observations of the eclipsing binary ZZ UMa have been carried out
during eight campaigns at Calar Alto Observatory, (Almeria, Spain).
The 1.5 m telescope operated by the Spanish Observatorio Astronómico
Nacional was used, equipped with a mono-channel photometer or with a
four-channel photometer both using Strömgren u, v, b, y filters
as well as Crawford's narrow and wide filters centred on the H
line.
All the measurements were made within the framework of a photometric
observational program of late-type eclipsing binaries.
The poor atmospheric conditions in many of the observing campaigns made
it necessary to observe ZZ UMa during eight campaigns to obtain the light
curves (294 points) which were covered in average twice. Table 1 (click here)
lists the dates of the observing campaigns, the photometer used and the amount
of useful observing time.
Nightly extinction coefficients were calculated for each night, using an adequate sample of standard stars observed at least three times at an air mass range from 1 to 2. Following the procedure described by Grönbech et al. (1976), we determined the night corrections L(n) for each observing period in order to obtain the magnitudes in the instrumental system. Together with the program objects we observed a selected set of standard stars from the list of Perry et al. (1987), and Olsen (1991) in order to transform the measurements into the standard Strömgren and Crawford's systems.
HD 15242 and HD 15251 were observed as comparison and check stars respectively
for differential photometry, both being of similar spectral type and
apparent magnitude as ZZ UMa.
The constancy of the comparison was checked every night. The differences
(HD 15242 -
HD 15251) for consecutive measurements were calculated
and the internal rms errors for the 135 points obtained were 0.004, 0.004, 0.012,
0.018 and 0.016 expressed in magnitudes for V, (b-y), m1, c1,
and respectively. This accuracy is of the same order as that obtained
for main-program stars. So, we can conclude that the comparison had constant
flux during the observing periods.
Differential measurements in the standard system for ZZ UMa, with respect to
HD15242 were calculated. Figure 3 (click here) shows the differential light
curve of ZZ UMa in the y filter. Tables with these first light
curves have been given in Paper I.
A more detailed description of the observations, the reduction of the data, and an estimation of the accuracy of the photometry can be found in Paper I as well.
| first night | last night | photometer | % useful time |
| 13/03/90 | 25/03/90 | monochannel | 20% |
| 02/01/91 | 15/01/91 | monochannel | 23% |
| 17/01/92 | 27/01/92 | multichannel | 47% |
| 25/01/93 | 31/01/93 | multichannel | 17% |
| 04/04/94 | 14/04/94 | monochannel | 21% |
| 02/06/95 | 12/06/95 | monochannel | 20% |
| 22/11/95 | 02/12/95 | multichannel | 18% |
| 15/05/96 | 25/05/96 | monochannel | 3% |