Photoelectric photometry in B and V bands for YY Eri was conducted over four nights in November, 1984, with the 35-cm Cassegrain reflector of the Yunnan Observatory in China. A 1p21 photomultiplier was used in the observations. The two filters employed were the following: a Corning 5030 of stock thickness cemented with 2 mm Schott GG-13 for the blue region, and a Corning 3389 of Stock thickness for the yellow region. A circular diaphragm of 30'' was used thoughout, and an integration time of 20 seconds for both stars and sky was chosen.
BD and BD
were chosen as comparison star
and check star, respectively, and measured alternatively between the
observations of the binary. Nightly extinction coefficients were
determined from observations of the comparison star, and the differential
extinction correction were made. The observations were transformed into
the UBV system with the aid of six standard stars in the Pleiades during
the period of observations. The magnitude differences between the check
star and the comparison star were constant within probable errors of
mag(V) and
mag(B) during the observations.
From the observations, three times of primary minimum light and two times of secondary minimum light were derived by means of polynomial fitting and are listed in Table 1. Because of the complexities in the orbital period change of YY Eri, to combine the observations, we have adopted the light ephemeris found by least square method from the minima in the Table 1 and the minima published by Marco et al. (1993) as follows:
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