CY AQR is a delta Scutii type star with an 88 minute period of variability. For more details see
Doug Welch's page. . The following light curve was taken the night of 20 September 1998 (UT) from St. Louis, Missouri using an 8-in Celestron Ultima 2000 in Alt-Az mode and a SBIG ST-7 CCD camera with an Optec MaxField 0.33 focal reducer. The field was located using the RA-DEC mode of the telescope after two star alignment. The scope was left to track while the camera was commanded to take one-minute exposures every 5 minutes using the auto-dark mode (i.e., an initial one-minute dark exposure was subtracted from each image). Data taking continued for about 1 1/2 hours until clouds rolled in. The images were reduced by measuring the instrumental magnitudes of the variable and two reference stars - one a little brighter and one a little dimmer than the variable. The cross-hair function of CCDOPS with an 11x11 box size was used to determine the instrumental magnitude. The sky background was sampled at 4 locations around each star and the average value of the four measurements was taken as the value to use. With this data in hand, the change in the variable was calculated from the formula 0.5*(C1 + C2) - V where C1 and C2 are the comparison values and V is the value for the variable. This calculation smoothes any variations between the comparison stars and shows a brightening as a positive change and a dimming as a negative change. To check the comparison stars, the difference C1 - C2 was also taken. The RMS error in the C1-C2 measurements was 0.01 magnitude.
On the night of 26-27 September 1998, Wayne and I were able to get another, much longer, set
of measurements covering three complete cycles of the star. This time we took
data at two minute intervals so our resolution of the light curve is more detailed.
Below is the data curve processed as before.
The General Catalog of Variable Stars lists and Epoch of 34308.4314 and a period of
0.061038328 days for CY Aqr. Assuming the epoch is for the maximum point of the light
curve, I calculate there have been some 274,718 cycles of CY Aqr between the epoch of
the GCVS and the first of the maxima noted above. This would indicate the period derived
from our measurements is within 0.002 seconds of the period value given in the GCVS! Even so,
this difference adds up to nearly 10 minutes over that long span. Using the GCVS period,
we can combine the four sets of data into a composite light curve as shown below.
