We have conducted a variability survey of the Local Group galaxy M33, using g', r', and i' observations from 27 nights spanning 17 months, made with the MegaPrime/MegaCam instrument on the 3.6m CFHT telescope (Canada-France-Hawaii Telescope). We identify more than 36000 variable sources with g', r', i'<~24, out of approximately two million point sources in a 1-deg^2^ field of view. This increases the number of known variables in this galaxy by more than a factor of 20. In this paper, we provide a brief description of the data and a general overview of the variable star population which includes more than 1300 candidate variable blue and red supergiant stars, more than 2000 Cepheids, and more than 19000 long-period variable asymptotic giant branch and red giant branch stars.
We present VI-band photometry for stars in the metal-rich globular cluster NGC 6496. Our time-series data were cadenced to search for long-period variables (LPVs) over a span of nearly two years, and our variability search yielded the discovery of 13 new variable stars, of which 6 are LPVs, 2 are suspected LPVs, and 5 are short-period eclipsing binaries. An additional star was found in the ASAS database, and we clarify its type and period. We argue that all of the eclipsing binaries are field stars, while five to six of the LPVs are members of NGC 6496. We compare the period-luminosity distribution of these LPVs with those of LPVs in the Large Magellanic Cloud and 47 Tucanae, and with theoretical pulsation models. We also present a VI color-magnitude diagram, display the evolutionary states of the variables, and match isochrones to determine a reddening of E(B-V)=0.21+/-0.02mag and apparent distance modulus of 15.60+/-0.15mag.
Tables 11-50 contain V band light curves for 40 variables reported in the paper. Tables 51-53 and 54-56 contain VI photometry presented in Figs. 12 and 13, respectively.
Tables 1-30 contain V band light curves for 30 variables reported in the paper. Tables 31-33 and 34-36 contain VI photometry presented in Figs. 8 and 9, respectively.
The Kilodegree Extremely Little Telescope (KELT) project is a small aperture, wide-angle search for planetary transits of solar-type stars. In this paper, we present the results of a commissioning campaign with the KELT telescope to observe the open cluster Praesepe for 34 nights in early 2005. Light curves were obtained for 69337 stars, out of which we identify 58 long-period variables and 152 periodic variables. Sixteen of these are previously known as variable, yielding 194 newly discovered variable stars for which we provide properties and light curves. We also searched for planetary-like transits, finding four transit candidates. Follow-up observations indicate that two of the candidates are astrophysical false positives, with two candidates remaining as potential planetary transits.
We describe a survey for variable stars in the Sextans dwarf spheroidal (dSph) galaxy based on the analysis of 113 B and 48 V CCD images of four fields covering a total area of 18'x18'. We have identified 44 variables: 36 RR Lyr star, 6 anomalous Cepheids, one long-period red variable, all probable members of Sextans, and one foreground contact binary. We have used the pulsating stars to derive a true distance modulus of 19.67+/-0.15 for Sextans (or D=86+/-6kpc), where the error is primarily due to uncertainties in the luminosity-metallicity relation for RR Lyr stars. Based on our new data we conclude that [Fe/H]_Sex=-1.6+/-0.2, somewhat higher than the value from Suntzeff et al. (1993ApJ...418..208S) obtained from the analysis of fiber spectroscopy of the near-IR Calcium triplet. We present a new deep color-magnitude diagram for Sextans which reveals the presence of anomalous Cepheids in the galaxy. This young population may represent as much as 25% of the total stellar content of Sextans. We find a surprisingly strong correlation between the frequency of anomalous Cepheids in dSph galaxies and galaxian luminosity and speculate on the possible origin of this strange effect. The RR Lyr stars in Sextans do not exhibit the Oosterhoff dichotomy observed in globular clusters and in the Galactic halo field.
We present a multiyear survey aimed at collecting (1) high-precision (~5 milli-mag), (2) fast-cadence (~3-min), and (3) relatively long duration (~10d) multiband photometric series. The goal of the survey is to discover and characterize efficiently variable objects and exoplanetary transits in four fields containing five nearby open clusters spanning a broad range of ages. More in detail, our project will (1) constitute a preparatory survey for the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) mounted at the Telescopio Nazionale Galileo (TNG), which will be used for spectroscopic follow-up of any target of interest that this survey discovers or characterizes, (2) measure rotational periods and estimate the activity level of targets we are already monitoring with HARPS and HARPS-N for exoplanet transit search, and (3) long-term characterization of selected targets of interest in open clusters within the planned K2 fields. In this first paper, we give an overview of the project, and report on the variability of objects within the first of our selected fields, which contains two open clusters: M35 and NGC 2158. We detect 519 variable objects, 273 of which are new discoveries, while the periods of most of the previously known variables are considerably improved.
We present time-series CCD photometry of a field in the newly discovered dwarf spheroidal galaxy in Sagittarius (hereafter Sgr), and of a nearby control field. These data, which consist of VI images obtained during the 1994 OGLE season, were used to identify and study variable stars in both fields. We discovered ten variable stars in the Sgr field, nine of which have light curves and periods consistent with RR Lyr stars or anomalous Cepheids. The control field contains four short-period contact eclipsing binaries, but no pulsating variables. The variables in the Sgr field include a bright RR Lyr star that is almost certainly located in front of Sgr in the galactic bulge, a short-period contact binary located near or within Sgr, and a short-period pulsating star that may either be a foreground halo RR Lyr star or an anomalous Cepheid within Sgr. The seven remaining variables in the Sgr field are RR Lyr stars with very similar mean apparent magnitudes; we conclude that they are members of Sgr. We estimate the total number of RR Lyr stars in Sgr to be 1930+/-730 if M(V,Sgr)=-13, or 310+/-120 if M(V,Sgr)=-11. The frequency of pulsating variables in Sgr is consistent with earlier conclusions that the galaxy consists of a predominant old (age>~10Gyr) population.
Differential time series photometry has been derived for 46,422 main-sequence stars in the core of 47 Tucanae. The observations consisted of near-continuous 160 s exposures alternating between the F555W and F814W filters for 8.3 days in 1999 July with the Wide Field Planetary Camera 2 on the Hubble Space Telescope. Using Fourier and other search methods, 11 detached eclipsing binaries and 15 W Ursa Majoris stars have been discovered plus an additional 10 contact or near-contact noneclipsing systems. After correction for nonuniform area coverage of the survey, the observed frequencies of detached eclipsing binaries and W UMa stars within 90" of the cluster center are 0.022% and 0.031%, respectively. The data were taken over an 8.3 day period, 1999 July 3-11, during which HST was pointed continuously at 47 Tuc.
Repeated imaging observations have been made of NGC 4527 with the Hubble Space Telescope between 1999 April and June, over an interval of 69 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the Type Ia supernova SN 1991T, which showed relatively unusual behaviour by having both an abnormal spectrum near light maximum, and a slower declining light curve than the prototypical Branch-normal SNe Ia. A total of 86 variables that are putative Cepheids have been found, with periods ranging from 7.4 days to over 70 days.
