The present observations were carried out at the European Southern Observatory
(La Silla, Chile) over the periods
7-17 September and 30 September - 10 October
1990, by using the 0.5 m and the 1.0 m ESO telescopes, respectively.
Both instruments were equipped with a single-channel
photon-counting photometer, a thermoelectrically cooled Hamamatzu R-943/02
photomultiplier and standard ESO filters matching the 
system.
In order to obtain accurate differential photometry, for each program star (v)
a comparison (c) and a check (ck) star were also observed (see Table 1 (click here)).
Each measurement consisted in the average of 10-15 1-sec. integrations in each filter, according to the color sequence U-B-V-R-I. A complete observation consisted
Figure 2: V-band light curve and colors of
HD 8435 = BC Phe. Phases are reckoned from the photometric ephemeris
(Cutispoto 1995)
Table 2: Mean atmospheric extinction coefficients for La Silla site,
obtained over the period 7 Sep. - 10 Oct. 1990
Figure 3: V light long-term variability of HD 8435 = BC Phe.
The vertical bars indicate the peak-to-peak amplitude of the light curve
in sequential c-v-v-v-v-ck-c
measurements. From
these data, four v-c and one ck-c
differential magnitudes were computed; the four v-c values were
finally averaged to obtain one data point. The observations were
corrected for atmospheric extinction and transformed into the
standard 
system. The atmospheric extinction
coefficients were obtained during clear nights by observing two
standards of very different spectral type in the 1-2.5 air mass
range, while transformation coefficients were inferred by
observing E-region standard stars (Menzies et al.
1989). The mean values of the extinction coefficients for
La Silla are reported in Table 2 (click here). Note that these values
have been obtained less than one year before the eruption of Mt.
Pinatubo (June 1991). The typical error of our differential
photometry is of the order of 0.005 magnitudes, with somewhat
larger values (up to 0.01 magnitudes) in the U-band for the
observations with the 0.5 m telescope due to the low photon
counting level. The brighest V magnitude and corresponding
colors obtained for the program stars, and the standard deviations
(
) for the v-c and ck-c mean differential V-band
magnitudes obtained over N nights are reported in Table
3 (click here). The V magnitudes and colors of the comparison
and check stars were obtained via standard stars (Landolt
1983; Menzies et al. 1989; Menzies &
Laing 1988) and are given in Table 4 (click here). Taking
into account the accuracy of the standard stars data and the
extinction and transformation errors, the typical accuracy of the
absolute photometry in Table 3 (click here) is of the order of 0.01
magnitude, with somewhat larger values (up to 0.02 magnitudes) for the U-B color.