amplitude 211 +/- 4 km/s and period 6.473 +/- 0.001 days. The deduced mass function of 6.26 +/- 0.31 solar masses is a firm lower limit to the mass of

Results of radio continuum and optical emission-line observations of the type 1 Seyfert galaxy NGC 3516 are presented. The radio maps reveal an elongated one-sided curved structure, which comprises a series of small-scale 'blobs' and extends up to 4 kpc from the nucleus. This radio structure is aligned and cospatial with one side of the double