AAS 206th Meeting, 29 May - 2 June 2005
Session 41 Variable Stars
Poster, Wednesday, 10:00am-7:00pm, Thursday, 9:20am-2:00pm, June 1, 2005, Ballroom A

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[41.06] A Technique to Search for Rapid Variations in Stellar Flux

J.A. Wilkerson, T.S. Brown, K.A. Frank, B.K. Lacoul, A.O. Nugent (Luther College)

We have tested a technique for stellar photometry utilizing modest equipment at a deep atmosphere site. We acquire thousands of unfiltered images, typically a few seconds in duration, of a star-rich field each night. Star flux measurements are normalized frame-to-frame using mean or median values of star flux determined from the entire field. Histograms of each star's measured flux values are fit with Gaussian curves. Individual large flux deviations might arise from occultation or gravitational microlensing events. The flux resolution of our system, defined as the standard deviation divided by the mean of our Gaussian fit, provides a useful measure of photometric quality. Using more than 100,000 images of fields containing the open clusters M21, M23, M26, M67 and NGC 129, we have determined that air mass is the primary factor limiting our bright-star flux resolution and have measured flux resolution limits ranging from about .020 for stars at altitudes below 20 to about .005 for stars at altitudes above 75. To date we have made more than 50 million individual star flux determinations. We present the details of our photometric tests and the application of our technique to searches for previously undetected populations of objects. Our flux resolution limits can be enhanced by the summing of successive images. At high altitudes our resolution limits without such summing already suggest a possible sensitivity to extra-solar planet transits and we are initiating a search of our data for indications of such transits. Finally, we have performed initial tests of the utility of our data for use in searches for classical variability in stars. A preliminary study of the field containing NGC 129 revealed evidence of periodic or pseudo-periodic variability in seven stars. We are grateful for support from the Roy J. Carver Charitable Trust and the Iowa College Foundation.

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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.