Astron. Astrophys. 363, 1029-1039 (2000)

2. Observations and data reductions

2.1. Spectroscopy

The spectroscopic observations were made on seven nights in April and May 1998 with the ESO 3.5-m NTT at La Silla. The observing time was divided into two runs: the first on April 17-20 and the second on May 29-31. The EMMI spectrograph in its red medium dispersion mode (REMD), grating #8, and the red arm CCD camera #36 were used. This setup and the slit width of one arcsecond yielded a spectral resolution of , and a spectral range of 4450-7025 . A spectrum with the grating #13 was additionally taken in the first night, providing a wider wavelength range of 4188-9623 . He-Ar comparison spectra were taken in intervals of typically 30 minutes. For the scientific exposures, 120-300 s integration times were used. The other calibration frames (bias and flat images) were taken during the daytime. A summary of the observing log is given in Table 1. Since the three frames on April 17 were only taken for test purposes, they were not used for detailed analyses but only for obtaining a general view of the spectral features.

Table 1. An observing log of the spectroscopy.
Notes:
*) including one snapshot with the grating #13 of the NTT REMD (Fig. 2)

The data reduction was performed in a standard manner using the IRAF ² software. Wavelength calibrations with typical of about 0.4  were obtained using the He-Ar comparison spectra. Flux calibrations were performed with EG 274 as a standard star before the spectra were finally normalized to the continuum. Velocities relative to the Local Standard of Rest were used for the analyses presented in this paper.

2.2. Photometry

We measured integrated fluxes in the spectra of the object and a comparison star placed in the same slit as the variable during the second NTT run (1998 May 29-31). The comparison star is 26.8 arcseconds South and 11.6 arcseconds West of the object. After rejecting spectra with poor S/N due to bad slit centering, we obtained the relative brightnesses providing a set of "slit differential magnitudes".

We additionally obtained time-resolved CCD photometric observations in order to better define the photometric characteristics of the object. The photometric observations were done using an unfiltered KAF-0400 CCD camera (SBIG ST-7) attached to a 25-cm Schmidt-Cassegrain telescope (Meade LX200) on the rooftop of the Department of Astronomy, Kyoto University, during April and May 1999. The exposure time was set to 30 s. The frames were dark-subtracted, flat-fielded, and analyzed using a -based aperture and PSF photometry package developed by one of the authors (T.K.). We determined the relative magnitudes of the object using the local comparison star GSC 6805.837 (V = 12.893, = 1.772), whose constancy was confirmed by comparison with GSC 6805.1166 (V = 14.602, = 0.838). A heliocentric time correction was applied before the analysis. The 1999 Kyoto run is summarized in Table 2.

Table 2. An observing log of the Kyoto photometry.

© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000
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