Photometric monitoring of the blazar 3C 345 for the period 1996–2006

We present the results of the blazar 3C 345 monitoring in Johnson‐Cousins BVRI bands for the period 1996–2006. We have collected 29 V and 43 R data points for this period; the BI light curves contain a few measurements only. The accuracy of our photometry is not better than 0.03 mag in the VR bands. The total amplitude of the variability obtained from our data is 2.06 mag in the V and 2.25 mag in the R band. 3C 345 showed periods of flaring activity during 1998/99 and 2001: a maximum of the blazar brightness was detected in 2001 February – 15.345 mag in the V and 14.944 mag in the R band. We confirm that during brighter stages 3C 345 becomes redder; for higher fluxes the colour index seems to be less dependent on the magnitude. The intra‐night monitoring of 3C 345 in three consecutive nights in 2001 August revealed no significant intra‐night variability; 3C 345 did not show evident flux changes over timescales of weeks around the period of the intra‐night monitoring. This result supports the existing facts that intra‐night variability is correlated with rapid flux changes rather than with specific flux levels. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Regularities in the long-term optical light curve of the black hole candidate binary A0620 − 00 (V616 Mon)

We have monitored the R I magnitudes of the black hole candidate system A0620 − 00 (V616 Mon) in the years 1991–1995 at the Wise Observatory. Combining our data with some additional measurements, we analyse a sparsely covered 7-yr light curve of the star. We find that the average R -band magnitude varies on a time-scale of a few hundred days, with a peak-to-peak amplitude of 0.3 mag. The two maxima in the well-known double hump binary cycle, as well as one of the minima between them, vary by a few per cent relative to one another, in a seemingly random way. One maximum is, on average, higher by 0.05 mag than the other. The depth of the second minimum varies with significantly higher amplitude, in clear correlation with the long-term variability of the mean magnitude of the system. It is shallower than the other minimum at times of maximum light. It deepens when the system brightness declines, and it becomes the deeper of the two minima at times of minimum system light. According to the commonly acceptable phasing of the binary cycle, the systematically varying minimum corresponds to the inferior conjunction of the red dwarf. We cannot suggest any simple geometrical model for explaining the regularities that we find in the long-term photometric behaviour of the V616 Mon binary system.     

Variable stars in the Bochum Galactic Disk Survey

We present a first overview of variable stars in the Bochum Galactic Disk Survey (GDS) with emphasis on eclipsing binaries (EBs). This ongoing survey is performed by a robotic twin refractor at the Universitätssternwarte Bochum located near Cerro Armazones in Chile. It comprises a mosaic of 268 fields in a stripe of Δb = ±3° along the Galactic plane observed once per month simultaneously in the Sloan r and i filters with a detection limit of r_s ∼ 16 mag and i_s ∼ 15 mag. The data from the first three years until the end of February 2014 yields a total of 41718 variable stars with variability amplitudes between 0.1–6 mag. A cross‐match with SIMBAD identified 11 465 of these variables unambiguously, while 2184 had multiple matches; most of the remaining stars could be matched with 2MASS objects. Among the SIMBAD‐listed objects with single matches, only 1982 turned out as known variables while a further 256 are suspected of variability. That leaves a total of 39480 potentially new variables. The group of known variables comprises 419 stars (21 %) that are classified as EBs while 443 (22%) are of other types; for the remaining 1120 catalogued variables (57 %) the type is unknown. Investigating variability as a function of spectral type, we find that SIMBAD provides spectral types for 2811 (25 %) of the identified stars. Spectral classes B (26 %), A (20 %), and M (25%) contain the most numerous variables, while all other classes contribute less than 10% each. More than half of the B (55 %) and A (56%) stars are designated as EBs, suggesting that hundreds of new B‐ and A‐type EBs may be contained in the GDS archive. In contrast, among the numerous M stars no EBs are known. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

JOINT LIGHTCURVE OBSERVATIONS OF 10 NEAR-EARTH ASTEROIDS FROM MODRA AND ONDŘEJOV

The effort in photometry of near-Earth asteroids (NEAs) at Modra Observatory has been enhanced following a recent collaboration with Ondřejov Observatory. We present a part of our collaborative work on measuring rotation lightcurve data for 10 NEAs. We derived following synodic periods P and amplitudes of their composite lightcurves: (3553), 3.1944 h, 0.08 mag; (22753), 10.24 h, 0.11 mag; (31669), 5.807 h, 0.07–0.27 mag; (40267), 4.9568 h, 1.01–1.11 mag; (66146), 2.3774 h, 0.12–0.15 mag; (88188), 2.6906 h, 0.06 mag; (103067), 9.489 h, 0.49 mag; 2001 CB₂₁, 3.302 h, 0.19 mag; 2004 LJ₁, 2.7247 h, 0.17–0.59 mag; 2004 XO₁₄, 8.417 h, 0.19–0.25 mag. While the derived periods are unique (the reliability code U=3) for most of the objects, those of (3553), (22753) and 2001 CB₂₁ are somewhat less reliable (U=2). We checked all the U=3 data for deviations from strict periodicity, but found no significant attenuation that would indicate the presence of a satellite. Absolute magnitudes in Cousins R band (H _R ) were derived for (3553), 16.05; (40267), 15.59; (88188), 16.04; 2004 XO₁₄, 15.84; errors of the first three H _R estimates are 0.20 mag, but that of 2004 XO₁₄ is <0.10 mag.     

The optical variability of the Seyfert galaxies NGC 4051 and NGC 1068

The optical (BV) monitoring data for the Seyfert galaxies NGC 4051 and NGC 1068 are presented in this paper. NGC 4051 showed a variation of 0.43 mag in 21 minutes in B band from its bright nucleus, and the nucleus of NGC 1068 exhibited a variability of 0.46 mag in B band in a timescale of 1.8 hours. These results argued that the optical emission from the nuclei of the two Seyfert galaxies could be dominated by the nonthermal radiation. The data in this paper, however, are only marginal evidence on the rapid optical variability of these two Seyferts, and further monitoring is needed to confirm this type of variability.     

The irregular galaxy Cassiopeia 1 – a new member of the Local group

A photometry in the V, R, I (Cousins) system has been performed for stars in the galaxy Cassiopeia 1. The resulting colour-agnitude (CM) diagram of Cas 1 reveals the existence of blue stars and the absence of red ones. From an analysis of the CM diagram of the galaxy it is concluded that A_v = 4.0 mag, and the distance modulus (m – M)_o = 24.5 mag, corresponding to a distance of 790 kpc. The visual magnitude of the galaxy is V = 14^m.62 (M_v = −13^m.8) and the colour index (V – R) = 0.89 mag. From the distance determination the galaxy Cassiopeia 1 is a member of the Local group.     

Johnson‐Cousins magnitudes of comparison stars in the fields of ten Seyfert galaxies

We present UBVR_CI_C magnitudes of 49 comparison stars in the fields of the Seyfert galaxies Mrk 335, Mrk 79, Mrk 279, Mrk 506, 3C 382, 3C 390.3, NGC 6814, Mrk 304, Ark 564, and NGC 7469 in order to facilitate the photometric monitoring of these objects; 36 of the stars have not been calibrated before. The comparison stars are situated in 5 × 5 arcmin fields centred on the Seyfert galaxies, their V band flux ranges from 11.7 to 18.2 mag with a median value of 16.3 mag, and their B – V colour index ranges from 0.4 to 1.6 mag with a median value of 0.8 mag. The median errors of the calibrated UBVR_CI_C magnitudes are 0.08, 0.04, 0.03, 0.04, and 0.06 mag, respectively. Comparison stars were calibrated for the first time in three of the fields (Mrk 506, 3C 382, and Mrk 304). The comparison sequences in the other fields were improved in various aspects. Extra stars were calibrated in four fields (Mrk 335, Mrk 79, NGC 6814, and NGC 7469) – most of these stars are fainter and are situated closer to the Seyfert galaxies compared to the existing comparison stars. The passband coverage of the sequences in five fields (Mrk 335, Mrk 79, Mrk 279, NGC 6814, and Ark 564) was complemented with the U band. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical R-band variability of seven X-ray-selected BL Lacertae objects

This paper presents the results of optical CCD photometry in the Cousins R band for seven X-ray-selected BL Lacertae objects. Observations have been performed with the 70-cm meniscus telescope of Abastumani Astrophysical Observatory, Georgia. The data obtained provide important information on sources that have been rarely observed in the optical band. The targets show clear long-term variability with time-scales of 1.5–5 yr. The maximum amplitudes are slightly greater than 1 mag. 1ES 0323+022, 0502+675 and 0806+524 show clear non-periodical behaviour. 1ES 1028+511 changes quasi-periodically but further monitoring for periodicity confirmation and period derivation is needed. Overall brightness variation is maximal for 1ES 0647+250 with  Δ R = 1.29  mag. Two-peak maxima, indicating the existence of reverse shocks in blazar jets, are observed for 1ES 0502+675, 0647+250, 0806+524 and 1517+656. The targets do not show intra-night variability. Day-to-day changes with amplitudes of 0.1–0.32 mag coincide mainly with short-term bursts. The latter are seen at faint (quiet) stages as during flaring activities. This fact leads to the suggestion that both hot-spot and shock-in-jet models explaining the origin of short-term bursts should be reasonable.     

Structural investigations in the central part of the coma cluster on the base of equidensity diagrams. II

On the base of Tautenburg UBV-Schmidt plates equidensitometric diameters of galaxies of ROOD and BAUM 's list are given and the ellipticities in the three colours are determined. It was found that there is no difference in the ellipticities depending on the colours, on the average. The percentage of spherical objects (ε = 0.00) was found to 21.5 per cent. The surface brightness for 213 objects in the system V is given. The mean surface brightness is 22.75 mag/□′ with a dispersion of 2.5 mag/□′. It shows only a very slight dependence on the integrated magnitude.     

Study of the galactic cluster NGC 6823

PhotoelectricUBV magnitudes have been determined for 41 stars in NGC 6823. The reddening across the cluster field is determined and found that it varies fromE(B-V)=0.60 to 1.16 mag. The true distance modulus to the cluster is estimated at 12.7±0.3 mag. It is found that cluster stars are not co-equal in age.     

A two-color CCD survey of the North Celestial Cap: I. The method

We describe technical aspects of an astrometric and photometric survey of the North Celestial Cap (NCC), from the Pole (δ=90°) to δ=80°, in support of the TAUVEX mission. This region, at galactic latitudes from ∼17° to ∼37°, has poor coverage in modern CCD-based surveys. The observations are performed with the Wise Observatory one-meter reflector and with a new mosaic CCD camera (LAIWO) that images in the Johnson–Cousins R and I bands a one-square-degree field with sub-arcsec pixels. The images are treated using IRAF and SExtractor to produce a final catalogue of sources. The astrometry, based on the USNO-A2.0 catalogue, is good to ∼1 arcsec and the photometry is good to ∼0.1 mag for point sources brighter than R=20.0 or I=19.1 mag. The limiting magnitudes of the survey, defined at photometric errors smaller than 0.15 mag, are 20.6 mag (R) and 19.6 (I). We separate stars from non-stellar objects based on the object shapes in the R and I bands, attempting to reproduce the SDSS star/galaxy dichotomy. The completeness test indicates that the catalogue is complete to the limiting magnitudes.     

Analysis of the light curve of the magnetic CP star HD 56022

An examination of the published observational data concerning the light curves of magnetic CP stars has shown that only one star — HD 56022 — shows a light curve with a very long phase interval of light constancy. Only for this type of variability it is imaginable that the equatorial symmetry of the surface brightness distribution could be excluded. However, the analysis of the light curve of HD 56022 in the colour u of the Strömgren system has indicated that the possibly equatorial position of the small bright spot is not in contradiction to this observed curve. From the analysis in u the maximum amplitude of a light curve at another wavelength, where the curve is in counterphase to the light curve in u, can be predicted. The amplitude of such a light curve must be much smaller than 0.1 mag. From unpublished observations of HD 56022 by the satellites TD-1 A and ANS we have determined the amplitude at $LD = 155 nm, where the light curve is in counterphase to that in u, to be 0.2 mag. The consequences from the contradiction between the model and the observations in UV are discussed.     

Recent photometry of symbiotic stars

We present new photometric observations of 15 symbiotic stars covering their last orbital cycle(s) from 2003.9 to 2007.2. We obtained our data by both classical photoelectric and CCD photometry. Main results are: EG And brightened by ∼0.3 mag in U from 2003. A ∼0.5 mag deep primary minimum developed in the U light curve (LC) at the end of 2006. ZAnd continues its recent activity that began during the 2000 autumn. A new small outburst started in summer of 2004 with a peak U magnitude of ∼ 9.2. During the spring of 2006 the star entered a massive outburst. It reached its historical maximum at U ∼ 8.0 in 2006 July. AEAra erupted in 2006 February with Δm_vis ∼ 1.2 mag. BF Cyg entered a new active stage in 2006 August. A brightness maximum (U ∼ 9.4) was measured during 2006 September. CH Cyg persists in a quiescent phase. During 2006 June–December a ∼ 2 mag decline in all colours was measured. CI Cyg started a new active phase during 2006 May–June. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoelectric light and colour variations in V471 Tauri

A new investigation of the variations in the light curves and in the period of the eclipsing binary V471 Tau is presented. The collected observational data have been re-examined and, in addition to old information, it was found that (i) the decrease in the period of the system slows down and (ii) that the mean brightness of the system has been increasing and this is greater at the longer wavelength. For the last seven years the increase in the brightness is estimated to be 0.15 mag inB and 0.18 mag inV bands respectively. Therefore, we conclude that the colour of the system is about 0.03 mag redder in 1980 than in 1973.     

The lightcurve of nova cygni 1975 (V 1500 Cyg) from the outburst to July 1977

On the basis of photoelectric observations performed at the Teramo Observatory, the V lightcurve of Nova Cygni 1975 from August 1975 to July 1977 is given. Since three days after maximum thereafter, the decline pursued smoothly according the law V = 2.5 + 3.9 lg t, and 680 days after maximum the star had weakened by 12.5 mag. The well-known shortperiod light variation, which at the time of the early decline showed an amplitude smaller than 0.2 mag in V light, on December 13, 1976, displayed an amplitude as high as 0.5 mag.     

Search for hard lags with intra‐night optical observations of BL Lacertae

It is generally believed that the high energy end of synchrotron emission, generated by the most energetic tail of relativistic electrons in the jets, account for the X‐ray emission of high‐energy peaked BL Lac objects (HBLs) and the optical emission of intermediate‐energy peaked BL Lac objects (IBLs). It is thus expected that both should show similar variability characteristics. One of the important variability parameters is the inter‐band time lag which probes the acceleration and cooling of relativistic particles responsible for the emission. The switches between soft and hard lags have been detected in the intra‐day X‐ray variability of a few HBLs, which is not the case for the intra‐day optical variability of IBLs yet. We present the results of our intra‐night optical observations for BL Lacertae, aiming at searching for hard lags of its optical variations, performed with the 80 cm telescope in fourteen nights of 2010 September‐November. Intra‐night changes of ∼0.2 mag were detected in most of nights. The intra‐night variability amplitude tends to become larger from red to blue wavelength, and the optical spectrum hardens with increasing brightness. The intra‐night variations correlate between different wavebands, but we did not find significant time lags, either soft or hard. Nevertheless, on November 2, the B band variations showed a sign of lagging the R band ones by 317±214 s. The claim of this hard lag is strongly limited by the photometric precision and time resolution. Therefore, the switches between soft and hard lags of IBLs in the optical bands needs further demonstration with more higher quality observations. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometric observations of the binary system V350 Lacertae

DifferentialUBV observations of the small amplitude (0.12 mag inV) single-lined active binary V350 Lac are presented. It was observed that the light minima occur in conjunction time. A shift of the light curve (0.05 in orbital phase) towards lower phases could be due to a small error in the light elements. The primary minimum is about 0.04 mag deeper than the secondary. It was shown that different depths of two light minima are not produced by the reflection effect but due primarily to gravity darkening on the tidally elongated and synchronously rotating visible component. An O'Connel effect observed as the brighter primary maximum could be an indication of starspot activity or gas streaming between the components.     

Binary statistics from Hipparcos data – a progress report

The Hipparcos data are an important source for constraining the statistical distribution functions for the binaries in the general field. The present study uses the resolved binaries (separation 0.1‐10 arcsec, magnitude‐differences below 4 mag) to check directly the frequency of main‐sequence binaries with (linear) separations 30‐500 a.u. and mass‐ratios 0.6‐1.0. Complete Hipparcos samples have limiting apparent magnitudes brighter than mag 8, and contain therefore rather few stars. By modelling the completeness using the Tycho observations (complete to mag 10), we may increase substantially the number of useable Hipparcos stars while keeping a tolerable level of systematic uncertainty. The results, for stellar masses not much above solar, show binary frequencies typically a factor two above those usually assumed. Also, although the mass‐ratio distribution function generally decreases towards larger q, there is a definite narrow peak at q = 1. In order to use the Hipparcos data to full advantage, a more indirect approach is necessary. By modelling both the local Galaxy and the Hipparcos observations, one may put constraints also on the number of closer binaries which show up in the Hipparcos Catalog as non‐linear proper motions.     

A colour-agnitude diagram of the Pisces dwarf galaxy

We present B, V and R band CCD images of the dwarf galaxy LGS-3 (Pisces dwarf). About 180 stars and diffuse objects were found and processed in these frames. The colour-magnitude diagram shows a prominent red giant branch and a few blue stars only. Details of the morphological properties and colour-agnitude diagram indicate to an intermediate (between dIrr and dSph) type of LGS-3. We estimate the galaxy distance modulus to be about (m - M)₀ = 23.9 ± 0.3 mag on the basis of the tip of the red giant branch. We measured the galaxy colour to be about B–V = 0.8 mag and the linear diameter 700 pc, which is the smallest one in the Local group.     

Variable stars in the globular cluster NGC 6362

We report the results of a CCD search for short-period variables in the field of a southern globular cluster NGC 6362. We identified 19 new candidate variables, five of which are cluster RR Lyraes, four are probable SX Phe-type stars and eight are eclipsing binaries. Of the discovered binaries, three are EA-type systems, two of which are located on the cluster CMD in the turn-off region and the third 1 mag above the turn-off point, in the yellow straggler region. Five other systems are of W UMa type, three of which are foreground objects and two are likely cluster members. The remaining two candidates exhibit a modulation of the brightness level with an amplitude of 0.1–0.2 mag; further observations are needed to reveal the nature of their variability. Phased VI light curves for 20 variables (18 RR Lyrae stars and two blue stragglers) located in the central region of the cluster are presented.