3. The times of maximum and minimum light
Since it is important to derive the times of minimum or maximum light with a consistent method, we have derived moments of light extremum in the same way as applied by Sterken et al. (1987), viz. by fitting a polynomial of third degree over a time interval that is symmetric with respect to an eye-estimated time of extremum. All were calculated using data in a time interval of 60 days centered on the estimated maximum; the were calculated using a time interval of 120 days centered on the estimated minimum. The results are given in Tables 1 and 2. The difference in base time is necessary due to the presence of the hump on the rising branch of the light curve, so both intervals were chosen in such a way as to exclude any features belonging to the hump phase. As such, the number of data points at minimum often exceeds the number available at maximum, though in many cases the maxima are better covered. The number of available magnitudes and their quality (especially during minimum light) determine the accuracy of the calculated time of extremum. We estimate the times of minimum/maximum to be accurate within 0:d5-10 d.
Table 1. JD of maximum light and cycle number E.
Table 2. JD of minimum and cycle number E.
© European Southern Observatory (ESO) 1999
Online publication: December 22, 1998