The photoelectric observations were collected at two sites, with different telescopes and equipment: the ZEISS 60cm telescope of PDO-LNA-CNPq with a single-channel TEXAS photometer and the Danish 50cm telescope (SAT) at ESO with a 6-channel photometer. Although the uvby photometric system was used in all runs, it is natural to expect differences between the two sets of data, caused by differences in the equipment (e.g. filter transmission) and in the site properties (altitude and humidity).
During 35 nights (10 from Jun. 16 to Aug. 17, 1989, 9 from Jul. 30 to Aug. 15, 1990, 16 from May 23 to Jun. 18, 1991) V 3903Sgr was observed at PDO (LNA-CNPq, Brasópolis, Brazil), with the 60 cm telescope and a single-channel photometer equipped with a photon counting system. A slightly elliptical diaphragm with major axis was used (Cunha 1990). No other star was detected inside this diaphragm with an image intensifier placed at the eyepiece, despite the richness of the field close to V 3903Sgr.
Extinction corrections were based on the nightly coefficients from the four comparison stars and other constant stars. When needed, linear or quadratic corrections were applied for eventual instrumental drifts, since the temperature of the cooled photomultiplier was kept C below the (variable) ambient temperature and/or for variations in the atmosphere transparency during the night. The dead time of the RCA 8850 tube (spectral response 116, RCA Photomultiplier Tubes Catalogue, 1971) was accounted for in the reduction procedure.
HD , HD , HD (7 Sgr) and HD , all close (maximum projected distance in the sky of ) to V 3903 Sgr, were used as comparison stars and observed alternately between the measurements of V 3903 Sgr. All four stars were found to be constant within the observational accuracy throughout the observing periods. The observations of C2, C3 and C4 were transformed to C1 by means of the constant difference of magnitude between them and C1 obtained from all nights. For completeness we repeat here Table 1 (click here) from Vaz et al. (1997), with information for V 3903 Sgr and the comparison stars.
The light curves V 3903 Sgr - HD in the instrumental system u (478 points), v (532), b (544), y (537), are shown in Fig. 1 (click here) and are accessible in electronic form at the CDS as Table 2. Typical rms errors of one magnitude difference between the comparison stars were found to be: , , , . Most of the phases were covered at least twice.
Figure 1: uvby magnitude differences V 3903 Sgr-HD165999 obtained at PDO, with the theoretical light curves (Vaz et al. 1997)
V 3903 Sgr was also observed, during 32 nights (3 from May 04 to 17, 1990, 3 from Apr. 12 to 25, 1991, Jun. 06 and 18, 1993 and 24 from Jun. 06 to Aug. 09 1994), with the 50cm Strömgren Automatic Telescope at ESO, La Silla, Chile. The instrument was equipped with the six-channel spectrograph-photometer (four channels for simultaneous uvby photometry and two channels for simultaneous measurements of narrow and wide filters) and the photon counting system described by Nielsen et al. (1987). In the measurements taken from 1990 to 1993 a circular diaphragm of diameter was used, but in 1994 observations a diameter diaphragm was used.
The comparison stars used in the PDO observations, (Table 1 (click here)), were adopted, and they were constant within the observational accuracy throughout the observing period. Each night several variables were observed, and the nightly extinction corrections were based on coefficients determined from all the comparison stars. As happened in the reduction of PDO measurements, linear or quadratic corrections for instrumental drift and/or changes in sky transparency during the night were applied when needed. The dead times of the six EMI 9789QA uncooled photomultipliers, which have S11 spectral response, were accounted for in the reduction procedure.
Typical rms errors of one magnitude difference between the comparison stars in the ESO measurements were found to be: , , , . Most of the phases were covered at least twice. The light curves are shown in Fig. 3 of Vaz et al. (1997) and the observations are available in electronic form at the CDS, as Tables 3 and 4. Table 3 contains 180 magnitude differences V 3903 Sgr - HD in the instrumental system for 1990, 1991 and 1993, obtained with the diaphragm of diameter, and Table 4 contains the 1994 observations (507 points, instrumental system), which were obtained with a diaphragm of diameter.