Abstract. -We report results of photometric monitoring of the NGC 2243 field in V and I filters. Two W UMatype systems and three detached eclipsing binaries were discovered. Both contact systems are likely members of the cluster. One of the detached binaries -variable V1 -has a period P=1.188 day. This variable is located at the cluster's turnoff in the color-magnitude diagram. Determination of parameters for components of V1 can provide direct information about properties of turnoff stars in NGC 2243 as well as to allow direct determination of cluster's distance. A background RR Lyr variable was found in the monitored field. The reddening of NGC 2243 is estimated at E(V − I) = 0.10 ± 0.04 based on the V −I color exhibited by this star at minimum light. The observed distribution of colors for the background halo stars shows a cutoff at (V − I) ≈ 0.60 what implies E(V − I) ≤ 0.12 for the cluster.
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.
We present the results of a search for dwarf novae (DNe) in globular clusters (GCs). It is based on the largest available homogeneous sample of observations, in terms of the time‐span, number of observations and number of clusters. It includes 16 Galactic GCs and yielded two new certain DNe: M55‐CV1 and M22‐CV2. All previously known systems located in our fields were recovered, too. We surveyed M4, M5, M10, M12, M22, M30, M55, NGC 288, NGC 362, NGC 2808, NGC 3201, NGC 4372, NGC 6362, NGC 6752, ω Centauri (NGC 5139) and 47 Tucanae (NGC 104). The discovery of two DNe, namely M55‐CV1 and M22‐CV2, was already reported by Kaluzny et al. and Pietrukowicz et al., respectively. In the remaining 14 GCs, we found no certain new DNe. Our result raises the total number of known DNe in the Galactic GCs to 12 DNe, distributed among seven clusters. Our survey recovered all three already known erupting cataclysmic variables (CVs) located in our fields, namely M5‐V101, M22‐CV1, and V4 in the foreground of M30. To assess the efficiency of the survey, we analysed images with inserted artificial stars mimicking outbursts of the prototype DNe SS Cygni and U Geminorum. Depending on the conditions, we recovered between 16–100 per cent of these artificial stars. The efficiency seems to be predominantly affected by duty cycle/time‐sampling and much less by distance/magnitude. Except for saturated tiny collapsed cores of M30, NGC 362 and NGC 6752 (and also the dense core of NGC 2808), crowding effects in the V band were avoided by our image subtraction technique augmented with auxiliary unsaturated B‐band images. Our results clearly demonstrate that in GCs common types of DNe are very rare indeed. However, great care must be taken before these conclusions can be extended to the CV population in GCs.
We use photometric and spectroscopic observations of the detached eclipsing binaries V40 and V41 in the globular cluster NGC 6362 to derive masses, radii, and luminosities of the component stars. The orbital periods of these systems are 5.30 and 17.89 d, respectively. The measured masses of the primary and secondary components (M p , M s ) are (0.8337±0.0063, 0.7947±0.0048) M ⊙ for V40 and (0.8215±0.0058, 0.7280±0.0047) M ⊙ for V41. The measured radii (R p , R s ) are (1.3253±0.0075, 0.997±0.013) R ⊙ for V40 and (1.0739±0.0048, 0.7307±0.0046) R ⊙ for V41. Based on the derived luminosities, we find that the distance modulus of the cluster is 14.74±0.04 mag -in good agreement with 14.72 mag obtained from CMD fitting. We compare the absolute parameters of component stars with theoretical isochrones in mass-radius and mass-luminosity diagrams. For assumed abundances [Fe/H] = -1.07, [α/Fe] = 0.4, and Y = 0.25 we find the most probable age of V40 to be 11.7±0.2 Gyr, compatible with the age of the cluster derived from CMD fitting (12.5±0.5 Gyr). V41 seems to be markedly younger than V40. If independently confirmed, this result will suggest that V41 belongs to the younger of the two stellar populations recently discovered in NGC 6362. The orbits of both systems are eccentric. Given the orbital period and age of V40, its orbit should have been tidally circularized some ∼7 Gyr ago. The observed eccentricity is most likely the result of a relatively recent close stellar encounter. : individual (NGC 6362) -stars: individual (V40 NGC 6362, V41 NGC 6362) * This paper includes data gathered with the 6.5-m Magellan Baade and Clay Telescopes, and the 2.5-m du Pont Telescope located at Las Campanas Observatory, Chile.
BV photometry is presented for 12 RR Lyr variables discovered in the presumably young galactic globular cluster Ruprecht 106. All variables are type RRab, and their periods span a narrow range from 0.574 to 0.652 day. We report also on the discovery of 3 SX Phe variables among the cluster blue stragglers. A likely background RR Lyr variable and two foreground contact binaries were also found in the cluster eld. The reddening of Ruprecht 106 is estimated at E(B V ) = 0:20 based on the (B-V) colors exhibited by the cluster RR Lyr variables at minimum light. Analysis of the period" versus \amplitude" and \period" versus \rise-time" diagrams suggests similar metallicities of Ruprecht 106 and M3. A peak (or bump) is present in the luminosity function of the red giant branch of Ru 106. Its position relative to the horizontal branch is consistent with a cluster metallicity of Fe=H] 1:6.
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