As a part of an extensive program focused on the global properties and evolution of active stars, high-precision UBV(RI)_c_ and UBV photometry of 31 selected stars is presented. The UBV(RI)_c_ observations were collected at the European Southern Observatory over the 31 December 1992-18 January 1993 and the 20 November-3 December 1993 intervals. Additional UBV photometry obtained by the ``Phoenix" and by the Catania Astrophysical Observatory Automatic Photoelectric Telescopes from 1990 to 1993 is also presented for some of the program stars. Significant evolution of the light curves, period variations and evidence for long-term variability of the global degree of spottedness are found. Some spectral classifications are revised and the inferred photometric parallaxes are compared, whenever possible, with the values measured by the Hipparcos satellite (Cat. <I/239>). These observations are finalized to the construction of an extended photometric database, which can give important clues on topics such as the stability of spotted areas, differential rotation, solar-like cycles and the correlation between inhomogeneities at different atmospheric levels.
In the framework of an extensive program focusing on the global properties and evolution of active stars, high-precision UBV(RI)c photometry of 19 selected stars, collected at ESO over the 15-31 March 1991 interval is presented. Significant evolution of the light curves, period variations and evidence for long-term variability of the global degree of spottedness are found. Most of the spectral classification are discussed. A flare event was detected for the star HD 127535 = V841 Cen. These observations contribute to the establishment of a time-extended photometric database which can give important clues on topics such as the stability of spotted areas, differential rotation, solar-like cycles and the correlation between inhomogeneities at different atmospheric levels.
As part of an extensive program focused on the global properties and evolution of active stars, high-precision UBV(RI)c and UBV photometry of 18 selected stars is presented. UBV(RI)c observations were collected at the European Southern Observatory over the intervals 21-28 September 1994 and 25 November - 05 December 1994. Additional UBV photometry obtained late in 1994 by Catania Astrophysical Observatory Automatic Photoelectric Telescope is also presented. Significant evolution of the light curves, period variations and evidence for long-term variability of the global degree of spottedness are found. Some spectral classifications are revised and photometric parallaxes are compared, whenever possible, with the values measured by the Hipparcos satellite. These observations are finalized to the construction of an extended photometric database, which can give important clues on topics such as the stability of spotted areas, differential stellar rotation, solar-like activity cycles and the correlation between inhomogeneities at different atmospheric levels.
Accurate BV(RI)c light and colour curves of the Mira variable in the dust-free symbiotic system K4-46 are presented and discussed. They cover several consecutive pulsations cycles. The Mira mean period is 284.2d, the reddening sums to E(B-V)=0.35 and the distance is 10kpc. Absolute spectrophotometry at both maximum and minimum brightness of the Mira is presented.
Deep CCD UBV(RI)c photometry has been carried out in the area of the open cluster Stock 16. The different photometric diagrams indicate the presence of three superimposed stellar groups, all composed of early type stars.
UBVR_C_I_C_ photometry of the W UMa eclipsing binary FI Bootis has been obtained and analyzed simultaneously with previously published photometry and radial velocities. The analysis of the light and radial velocity curves shows that the system is an A-type W UMa system consisting of stars with masses 0.82 and 0.31M_{sun}_.
RR Gem is one of the few Blazhko RR Lyrae which has extended enough photometric observations available to study the long-term courses of its pulsation and modulation properties in detail. We investigate the pulsation and modulation properties and the relations between them in RR Gem using the last 70 years' photometric observations in order to gain further insight into the nature of the Blazhko modulation. Photographic, photoelectric and CCD light curves obtained at the Konkoly Observatory and other authors' published maxima observations are studied. Detailed analysis of the light curves, maximum brightness and O-C data are carried out.
In the framework of an extensive program focusing on the global properties and evolution of active stars, high-precision UBV(RI)_c_ photometry of 9 selected stars, collected at the European Southern Observatory over the intervals 7-17 September and 30 September - 10 October 1990, is presented. Significant evolution of the light curves, period variations and evidence for long-term variability of the global degree of spottedness are found. Some of the spectral classifications are discussed. These observations contribute to the establishment of a time-extended photometric database which can give important clues on topics such as the stability of the spotted areas, differential rotation, solar-like cycles and the correlation between inhomogeneities at different atmospheric levels. For a description of the UBV and (RI)c photometric systems, see e.g. General Catalog of Photometric Data <GCPD/01> and <GCPD/54>
The three open clusters Be 15, Be 80 and NGC 2192 have been observed using CCD UBV(RI)C photometry at the San Pedro Martir Observatory, Mexico within the framework of our open-cluster survey. The fundamental parameters of interstellar reddening, distance and age have been derived, and also the metallicity for NGC 2192 (solar metallicity has been assumed for the other two).
We present UBVRI photometry of the open cluster NGC 2422 (age~10^8^yr) down to a limiting magnitude V=~19. These data are used to derive the Luminosity and Mass Functions and to study the cluster spatial distribution. By considering the color-magnitude diagram data and adopting a representative cluster main sequence, we obtained a list of candidate cluster members based on a photometric criterion.
