Equipment and Procedure: A Meade 10" LX 200 Schmidt Cassegrain telescope was used with an SBIG ST-7xe CCD. The CCD consists of two chips; the main imager is a Kodak KAF401e array of 750 x 510 9 nm pixels. A separate guiding chip is positioned beside the main chip. An f3.3 focal reducer was placed in front of the camera to create a focal length of 825 mm @ f3.3 for the system. The resulting field of view with the ST-7xe camera was 20 x 30 arc minutes. The CCD was equipped with a filter wheel holding Bessel BVRI standardized photometric filters, with the majority of the data collected in the I-band. The software Maxim DL was used for camera control, image calibration, and photometry. The open-source software Munidos (Hroch 2001) was used with the additional open-source programs Readall and Varfind to search the images for variable stars (Kral 2003). The programs were grouped using MS DOS batch files, allowing the data-reduction process to be somewhat automated. Period 98 was used to perform Fourier analysis on the data (Sperl 1998).

Images were collected using the following method. The telescope was pointed at a bright star, and the CCD was focused. Then the telescope was pointed at the target field and a guide star was acquired. The guide chip was set up with Maxim DL to image once a second and issue tracking corrections to the telescope. The main CCD chip was set to take a series of exposures of 1-2 minutes separated by one minute. This allowed for 20-30 images per hour. Images of the twilight sky were also taken. These "flat frames" were used later when calibrating the raw images to correct for uneven illumination of the CCD chip. Dark frames, or images of the camera's internal noise, were also taken. These were later subtracted out of the raw images to reduce noise in the final image.

These images were analyzed in two steps, using the Munidos suite (comprised of Munidos, Readall, and Varfind) and Maxim DL. The series of images of one cluster were all placed into one folder. They were then calibrated using flat and dark frames. Next, the images were fed into an MS DOS batch file that was created to use Munidos to measure the brightness of all of the stars in each frame. The Readall routine was then recruited to sort the data and match the star names between images. Finally, Varfind was employed to compute the average magnitude of each star, and the standard deviation of that star's data. The magnitude vs. standard deviation data was then exported into Excel, where it was plotted. The resulting graph forms a well-defined "error curve" based on the signal-to-noise ratio of the stars in the image (Data Section, Figure 1). Outliers from this curve were identified as potential variable stars.

Once the candidate stars were identified, they were investigated further with Maxim DL. The light curve of each star was plotted using differential photometry, a technique in which the brightness of the variable star is compared to the brightness of several constant comparison stars in each image. Most of the stars with high data scatter are not truly variable but only appear to vary because of interference from nearby stars. These can be sorted out by inspecting the images and the light curves. The data for the stars that are truly variable were then saved and plotted in Excel.