Publications (3)3.58 Total impact
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Article: A Search for Variable Stars and Planetary Occultations in NGC 2301 II: Variability
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ABSTRACT: We performed R-band time series observations of the young, metal rich open cluster NGC 2301 for 12 nights in Feb. 2004. B images were also obtained and color magnitude diagrams, having limits of R=19.5 and B=21.5, were produced. Only asmall effort was made to determine cluster membership as our magnitude limits are far deeper than previously published values. Our photometric precision, for the brightest 5 magnitudes of sources, is 1-2 mmag. We determine that for the $\sim$4000 stars which have time-series data, 56% are variable and of these, approximately 13% are observed to exhibit periodic light curves ranging from tens of minutes to days. We present some examples of the light curves obtained and produce cuts in variability space based on parameters such as color and amplitude. The percentage of variability is approximately equal across all colors with the majority of variables having amplitudes of 0.15 magnitudes or less. In general, redder stars show larger variability amplitudes. We find a smooth decline in the number of periodic variables toward longer period. This decline is probably due to a transition from intrinsic to extrinsic variability and, in part, to our limited observing period of 12 nights. Essentially all the A and F main sequence stars in our sample are variable ($\sim$2 mmag and larger) and most present complex light curves containing multiple periods suggestive of their inclusion in the $\delta$Sct and $\gamma$Dor classes. A variable non-cluster member giant and two variable white dwarf candidates are discussed. Our equational description of variability is shown to be an excellent predictive tool for determining the cumulative fraction of variables that will be observed in a photometric survey. Our entire dataset is available electronically. Comment: 25 pages, 21 figures Accepted to PASP09/2005; -
Article: A Search for Variable Stars and Planetary Occultations in NGC2301 I: Techniques
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ABSTRACT: We observed the young open cluster NGC 2301 for 14 nights in Feb. 2004 using the orthogonal transfer CCD camera (OPTIC). We used PSF shaping techniques ("square stars") during the observations allowing a larger dynamic range (4.5 magnitudes) of high photometric precision results ($\le$2 mmag) to be obtained. These results are better than similar observing campaigns using standard CCD imagers. This paper discusses our observational techniques and presents initial results for the variability statistics found in NGC 2301. Details of the variability statistics as functions of color, variability type, stellar type, and cluster location will appear in paper II.01/2005; -
Article: Photometric Observations Using Orthogonal Transfer CCDs
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ABSTRACT: Orthogonal transfer CCDs (OTCCDs) were developed to compensate for real-time image motion, essentially providing tip/tilt corrections without additional optics or moving parts. Because of the complex gate structures of OTCCDs, their ability to provide high-precision photometric observations and their use as high-speed photometers were unclear. We detail new observations obtained with the OPTIC camera at the University of Hawaii's 2.2 m telescope on Mauna Kea that explore both of these areas. We find that OTCCDs provide equally good results in terms of typical time-series differential photometry (compared with typical CCDs) and that their high-speed photometric application is superb. Using point-spread function-shaping techniques, we obtained time-series photometric observations with precisions of <~660 μmag per 180 s integration. Extending this technique to very bright stars, the potential to reach differential precisions near 10-5 per exposure is investigated.Publications of the Astronomical Society of the Pacific 10/2003; 115:1340-1350. · 3.58 Impact Factor
