3 The period of the system from the times of minima

The present observations, obtained at Merate Observatory and ESO, were used to calculate new times of minima by using Kwee & Van Woerden (KW) method. The new minima times are given in Table 2. The successive columns give the HJD of minimum, the error, the number of cycles E, the $\rm (O - C)$ values and the type of minimum (I: primary, II: secondary). A least-squares solution, applied to all minima listed in Table 2, yields the following ephemeris which has been used for the calculation of $\rm O - C$ values.

The $\rm O - C$ behaviour for all the existing minima times, computed by using the above ephemeris, is shown in Fig. 2. The existing data are not enough to draw definite conclusions about the variation of the period. The GCSV, IV ed., (Kholopov et al. 1985) gives a period 1.0940197 d. This period was calculated by Abhyankar (1962) using well determined minima times over a period of 24 years. Our new ephemeris, based on the present observations, suggests a shorter period.

  

Table 2: New times of minima of YY CMi

  

Figure 2: The $\rm O - C$ diagram of YY CMi