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2. Observations and data reduction

The observations were carried out using the facilities of Laboratório Nacional de Astrofísica (LNA/CNPq), in southeast Brazil. The spectroscopic observations (Table 1) were obtained with a Boller & Chivens Cassegrain spectrograph attached to the 1.6-m telescope. Two gratings with 300 and 900 lines/mm were used, which provide about 10 Å and 3.5 Å resolution (as derived from the FWHM of the lines from comparison lamps). The detector used was a GEC P88230 CCD (tex2html_wrap_inline948, 22.5 tex2html_wrap_inline950m/pixel) with UV coating. In the near infrared we used a OG550 filter in order to cut the blue portion of the second order spectrum.

The spectra were extracted using the Image Reduction and Analysis Facility (IRAFgif) software installed at the SUN workstations of the Astrophysics Division at INPE. Spectrophotometric standard stars from the lists of Stone & Baldwin (1983) and Taylor (1984) were observed each night to flux calibrate the spectra. The integrated line fluxes of DQ Ser were computed using the "splot'' task of IRAF, and are presented in Table 3 (click here). The line fluxes were not corrected for reddening and we estimate the absolute fluxes to be accurate to about 30%, while relative line fluxes being more accurate.

Figure 2: Finding chart for DQ Ser a) and DT Ser b). These images were obtained in the I filter and cover about tex2html_wrap_inline954 arcmin. North is up and east is right

The UBVRI data were collected using the FOTRAP photometer at the 0.6-m Zeiss and 1.6-m Boller & Chivens telescopes. This photometer uses a high-speed rotating (1200 rpm) filter wheel which allows quasi-simultaneous photometry in 5 bands. The detector used was a thermoelectrically cooled Hamamatsu R943-02 photomultiplier operated in pulse counting mode.

The instrumental magnitudes were transformed to the tex2html_wrap_inline958 system by observing standard stars in the E-regions (Graham 1982). The data obtained are shown in Table 2 (click here). The uncertainties (Cols. 7 to 11) take into account the errors due to photon noise in the measurements and errors associated with the transformation to the standard system. A more complete description of the procedures of reduction, as well of the FOTRAP photometer and the photometric system, can be found in Jablonski et al. (1994).

Table 3: Observed lines fluxes of DQ Ser scaled to Htex2html_wrap_inline960=1.00 or Htex2html_wrap_inline962 = 1.00

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