A SEARCH FOR LOW-AMPLITUDE VARIABILITY IN SIX OPEN CLUSTERS USING THE ROBUST MEDIAN STATISTIC

We used point-spread function fitting and a differential ensemble determined from a robust median statistic (RoMS) to examine stars in six open clusters in a search for δ Scuti variables. In the search for new variable stars among hundreds or thousands of stars, the RoMS is proved more effective for finding low-amplitude variables than the traditional error-curve approach. This high-precision differential approach was applied to the open clusters NGC 225, NGC 559, NGC 6811, NGC 6940, NGC 7142, and NGC 7160. Thirteen variables, 29 suspected variables, and 65 potential variables were found, and time-series data of the variables are presented. Among the 13 variables we found nine new δ Scuti variables.