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2. Observations and data reduction

The target stars observed in the present program were selected among the objects classified as L, L:, I, I:, IS and IS: in the General Catalogue of Variable Stars-GCVS (Kukarkin et al. 1969 and later supplements; Kholopov et al. 1985, 1987) and in the New Catalogue of Suspected Variable Stars-NSV (Kukarkin et al. 1982). Objects with tex2html_wrap_inline640<+10tex2html_wrap_inline646 were chosen.

The observations were carried out from 1985 to 1994 with the 0.6-m Zeiss and 1.6-m Boller & Chivens telescopes of the Laboratório Nacional de Astrofísica (LNA/CNPq), in southeast Brazil. The FOTEX and FOTRAP photometers were used. The former is a conventional one channel UBV photometer equipped with a thermoelectrically cooled EMI 9789QA photomultiplier operating in the photon counting mode, while the second photometer uses a high-speed (1200 rpm) rotating filter wheel which allows quasi-simultaneous photometry in the tex2html_wrap_inline650 bands. The detector used in this case is a thermoelectrically cooled Hamamatsu R943-02 photomultiplier.

Integration times of 5 to 20 s (depending on the brightness of the star) were used with the FOTEX photometer. Usually, 5 readings on the star and 5 on the sky were done with diaphragms of 19tex2html_wrap_inline652 and 12tex2html_wrap_inline654 in diameter for the 0.6-m and 1.6-m telescopes, respectively. In the FOTRAP photometer the integration time can be set by selecting the number of rotation cycles of filter wheel (normally 50 cycles, providing 19.8 s of integration per filter) or by setting a threshold to the observational error, normally 0.5tex2html_wrap_inline656 in the worst case, usually the U filter. Diaphragms of the same size as used in the FOTEX were also used in this photometer.

Photometric sequences of standard stars from Landolt (1973) or Graham (1982) were observed each night in order to correct for the effects of atmospheric extinction and to transform the observations to the standard systems. For a few nights in which we did not have calibration sequences we used transformation coefficients determined in the same mission being, in most cases, calibrations from previous or subsequent nights. The procedures that we used for the reduction of the data are those described in Jablonski et al. (1994). This reference also contain a detailed description of the FOTRAP photometer and the photometric system.

Observations in the U filter with the FOTEX photometer were made, preferentially, for stars bluer than B-V = 1.4 and for some of the brightest red stars. For many of the blue and bluish objects more than one measurement was done. In this case, we are interested in search for variabilities with time scales from several hours to few days.

The tex2html_wrap_inline664 data obtained are shown in Cols. 3 to 7 in Table 1 (this table is only available in electronic form, see footnote at the beginning of the paper). The associated uncertainties (Cols. 8 to 12) take into account the errors due to photon noise in the measurements and errors associated with the transformation to standard system. Column 2 shows the time of the middle of the observation in heliocentric Julian day. y


We are grateful to the LNA staff for the observing assistance during the missions. We also thank the referee, R. Viotti, for his valuable comments and suggestions. D. Cieslinski acknowledges the support of CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo), under grants 140587/89-6 and 85/1383-9.

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