In 1990 January and 1994 January-March, photoelectric observations were made with the 60 cm reflector and a single-channel photon-counting photometer at the Xinglong station of the Beijing Astronomical Observatory (BAO). Three primary and three secondary minima were observed in these two seasons. In 1994, a total of 129 observations in V and 122 in B were secured, covering well a full light curve.
The comparison and check stars were carefully chosen and a finding chart for them was published by Zhang et al. (1994). Table 1 (click here) presents the coordinates and UBV values of the comparison and check stars. All the observations were corrected for differential atmospheric extinction and transformed into the standard UBV system. In order to eliminate the probable influence caused by the colour difference between HL Aur and the comparison star used, secondary extinction coefficients were adopted in the data reduction. The probable errors for a single observation are estimated to be 0.008 mag in V and 0.010 in B, respectively.
Table 1: The coordinates and UBV values of the comparison and check stars
Table 2 (click here) lists our new determinations of the times of minimum by the K-W method. The differential magnitudes between the variable and comparison stars are given in Tables 3a and b. The characteristics of the light curves of this system are given in Table 4 (click here).
Table 2: New times of minima of HL Aur