Recent progress in the seismic interpretation of field beta Cep stars has resulted in improvements of the physics in the stellar structure and evolution models of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. To improve our comprehension of the beta Cep stars, we studied the young open cluster NGC 884 to discover new B-type pulsators, besides the two known beta Cep stars, and other variable stars. An extensive multi-site campaign was set up to gather accurate CCD photometry time series in four filters (U, B, V, I) of a field of NGC 884. The images were calibrated and reduced to transform the CCD frames into interpretable light curves. Various variability indicators and frequency analyses were applied to detect variable stars in the field.
Long-term photometric and spectroscopic observations of the yellow symbiotic star LT Del are analyzed. UBV light curves are presented. Based on the observations of 20 cycles, we have refined the orbital period of the star, P=476.0d+/-1.0d. The brightness has been found to be unstable at some orbital phases with an amplitude up to 0.3m.
New photometry obtained in 2000-2008 is presented for the post-AGB star IRAS 22272+5435 = V354 Lac. The star showed semi-regular light variations with varying amplitudes.
We present new results of our UBV photometry for HD 179821=V1427 Aql, an F supergiant with an infrared excess, from 2000 to 2008. The semiregular low-amplitude ({Delta}=0.05-0.20mag) photometric variability of the star with a cycle period from 130 to 200 days is caused by pulsations, along with the instability of a variable stellar wind. V1427 Aql also exhibits a long-term trend in the brightness and colors that is probably attributable to a change in the stellar temperature as a result of mass loss episodes, which cause variations in the continuum formation level. We present the results of our JHKLM photometry for V1427 Aql in 1992-2008.
The catalog contains approximatively 10,000 photoelectric observations of Cepheid variable stars, observed by the authors or derived from published data. The catalog contains data on more than 300 stars; of these approximately 230 can be classified as "well-observed".
Photoelectric UBV photometry and star counts are presented for stars in the previously unstudied open cluster Ruprecht 91, supplemented by observations for stars in adjacent regions surrounding the Cepheids SX Car and VY Car, including new observations for the latter. Ruprecht 91 is typical of groups associated with Cepheids, with an evolutionary age of ~8x10^7^yr, but it is only 980+/-8pc distant, much closer than the Cepheids.
We present all available UBV photometry of the symbiotic binary EG And obtained during the last 10 years. The light curves display a double wave through one orbital cycle. It is shown that this behaviour cannot be explained by eclipses of the two detached sources of the continuum radiation. The present models of EG And are not able to simulate satisfactorily variation in both the far ultraviolet and the optical continuum.
The rapidly rotating active stars FK Com and HD 199178 are investigated using extensive long-term photometry. The data set includes previously unpublished photometry, obtained at the Rozhen National Astronomical Observatory. We look for periodicities in the long-term photometric behaviour of both stars, as well as for spots, using light curve modelling. Special attention is paid to the behaviour of the "flip-flop" phenomenon.
Photometric observations of LQ Hya (HD 82558) obtained in 1995-2001 with the Phoenix 10 robotic telescope (Arizona) in the UBV bands with HD 82447 as the comparison star.
