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.
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 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.
AST3-1 is the second-generation wide-field optical photometric telescope dedicated to time-domain astronomy at Dome A, Antarctica. Here, we present the results of an i-band images survey from AST3-1 toward one Galactic disk field. Based on time-series photometry of 92583 stars, 560 variable stars were detected with i magnitude {<=}16.5mag during eight days of observations; 339 of these are previously unknown variables. We tentatively classify the 560 variables as 285 eclipsing binaries (EW, EB, and EA), 27 pulsating variable stars ({delta} Scuti, {gamma} Doradus, {delta} Cephei variable, and RR Lyrae stars), and 248 other types of variables (unclassified periodic, multiperiodic, and aperiodic variable stars). Of the eclipsing binaries, 34 show O'Connell effects. One of the aperiodic variables shows a plateau light curve and another variable shows a secondary maximum after peak brightness. We also detected a complex binary system with an RS CVn-like light-curve morphology; this object is being followed-up spectroscopically using the Gemini South telescope.
Time-series photometry of the CoRoT field SRa01 was carried out with the Berlin Exoplanet Search Telescope II in 2008/2009. A total of 1161 variable stars were detected, of which 241 were previously known and 920 are newly found. Several new, variable young stellar objects have been discovered. The study of the spatial distribution of eclipsing binaries revealed the higher relative frequency of Algols toward the center of the young open cluster NGC 2264. In general Algol frequency obeys an isotropic distribution of their angular momentum vectors, except inside the cluster, where a specific orientation of the inclinations is the case. We suggest that we see the orbital plane of the binaries almost edge-on.
We present the results of variable star searches of the M31 dwarf spheroidal (dSph) companions Andromeda I and Andromeda III using the Hubble Space Telescope. A total of 100 variable stars were found in And I, while 56 were found in And III. One variable found in And I and another in And III may be type II Cepheids. In addition to this variable in And III, another four variables are anomalous Cepheids (ACs). So far, no definite ACs have been discovered in And I.
We have surveyed Andromeda VI, a dwarf spheroidal galaxy companion to M31, for variable stars by using F450W and F555W observations obtained with the Hubble Space Telescope on 1999 October 25 and 1999 October 27 (WFPC2 instrument). A total of 118 variables were found, including 111 RR Lyrae stars, six anomalous Cepheids, and one variable that we were unable to classify. We find that the Andromeda VI anomalous Cepheids have properties consistent with those of anomalous Cepheids in other dwarf spheroidal galaxies. We revise the existing period-luminosity relations for these variables. Further, using these and other available data, we show that there is no clear difference between fundamental and first-overtone anomalous Cepheids in a period-amplitude diagram at shorter periods, unlike the RR Lyrae stars. For the Andromeda VI RR Lyrae stars, we find that they lie close to the Oosterhoff type I Galactic globular clusters in the period-amplitude diagram, although the mean period of the RRab stars, <P_ab_>=0.588days, is slightly longer than that of the typical Oosterhoff type I cluster. The mean V magnitude of the RR Lyrae stars in Andromeda VI is 25.29+/-0.03, resulting in a distance 815+/-25kpc on the Lee, Demarque, & Zinn (1990ApJ...350..155L) distance scale. This is consistent with the distance derived from the I magnitude of the tip of the red giant branch. Similarly, the properties of the RR Lyrae stars indicate a mean abundance for Andromeda VI that is consistent with that derived from the mean red giant branch color.
We present a catalog of photometrically variable stars discovered within two 21.3'x21.3' fields centered on the Cygnus OB2 association (Cyg OB2). There have hitherto been no deep optical variability studies of Cyg OB2, despite it being replete with early-type massive stars, likely due to the high and variable extinction (up to A_V_~20) that permeates much of the region. Here, we provide results of the first variability study with this combination of spatial coverage (~0.5deg) and photometric depth (R~21mag). We find 121 stars to be variable in both R and I bands, 115 of them newly discovered. Of the 121 variables, we identify 27 eclipsing binaries and eclipsing-binary candidates, 52 pulsating variables, and 20 potential Herbig Ae/Be stars. Confirming both the status and the cluster membership of the Herbig Ae/Be stars would address the uncertainty regarding the age and star formation history of Cyg OB2. We match our catalog to known variables and binaries in the region, Two Micron All Sky Survey near-IR data, and Chandra X-ray observations to find counterparts to new variables in other wavelengths.
We present a new study of the variable star population in globular cluster 5 of the Fornax dSph, based on B and V time series photometry obtained with the MagIC camera of the 6.5m Magellan Clay telescope and complementary Hubble Space Telescope archive data. Light curves and accurate periodicities were obtained for 30 RR Lyrae stars and one SX Phoenicis variable. The RR Lyrae sample includes 15 fundamental-mode pulsators, 13 first-overtone pulsators, one candidate double-mode pulsator and one RR Lyrae star with uncertain type classification. The average and minimum periods of the ab-type RR Lyrae stars, <P_ab_>=0.590days, P_ab,min_=0.53297days and the position in the horizontal branch type-metallicity plane, indicate that the cluster has Oosterhoff-intermediate properties, basically confirming previous indications by Mackey & Gilmore, although with some differences both in the period and type classification of individual variables.
