Monochromatic extinction coefficients at four wavelengths have been obtained over a period of more than two years at the Observatorio del Teide (Izaña Tenerife) using a full disc, direct sunlight, quadruple photometer devoted to the detection of integral luminosity oscillations of the Sun. The mean extinction coefficients (0.13 at 500 nm) show a

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CCD photometry of resolved dwarf irregular galaxies was obtained with the 4-m Cerro Tololo Interamerican Observatory telescope in February 1985. BV data from 77 stars in DDO 187 are used to infer a distance modulus of 28.2 + or - 0.6, placing this galaxy out of the Local Group, at a distance of 4.4 + or - 1.0 Mpc. In the second part, UBV photometry

The authors present CCD UBV photometry of 142 resolved stars in the Local Group dwarf irregular galaxy GR 8. Its distance modulus has been found to be 25.0. The luminosity function has been derived. The percentage of the total luminosity in stars brighter than MV = -2 is found to be about 30%. The derived differential (IMF) for stars with masses

Two EXOSAT observations of gamma-ray burst error boxes and their possibly associated optical transients are discussed. No point source was detected in either box. A comparison with Einstein data (Pizzichini et al., 1986) is made for one of them (November 19, 1978). The data are interpreted in the framework of neutron star models for gamma-ray