2 Observations

YY CMi was observed in the framework of a two-site campaign (European Southern Observatory, La Silla, Chile and Merate Observatory, Italy) devoted to the $\delta$ Scuti star BI CMi (Mantegazza & Poretti 1994). The 277 ESO observations cover 14 consecutive nights (from JD 2448280 to JD 2448293), while the Merate ones are distributed over 8 nights (from JD 2448273 to JD 2448291). We have observations from the two sites in the same night for 5 cases; since on these nights there is a partial superimposition of the observations for almost two hours, it was possible to get an excellent alignment between the two datasets. The individual V observations are given in Table 1 and the respective light curve is shown in Fig. 1.

  

Table 1: Individual V observations of YY CMi

 

Table 1: continued

We have performed differential photometry in the V band with respect to the two comparison stars HD 66925 and HD 67028; since the light variability of the $\delta$ Sct star BI CMi was faster than that of YY CMi, the latter was measured once every five cycles. The comparison of the differential magnitudes between the two comparison stars has shown, as expected, a different accuracy between the data gathered at La Silla and at Merate: the former have a mean standard deviation of 4.4 mmag for each measurement, against the 8.6 mmag for the latter (a value quite high due to unfavourable declination of the field with respect to the latitude of Merate Observatory). Moreover, Mantegazza & Poretti (1994) discussed the possible microvariability of HD 67028.

  

Figure 1: The individual V observations of YY CMi