Determination of the rotation periods for the roAp stars HD 9289 and HD 190290 and non-detection of rotational amplitude modulation in the roAp stars HD 75425 and HD 217522




We present differential photometric observations of four rapidly oscillating Ap stars to determine their rotation periods. Based on 55 observations (over four seasons) of HD 9289, it was found to rotate with a period of 8.55 ± 0.08 d. Similarly, 21 observations in one season were used to determine the rotation period of HD 190290 (4.03 ± 0.13 d). Differential photometry of HD 75425 (50 observations over three consecutive seasons) showed that it exhibits no photometric variability above 4 mmag. Differential photometry of HD 217522 (60 observations over three seasons) revealed no periodic photometric variability greater than 6 mmag.