Johnson B CCD photometry of quasars and other active nuclei were obtained with the 1-m and 2.5-m reflectors of the Roque de los Muchachos Observatory in the Canary Islands between 1986 and 1987. Data are presented for PKS 1538+149, 3C 345, 3C 351, and BL Lac. Error sources are discussed, and it is noted that at least part of the error is due to

In this paper the approximate Lambda-Operator (ALO) developed by Olson, Auer and Buchler (OAB, 1986) is inspected from a more mathematical standpoint and compared to presently most commonly applied ALOs. For simple model calculations,it is shown that OAB's operator which contains no arbitrary parameter always works close to the optimum convergence

A statistical study of the decay of sunspots and sunspot groups is carried out using data contained in the Greenwich Photoheliographic Results. The period studied spans more than six decades, namely from 1874 to 1939. The adequacy of exponential, quadratic and linear decay laws to the area decay data is considered. The dependence, or otherwise, of

The paper reports measurements of the integrated fluxes over the wavelength range 380 nm - 900 nm for 216 stars using a Reticon spectrometer in conjunction with the 1 m Kapteyn telescope of the Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Methods are proposed for deriving visible integrated fluxes from 13

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The authors present simultaneous UBVRI and infrared JHKL light curves of the short-period RS CVn system ER Vul, and study both the mean level and depths of eclipses. They also point out some peculiar features, present in the light curves over time, which are frequently shown by other RS CVn short-period systems at about the same phase values