A total of 48 times of minimum are collected in Table 5. We assigned different weights: 1, 2, and 10, for visual, photographic and photoeletric observations, respectively. A weight of 5 is given to the time of minimum derived from somewhat incomplete observations.
By the least squares method we obtain the following new linear
ephemeris:
From the photoelectric times of minimum a linear ephemeris
is derived as follows:
The O-C values of the times of minimum are calculated from
Eq. (1) and plotted in Fig. 1 (click here).
It was found that the period of HL Aur appears to be constant
over the past 65 years even though the visual and photographic observations
display large scatter in the 
diagram.
Figure 1: The 
diagram of the minimum times of HL Aur, the dots
represent visual or photographic observations and the small circles
represent photoelectric observations
Table 4: The light curve characteristics of HL Aur