We detected tertiary components of close binaries from spectroscopy and light curve modelling, investigated the light-travel time effect and the possibility of magnetic activity cycles, measured mass ratios for unstudied systems, and derived absolute parameters. We carried out new photometric and spectroscopic observations of five bright close eclipsing binaries, predominantly in the southern skies. We obtained full Johnson BV light curves, which were modelled with the Wilson-Devinney code. Radial velocities were measured with the cross-correlation method using IAU radial velocity standards as spectral templates. Period changes were studied with the O-C method, utilising published epochs of minimum light (XY Leo) and ASAS photometry (VZ Lib). For three objects (DX Tuc, QY Hya, V870 Ara), absolute parameters have been determined for the first time. We spectroscopically detected the tertiary components in XY Leo and VZ Lib and discovered one in QY Hya. For XY Leo we updated the light-time effect parameters and detected a secondary periodicity of about 5100d in the O-C diagram that may hint at the existence of short-period magnetic cycles. A combination of recent photometric data shows that the orbital period of the tertiary star in VZ Lib is likely to be over 1500d. QY Hya is a semi-detached X-ray active binary in a triple system with K and M-type components, while V870 Ara is a contact binary with the third smallest spectroscopic mass ratio for a W UMa star to date. Being close to the theoretical minimum for contact binaries, this small mass ratio suggests that V870 Ara has the potential of constraining evolutionary scenarios of binary mergers. The inferred distances to these systems are compatible with the Hipparcos parallaxes.
CCD observations in B, V and I passbands have been used to generate deep V, (B-V) and V, (V-I) colour-magnitude diagrams for the open cluster NGC 7510. The sample consists of 592 stars reaching down to V=21mag. There appears to be non- uniform extinction over the face of the cluster with the value of colour excess, E(B-V), ranging from 1.0 to 1.3mag. The law of interstellar extinction in the direction of the cluster is found to be normal. A broad main sequence is clearly visible in both colour-magnitude diagrams. From the bluest part of the colour-magnitude diagrams, the true distance modulus to the cluster has been estimated as 12.5+/-0.3mag and an upper limit of 10 Myr has been assigned for the cluster age.
We present deep wide-field VI CCD photometry of the Sextans dwarf spheroidal galaxy (dSph) in the Local Group, covering a field of 42'x28' located at the center of the galaxy (supplemented by short B photometry). The limiting magnitudes with 50% completeness are V=24.4mag and I=23.6mag.
In 2008-2013, we obtained 11333 CCD BV Ic frames for 57 Cepheids from the General Catalogue of Variable Stars. We performed our observations with the 76-cm telescope of the South AfricanAstronomicalObservatory (SAAO, South Africa) and the 40-cm telescope of the Cerro Armazones Astronomical Observatory of the Universidad Catolica del Norte (OCA, Chile) using the SBIG ST-10XME CCD camera. The tables of observations, the plots of light curves, and the current light elements are presented. Comparison of our light curves with those constructed from photoelectric observations shows that the differences between their mean magnitudes exceed 0.05mag in 20% of the cases. This suggests the necessity of performing CCD observations for all Cepheids.
We took a total of 1175 B, V, and Ic-band CCD frames for 11 GCVS RR Lyr-type variables, for which only the coordinates were known. Observations were made with the 76-crn telescope of the South African Astronomical Observatory. We confirm the variability types, determine the periods, and build the light curves for five objects: BL Aps (P=0.598d), GR Pav (P=0.583d), HI Pav (P=0.643d), HZ Pav (P=0.803d), and IR Pav (P=0.561d). The objects SY Aps (P=0.279d) and IV Pav (P=0.408d) proved to be W UMa-type eclipsing variables; TW Aps (P=0.149d), an SX Phe-type variable; TT Aps (P=482d), an SRD-type semiregular variable, and SW Aps and GI Pav, constant stars.
We present time-series data on the variable stars of the galactic globular cluster Messier 3 (M3). We give BVI_C_ light curves for 226 RR Lyrae, 2 SX Phe and 1 W Vir type variables, along with estimated fundamental photometric parameters such as intensity and magnitude-averaged brightness and pulsation periods. In some cases, the periods we have found significantly differ from the previously published ones. This is the first published light curve and period determination for variable V266. The I-band light curve has not been observed previously for numerous (76) variables. Three new RR Lyrae variables have been discovered. Groups of RR Lyrae variables that belong to different evolutionary stages and have been separated previously on the basis of V data were found here for all colours and colour indices by cluster analysis. The I-band period-luminosity relation is also discussed. From the 66 modulated (Blazhko type) RR Lyrae stars we investigated, six are newly identified and two of them are first overtone pulsators. In the case of 13 RR Lyrae, the period of Blazhko cycle has been estimated for the first time. V252 is identified as a new RRd variable. Amplitude ratios of RRd stars have been investigated to search possible mode content changes. In contrast to previous publications no changes have been found. Problems with the sampling of the time-series of typical cluster variability surveys are demonstrated.
A total of 2097 photometric observations in the BVI_C_ system are presented for 117 Cepheids located in the southern hemisphere. The main purpose of the photometry is to provide new epochs of maximum brightness for studying Cepheid period changes, as well as to establish current light elements for the Cepheids.
We have obtained CCD BVI_KC_ photometry down to V~21.5 for the open cluster Lynga 11 and its surrounding field. This previously unstudied object appears to be rich and highly absorbed. A cluster angular radius of 4.5+/-0.5, equivalent to (3.0+/-0.3)pc, is estimated from star counts in 100-pixel a side boxes distributed throughout the whole observed field. Our analysis suggests that Lynga 11 is moderately young and probably of solar metallicity.
In 2008-2010, we obtained 6095 CCD frames in the BVIc photometric system for 49 classical Cepheids discovered in the ASAS-3 project. The observations were obtained on the 76-cm telescope of the South African Astronomical Observatory (SAAO, RSA) and the 40-cm telescope of the Cerro Armazones Observatory of the Catholic University of the North (OCA, Chile), with a SBIGCCD ST-10XME camera. We present tabulated observations, light curves, and revised elements for the brightness variations.
We present a new, BVIc photometric survey of the young open cluster IC 4665, which improves on previous studies of this young cluster by incorporating a rigorous standardization procedure, thus providing high-fidelity colors and magnitudes for cluster members. We use this new photometric dataset to reevaluate the properties (age and distance) of IC 4665.