We present the results of the optical monitoring of the BL Lac object ON 231 from 1997 to the spring 2001, including the large outburst of spring 1998. After this event the mean source luminosity declined slowly and continued to show changes greater than one magnitude. A simple analysis of the variability time scales in the best-sampled segments of the light curve reveals that the luminosity changes were faster during the burst and slowed down in the subsequent years.
Table 2 reports the journal of observations. For each date the measured magnitudes and their uncertainties in the four filters together with the used telescope are given. In some occasions several images were made in the course of the same night to search for intraday variability; these nights are indicated by an asterisk. The magnitude uncertainties have been evaluated by taking into account the mean dispersion of the internal error, but not the errors on the absolute calibration.
We address the topic of the intra-night optical variability of the BL Lac object S5 0716+714. To this purpose a long-term observational campaign was carried out, from 1996 to 2003, which allowed the collection of a very large data set, containing 10675 photometric measurements obtained in 102 nights. The source brightness varied in a range of about 2mag, although the majority of the observations were performed when it was in the range 13.0<R<13.75. Variability time scales were estimated from the rates of magnitude variation, which were found to have a distribution function well fitted by an exponential law with a mean value of 0.027mag/h, corresponding to an e-folding time scale of the flux {tau}_F_=37.6h. The highest rates of magnitude variation were around 0.10-0.12mag/h and lasted less than 2h. These rates were observed only when the source had an R magnitude <13.4, but this finding cannot be considered significant because of the low statistical occurrence. The distribution of {tau}_F_ has a well-defined modal value at 19h. Assuming the recent estimate of the beaming factor {delta} about 20, we derived a typical size of the emitting region of about (5x10^16^)/(1+z)cm. The possibility of searching for a possible correlation between the mean magnitude variation rate and the long-term changes in the velocity of the superluminal components in the jet is discussed.
Photometric observations of the radio source S5 0716+71 were obtained in Johnson-Cousins BVRI filters from 1998 to 2001. with Zeiss-600 and Zeiss-1000 telescopes of SAO of the Russian Academy of Science.
We present UBVIc CCD photometry of the young open cluster Stock 8 with the aim of studying its basic properties such as the amount of interstellar extinction, distance, age, stellar contents and initial mass function (IMF). We also studied the star formation scenario in this region. From optical data, the radius of the cluster is found to be ~6arcmin (~3.6pc) and the reddening within the cluster region varies from E(B-V)=0.40 to 0.60mag. The cluster is located at a distance of 2.05+/-0.10kpc. Using H{alpha} slitless spectroscopy and Two Micron All Sky Survey (2MASS) near-infrared (NIR) data we identified H{alpha} emission and NIR-excess young stellar objects (YSOs), respectively.
We present FCAPT differential Johnson BV and Cousins RI photometry and radial velocities of the S-type AGB stars RS Cnc, ST Her, OP Her and HR Peg. We performed multiperiodic analyses of this photometry to learn about the frequencies of variability. The B, V, R, and I light curves are generally in phase. RS Cnc has periods of order 122 and 248 days. Repeating the analyses using our data with the extensive V and R photometry of Percy et al. (2001PASP..113..983P) shows several periods near 248 days and a period near 135 days. The primary period of ST Her appears to be about 144 days although it is manifested most readily by its 103 day alias. OP Her and HR Peg exhibit periods, respectively, of about 416 and 116 days and of 54 and 74 days. The differences between our data set and the larger one of Percy et al. (2001PASP..113..983P) for RS Cnc raises important questions about multiperiodic analyses for AGB stars.
File table1.dat contains the UBV(RI)c magnitudes of the symbiotic stars AS 323, Ap 3-1, CM Aql, V1413 Aql, V443 Her, V627 Cas, V919 Sgr estimated on the Asiago archive plates. The date is given in the year/month/day format, and the magnitude is estimated in steps of 0.05mag
We present the results of a deep, wide-field CCD survey for the open cluster NGC 3532. Our new BV(RI)c photometry effectively covers a one square degree area and reaches an unprecedented depth of V~21 to reveal that NGC 3532 is a rich open cluster that harbors a large number of faint, low-mass stars. We employ a number of methods to reduce the impact of field star contamination in the cluster color-magnitude diagrams (CMDs), including supplementing our photometry with JHKs data from the 2MASS catalog. These efforts allow us to define a robust sample of candidate main-sequence stars suitable for a purely empirical determination of the cluster's parameters by comparing them to the well-established Hyades main sequence.
We have obtained BVRI photometry for 21 stellar fields located in directions towards the central 3.5{deg} of the Galaxy. Each field is 10x10 arcmin in size, and a total of ~2x10^5^ stars were measured.
New multiband CCD photometry is presented for the eclipsing binary GW Gem; the RI light curves are the first ever compiled. Four new minimum timings have been determined. Our analysis of eclipse timings observed during the past 79 years indicates a continuous period increase at a fractional rate of +(1.2+/-0.1)x10^10^, in excellent agreement with the value +1.1x10^-10^ calculated from the Wilson-Devinney binary code. The new light curves display an inverse O'Connell effect increasing toward longer wavelengths. Hot- and cool-spot models are developed to describe these variations but we prefer a cool spot on the secondary star. Our light-curve synthesis reveals that GW Gem is in a semidetached, but near-contact, configuration. It appears to consist of a near-main-sequence primary star with a spectral type of about A7 and an evolved early K-type secondary star that completely fills its inner Roche lobe. Mass transfer from the secondary to the primary component is responsible for the observed secular period change.
